Spatial scaling of species richness–productivity relationships for local communities: analytical results from a neutral model

A critical assessment of the biodiversity-productivity relationship in forests and implications for conservation

The question of whether biodiversity conservation and carbon conservation can be synergistic hinges on the form of the biodiversity-productivity relationship (BPR), a fundamental ecological pattern. The stakes are particularly high when it comes to forests, which at a global level comprises a large fraction of both biodiversity and carbon. And yet, in forests, the BPR is relatively poorly understood. In this review, we critically evaluate research on forest BPRs, focussing on the experimental and observational studies of the last 2 decades. We find general support for a positive forest BPR, suggesting that biodiversity and carbon conservation are synergistic to a degree. However, we identify several major caveats: (i) although, on average, productivity may increase with biodiversity, the highest-yielding forests are often monocultures of very productive species; (ii) productivity typically saturates at fewer than ten species; (iii) positive BPRs can be driven by some third variable, in particular stem density, instead of a causal arrow from biodiversity to productivity; (iv) the BPR's sign and magnitude varies across spatial grains and extents, and it may be weak at scales relevant to conservation; and (v) most productivity estimates in forests are associated with large errors. We conclude by explaining the importance of these caveats for both conservation programmes focussed on protection of existing forests and conservation programmes focussed on restoring or replanting forests.

Responses of diversity, productivity, and stability to the nitrogen input in a tropical grassland

Atmospheric nitrogen (N) deposition is a matter of serious concern for the structure and functioning of global ecosystems, but the effect of N application of species diversity (D), primary productivity (P), and stability (S) of tropical grassland ecosystems is not known. The present study reports the effects of different levels of N application on species composition, and the D, P, S, and their relationships in a tropical grassland. Within the experimental grassland, 72 1 × 1 m plots with 6 N-input levels and with 12 replicates, were established in 2013. For 3 yr, different doses of urea as a source of N were applied to the plots. Data on individuals and biomass of each species were recorded and statistically analyzed. The study revealed that the N applied caused variations in species composition, D, P, and S. Below the 90 kg N dose, D was positively related to P and S while, above this level, the relations were negative due to N-induced responses of species and functional group composition as well as biomass distribution among them. The optimum applied N levels for maximum D (50-60 kg N), P (120 kg N), and a positive relationship of S with D (up to 90 kg N treatment) suggested that the 90-kg N dose could be the maximum dose of N that the grassland can tolerate. Hence, N application should not exceed the 90-kg level for sustainability of the structure and functioning of tropical grassland ecosystems.