Complex spatial structure in a population of Didymopanax pittieri, a tree of wind-exposed lower montane rain forest
Complex spatial structure in a population of Didymopanax pittieri, a tree of wind-exposed lower montane rain forest
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Didymopanaxpittieri（一种暴露于风的低山雨林树）种群的复杂空间结构
作者：
R. Lawton;R. Lawton
Didymopanax pittieri是一种常见的不耐阴树，在哥斯达黎加的科迪勒拉德蒂拉兰（Cordillera de Tilarán）的低山地雨林中，在风吹山脊的矮林中定居在树落间隙中。全是D。在蒙特韦尔德云雾森林保护区的一个网格化研究流域的一个5.2公顷的小精灵森林部分中，定位、绘制和测量了高于0.5米的pittieri。当地居民D。pittieri在空间上是不均匀的，因为密度随着风暴露的增加而增加;在山脊的山顶附近比在迎风坡的低处多。利用Ripley's K.对四个大小级的D.调查了不同胸径（<5 cm、5-10 cm、10-20 cm和>20 cm）的皮氏木。在由风暴露驱动的大尺度密度趋势中，D。在树倒林隙尺度和聚集林隙斑块尺度上，皮氏木幼树呈丛生状分布。D. pittieri 5-10厘米dbh是随机分布的，显然是由于在间隙期更新的早期阶段树苗丛的竞争性稀疏造成的。D.胸径大于10 cm的小乔木在比林隙斑块更大的尺度上过度分散。自然干扰可以影响不耐荫树种种群在不同空间尺度上的分布，并在不同生活史阶段产生不协调的影响。
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.