The authors of this study clipped juvenile poplar (Populus balsamifera), willow (Salix bebbiana), birch (Betula papyrifera), alder (Alnus crispa) and aspen (Populus tremuloides) to determine if the chemical defenses of these species increased in reaction to herbivory. Clipping did not significantly effect concentrations of carbohydrates, nitrogen, phosphorous, resin or tannins in annual growth two growing seasons after clipping treatments were applied. Plant tannin and resin levels were inversely related. Plants with high levels of resin, such as birch, had low levels of tannin, and plants with high levels of tannin, such as willow and alder, had low levels of resin. These results suggest that the five species studied did not respond to herbivory by enhancing chemical defense mechanisms and that the plants studied generally used only one chemical defense mechanism, tannins or resins.
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