Impact of the American Chestnut Blight on Aquatic Shredding Macroinvertebrates

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Abstract
The American chestnut (Castanea dentata) was a dominant canopy tree throughout a large area of the deciduous forest of eastern North America until its virtual extirpation during the early 1900s due to an introduced fungal blight. It was replaced mainly by species of oak and, in places, hickory. This study examined some of the potential effects that this species shift may have had on headwater streams, focusing on processing rates and nutritional quality of chestnut versus red oak (Quercus rubra) and pignut hickory (Carya glabra), and on consumption rates and growth and fecundity of shredding macroinvertebrates fed the different leaf species. Processing rates of chestnut and hickory leaves were significantly faster than that for oak. Protein analyses showed that the nutritional quality of leaves varied in a manner similar to the processing coefficients. Laboratory studies showed that the limnephilid caddisfly Pycnopsyche luculenta consumed significantly more chestnut and hickory leaves than oak leaves. The cranefly Tipula abdominalis showed a similar but non-significant trend. Experiments with the nemourid stonefly Shipsa rotunda indicated that leaf species consumed did not affect emergence success, adult sex ratios, or mean time to emergence. However, individuals reared on chestnut had significantly faster specific growth rates and adult body mass than individuals reared on oak. There was a trend toward greater fecundity of females reared on chestnut versus oak leaves. Shipsa exhibited a response to hickory leaves that was similar to that for chestnut. Headwater streams in the area affected by the blight may have experienced subtle changes at the population, community, and ecosystem levels due to the demise of the chestnut.

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