The effect of agricultural diversity and crop choice on functional capacity change in grassland conversions.
Abstract
Given that approximately one-quarter of grasslands worldwide have been converted to agriculture, understanding the consequences of agricultural conversion for ecosystem functioning can provide insight into potential changes in the world's most intensively managed biomes. The Great Plains of the United States represents a major grassland region that has experienced substantial conversion of prairie grassland ecosystems to agriculture, leading to widespread changes in plant species composition and functional trait diversity. While the converted system dramatically improves food, fuel and fibre production, changes in plant trait diversity may alter the capacity of these ecosystems to provide sustaining and regulating services to society. Using three key plant functional traits, we illustrate how the trait composition and trait diversity of the Great Plains plant communities has been dramatically altered when visualized in multidimensional trait space, showing strong displacement and a 10-fold reduction in trait space volumes, as systems have shifted from grassland to agricultural regimes. However, individual case studies demonstrate large variation in the direction and magnitude of trait diversity change during conversion, with some case studies exhibiting much larger reductions in trait diversity from the average on conversion, largely a consequence of the changes in species richness accompanying agricultural conversion. Synthesis and applications. The conversion of grassland to agriculture does not necessarily lead to a loss of functional trait diversity, as crop choice and diversity can ameliorate the functional trait differences between native-dominated and agricultural communities. In this study, regardless of the sign and magnitude of change in trait space, a shift in trait range was observed, reflecting the dramatically different selection that agricultural plant functional traits experience compared with their native counterparts. Historical agricultural policy and modern land-use patterns have led to a landscape with decreasing plant diversity and functional capacity. However, initiatives to increase agricultural diversity on-farm and at the landscape level through the implementation of cover crops of the perennialization of cropping systems may allow ecosystems to recover and maintain greater functional capacity.