Long-Term and Large-Scale Perspectives on the Relationship between Biodiversity and Ecosystem Functioning

E have historically been interested in the relationship between biodiversity and ecosystem functioning. Widespread loss of diversity caused by anthropogenic forces has heightened this interest and fostered a desire to determine the mechanisms underlying these relationships. Species diversity is expected to affect ecosystem processes, because the number and kinds of species present determine the specific traits represented in an ecosystem. Species traits may directly mediate energy and material fluxes or may alter abiotic conditions (e.g., disturbance, climate, and limiting resources) that regulate process rates. The components of species diversity that determine this expression of traits in an ecosystem include the number of species present (species richness), their relative abundances (species evenness), the particular species present (species composition), the interactions among species (nonadditive effects), and the temporal and spatial variation in these properties. Research conducted at sites in the Long Term Ecological Research (LTER) Network provides long-term data not only from observations of natural variation but also from experimental manipulation of populations, communities, and ecosystems. This information is essential for determining the temporal and spatial scales at which species traits and species diversity exert their effects—information crucial for resolving recent debates surrounding the interpretation of experiments designed to examine the relationship between biodiversity and ecosystem functioning and the applicability of those experiments to the “real world” (e.g., Huston 1997, Huston et al. 2000, Wardle et al. 2000). In this overview we explore how the many types of research from LTER sites contribute to our understanding of the relationship between ecosystem functioning and the components of diversity described above. Following the theme of this special section and of the LTER program, we focus on how the spatial and temporal scales of studies of diversity and ecosystem functioning may influence their results. (We use “functioning” to mean “showing activity”; this term avoids any implication that