Vegetation structural characteristics and topographic factors in the remnant moist Afromontane forest of Wondo Genet, south central Ethiopia

For forest ecosystem management to be effective, knowledge of the horizontal and vertical structural diversity of a forest is essential. The moist Afromontane highlands of Wondo Genet in south-central Ethiopia present an opportunity to restore and rehabilitate and enhance the ecosystem services to be obtained from this forest sustainably. We focused on the forest structural characteristics to better understand the current forest conditions to assist in the sustainable management of this resource. A total of 75 （20 m × 20 m） quadrats were sampled and diame- ter at breast height （DBH） 〉2 cm and stem height 〉2 m were measured. Species identity and abundance, elevation, slope, and aspect were recorded for each plot. Structural characteristics were computed for each plot. Relationship of topographic factors with vegetation characteristics was conducted using R-Software. A total of 72 woody species was re- corded. Whereas, the overall diameter distribution shows an inverted J-shaped curve, the basal area followed a bell-shaped pattern. Five types of population structures are revealed. The mean tree density and basal area was 397.3 stems.ha-1 and 31.4 m2.ha-1, respectively. Only 2.8% of the tree species have densities of 〉25 stems.ha^-1 and the percentage dis- tribution of trees show 56.2% in the DBH class 2-10 cm, indicating that the forest is dominated by medium-sized trees. Celtis africana （8.81 m2.ha^-1） and Pouteria adolfi-friederieii （5.13 m2.ha^-1） make the highest contribution to the basal area and species importance value index. The families/species with the highest importance value index are Ulmaceae, Fabacea and Sapotaceae. Species abundance （r2 = 0.32, p 〈0.001） and species richness （P =0.50, p 〈0.001） are positively related with tree density. Tree density is negatively related with elevation （~ = -0.36, p 〈0.001）, slope （r2 =-0.15, p 〈0.001） and aspect （r2 = -0.07, p 〈0.05）. While basal area is negatively related with elevation （r2 =-0.14, p 〈0.001）, it has a positive relationship with tree density （r2 =0.28, p 〈0.001 and species richness （r2 =0.098）. Species with poor population structure should be assisted by restoration tasks and further anthropogenic distur- bance such as illegal logging and fuel wood extraction should be re- stricted.

Influence of topographic aspect on floristic diversity, structure and treeline of afromontane cloud forests in the Bale Mountains,Ethiopia

We studied the influence of east and west aspects on floristic composition, diversity, structure and treeline of afromontane cloud forests at Rira in the Bale Mountains, southeast Ethiopia. In addition, we studied how aspect relates to and/or interacts with other topographic and edaphic factors in influencing vegetation diversity. Strati- fied systematic plot sampling was used to survey the floristic composition, diversity and structure of forests on east- and west-facing slopes. The sample plot size was 20 x 20 m and a total of 36 plots were inventoried. A total of 72 composite soil samples were collected and analysed. Woody species richness of the forest on the east-facing slope was 1.7 times higher than on the west-facing slope. Shannon, Simpson and Log-series alpha diversity indices and evenness of forests on the east-facing slope were sig- nificantly higher than on the west-facing slope. NMDS ordination indicated that the east- and west-facing slopes formed two clusters of species and aspect explained 55.2 % and 10.4 % of the variation in species richness and abun- dance, respectively. There was no significant difference between aspects in stand structure except in dominantheight, which was higher on the east-facing slopes. There was significant interaction between aspect and elevation in influencing woody species diversity. The four plant com- munity groups, which were identified using cluster and indicator species analysis were represented differently on the east and west aspects. The treeline on the east-facing slope （3352 m） was located about 110 m higher than on the west-facing slope （3240 m）. Soil moisture deficiency was unlikely to be a limiting factor on either site. Near the equator, east-west aspect was shown to have considerable impact on floristic composition, diversity, structure, and treeline position of montane forests. Diurnal cloud move- ment patterns and its impact on microclimate of slope aspect should be taken into account in future studies of cloud forest diversity, structure, and treeline position.

Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest, northern Ethiopia

Arbuscular mycorrhiza fungi(AMF) are vital in the regeneration of vegetation in disturbed ecosystems due to their numerous ecological advantages and therefore are good indicators of soil and ecosystem health at large. This study was aimed at determining how the seasonal, vegetation cover density, edaphic and anthropogenic factors affect AMF root colonization(RC) and spore density(SD)in Desa’a dry Afromontane forest. AMF RC and SD in the rhizosphere of five dominant woody species, Juniperus procera, Olea europaea, Maytenus arbutifolia, Carissa spinarum and Dodonaea angustifolia growing in Desa’a forest were studied during the rainy and the dry seasons in three permanent study vegetation cover density plots(dense, medium, and poor). Each plot(160 x40 m2) has two management practices(fenced and unfenced plots) of area. A 100 g sample of rhizosphere soil from moisturefree composite soil was used to determine spore density.Spore density ranged from 50 to 4467 spores/100 g soil,and all species were colonized by AMF within a range of 4–95%. Glomus was the dominant genus in the rhizosphere of all species. Vegetation cover density strongly affected SD and RC. The SD was significantly higher(p < 0.05) in the poor vegetation cover density than in the other two and lowest in the dense cover; root colonization showed the reverse trend. Management practices significantly(p <0.05) influenced AMF SD and RC, with the fenced plots being more favoured. Seasons significantly(p < 0.05) affected RC and SD. More RC and SD were observed in the wet period than the dry period. Correlating AMF SD and RC with soil physical and chemical properties showed no significant difference(p> 0.05) except for total nitrogen. Disturbance, vegetation cover density, season and total nitrogen are significant factors that control the dynamics and management interventions to maintain the forest health of dry Afromontane forests.

Climate forcing of tree growth in dry Afromontane forest fragments of Northern Ethiopia:evidence from multi-species responses

Background: Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea p. cuspidate and Podocarpus falcatus). Thesubsp. collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall. Results: The results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region. Conclusions: Overall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.

Vegetation structure and regeneration status of the moist,evergreen, afromontane Bore–Anferara–Wadera forest in southern Ethiopia

In a survey of the Bore–Anferara–Wadera forest to study the vegetation structure and regeneration status of woody plant species, 112 quadrats were systematically sampled along altitudinal transects to collect vegetation data. Nested sample plots of 30 m × 30 m and 5 m × 5 m were laid for collecting data on abundance and some variables of tree and shrub size. The regeneration status of woody species was assessed by counting all seedlings within the main sample plot. Woody plant species taller than or equal to 3 m were counted and their height and DBH measured. Density, frequency, basal area and importance value(IV) of woody plant species were computed. A total of 136 vascular plant species belonging to119 genera and 63 families were recorded. The overall Shannon—Wiener diversity value was 3.84 and evenness was 0.78. Total density of trees and shrubs with DBH >2 cm was 1047 ha-1. Size class distribution of woody species across different DBH and height classes indicated a relatively high proportion of individuals at lower classes,suggesting impacts of past anthropogenic disturbances.Analysis of population structure and regeneration status of the forest revealed various patterns of population dynamics where some species were represented by only a few mature plants, suggesting that they are on the verge of local extinction and that immediate conservation measures should be taken. The results highlight the need for joint management and conservation measures by the government, local people and other stakeholders to abate the rapid rate of deforestation and promote sustainable utilization of the forest resources in this forest in southern Ethiopia.

The arbuscular mycorrhizal fungi status of selected tree nurseries in the Ethiopian highlands

We investigated the arbuscular mycorrhizal fungi(AMF)status of ten nurseries suitable for restoration of dry evergreen Afromontane forests in Ethiopia.We quantified AMF root colonization(RC)and spore abundance(SA)in seedlings of nine native tree species namely Acacia abyssinica Hochst.ex Benth.,Cordia africana Lam.,Dovyalis abyssinica(A.Rich.)Warb.,H agenia abyssinica J.F.Gmel.,Juniperus procera Hochst.ex Endl.,Millettia ferruginea(Hochst.)Baker,Olea europaea L.subsp.c uspidata(Wall.ex G.Don)Cif.,Podocarpus falcatus(Thunb.)R.Br.ex Mirb.and Prunus africana(Hook.f.)Kalkman.We used the ink and vinegar method to stain AMF in roots.RC levels ranged from 8.00 to 99.67%and were generally higher than the RC levels reported from other similar nurseries in Ethiopia.SA levels ranged from 1 to 25 spores g~(-1)and werecomparable with some reports from the field in Ethiopia but they were lower than levels reported by another similar study.RC was more affected by host species than nursery location,while the reverse was true for SA.The results also showed that nursery management could improve AMF status among seedlings.When all nursery tree species were considered,RC and SA levels were unrelated.No strong correlation existed between the nursery management variables considered and RC or SA.However,considering C.africana,J.procera and P.falcatus separately,RC-age(r_(s)=0.829,P=0.042)correlation for O.europaea and RC-pot diameter(r_(s)=0.820,P=0.046),RC-pot volume(r_(s)=0.928,P=0.008)and SA-age(r_(s)=0.943,P=0.005)correlations for C.africana,were significant,strong and positive.Generally,most of the tree species and particularly,early-mid successional tree species had sufficient AMF inoculum.Hence,only the mid-late successional tree species;J.procera,P.falcatus,and P.africana may require AMF inoculation,preferably,during filed planting.Based on our results,age and pot volume were identified to be important variables potentially affecting RC and SA.To better understand the effects of these and other nursery management variables,additional study is required.We demonstrated for the first time that black Hero ink is suitable for staining root AMF and can be used in future AMF research.

Quantifying multiple-site compositional turnover in an Afrotemperate forest, using zeta diversity

Background： Species turnover is typically measured by partitioning diversity components into alpha and pairwise beta diversity. However, alpha and beta components cannot express the full spectrum of multiple-site compositional turnover. To this end, zeta diversity has been proposed as an extended framework to allow complete biodiversity partitioning and to measure multiple-site species turnover. We use a zeta-diversity framework to explore the turnover and potential community assembly processes of an African Montane Forest. Methods： Using a 20 m grid, we explore the species turnover in a 4.55 ha forest plot located in the Garden Route National Park of South Africa, with 47 and 27 canopy and sub-canopy tree species in the regional poo We first calculate how zeta diversity declines and how the probability of retention of species with particular occupancies changes with increasing zeta orders （i.e. the number of sites [grid cells] involved in the calculation）. Using null models with row sums and column sums constrained respectively, we explore whether species turnover is driven by mechanisms of ecological differences （species-specific occupancies） or habitat heterogeneity （site-specific alpha diversity and thus environmental filters）. Results： The decline of zeta diversity with zeta order followed a power law; that is, the probability of retention increased with species occupancies, suggesting common species being more likely to be discovered in extra sites. The null model retaining row sums （species＇ occupancy） of the species-by-site matrix recreated perfectly the decline of zeta diversity, while the null model of habitat heterogeneity （retaining column sums） was rejected. This suggests that mechanisms driving species-specific occupancies （i.e. ecological differences between species） dictate the multi-site species turnover in the community. The spatial patterns of zeta diversity revealed little spatial structuring forces, supporting a fine-grain structure in these southern Cape forests. Conclusions： The framework of zeta diversity revealed mechanisms driving the large discrepancies in the occupancy among species that are behind the species turnover in the African Montane forest plot. Future studies could further link species turnover to spatial distance decay. Environmental filters and temporal turnover from landscape demography could bring a cohesive understanding of community assembly in these unique forest ecosystems.