Temporal Changes in Resource Heterogeneity and Vegetation Response in Tree-Fall Gaps

在太平洋西北部的针叶林中，假设成熟森林中大树死亡造成的冠层间隙决定了这些森林的物种组成和未来发展。1990年，研究者在两种不同年龄的针叶林中建立了不同大小的实验林隙。主要目标是确定在林隙形成之前和之后，植被的组成和丰富程度以及资源的可得性（如光照和水分）对原生林发展格局的影响。研究人员将在实验间隙中继续长期测量植物多样性和丰度，以及光照和土壤湿度水平。最近关于太平洋西北地区联邦土地管理的计划强调管理幼林，以鼓励更大的物种多样性和结构，这是原始森林的特征。让林分自然老化可能会实现这一目标，但选择性采伐也被认为是一种更快地实现结构复杂性的方法，同时允许提取一些商品。这项研究将有助于了解树冠间隙如何影响原始森林的发展，原始结构自然发展需要多长时间，以及不同大小的开口是否可以选择性地采伐模拟这一过程。该研究还将为不同乔木和林下植物建立和生长的最适宜林隙大小以及现有植被对树木生存和生长的影响提供新的信息。

In the coniferous forests of the Pacific Northwest, canopy gaps created by the death of large trees within mature forests are hypothesized to determine the species composition and future development of those forests. In 1990, the investigators established experimental canopy gaps of different sizes within two conifer forests of different age. The main objectives have been to determine the influence of the composition and abundance of vegetation and the availability of resources (e.g. light and moisture) prior to and immediately after gap formation on the pattern of development in old growth forests. The investigators will continue their long-term measurements of plant diversity and abundance, and of light and soil moisture levels, in the experimental gaps. Recent plans for management of federal lands in the Pacific Northwest emphasize managing young forests to encourage a greater diversity of species and structure that is characteristic of old-growth forests. Allowing stands to age naturally may accomplish this goal, but selective tree harvest has also been proposed as a way to achieve structural complexity more rapidly while allowing some commodity extraction. This study will aid in understanding how canopy gaps influence development of old-growth forests, how long it might take for old-growth structure to develop naturally, and whether selective harvest of different sizes of openings can mimic this process. This study will also provide new information on the most appropriate gap size for the establishment and growth of different tree and understory plant species, and the effect of existing vegetation on tree survival and growth.