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Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem functioning are largely unknown1-3. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use4,5. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa's largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained-on average-54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions.

Many experiments have shown that biodiversity enhances ecosystem functioning. However, we have little understanding of how environmental heterogeneity shapes the effect of diversity on ecosystem functioning and to what extent this diversity effect is mediated by variation in species richness or species turnover. This knowledge is crucial to scaling up the results of experiments from local to regional scales. Here we quantify the diversity effect and its components-that is, the contributions of variation in species richness and species turnover-for 22 ecosystem functions of microorganisms, plants and animals across 13 major ecosystem types on Mt Kilimanjaro, Tanzania. Environmental heterogeneity across ecosystem types on average increased the diversity effect from explaining 49% to 72% of the variation in ecosystem functions. In contrast to our expectation, the diversity effect was more strongly mediated by variation in species richness than by species turnover. Our findings reveal that environmental heterogeneity strengthens the relationship between biodiversity and ecosystem functioning and that species richness is a stronger driver of ecosystem functioning than species turnover. Based on a broad range of taxa and ecosystem functions in a non-experimental system, these results are in line with predictions from biodiversity experiments and emphasize that conserving biodiversity is essential for maintaining ecosystem functioning.

AIMS: We tested whether plant species niche breadths decrease with increasing species richness due to competition on temperature, precipitation and disturbance gradients. We assumed that niche optima, niche breadth and niche volume are related to plant functional traits, indicating competitive ability and adaptation to environmental stress. Finally, we wanted to identify habitats dominated by species with small niche breadths most prone to environmental change. LOCATION: Southern slopes of Mount Kilimanjaro, Tanzania. METHODS: We calculated species distribution models for 1,492 plant species based on the presence/absence data on 969 plots using generalized linear models. We derived niche breadths, optima and volumes and investigated their relationship with plant functional traits with principal component regression to account for high trait correlations. RESULTS: Niche breadths of individual species increased with elevation, precipitation and disturbance. Averaged community elevation niche breadth and niche volume decreased with increasing species richness. Plant functional traits explained about 40% and 50% of the variation in niche optima and breadths, respectively. Size and growth traits were significant predictors of niche breadths on all gradients, whereas traits indicating reproductive strategy were not significant on the precipitation gradient. MAIN CONCLUSIONS: Our results support the notion of decreasing niche breadth with increasing temperature, possibly a result of competition due to increased diversification rates and hence species richness. However, the complexity of the niche breadth–species richness patterns on the other gradients shows that additional covariables shape species niche breadths apart from competition. Plant species with narrow niche breadths dominated natural savannas around Mount Kilimanjaro, indicating strong sensitivity to the ongoing conversion of savanna to fields and grasslands.

In this study, we quantify the impacts of climate and land use on soil N2O and CH4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured GHG fluxes from twelve different ecosystems along climate and land-use gradients at Mt. Kilimanjaro, combining long-term in situ chamber and laboratory soil-core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N2O and CH4, respectively. N2O emissions correlated positively with soil moisture and total soil nitrogen content. CH4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N2O emissions of tropical montane forests were generally low (< 1.2 kg N ha−1 yr−1), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha−1 yr−1). Forest soils with well-aerated litter layers were a significant sink for atmospheric CH4 (up to 4 kg C ha−1 yr−1) regardless of low mean annual temperatures at higher elevations. Land-use intensification significantly increased the soil N2O source strength and significantly decreased the soil CH4 sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non-CO2 GHG emissions following land-use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N2O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land-use change. This article is protected by copyright. All rights reserved.

Question How do community-weighted means of traits (CWM) and functional dispersion (FDis), a measure of trait variability, change in response to gradients of temperature, precipitation, soil nutrients, and disturbance? Is the decrease in trait similarity between plots continuous or discontinuous? Is species turnover between plots linked to trait turnover? Location Mount Kilimanjaro, Tanzania, Africa. Methods Sixty plots were established in twelve major vegetation types on Mount Kilimanjaro, covering large gradients of temperature, precipitation, soil nutrients, and anthropogenic disturbance representing the dominant ecosystems in East Africa. Environmental data, plant abundances, and plant traits were recorded for each plot. Trait CWM and FDis were related to environmental factors with partial least squares regressions. Trait similarity between pairs of plots was assessed with a null-model approach. Results Both CWM and FDis of most traits responded strongly to environmental factors, particularly to precipitation and disturbance. FDis of traits associated with growth and reproduction mostly increased with temperature and precipitation, and decreased with disturbance. Pairwise plot comparisons revealed an inverse relationship of trait similarity with differences in temperature, precipitation, and anthropogenic disturbance, respectively. However, changes in similarity were often discontinuous rather than continuous. Several vegetation types differed strongly in species composition but not in traits. Conclusions Trait dispersion indicating functional niches increased with productivity and temperature. Conversely, low-productivity conditions were characterized by trait convergence. Discontinuous changes in trait similarity between plots suggested tipping points at which trait expressions change strongly to adjust to environmental conditions. Large sections of the temperature gradient were characterized by species turnover with only minor changes in traits, indicating that the functional composition may be resilient against gradual environmental changes until a tipping point is reached. This article is protected by copyright. All rights reserved.

In our study at Mt. Kilimanjaro, East Africa, we quantified gross rates of ammonification, nitrification, nitrogen immobilization, and dissimilatory nitrate reduction to ammonium in soils across different land uses, climate zones (savanna, montane forest ecosystems, extensive agroforest homegarden, and intensively managed coffee plantation), and seasons (dry, wet, and transition from dry to wet season) to identify if and to what extent conversion of natural ecosystems to cultivated land has affected key soil microbial nitrogen turnover processes. Overall variation of gross soil nitrogen turnover rates across different ecosystems was more pronounced than seasonal variations, with the highest turnover rates occurring at the transition between dry and wet seasons. Nitrogen production and immobilization rates positively correlated with soil organic carbon and total nitrogen concentrations as well as substrate availability of dissolved organic carbon and nitrogen r > 0.67, P

Variations in the stable isotopic composition of carbon (δ13C) and nitrogen (δ15N) of fresh leaves, litter and topsoils were used to characterize soil organic matter dynamics of twelve tropical ecosystems in the Mount Kilimanjaro region, Tanzania. We studied a total of 60 sites distributed along five individual elevational transects (860–4550 m a.s.l.), which define a strong climatic and land use gradient encompassing semi-natural and managed ecosystems. The combined effects of contrasting environmental conditions, vegetation, soil, and management practices had a strong impact on the δ13C and δ15N values observed in the different ecosystems. The relative abundance of C3 and C4 plants greatly determined the δ13C of a given ecosystem. In contrast, δ15N values were largely controlled by land-use intensification and climatic conditions. Both δ15N values and calculated δ15N-based enrichment factors (δ15Nlitter–δ15Nsoil) indicate tightest nitrogen cycling at high-elevation (> 3000 m a.s.l.) ecosystems, and more open nitrogen cycling both in grass-dominated and intensively managed cropping systems. The negative correlation of δ15N values with soil nitrogen content and the positive correlation with mean annual temperature suggest reduced mineralisation rates, and thus limited nitrogen availability, at least in high-elevation ecosystems. By contrast, intensively managed systems are characterized by lower soil nitrogen contents and warmer conditions, leading together with nitrogen fertilizer inputs to lower nitrogen retention, and thus, significantly higher soil δ15N values. A simple function driven by soil nitrogen content and mean annual temperature explained 68 % of the variability in soil δ15N values across all sites. Based on our results, we suggest that in addition to land use intensification, increasing temperatures in a changing climate may promote soil carbon and nitrogen losses, thus altering the otherwise stable soil organic matter dynamics of Mt. Kilimanjaro’s forest ecosystems.

Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem functioning are largely unknown

Tropical ecosystems are under increasing pressure of land-use changes, strongly affecting the carbon cycle. Conversion from natural to agri-cultural ecosystems is often accompanied by a decrease in the stocks of organic and microbial carbon (Corg, Cmic) as well as changes in microbial activity and litter decomposition. Eleven ecosystems along an elevation gradient on the slopes of Mt. Kilimanjaro were used to investigate impacts of land-use changes on Corg and Cmic stocks as well as the specific metabolic respiration quotient (qsCO2) in surface soils. Six natural, two semi-natural and three intensively used agricultural ecosystems were investigated on an elevation gradient from 950 to 3,880 m asl. To estimate the effects of precipitation, rainfall regimes of 3·6 and 20·0 mm were simulated. Corg stocks were controlled by water availability, temperature and net primary production. Agricultural management resulted in decreases of Corg and Cmic stocks by 38% and 76%, respectively. In addition, agricultural systems were characterized by low Cmic:Corg ratios, indicating a decline in available substrate. Enhanced land-use intensity leads to increased qsCO2 (agricultural > semi-natural > natural). The traditional homegardens stood out as a sustainable land-use form with high substrate availability and microbial efficiency. Soil CO2 efflux and qsCO2 generally increased with precipitation level. We conclude that soils of Mt. Kilimanjaro's ecosystems are highly sensitive to land-use changes and are vulnerable to changes in precipitation, especially at low elevations. Even though qsCO2 was measured under different water contents, it can be used as an indicator of ecosystem disturbances caused by land-use and management practices. Copyright © 2015 John Wiley & Sons, Ltd.

In this study, we quantify the impacts of climate and land use on soil N

Grazing of grasslands changes soil physical and chemical properties as well as vegetation characteristics, such as vegetation cover, species composition and biomass production. In consequence, nutrient allocation and water storage in the top soil are affected. Land use and management changes alter these processes. Knowledge on the impacts of grazing management on nutrient and water fluxes is necessary because of the global importance of grasslands for carbon sequestration. Soil water in semi-arid areas is a limiting factor for matter fluxes and the intrinsic interaction between soil, vegetation and atmosphere. It is therefore desirable to understand the effects of grazing management and stocking rate on the spatial and temporal distribution of soil moisture. In the present study, we address the question how spatio-temporal soil moisture distribution on grazed and ungrazed grassland sites is affected by soil and vegetation properties. The study took place in the Xilin river catchment in Inner Mongolia (PR China). It is a semi-arid steppe environment, which is characterized by still moderate grazing compared to other regions in central Inner Mongolia. However, stocking rates have locally increased and resulted in a degradation of soils and vegetation also in the upper Xilin River basin. We used a multivariate geostatistical approach to reveal spatial dependencies between soil moisture distribution and soil or vegetation parameters. Overall, 7 soil and vegetation parameters (bulk density, sand, silt and clay content, mean weight diameter, mean carbon content of the soil, vegetation cover) and 57 soil moisture data sets were recorded on 100 gridded points on four sites subject to different grazing intensities. Increasing stocking rates accelerated the influence of soil and vegetation parameters on soil moisture. However, the correlation was rather weak, except for a site with high stocking rate where higher correlations were found. Low nugget ratios indicate spatial dependency between soil or plant parameters and soil moisture on a long-term ungrazed site. However, the effect was not found for a second ungrazed site that had been excluded from grazing for a shorter period. Furthermore the most important soil and vegetation parameters for predicting soil moisture distribution varied between different grazing intensities. Therefore, predicting soil moisture by using secondary variables requires a careful selection of the soil or vegetation parameters.