Print PageClimate change and increased woody plant cover are critical threats to the conservation of grasslands. Climate drives many ecological processes in grasslands, while changes in land management, such as reduced fire frequency, coupled with global change drivers can increase woody plant abundance and alter grasslands ecosystem functioning. Long-term research and experiments conducted at the Konza Prairie Biological Station (KPBS) are examining the ecological impacts of changing climate and land-cover in tallgrass prairie. We synthesize data from a combination of long-term measurements of woody plant cover and ecosystem processes coupled with extensive manipulative experiments and discuss the ecosystem consequences of increased woody plant cover in the context of grassland responses to climatic variability and climate change. We also present results from an on-going experiment, in which long-term fire treatments were ‘reversed’ on two watersheds previously burned annually and two watersheds protected from fire for ~20 yrs to assess the legacy effects of fire history on trajectories of response to altered fire frequency.
Results/Conclusions
Over 20 yrs of data on plant cover under different fire regimes at KPBS reveals that the transition from grassland to shrubland is contingent upon fire-free intervals, which facilitate recruitment of new individuals and additional woody plant species. Shrub cover can increase with periodic fires, and infrequent fires accelerate the spread of some shrub species. Long-term data show that shrub cover increased most dramatically in sites with a fire frequency of once every 4 years (increase > 28%) followed by sites in which fire occurred only once during the 18-yr period (increase > 23%). Annual spring fires effectively prevented the recruitment of new woody plant species, but even with this high fire frequency, shrub cover increased slightly (3%). Increased woody plant cover leads to changes in ecosystem processes, including greater total plant productivity and C and N storage, but lower herbaceous plant productivity. Long-term data on plant productivity was used to assess the sensitivity of grass-dominated areas to interannual climate variability, while manipulative experiments allowed us to measure responses to potential climate change. Both land-cover change and climate change altered important C and N cycling processes. However, comparison of the magnitude of responses to land-cover change with responses to both natural and experimentally increased climatic variability in grass-dominated areas suggests that the impacts of land-cover change are likely to exceed those of moderate climate change in these grasslands.
