Ethiopia is land of geographical contrasts with elevations that range from 125 m below sea level in the Danakil Depression to 4533 m above sea level in the Semien Mountains, a world heritage site. The diverse climate of various ecological regions of the country has driven the establishment of diverse vegetation, which range from Afroalpine vegetation in the mountains to the arid and semi-arid vegetation type in the lowlands. The formation of Ethiopian vegetation is highly connected to the climate and geological history of the country. Highland uplift and rift formation due to volcanic forces formed novel habitats with different topography and climatic conditions that have ultimately become drivers for vegetation diversification. Due to Ethiopia's connection with the temperate biome in the north and the Arabian Peninsula during the dry glacial period, the biotic assemblage of Ethiopian highlands consists of both Afrotropical and palearctic biota. In general, eight distinct vegetation types have been identified in Ethiopia, based mainly on elevation and climate gradients. These vegetation types host their own unique species, but also share several common species. Some of the vegetation types are identified as centers of endemism and have subsequently been identified globally as the East African Afromontane hotspot. Ethiopia is biologically rich, with more than 6500 vascular plant species. Of these species, 12% are endemic mainly due to geographical isolation and unique climatic conditions. However, researchers have yet to extensively investigate the ecology, phenology, as well as the evolutionary, genetics, and conservation status of Ethiopian vegetations at community and species level over space and time. This lack of research is a barrier to achieving the goal of zero global plant extinctions. Taxa extinction risk assessment has not been extensively carried out for majority of Ethiopian species. Detailed research is needed to explore how vegetation and species respond to rapidly growing environmental change. Currently, human-induced climate change and habitat fragmentation are severely threatening the country's biodiversity, and the consequences of these effects have not been studied at large. Furthermore, we still lack scientific evidence on how micro- and macro-ecological and evolutionary processes have been shaping vegetation structures in this climatically, topographically, and geologically diverse country. These gaps in our knowledge represent an opportunity for ecologists, geneticists, evolutionary biologists, conservation biologists, and other experts to investigate the biodiversity status and the complex ecological processes involved in structuring vegetation dynamics so as to help take effective conservation actions.

Environmental filtering consistently shapes the functional and phylogenetic structure of species across space within diverse forests. However, poor descriptions of community functional and lineage distributions across space hamper the accurate understanding of coexistence mechanisms. We combined environmental variables and geographic space to explore how traits and lineages are filtered by environmental factors using extended RLQ and fourth-corner analyses across different spatial scales. The dispersion patterns of traits and lineages were also examined in a 20-ha tropical rainforest dynamics plot in southwest China. We found that environmental filtering was detected across all spatial scales except the largest scale (100 × 100 m). Generally, the associations between functional traits and environmental variables were more or less consistent across spatial scales. Species with high resource acquisition-related traits were associated with the resource-rich part of the plot across the different spatial scales, whereas resource-conserving functional traits were distributed in limited-resource environments. Furthermore, we found phylogenetic and functional clustering at all spatial scales. Similar functional strategies were also detected among distantly related species, suggesting that phylogenetic distance is not necessarily a proxy for functional distance. In summary, environmental filtering considerably structured the trait and lineage assemblages in this species-rich tropical rainforest.

Background and Aims Our understanding of plant responses to biotic and abiotic drivers are largely based on aboveground plant traits, with little focus on belowground traits despite their key role in water and nutrient uptake. Here, we aimed to understand the extent to which above and belowground traits are coordinated, and how these traits respond to soil moisture gradients and plant intraspecific competition. Methods We chose seedlings of five tropical tree species and grew them in a greenhouse for 16 weeks under a soil moisture gradient (low (drought), medium, and high (well-watered) moisture levels) with and without intraspecific competition. At harvest, we measured nine above and five belowground traits of all seedlings based on standard protocols. Key Results In response to the soil moisture gradient, aboveground traits are found to be consistent with the leaf economics spectrum whereas belowground traits are inconsistent with the root economics spectrum. We found high specific leaf area and total leaf area in well-watered conditions while high leaf dry matter content, leaf thickness and stem dry matter content were observed in drought conditions. However, belowground traits showed contrasting patterns with high specific root length but low root branching index in the low water treatment. The correlations between above and belowground traits across the soil moisture gradient were variable. That is, specific leaf area was positively correlated with specific root length, while it was negatively correlated with root average diameter across moisture levels. However, leaf dry matter content was unexpectedly positively correlated with both specific root length and root branching index. Intraspecific competition has influenced both above and belowground traits, but interacted with soil moisture to affect only belowground traits. Consistent with functional equilibrium theory, more biomass was allocated to roots under drought conditions, and to leaves under sufficient soil moisture conditions. Conclusions Our results indicate that the response of belowground traits to plant intraspecific competition and soil moisture conditions may not be inferred using aboveground traits suggesting that multiple resource use axes are needed to understand plant ecological strategies. Lack of consistent leaf—root trait correlations across the soil moisture gradient highlight the multidimensionality of plant trait relationships which needs more exploration.

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Questions Linking tree growth dynamics to functional traits and neighborhood conditions that are measured at a single time point gives limited insights into the direction of forest structural and functional change. We used trait and neighborhood data collected at different time points for each individual tree of 15 Ficus species to test how trait (temporal trait plasticity) and neighborhood crowding change over time, and to test how their temporal change affects individual growth rate. We asked the following questions: (i) how do traits, neighborhood crowding, and growth of individual trees change over time; (ii) are functional traits and neighborhood crowding temporally consistent in their association with growth rate of individuals; and (iii) do temporal trait plasticity and changes in neighborhood crowding better predict the relative growth rate of individuals compared to using only a single snapshot of traits and neighborhood crowding? Location Xishuangbanna Tropical Seasonal Rainforest, southwest China. Methods We collected traits (specific leaf area [SLA], leaf area (LA), leaf dry matter content [LDMC], leaf chlorophyll, leaf thickness, and leaf succulence) at two time points (2010 and 2017) for 472 individuals of 15 Ficus species. We used linear mixed‐effect models to test the effect of temporal trait plasticity and neighborhood crowding on the relative growth rate of individuals. Results We found that the temporal change in trait values predicts the growth rate of individuals better compared to static trait values in the initial and final censuses. We found significant temporal changes in individual traits suggesting a shift in ecological strategies from being acquisitive to conservative. A difference in neighborhood crowding between the two census years was also observed, indicating that the neighborhood effect on growth might also change over time. Conclusions Our results in general highlight the need to consider the temporal dimension of traits and biotic interactions, as our results suggest that growth–trait relationships may vary between time points, allowing us to understand the demographic response of species to temporal environmental change through functional traits.

Environmental and dispersal-based processes have been widely investigated for the understanding of community assembly. However, the relative importance of these ecological processes across spatial scales, life history stages and forest types needs to be largely studied. We test the variability of ecological processes in shaping tree community composition across life stages and spatial scales, and in particular, the hypothesis that dispersal limitation dominates at smaller scales and early life stages, but environmental filtering at larger scales and later life stages. We used spatially explicit point process models to estimate the relative importance of environmental and dispersal processes and their combined effect on beta diversity across spatial scales and life stages in tropical and subtropical forests. These models fit the observed species distribution pattern and generated realizations of the fitted models for each species. We found that the importance of environmental and dispersal processes did not shift with life stages or vegetation types, but did with spatial scales. Dispersal provided the best explanation of large-scale patterns, but dispersal combined with environmental selection was superior for small-scale patterns. In conclusion, we confirm the importance of spatial scale for the effects and identification of community assembly mechanisms. Our results also suggest that the importance of both dispersal and environmental processes for community assembly could be pervasive across life stages and vegetation types. The generality of these findings should be tested further in different vegetation types and life stages to assess whether specific ecological processes have consistent effects on community structure across life stages and vegetation types.

AimsIt is widely accepted that deterministic and neutral dispersal processes are two of the principal mechanisms driving community assembly. However, the relative importance of these ecological drivers between distinct life stages both at community and individual species levels remains poorly understood in different vegetation types. Here, we address the following questions: (a) is there a ubiquitous process shaping tree assemblage; (b) how does the relative importance of environmental and dispersal processes vary through ontogeny in different vegetation types; and (c) will the spatial patterns of trees at community and individual species levels reflect similar contribution between ecological processes?LocationYunnan province, southwest China.MethodsWe used the Homogeneous Poisson, Homogeneous Thomas, Inhomogeneous Poisson, and Inhomogeneous Thomas point process models to predict the effect of stochastic, dispersal and/or environmental processes, respectively, on the distribution of trees across ontogeny in tropical, subtropical and subalpine forests. To evaluate the relative importance of models, we compared the observed and simulated patterns of the species–area relationship and the pair correlation function g(r) at community and species level, respectively.ResultsThe Homogeneous Thomas model was the model with the lowest Akaike information criterion (AIC) scores across ontogeny and forest types at community level. At the species level, however, Homogeneous Thomas, and Inhomogeneous Thomas predicted the distribution of large and small trees, respectively, with lower AIC values in two of our three plots. In the third plot, the Homogeneous Thomas model is dominant across ontogeny at the species level.ConclusionsTree communities are assembled mainly by the dispersal process at community level. The relative importance of ecological processes for species distribution varies across life stages at the species level, suggesting that there is an ontogenetic shift of ecological processes in shaping tree distribution. Using different summary statistics at both community and species levels helps to discern the different spatial structures of species and increases our appreciation of the processes underpinning community assembly.