The connection between plant productivity and biodiversity is a significant topic in ecology, although it has been controversial for decades. Both productivity and species diversity are constricted by other variables such as climate, ecosystem type, and land use intensity. According to some research on the correlation between plant diversity and ecosystem functioning is that productivity increases as species diversity increases. One reasoning for this is that the likelihood of discovering a highly productive species increases as the number of species initially present in an ecosystem increases.
Other researchers believe that the relationship between species diversity and productivity is unimodal within an ecosystem. A 1999 study on grassland ecosystems in Europe, for example, found that increasing species diversity initially increased productivity but gradually leveled off at intermediate levels of diversity. More recently, a meta-analysis of 44 studies from various ecosystem types observed that the interaction between diversity and production was unimodal in all but one study.