Complex spatial structure in a population of <Emphasis Type="Italic">Didymopanax pittieri</Emphasis>, a tree of wind-exposed lower montane rain forest |
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Authors: | Robert M Lawton Robert O Lawton |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA;(2) Department of Biological Sciences, University of Alabama in Huntsville, Huntsville, AL, 35899, USA |
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Abstract: | Didymopanax pittieri is a common shade-intolerant tree colonizing treefall gaps in the elfin forests on windswept ridgecrests in the lower montane
rain forests of the Cordillera de Tilarán, Costa Rica. All D. pittieri taller than >0.5 m in a 5.2-ha elfin forested portion of a gridded study watershed in the Monteverde Cloud Forest Preserve
were located, mapped, and measured. This local population of D. pittieri is spatially inhomogeneous, in that density increases with increasing wind exposure; D. pittieri are more abundant near ridge crests than lower on windward slopes. The important and ubiquitous phenomenon of spatial inhomogeneity
in population density is addressed and corrected for in spatial analyses by the application of the inhomogeneous version of
Ripley’s K. The spatial patterns of four size classes of D. pittieri (<5 cm dbh, 5–10 cm dbh, 10–20 cm dbh, and >20 cm dbh) were investigated. Within the large-scale trend in density driven
by wind exposure, D. pittieri saplings are clumped at the scale of treefall gaps and at the scale of patches of aggregated gaps. D. pittieri 5–10 cm dbh are randomly distributed, apparently due to competitive thinning of sapling clumps during the early stages of
gap-phase regeneration. D. pittieri larger than 10 cm dbh are overdispersed at a scale larger than that of patches of gaps. Natural disturbance can influence
the distribution of shade intolerant tree populations at several different spatial scales, and can have discordant effects
at different life history stages. |
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