Feb. 5, 2001 MANHATTAN — Tallgrass prairies. One of America's most endangered ecosystems.
While their size has diminished over the years — only an estimated 5 percent of the original tallgrass prairie in the United States exists today — their importance in the ability to predict climate changes has not, according to research conducted by two Kansas State University scientists.
Long-term studies in tallgrass prairies may be able to predict and help researchers better understand how ecosystems across North America might respond to certain aspects of climate change, such as global warming; droughts and changes in precipitation amounts, according to K-State biology professor Alan Knapp. His research, co-authored by Melinda Smith, a doctoral student in biology, is published in the Jan. 19 issue of Science
Knapp and Smith compiled data from 11 long-term ecological research sites across North America, selecting only those sites that had the best and longest-term data on plant growth — known as production — and precipitation. One of their goals was to determine which biomes, among deserts, grasslands and forests, had more variable production; which biomes responded most to precipitation variability.
"In this study, we were particularly interested in how different ecosystems respond to variations in rainfall," Knapp said. "If rainfall patterns change and variability changes in the future — as predicted by climate models — how will that affect plant growth and which ecosystems will be the most responsive?"
Knapp and Smith made a simple prediction. If the greatest precipitation variability from year-to-year occurs in deserts and deserts are the most water-limited biomes, then plant growth in deserts would be expected to change dramatically from year-to-year; grasslands would be less variable from year-to-year and forests would be the least variable of all.
Instead the data indicated their hypothesis wasn't supported at all.
"It turns out that what we found instead was that grasslands — in the regions we live — have the greater year-to-year variation in plant growth than in any other biome, even though rainfall variability isn't as high here as it is in deserts, Knapp said.
That piqued Knapp and Smith's interest and led them to search for other explanations.
"One of the important differences between grasslands and deserts is that grasslands have a higher density of plants, and these plants can grow faster than desert plants " Knapp said "If you think about a desert environment, there's lots of bare ground between plants.
Knapp said even though regions with tallgrass prairies have less rainfall variability, the ecosystem and its plants are well adapted to respond to that variability.
"They grow very rapidly in wet years, yet can survive drought years as well," Knapp said. "So we see the greatest variation in year-to-year production in grasslands as opposed to deserts, and we see very little year-to-year variation in production in forest sites. "
According to both Knapp and Smith, they were intrigued that their analysis didn't fit their initial prediction.
"We knew the plant growth and precipitation are strongly related as you move across North America," Knapp said. "We assumed that variability in precipitation and variability in production would also be strongly related across North America. It turns out they're not. One has to factor in the characteristics of the biome as well, the potential responses of the plants, how dense they are; how fast they can grow. You have to factor in these biological characteristics with rainfall patterns to explain these patterns of variation in production across North America."
Knapp said although Kansans already have a strong affinity for the state's tallgrass prairies, this research gives the prairies "added value" in terms of their potential role in detecting changes in future climates.
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