. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. Big Muddy, Saline and Cache Rivers Watershed 99 stream quality (Table 50). However, the decline is not statistically significant. In addition, changes in several other indicators (including taxa richness and taxa dominance) suggest degradation, though these changes are also statistically insignificant. It will take more years of data before trends can be assessed with confidence. Table 50. MBI Values Table 51. Tre
. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. Big Muddy, Saline and Cache Rivers Watershed 99 stream quality (Table 50). However, the decline is not statistically significant. In addition, changes in several other indicators (including taxa richness and taxa dominance) suggest degradation, though these changes are also statistically insignificant. It will take more years of data before trends can be assessed with confidence. Table 50. MBI Values Table 51. Tree Species with the Highest Importance Values Statistic 1995 1996 1997 1998 1999 Overall Average Standard deviation Minimum Maximimi Number of sites 304 14 29 .35 48 48 174 * Only samples with til letisl 25 oriiiiiiisnis were hicliideil in the analysis. ForestWatch volunteers monitored 13 forest sites in the fall of 1998. Twelve were upland forests (nine oak-hickor)-, two tulip, one beech-maple) and one was an ash-cotton wood bottomland forest .Tree species ricliness ranged from seven to 17 species, with an average of 13 tree species per site, slightly above the statewide average of species per site with only seven species was a beech- maple upland with a relatively low tree abundance of 62 trees in a monitoring area of 1500 vrr (the statewide average w as 11 1 trees). Forty-nniL ull \.i ueri. ivluilIccI hi the water- shed, the most in the state (75 taxa were reported statewide). This is not surprising since souliiern Illinois contains species found in both northern and southern latitudes. In general, the trees that weiv most abundant also had the largesi areas and highest importance values (Table 51). Importance Value Species % of total trees counted (n= 1,448) % of total area () Hickory 16",, 20% White oa
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