Forest diversity in fragmented landscapes of northern Ethiopia and implications for conservation

Deforestation and habitat fragmentation that arise largely due to the conversion of forests to other agricultural land-use types and over-utilization of forest resources to satisfy the food and energy requirements of the increasing population are major environmental concerns in northern Ethiopia. Understanding plant species diversity and spatial distribution along environmental gradients is crucial in the management of the remnant forest ecosystems. However, the ecology of the forest remnants in northern Ethiopia is poorly studied. The purpose of this study is therefore to (i) investigate plant species diversity and natural regeneration in relation to selected environmental factors, (ii) quantify the elevation patterns of species diversity and community composition, (iii) examine the extent and spatial distribution pattern of standing dead stems and the effect of mass tree dieback on forest structure and diversity, and (iv) compare the regeneration response of Juniperus procera and Olea europaea subsp. cuspidata in an openaccess forest area to a closed forest management system. The study was conducted in the Desa’a and Hugumburda Afromontane forest remnants, which are the largest forest fragments in northern Ethiopia and are national forest priority areas. A total of 153 species belonging to 63 families was found in the study area; shrub and herb species dominate (ca. 70 %). The vegetation is mainly a dry Afromontane forest type with Juniperus and Olea as the dominant species; a riverine plant community in Hugumburda forest represents a moist forest type. Elevation, slope, soil depth, distance to the nearest stream, soil moisture, and forest disturbance are the main environmental factors influencing species distribution and partitioned plant communities. The diversity of species and the composition of plant communities in Desa’a forest significantly respond to elevation. Species richness and diversity show a unimodal, humpshaped relationship with elevation that peaked at mid elevation (1900 – 2200 m). The beta diversity values indicate medium species turnover along an elevational gradient. The percentages of dead standing trees (snags) due to natural disturbance at Desa’a forest are high for both J. procera (57 ± 7 %) and O. europaea subsp. cuspidata (60 ± 5 %), but show a decreasing trend with increasing elevation suggesting that restoration is more urgent at the lower elevations. Higher tree dieback at the lower elevation has pushed the tree species to the higher elevation by about 500 m, and this can lead to a shift in the forest-shrubland ecotone to higher elevations. Total stand density and basal area are reduced by 30 and 44 % when excluding snags of the two species, respectively. Thus, mass tree dieback of the two key species strongly influences the forest structure. High amounts of dead standing biomass are a particular risk in a fire-prone semi-arid forest environment, and controlling snag densities is of critical concern in the management of the remaining dry Afromontane forests in northern Ethiopia. The natural regeneration of native tree species in both forest remnants is low. Exclosure was found to be an effective management option to improve the regeneration of O. europaea, but it does not improve the regeneration of J. procera. Thus, a closed management system in the open-access and degraded forests may not guarantee a successful regeneration of native woody species. It rather favors grass and herbaceous species and can lead to a gradual conversion of the forest land to wooded grassland. Most of the seedlings in forest remnants are shrubs, while tree species are less diverse and abundant. The standing vegetation is only partly represented in the seedling bank and many of the rare tree species, e.g. Afrocarpus falcatus, show poor or no regeneration. A smaller number of saplings than mature individuals suggest that locally some forest species are experiencing extinction. Thus, it is important to give conservation priority to the last Afromontane forest remnants in northern Ethiopia to achieve local, national and international biodiversity conservation goals.Biodiversität in den Wäldern der fragmentierten Landchaften von Nordäthiopien und die Folgerungen für ihren Schutz Abholzung und die Fragmentierung der Lebensräume, hauptsächlich als Folge der Umwandlung der Wälder in andere landwirtschaftliche Nutzungen sowie die Ausbeutung der Waldressourcen, um den Nahrungsmittel- und Energiebedarf der wachsenden Bevölkerung zu befriedigen, verursachen erhebliche Umweltprobleme in Nordäthiopien. Kenntnisse der Pflanzenvielfalt und räumlichen Verteilung entlang Umweltgradienten ist entscheidend bei der Bewirtschaftung der verbleibenden Waldökosysteme. Jedoch ist die Ökologie der noch vorhandenen Waldfragmente in Nordäthiopien nur wenig untersucht. Das Ziel dieser Studie ist daher (i) die Vielfalt der Pflanzenarten und ihre natürliche Regeneration im Zusammenhang mit ausgewählten Umweltfaktoren zu untersuchen, (ii) die höhenabhängige Verteilung der Artenvielfalt und die Zusammensetzung der Pflanzengemeinschaften zu quantifizieren, (iii) das Ausmaß und die räumliche Verteilung stehender toter Baumstämme sowie die Auswirkungen eines Baumsterbens auf die Waldstruktur und -vielfalt zu untersuchen, und (iv) den Einfluss eines geschlossenen Waldbewirtschaftungssystems mit dem eines zugänglichen Waldes auf die Regeneration von Juniperus procera und Olea europaea subsp. cuspidata zu vergleichen. Die Studie wurde in den afromontanen Wäldern Desa’a und Hugumburda, die größten Waldfragmente in Nordäthiopien und mit nationaler Schutzpriorität, durchgeführt. Insgesamt 153 Arten aus 63 Familien kommen im Untersuchungsgebiet vor; Strauch- und Kräuterarten dominieren (ca. 70 %). Die Vegetation ist hauptsächlich vom trockenen afromontanen Waldtyp mit den dominierenden Arten Juniperus und Olea; eine gewässernahe Pflanzengesellschaft im Hugumburda Wald ist vom Typ Feuchtwald. Höhenlage, Hangneigung, Bodentiefe, Nähe zum nächsten Kleingewässer, Bodenfeuchte und anthropogene Störungen sind die wichtigsten Umweltfaktoren, die die Artenverteilung und die Zusammensetzung der Pflanzengesellschaften beeinflussen. Die Artenvielfalt und die Zusammensetzung der Pflanzengesellschaften in Desa’a Wald sind signifikant abhängig von der Höhenlage. Artenreichtum und Diversität bilden eine unimodale Beziehung mit der Höhenlage; der höchste Wert ist bei einer mittleren Höhenlage (1900 - 2200 m). Die Betadiversitätswerte deuten auf einen mittleren Artenwechsel entlang eines Höhengradienten hin. Die Anteile stehender toter Baumstämme als Folge natürlicher Störungen im Desa’a Wald sind hoch, sowohl für J. procera (57 ± 7 %) als auch für O. europaea subsp. cuspidata (60 ± 5 %), zeigen jedoch einen abnehmenden Trend mit zunehmender Höhenlage, was darauf hindeutet, dass Rekultivierungsmaßnahmen in den unteren Höhenlagen dringender sind als in höheren. Das stärkere Baumsterben in den unteren Höhenlagen hat dazu geführt, dass das Vorkommen der betroffenen Baumarten sich um ca. 500 m nach oben verschoben hat. Dies kann auch zu einer Verschiebung der Wald-Buschland-Vegetation in höhere Lagen führen. Bestandsdichte bzw. Basalfläche sind um 30 bzw. 44 % reduziert wenn die stehenden toten Individuen der beiden Arten nicht berücksichtigt werden; das Absterben der beiden Hauptbaumarten beeinflusst also stark die Waldstruktur. Große Mengen toter Baumbiomasse sind ein besonderes Waldbrandrisiko in einem semiariden Wald und die Kontrolle der Dichte des Totholzes ist von entscheidender Bedeutung bei der Bewirtschaftung der noch verbleibenden trockenen afromontanen Wälder in Nordäthiopien. Die natürliche Regeneration der einheimischen Baumarten in den beiden untersuchten Waldfragmenten ist niedrig. Es zeigt sich, dass eingezäunte Flächen eine wirksame Bewirtschaftungsoption sind, um die Regeneration von O. europaea zu begünstigen. Diese Maßnahme bleibt jedoch ohne Wirkung auf J. procera. Daher würde ein Bewirtschaftungssystem mit Zugangsbeschränkungen in den offenen, degradierten Wäldern eine erfolgreiche Regeneration der einheimischen Holzgewächse nicht garantieren. Es werden eher Gras- und Kräuterarten begünstigt, was zu einer langsamen Umwandlung des Waldes in Grasland mit Gehölzen führen kann. Die meisten Keimlinge in den Waldfragmenten sind von Straucharten, während Baumarten weniger vielfältig bzw. zahlreich sind. Die bestandsbildenden Arten sind nur zum Teil in der Samenbank vertreten, und viele der seltenen Arten, z. B. Afrocarpus falcatus, zeigen wenig bzw. gar keine Regeneration. Die geringe Bedeutung von Jungwuchs im Vergleich zu den voll ausgewachsenen Baumindividuen deutet daraufhin, dass lokal einige bestandsbildenden Baumarten aussterben könnten. Daher muss den letzten afromontanen Waldfragmenten in Nordäthiopien eine hohe Schutzpriorität eingeräumt werden, auch um die lokalen, nationalen und internationalen Ziele zum Schutze der Artenvielfalt zu erreichen

Allometric equations for below-ground biomass of four key woody species in West African savanna-woodlands

Accurate estimates of both above-ground biomass (AGB) and below-ground biomass (BGB) are essential for estimating carbon (C) balances at various geographical scales and formulating effective climate change mitigation programs. However, estimating BGB is challenging, particularly for forest ecosystems, so robust allometric equations are needed. To obtain such equations for savanna-woodlands of the West African north sudanian zone, we selected four common native woody species (Anogeissus leiocarpa (DC.) Guill. & Perr., Detarium microcarpum Guill. & Perr., Piliostigma thonningii (Schumach.) Milne-Redh. and Vitellaria paradoxa C. F. Gaertn.). At two sites in Burkina Faso, we determined the BGB of 30 trees of each of these species by excavation, and measured various above-ground dimensional variables. The root: shoot ratio varied widely among the species, from 0.1 to 3.4. Depending on the species, allometric equations based on stem basal area at 20 cm height, basal area at breast height and tree height explained 50-95% of the variation in BGB. The best generic equation we obtained, based on basal area at 20 cm, explained 60% of the variation in BGB across the species. Three previously published generic allometric equations underestimated BGB by 8 to 63%. The presented equations should significantly improve the accuracy of BGB estimates in savanna-woodlands and help avoid costly needs to excavate root systems.Peer reviewe

Including soil organic carbon into nationally determined contributions: Insights from Kenya

Healthy soils are the foundation of sustainable and regenerative food systems and provide several vital ecosystem services. Sequestering carbon in agricultural soils, for example, can have mutual benefits for climate change mitigation and adaptation, food and nutrition security, biodiversity, and water resilience. Despite these benefits, there are few policies that incentivize farmers to invest in maintaining and improving soil health. This policy brief highlights opportunities for the inclusion of soil health and soil organic carbon (SOC) into the Nationally Determined Contributions (NDCs) as a key step for governments to support farmers in investing in their soil. This activity builds on recent assessments including a paper that extensively reviewed the first-round of 184 NDCs concluding that only 28 countries referred to SOC, peatlands or wetlands (1). This review and the subsequent interviews with experts (n=8) indicated the importance of understanding the impact of land management on SOC storage and dynamics (1). As a follow-up, Rose et al (2) focused on the updated NDCs and found that the number of countries that included SOC in their updated NDC increased compared to the first-round NDC process (2). This review also highlighted that 19 countries highlighted the need for financing for SOC and related measures (2)

Spectral Soil Analysis & Household Surveys: A Guidebook for Integration

This Guidebook is intended to be a reference for survey practitioners looking for guidance on integrating soil health testing in household and farm surveys. The role of soil in agrarian societies is unquestionable, yet the complex nature of soil makes it much more challenging to measure than agricultural inputs such as fertilizers or pesticides. Historically, household surveys either include subjective questions of farmer assessment or rely on national-level soil maps to control for land quality, if anything at all. Recent scientific advances in laboratory soil analysis—via spectral soil testing—have opened the door to more rapid, cost-effective objective measurement of soil health in household surveys. This Guidebook explores the nascent possibility of integrating plot-level soil testing in household surveys through a presentation of results comparing various soil assessment methods and a step-by-step guide for practical implementation. In partnership with the World Agroforestry Centre (ICRAF), the Living Standards Measurement Study of the World Bank’s Development Data Group set out to validate (1) the feasibility of implementing spectral soil analysis in household surveys, and (2) the value of subjective farmer assessments of soil quality compared with objective measures in order to determine the need for objective soil analysis, specifically in low-income, smallholder agricultural contexts. These objectives were met by implementing two methodological validation studies, one in Ethiopia and one in Uganda. In both studies, plot-level soil samples were collected following identical international best-practice field protocols and analyzed using wet chemistry and spectral analysis methods at ICRAF’s Soil-Plant Spectral Diagnostics Laboratory. Additionally, plot managers were administered a series of subjective questions that are often used to gauge soil health in national household surveys. These studies resulted in two uniquely rich datasets that allow for comparison of subjective indicators of soil quality against laboratory results. Both laboratory and subjective results can also be compared with publicly available geospatial data, as all plots were georeferenced

Developing gender-equitable ecological restoration initiatives: A synthesis of guidance to improve restoration practice

Ecological restoration has the potential to contribute to all Sustainable Development Goals (SDGs). Yet, social issues, including gender relations, often remain unaddressed in ecological restoration initiatives. As the UN Decade on Ecosystem Restoration begins, it is critical to learn from existing knowledge and experiences to restore degraded lands in ways that enhance the equity of restoration, and ensure that restoration initiatives and agendas leave no one behind. This 'guide to guides' places existing resources and guidance materials (frameworks, tools, guidelines, and manuals) designed to enhance equity in restoration initiatives in a common 'Reach, Benefit, Empower, Transform' framework, and highlights the strengths that different resource materials bring to understanding and planning for gender-equitable restoration. As per the framework, the guide provides actionable strategies and recommendations for the design, implementation, and monitoring, evaluation, learning and impact assessment (MELIA) of gender-equitable restoration initiatives. The ultimate goal is to enhance the equity and sustainability of restoration initiatives and allow restoration to achieve its full potential to advance all the SDGs

Relationship between carbon stocks and tree species diversity in a humid Guinean savanna landscape in northern Sierra Leone

Global sustainable development goals include reducing greenhouse gas emissions from land-use change and maintaining biodiversity. Many studies have examined carbon stocks and tree species diversity, but few have studied the humid Guinean savanna ecosystem. This study focuses on a humid savanna landscape in northern Sierra Leone, aiming to assess carbon stocks and tree species diversity and compare their relationships in different vegetation types. We surveyed 160 sample plots (0.1 ha) in the field for tree species, aboveground carbon (AGC) and soil organic carbon (SOC). In total, 90 tree species were identified in the field. Gmelina arborea, an exotic tree species common in the foothills of the Kuru Hills Forest Reserve, and Combretum glutinosum, Pterocarpus erinaceous and Terminaria glaucescens, which are typical savanna trees, were the most common species. At landscape level, the mean AGC stock was 29.4 Mg C ha(-1) (SD 21.3) and mean topsoil (0-20 cm depth) SOC stock was 42.2 Mg C ha(-1) (SD 20.6). Mean tree species richness and Shannon index per plot were 7 (SD 4) and 1.6 (SD 0.6), respectively. Forests and woodlands had significantly higher mean AGC and tree species richness than bushland, wooded grassland or cropland (p <0.05). In the forest and bushland, a small number of large diameter trees covered a large portion of the total AGC stocks. Furthermore, a moderate linear correlation was observed between AGC and tree species richness (r = 0.475, p <0.001) and AGC and Shannon index (r = 0.375, p <0.05). The correlation between AGC and SOC was weak (r = 0.17, p <0.05). The results emphasise the role of forests and woodlands and large diameter trees in retaining AGC stocks and tree species diversity in the savanna ecosystem.Peer reviewe

Effects of Forest Composition and Disturbance on Arbuscular Mycorrhizae Spore Density, Arbuscular Mycorrhizae Root Colonization and Soil Carbon Stocks in a Dry Afromontane Forest in Northern Ethiopia

We investigated arbuscular mycorrhizal fungi (AMF) spore density and root colonization in three distinct dry Afromontane forest plant communities, representing differing levels of disturbance and soil properties. Soil and root samples were collected from sixty-five 50 × 50-m plots from four plant communities. We collected data for AMF spore density, AMF root colonization and soil organic carbon stocks in 0–25 and 25–50 cm soil depth ranges. AMF spore density, and root colonization differed significantly among plant communities. The least disturbed Juniperus procera–Maytenus senegalensis (Jupr-Mase) plant community, which contained high tree and shrub density, had the highest AMF spore density, root colonization and soil carbon stocks. The most disturbed Cadia purpurea–Opuntia ficus-indica (Capu-Opfi) community which contained the lowest tree and shrub density supported the lowest AMF spore density, root colonization and soil carbon stocks. There was no significant difference in spore density between the two soil depths, but AMF root colonization was significantly higher in the upper soil than in the subsoil (p < 0.001). The difference in soil properties was not uniform between plant communities. Conserving remnant dry Afromontane forests and restoring the degraded forests are critical to improve and maintain forest ecosystem functioning and sustain ecosystem services

Sensitivity of Above-Ground Biomass Estimates to Height-Diameter Modelling in Mixed-Species West African Woodlands

Peer reviewe

Including soil organic carbon into nationally determined contributions: Insights from Ethiopia

Healthy soils are the foundation of sustainable and regenerative food systems and provide several vital ecosystem services. Sequestering carbon in agricultural soils, for example, can have mutual benefits for climate change mitigation and adaptation, food and nutrition security, biodiversity, and water resilience. Despite these benefits, there are few policies that incentivize farmers to invest in maintaining and improving soil health. This policy brief highlights opportunities for the inclusion of soil health and soil organic carbon (SOC) into the Nationally Determined Contribution (NDC) in Ethiopia as a key step for governments to support farmers in investing in their soil. We interviewed key informants involved in the NDC process to understand the process for the developing the NDC targets and investigated reasons why policy makers did or did not include soil in these targets

Forests, Farms, and Fallows: The Dynamics of Tree Cover Transition in the Southern Part of the Uluguru Mountains, Tanzania

This research article was published by MDPI, 2021Forests and woodlands remain under threat in tropical Africa due to excessive exploitation and inadequate management interventions, and the isolated success stories of tree retention and tree cover transition on African agricultural land are less well documented. In this study, we characterize the status of tree cover in a landscape that contains forest patches, fallows, and farms in the southern part of Uluguru Mountains. We aimed to unveil the practices of traditional tree fallow system which is socially acceptable in local settings and how it provides a buffering effects to minimize forest disturbances and thus represents an important step towards tree cover transition. We assessed land cover dynamics for the period of 1995 to 2020 and compared tree stocking for forest patches, fallows, and farms. We found that tree biomass carbon stocks were 56 ± 5 t/ha in forest patches, 33 ± 7 t/ha in fallows, and 9 ± 2 t/ha on farms. In terms of land cover, farms shrank at intensifying rates over time for the entire assessment period of 1995–2020. Forest cover decreased from 1995–2014, with the reduction rate slowing from 2007–2014 and the trend reversing from 2014–2020, such that forest cover showed a net increase across the entire study period. Fallow consistently and progressively increased from 1995–2020. We conclude that traditional tree fallows in the study site remain a significant element of land management practice among communities, and there appears to be a trend towards intensified tree-based farming. The gains in fallowed land represent an embracing of a traditional land management system that supports rotational and alternate uses of cropping space as well as providing a buffering effect to limit over-exploitation of forests. In order to maximize tree cover and carbon stocks in the farm landscape, this well-known traditional tree fallow system can be further optimized through the incorporation of additional innovations