Aim  In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. Location  World‐wide. Methods  We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. Main conclusions  The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across‐studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.

Summary 1.Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant-plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant-plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.

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For evaluating climate change impacts on biodiversity, extensive experiments are urgently needed to complement popular non-mechanistic models which map future ecosystem properties onto their current climatic niche. Here, we experimentally test the main prediction of these models by means of a novel multi-site approach. We implement rainfall manipulations—irrigation and drought—to dryland plant communities situated along a steep climatic gradient in a global biodiversity hotspot containing many wild progenitors of crops. Despite the large extent of our study, spanning nine plant generations and many species, very few differences between treatments were observed in the vegetation response variables: biomass, species composition, species richness and density. The lack of a clear drought effect challenges studies classifying dryland ecosystems as most vulnerable to global change. We attribute this resistance to the tremendous temporal and spatial heterogeneity under which the plants have evolved, concluding that this should be accounted for when predicting future biodiversity change.

Summary 1Interactions among plants strongly influence the structure and dynamics of plant populations and communities. However, most empirical studies of plant-plant interactions failed to make repeated measures of responses to neighbouring individuals and thereby neglected possible changes in interactions throughout the life history of the plants.2 We tested the hypothesis that competition between annual species intensifies from early to late life-history stages, by sequentially measuring interactions in neighbourremoval experiments at three study sites located along a rainfall gradient in Israel. 3 Two annual species, Biscutella didyma and Hymenocarpos circinnatus , grew with and without neighbours in their natural habitats. Five response variables representing consecutive life-history stages (seedling survival, juvenile biomass, adult survival, number of seeds and final biomass) were recorded throughout the whole growing season. 4 The direction and intensity of interactions varied considerably between environments and life stages. On average, growth-related response variables indicated higher competition intensity at the productive end of the climatic gradient, while survival indicated either facilitation at the dry end or no trend along the gradient. 5 Temporal changes occurred, with moderate facilitation soon after germination shifting to strong competition at the end of the growing season. 6 Our results demonstrate that the outcome of experimental studies on plant-plant interactions may depend not only on the environmental productivity but more so on the life stage at which the target plant is studied.

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

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