Abstract
Species richness generally promotes ecosystem productivity, although the shape of the relationship varies and remains the subject of debate. One reason for this uncertainty lies in the multitude of methodological approaches to sampling biodiversity and productivity, some of which can be subjective. Remote sensing offers new, objective ways of assessing productivity and biodiversity. In this study, we tested the species richness–productivity relationship using a common remote sensing index, the Normalized Difference Vegetation Index (NDVI), as a measure of productivity in experimental prairie grassland plots (Cedar Creek). Our study spanned a growing season (May to October, 2014) to evaluate dynamic changes in the NDVI–species richness relationship through time and in relation to environmental variables and phenology. We show that NDVI, which is strongly associated with vegetation percent cover and biomass, is related to biodiversity for this prairie site, but it is also strongly influenced by other factors, including canopy growth stage, short-term water stress and shifting flowering patterns. Remarkably, the NDVI-biodiversity correlation peaked at mid-season, a period of warm, dry conditions and anthesis, when NDVI reached a local minimum. These findings confirm a positive, but dynamic, productivity–diversity relationship and highlight the benefit of optical remote sensing as an objective and non-invasive tool for assessing diversity–productivity relationships.
Highlights
The species richness–productivity relationship has long been of interest in ecology
Consistent with previous studies at this site [2], high species richness plots tended to have higher biomass and percent cover, but biomass was more strongly related to species richness than percent cover (Figure 3). Both biomass and vegetation percent cover showed logarithmic relationships with species richness (Figure 3), similar to previous patterns observed at BioDIV [2]
The mean vegetation percent cover increased with increasing species richness, the variation of percent cover among low species richness plots was higher than the variation of biomass, with some of the low richness plots having a very high vegetation percent cover, causing a weak relationship between species richness and cover (Figure 3b)
Summary
The species richness–productivity relationship has long been of interest in ecology. Much of the recent Biodiversity-Ecosystem Function (BEF) research has developed from a series of landmark experiments at Cedar Creek that consistently demonstrated that biodiversity enhances productivity in experimental grassland systems [1,2,3]. The complementarity hypothesis suggests that the presence of multiple species in a high richness community can increase production via more efficient resource capture. In reviews of the BEF literature, a variety of biodiversity–productivity relationships have been reported [7,8] Both unimodal and positive relationships are commonly reported between productivity and richness, and this relationship can be affected by community composition, resource levels (e.g., fertilizer or irrigation levels) and nature of disturbance [8,9,10]. Highly productive sites are known to be resource rich and species poor. These high productivity and low diversity sites are typically highly managed via irrigation or fertilizer application [8] and often lead to declines in the species richness relationships at high productivity. Variation in the relationship between biodiversity and ecosystem function is known to depend on resource availability [11] and environmental drivers, drought stress, has been shown to constrain biomass in prairie systems [12,13]
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