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，即从干扰中恢复的过程，是造成生态系统结构和功能变化的主要原因。本研究的主要目的是了解演替过程，研究者认为，群落水平属性和演替过程的大多数演替变化可以最好地理解为种群过程的结果。虽然通常使用永久样地来检查成熟树木的动态，但由于没有适当的数据，幼苗和树苗的动态几乎没有得到研究。在美国国家科学基金会环境生物学长期研究项目（LTREB）的支持下，研究人员从许多类型和年龄的森林的永久地块收集了幼苗和树苗的数据，观察时间长达13年。因此，研究人员在研究与演替和地点特征相关的幼苗和树苗的动态方面处于独特的地位。LTREB数据集将用于解决与幼苗和采样动态相关的问题，例如：(1)幼苗和树苗的建立、生长和存活如何随演替和立地条件而变化？(2)幼苗间竞争是否显著？我们猜测除了树冠间隙外，树冠与树冠的竞争控制着幼苗动态，但如果幼苗的相互作用很重要，则需要将其添加到森林模拟模型中。(3)冠层树木对同种树苗和树苗的抑制是否存在差异？这是一种普遍的假设，但在温带森林中基本上没有得到验证。(4)每年的气候变化能否解释相似树种的共存？同样，这是一个流行但未经验证的假设。(5)在演替过程中，幼苗活力的变化是否与现有的冠层衍生竞争变化模型一致（见Peet和Christensen 1987）？这项研究将从人口的角度对演替模式提供一个独特的观点。

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.