Plant diversity speeds-up belowground recovery
By Ryan Klopf (Virginia Dept. Conservation and Recreation)
Sara Baer (Southern Illinois University Carbondale)
Elizabeth Bach (Colorado State University)
Johan Six (Swiss Federal Institute of Technology)
“Prairie was, in fact, a community of plants and animals so organized as to build, through the centuries, the rich soil which now feeds us.” -Aldo Leopold, Prairie: The Forgotten Flora (1942)*.
Tallgrass prairie restorations planted with high plant diversity (left) and low plant diversity (right). Photo credit: Ryan Klopf
The tallgrass prairie of the U.S. Midwest is one of the most endangered ecosystems in the world, with >99% of the ecosystem converted to cultivation in some states. Restoring farmland in the Midwest back to tallgrass prairie has been of public interest since the days of Aldo Leopold. Much of this restoration work, however, has focused on reconstructing native plant communities with the assumption that animals and ecosystem functions will follow in time. Many land managers have also questioned whether their efforts to restore diverse plant communities has added benefit to soil recovery from the long legacy of agriculture. Ecologists have conducted many studies to test whether biodiversity influences ecosystem functioning (e.g., aboveground productivity). Most tests, however, been performed at small scales with controlled numbers of species in relatively simple plant or aquatic communities (e.g., <20 species). Many of these studies show that higher biodiversity has a positive effect on ecosystem functioning, particularly aboveground. The application of this theory to the practice of ecological conservation and restoration at large scales and under less controlled conditions has been limited. To fill this application gap, we measured the rate of belowground recovery in former agricultural fields restored to high diversity prairie and low diversity grassland (Klopf et al. 2017).
Soil from a high plant diversity restoration. Photo credit: Elizabeth Bach
The fields used in this study were restored using two different approaches. One set of fields were restored through the USDA’s Conservation Reserve Program (CRP), a federal program that pays landowners to convert marginal crop land to perennial vegetation. A main goal of this program is to reduce and prevent soil erosion. As such, fields restored to prairie through the CRP program generally include <10 plant species. Previous work has shown the low diversity CRP approach can increase soil carbon storage over decades (Baer et al. 2002, 2010). The set of fields used in our study were restored by The Nature Conservancy, with the goal of reconstructing diverse tallgrass prairies communities to protect rare plants and animals. As such, these restorations are planted with >30 locally collected native prairie plant species and actively managed using frequent fire to reduce weeds (non-native plants). All fields were located on similar soils within a two county region of Illinois, USA. Fields under both practices ranged in age (time since restoration) from 2-22 years.
Our findings showed that restoring and managing for more diverse plant communities can improve recovery of belowground biology and functioning in predictable ways. Specifically, we found greater accumulation of roots, more predictable recovery of soil microorganisms (bacteria and fungal biomass), more rapid improvement in soil structure (less compaction), and less nitrogen available for loss from the system in prairie restored and managed for high plant diversity relative to the low diversity grassland plantings. Thus, the hypothesis that biodiversity promotes ecosystem functioning is relevant to large-scale conservation and restoration practices on the landscape.
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*This handwritten essay is included in: Sayre, R.F. 1999. Recovering the Prairie. University of Wisconsin Press. Madison, Wisconsin