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The complex relationship between species richness and area can be simplified by decomposing spatial scale into its components: grain, extent, and number of samples. We designed a 256 x 256-m study grid in the Oosting Natural Area in the Duke Forest, Orange County, North Carolina, such that the effects of these components can be disentangled. We found that grain, extent, and the number of samples all influenced the species-area relationship, although the effects of grain were dominant. We also found that species richness patterns were neither self-similar nor hierarchical. The degree to which diversity occurs in "hot spots" increases as a function of both grain and extent, but diversity hot spots tend to persist across a wide range of grains.
Palmer et al. (Tue,) studied this question.