An Ecosystem in Transition: Causes and Consequences of the Conversion of Mesic Grassland to Shrubland

Woody plant expansion is one of the greatest contemporary threats to mesic grasslands of the central United States. In this article, we synthesize more than 20 years of research to elucidate the causes and consequences of the ongoing transition of C 4 -dominated grasslands to savanna-like ecosystems codominated by grasses and woody plants. This transition is contingent on fire-free intervals, which provide the opportunity for recruitment both of new individuals and of additional shrub and tree species into this grassland. Once shrubs establish, their cover increases regardless of fire frequency, and infrequent fires accelerate the spread of some shrub species. This process has resulted in a new dynamic state…

• NS
  National Science Foundation
• NA
  National Aeronautics and Space Administration
• NC
  Nature Conservancy