Based on the analysis of 600 vegetation plots using the method of Braun-Blanquet (1964) the composition of the whole vascular forest plant flora with about 1220 species was studied in the forests of ...Mt. Kilimanjaro. The altitudinal distribution of all strata (trees, shrubs, epiphytes, lianas and herbs) along a transect of 2400 m is discussed with respect to altitudinal zonation and ecological factors. With uni-dimensionally constraint clustering significant discontinuities were revealed that occurred simultaneously in the different strata. Thus even in structurally highly complex, multilayered tropical montane forests distinct community units exist that can be surveyed and classified by the Braun-Blanquet approach. This observed zonation was significantly correlated with altitude, temperature and soil acidity (pH); rainfall was of importance in particular for the zonation of epiphytes. Other key factors were humidity (influenced by stable cloud condensation belts) and minimum temperature (in particular the occurrence of frost at 2700 m altitude upslope). The contrary results of other transect studies in East Africa in respect to continuity of change in floristic composition appear to be caused by different sampling methods and intensities or mixing of data from areas with different climate conditions, whereas species richness did not influence the clarity of floristic discontinuities on Kilimanjaro and other parts of East Africa.
Issue Title: Themed Issue: Forest Diversity and Management: Safeguarding the Earth's Biota Natural flora, vegetation, diversity and structure of 62 traditional coffee-banana plantations on ...Kilimanjaro were investigated and compared with the other vegetation formations on this volcano on basis of over 1400 plots following the method of Braun-Blanquet. The vegetation of the so-called Chagga homegardens belongs floristically to the formation of ruderal vegetation forming two main communities that are determined by altitude. These coffee-banana plantations maintain a high biodiversity with about 520 vascular plant species including over 400 non-cultivated plants. Most species (194) occurring in the Chagga homegardens are forest species, followed by 128 ruderal species, including 41 neophytes. Typical of the agroforestry system of the Chagga homegardens is their multilayered vegetation structure similar to a tropical montane forest with trees, shrubs, lianas, epiphytes and herbs. Beside relicts of the former forest cover, which lost most of their former habitats, there are on the other hand (apophytic) forest species, which were directly or indirectly favoured by the land use of the Chagga people. High demand of wood, the introduction of coffee varieties that are sun-tolerant and low coffee prizes on the world marked endanger this effective and sustainable system.PUBLICATION ABSTRACT
In most habitats, vegetation provides the main structure of the environment. This complexity can facilitate biodiversity and ecosystem services. Therefore, measures of vegetation structure can serve ...as indicators in ecosystem management. However, many structural measures are laborious and require expert knowledge. Here, we used consistent and convenient measures to assess vegetation structure over an exceptionally broad elevation gradient of 866-4550 m above sea level at Mount Kilimanjaro, Tanzania. Additionally, we compared (human)-modified habitats, including maize fields, traditionally managed home gardens, grasslands, commercial coffee farms and logged and burned forests with natural habitats along this elevation gradient. We distinguished vertical and horizontal vegetation structure to account for habitat complexity and heterogeneity. Vertical vegetation structure (assessed as number, width and density of vegetation layers, maximum canopy height, leaf area index and vegetation cover) displayed a unimodal elevation pattern, peaking at intermediate elevations in montane forests, whereas horizontal structure (assessed as coefficient of variation of number, width and density of vegetation layers, maximum canopy height, leaf area index and vegetation cover) was lowest at intermediate altitudes. Overall, vertical structure was consistently lower in modified than in natural habitat types, whereas horizontal structure was inconsistently different in modified than in natural habitat types, depending on the specific structural measure and habitat type. Our study shows how vertical and horizontal vegetation structure can be assessed efficiently in various habitat types in tropical mountain regions, and we suggest to apply this as a tool for informing future biodiversity and ecosystem service studies.
Cloud forests are of great importance in the hydrological functioning of watersheds in subhumid East Africa. However, the montane forests of Mt. Kilimanjaro are heavily threatened by global change ...impacts. Based on an evaluation of over 1500 vegetation plots and interpretation of satellite imagery from 1976 and 2000, land-cover changes on Kilimanjaro were evaluated and their impact on the water balance estimated. While the vanishing glaciers of Kilimanjaro attract broad interest, the associated increase of frequency and intensity of fires on the slopes of Kilimanjaro is less conspicuous but ecologically far more significant. These climate change-induced fires have lead to changes in species composition and structure of the forests and to a downward shift of the upper forest line by several hundred metres. During the last 70 years, Kilimanjaro has lost nearly one-third of its forest cover, in the upper areas caused by fire, on the lower forest border mainly caused by clearing. The loss of 150 km² of cloud forest - the most effective source in the upper montane and subalpine fog interception zone - caused by fire during the last three decades means a considerable reduction in water yield. In contrast to common belief, global warming does not necessarily cause upward migration of plants and animals. On Kilimanjaro the opposite trend is under way, with consequences more harmful than those due to the loss of the showy ice cap of Africa's highest mountain.
Aim: Elevational gradients offer an outstanding opportunity to assess factors determining patterns of species richness, but along single transects potential explanatory factors often covary, making ...it difficult to distinguish between competing hypotheses. Many previous studies on plants have interpreted their results as supporting the mid-domain effect (MDE) as a major determinant of species richness, even when climatic factors showed similarly high explanatory power. We compared fern species richness along 20 elevational transects to quantify the relative contribution of climate and MDE as drivers of elevational richness patterns. Location: Twenty transects world-wide. Methods: Ferns were sampled in 1039 plots of 400-2500 m² each. Mean annual precipitation and temperature, epiphytic bryophyte cover (as a proxy for air humidity) and MDE predictions were included as independent variables. For each transect, we calculated multiple linear models and partitioned the variance to assess the relative contribution of the independent variables, selecting the most parsimonious models based on Akaike weights and multi-model inference. Results: Along most individual gradients, nearly all variance of fern species richness that could be attributed to either space or MDEs was collinear with climatic factors. Yet, the comparison across transects showed that elevational richness patterns are most parsimoniously accounted for by climatic conditions, especially by low water availability at low elevations and in dry regions in general, and by low temperatures at high elevations and in extra-tropical regions. Main conclusions: Fern species richness is most closely related to climatic factors, and while MDE, surface area and metapopulation processes may somewhat modify the patterns, their importance has been overstated in the past. Future research challenges include determining whether the richness-climate relationship reflects: (1) a direct relationship through the physiological tolerance of the plants, (2) an indirect influence of climate on ecosystem productivity, or (3) an evolutionary legacy of longer or faster diversification processes under certain climatic conditions.
Spatially high resolution climate information is required for a variety of applications in but not limited to functional biodiversity research. In order to scale the generally plot-based research ...findings to a landscape level, spatial interpolation methods of meteorological variables are required. Based on a network of temperature observation plots across the southern slopes of Mt. Kilimanjaro, the skill of 14 machine learning algorithms in predicting spatial temperature patterns is tested and evaluated against the heavily utilized kriging approach. Based on a 10-fold cross-validation testing design, regression trees generally perform better than linear and non-linear regression models. The best individual performance has been observed by the stochastic gradient boosting model followed by Cubist, random forest and model averaged neural networks which except for the latter are all regression tree-based algorithms. While these machine learning algorithms perform better than kriging in a quantitative evaluation, the overall visual interpretation of the resulting air temperature maps is ambiguous. Here, a combined Cubist and residual kriging approach can be considered the best solution.
Leaf-wax n-alkanes are produced by terrestrial plants, and through long-term preservation in sediments their stable hydrogen-isotopic signature (δ2Hwax) provides useful information on past ...hydrological variation for paleoclimate reconstructions. However, gaps remain in our understanding of the relationships between the isotopic signatures of leaf waxes and the plants’ source water. In this study, we investigated the influence of plant growth form, habitat and season on the distribution patterns and δ2Hwax values of 14 plant species (among which are two grasses, five trees and seven shrubs) sampled during four successive dry and wet seasons in three distinct habitats around Lake Chala in equatorial East Africa. Variation in δ2Hwax was analyzed with linear mixed-effect models and compared with the associated values of xylem water (δ2Hxylem), leaf water (δ2Hleaf) and biosynthetic hydrogen fractionation (εbio). Our results show that plant growth form was the most important driver of modern-day δ2Hwax variability in the study area, and that differences in δ2Hwax among habitats to a large extent reflect how each major growth forms is represented in those habitats. Individual plant species appear to express substantial species-specific isotopic fractionation that cannot be attributed to the tested external factors but rather seem to depend on intrinsic (e.g., plant phenological and biosynthesis-related) factors. For the purpose of calibrating δ2Hwax signatures against vegetation types, it is thus crucial to analyze representative samples of the plant communities present in the study area. Our results further indicate that paleohydrological studies in regions receiving rain from multiple moisture sources must take into account possible seasonal bias in the δ2Hwax signature relative to annual rainfall, due to unequal use of those moisture sources by the plants. Finally, the strong influence of plant growth form on δ2Hwax values argues for δ2Hwax variation in paleo-records being evaluated in conjunction with independent proxy data on changes in vegetation composition. Differences in n-alkane distribution patterns among trees, shrubs and grasses (e.g., average chain length, carbon preference index and C31/(C29 + C31) ratio) may provide such proxies, and can be produced from the same leaf-wax n-alkane dataset used to determine δ2Hwax.
Agroforestry integrates trees in agricultural landscapes for socio-economic and ecological benefits. On Kilimanjaro, the agroforestry system of the Chagga homegardens harbours a high diversity of ...vascular plants and animals. In contrast, the commercial coffee plantations represent a monocultural type of agroforestry and are managed more intensively. The aim of this study is to investigate the bryophyte flora of these differently managed agroforestry systems on Kilimanjaro and to highlight their function for biodiversity and as a refuge for bryophytes. We used 10 of the permanent monitoring plots of the DFG-funded Kili-project, each of 20 × 50 m. We recorded the species separately on the ground, on dead wood, on coffee trees and on trees taller than 2 metres using rope-based canopy access methods from arboriculture. In total we found 68 bryophyte species, which (without the 10 new records) corresponds to 45% of the known bryophyte species of the submontane and colline zone of Kilimanjaro. The strongest correlation for the total number of species per plot was with elevation, followed by land use intensity and mean annual precipitation (all, except land use intensity with a positive trend). Our study shows that homegardens and partly also commercial coffee plantations on Kilimanjaro can serve as refuges for former forest dwellers. This ability to conserve nature is enhanced by less intensive land management without using pesticides. As the market for organic products grows, such ecological management could provide coffee farms with a stable income while protecting their biodiversity.
Species' functional traits set the blueprint for pair-wise interactions in ecological networks. Yet, it is unknown to what extent the functional diversity of plant and animal communities controls ...network assembly along environmental gradients in real-world ecosystems. Here we address this question with a unique dataset of mutualistic bird-fruit, bird-flower and insect-flower interaction networks and associated functional traits of 200 plant and 282 animal species sampled along broad climate and land-use gradients on Mt. Kilimanjaro. We show that plant functional diversity is mainly limited by precipitation, while animal functional diversity is primarily limited by temperature. Furthermore, shifts in plant and animal functional diversity along the elevational gradient control the niche breadth and partitioning of the respective other trophic level. These findings reveal that climatic constraints on the functional diversity of either plants or animals determine the relative importance of bottom-up and top-down control in plant-animal interaction networks.
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