Spatial variability in the nutrient composition of Populus tremuloides: clone-to-clone differences and implications for cervids

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Abstract
Populus tremuloides, a clonal angiosperm, is a major food item for many temperate-region herbivores. Clonal variation in chemical composition has potentially important implications for vertebrate herbivores because a single clone may be areally large and hence, may comprise a large part of available forage. The objectives of this study were: (1) to examine spatial variability in nutrient concentrations and quality within and among 24 clones of trembling aspen, and (2) to evaluate these differences with respect to cervid nutritional requirements; notably Cervus elaphus and Odocoileus hemionus. Between-clone concentrations of all chemical components were significantly different. In terms of cervid nutrition, most clones provided adequate concentrations of Ca, Mg, Mn, and Zn. Crude protein was limiting in some clones and P in most. Additionally, P metabolism may be impaired by the high Ca:P ratios typical of some clones. Of the structural constituents, neutral detergent fiber showed the greatest intraclonal variability. Dry-matter digestibility varied sufficiently to conjecture that cervid energy balances may be affected. Overall, although clone-to-clone differences were not so substantial to conclude that selective browsing would be nutritionally cost-effective, it is proposed that cervids stand to benefit by fortuitously browsing on nutritionally superior clones owing to the multiplier effect.