Ayres Abstracts

Suomela, J. and M. P. Ayres. 1994. Within-tree and among-tree variation in leaf characteristics of mountain birch and its implication for herbivory. Oikos 70:212-222.  pdf
We employed a nested sampling design to quantify hierarchical patterns of variation in leaf characteristics of the polycormic tree, Betula pubescens ssp. tortuosa. Sampling levels included trees, ramets within trees, branches within ramets, short shoots within branches, and leaves within short shoots. Leaf water content, specific weight, toughness, and nitrogen content were measured. We used only short shoot leaves. i.e. leaves of the same age. All hierarchical levels contributed significant components of variation. Trees, and ramets within trees, usually contributed more variation than branches or shoots. Trees accounted for 12 to 64% of the total variance (least in toughness, most in nitrogen content). Within-tree variation due to different hierarchical levels was surprisingly large: 40 to 44% of the total variance in water content, specific weight, and toughness was explained by ramets, branches, and shoots. For water content and toughness, ramets within trees were actually more variable than trees. Variance estimates were quite constant between years. Extensive within-tree variation apparently arises from the organization of trees into modules that are more or less physiologically autonomous and may even differ genetically due to somatic mutations. Unlike other traits, leaf nitrogen was invariant across ramets, indicating that processes of nitrogen allocation tend to be relatively well integrated on a whole plant basis. Complex patterns of intra-specific variation in their host plants complicate the oviposition and foraging behavior of herbivores. Results the need for studies that treat variance as a quantitative attribute of individual trees. We offer some recommendations for optimizing sampling efficiency, and avoiding pseudoreplication, in experiments that involve trees.
Betula pubescence ssp. tortuosa; Sampling design; Sampling efficiency; Pseudoreplication

 

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