In the race to restore some of North America’s most biodiverse and threatened ecosystems, a straightforward first step is likely among the most important.
New research by a team of scientists at the University of Wisconsin–Madison and Michigan State University shows that degraded savanna ecosystems can reap lasting benefits from a single seeding of native understory plants. The study underscores the long-term value of even a brief burst of targeted land management in efforts to restore fallow agricultural fields and other landscapes scarred by human activity.
The eight-year experiment centered on three large tracts of federal land within the historical range of the longleaf pine savanna ecosystem. This biodiversity hotspot once spanned some 90 million acres but has largely vanished. Less than five percent of the continent’s longleaf pine savanna remains, and much of what does persist is a shadow of the unspoiled ecosystem of the past.
“In a high-quality longleaf stand, you can find more than 30 species in a square meter. It’s incredible,” says John Orrock, Wayland E. Noland Distinguished Chair in Integrative Biology. Orrock and Ellen Damschen, Mary Herman Rubinstein Professor of Integrative Biology, were part of the team that led the study.
After assessing more than 230 sites, the team selected 48 meeting criteria that allowed them to gauge whether factors like the space between trees would measurably affect whether native understory plants could establish or persist.
The researchers planted the sites with seeds from about two dozen species of native non-woody plants collected locally, including purple milkweed and sweet goldenrod. They returned periodically to document how successful each species was in becoming established and, crucially, how well they persisted.
They found that factors like needle depth, tree spacing, and seasonal temperature and precipitation did have some influence on the initial success of seeding. Cooler and wetter conditions promoted better establishment, as did shallower needle depth and more space between trees. These latter conditions reflect the ecosystem’s natural state of periodic low-intensity wildfires that consume leaf litter and saplings.
Once a diverse understory of savanna plants became established, its long-term persistence was relatively unaffected by environmental factors—with one exception. Higher temperatures during the height of the growing season were associated with poorer long-term survival among some species, indicating one threat posed by a warming climate.
The study also demonstrates that a single addition of native seeds can have clear benefits that last for years. The researchers are optimistic that their results can help land managers direct limited resources toward restoration strategies with the greatest chance of success.
While the results are most applicable in the context of the longleaf pine savanna ecosystem, they could prove useful for management of similar ecosystems, such as the oak savanna that once dominated large swaths of Wisconsin and the Midwest.
“I see a lot of parallels in the work that we do both here in Wisconsin in tallgrass prairie and oak savanna and longleaf pine savanna in the southeast,” says Damschen.