. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Trends in Trends • 75 woody plants. (Figure 11-3) Illinois' secondary-growth forest is almost all edge—small plots with very high edge-to-center ratios or riparian forests that have in effect no center at all, making them more vulnerable to invasion by weedy exotics. The Trend Toward Unstable Systems Habitat fragmentation and competition from exotic species have combined to render once-stable ecosyste
. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Trends in Trends • 75 woody plants. (Figure 11-3) Illinois' secondary-growth forest is almost all edge—small plots with very high edge-to-center ratios or riparian forests that have in effect no center at all, making them more vulnerable to invasion by weedy exotics. The Trend Toward Unstable Systems Habitat fragmentation and competition from exotic species have combined to render once-stable ecosystems less so. Lake Michigan is just one example. The decimation of the lake's natural predators by the sea lamprey in the 1950s allowed populations of their common prey, the tiny alewife, to explode. The alewife then decimated native prey fish such as the emerald shiner. The alewife in turn so proliferated that it outpaced its food supply and suffered beach-clogging die-offs in the 1960s; the die-off, in turn, starved the introduced salmonid sportfish that, having been introduced to control the alewife, had come to depend on it. The Trend Toward Managed Ecosystems Management by humans in many cases is the only alternative to habitat and species loss in ecosystems unable to sustain them- selves, and seems likely to become a trend. Managed ecosystems are hardly new to Illinois. Native Americans burned prairies to trap game, among other purposes. Indeed, one could describe the human history of the state as a centuries-long unplanned experiment in ecosystem management. Figure 11-4 Annual 7-Day High Flow Series of the Kaskaskia River at Carlyle c 35,000 ,? Q. 30,000 1 LL 25,000 0 0 g U- CD T 10,000 03 Q 5,000 Flood control begins at Carlyle Lake. 0 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 Source: Water Resources^ Illinois State Water Survev. I '594 However, human management of complex ecosystems can have unnatural "down- stream" effects in bot
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