Influence of seral stage and season on leaf chemistry of southeastern Alaska deer forage

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Abstract
The relationships between seral stage and nutrient and organic composition of five plant species used as forage by Sitka black-tailed deer were investigated in hemlock–spruce forest in southeastern Alaska. One shrub, three forbs, and one conifer species were collected during May, July, and October to ascertain differences among seral stands in seasonal patterns of nutrient levels, in vitro dry matter digestibility, astringency, and the concentrations of phenolics, terpenes, total nonstructural carbohydrates, and cyanide. In the shrub and forbs, concentrations of N, P, and K tended to be higher in leaves from forested than from open clear-cut areas, and higher in May than in July and October. These nutrients tended to covary in an opposite manner to Ca, Mg, and Na and in a similar manner to the trace elements Cu, Zn, Mn, and Fe, although these patterns were inconsistent. In these species there was also a general pattern of higher levels of total nonstructural carbohydrates, astringency, and phenolics in the three young open stands than in the shaded forest understories of the two oldest stands. Dry matter digestibility did not differ across stands but did vary seasonally. The among-stand differences in foliage chemical composition may have resulted from differences in the availability of light. While seral stage affected both the inorganic and organic quality of understory forage species, the combined results suggest that the impact on N economy of deer is greater than that on their energy economy.

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