One of the central goals of ecology is to determine the mechanisms that enable coexistence among species. Evidence is accruing that conspecific negative density dependence (CNDD), the process by which plant seedlings are unable to survive in the area surrounding adults of their same species, is a major contributor to tree species coexistence. However, for CNDD to maintain diversity, three conditions must be met. First, CNDD must maintain diversity for the majority of the woody plant community (rather than merely specific groups). Second, the pattern of repelled recruitment must increase in with plant size. Third, CNDD must occurs across life history strategies and not be restricted to a single life history strategy. These three conditions are rarely tested simultaneously. In this study, we simultaneously test all three conditions in a woody plant community in a North American temperate forest. We examined whether the different woody plant growth forms (shrubs, understory trees, mid-story trees, canopy trees, and lianas) at different ontogenetic stages (seedling, sapling, and adult) were overdispersed – a spatial pattern indicative of CNDD – using spatial point pattern analysis across life history stages and strategies. We found that there was a strong signal of overdispersal at the community level. However, this pattern was driven by adult canopy trees. By contrast, understory plants, which can constitute up to 80% of temperate forest plant diversity, were not overdispersed as adults. The lack of overdispersal suggests that CNDD is unlikely to be a major mechanism maintaining understory plant diversity. The focus on trees for the vast majority of CNDD studies may have biased the perception of the prevalence of CNDD as a dominant mechanism that maintains community-level diversity when, according to our data, CNDD may be restricted largely to trees.

中文翻译：

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我们是否为树木而错过森林？温带落叶林中的同种负密度依赖性

生态学的中心目标之一是确定使物种之间共存的机制。有证据表明，同种负密度依赖性（CNDD）是植物幼苗无法在同一物种成年周围生存的过程，是造成树种共存的主要因素。但是，为了使CNDD保持多样性，必须满足三个条件。首先，CNDD必须为大多数木本植物群落（而不仅仅是特定群体）保持多样性。其次，排斥招募的模式必须随着工厂规模的增加而增加。第三，CNDD必须在整个生命史策略中发生，而不仅限于单个生命史策略。很少同时测试这三个条件。在这个研究中，我们同时在北美温带森林的木本植物群落中测试了所有三个条件。我们检查了在不同的个体发育阶段（幼苗，幼树和成年）的不同木本植物生长形式（灌木，林下树木，中层树木，冠层树木和藤本植物）是否过度分散（使用CNDD表示的空间格局），使用空间人生历程阶段和策略的点模式分析。我们发现，在社区一级存在过度分散的强烈信号。但是，这种模式是由成年树冠驱动的。相比之下，可构成温带森林植物多样性高达80％的林下植物成年后并未过度分散。缺乏过度分散表明，CNDD不太可能是维持林下植物多样性的主要机制。