Boswellia neglecta is a small tree that produces commercially important oleo-resin known as frankincense. This frankincense has been used for varied purposes, and it is a source of income for rural households in southern and south-eastern Ethiopia. The study was carried out in dry lands of Bena-Tsemay Woreda in South Omo, South Western Ethiopia aimed to assess the population status of Boswellia neglecta and to test its resin quality. A total of 45 sample quadrats, measuring 1600m2 each and 300m apart had been laid out by using systematic sampling techniques. Quadrats were distributed in east-west compass directions along established transect lines located at approximately 500m from each other. In each quadrat, vegetation data such as identity, DBH, height, and counting of seedlings and saplings were made.
To test the resin quality, sample was collected from systematically assigned matured trees in the study area. The status of populations of B. neglecta and other woody species in the study area were examined by estimating density,
abundance, frequency, dominance, and importance value index and population structure. The physicochemical analysis of the resin: moisture, ash, pH, N content, optical rotation and essential oil extraction were determined using standard laboratory procedures.
Häufig gestellte Fragen zu: Population Status von Boswellia neglecta und physikochemische Eigenschaften seiner Produkte aus Süd-Omo, Südethiopien
Was ist das Hauptziel dieser Studie?
Das Hauptziel dieser Studie bestand darin, den Populationsstatus des Baumes Boswellia neglecta und die physikochemischen Eigenschaften seiner Produkte aus Süd-Omo, Südethiopien, zu bestimmen.
Welche spezifischen Ziele wurden in der Studie verfolgt?
Die spezifischen Ziele waren: (1) Quantifizierung der Populationsstruktur, des Regenerationstatus und des Wichtigkeitswertindex von B. neglecta im Bena-Tsemay Woreda; (2) Charakterisierung der Qualität des Weihrauchs von B. neglecta-Bäumen; (3) Bestimmung der Ausbeute an ätherischem Öl aus dem Harz von B. neglecta.
Welche Forschungsfragen wurden in der Studie untersucht?
Die Forschungsfragen lauteten: (1) Wie ist die Populationsstruktur, der aktuelle Regenerationstatus, die Häufigkeit, Dominanz und der Wichtigkeitswertindex von B. neglecta in den Tiefebenen von Bena-Tsemay? (2) Erfüllt Weihrauch/Harz von B. neglecta die Qualitätsmerkmale von Harz? (3) Welche Ausbeute wird aus dem Harz der B. neglecta-Art gewonnen?
Wo wurde die Studie durchgeführt?
Die Studie wurde im Bezirk Bena-Tsemay in Süd-Omo, Südwestäthiopien, durchgeführt. Die spezifischen Studiengebiete waren Luka und Enchete Kebeles innerhalb dieses Bezirks.
Welche Methoden wurden zur Datenerhebung verwendet?
Es wurde eine systematische Stichprobenmethode mit Transektlinien in Nord-Süd-Richtung verwendet. Insgesamt wurden 45 Quadrate angelegt, um Daten zur Vegetation zu sammeln. In jedem Quadrat wurden Daten zu allen Arten, Durchmesser am Brusthöhen (DBH), Höhe, Anzahl der Sämlinge und Jungbäume erfasst. Es wurden auch Harzproben von systematisch ausgewählten, ausgewachsenen Bäumen gesammelt.
Welche physikochemischen Eigenschaften des Harzes wurden analysiert?
Die Analyse umfasste die Bestimmung von Feuchtigkeitsgehalt, Aschegehalt, pH-Wert, Stickstoffgehalt, Proteingehalt und ätherischem Öl Gehalt.
Wie wurde das ätherische Öl extrahiert?
Das ätherische Öl wurde mittels Wasserdampfdestillation extrahiert.
Welche Ergebnisse wurden bezüglich der Populationsstruktur von B. neglecta erzielt?
Die Populationsstruktur von B. neglecta zeigte eine glockenförmige oder unimodale Verteilung, was auf eine beeinträchtigte Regeneration hinweist. Die Anzahl der Individuen war in den unteren und höheren Durchmesserklassen gering.
Welche Ergebnisse wurden zu den physikochemischen Eigenschaften des Harzes erhalten?
Das Harz von B. neglecta wies einen Feuchtigkeitsgehalt von 2,68 %, einen Aschegehalt von 0,99 %, einen pH-Wert von 5,73, eine optische Drehung von -31,6 bei 23,2 °C, einen Stickstoffgehalt von 0,27 %, einen Proteingehalt von 1,69 % und eine Ausbeute an flüchtigem Öl von 5,92 % auf.
Welche Hauptkomponenten wurden im ätherischen Öl von B. neglecta identifiziert?
Die Hauptkomponenten des ätherischen Öls waren Methylester von Elaidinsäure (25,92 %), Linolsäure (25,29 %), Isohexadecansäure (13,62 %) und α-Pinen (6,27 %).
Welche Schlussfolgerungen wurden gezogen?
B. neglecta ist eine wirtschaftlich wichtige Baumart mit hoher Dichte und hohem IVI, weist aber einen schlechten Regenerationsstatus auf. Das Harz aus dem Bezirk Bena-Tsemay weist eine ähnliche Qualität wie Gummi arabicum von Acacia-Arten auf. Das ätherische Öl enthält viele chemische Bestandteile und trägt stark zu medizinischen Werten und industriellen Anwendungen bei.
Welche Empfehlungen werden gegeben?
Es werden Verbesserungen im Management des Waldes, die Entwicklung geeigneter Abbautechniken, Marktstudien, Ertragsstudien und weitere Untersuchungen zu den biologischen Aktivitäten des ätherischen Öls empfohlen.
Table of contents
Acknowledgement
List of Abbreviations
Table of contents
List of tables
List of figures
Appendixes
Abstract
1 Introduction
1.1 Background
1.2 Statement of the problem
1.3 Objectives
1.3.1 General objective
1.3.2 Specific objectives
1.4 Research questions
1.5 Significance of study
2 Literature Review
2.1 Non-Timber Forest Products (NTFPs) in Ethiopia
2.1.1 NTFPs for Conservation of Forest Resources
2.1.2 NTFPs for Economy
2.2 Acacia-Commiphora woodlands and its potential for development of dry lands
2.3 Boswellia neglecta and ecological range
2.3.1 The family Burseraceae
2.3.2 The genus Boswellia
2.3.3 Boswellia neglecta and its ecological range
2.4 Natural Resin/Frankincense and its uses
2.4.1 Collection of Resin
2.4.2 Quality and Standardization of Gum Resin Vs Oleo-resins
2.5 Population Structure
2.6 Frequency and Important Value Index
3 Materials and Methods
3.1 Description of the Study Area
3.2 Methods of data collection
3.2.1 Selection of the study Kebeles
3.2.2 Vegetation Assessment
3.3 Plant Material
3.3.1 Resin sample collection and its Analysis
3.3.2 Sample preparations
3.4 Physicochemical Characteristic Analyses
3.4.1 Moisture Content Determination
3.4.2 Ash Content
3.4.3 pH Determination
3.4.4 Nitrogen Content
3.4.5 Protein Content
3.4.6 Extraction of Essential Oil
3.5 Data Analyses
3.5.1 Vegetation Data Analyses
3.5.2 Analysis of Constituents and Optical Rotation of Essential Oil
4 Results
4.1 Floristic composition of woody species
4.1.1 Plot number-species accumulation curve
4.1.2 Floristic composition of woody species
4.1.3 Density, frequency, dominance and importance value index of woody species
4.1.4 Population structure
4.1.5 Regeneration status
4.2 Physicochemical Characteristics of the Resin and its Oil
4.3 Yield (%V/W) of Essential Oil
4.4 Constituents of the Essential Oil
5 Discussion
5.1 Floristic composition
5.2 Density, frequency, dominance and importance value index
5.3 Regeneration status
5.4 Population structure of B. neglecta
5.5 Physicochemical Characteristics of the Resin and essential oil
5.5.1 Moisture Content
5.5.2 pH Content
5.5.3 Nitrogen and Protein Content
5.5.4 Ash Content
5.6 Extraction of Essential Oil
5.6.1 Essential oil appearance and yield
5.6.2 Optical Rotation of the essential oil
5.6.3 Constituents of Essential Oil of Boswellia neglecta
6 Conclusion and Recommendations
6.1 Conclusion
6.2 Recommendations
References
Appendices
Acknowledgement
Indeed, the first and foremost enthusiastic appreciation goes to my supervisors Dr. Motuma Tolera and Dr. Bekele Lemma during my study for their unreserved energy, consistent guidance, constructive criticism and comments.
I would like to thank SARI and JARC for their financial support and Bena-Tsemay Woreda ARD office and Luka and Enchete Kebele Admistration office for allowing me to conduct my research. I was very pleased to express my appreciation to AAU School of Chemical and Bio Engineering, Food and chemical Engineering Laboratory for their permission to utilize the laboratory equipment without restrictions. I would like once again to thank Ato Asmelash Tesfaye Directorate of Natural Resources Research Work process for his extended and friendly supports from the very inception of the research idea up to its materialization. Mr. Shagnachehu and Oyeta with them team mates who really had played significant role in sample and Vegetative data collections easier during field work in such a harsh environment. Akililu and Hentsa deserve gratitude for your kind collaborations during laboratory work. I am keen to extend my gratitude to Dagnew and Fikir mariam who are always ahead to make easier the tedious laboratory procedures for me. I would also like to express my deepest respect to Denbela Hiddosa for his constructive comments on the draft thesis and throughout the proposal draft. My deepest gratitude goes to all friends and colleagues whom made my stay remarkable at Wondo Genet My deepest gratitude goes to my family, for your indescribable support and inspiration. All glory is to the Almighty God for making everything to be possible.
List of Abbreviations
Abbildung in dieser Leseprobe nicht enthalten
List of tables
Table 1: International gum arabic and resin quality specifications
Table 2: The major components of the essential oil from B. neglecta and other Boswellia species from localities in Ethiopia
Table 3: List of species encountered in the study quadrats at studied Woreda in abundance order
Table 4: Physicochemical characteristics of the resin sample from B. neglecta species
Table 5: Relative compositions (%) of peak area volatile components from frankincense collected of B. neglecta ( Bena-Tsemay) and Ethiopian Boswellia
List of figures
Figure 1: Boswellia neglecta tree species
Figure 2: Location of the study area
Figure 3: B. neglecta tears from the field
Figure 4: Grounded and coded coarse sample
Figure 5: Hydro-distillation Setup employed during sample was extracted
Figure 6: Plot number-species accumulation curve of woody species in the dry landof Bena-tsemay Woreda
Figure 7: Population structure of B. neglecta at Bena-Tsemay Woreda
Figure 8: Height class distribution of the B. neglecta at Bena-Tsemay Woreda
Figure 9:Regenerationstatus(seedling + sapling)of woodyspecies Bena-Tsemay Woreda
Figure 10:Total ion current chromatogram showing the range of terpenic compounds present in oil of B. neglecta (Bena-Tsemay)
Appendixes
Appendix 1: Thelistofspeciesthatincludescientificname,localname,familyandlife formofallwoodyspeciesencounteredatstudyWoreda
Appendix 2 : Extracted ion current chromatogram showing key triterpenic compounds in oil of B. neglecta (Bena-Tsemay)
Appendix 3 : The analyzed compounds from the essential oil by IUPAC name, common name, and concentration
Abstract
Boswellia neglecta is a small tree that produces commercially important oleo-resin known as frankincense. This frankincense has been used for varied purposes, and it is a source of income for rural households in southern and south-eastern Ethiopia. The study was carried out in dry lands of Bena-Tsemay Woreda in South Omo, South Western Ethiopia aimed to assess the population status of Boswellia neglecta and to test its resin quality. A total of 45 sample quadrats, measuring 1600m2 each and 300m apart had been laid out by using systematic sampling techniques. Quadrats were distributed in east-west compass directions along established transect lines located at approximately 500m from each other. In each quadrat, vegetation data such as identity, DBH, height, and counting of seedlings and saplings were made. To test the resin quality, sample was collected from systematically assigned matured trees in the study area. The status of populations of B. neglecta and other woody species in the study area were examined by estimating density, abundance, frequency, dominance, and importance value index and population structure. The physicochemical analysis of the resin: moisture, ash, pH, N content, optical rotation and essential oil extraction were determined using standard laboratory procedures. The results demonstrated that the density, abundance, frequency, dominance and importance value index for B. neglecta are high in the area. The population structure of B. neglecta shows a bell-shaped diameter distribution which shows hampered regeneration. The physicochemical characteristics of resin data revealed that resin of B. neglecta trees has 2.68% moisture content, 0.99% ash content, 5.73 pH, optical rotation of -31.6 at 23.2°C, 0.27% of nitrogen content, 1.69% of protein and 5.92% volatile oil yield. The essential oil obtained by hydro distillation of resin of B. neglecta shows that B. neglecta has thirty-eight (38) peaks of GC-MS in terms of quality, which correspond to seventy-six (76) different compounds in the oil. Methyl elaidate (25.92%), Methyl linoleate (25.29%), Methyl isohexadecanoate (13.62%) and α-pinene (6.27%) are found to be the major components. The physicochemical characteristic of the resin and its oil constituents are in good agreement with qualities reported by similar studies and fitted well to international standards. Also, the resin from the Bena-Tsemay district possesses matching quality to gum arabic from Acacia species. Above all, B. neglecta is one of economically important tree species with higher density and higher IVI in study area but has a poor regeneration status. Therefore, there should be an improved management activity on woodland and appropriate tapping technology for a sustainable resin production. Also, more research is recommended to see the market value and to identify biological activities of essential oil in the agro-chemical industry.
Keywords: frankincense, Physico-chemical, essential oil, hydro distillation, Methyl elaidate, Methyl linoleate, Methyl isohexadecanoate , South Omo
1 Introduction
1.1 Background
The exploitation and management of Non–Timber Forest Products (NTFPs) is increasingly proposed as a potential means of ensuring sustainable management of forests and their biodiversity (Lemenih and Teketay, 2004). NTFPs are frequently touted as important to household consumptions and increase the value of standing forest to discourage deforestation (Wilkie et al., 2001).
Drylands of Ethiopia host forests that are comprised of the largest proportion of forest resources which accounts for about 48% of the total land mass (WBISPP, 2004). These forest lands are endowed with the major gum and resin producing genera of Acacia, Boswellia and Commiphora vegetations which have contributing cultural, economic and ecological importance (Worku et al., 2012). Gums and resins are the most widely used and traded NTFPs other than items consumed directly as food, fodder and medicine (Lemenih and Teketay 2003a). Moreover, the Acacia, Boswellia and Commiphora species have been providing multiple ecological services which help to fight desertification, soil erosions and Carbon sequestration (Lemenih and Teketay, 2004). The studies made in Ethiopia by Lemenih et al. (2003) and Worku et al. (2011) had demonstrated that 12 Acacia, 17 Commiphora, 6 Boswellia and 3 Sterculia species are identified as potential yielders of commercial gums and resins. Although resin-producing species are widely distributed in the plant kingdom, copious amount of commercially valuable resins are produced from few families, (e.g., Burseraceae, Pinaceae and Leguminosae) (FAO, 1995).
Boswellia neglecta which is among the resin bearing species is dominantly found in the dry Acacia–Commiphora woodlands of the South and South Eastern parts of the country (Lemenih and Kassa, 2011; Worku et al., 2011). An oleo-gum resin constitutes 80% of total output of resins, gum Arabic 14 % and myrrh 6 % (Desalegn and Tadesse, 2004). Among this incense of B. neglecta is widely used in Ethiopia, and traded as ‘Borena type’ olibanum (Moges, 2004). The Borana-type frankincense is produced from B. neglecta growing in the Southern and South-Eastern part of the country (Tadesse et al., 2007) and it is locally named as “tikuretan” (meaning: black incense) (Fikir et al., 2016). Internationally the resin/frankincense is an important commodity as it is a source of essential oils, cosmetic and pharmaceutical industries (Lemenih and Teketay, 2003). In addition to its commercial product, Boswellia has important ecological role owing to the environmental conditions that the species is naturally distributed. The species are also valuable to the rural communities as sources of wood for fuel, farm implements and construction, fodder, in traditional apiculture, as medicines and for various environmental services such as soil & water conservation, provide plant cover and shade (Chikamai, 2003; Pretzsch et al., 2011). Boswellia is common lowland tree species in South Omo mixed with other species like Acacia, Combretum, Terminalia and Commiphora species on slopes and land hills (Admasu et al., 2010). For conservation and proper management of the existing Boswellia stands in Bena-Tsemay, it is important to understand the species population structure, density and natural regeneration and important value index.
The resin is one of NTFPs which have produced from Boswellia and Commiphora species by hydro-distillation process and characterized as essential oils. Essential oils are highly concentrated volatile/aromatic substances which are isolated by a physical process from parts of plants (Kumar, 2010; Rav et al., 2011) and they are important for various purposes in a consumer goods such as detergents, soaps, toilet products, cosmetics, pharmaceuticals, perfumes, confectionery food products, soft drinks, distilled alcoholic beverages (hard drinks) and insecticides (Atti-Santos et al., 2005). Quality control of resins/essential oil is important for sustainability in the market. The quality of resin depends on those physical and chemical parameters (Anwar et al., 2011).
1.2 Statement of the problem
The livelihood of pastoralists in most part of Ethiopia has been largely based on forests and woodlands as sources of firewood, charcoal and NTFPs such as, frankincense, food, fiber and folk medicines. Because the ecological balance in arid and semi-arid lands (ASAL) is delicate, sustainable land resource use practices are required if pastoralist’s basic needs for the future are to be fulfilled (Karmann and Lorbach, 1996).
Several tree species, mainly in tropical and subtropical zones, produce resins (Langenheim, 1994). B. neglecta is one of these a frankincense-producing tree species dominantly found in the dry woodlands of South eastern Ethiopia (Tadesse et al., 2007). Sustaining or even extending the income from B. neglecta is a primary issue in the region, notably because frankincense production from another species, B. papyrifera, is hampered by lack of successful recruitment (Tolera et al., 2013) and high rates of adult tree mortality (Groenendijk et al., 2012). Hence, there is an urgent need to develop sustainable management options for these forests and their resources to better benefit the local, national and international communities. Moreover, frankincense bearing species compositions in the study area are facing serious problems of degradation due to the recurrent drought and the ultimate outcome of deforestation (Mengistu et al., 2005). Hence, these have led to decline in productivity of resin bearing tree resources.
Natural resins are invaluable components of non-timber forest products (NTFPs) especially among the ASAL communities (Gitau, 2015). As such, the industry/resin processing is an indispensable source of income for international trade on the products exists. The communities in B. neglecta resin production areas in Bena-Tsemay are however characterized by low standards of living as exhibited by poverty, lack of social services and poor infrastructure. This drives them to engage in unsustainable methods of exploitation of the tree species such as charcoal burning which exacerbates their plight.
To mitigate these risks in the resin industry, study on the properties, extraction and chemical investigation of these NTFPs as sources of building blocks for the chemical industry, is necessary. This move can position them in the local and international market. Intensive research has been done on some gum and gum-resin producing species such as Acacia species , Boswellia and Commiphora species in different localities in Ethiopia as well as in the world . Many of their benefits have been revealed resulting in an established market structure that significantly benefits the respective local communities. Furthermore, in to the study area, the comprehensive study on population status, extraction and chemical composition of resin of B. neglecta have not been carried out at Bena- Tsemay Woreda .
1.3 Objectives
1.3.1 General objective
The general objective of the study was to determine population status of B. neglecta tree and physicochemical characteristics of its products from South Omo, Southern Ethiopia.
1.3.2 Specific objectives
- To quantify the population structure, regeneration status and importance value index of B. neglecta growing in Bena-TsemayWoreda;
- To characterize the quality of frankincense from the B. neglecta trees;
- To determine essential oil yield from the resin of B. neglecta.
1.4 Research questions
The following research questions were emanated from the above objectives:
- How is the population structure, current regeneration status, abundance, frequency, dominance and importance value index of B. neglecta in the lowlands of Bena- Tsemay?
- Does frankincense/resin from B. neglecta fulfill quality measures of resin?
- What amount of yield is obtained from resin of B. neglecta species?
1.5 Significance of study
The NTFPs has contributed significantly to both rural livelihoods, the national economy and ecosystem stability. It contributes to local livelihoods in terms of cash income and of subsistence local use. Therefore, this study would contribute in generating reliable data on the population status such as population structure, regeneration trends, abundance, frequencies, dominance and important value index. This information is important foundations to devise strategic plan and design so as to conserve and sustainably utilize the studied trees economic and ecological benefits. Moreover, also this study would generate and documented information on resin quality, extracted essential oil yield from resin. Also these studies generate reliable data regarding the oil’s chemical composition and identify compositional quality on B . negelecta tree to benefit the pastoralists and community nearby. Research organizations and Researchers whom interest in conducting further studies would be benefited from this study through easily identifying the research gaps and recommendation of this study work.
2 Literature Review
2.1 Non-Timber Forest Products (NTFPs) in Ethiopia
Ethiopia is home to one of the most diverse flora and fauna in Africa. The higher floristic diversity of Ethiopia provides a variety of NTFPs of various uses to the people. There are many non-wood forest products the production and consumption of all of which is not documented (Limenih, 2004). NTFPs generally embrace all materials of a biological source excepting timber which is being extracted on an industrial scale obtained from forested landscape. NTFPs identified in Ethiopia include gum acacia, frankincense, myrrh, spices and condiments, traditional medicine, wild honey and beeswax, bamboo, wild palm, wild food, fibers, tannins and dyes, latex, thatching, wild edible and non-edible products, essential oils and aromatic plants, and insecticides. NTFPs have been harvested by human populations for subsistence use and trade for thousands of years (Ticktin, 2004). NTFPs obtained from plant resources, including seeds, flowers, fruits, leaves, roots, bark, latex, resins and other non-wood plant parts, have gained much attention in conservation circles (Ticktin, 2004). Finally, interest in NTFPs has been linked to the issue of empowering local people, and recognizing and legally securing their rights to manage their forest resources (Arnold and Perez, 2001).
2.1.1 NTFPs for Conservation of Forest Resources
Interest in NTFPs has grown with the increasing awareness of tropical forest problems and harvest is believed to be less ecologically destructive. NTFPs have been assumed to contribute effectively to the preservation of tropical forests and the development of forest dwellers' economic situation by raising awareness of the value of natural resources (Schroder, 2001). The maintenance of a forest like structure associated with production of NTFPs is generally acknowledged as being positive, contributing to some of the classical forest environmental functions such as carbon storage, nutrient cycling, erosion control, hydrological regulation, and biodiversity conservation, while providing an important source of income (Arnold and Perez, 2001).
2.1.2 NTFPs for Economy
NTFPs can help communities to meet their needs without destroying the forest resource (FAO, 1995b, c). Also, NTFPs are well known worldwide for their aid to national and local economies (Lemenih et al., 2003). For instance, in India over 50% of forest revenues and 70% of forest export income comes from NTFPs (Shiva, 1993). The potential profits from sustainable harvesting of NTFPs could be considerably higher than timber income or income from agricultural or plantation uses of the forest sites. NTFPS contribute to household self-sufficiency, food security, income generation, accumulation of savings and risk minimization, and fill seasonal and other food or income gaps (Arnold and Perez, 1996). Likewise, NTFPs, such as gums and incense, resins and spices, or honey and wax from beekeeping, play an important role in the consumption patterns and income diversification of rural communities of Ethiopia (Vivero Pol, 2002).
2.2 Acacia-Commiphora woodlands and its potential for development of dry lands
Woodland and bush land vegetations in Ethiopia are largely limited to the pastoral and agro-pastoral zones of the country (Mengistu et al., 2005). These lands are important sources of fuel wood and construction material for the local communities; production of charcoal for urban markets and collection of NTFPs such as gum and gum-resins, essential oils, edible fruits and seeds, roots, tubers, leaves, barks, and honey. They are the principal sources of fodder and water for the livestock and the major means of medication for the pastoral communities. Moreover, plant formation plays the major function in maintaining the ecosystem functioning. Generally, as it is elsewhere in various part of the dry land environments in the world, NTFPs are extensively used to supplement diets and household income in Ethiopia, notably during the dry season and to help meet medicinal needs. Arid to semi-arid sub-regions and the grassland areas of eastern and southern Africa, as well as areas currently under the threats from land degradation and desertification are particularly vulnerable, which is also the case in Ethiopia.
Meanwhile, the key role of the characteristic species comprising the Acacia-Commiphora woodland and other dry land vegetation formation in combating the ever-expanding desertification is very important, as dry land adapted species are known to grow in harsh and marginalized environments (FAO, 1995). The dominant vegetation types that found in woodlands of South Omo are the Acacia-Commiphora and Combretum-Terminalia wood lands which are dominated with Acacia, Balanites, Commiphora, Boswellia neglecta, C ombretum, Terminalia and Stericulia species (Assefa and Abebe, 2011). Some of the member species of the genera Commiphora, Boswellia, Acacia and Sterculia are known to yield commercially valuable products, principally gums and resins.
2.3 Boswellia neglecta and ecological range
2.3.1 The family Burseraceae
Burseraceae is a family represented by 17 genera and 500-600 species, wide spread in all tropical regions and reached to subtropics. They are trees or shrubs often spiny; often with latex, resins or oils which are strongly aromatic. It is often a dominant constituent of the vegetation in dry lowland areas. In Ethiopia 2 genera (Boswellia and Commiphora) and 58 species are present (Vollesen, 1989).
2.3.2 The genus Boswellia
The genus Boswellia has about 20 species happening in the dry regions from West Africa to Arabia and South to North East Tanzania, also in India and one species in Madagascar. The genus is centered in northeast Africa where about 75 % of the species is common to the area. They are trees or shrubs; outer barks often shedding in parchment flakes, inner bark greenish, with watery aromatic resins, and wood with milky latex (Bekele& Tongans , 2007).
2.3.3 Boswellia neglecta and its ecological range
B. neglecta is ecologically adapted, commercially and socio-culturally favorite species. B. neglecta occurs in Ethiopia, Kenya, Somalia, Tanzania, and Uganda (PROTA4U: https://www.prota4u.org/protaindex.asp- 2016). This species grows in well-drained soil with limited access to water (Mokria et al., 2017). B. neglecta grows up to a height of 6 meters and a stem diameter of 30 centimeter with thick grey-brown bark (Rijkers et al., 2006a).
Abbildung in dieser Leseprobe nicht enthalten
Figure 1: Boswellia neglecta tree species (Photo by Alemayehu, 2018).
2.4 Natural Resin/Frankincense and its uses
Resins are formed as oxidation products of various essential oils and are very complex and varied in chemical composition. The resin is usually secreted in definite cavities or passages. It frequently oozes out through the bark and hardens on exposure to air. Resinous substances may occur alone or in combination with essential oils or gums. Resins, unlike gums, are insoluble in water, but they dissolve in ether, alcohol and other solvents.
The major resin sources of the world today are Ethiopia, Somalia and northeast Kenya (Provan et al., 1987). In Ethiopia, resins are produced by several tree species, and three types of frankincense are well known according to their origin: Tigray, Ogaden and Borana type. Tigray and Ogaden types represent frankincense produced in northern and north western as well as eastern parts of Ethiopia, respectively (Lemenih and Kassa, 2011). This frankincense has been used for different purposes, and it is a source of income & medicinal value for rural households (Worku et al., 2011; Mekonnen et al., 2013; Mengistu et al., 2012).
Currently, it is widely traded as incense on local markets (Mekonnen et al., 2013). Frankincense has a wide use including incense in homes, formulation of a number of modern perfumes and as medicine (Tucker, 1986). Resin/Frankincense is a complex mixture composed of about 5-9 % highly aromatic essential oil (mono- and sesquiterpenes), 65-85 % alcohol soluble resins (diterpenes, triterpenes) and the remaining water-soluble resins (Tucker, 1986). Mono and sesquiterpenes are highly volatile compounds, diterpenes exhibit low volatility, triterpenes very low volatility and polysaccharides are not volatile (Hamm et al., 2005).
2.4.1 Collection of Resin
Frankincense/Olibanum is the oleo-gum resin harvested from several diverse trees belonging to the genus Boswellia. Production and/or harvesting of the product is mainly done by collecting the naturally oozed product from the trunk and branches of the tree, as well as from the ground (Fikir et al., 2016).During dry season, white or black resin oozes from the bark of B. neglecta but the white resin changes to black at a time of hot season (Worku, 2006) . In the Borana, South Omo, the southern part of Ethiopia (B. neglecta), there is not yet developed tapping strategy of resin production (Mengistu et al., 2012; Fikir et al., 2016).
2.4.2 Quality and Standardization of Gum Resin Vs Oleo-resins
Commercialization of gums and resins depends on their quality, which is normally determined using some physical properties such as moisture, total ash content, pH, volatile matter, nitrogen content and optical rotation (Gitau, 2015; Srivastava et al., 2016). The assessment of gum & resin quality in the world market relies on international specifications which are based on some physicochemical parameters of the Sudan gum from Acacia Senegal variety Senegal, Commiphora and Boswellia species (Table 1).
Table 1: International gum arabic and resin quality specifications.
Abbildung in dieser Leseprobe nicht enthalten
Adapted from: (FAO, 1990; Gitau, 2015; Srivastava et al., 2016).
These properties may however vary depending on age of trees, exudation time, season, storage type and climate (Montenegro et al., 2012). In addition, some other parameters such as total soluble fiber, refractive index, intrinsic viscosity and pH are also important.
Moisture content facilitates solubility of the hydrophilic carbohydrates and the hydrophobic proteins and the ash content indicates the critical foreign matter levels, total matter insoluble in acid and salts of calcium, magnesium and potassium. The volatile matter indicates the type and level of polymerization of the sugar components which highly determines their use as emulsifiers and stabilizers in the manufacture of pharmaceuticals such as cough syrups. Nitrogen content shows the number of amino acid constituents, while optical rotation identifies the nature and source of the sugars present (Lelon et al., 2010). These parameters can form the basis for determining the quality of gum resin Vs oleo-resins and also its evaluation as a potential substitute for gum arabic in formulations. In order to promote the commerce of olio-gum resins, knowledge on the chemistry for each resin type is crucial.
2.4.2.1 Essential Oils of Resin
Aromatic plants contain odorous, volatile, hydrophobic and highly concentrated compounds called essential oils/volatile oil. These are obtained from various parts of the plant such as flowers, buds, seeds, leaves, twigs, bark, wood, fruits and roots (Negi, 2012). They are the end products of secondary metabolism, and most of their components are terpenoids, generally monoterpenes and sesquiterpenes, as well as some diterpenes and aromatic compounds, such as phenylpropane derivatives (Greathead, 2003). A considerable amount of essential oils is contained in oleoresins in addition to the resinous materials. Thus, they are often liquid in nature. They have a distinct aroma, flavor and balsamic odors. Among the oleoresins we find the turpentine, balsams and elemis (Srivastava et al., 2016). Also, essential oils are characterized by their odour, oil-like appearance and ability to volatilize at room temperature. Aromatic compounds predominate in certain volatile oils (WHO, 2011).
Detailed compositional analysis of volatile compounds of the oils can be obtained by gas chromatography and mass spectrometry (GC-MS) (Brenes and Roura, 2010). GC-MS are standard equipment used to analyze different chemical components present in essential oil. GC/MS is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a sample. The evaluation of the results of GC-MS measurements was accomplished by comparing mass spectra and retention indices with published data and a spectral library established under identical experimental conditions (Hochmuth et al., 2001).
Hydro distillation is the most frequently used technique to isolate these lipophilic mixtures. In addition to their ecological significance in nature, essential oils are important raw materials for perfume, cosmetic, food and pharmaceutical industries.
2.4.2.2 Essential oils from Boswellia species
Provan et al.(1987) analyzed different resins of B. neglecta collected from Kenya and reported concentration ranges for the major components: α-pinene(2–69%), limonene (0–40%) and terpinen-4-ol (0–5%).Also, chemical profile of the oil can be used as a chemotaxonomical marker to distinguish between the different commercial varieties of frankincense (Table 2).
Table 2: The major components of the essential oil from B. neglecta and other Boswellia species from localities in Ethiopia.
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2.5 Population Structure
Population structure is defined as the distribution of individuals of each species in arbitrarily diameter-height size classes to provide the overall regeneration profile of the study species (Shibru and Balacha, 2004). Information on population structure of a tree species indicates the history of the past disturbance to that species and the environment and hence, used to forecast the future trend and respect the healthy regeneration of the particular species underutilization (Peters, 1996; G/Hiwot, 2003).It can show the regeneration status of a species and whether the recruitment occurs continuously or periodically (Mengistu et al., 2005). Population structure is extremely useful tool for orienting management activities and, perhaps most important for assessing both the potential of a given resources and the impact of NTFPs extraction (Peters, 1996). Analyses of population structure have then something to do with the future management of the key and untapped resources of the dryland of Ethiopia.
Ecologists often use diameter and height size-class distribution to indicate the health of a population because of a lack of well-defined growth rings and the difficulty of accurately determining tree age in the tropics. Accordingly, population structure can be constructed by employing the total number of individual that were grouped into different arbitrary diameter and height classes, and summarized using descriptive and simple statistical calculations for both diameter and height class distributions of each species and has been shown by simple frequency histogram (G/Hiwot, 2003; Mengistu et al., 2005). For this particular study, population structure was constructed following this approach.
The population structure of a given species can be roughly grouped in to three types. Type I, II and III. Type I, shows the case in which diameter/height size class distribution of the species displays a greater number of smaller trees than big trees and almost constant reduction in number from one size class to the next (Shibru and Balcha, 2004; Eshete et al., 2005). Such a pattern skewed to a reversed J-shape distribution in a forest are considered to have a favorable status of regeneration and recruitment and hence, stable and healthy population (G/Hiwot, 2003). Type II, is characteristic of species that show discontinuous, irregular and/or periodic recruitment. In this type, the frequency exhibited, for instance, in diameter/height size class causes discontinuities in the structure of the population as the established seedlings and saplings grow in to larger size classes. Type III, reflects a species whose regeneration is severely limited for some reasons (Peters, 1996). Hence, knowledge about the category in which our study species falls is important issue before planning to utilize the resources.
2.6 Frequency and Important Value Index
Frequency is defined as the proportion of sample quadrates in which individuals of a species are recorded. Frequency measures reveal the uniformity of the distribution of the species in the study area, which again tell about the habitat preference of the species the homogeneity of the stand under consideration (Silvertown and Doust, 1993; Kent and Coker, 1992).
The important value index (IVI) permits a comparison of species in a given forest type and depict the sociological structure of a population in its totality in the community. It often reflects the extent of the dominance, occurrence and abundance of a given species in relation to other associated species in an area (G/Hiwot, 2003; Shibru and Balcha, 2004). It is also important to compare the ecological significance of a given species. Therefore, it is a good index for summarizing vegetation characteristics and ranking species for management and conservation practices.
3 Materials and Methods
3.1 Description of the Study Area
The study was conducted in Bena-Tsemay district of South Omo in South Western Ethiopia. South Omo Zone is located between the lower reaches of the Omo River in the West and the Woito and Sagan Rivers in the East. The human population of the district is 55,590, of whom 28,087 are male and 27,503 females (CSA, 2007). The two dominant ethnic groups, Benna and Tsemay, comprise 27,022 (48.6%) and 20,046 (36.1%) of the population, respectively, while the remaining 8,522 (15.3%) are from other ethnic groups. In addition, the district is endowed with substantial vegetation resources, particularly the Combretum-Terminalia and Acacia-Commiphora woodlands, which are also used as rangelands and common property resources of the whole community (Soromessa et al., 2004).
The district receives bimodal rainfall; the first peak, from mid-March to the end of April, which is important for crop production and the second peak, from mid-October to the beginning of November, which is short and important only for pasture establishments. The lower altitude, below 700m a.s.l. which is inhabited by the Tsemay ethnic group and whiles the area above 1000m a.s.l. is predominantly inhabited by the Benna ethnic group with elevations ranging from 567−1,800m a.s.l. (Admasu et al., 2010). Average annual minimum and maximum temperatures are 16°C and 40°C respectively (Admasu et al., 2010) and the major soil types of the area are Eutric fluvisols (in the flat lands of the Tsemay) and Eutric and Chromic Cambisols (in the rolling plateau of the Benna area) (Soromessa et al., 2004). With regards to the livestock population, there are 179,918 head of cattle, 82,178 goats, 28,494 sheep, 18,885 donkeys and 80,000 traditional beehives (CSA, 2007).
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Figure 2: Location of the study area
3.2 Methods of data collection
Initially, informal discussion with different stakeholders were made among which were the Zonal, woreda and kebele administrative bodies that have been serving on mandate area. Both vegetation data and resin sample were collected to capture important information in order to address the specific objectives of the study.
3.2.1 Selection of the study Kebeles
Bena-Tsemay district was selected based on the potential and distribution of study tree in the South Omo drylands. This was followed by a thorough discussion with different bodies among which were the District Agricultural experts, DA’s and Natural Gum Resin Processing and Marketing Enterprise (NGRPME), Bena-Tsemay branch, and local elders who have knowledge on the study tree. The discussion was focused on the distribution of the study tree and accessibility of the district for the study. Finally, an intensive field reconnaissance survey was made to complement the previous efforts to select the study district.
Within the selected district, sites, with relatively good population of the study tree, were purposively selected. Luka and Enchete Kebeles were selected from the Bena-Tsemay Woreda for this study. Within Luka and Enchete, four sites namely: Orro near to Tseyantie Kebele, about 3-5 killometers, and Dorebaka 6 killometers from Luka village, Ollo 10 killometers from enchete village in South Eastern direction were selected as specific study site. The other specific study site was Biralie, which was 12-15 kilometers from Enchete village in South Western direction on the way to Konso district.
3.2.2 Vegetation Assessment
The data was collected using systematic sampling method using transect lines laid in a North-South direction. A total of 45 (26 at Luka and 19 at Enchete) quadrats were used to collect data on the vegetation of the total area that covers 144 ha. Transect lines were laid at 500 meters distance apart. Generally, systematically laid transect lines were opted since it was considerable importance in the description of vegetation changes along environmental gradients or in relation to some marked features of topography (Pearson et al., 2005). Along each transect line quadrats having a size of 40 x 40 meters (1600m2) were systematically laid at the distance of 300 meters.
In each quadrat, all woody species were identified and diameter at breast height (DBH) for all woody species ≥ 2.5 cm and height ≥ 1.5m were measured (Eshete et al., 2011). Tree diameter was measured using Caliper, while tree height was measured using Clino meter. In this study, tree/shrubs are defined as woody species with height 2meter and heights of ≤ 1.5m were considered as saplings/seedlings, counted and recorded (Eshete et al., 2011). Tree/shrub forked below 1.3m, individual stems were separately measured and counted as two.
Regeneration pattern of study species were assessed by employing total count of seedlings/saplings within the main quadrats. In this case, to make counting easier, each main plot was sub-divided into four squares (100m2) at each corner using ropes and pegs and counting was made within these sub-plots. Most plant species were identified in the field but voucher specimens were prepared those species which were difficult to identify in the field. The collected herbarium specimens were identified at the National Herbarium of Addis Ababa University (AAU) (Hedberg et al., 2006).
Abundance: Two sets of abundance value were calculated in this study. (i) average abundance per quadrats, calculated as the sum of the number of stems of a species from all quadrats were divided by the total number of quadrats, (ii) Relative abundance, calculated as the percentage of the abundance of each species were divided by the total stem number of all woody species ha-1 (G/Hiwot,2003).
Density: Was calculated by summing up all the stems across all sample quadrats (abundance) and translated to hectare base for all the woody species encountered in the study quadrats.
Frequency: Two sets of frequency were computed (Kent and Coker, 1994; G/Hiwot, 2003). Absolute frequency, which is the number of quadrats in which the species recorded (W/Mariam, 2003), and relative frequency of a species, computed as the ratio of the absolute frequency of the species to the sum total of the frequency of all species.
Dominance: Two set of dominance were calculated: absolute dominance (the sum of basal areas of the individuals in m2 /ha), and relative dominance, which is the percentage of the total basal area of a given species out of the total measured stem basal areas of all species. Dominance was calculated for individual stems with DBH 2.5cm.
Basal Area: was calculated for all woody species with DBH 2.5cm as
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Where, BA = basal area in m2; π =3.14; d =diameter at breast height.
Population Structure: Population structure of the study tree (B. neglecta) was constructed to provide the overall regeneration profile of the specific study species. To determine the population structure, the study trees encountered were grouped into an arbitrary diameter class of size 2.5cm and height 1.5m (2.5 – 5 cm, 5.1 – 7.5, 7.6 – 9.5 cm, … 38.1 – 40.5) and by 1.5 m height classes (1.5 – 3 m, 3.1 – 4.5 m, 4.6 – 6 m …27.1 – 28.5) and structure of the tree was depicted using frequency histogram of both diameter and height class distributions (Eshete et al., 2005). The resulted frequency histogram was then interpreted as an indication of variations in population regeneration pattern/dynamics (Shibru and Balcha, 2004). Further, the histogram was compared and categorized into one of three most common size-class distributions exhibited by tropical tree population (Peters, 1996). These are: Type I, II and III, whose meaning is discussed in literature and discussion section.
Regeneration status: The regeneration status of the study trees in particular was summarized based on the total count of seedling and sapling of each species across all quadrats and presented in tables and frequency histograms (Argaw et al., 1999).
Importance Value Index (IVI): IVI was calculated as the sum of relative abundance (%), relative dominance (%), and relative frequency (%) of the species (Kent and Coker, 1994), where:
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3.3 Plant Material
3.3.1 Resin sample collection and its Analysis
The resin sample was collected from 10 systematically identified B. neglecta trees in study area. The collected resins sample from the 10 trees was bulked in laboratory according to Yebeyen (2006) recommendation. Sub-samples for the determination of various physicochemical analyses was picked from the bulk resins sample and packed in transparent polyethylene bags, sealed and then coded. The resin was light yellow to dark brown in color and varying from slightly sticky to dry (Fig. 3).
3.3.2 Sample preparations
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Figure 3: B. neglecta tears from the field (Photo by Alemayehu, 2018).
For the chemical analysis, a sample was air dried and then grounded mechanically into a coarse product (Fig. 4). Some of the grounded resin was further grounded into a powder using pestle and mortar and then mixed thoroughly to make a homogeneous sample stock (Gitau, 2015). Sample was coded and stored in tightly sealed polyethylene bags at room temperature.
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Figure 4: Grounded and coded coarse sample (Photo by Alemayehu, 2018).
3.4 Physicochemical Characteristic Analyses
The physicochemical property analysis was carried out at the AAU School of Chemical and Bio Engineering, Food and chemical Engineering Laboratory. Resin samples were analyzed for quality indicator parameters like: moisture content, Ash content, pH, N content, protein content and essential oil contents (Gitau, 2015; Srivastava et al., 2016) as follows.
3.4.1 Moisture Content Determination
Fresh resin (2g) sample was oven dried at 105 oC for 5 hr. (FAO, 1999). Oven dry mass was weighed after allowing the samples to cool in desiccators before reweighing. The moisture content was determined in three pseudo-replicates. The percentage moisture content was calculated by using following relation (FAO, 1999; Daniel et al., 2009).
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Where; w = loss in weight in g of the material upon drying (fresh – dry weight)
W = weight in g of the material taken for the test/sample (Fresh weight)
3.4.2 Ash Content
Each oven-dried sample from the moisture determination was transferred onto platinum crucibles and placed in a furnace (Nabertherm, LH15/14). The temperature was raised to and maintained at 550 °C for 1 hour. The sample was cooled in desiccators, weighed and reheated in the furnace for another 30 minutes. This cycle was repeated until the variation between two successive weights was less than 1mg. The final weight was recorded. The percentage of ash content was calculated according to recommendation of Gitau (2015).
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Where; W o= Initial weight of sample in grams
W 1 = Final weight of the ash in grams
3.4.3 pH Determination
A 25% resin solution was prepared. The pH of the resin solution was determined by a glass electrode microprocessor pH meter (HANNA 240) after calibrating the meter with buffer solutions of known pH (Gitau, 2015). The measurements were pseudo-repeated three times.
3.4.4 Nitrogen Content
Nitrogen content was determined according to AOAC (2000). Pulverized sample (1.0 g) was accurately placed into micro Kjeldahl digestion flasks and about 2.0g of mixed catalyst (K2SO4, CuSO4 and Selenium) was added into the flask followed by 10ml concentrated Sulphuric acid. The mixture was digested in a digestion block at 420°C for 2 to 3 hours until a clear solution was obtained. After cooling, the solution was diluted to 100ml using de-ionized water and 10ml of the diluted solution distilled with 8ml 40% NaOH using a nitrogen distiller (Gerhardt-Vapodest). The ammonia released was bubbled into a receiver flask containing 10ml of 4% Boric acid. The solution in the receiver flask was then back titrated with 0.01N H2SO4.
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3.4.5 Protein Content
Protein content was determined as according to recommendation of FAO (2002)
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3.4.6 Extraction of Essential Oil
For extraction, 200g of the ground sample of B. neglectas’ oleoresin was taken and conducted according to recommendation of Loghmani et al. (2007). The aromatic plant material was packed in a 1000ml round bottom flask and a sufficient quantity of water was added and brought to a boil in to thermal oil. Due to the influence of hot water and steam, the essential oil was freed from the resins. The vapor mixture of water and oil was condensed by indirect cooling with water. From the condenser, distillate flew into a separator, where oil was separated automatically from the distillate water. The extracted oil was dried over anhydrous sodium sulphate (Na2SO4). The dried oil was stored under refrigeration until analyzed. The oil of resin was measured and the percentage of essential oil content was calculated by calculation developed by Bhuiyan et al. (2010) and Zheljazkov et al. (2010).
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Where; w = Weight of oil after extraction
W = Weight of the ground or milled for oil extraction
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Figure 5: Hydro-distillation Setup employed during sample was extracted (Photo by Alemayehu, 2018).
3.5 Data Analyses
3.5.1 Vegetation Data Analyses
Data such as frequencies, density, dominance and Importance Value Index were entered in to MS Excel computer program was used. Descriptive statistics was employed to describe the various variables.
3.5.2 Analysis of Constituents and Optical Rotation of Essential Oil
3.5.2.1 Analysis of Constituents of the Essential Oil (GC–MS)
The oil was analyzed by GC–MS; a Hewlett-Packard GCD system as described in Baser et al. (2003). A sample volume of 1.0 μl was injected, applying split mode (split ratio 100:1), into HP-5 MS capillary column (60 m × 0.25 mm i.d., 0.25 μm film thickness) was used with helium as carrier gas at a flow rate of 1 ml/min. GC oven temperature was kept at 60 °C for 10 min and raised to 220 °C at a rate of 4°C/min, and then kept constant at 220 °C for 10 min and raised to 240 °C at a rate of 1 °C/min. The injector temperature was at 250 °C. Mass Spectrometry system, with ionization energy (70 eV), was used for GC/MS detection. Mass scanning range will be m/z 41.1–328.4. Library search was carried out using Wiley GC–MS Library and Tawas-Bay-Antique-Market Library of essential oil Constituents. Relative percentage amounts were calculated from total ion current (TIC) by the computer. The components of the analysts were identified through matching their retention indices and mass spectra to those of standards from the National Institute of Science and Technology library database.
3.5.2.2 Analysis of Optical Rotation of the Essential Oil
10ml Polari meter tube containing oil was placed in the trough of the instrument between polarizer and analyzer. Care was taken in filling the tube to avoid the air bubble formation which could disturb the rotation of light. Analyzer was slowly turned until both the halves of the field were viewed through the telescope. The direction of rotation was determined, if the analyzer was turned counter clock wise from the zero position to obtain the final reading, the rotation is levo (-) if clock wise and dextro (+) if anti clockwise (Juliani et al., 2004). This step was pseudo-repeated three times.
4 Results
4.1 Floristic composition of woody species
4.1.1 Plot number-species accumulation curve
The plot number-species accumulation curve of woody species of the studied site flattened before the total number of samples considered were exhausted (Fig.6) showing that sufficient number of samples was considered to determine woody species. The curve was starts to flatten after the 40th plot.
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Figure 6: Plot number-species accumulation curve of woody species in the dry land of Bena-tsemay Woreda.
4.1.2 Floristic composition of woody species
From the established sample quadrats at study district of Bena-Tsemay, a total of 25 woody species (i.e., species richness) distributed in 11 families were encountered (Appendix 1). Among the families, Burseraceae was the most diverse family with 8 species and constituting 32% of the species composition. Fabaceae was the second diverse family represented with 5 species and constituted 20% of the species composition of the study area. Tiliaceae ranked third in terms of diversity at the study district. The families Capparidaceae and Combretaceae were represented by two species each, and four families were each represented by just one species (Appendix 1).
4.1.3 Density, frequency, dominance and importance value index of woody species
The total density of all woody species was found to be 960 stems ha-1 (Table 3). The density values of all the woody species ranged between 3 (C. aculeatum) to 142 (B. neglecta. A few species of trees, tree/shrubs and shrubs were found to predominate the density of the vegetation of the study area. B. neglecta , Boscia coriacea , Commiphora africana , Albizia schimperiana and Ocimum americanum contributed to 59.27% of the total density at the study site.
Table 3: List of species encountered in the study quadrats at studied Woreda in abundance order. (RO= rank order of the average abundance per quadrats of the species).
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In the table above, RO = Rank order of the average abundance per quadrats of the species (N) in a descending; D= density/ha; N= average abundance per plot; %N= relative abundance of the species; F=absolute frequency; %RF= relative frequency; DO= Dominance; RDO= relative dominance; %IVI= percent IVI).
B. neglecta, B. coriacea and C. africana were the three top abundant oleo-gum resins bearing species with 142, 138 and 137 individual ha -1 respectively. A. schimperiana, and O. americanum were the 4th and 5th abundant woody species in study area. In comparative terms, Commiphora bruceae, Acacia nilotica, Sterculia africana and Combretum aculeatum were found to be least abundant woody species at the study site (Table 3).
Horizontal distribution of the species along the transect lines showed that existence of variation from quadrat to quadrat in to the study site. B. neglecta and C. africana were found to be the top two frequent resin bearing species with 44 and 42 respectively out of 45 sample quadrats. Whereas, A. schimperiana and Commiphora boranensis were found to be the3rd and 4th frequent woody species with were 39 and 38 quadrats respectively out of 45 sampled quadrats. In contrast, Boscia coriacea , O. americanum, Acacia senegal and Lannea schimperi were encountered only in few quadrats with 28, 23, 28 and 26 respectively out of 45 sampled quadrats B. neglecta and all other woody specie were found to be in more or less average frequencies. Among the woody species, Salvadora perisca was among the least frequent species encountered in only two to three sample quadrats.
Generally, frequency of the encountered species ranges from 2 to 44 at study area. The result of the quantitative analyses of the density, frequency, dominance, and importance value of woody species encountered at the study site is presented above in Table 3. The result of the analyses of dominance revealed that, B. neglecta, B. coriacea , C. africana , A. schimperiana , and O. americanum were the five top dominant species. Maruwa angolenesis, Lannea humilis and C. bruceae were found to be the least dominant species among the woody species in to study area (Table 3). The total basal area ha-1 of B. neglecta was found to be 0.94 m2 ha-1.
The Importance Value Index (IVI) of all woody species ranged between 1.53 (C. aculeatum) and 44.51 (B. neglecta) (Table 3). Based on the result of the comparison of individual species in terms of their IVI, B. neglecta was the first most important species comprised 44.51% (Tables 3), whereas, C. africana, B. coriacea , A. schimperiana , O. americanum , Lannea schimperi, and C. boranensis were species with relatively higher IVI in at the study area. However, S . africana and Combretum aculeatum were species with least IVI woody species in to the study area.
4.1.4 Population structure
Population structure of B. neglecta exhibited bell-shape or unimodal distribution, where there was small number of individuals in the lower and higher diameter classes (Fig.7). This means the species got some individual of seedling and/or sapling that belong to the first class, which demonstrated hampered regeneration.
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Figure 7: Population structure of B. neglecta at Bena-Tsemay Woreda. (DC in cm: 1 = <2.5cm, 2 = 2.5-7.5, 3 = 7.51-12.5, 4= 12.51-17.5, 5 = 17.51-22.5, 6 = ≥22.51).
Analysis of diameter size class distribution showed that abundance of stems was very high at second diameter classes. Good abundance of individual stems was found at first, third, and fourth diameter class with declined sharply at higher diameter classes (Fig.7). It can also show the regeneration status of the study tree species encountered at the study area was grouped into three categories: type I, II, and III. Accordingly, B. neglecta was grouped in type-II, is characteristic of species that show discontinuous, irregular and/or periodic recruitment distribution pattern in the district (Fig.7).
At height class distribution, in contrast, the population structure exhibited a sort of bimodal distribution for the diameter classes with few individuals in the lowest class, followed by the highest number of individuals in the next class, a sharp decline at the next higher class followed by a progressive increase up to the middle class and another sharp decline towards the upper classes (Fig. 8).
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Figure 8: Height class distribution of the B. neglecta at Bena-Tsemay Woreda. (HC in m: 1= <1.5, 2 = 1.5-3.5, 3 = 3.51-5.5, 4 = 5.51-7.5, 5 = 7.51-9.5, 6 = 9.51-11.5, 7 = ≥11.51).
4.1.5 Regeneration status
The density/ha of seedlings and/or saplings of the study tree and other woody species were found to be 16 and 149 respectively at study area. Density ha-1 of seedlings and saplings of woody were given in (Fig.9).
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Figure 9: Regeneration status (seedling + sapling) of woody species Bena-Tsemay Woreda.
Based on the comparison of the regeneration status of the woody species among them, in to study area, C. africana, and C. boiviniana were the top two species with better density of seedling/sapling, followed by O. americanum and Commiphora myrrh. Also compared to the other woody species, A. nilotica and Acacia tortilis were found to only few individuals at late stage which has been showing hampered regeneration condition (Fig.9). Finally, C. aculeatum was found to be without seedlings/saplings at the study site (Fig.9).
4.2 Physicochemical Characteristics of the Resin and its Oil
Summary of laboratory analytical data of physicochemical properties of resin samples of B. neglecta were presented in (Table 4).
Table 4: Physicochemical characteristics of the resin sample from B. neglecta species.
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a 6.25 Nitrogen Conversion Factor (FAO,2002); a at 23.2°C temperature; only for essential oil.
4.3 Yield (%V/W) of Essential Oil
In this study, yield of the essential oil extracted was 5.92 ±1.06/ in the range 5.17 – 6.7 %.
4.4 Constituents of the Essential Oil
Results are presented as total ion current (TIC) chromatograms of the hydro-distilled oil extract (Fig. 10). The components identified and discussed in the text have been labeled by their retention time.
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Figure 10: Total ion current chromatogram showing the range of terpenic compounds present in oil of B. neglecta (Bena-Tsemay).
They probably derive from the former as the remainder of the molecules were found to be characteristic of natural resins of archaeological interest and comprised: mono-(4.91- 6.95), sesqui-(9.87-16.38) both of them were highly aromatic essential oil; di- (18.98-19.96) and triterpenes (21.54-26.22) (Fig.10; Table 5; Appendix 2). Relative abundance of oil with its retention time in terpenic range was: mono-: α-pinene (6.27%) to Cineole (3.89%); sesqui- Terpinen-4-o1 to Methyl myristate both of them were highly volatile compounds; di- (Methyl isohexadecanoate to Ethyl palmitate) and triterpenes (Butyl phthalate to Methyl eicosanoate)- low and very low volatility respectively (Fig. 10; Table 5).
A typical GC-MS chromatogram showing the separation of the tested essential oil chemical constituents, together with their actually recorded retention times, is presented as Fig.10; Appendix 2 & 3. Out of three components per each retention time a peak quality was screened, so a total of 38 peak compounds were identified in the essential oil, accounting for 99.97% of the total oil, which correspond to seventy-six (76) different compounds. Peak identifiers qualitative and quantitative chemical compositional results are given in Table 5.
Table 5: Relative compositions (%) of peak area volatile components from frankincense collected of B. neglecta (Bena-Tsemay) and Ethiopian Boswellia.
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A*, A, B. neglecta; B, B. rivae; C, B. pirottae; D , B. papyrifera ( A, B, C & D Dekebo et al. ( 1999); Baser et al. (2003)); R.T., Retention time for study tree; a Confirmed by co-injection.
The essential oil tested contained high amount of peak area with constituents: Methyl elaidate (25.92%) and Methyl linoleate (25.29%) followed by of Methyl isohexadecanoate (13.62%) & α-pinene (6.27%). Some least minor compounds including Eicosamethyl cyclodecasiloxane (0.06%), n-Heptadecane (0.07%) and Hexadecamethyl-cyclooctasioxane (0.07%) were also detected.
5 Discussion
5.1 Floristic composition
The floristic characteristics of given vegetation can be described in terms of its richness in species, abundance, frequency, dominance and IVI (Lamprecht, 1989). In this study, a total of 25 woody species were identified including B. neglecta. The finding obtained from this study on the species composition is comparable to values of, 23 and 22 woody species reported by worku (2006) and Eshete et al. (2011) from Yabello, Southern Ethioia and Aberegelle Northern Ethiopia woodland respectively. However, the higher value was obtained from the current study on species composition than early reported value by Adem et al. (2014) which demonstrated that16 tree species composition in Hammer woodland of Ethiopia and but it was lower than reported value of 43 species by the worku (2006) for the woodland of Arero. The lower values from the current study that what reported by worku (2006) for Arero woodland is due to the inhabitants of Bena-Tsemay an agro-pastoral lifestyle as witnessed by the existence of several permanent villages and small farmlands encroaching the Woodlands surrounding these villages. Such a permanent settlement accompanied with a continuous grazing and farmland expansion probably had its adverse effect on the natural regeneration.
5.2 Density, frequency, dominance and importance value index
The more the density of oleo-resin bearing species the better the opportunity to collect more, as it is only a small amount a single tree can yield per year (Eshete, et al, 2005). The study revealed the existence of variation in density among the woody and resin yielding species, which point the need for care during planing for management and collection. B. neglecta had the highest density of 142 individual stems ha-1 thus accounting for 14.79% of the stem composition of the study woodland in terms of tree density and thus creating good opportunity to plan for bulk collection from this species. The values observed from this study on plant density was comparable to values reported by the Worku (2006) which shown that the stem densities ha-1 was ranging from 65 to 162 for B. neglecta at Borana Zone, Southern Ethiopia while it was within range of values reported by the Eshet et al. (2005) who counted between 87 and 175 stems per ha for B. papryifera in Tigray Region, Northern, Ethiopia. Inconsistency, in stem densities might be due to the effect of land use history, climate regime and species characteristics. The Adem et al. (2014) reported that the plant density in a particular area could be affected by climate, land using history and species characteristics.
Frequency analyses in the present study revealed that most of the study species was in more or less good distribution status across the study quadrats. B. neglecta exhibited higher frequency of occurrence indicating existing potential of resin production in to the study area than C. africana. This is due to B. neglecta species either habitat restricted or their population may be affected by human impacts. Mokria et al. (2017) reported that well-drained soil with limited access to water sites preference of B. neglecta and whereas, Eshete et al., (2005) reported the sloppy and rocky sites preference of B. papyrifera which supports results from the current study.
Dominance refers to the degree of coverage of a species as an expression of the space it occupies and is often expressed based on the result of stem basal area (Kent and Coker, 1992). Accordingly, B. neglecta and B. coriacea were the first most dominant species in terms of their basal area. The highest dominance of B. neglecta species indicates the possibility of bulk collection of resins. As basal area provides the measure of the relative importance of the species than simple stem count, species with largest contribution in dominance value could be considered as the most important species in the study vegetation (Shibru and Balcha, 2004). The result further showed that some of the woody species, even though they were less abundant in terms of individual count, they were found to be at least the second dominant species in the area. B. aegyptica and Grewia velutina were some of the species scarcely located per hectare, yet with relatively average dominance and this is because of the big diameter size they had.
The important value index (IVI) is important to compare the ecological significance of a given species. It enables prioritizing species for management and conservation interventions: species with lowest IVIs might benefit from conservation and management interventions (Lamprecht 1989). B. neglecta hold the top largest value of IVI and C. africana followed next largest value of IVI this is due to it is resilient to disturbance. Similar result was reported for B. papyrifera from Benishangul-Gumuz National Regional State, western Ethiopia (Yilma et al., 2016). As it had been observed, this species was highly dense across the study area. This implies their ecological significance to the ecosystem (Akwee et al., 2010). C. africana, B. coriacea , A . schimperiana , O. americanum , Lannea schimperi, and Commiphora boranensis were among the species with relatively high IVI at study area, which shows that these species were among the best adapted, dominant and with more or less good population status in the area. Similar results were also reported from Arero and Yabello districts in Borana Zone where woody species contributed relatively high IVI, respectively (Worku et al., 2012). Also Issango (2004) showed that woody species with high resistance to anthropogenic disturbance and those with efficient regeneration capacity have relatively high chance of remaining the dominant and important species at an area. On the other hand, among the woody species S. africana and C . aculeatum were species with least observed IVI. As mentioned earlier, information on IVI of a given species can tell us the population status of that woody species (Lamprecht, 1989) and be used to prioritize species for conservation to save them as they are important first in terms of ecological service they provide and second from the point of timber production. Further, this could also be seen as an indication of the potential of collecting a large amount of resin in study area.
5.3 Regeneration status
According to G/Hiwot (2003), density of seedlings/saplings would indicate the status of the regeneration of a given population of trees. The result of regeneration analyses of the study species and particular species indicated, the study species was in poor regeneration condition during the survey time, while others were relatively in good condition. The O. americanum how relatively good regeneration contributing more than 7.46% to the total density of regeneration followed by C. boiviniana (7.16%) and C.africana (5.97%). The good regeneration status of O. americanum in the study woodland might be the abundant seed production and soil seed bank formation of the species (Teketay, 1996). However, the result of regeneration in general indicated the sustainability and possibilities of future commercialization of resource (resin) and timber from the natural stand of trees in the study area. On other hand, encountered seedlings/saplings of B. neglecta trees were fewer than other associated woody species in the study area. Accordingly, soil seed banks attributed to fewer through germination immediately after dispersal, which might also indicate that seeds lack dormancy (Woldeselassie, 2001). However, germination of seeds following dispersal during the rainy season could be a regeneration strategy of the plant used to escape damage from fire during the following dry season. Such relatively poor regeneration condition of the study species may be attributed to the agro-pastoralist nature of the mode of life at the area which leads to a continuous trampling and free grazing which may again hinder regeneration of this species.
The result of the regeneration analyses further showed, even if there was variation in density, and horizontal distributions, all the study species at district was represented at sapling stage. It was revealed by the key informants that most of the Boswellia and Commiphora species were palatable for livestock. According to them, early stages of this species are very much liked by small calves, goats and sheep and this might also lead to the poor regeneration condition of this species. During the field stay, it was observed that there were large numbers of small ruminants (goats and sheep) freely grazing in the study woodlands at study area, which is because of the newly created market opportunity for goats and sheep at area.
5.4 Population structure of B. neglecta
In general, the vegetation of the study site fall in type-I, suggesting there was good regeneration status. The population structure of the vegetation of district exhibited the highest abundance at the lower diameter classes with a gradual decrease to the bigger class. This implied good opportunity to sustainably manage and use the vegetation resources (Peters, 1996). In other words, the presence of small sized individuals in abundance in a given forest will be seen as the reserve for replacing cut, large sized and old individuals (Yeshitla and Balcha, 2003).
The result of the present study indicated that the diameter class distribution of the B. neglecta species of the study woodland roughly fall under type-II indicate that species had a periodic recruitment. In this group, though the recruitment was periodical, there was reasonable number of seedlings and relatively large number of middle-class individual that could be managed for resin production. Also, it is exhibit unstable and under threat due to lack of recruitments through regeneration. The findings obtained from this study on population structure of B. neglecta was agreed with what Worku (2006) and Adam and Osman (2008) reported from Arero district, Borana lowland and B. papyrifera respectively from Jebel Mrarra, Darfur; Sudan. Several studies from Ethiopia by different authors (Eshete et al. 2005; Lemeneh et al. 2007) and in Eritrea (Ogbazghi, 2001) and in north western Ethiopia (Alem et al., 2011) have also reported unstable populations of B. papyrifera in different sites. This is an indication that the species is under threat not only in the study area but also in several geographical locations in the region of its distribution due to continuous tapping for incense production, human induced fire, overgrazing and climatic anomalies. For instance, Rijkers et al. (2006) illustrated that untapped trees produce three times higher healthy and filled seeds than tapped trees with germination success being highest in stands with untapped trees (> 80%) and lowest in ones with tapped trees (< 16). The same authors also indicated that at tree level, sexual reproduction decreased with increasing tapping regime irrespective of tree size.
Finally, the overall regeneration profile of the study species suggests the possibility of future commercialization of this versatile resource in general and the sustainable production of resin at the study area. On the other hand, the forgoing discussion revealed there are progressing problems of drought and the advancing nature of the harshness of the environment, which made livestock and agricultural sectors unpredictable (Worku, 2006). Hence, integration of resin with these activities could be considered as an alternative source of livelihood in South Omo dry land as managing the woodland as non-timber source, in general and oleo-gum resins, in particular is a dual purpose helping to meet both the objectives of livelihoods and combating desertification (Lemenih and Teketay, 2004).
5.5 Physicochemical Characteristics of the Resin and essential oil
Studies of various physicochemical characteristics identify the practical importance and provide bases for suitability and utility of resin and oil of plant origin in daily life. Generally, the color of the resin collected from the Benna-Tsemay looks black. It is solid and a brake with a bumpy fracture and it melts when heated or placed in sunlight and just like gum arabic of high quality (FAO, 1990). As presented in literature resins unlike gums, are insoluble in water, but they dissolve in ether, alcohol and other solvents (Srivastava et al., 2016). With the same author, it has its own characteristic balsamic odors. Their ability to harden gradually, as the oil that they contain evaporates, makes possible commercial varnishes. The fact that resin, especially the one from B. neglecta, is a major content accounts for its sensory characteristics and determine its incense in homes, formulation of a number of modern perfumes fragrance and flavor applications, depending on their aromatic volatile oil content (Tucker, 1986; Gebrehiwot, 2003). In addition to its fragrance and flavor application its oil composition used for different purpose, like cosmetics, medicinal value, made that the specifications set on its quality attributes are very strict.
5.5.1 Moisture Content
The resin sample had a moisture content of 2.68% ±0.50. This value was lower than the moisture content of gum resin reported from Commiphora africana (10.6±0.04 %) (Gundidza et al., 2011). Similarly higher moisture content was reported in other studies done by Yebeyen et al.(2009) for gum arabic from A. senegal, which reported a moisture content of 15% in the central rift valley of Ethiopia and Daoub et al. (2016) for some natural Acacia gums, reported a moisture content in the range of 8.35-9.76% in the Sudan. Low moisture content is typical of resins. However, gums have relatively higher moisture contents (FAO, 1990). However, the difference might be due to age of trees, exudation time, season, storage type and climate (Lopez-Franco et al., 2012; Montenegro et al., 2012). The low value (below the excepted level) further underscores reduced susceptibility of the gum resin to microbial degradation (Gitau, 2015).
5.5.2 pH Content
The resin samples had a pH value of 5.73±0.01. This value was relatively higher and less acidic as compared with those of gum resin of Commiphora schimperi (5.35) (Mwendwa, 2007) and Commiphora schimperi (5.39) in the works of Chesori (2008) in Kenya. It was also higher compared with the results gum arabic from A. Senegal in Ethiopia , which had a pH values of 4.04 (Yebeyen et al., 2009) and natural Acacia gums in Sudan, which had pH values in the range of 4.45-4.94 (Daoub et al., 2016).
5.5.3 Nitrogen and Protein Content
The nitrogen content of the samples was 0.27% w/w, while the protein content was 1.69. The nitrogen content of B. neglecta is within the range 0.26-0.39% of the reports of FAO (1990). The nitrogen content value was lower than gum arabic from A. senegal, which had a nitrogen content of 0.35% in Ethiopia (yebeyen et al., 2009) and within the range of gum arabic from Acacia species in Sudan, which had a nitrogen content in the range 0.243-1.549% (Daoub et al., 2016). The protein content of B. neglecta in the present study was within the range of 1.61-10.38% which was reported in the works of Daoub et al. (2016). The protein value also showed lower value to the result (2.31%) of gum arabic from A. senegal (yebeyen et al., 2009).
5.5.4 Ash Content
The ash content of B. neglecta resin was 0.99±0.01 in this study. The ash content represents the quantity of inorganic matter. The inorganic matter content is a good quality indicator and the lower the value the higher the degree of purity (Glicksman, 1970). The maximum limit of total ash content for incense in homes, formulation of a number of modern perfumes and as medicine quality of resin in range 0.05 to 0.5% was acceptable (Srivastava et al., 2016). But, in the present study ash content value was higher than the upper limit of the range. It is also of even higher value for gum arabic in the studies of Yebeyen et al. (2009) for A. senegal which had an ash content of 3.56% , and in the works of Daoub et al. (2016), for Acacia species which had ash content in the range of 2.05-3.4%. Ash content for the purity of gum Arabic was higher than resins according to international specification (FAO, 1990). Moreover, the variations in ash content of resins can be attributed to other factors such as the degree of verification, environmental conditions and picking time (Lopez-Franco et al., 2012; Montenegro et al., 2012). Following this criterion, the B. neglecta resin from the study areas can be said to be of poor quality since the impurity levels are higher than the upper limit. They illustrate a high content of foreign matter, salts of potassium, calcium and magnesium, and acid insoluble matter. The ash content is higher than the maximum recommended limit (≤ 0.5%) for use in food and pharmaceutical formulations (FAO, 1990).
5.6 Extraction of Essential Oil
5.6.1 Essential oil appearance and yield
Essential oils are characterized by their odour, oil-like appearance and ability to volatilize at room temperature (WHO, 2011). From previous literature, it has its own characteristic; they are often liquid in nature and have a distinct aroma, flavor and balsamic odors (Srivastava et al., 2016). Also, the appearance of essential oil was dark yellow in color. This was comparable to the study done by Basar (2005) for B. neglecta and B. rivae from Ethiopia as “Borena” and “Ogaden” type, respectively.
The percent yield of essential oil in the present study was 5.92% ± 1.06. This value is higher than the yield obtained in the studies of Baser et al. (2003) for B. neglecta (5%) , B. pirottae (5%) and B. rivae (4%). The yield from B. neglecta resin from the study area was higher than the maximum for the range essential oil yield (0.5-0.8 %) for B. neglecta growing in Konso, Southern Ethiopia (Fanta et al., 2013) and for B. papyrifera growing in Metema, North Ethiopia (Dekebo et al., 1999). In addition, the yield in the present study was more than specifications range of 1.5-2 % from most oleo-resins producing species (Srivastava et al., 2016), which may indicate a better production of resins can be obtained from B. neglecta in the study area. The inconsistencies on reins of oil content properties with location and/or tree have been reported and it can be attributed to the age of trees, exudation time, season, storage type and climate (Montenegro et al., 2012).
5.6.2 Optical Rotation of the essential oil
The essential oil was optically active, and was found to be levorotatory because the rotation is counter clock wise. The value was in the range -26 to-34 at 21°C and -30 to -34 at 26°C, which was within acceptable range of the previous report on the gum Arabic by different authors (FAO, 1990; Al Assaf et al., 2005; Abdelrahman, 2011). The specific rotation value of B. neglecta resin however was lower than C. abyssinica gum resin, whose optical rotation is from -44.50 to -510(Gitau, 2015).
5.6.3 Constituents of Essential Oil of Boswellia neglecta
In earlier literature the commercially important resin called frankincense was believed to originate from Tigray, Ogaden and Borana type . However, the Borana-type frankincense, produced from B. neglecta was found in abundance in the Southern and South-Eastern parts of Ethiopia (Tadesse et al., 2007). In a previous study by Baser et al. (2003), of the essential oil of the resin of B. neglecta from Dibuluk: Thujene, α-pinene and terpinen-4-ol were found to be the most abundant components. Also, according to Fanta et al. (2013), n-octyl acetate, neocembrene A,verticillol, biformene and nerolidyl propionate were found to be the most abundant components of the essential oils of the resin from B. neglecta at Konso. In this study, the oil of B. neglecta was characterized by Methyl elaidate (25.92%) and Methyl linoleate (25.29%) as the predominant and Methyl isohexadecanoate and α-pinene as minor components which has not reported in the previous studies (Dekebo et al., 1999; Baser et al., 2003; Basar, 2005) and Fanta et al. (2013) except the component α-pinene. Its essential oil comprises almost entirely sesquiterpenoids with the components from Terpinen-4-o1 to Methyl myristate. These results are comparable with the previous study done by (Dekebo et al., 1999; Baser et al., 2003; Brettel et al., 2013). The presence of lower molecular weight mono and sesquiterpenes is of considerable interest as these highly volatile components are rarely survive in aged resinous materials and are rapidly lost upon heating. In addition, diterpenes exhibit low volatility and triterpenes very low volatility.
In this study, the oil of B. neglecta with components α-pinene, Limonene and α-Terpineolare found in common with components reported for B. neglecta, B. rivae, B. pirottae and B. papyrifera from different localities in Ethiopia (Dekebo et al., 1999; Baser et al., 2003). Also, the oil of B. neglecta with components: Sabinene, Terpinen-4-o1 and.α.-Terpinyl acetateare found in line with components reported for B. neglecta, B. rivae and B. pirottae from different localities in Ethiopia (Baser et al., 2003; Basar, 2005). B. neglecta collected from Bena-Tsemay shows α-pinene (6.27%), limonene (0.81%) and terpinen-4-ol (1.04%) as the main constituents qualitatively. This result is acceptable as compared with the results from the earlier literature analyzed for the major components of resins from B. neglecta which show the concentration ranges for α-pinene (2–69%), limonene (0–40%) and terpinen-4-ol (0–5%). The composition of the oil differs according to the climate, harvest conditions, and geographical source (Mikhaeil et al., 2003).
6 Conclusion and Recommendations
6.1 Conclusion
The analysis of population status of tree species at the study district generally show presence of good regeneration status. However, the number of individuals dramatically falls at higher size classes, which is probably due to high rate of harvest of material trees. B. neglecta is one of the economically important tree species with higher density and high IVI. However, its regeneration status was found to be poor. Although, it has a poor regeneration however, there is a possibility to start the resin or “tikur etan ” (meaning: black incense) business in the area with the existing harvestable number of B. neglecta trees in the area, as this could supplement the income from agricultural production in the area.
The physico-chemical properties of the resin & its volatile oil extraction from B. neglecta in the study area were determined. As a result, the physicochemical characteristic of the resin sample showed good agreement with similar studies and international standards. The resin from the Bena-Tsemay district possesses matching quality to gum arabic of commerce from B.neglecta for commercialization purpose.
The major components of the essential oil of B. neglecta were α-pinene (6.27%), Methyl isohexadecanoate (13.62), Methyl linoleate (25.29%) and Methyl oleate (25.92%) in ascending order of their compositions. Moreover, Methyl isohexadecanoate, Methyl linoleate and Methyl oleate were components, which were not reported in a previous study. B. neglecta resin contains many chemical constituents and the essential oil of this tree has much contribution in medicinal values and in industry for other purpose like perfume.
6.2 Recommendations
For attempts to develop, manage and sustainable use the resin resources of the Bena-Tsemay, the following recommendations are given:
- Improved management i.e., resources development, conservation and utilization of the woodland is needed.
- Appropriate tapping technology should be developed and training should be given to enhance its contribution to livelihood.
- Yield study should be followed in order to determine the amount of resin produced from the area whether the amount satisfy commercialization purpose.
- Market studies should go hand–in–hand with the development of the countries' B. neglecta resource base for resin production.
- Use different types of extraction methods such as Hydro distillation and the use of steam distillation to compare the yield in terms of quantity and quality.
- Quality-related physico-chemical analysis of essential oil should be conducted to control the quality of essential oil.
- Biological activities of essential oil should be determined.
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Appendices
Appendix 1:The list of species that include scientific name, local name, family and life form of all woody species encountered at study Woreda.
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Appendix 2 : Extracted ion current chromatogram showing key triterpenic compounds in oil of B. neglecta (Bena-Tsemay).
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Appendix 3 : The analyzed compounds from the essential oil by IUPAC name, common name, and concentration.
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- Quote paper
- Alemayehu Hido (Author), 2018, Population Status and Resin Quality of Frankincense "Boswellia neglecta" (Burseraceae) Growing in South Omo, Southwestern Ethiopia, Munich, GRIN Verlag, https://www.grin.com/document/1189322
