Increasing growing-season length in Illinois as an indicator of climatic change

Systematic changes and natural variations in growing-season length and associated statistics have important implications for natural and managed ecosystems. Many plants and insects are particularly sensitive to the timing of extreme events early in the growing season. Using data from the state of Illinois, daily minimum air temperature is analyzed for a variety of systematic changes in growing-season length and the timing of frost events. A variety of critical air temperatures and trend-estimation methods show that growing-season length in Illinois has increased at nearly all long-term climatic stations (daily HCN stations). Many stations show increased growing seasons of 20 days (or more) per 100 years, although the average increase is closer to one week. Nearly all of these changes are the result of later occurrences spring ‘frosts'. The use of a multiresolution Fourier transform (MFT) and analysis of the temporal evolution of probability density functions provide additional evidence of growing-season length changes. Increasing growing-season length and later spring frosts have multiple impacts, both positive and negative. In terms of agriculture, these changes allow earlier planting times, ensuring crop maturation and permitting the possibility of multiple cropping. Associated changes in soil-water availability and increases in insect damage, however, may reduce or reverse the benefits discussed above. Among other impacts, natural ecosystems may experience changes in species distributions as a result of growing-season changes