Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
http://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (http://www.sciepub.com)

Underutilized Natural Gum and Resin Resources in Ethiopia for Future Directions and Commercial Utilization

Wubalem Tadesse*, Tatek Dejene, Gizachew Zeleke, Getachew Desalegn

Central Ethiopia Environment and Forest Research Center (CEE-FRC), Ethiopian Environment and Forest Research Institute (EEFRI), Addis Ababa, Ethiopia

Abstract: The drylands of Ethiopia are well known for their natural gum and resin producing tree and shrub species such as Acacia, Boswellia, Commiphora and Sterculia. The production and trade volumes of gums and resins in the country showed a declining trend since 2010. The present review work is focused on availability of alternative underutilized tree and shrub species to indicate the diverse gum and resin market opportunities. Several Sub-Saharan African countries are producing gum and resin products from diversified species. Gum arabic is collected from Acacia senegal (L) Willd, Acacia seyal DEL, and Acacia polyacantha Willd species. Three countries namely Sudan, Nigeria, Chad contribute about 97% to the international market, while Ethiopia's contribution is 0.9%. World demand for karaya gum from Sterculia setigera DEL is about 7,000 tonne and in Africa, Senegal is the leading exporter. Despite the huge resources of A. senegal, A. seyal and A. polyacantha, Ethiopia producing very low quantity, and gum is collected from natural oozes of trunks or branches. S. setigera is also found in the country, although gum karaya is not yet under production. South and south eastern parts of Ethiopia hosts abundant species of Acacia, Boswellia and Commiphora. Gum-resin products are collected from natural exudates by herdsmen, women and children while herding and doing other activities, indicating its adverse effects on quality and quantity. Very small proportions of Myrrh and gum opopanax enter the local market. Other constraints are, lack of appropriate institutions, infrastructure, tapping technologies and market information. Therefore, appropriate policy formulation, research and development interventions, are recommended for supporting sustainable management, production and marketing of products.

Keywords: deforestation, oleoresin, marketing, species diversity, tapping, value addition

Received April 06, 2020; Revised May 08, 2020; Accepted May 15, 2020

Citation: Wubalem Tadesse, Tatek Dejene, Gizachew Zeleke, Getachew Desalegn, Underutilized Natural Gum and Resin Resources in Ethiopia for Future Directions and Commercial Utilization. World Journal of Agricultural Research, 8 (2). 32-38. January 2020. doi:10.12691/wjar-8-2-2

1. Introduction

In Africa, where 60% of rural dwellers are poor, dry forests represent important resources base for livelihoods and economic development. About 320 million people in the continent depend on dry forest resources to meet many of their basic needs [1]. Dry forests and woodlands in sub-Saharan Africa, despite their fragility, are endowed with rich biodiversity and provide versatile economic and ecological benefits to the society [2]. Commercialization of NTFPs in the region offers an opportunity for income generation and livelihood diversification. The drylands of East Africa, in particular, are known for their potential and long tradition of extraction and commercialization of natural gum and resin products. Exudates from the genera Acacia, Boswellia and Commiphora has been used for both domestics and the international markets [2].

Drylands of Ethiopia are dominated by ecologically and socio-economically important species of the genera Acacia, Boswellia, Commiphora and Sterculia. Particularly, Frankincense, obtained from different Boswellia species, Myrrha and Opopanax from diverse Commiphora species and Gum arabic of Acacia species are among the many dry forest based export products of the country. In almost all dryland areas of Ethiopia, gums and resin bearing species occupies significant portion of the land mass [3,4]. About 13 species of Acacia, 16 species of Commiphora and six species of Boswellia are known as potential yielders of commercial gums and resins in Ethiopia. Among these, gums from two species of Acacia and gum resins from three-four species of Commiphora and five species of Boswellia are currently produced commercially [5].

Frankincense obtained from B. papyrifera is the main commercialized product, representing more than 70% of the Ethiopia's natural gum and resins production, export volume and the amount of revenue [4]. However, the leading frankincense producing tree species, B. papyrifera, over the decades is facing uncertain future/lacking regeneration due to several and interrelated anthropogenic and environmental challenges mainly expansion of agricultural lands, overgrazing, population increase and the ever-growing demand for construction and fuel wood, forest fire, pests and diseases, unsustainable resource utilization. are among the major challenges affecting B. papyrifera regeneration in Ethiopia [4,6,7]. Studies made on the population dynamics, population structure, ecological physiology, growth dynamics indicated that B. papyrifera is declining at alarming rate and will disappear in five - six decades unless serious measures are considered. The volume of frankincense production is also expected to halve in 15-20 years, if the current management practices continues as it is [6].

The production and trade volumes of gums and resins in Ethiopia have been increasing between 1998 and 2007 [5]. However, production and export data of natural gum and resin resources shows an overall declining trend, and so does value of the export [8]. It is time to search for other alternative and underutilized potential tree and shrub species for natural gum and resin production and commercialization. Therefore, the present review work is focused on the availability of alternative potential species namely A. Senegal, A. seyal, A. polyacantha, S. setigera and Oleo gum resin producing different introduced Pinus species. The species distribution and characterization of their products thereby diversifies opportunities to find new market niches.

2. Major Natural Gum and Resin Producing Species in African Countries

Several Sub-Saharan African countries are producing and commercializing natural gum and resin products from diversified dry land tree species to national and international markets. A. Senegal, A. seyal, A. polyacantha, S. setigera, Oleo gum resin from Pinus species are among the widely used for production and commercialization of natural gum and resin products [9].

African countries export about 100,000 tonnes of gum arabic annually, and demand is projected to reach 150,000 tonnes by 2020. World export demand for karaya gum is about 7, 000 tonnes, of which Senegal exports about 1,000 tonnes. The global export demand for Frankincense is estimated at about 10,000 tonnes per year. The principal exporters of aromatic resins are Ethiopia (3,000 tonnes), Kenya (2,361 tonnes), Somalia (1,200 tonnes) and Eritrea (400 tonnes). Globally, the resource potential of gums and resins far exceeds production [10].

Gum Arabic. Commercial gum arabic is collected from a number of Acacia species, of which A. senegal, A. seyal, and A. polyacantha are the most widespread in the gum belt. Gum arabic or acacia gum is a tree gum exudate and has been an important part of commerce since ancient times. The trees grow widely across the Sahel belt of Africa situated in the north of the equator up to the Sahara Desert and from Senegal in the west to Somalia in the east [10]. African countries export about 100,000 tonnes of gum arabic annually, and demand is projected to reach 150,000 tonnes by 2020 [10]. Sudan is one of the biggest gum arabic producers in the world and produces more than 80% of the total world gum Arabic (Table 1).

Gum karaya. The genus Sterculia is a native of dry deciduous forests of tropical climates. It is found in the Sudano-Sahel and in the Sudan-Guinea zones: Togo, eastwards to Sudan and Somalia, East Africa, Angola Gambia, Nigeria, Senegal, Ethiopia, Eritrea, Kenya, Malawi, Tanzania. Sudan has very large areas of Sterculia in Africa [11]. World export demand for karaya gum is about 7,000 tonnes [10]. In Africa, commercial production of Gum karaya is taking place in Senegal, which is the world-leading exporter (around 1,000tonne/year) [12,13].

Oleoresin. Oleoresin or resin from pine plantations is being produced from different African countries. Kenya from P. elliottii, P. caribaea, and P. radiata; South Africa from P. elliottii and P. caribaea; Zimbabwe from Pinus elliottii; Uganda from P. caribaea; Malawi from P. elliottii and P. kesiya; Zambia from P. merkusii and P. kesiya; Tanzania from P. elliottii and P. caribaea [13]. Management of the pine species for resin in addition to timber has a definite added economic advantage both at community (provides employment) and national (import substitution or foreign exchange) levels and an incentive to sustainable forest management based on the principle of multiple uses [13].

Table 1. Exports of Gum arabic (ton) from different African countries from 2001-2010 [10].

3. Underutilized Potential Natural Gum and Resin Producing Tree/Shrub Species in Ethiopia

3.1. A. senegal and A. seyal

A. senegal and A. seyal are mainly found widely distributed in Acacia-Commiphora (small-leaved) deciduous woodlands. The vegetation type is located between 900-1900 m.a.s.l. found in the Rift Valley, eastern and south-eastern lowlands of Ethiopia [14,15,16].

The physic-chemical characteristics of the gum arabic produced in Ethiopia agrees well with values of same quality characteristics of gum arabic reported from Sudan and other exporting countries, and also conforms well to international standards in all aspects. Indeed, it is possible to utilize the gum arabic resource of the Central Rift Valley of Ethiopia for commercial and/or industrial purposes [17].

[18] introduced tapping and evaluated the gum arabic yield from natural stands of A. senegal and the growth of six provenances in different parts of the country. Tapping was done with a specially designed axe and special tool “Sunki”. Trees were tapped to give strips of relatively similar depth, width and length. Yields recorded were comparable to those reported for the Sudan, the leading producer of gum arabic. Thus, tapping trees during the appropriate months and at the appropriate positions can enhance the production of gum arabic from natural stands of A. senegal. They recommend tapping of branches starting from October when the leaf color begins to change [18].

Despite the high potential of the resource base, the current annual production and export of gum arabic from Ethiopia is very low [5,11]. This is due to the lack of proper production technique. Current production is based mainly on collection of gum from natural oozes from tree trunks or branches. Moreover, knowledge of establishment techniques, yield and quality of gum from different provenances, optimum age for tapping, phenological records and silvicultural management requirements of the species are limited or lacking [18].

Therefore, this multipurpose dryland species has to be promoted, by introducing tapping techniques utilized in Sudan and tested in Ethiopia and maximize their utilization potential in the country by compensating the critical challenge faced on B. papyrifera, the main natural gum producing tree species in the country.

3.2. Acacia polyacantha Willd

A. polyacantha is a widespread acacia found from India to tropical Africa. In Ethiopia, commonly found in wooded grassland, deciduous woodland and bushland and riverine forests of Shoa, Gonder, Gojam, Western Tigray, Ilubabor, Kefa, Gamo Gofa and Sidamo areas, 500-1,600 m [19]. B. papyrifera and A. polyacantha grow in dry Combretum Terminalia woodlands and wooded grass-lands in the north [20]. Even though, the species is found in different drylands of the country, gum is not produced and commercialized in the country so far.

3.3. Sterculia setigera DEL

In Ethiopia, it is found in association with Acacia-Commiphora-woodland, wooded grassland and bush land, on rocky slopes or black cotton soil, dry riverine forest extending from 700-1900 m.a.s.l. [4,11]. The species is among the most ecologically important woody species in Combretum-terminalia woodlands, mainly in Metema area with the highest Importance Value Index [20].

Even though, S. setigera, is abundant throughout the country, gum karaya is not yet under commercial production and marketing in Ethiopia [5]. The species use has been limited to its wood products.

3.4. Oleoresin Commercial Products from Pinus Species

Fast growing exotic tree species including 15 Eucalyptus, Acacia and Pines species were introduced to Ethiopia during 1895 [21]. Pinus patula Schldl. et Cham. and Pinus radiata D. Don are the two Pine species widely planted for timber production in different parts of the country. Pinus caribaea Morelet was first introduced around Bonga in 1975, to study the performance, in areas with the altitude ranging of 1,500 to 1,700 m. The species is also planted in Suba forest. The species has the potential to be planted as an alternative to Pinus patula on similar sites [22].

The chemical composition obtained from resins of P. Caribaea and P. radiata growing in Ethiopia were investigated. Twenty compounds were identified representing ca 92-99% of the total oil. α and ß - pinene were the main components of P. radiata, representing 83.1% of the total oil. As α and ß - pinene are important intermediate in the manufacture of synthetic aroma compounds and flavouring ingredients. P. caribaea and P. radiata resins may serve as good source of these compounds [23].

Table 2. Production and export of natural gums and resins (Tonnes) from Ethiopian dry lands between the years 2007 to 2016 [8]

Table 3. Pine species introduced to Ethiopia for research purposes and having potential for ole-resin production

Even though, there is no formal tapping and resin extraction from Pinus trees in Ethiopia, it is common to see debarked and, hence, damaged pine stems at Bonga site mainly for resin extraction [24]. This clearly indicates the possibility of introducing tapping methods to potentially resin producing pine species in Ethiopia. Lists of available Pinus species in experimental plots are presented in Table 3.

3.5. Other Potential Species in South and South-eastern Ethiopia

Several studies confirmed the existence of potential gum and resin bearing species of Acacia, Boswellia and Commiphora species in different parts of South and south- eastern regions of the country. These regions support more diverse species, and hence greater opportunity for marketing of different products [3,7,27,28]. Numerous studies confirm that oleo-gum resins obtained from the vegetation resources in the region play signiﬁcant role in the economy of rural households and in the country.

Resins from Boswellia rivae (Engl.), B. ogadensis (Vollesen), B. neglecta (S. moore) and B. microphylla (Chior.) are collected and traded as frankincense in these areas (Lemenih et al. 2003).Next to frankincense, gum-resins from four Commiphora species namely Commiphora africana, C. myrrh(syn. C. molmol), C. habessinica, and C. schimperi were the major products collected and utilized in Southern Ethiopia [1]. The botanical origin of opopanax also known as scented myrrh is C. guidottii, a species found in abundance in eastern Ethiopia and Somalia. The highly pleasant aromatic oil of B. pirottae, an endemic species of Ethiopia, is distinguished by a high content of trans-verbenol (15.5%) and terpinen-4-ol (14.6%) [29]. Gum arabic obtained from A. Senegal, gum talha from A. seyal are also potentially available in these areas [30,31].

In northern frankincense production areas (from B. papyrifera), there are many private and state companies engaged in the production and marketing of gum and resins, and they create seasonal employment opportunities for the tapping, collection, and grading of frankincense. However, natural gum and resin products from southern region are collected from natural exudates and no tapping at all [3,20,30]. The producers are mainly herdsmen, women and children, and they do the collection side by side with herding and doing other activities. Once collected, the products transported to available markets and/or soled to occasionally appearing buyers at village level [3]. This indicates its adverse effect on the quality and quantity of gum produced and thus on the role that it could play both at local and national levels. Moreover, the mixing up of gums and resins of different Commiphora species for increasing trade volume is a common phenomenon of adulteration, resulting in poor quality which again severely affecting marketing of gums and incenses in Borena [3]. Furthermore, other identified constraints in south and southern Ethiopia are: (i) lack of appropriate institutions and capacity, (ii) infrastructure facilities, (iii) appropriate tapping technologies, (iv) access to market, (iv) market information and fair markets prices, (vi) established cooperatives, etc. [27].

Figure 1. Distribution of natural gum and resin bearing species in Ethiopia [34]

In north Ethiopia gum and resin production is an established and relatively intensive practice, organized commercial production started in 1940s; access and harvesting rights are controlled by formal institutions. But in the south gum and resin production is relatively new and less intensive; organized commercial collection is recent, but subsistence production has long history and access and harvesting rights are part of the traditional grazing land management [32].

Therefore, establishing and strengthen relevant institutions (government and non-government) has paramount importance for sustainable management and utilization of gum and resin resources; support extension service aid development of a supply chain that could generate more cash for the poor [28]. It would also be beneﬁcial to develop suitable tapping, processing, and handling technologies that could add value to the products [1] and for promoting the sustainable management of woodland resources through organized production and commercialization of high value oleo-gum resins [33]. Hence, development of innovative technologies and infrastructure remains as key issues [28] that need intervention measures.

Hence, appropriate policies and institutions are crucial for achieving the sustainable and socially acceptable harvesting of gum and resin resources. Policy and institutional reforms should revolve around gender equity, community-based resource management, and secure land tenure and tree ownership, with the aim of facilitating equal access to and control over benefits from the use of these resources. Equally important are the provision of incentives and the empowerment of resource users in accessing markets to seize the opportunities presented by regional and global markets for gums and resins [10].

4. Value Addition and Marketing

Underutilization and lack of value addition restricts appropriate utilization of Ethiopia’s dry forest products and other resources. Therefore, most of the NTFPs products are commercialized without value addition and the country forced to import value added products with huge foreign currencies. The technologies used in the collection of gums and resins, and attempts to add value, have remained back-warding and largely unchanged for decades. Value-adding activities are limited to cleaning, sorting and grading. Therefore, it is necessary to improve production and processing aspects. Attributes considered in grading gums and resins are size, colour, source area and content of impurities [35]. Therefore, value addition and strengthening marketing information system to the natural gum and resin products should be promoted in order to increase foreign currency and employment opportunities.

While the international market prices of raw gum arabic continue to fluctuate the international prices of processed gum arabic is either stable or increasing. Poverty reduction in the producing countries of gum arabic can only be achieved through gum arabic only if value is added to this product through processing to enable them obtain higher profits [36]. In marketing, demand requirements of stable supply in quantity and quality deserve more attention. This will require organizational and capacity building for all actors in the chain. The marketing system needs to encourage different types of value addition, in particular quality upgrading by the producers. This could even lead to employment creation and an increase in revenues. The creation of associations or other forms of coalition has the potential to increase producers’ bargaining power and their willingness to collect more and better gum [37].

5. Conclusions and Recommendations

Deforestation and forest degradation are among the repeatedly reported major challenges seriously affecting dry forest resources of Ethiopia. Agricultural expansion, re-settlement, unsustainable product harvesting, free grazing, lack of natural regeneration of tree species, etc. are among the major consequences of deforestation and un-sustainable utilization. Due to these interrelated challenges in dry forest resources, the socio-economic and ecological contribution of natural gum and resin products obtained from these forests are severely affected. In Ethiopia, scholars concur that there is a general lack of awareness among policy makers and associated institutional constraints (e.g. property rights over forests and their products) are negatively affecting an optimal economic use of dry forests for livelihoods and export promotion. This is leading to their conversion and deforestation through investments and resettlement programs that instigate cropland expansion. Therefore, policy makers should critically evaluate their decision making processes related to resettlement and agro-business investment programs in the frankincense and other gum-resin bearing species harboring woodlands.

Ethiopia hosts very diverse and potential natural gum and resin producing species, and historically is among the first in commercializing those products since millennia. However, currently the country depends on a single species B. papyrifera and its frankincense product, where the species faces uncertain future of disappearance, and hence its annual production and exports are in a declining trend. Whereas, other sub Saharan African countries are diversifying their natural gum and gum production from diversified species of Acacia, Boswellia, Commiphora, Sterculia and Pines besides strengthening their institutions by giving more attention to the sector and its socio-economic potential and environmental importance.

Therefore, taking into account the enormous socio-economic and ecological contributions of dry forest resources in general and natural gum and resin sector in particular, the Ethiopia has to sustainably manage and utilize its high value and renewable natural resources by strengthening its institutions, infrastructures including processing and marketing of the exportable products. The absence of appropriate institutions and governance mechanisms, ecological knowledge of the different species, and technical support might also lead to irreversible resource degradation from over-exploitation of very limited species, while other potential species have been still untouched or underutilized.

In the face of the increasing national and international demand for natural gum and resins and the subsequent emerging opportunities, appropriate policy formulation and research and development interventions, has to be put in place for supporting sustainable exploitation of commercial natural gum and resin production while ensuring conservation and development of the resource base. Sustainable management of natural gum and resin resource potentials requires an integrated enabling policy and institutional framework to safeguard social and environment concerns associated with the commercialization of the natural products from communal lands. Promote value addition of gum and resin products will significantly contribute to product diversification and hence job creation and import substitution. Organized production and market information system management must be in place and should not be haphazard. Besides, Integrated and in-depth research on alternative mechanisms and methods for the best species B. papyrifera regeneration, which is endangered now recommended.

Acknowledgments

We are grateful SUSTFUNGI project for the financial support that has been provided for the trip and the stay of Wubalem Tadesse and Gizachew Zeleke to Spain, and the Forestry Research Center (CIFOR) of the National Institute of Agricultural research (INIA) for hosting and arranging to them literature review database facilities.

References

[1]   | Fikir D, Tadesse W, Gure A (2016). Economic Contribution to Local Livelihoods and Households Dependency on Dry Land Forest Products in Hammer District , Southeastern Ethiopia. Int. J. For. Res. 2016, 11. 2016
[2]   | Alemu A, Pretzsch J, Secco L., Mohamod TE (2014). Contribution of small-scale gum and resin commercialization to local livelihood and rural economic development in the drylands of Eastern Africa. Forests 5, 952-977.
[3]   | Worku A(2006). Population Status and Socio-economic Importance of Gum and Resin Bearing Species in Borana Lowlands, southern Ethiopia. MScThesis. Addis Ababa Univ. Dep. Biol. Addis Ababa University.
[4]   | Tadesse W, Desalegn G, Alia R, (2007). Natural gum and resin bearing species of Ethiopia and their potential applications. Investig. Agrar. Sist. y Recur. For. 16, 211.
[5]   | Lemenih M (2011). Resource base of gums and resins and challenges of productivity, in: Lemenih, M., Kassa, H. (Eds.), Opportunities and Challenges for Sustainable Production and Marketing of Gums and Resins in Ethiopia. Center for International Forestry Research, Addis Ababa, pp. 13-40.
[6]   | Eshete A (2011). The Frankincense Tree of Ethiopia ecology, ecology, productivity and population dynamics. Doctoral thesis. Wageningen University.
[7]   | Lemenih M, Kassa H (2011). Opportunities and challenges for sustainable production and marketing of gums and resins in Ethiopia, Opportunities and challenges for sustainable production and marketing of gums and resins in Ethiopia.
[8]   | NFSDPE (2018). National Forest Sector Development Program National Forest Sector Development Programme. Volume 1. (Acced on April 20, 2019).
[9]   | Mariod E (2018). Gum Arabic Structure, Properties, Application and Economics. Elsevier Academic Press. 313 Pages.
[10]   | NGARA (The Network For Natural Gums And Resins In Africa), (2017). Overview and framework of priorities 2017-2030. Nat. Gums Resins Africa. 40 pages.
[11]   | Tadesse W, Desalegn G (2009). Sterculia Setigera Del. Potential Dryland Resource For The Production of Gum Karaya in Ethiopia: Review. Ethiop. J. Nat. Resour. 11, 83-98.
[12]   | FAO (1995). Naval stores : turpentine and rosin from pine pine resin resin naval stores : and rosin from pine pine resin resin. FAO, Rome. 53 Pages.
[13]   | Chikamai B, Tchatat M, Julius C, Ousseynou N (2015). Forest Management for Non-Wood Forest Products and Services in Sub-Saharan Africa. Discov. Innov., 2009; 21(SFM Spec. Ed. No. 1) 50-59.
[14]   | Gebrekirstos A, Mitlo R, Teketay D, Worbes M (2008). Climate - growth relationships of the dominant tree species from semi-arid savanna woodland in Ethiopia. Trees 22, 631-641.
[15]   | Atmadja S, Eshete A, Boissière M (2019). Guidelines on sustainable forest management in drylands of Ethiopia, Arid Zone Forest and Forestry Working Paper No 1. Food and Agriculture Organization of the United Nations and Center for International Forestry Research, Rome.
[16]   | Soromessa T, Teketay D, Demissew S (2004). Ecological study of the vegetation in Gamo Gofa zone, Southern Ethiopia. Trop. Ecol. 45, 209-221.
[17]   | Yebeyen D, Lemenih M, Feleke S (2007). Characteristics and quality of gum arabic from naturally grown Acacia senegal (Linne) Willd. trees in the Central Rift Valley of Ethiopia. Food Hydrocoll. 23, 175-180.
[18]   | Alemu A, Yilma Z, Eshete A, Dejene T (2013). Growth performance and gum arabic production of Acacia senegal in northwest lowlands of Ethiopia. J. For. Res. 24, 471-476.
[19]   | Bekele-Tesemma A (2007). Useful trees and shrubs of Ethiopia: Identification, Propagation and Management for 17 Agroclimatic Zones, World Agro. ed. RELMA in ICRAF Project, Nairobi Kenya. 559 Pages.
[20]   | Adamu H (2014). Pattern Ecological Study of the Woodland Vegetation in Metema Area, Northwestern Ethiopia. Doctoral thesis. Stellenbosch University.

[21]  
Gil L, Tadesse W, Tolosana E, López R (2010). Eucalyptus Species Management, History, Status, and Trends in Ethiopia, in: Gil, L., Tadesse, W., Tolosana, E., López, R. (Eds.), Proceeding of the Conference on Eucalyptus Species Management, History, Status, and Trends in Ethiopia 15-17 September 2010, Ethiopian Institute of Agricultural Research, Addis Ababa, Ethiopia. UPM, Addis Ababa, Ethiopia, p. 414.

[22]   | Mihretu M, (2004). Growth Performance of Some Indigenous and Exotic Tree Species in Southwestern Ethiopia. Ethiopian Institute of Agricultural Research. Addis Ababa, Ethiopia. 47 Pages.
[23]   | Dagne E, Bekele T, Bisrrat D, Alemayehu M, Worku T, Elokaokich JP (1999). Essential oils of resins from three Pinus species growing in Ethiopia and Uganda. SINET Ethiop. J. Sci., 22(2) 253-257, 1999 253-257.
[24]   | Gezahgne A, Mulatu Y, Haile Giorgis D, Gebre T (2017). Report on field trip made to evaluate status of the existing seed stands and old research sites in Southwestern Ethiopia. Addis Ababa, Ethiopia. 23 Pages.
[25]   | Tadesse S, Teshome M (2015). Field report on the existing species trial sites in South Western Ethiopia. Addis Ababa, Ethiopia.
[26]   | Hvidberg-Hansen H (1978). The Growth of Some Exotic Forest Trees in the Munessa Forest, Ethiopia. The Commonwealth Forestry Review, 57(3 (173)), 181-189.
[27]   | Worku A, Lemenih M, Fetene M, Teketay D (2011). Socio-Economic Importance of Gum and Resin Resources in The Dry Woodlands of Borana. For. Trees Livelihoods 20, 137-156.
[28]   | Adem M, Worku, A, Lemenih, M, Tadesse W, Pretzsch J (2014). Diversity, regeneration status and population structure of gum- and resin-bearing woody species in south Omo zone, Southern Ethiopia. J. For. Res. 25 (2), 319-328.
[29]   | Baser KHC, Demirci B, Dekebo A, Dagne E (2003). Essential oils of some Boswellia spp ., Myrrh and Opopanax. Flavour Fragr. J. 18, 153-156.
[30]   | Lemenih M, Abebe T, Olsson M (2003). Gum and resin resources from some Acacia , Boswellia and Commiphora species and their economic contributions in Liban , south-east. J. Arid Environ. 55, 465-482.
[31]   | Dalle GT, Brigitte LM, Sselstein J(2005). Plant Biodiversity and Ethnobotany of Borana Pastoralists in Southern Oromia, Ethiopia. Econ. Bot. 59(1), 43-65.
[32]   | Woldeamanuel T (2011). Dryland resources, livelihoods and institutions. Doctoral thesis. Wageningen University, Wageningen, The Netherlands.
[33]   | Worku A, Teketay D, Lemenih M, Fetene M, (2015). Diversity, regeneration status, and Population structures of gum and resin producing woody species in Borana, Southern Ethiopia. For. Trees Livelihoods. Volume 21, 2012 - Issue 2. Pages 85-96.
[34]   | Anonymous, (ND). Digitized from Forestry and Wildlife Conservation D-AUTH; Forest Inventory Surveying and management Planning, October 1984, scale 1: 9.5m.
[35]   | Kassa H, Tefera B, Fitwi G (2011). Preliminary value chain analysis of gum and resin marketing in Ethiopia Issues for policy and research. CIFOR 12.
[36]   | Muller D, Okoro C (2004). Production and marketing of gum arabic, NGARA Publication Series 2, September, 2004. https://docplayer.fr/2311376-Production-and-marketing-of-gum-arabic-didier-muller-and-chidume-okoro.html.
[37]   | Mujawamariya G, Madi OP, Zoubeirou AM, Sene A, Maisharou A (2013). Common challenges in gum arabic production and commercialization in West Africa: a comparative study of Cameroon , Niger and Senegal. Int. For. Rev. 15, 182-199.