Despite controversy in recent years surrounding the humped-back model (HBM) of plant species richness, which says that plant diversity peaks when the environment is moderately hospitable, a new study using data from six continents provides strong evidence supporting the theory. Further understanding the mechanisms underlying the balance between plant productivity and diversity can give direction to future research, such as into managing plant ecosystems.

The concept behind HBM is that environmental stress, such as low water availability, can cause low plant productivity, and yet at high productivity a few highly competitive species tend to dominate -- making moderate productivity and diversity the sweet spot.

However, studies evaluating the accuracy of HBM have found mixed results. To more closely examine the relationship between plant productivity and diversity, Lauchlan Fraser and colleagues conducted globally coordinated surveys across 30 sites in 19 countries and six continents.

All surveys involved identifying and tallying plant species, as well as harvesting plant biomass and dead plant matter. Their data reveal a very strong correlation reflective of the HBM. The authors suggest that their data better reflect the true nature of plant diversity and productivity compared to previous studies that refute the HBM because they include substantially more biomass samples and greater areas of land.

Also unlike previous studies refuting HBM, Fraser and colleagues included samples of dead plant matter, which can provide a more reliable measure of annual aboveground production. The authors argue that HBM is likely an accurate reflection of plant production and diversity, bringing us one step closer to understanding the rich array of flora and fauna that surrounds us.