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Now showing items 1 - 8 of 8

  • Frankincense in peril

    Bongers, Frans   Groenendijk, Peter   Bekele, Tesfaye   Birhane, Emiru   Damtew, Abebe   Decuyper, Mathieu   Eshete, Abeje   Gezahgne, Alemu   Girma, Atkilt   Khamis, Mohamed A.   Lemenih, Mulugeta   Mengistu, Tefera   Ogbazghi, Woldeselassie   Sass-Klaassen, Ute   Tadesse, Wubalem   Teshome, Mindaye   Tolera, Motuma   Sterck, Frank J.   Zuidema, Pieter A.  

    The harvest of plant parts and exudates from wild populations contributes to the income, food security and livelihoods of many millions of people worldwide. Frankincense, an aromatic resin sourced from natural populations of Boswellia trees and shrubs, has been cherished by world societies for centuries. Boswellia populations are threatened by over-exploitation and ecosystem degradation, jeopardizing future resin production. Here, we reveal evidence of population collapse of B. papyrifera- now the main source of frankincense-throughout its geographic range. Using inventories of 23 populations consisting of 21,786 trees, growth-ring data from 202 trees and demographic models on the basis of 7,246 trees, we find that over 75% of studied populations lack small trees, natural regeneration has been absent for decades, and projected frankincense production will be halved in 20 yr. These changes are caused by increased human population pressure on Boswellia woodlands through cattle grazing, frequent burns and reckless tapping. A literature review showed that other Boswellia species experience similar threats. Populations can be restored by establishing cattle exclosures and fire-breaks, and by planting trees and tapping trees more carefully. Concerted conservation and restoration efforts are urgently needed to secure the long-term availability of this iconic product.
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  • Trends and drivers of land use/land cover change in Western Ethiopia

    Betru, Teshome   Tolera, Motuma   Sahle, Kefyalew   Kassa, Habtemariam  

    Understanding the magnitude, direction and agents of land use/land cover change (LU/LCC) are important for planning sustainable management of natural resources. To this end, this study assessed the trends of LU/LCC and its drivers in Western Ethiopia. Landsat images of MSS (1978), TM (1986, 1991 and 2010), ETM + (1999) and OLI (2013 and 2016) were used to study the dynamics of LU/LCC. The land use/land cover (LU/LC) maps for each period were classified using a hybrid method by merging the outputs of supervised classification and intensive on-screen-digitizing techniques. The drivers of LU/LCC were studied using key informant interviews (KII) and focus group discussions (FGD). Four major LU/LC types namely forest, agriculture, shrub/grass, and settlement were identified with overall accuracies ranging from 91% to 94%. The result shows that forest was the dominant LU/LC type accounting for 69% in 1978 which later reduced to 13, 8.5 and 6.5 percent point (pp) in 1991, 2010, and 2016, respectively. Shrub/grasslands were also reduced by 11 pp from 2010 to 2016. Expansion of agricultural land was the major driver showing a radical increase by 13 pp between 2013 and 2016. Forest cover showed a reduction of 28 pp over the 38 years of the study period. In particular, 21.3%, 26%, and 16.6% of the forest was converted to shrub/grassland from 1986 to 1991, 1991 to 2010 and 2010 to 2016, respectively. But from 2010 to 2016, 19.13% of forest was converted to agriculture. The study showed that forest was first changed to shrub/grasslands and finally end up in agriculture showing that degradation is leading to deforestation. The result of FGDs and KIIs also showed that both small-scale subsistence agriculture and largescale commercial agriculture are the major proximate drivers of deforestation in the study area. Population pressure from a multi-sourced and continued inflow of immigrants, lack of integrated institutional frameworks and unsustainable exploitations of forest products are the major underlying causes of the observed changes. Proper land use planning, legal backing, and institutional integration are key recommendations to sustain forest resources of the study area.
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  • Trends and drivers of land use/land cover change in Western Ethiopia

    Betru, Teshome   Tolera, Motuma   Sahle, Kefyalew   Kassa, Habtemariam  

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  • Frankincense yield is related to tree size and resin-canal characteristics

    Tolera, Motuma   Sass-Klaassen, Ute   Eshete, Abeje   Bongers, Frans   Sterck, Frank  

    Highlights • Path analysis nicely decomposed the impact of tree characteristics on frankincense yield. • Frankincense yield increases with total resin-canal area in the bark, stem diameter, tree age, and tree leaf area. • However, frankincense yield is independent of the current radial growth rate. • Thicker trees have more resin canals and a larger total resin-canal area. • DBH indirectly effected frankincense yield through its direct effect on total resin-canal area. Abstract Boswellia papyrifera Hochst. is the most important global source of frankincense. Tree numbers are rapidly decreasing in many populations of B. papyrifera in Ethiopia, where most of the internationally traded frankincense comes from. Improper tapping is among the frequently mentioned reasons for this decrease within populations. We still lack sustainable techniques for frankincense tapping, and these techniques are not yet tuned to individual trees since we are unaware how tree characteristics influence frankincense yield. This study investigates the relationships between different tree characteristics and their relation to frankincense yield. We selected 53 trees and measured frankincense yield and their DBH, tree age, number of leaf apices, radial growth, bark thickness, total resin-canal area, and total number of resin canals in a cross-section. Regression and path analysis were used to unravel cause-effect relationships between tree characteristics and frankincense yield. Frankincense yield was independent of the actual radial growth rate, but increased with increasing total resin-canal area in the bark, stem diameter, tree age, and the number of leaf apices. We show that frankincense yield by trees is not only a simple function of tree size. Remarkably, trees that grew slower over their whole life history produced more frankincense, suggesting an intra-specific trade-off in growth rate and frankincense production. Overall, this study thus shows that frankincense production is the result of complex plant trait networks and long term tree life properties. The results contribute to management regimes that minimize the damage to trees, while maximizing benefits in terms of frankincense yield and can also be used for selection and propagation of trees which are well suited for frankincense production.
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  • Frankincense tree recruitment failed over the past half century

    Tolera, Motuma   Sass-Klaassen, Ute   Eshete, Abeje   Bongers, Frans   Sterck, Frank J.  

    Boswellia papyrifera (Burseraceae) trees grow in dry woodlands south of the Sahara and produce frankincense, the economically important olio-gum resin used for cultural and religious ceremonies throughout the world and as raw material in several industries. Across its distribution area, this species is threatened by farmland expansion, fire, improper tapping and overgrazing. Most of its populations lack saplings and small-sized trees (e.g. <10 cm). It is unknown whether the older, adult trees represent a single or several cohorts, representing single or plural regeneration and survival waves. To understand such long-term population dynamics, it is imperative to evaluate the age structure of the current populations. We used tree ring analysis to determine the age-diameter relationship. This study, (1) determines radial growth dynamics and age-diameter relationship of B. papyrifera, including verification of annual growth-ring formation, and (2) constructs the population age structure and discusses consequences thereof for population maintenance and long-term frankincense production. We could prove that B. papyrifera forms annual growth rings. The average radial annual growth rate of B. papyrifera is 1.15 mm (s.d. = 0.22) and varies significantly among the sampled trees. Age and diameter of B. papyrifera trees are significantly correlated. From the population-age structure, it becomes obvious that the current B. papyrifera populations lack successful recruitment since 1955, which we attribute to intensive grazing and fire associated with the escalating increase of human settlement in the area. Lack of recruitment leads to rapidly declining populations resulting in strongly reduced frankincense production. Management aimed at seedling survival and sustainable use of relic trees is urgent.
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  • Resin secretory structures of Boswellia papyrifera and implications for frankincense yield.

    Tolera, Motuma   Menger, David   Sass-Klaassen, Ute   Sterck, Frank J   Copini, Paul   Bongers, Frans  

    BACKGROUND AND AIMS: Frankincense, a gum-resin, has been tapped from Boswellia papyrifera trees for centuries. Despite the intensive tapping and economic interest of B. papyrifera, information on the resin secretory structures, which are responsible for synthesis, storage and transport of frankincense, is virtually absent. This study describes the type, architecture and distribution of resin secretory structures of B. papyrifera and its relevance for the ecophysiology and economic use of the tree.; METHODS: The type and architecture of resin secretory structures present in bark and wood was investigated from transversal, tangential and radial sections of bark and wood samples. The diameter and density (number of resin canals mm(-2)) of axial resin canals were determined from digital images of thin sections across the different zones of inner bark.; KEY RESULTS: Resin canals form a three-dimensional network within the inner bark. Yet, the intact resin-conducting and producing network is on average limited to the inner 6·6 mm of the inner bark. Within the inner bark, the density of non-lignified axial resin canals decreases and the density of lignified resin canals increases from the vascular cambium towards the outer bark. In the wood, only radial resin canals were encountered.; CONCLUSIONS: Frankincense tapping techniques can be improved based on knowledge of bark anatomy and distribution and architecture of resin secretory structures. The suggested new techniques will contribute to a more sustainable frankincense production that enhances the contribution of frankincense to rural livelihoods and the national economy.
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  • The frankincense tree Boswellia neglecta reveals high potential for restoration of woodlands in the Horn of Africa

    Mokria, Mulugeta   Tolera, Motuma   Sterck, Frank J.   Gebrekirstos, Aster   Bongers, Frans   Decuyper, Mathieu   Sass-Klaassen, Ute  

    Boswellia neglecta S. Moore is a frankincense-producing tree species dominantly found in the dry woodlands of southeastern Ethiopia. Currently, the population of this socio-economically and ecologically important species is threatened by complex anthropogenic and climate change related factors. Evaluation of tree age and its radial growth dynamics in relation to climate variables helps to understand the response of the species to climate change. It is also crucial for sustainable forest resource management and utilization. Dendrochronological and remote-sensing techniques were used to study periodicity of wood formation and leaf phenology and to assess the growth dynamics of B. neglecta. The results show that B. neglecta forms two growth rings per year in the study area. The growth ring structure is characterized by larger vessels at the beginning of each growing season and smaller vessels formed later in the growing season, suggesting adaptation to decreasing soil moisture deficits at the end of the growing season. Seasonality in cambial activity matches with a bimodal leaf phenological pattern. The mean annual radial growth rate of B. neglecta trees is 2.5 mm. Tree age varied between 16 and 28 years, with an average age of 22 years. The young age of these trees indicates recent colonization of B. neglecta in the study region. The growth rate and seasonal canopy greenness (expressed by Normalized Difference Vegetation Index - NDVI) were positively correlated with rainfall, suggesting that rainfall is the main climatic factor controlling growth of B. neglecta. The observed temporal changes in leaf phenology and vessel size across the growth rings indicate that the species is drought tolerant. Therefore, it can be regarded as a key tree species for restoration of moisture-related limited areas across the Horn of Africa. (C) 2016 Elsevier B.V. All rights reserved.
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  • Excessive pruning and limited regeneration:Are Faidherbia albida parklands heading for extinction in the Central Rift Valley of Ethiopia?

    Sida, Tesfaye Shiferaw   Baudron, Frederic   Deme, Dejene Adugna   Tolera, Motuma   Giller, Ken E.  

    Scattered Faidherbia albida trees provide multiple ecological and production benefits across the Sahel. The intensive management and use of this important tree may impede its regeneration. Regeneration bottlenecks were explored and population dynamics modelled. On experimental plots in which seed of F.albida was sown, exposure to the first 2 months of dry season resulted in a quarter of seedling mortality. Exposure to season-long free grazing and browsing caused significantly greater seedling mortality. Results from monitoring 100 permanent plots scattered over the landscape showed that adult population density was 4.2 +/- 0.3 (mean +/- SE) trees ha(-1) and dominated by old age classes. Sixty percent of the total population were older than 30 years. The mean density for juveniles was 1.4 +/- 0.2 (mean +/- SE) individuals ha(-1). The annual rates of decline were 1.2%, 51.3%, and 63.2% for adults, seedlings, and saplings, respectively. Our model predicted that the F.albida population will start to decline within 1-2 decades to eventually fall below 1 tree ha(-1) within 60 years under current management. The model highlighted that the limited seed source, caused by excessive pruning, was the main constraint for recruitment. Appropriate land management policy to ensure adequate seed production would avert current trends in decline of F.albida population.
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