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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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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. - \ 2019
Nature Sustainability 2 (2019). - ISSN 2398-9629 - p. 602 - 610.
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.
Uniquely regenerating frankincense tree populations in western Ethiopia
Teshome, Mindaye ; Eshete, Abeje ; Bongers, Frans - \ 2017
Forest Ecology and Management 389 (2017). - ISSN 0378-1127 - p. 127 - 135.
Climate factor - Dry land forest - Human disturbance - Population structure - Regeneration bottleneck
Dry tropical forests provide a wide range of forest products that directly support the livelihoods of people. These forests are the most threatened and least protected forests due to expansion of agriculture and pasture lands, unregulated grazing, forest fire, unregulated collection of wood and other forest products. Dry forests of Ethiopia are heavily affected by such human induced factors. The iconic Boswellia papyrifera (Del.) Hochst is a dominant tree species of this forest and the principal source of the globally traded frankincense. The species lacks regeneration in all forests evaluated so far. Frankincense forests in relatively wetter dry land areas with little or no human related disturbance are not evaluated so far. Here we quantified the regeneration status of the frankincense tree in such areas and evaluated these forests in comparison to non-regenerating frankincense forests elsewhere. We surveyed two-ha plots in each of five districts in Benishangul Gumuz Region, Western Ethiopia. The frankincense tree populations showed two different regeneration patterns: inverse J-shaped and bell-shaped pattern. The presence of regenerating populations in three of our study areas is in sharp contrast to all earlier studies on this species. The healthy regeneration might be related with the availability of more favourable conditions such as better precipitation, lower levels of anthropogenic disturbances and younger ages of the three woodlands. These unique, regenerating frankincense tree populations need recognition and should be delineated as priority areas for conservation, which includes their role as source of genetic material. Better attention of conservation practitioners, policy makers and frankincense companies may help this species to survive and therewith its emblematic frankincense.
Frankincense yield is related to tree size and resin-canal characteristics
Tolera, Motuma ; Sass-Klaassen, Ute ; Eshete, Abeje ; Bongers, Frans ; Sterck, Frank - \ 2015
Forest Ecology and Management 353 (2015). - ISSN 0378-1127 - p. 41 - 48.
Boswellia papyrifera - Frankincense - Path analysis - Resin canals - Tapping - Tree characteristics

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.

Frankincense tree recruitment failed over the past half century
Tolera Feyissa, M. ; Sass, U.G.W. ; Eshete, A. ; Bongers, F. ; Sterck, F.J. - \ 2013
Forest Ecology and Management 304 (2013). - ISSN 0378-1127 - p. 65 - 72.
annual growth rings - long-term growth - dry-forest trees - boswellia-papyrifera - pterocarpus-angolensis - population-dynamics - age-determination - acacia-erioloba - seed predation - tropical trees
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.
Le déclin dún parfumeur
Zuidema, P.A. ; Groenendijk, P. ; Eshete, A. ; Sterck, F.J. ; Bongers, F. - \ 2012
Quatre Temps 2012 (2012). - ISSN 0820-5515 - p. 36 - 38.
Frankincense production is determined by tree size and tapping frequency and intensity
Eshete, A. ; Sterck, F.J. ; Bongers, F. - \ 2012
Forest Ecology and Management 274 (2012). - ISSN 0378-1127 - p. 136 - 142.
umbellularia-californica - boswellia-papyrifera - resin - biosynthesis - plantation - conifers - yield - pine - deer
Resin production in trees probably depends on trade-offs within the tree, its environment and on tapping activities. Frankincense, the highly esteemed resin from dry woodland frankincense trees of Boswellia papyrifera is exploited in traditional ways for millennia. New exploitation practices lead to weak trees and non-sustainable resin production. For 500 trees from four populations of B. papyrifera we evaluated how frankincense yield is affected by different tapping intensities (number of incision spots) and frequencies (number of resin collection rounds during the dry season), since both of them have been intensified recently. These effects are considered for trees of different size, since larger trees probably provide more resources for resin production. We predicted that frankincense production would initially increase with tapping intensity and tapping frequency, but later level-off because of resin depletion. Frankincense production varied highly: yield per tree per year of all 500 monitored trees averaged 261 g (±231, but largely varied and ranged from 41 to 1829 g. We indeed found that resin yield increased with tapping intensity, but not anymore beyond an intensity of 6–9 incision spots. Yield peaked around the seventh collection round, and declined thereafter. Yield increased with trunk diameter, but leveled-off beyond trees with a stem diameter of >20 cm. These patterns were similar across populations, and between contrasting areas. Our results suggest that high tapping intensity risks short-term resource depletion, warranting tuning down the intensity of the current collection practices. Less intense tapping rounds per season will reduce damage, increase the health of tree populations, and contribute to long term frankincense production. This study thus allows for developing less damaging and more sustainable management for frankincense trees.
Effects of resin tapping and tree size on the purity, germination and storage behavior of Boswellia papyrifera (Del.) Hochst. seeds from Metema District, northwestern Ethiopia.
Eshete, A. ; Teketay, D. ; Lemenih, M. ; Bongers, F. - \ 2012
Forest Ecology and Management 269 (2012). - ISSN 0378-1127 - p. 31 - 36.
frankincense - forest - fire
Boswellia papyrifera (Del.) Hochst. is one of the tree species in dry woodlands of Ethiopia that provides several goods and services. Despite its wide economic and ecological importance, its area coverage is dwindling from time to time, and its natural regeneration is hampered. Hence, long-term prospect for a sustained supply of the goods and services from the species is becoming questionable. The objectives of this study were to investigate: (i) the effect of resin tapping and tree size (DBH) on seed susceptibility to insect attack and the production of viable seeds; and (ii) seed longevity and germination ecology of the seeds of B. papyrifera. We collected seeds from tapped and untapped B. papyrifera stands at Lemlem Terara in Metema District, northwestern Ethiopia. The result showed that both tapped and untapped stands produced comparable insect attacked seeds (tapped stands = 16.6%; untapped stands = 15.8%). Untapped trees yielded significantly (P <0.0001) higher viable seeds (59%) than continuously tapped trees (49.3%), and trees with medium size (20 cm DBH) provided more viable seeds than bigger (30 cm DBH) and younger trees (10 cm DBH). Longevity of B. papyrifera seeds indicated significant difference in viability under three different temperature regimes (5, 15 and 21 °C), three storage periods (6, 9 and 12 months) and two tapping regimes (tapped and untapped populations). Fire that produced temperatures above 100 °C was lethal to the seeds as it caused complete loss of germinability regardless of exposure time. However, heat with temperatures less than 100 °C did not cause loss of germinability even after an hour of exposure. We also found that light conditions had no significant impact on the germination percentage. In general, viability of the seeds was affected by tapping and tree size but not by storage conditions and period, modest temperature and light conditions.
Limitations to sustainable frankincense production: blocked regeneration, high adult mortality and declining populations
Groenendijk, P. ; Eshete, A. ; Sterck, F.J. ; Zuidema, P.A. ; Bongers, F. - \ 2012
Journal of Applied Ecology 49 (2012)1. - ISSN 0021-8901 - p. 164 - 173.
timber forest product - boswellia-papyrifera - dry forest - dynamics - ethiopia - models - trees - acacia - fire
1. Resins are highly valued non-timber forest products (NTFP). One of the most widely traded resins is frankincense, tapped from several Boswellia tree species (Burseraceae). Exploited Boswellia populations often show poor regeneration, but the demographic consequences of these bottlenecks are unknown. Here we report on the first large-scale demographic study of frankincense-producing trees. 2. We studied 12 populations of Boswellia papyrifera in northern Ethiopia, varying in altitude and productivity. Six of these populations had been tapped before and were tapped during the study. Survival, growth and fecundity were determined for 4370 trees and 2228 seedlings, in 22.8 ha over a 2-year period. We also studied a remote population where no grazing and tapping took place. Matrix models were used to project population growth and frankincense production under four restoration scenarios. 3. Population structures of both tapped and untapped populations showed clear gaps. Small seedlings were abundant in all populations, but none developed into persistent saplings. Such saplings were only present in the remote population. Fire and grazing are the likely causes of this regeneration bottleneck. 4. Adult mortality was high (6–7% per year) in both tapped and untapped populations, probably caused by beetle attacks and fire. Unexpectedly, tapped populations presented higher diameter growth rates and fecundity compared to untapped populations. These differences are probably caused by non-random selection of exploited populations by tappers. 5. Under the ‘business as usual’ scenario, population models projected a 90% decline in the size of tapped and untapped populations within 50 years and a 50% decline in frankincense yield within 15 years. Model simulations for restoration scenarios revealed that populations and frankincense production could only be sustained with intensive management leading to full sapling recruitment and a 50–75% reduction in adult mortality. 6.Synthesis and applications. Regeneration bottlenecks and high adult mortality are causing rapid decline in frankincense-producing tree populations in Ethiopia. This decline is unlikely to be a consequence of harvesting and is probably driven by fire, grazing and beetle attacks. Fire prevention and the establishment of non-grazing areas are needed. Our results show that other factors than exploitation may seriously threaten populations yielding NTFP
Diversity and production of Ethiopian dry woodlands explained by climate- and soil- stress gradients
Eshete, A. ; Sterck, F.J. ; Bongers, F. - \ 2011
Forest Ecology and Management 261 (2011)9. - ISSN 0378-1127 - p. 1499 - 1509.
species-diversity - altitudinal gradients - boswellia-papyrifera - deciduous forest - african savanna - rain-forest - costa-rica - frankincense - regeneration - communities
Dry woodlands cover about 14% of the total African land surface and represent about 25% of the natural vegetation. They are characterized by a seasonal climate, with a dry season of 4–7 months. Large parts of these ecosystems are degrading due to grazing, fire or exploitation by people. We studied species richness and productivity patterns of dry woodlands in Ethiopia. For such ecosystems, classic productivity and diversity hypotheses predict that species richness and productivity increase as the wet season length increases, and decrease when soil conditions create water stress. We inventoried and measured trees in 18 2-ha plots distributed in two sites, one higher altitude site with a shorter wet season than the lower altitude site. We found that the stand volume per hectare was lower in the site with a shorter wet season. Across all 18 plots we observed that stand volume decreased with soil water stress (estimated from texture and depth). This was in line with the prediction. The species richness was lower in the short-wet-season woodlands, but was unaffected by variation in soil conditions. This suggests that climate driven constraints (wet season length) set the limits to species richness, and not soil conditions. As far as we know, this study is one of the first studies that evaluated these productivity and diversity hypotheses for dry African woodlands. --------------------------------------------------------------------------------
The frankincense tree of Ethiopia : ecology, productivity and population dynamics
Eshete Wassie, A. - \ 2011
Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): Frank Sterck. - S.l. : s.n. - ISBN 9789085859536 - 149
boswellia - populatiedynamica - tappen (rubber) - modellen - harsen - klimaat - begrazing - soortenrijkdom - bosecologie - ethiopië - boswellia - population dynamics - tapping - models - resins - climate - grazing - species richness - forest ecology - ethiopia

Keywords: Boswellian papyrifera, Frankincense tree, matrix model, population dynamics,
population bottleneck, tapping.

Combretum – Terminalia woodlands and Acacia – Commiphora woodlands are the two
dominant vegetation types that cover large parts of the dry land areas in Ethiopia. Several of
their tree and shrub species yield economically valuable products such as gum Arabic,
frankincense and myrrh. Boswellia papyrifera provides the widely traded frankincense that
accounts for >80% of the export revenues that the country is earning from gum and resin
resources. Unfortunately, the Ethiopian dry woodlands and the B. papyrifera populations are
disappearing rapidly due to the combined effects of over-harvesting gums and resins,
overgrazing by livestock, recurrent fires, and excessive wood harvesting. The current lack of
small saplings in the remaining populations of Boswellia suggests that the populations may
not be sustained for the future.
The main objectives of this thesis were to determine diversity and production patterns in B.
papyrifera dominated dry woodlands, to show the regeneration status in various B. papyrifera
populations, and to evaluate the effects of environment, frankincense harvesting, and grazing
on the population dynamics of B. papyrifera. The main research questions were: (1) how do
environmental conditions affect the tree/shrub species richness and production of Ethiopian
dry woodlands? (2) what factors determine the frankincense production by B. papyrifera
trees? (3) how do the vital rates and population dynamics of B. papyrifera vary across
habitats that differ in soil conditions and biotic factors? (4) What are the major bottlenecks in
the life cycle of the trees that hinder the sustainability of the remaining populations? To
address these questions, tree populations were studied in the highlands of Abergelle and the
lowlands of Metema. Metema also has a longer wet season length, higher annual rainfall and
better soil fertility status than Abergelle.
In total 36 and 22 tree and shrub species representing 20 and 9 families were recorded in
Metema and Abergelle woodlands, respectively. The most dominant plant families were
Burseraceae, Fabaceae, Combretaceae and Anacardiaceae. The vegetation at both sites was
dominated by B. papyrifera. The two sites differed in species richness, diversity and
production. Metema, the site with the longer wet season, had a higher species richness,
diversity and production than Abergelle. The productivity of woodlands also increased with a
higher clay content and greater soil depth. Populations structures indeed lacked the saplings,
except for one very isolated population on a steep mountain slope.
The studied frankincense trees produced 41 to 840 gram of frankincense during a year with
seven collection rounds, and 185 to 1826 gram of frankincense during a year with 14
collection rounds. The variation in frankincense production was large across individuals.
Frankincense production increased with tree size, tapping intensity, and tapping frequency.
The increase in production, however, levelled-off beyond a stem diameter of 20 cm, a tapping
intensity of 9 spots, and a tapping intensity of 10 rounds. Growth rate, survival rate and
fruiting probability varied across populations, but were not related to soil conditions or biotic
factors. The growth rates of the 12 Metema populations varied between 0.86 to 0.98,
suggesting that they were all decreasing. Matrix model analyses indicated that the mortality
of adult trees was the major bottleneck for sustainable population growth, and that the lack of
sapling recruitment was a second major bottleneck. These bottlenecks appear both in tapped
and non-tapped stands. Remarkably, tapped stand showed higher growth rates than nontapped
stands, probably because productive stands were selected for harvesting resin.
All results suggest that the remaining populations of B. papyrifera will disappear in the near
future if the current situation continues. Frankincense production is expected to halve in 15-
20 years. Unexpectedly, tapping had no negative effect on vital rates, nor on population
growth rates indicating that other factors are responsible for the decline of the populations.
Adult mortality by insect infestation and windfall, and the negative impact of grazing and fire
on the establishment of saplings need extra attention. Management should be directed
towards releasing two major population bottlenecks (improve sapling regeneration, reduce
adult mortability) to maintain the Boswellia populations and frankincense production in the
future.

Juniperus procera (Cupressaceae) in Afromontane Forests in Ethiopia: From Tree Growth and Population Dynamics to Sustainable Forest Use
Sterck, F.J. ; Couralet, C. ; Nangendo, G. ; Wassie Eshete, Alemayehu ; Sahle, Y. ; Sass-Klaassen, U. ; Markesteijn, L. ; Bekele, T. ; Bongers, F. - \ 2010
In: Degraded Forests in Eastern Africa: management and resoration / Bongers, F, Tennigkeit, T, London : The Earthscan Forest Library - ISBN 9781844077670 - p. 291 - 303.
Incense Woodlands in Ethiopia and Eritrea: Regeneration Problems and Restoration Possibilities
Abiyu, A. ; Bongers, F. ; Eshete, A. ; Gebrehiwot, K. ; Kindu, M. ; Lemenih, M. ; Moges, Y. ; Ogbazghi, W. ; Sterck, F.J. - \ 2010
In: Degraded Forests in Eastern Africa: management and resoration / Bongers, F, Tennigkeit, T, London : The Earthscan Forest Library - ISBN 9781844077670 - p. 133 - 152.
Church Forests - Relics of Dry Afromontane Forests of Northern Ethiopia: Opportunities and Challenges for Conservation and Restoration
Wassie Eshete, Alemayehu ; Bongers, F. ; Sterck, F.J. ; Teketay, D. - \ 2010
In: Degraded Forests in Eastern Africa: management and resoration / Bongers, F, Tennigkeit, T, London : The Earthscan Forest Library - ISBN 9781844077670 - p. 123 - 132.
Species and structural diversity of church forests in a fragmented Ethiopian Highland landscape
Wassie Eshete, Alemayehu ; Sterck, F.J. ; Bongers, F. - \ 2010
Journal of Vegetation Science 21 (2010)5. - ISSN 1100-9233 - p. 938 - 948.
himalayan altitudinal gradient - tropical rain-forest - habitat fragmentation - montane forest - human impact - conservation - biodiversity - richness - disturbance - management
Question: Thousands of small isolated forest fragments remain around churches (“church forests”) in the almost completely deforested Ethiopian Highlands. We questioned how the forest structure and composition varied with altitude, forest area and human influence. Location: South Gondar, Amhara National Regional State, Northern Ethiopia. Methods: The structure and species composition was assessed for 810 plots in 28 church forests. All woody plants were inventoried, identified and measured (stem diameter) in seven to 56 10 m x 10-m plots per forest. Results: In total, 168 woody species were recorded, of which 160 were indigeneous. The basal area decreased with tree harvest intensity; understorey and middle-storey density (5 cm DBH trees) increased with altitude. The dominance of a small set of species increased with altitude and grazing intensity. Species richness decreased with altitude, mainly due to variation in the richness of the overstorey community. Moreover, species richness in the understorey decreased with grazing intensity. Conclusions: We show how tree harvesting intensity, grazing intensity and altitude contribute to observed variations in forest structure, composition and species richness. Species richness was, however, not related to forest area. Our study emphasizes the significant role played by the remaining church forests for conservation of woody plant species in North Ethiopian Highlands, and the need to protect these forests for plant species conservation purposes
Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests
Wassie Eshete, A. ; Bekele, T. ; Sterck, F.J. ; Teketay, D. ; Bongers, F. - \ 2010
African Journal of Ecology 48 (2010)2. - ISSN 0141-6707 - p. 461 - 471.
europaea ssp-cuspidata - tropical rain-forest - germination ecology - northern ethiopia - prunus-africana - fragments - distance - rodents - edge - microhabitat
Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches ('Church forests'). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety-two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests
Tree Regeneration in Church Forests of Ethiopia: Effects of Microsites and Management
Wassie Eshete, A. ; Sterck, F.J. ; Teketay, D. ; Bongers, F. - \ 2009
Biotropica 41 (2009)1. - ISSN 0006-3606 - p. 110 - 119.
tropical dry forest - alpine plant-communities - positive interactions - seedling establishment - natural regeneration - afromontane forests - juniperus-procera - northern ethiopia - statistics notes - rain-forest
Tree regeneration is severely hampered in the fragmented afromontane forests of northern Ethiopia. We explored how trees regenerate in remnant forests along the gradient from open field, forest edge to closed sites and canopy gaps inside the forest. We investigated the effects of seed sowing, litter removal, and weeding on the regeneration success along this gradient. Regeneration success was investigated for four indigenous tree species, and measured in terms of seedling establishment, growth, and survival. Species performed differently according to site conditions. Within the forest, local canopy openings facilitated seed germination (Ekebergia), seedling growth (all species except Olea), or survival (Ekebergia and Olea), suggesting that all species benefited from local high light conditions in the forest. Outside the forest, germination (all species) and growth rates (Juniperus and Olea) were lower in the open field, most probably due to water stress in the dry season. Outer edge conditions favored growth for three of the four species. Natural seed germination was, however, zero at any site for Juniperus and Olea and low for Ekebergia and Prunus in the open field. Soil scarification influenced germination positively, while weeding did not have a positive effect. These results suggest that simple measures may improve seedling establishment, and that, for some species, forest edges are particularly useful for growth and survival after succesful establishment. Together with erecting fences, needed to protect seedlings against grazing, seed sowing, planting seedling, and soil scarification may contribute to maintain and restore church forests in the fragmented landscapes of northern Ethiopia
Effects of livestock exclusion on tree regeneration in church forests of Ethiopia
Wassie Eshete, A. ; Sterck, F.J. ; Teketay, D. ; Bongers, F. - \ 2009
Forest Ecology and Management 257 (2009)3. - ISSN 0378-1127 - p. 765 - 772.
mexican cloud forest - tropical dry forest - ekebergia-capensis - statistics notes - costa-rica - survival - restoration - vegetation - seedlings - ecosystem
In Ethiopia, forests near churches, are the last remnant forest patches. These forests are currently under threat, probably due to diminishing areas of the forest itself and repeated grazing for extended periods by cattle. We assessed the effect of livestock exclusion on the regeneration of four indigenous tree species in two church forests. The four species have a high abundance and socioeconomic value, but limited regeneration in the two forests. We investigated the effect of grazing and trampling on seed germination, seedling survival, and seedling growth. Livestock grazing had a strong negative effect on germination, seedling growth and mortality. In fenced plots, more seeds germinated, seedling survival was higher and seedlings grew faster. Seed germination was higher inside the forest than in the adjacent open area for all species. Seedling survival was not different between forest interior and open fields, except for unfenced plots in the open fields where survival was lower because of the higher grazing pressure. In unfenced plots, no seedlings survived until the end of the year, indicating that grazers destroyed the seedling bank in and around the forest. The significant interaction between fencing and species on seed germination and seedling survival revealed that the magnitude of damage due to grazing can vary with species. We conclude that for effective indigenous tree species regeneration in these church forests, the control of livestock pressure is necessary. Seeds dispersed outside the forest will not have a chance to establish seedlings, grow and colonize the surroundings. Livestock grazing thus has a paramount impact on the long-term sustainability of church forests and their role in restoring the degraded surroundings.
IDE Ethiopia Survey 2007: Baseline Information
Eshete, A. ; Hiller, S.R.C.H. ; Ton, G. ; Vlaming, J. - \ 2008
Den Haag : LEI Wageningen UR / IDE (Ethiopia Report 1)
Ethiopian church forests : opportunities and challenges for restoration
Wassie Eshete, A. - \ 2007
Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): D. Teketay; Frank Sterck. - [S.l.] : S.n. - ISBN 9789085047681 - 204
bossen - bosecologie - verjonging - kerken - vegetatie - ethiopië - forests - forest ecology - regeneration - churches - vegetation - ethiopia
In Northern Ethiopia almost all dry Afromontane forests have been converted to open agricultural lands. Only small isolated fragments remain around churches ("church forests"), but these are many. This study analyses forest community structure and composition of the church forests, investigates major bottlenecks for regeneration of woody species, and explores opportunities and challenges for restoration. In this thesis, the following major questions are addressed: 1. How do forest structure, species composition and biodiversity vary
across church forests and what are the major factors driving such variations?
Factors considered are altitude, forest size and human influence. 2. What are the major bottlenecks in the regeneration of woody plants in
church forests? These bottlenecks are studied for one to seven church forests and a
major focus is given to the effects of soil seed bank and post-dispersal seed
predation on seedling establishment, and of livestock grazing, microsite gradients
and management interventions on seedling establishment, seedling survival and
growth. The species and structural composition of 28 forests located at different altitudes (range 1816 to 3111 masl) and of various sizes (range 1.6 to 100 ha) was assessed, in relation to altitude, forest area, livestock grazing intensity and wood harvest intensity. A total of 168 woody species (100 tree species, 51 shrubs and 17 lianas) representing 69 families were recorded in the 28 church forests studied. Out of these species, 160 were indigenous and only eight were exotic (2 shrub and 6 tree species) representing 6 families. These forests accommodate many species represented by single individuals (rare species) and also many species found only in single plots (unique), which makes church forests priority of conservation efforts. Forests differed strongly in species number (15 to 78), basal area (4.8 to 111.5 m2/ha), density (> 5 cm dbh: 267 to 1553/ha; >cm diameter: 619 to 2421/ha and; seedlings: o to 5263/ha). Altitude is the main factor determining species composition of these forests. Our results showed that altitudinal gradient is the main determinant of differences in species composition among these forests. Maximum similarity in species composition was found with minimum altitude difference between forests. Geographical distance had only a weak effect on similarity. Therefore their vas altitudinal distribution gives these forests the opportunity to hold most of the biodiversity resources of the area. This can be confirmed by the number of specie: we found in our 28 church forests (168) which is more than the expected number 0 species (125 woody species) listed in the study area by South Gondar Zona Department of Agriculture. Structural composition of these forests, on the other hand, is determined by human influence. In the understorey the interaction effect of altitude with human influence (particularly cattle interference) determines the species composition. Not only the species composition but also the number of seedlings were severely affected by cattle interference and few, if any, seedlings were found in some of the forests. In the long run this would probably lead to a human effect on overstorey composition of these forests as well. Forest area did not show a significant effect. This implies that although large sized forests are a necessary element of successful reproduction of woody species, small patches and appropriate matrix management could be useful complements for biodiversity conservation. For many tree species regeneration in most of these forests is very limited. Possible reasons for this limitation are addressed in field experiments. Soil seed bank analysis on seven of these forests showed that these forests accumulate large quantities of persistent seeds of herbaceous species in the soil, but only five (6%) of the 91 woody species recorded in the standing vegetation of the seven forests were represented in their soil seed banks. Most of the tree species do not accumulate seeds in the soil. In order to investigate the long term behavior of seeds in forest soil, we assessed seed viability of five tree species in four sites of one forest after being buried 6, 12, or 18 months. Seed viability decreased sharply with burial time in soil for all species except for seeds of Juniperus, which still had 91% of viability after 18 months. Species significantly affect "the viability of the seeds after 18 months of burial. The quick decline of seed viability in forest soil indicates that the study species do not have a persistent soil seed bank. The fact that most of the dominant tree species do not accumulate seeds and maintain viability in the soil suggests that their regeneration from seeds would be prevented by removal of mature individuals in the standing vegetation. The experiment of post-dispersal seed predation on seeds of six tree species in one forest showed that 92% of the seeds were predated within 3.5 months. Therefore lack of persistent soil seed bank aggravated by intense seed predation undermines seed availability for regeneration in church forests. For four selected tree species in two forests this study showed that livestock grazing is one of the main bottlenecks hampering seedling establishment, seedling survival and seedling growth. Almost none of the sown seeds were able to germinate in unfenced plots (in unfenced plots germination was 4 and 5%, compared to 57.5 and 63.3% in fenced plots, data for Dengolt and Gelawdios respectively). In the fenced plots, seedling survival was higher (Dengolt = 65 and Gelawdios = 56%) and seedlings grew faster while there was no survival in unfenced plots. This implies that controlling livestock grazing is of paramount importance for both the internal regeneration of church forests and for restoration of the degraded surroundings. The study also explored how tree regeneration varies along the gradient from the forest interior to the edge and open fields, and differs between canopy gaps and closed canopy sites inside the forest. Seedling establishment was more successful inside the forest and in particular in the gaps within the forest. The exposure effect between forest interior and exterior was not analogous to the exposure effect of gaps inside the forest. This result suggests that germination may be primarily influenced by moisture availability along the forest interior-open field gradient. Though seedling establishment is higher inside the forest, seedlings grew more rapidly and survived better on the outer edge of the forest. Our result revealed that the negative effect of edge on regeneration is seen on the inner edge while the outer edge has positive effect on seedlings survival. As a result of the interplay effects of light and moisture, the outer forest edge might become the optimal place for seedling survival and growth. This may indicate that seedlings can colonize and restore the forests on the degraded land from immediate surrounding areas of the church forests, given that the surrounding land is protected from grazing intervention and farming. Within the forest, light in gaps favored survival and growth of seedlings both in dry and wet periods. Perhaps, the soil moisture in gaps inside the forest was not as depleted as that outside the forest in the dry period. In general, the quantitative effect of microsite differed with species. Restoration experiments using management interventions (sowing seeds, planting seedlings, weeding, litter removal, soil scarification) showed that the combined effect of seed sowing and litter removal increased seedling establishment significantly for all the species. This implies that insufficient availability of seeds could be one of the constraints for regeneration in church forests. Weeding did not improve seedling survival and growth of the species, and had even a negative effect on some of them. The future existence of the woody flora and vegetation characteristic of dry Afromontane areas in Ethiopia depends on effective conservation and sustainable utilization of the remnant natural forest patches. If not possible to conserve all remnant forests, selection of church forests across altitudinal variation is important to accommodate most of the species diversity of the area. Maintaining viable populations in the forests and providing connections between forests is pivotal in this respect. Excluding cattle interference and reducing intensity of wood harvest are a prerequisite to facilitate regeneration in church forests. To offset the seed limitation sowing seeds combined with litter removal and slight soil scarification can be very useful. Sowing of seeds should be integrated with active reduction of predation and herbivory (e.g. in the form of enclosures and providing alternative food sources for predators). Seedling transplanting is another alternative to overcome some of the bottlenecks of germination especially moisture deficit and intense seed predation, but weeding might not be needed. Within the forest, opening up of the canopy may be required to facilitate seed germination and seedling performance depending on the species. Along the gradient from forest interior to edge and open field, seed sowing will be effective in the interior microsite, while transplanting seedling in the outer forest edge gives better survival and growth. These measures improve tree regeneration. Interconnecting these remnant forests by vegetation corridors following natural terrain or stream lines, or reducing the distance between them by creating buffer areas and plantations around them, and developing more patches in the landscapes are possible management activities. These will facilitate propagule and germplasm flow and ultimately may sustain these forests and help restoring the surrounding landscape.
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