Relationships between biodiversity and carbon stocks in forest ecosystems: A systematic literature review

A systematic literature review was conducted to explore the relationships between multiple measures of biodiversity (e.g. species diversity, functional divergence and dominance) and carbon (C) stocks (both aboveground and soil organic) in different forest ecosystems. A total of 47 studies, searched in Web of Science or Knowledge, were selected based on different biodiversity indices, strength of the datasets and particularly focusing on C stocks. The majority of relationships between species diversity or richness and C stocks were positive, while only few were negative. The niche complementarity and the mass ratio hypotheses are the two major hypotheses for explaining the effect of functional diversity on C stocks. These two hypotheses did not contradict each other but reflect the two different sides of functional trait attribute i.e., dominance and divergence. The majority of studies suggested that strong dominance by tall and conservative species, rather than a set of coexisting species with diverse heights and acquisitive role, results in more C stocks in various forest ecosystems. Thus, most of the studies supported mass ratio hypothesis instead of the niche complementarity hypothesis in terms of increasing C stocks in forest ecosystems. We concluded that experimental works in other forest ecosystems have shown that each measure of biodiversity often increases C stocks, although the extent to which direct causal relationships exist between biodiversity and C stocks in subtropical forests are still uncertain. Thus, a little is understood how multiple measures of biodiversity affect C stocks, when also considering the effects of biotic and abiotic components of an ecosystem.