Conserving and promoting evenness: Organic farming and fire-based wildland management as case studies

Background/Question/Methods

Healthy ecosystems include many species (high richness) with similar abundances (high evenness). Thus, both aspects of biodiversity are worthy of conservation. Conserving both richness and evenness simultaneously might be difficult, however, for example if the restoration of formerly-lost species to low densities brings a cost in reduced evenness. Using meta-analysis, we searched for benefits to biodiversity following adoption of two common land-management schemes, the adoption of organic practices by farmers and controlled burning by natural-land managers.

Results/Conclusions

Both conservation practices significantly increased evenness and overall abundance across taxonomic groups (arthropods, birds, chordates, plants, soil organisms). Surprisingly, evenness and richness varied independently, leading to no richness-evenness correlation and no significant overall change in richness. Both organic farming and burning favored rarer species, re-balancing communities as uncommon species gained individuals. Complementary community-assembly models confirmed that selectively nurturing rarer species averts a richness-evenness tradeoff. Our results support the assertion that richness and evenness capture separate facets of biodiversity, each needing individual attention during conservation.