Collaborative Research: Long-term Studies of Forest Dynamics: Analysis of Seedling and Sapling Populations

干扰在生态系统中几乎无处不在。因此，演替是从干扰中恢复的过程，是导致生态系统结构和功能发生很大变化的原因。这项研究的主要目的是了解演替过程，调查人员断言，社区一级的属性和过程中的大多数演替变化最好被理解为是人口过程的结果。虽然永久样地通常被用来研究成熟树木的动态，但苗木和幼树的动态实际上仍然没有被研究，仅仅是因为没有适当的数据可用。在国家科学基金会长期环境生物学研究(LTREB)计划的支持下，研究人员从各种类型和年龄的森林中收集了永久地块的苗木和树苗数据，观察时间长达13年。因此，调查人员在研究与演替和立地特征有关的苗木和树苗的动态方面具有独特的地位。LTREB数据集将被用来解决与苗木和取样的动态有关的问题，例如：(1)苗木和幼树的建立、生长和存活如何随演替和立地条件而变化？(2)苗木竞争是否重要？我们怀疑，除了在树冠空隙中，与树冠的竞争控制着树苗的动态，但如果树苗的相互作用很重要，那么它们将需要被添加到森林模拟模型中。(3)树冠是否对同种幼苗和幼树有不同程度的抑制作用？这是一个流行的假设，在温带森林中基本上没有得到检验。(4)年复一年的气候变化能解释相似树种的共存吗？再一次，这是一个流行但未经检验的假设。(5)苗木活力在演替过程中的变化是否与现有的冠层变化竞争模型一致(见Peet和Christensen，1987)？这项研究将从人口的角度为演替模式提供一个独特的视角。

Disturbance is nearly ubiquitous in ecological systems. Consequently, succession, the process of recovery from disturbance, is responsible for much variation in ecosystem structure and function. The primary objective of this research is to understand the process of succession, and the investigators assert that most successional changes in community-level properties and processes can best be understood as resulting from population processes. Although permanent plots are commonly used to examine the dynamics of mature trees, seedling and sapling dynamics remain virtually unstudied, simply because appropriate data have not been available. With the support of the National Science Foundation Long-term Research in Environmental Biology (LTREB) program, the investigators have collected seedling and sapling data from permanent plots in numerous types and ages of forests with observations ranging up to 13 years. Consequently the investigators are uniquely positioned to examine the dynamics of seedlings and saplings as related to succession and site characteristics. The LTREB dataset will be used to address questions related to the dynamics of seedlings and samplings such as the following: (1) How do seedling and sapling establishment, growth, and survival vary with succession and site conditions? (2) Is seedling-seedling competition significant? We suspect that competition with canopy trees controls seedling dynamics, except in canopy gaps, but if seedling interactions are important they will need to be added to forest simulation models. (3) Do canopy trees differentially inhibit conspecific seedlings and saplings? This is a popular hypothesis, largely untested in temperate forest. (4) Can year-to-year climatic variation explain co- existence of similar tree species? Again, this a popular but untested hypothesis. (5) Does seedling vigor change during succession in a fashion consistent with existing models of changing canopy-derived competition (see Peet and Christensen 1987)? This research will provide a unique perspective on successional patterns from a population standpoint.