Dissertation Research: The Influence of Isolated Trees on Forest Succession on a Pasture in the Tropical Wet Lowlands of Costa Rica

小行星9423554 浮游生态系统现在覆盖了新热带地区的大片区域。这些牧场上的森林演替知之甚少，但初步证据表明，牧场上孤立的树木可能作为殖民森林物种的“建立焦点”。起源于牧场孤立树木的演替模式可以用演替的成核模型来预测。 本论文研究的目的是了解孤立的树木如何促进森林恢复的废弃牧场在低地热带潮湿森林生活区。该项目将定量研究木本幼苗的物种组成和种子雨在开放的牧场和树冠下的孤立的树木，并将研究孤立的树种，树的大小，距离种子源种子雨和木本幼苗物种组成的四个孤立的树类群的树冠下发现的相对重要性。此外，该项目将试图确定牛草食动物对木本物种再生孤立的树木下，排除牛孤立的树地块，也将试图分离的影响，差异种子雨下孤立的树木类群的其他因素，可能会影响木本幼苗建立。后一个实验将通过收集每个分类群下的种子雨并将其放置在其他分类群的树冠下来完成。最后，本计画将对孤立树种下之光环境进行初步研究。 该项目将扩大我们对热带废弃牧场演替模式的理解，以及我们对热带森林生态系统干扰影响的了解。此外，该项目将能够提出在废弃牧场上有管理地恢复森林的战略。

9423554 Horvitz Pasture ecosystems now cover huge areas in the neotropics. Forest succession on these pastures is poorly understood, but preliminary evidence suggests that isolated trees in pastures may serve as "establishment foci" for colonizing forest species. Patterns of succession stemming from pasture isolated trees can be predicted with a nucleation model of succession. The aim of this dissertation research is to develop understanding of how isolated trees facilitate forest recovery on an abandoned pasture in a lowland tropical wet forest life zone. The project will quantitatively examine the species composition of woody seedlings and the seed rain in open pasture and beneath the canopies of isolated trees and will examine the relative importance of isolated tree species, tree size, and distance to seed sources on seed rain and the woody seedling species composition found under the canopies of four isolated tree taxa. In addition, the project will attempt to determine the effect of cattle herbivory on woody species regrowth under isolated trees by excluding cattle from isolated tree plots, and will also attempt to separate the effects of differential seed rain beneath the isolated tree taxa from other factors that may differentially affect woody seedling establishment. This latter experiment will be done by collecting seed rain under each taxa and placing it under the canopies of the other taxa. Finally, this project will descriptively study the light environment under the isolated tree taxa. This project will expand our understanding of successional patterns in tropical abandoned pastures and also our knowledge on the effects of disturbance on tropical forest ecosystems. In addition, this project will be able to suggest strategies for managed forest recovery on abandoned pastures.