Konza LTER

The Importance of Long-Term Studies for Understanding the Effects of Fire in Humid Grasslands

Long-term studies at Konza Prairie have addressed the ecological consequences of different fire frequencies in tallgrass prairie ecosystems. These studies include comparisons of ecosystem processes and plant species richness on watersheds subjected to different fire frequencies for more than 20 years. A recent assessment of this long-term dataset revealed the long-term consequences of different fire regimes could not be predicted by short-term responses to individual fires (Knapp et al. 1998). For example, comparisons of pre- and post-fire data on plant species composition would suggest that individual fires do not significantly alter plant species richness. However, the long-term record clearly indicates that repeated frequent fires decrease species richness, while infrequent burning may enhance the number of plant species present.

Long-term record of changes in plant species richness in response to different fire frequencies at Konza Prairie. Long-term annual burning significantly reduced plant species richness, while the short-term effects of fire were variable and inconsistent.

Likewise, the long-term record of aboveground net primary productivity (ANPP) demonstrates the importance of long-term studies to adequately assess the effects of fire on plant productivity. Splitting the long-term record into a series of “short-term” studies of 1-3 consecutive years yielded variable results with fire sometimes increasing, decreasing or not affecting plant productivity. However, analysis of data from any 10-year (or longer) consecutive period clearly demonstrates that, on average, fire stimulates ANPP in tallgrass prairie. Fire also increases the relative responsiveness of prairie to interannual variation in precipitation. However, a dataset >18 years in duration was required to show a statistically significant relationship between annual plant productivity and annual precipitation. Long-term fire treatments have also been important for understanding the influence of fire on N availability and plant responses. Studies of sites that are burned relatively infrequently suggest that N limitation is not affected by fire, while studies of sites with different long-term fire treatments clearly indicates that repeated fires lead to decreased N availability. These observations have been important in providing a mechanistic understanding for post-fire increases in ANPP associated with different fire return intervals (Seastedt and Knapp 1993, Blair 1997). Collectively, these studies clearly demonstrate the importance of long-term studies for understanding patterns and controls of ecological processes in tallgrass prairie.