Are we missing the forest for the trees? Conspecific negative density dependence in a temperate deciduous forest

Abstract

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 community-level 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 should extend to the majority of plant life history strategies. 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 understory and canopy woody species across height categories and dispersal syndromes 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. Across the whole community, larger individuals were more overdispersed than smaller individuals. The overdispersion of large individuals, however, was driven by canopy trees. By contrast, understory woody species were not overdispersed as adults. This finding indicates that 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.

Vertically stratified frugivore community composition and interaction frequency in a liana fruiting across forest strata

“…Extending these observations to other plant species implies that plants that only present fruits in the understorey experience much shorter dispersal distances than trees that exhibit most of their fruits in the canopy. For instance, Barry and Schnitzer (2021) observed differences in the conspecific negative density dependence between understorey and canopy trees, where canopy trees were more overdispersed than understorey trees.…”

Point-pattern analysis reveals density-dependent processes that influence structure of Juniperus virginiana L. stands

“…Conversely, several sites comprised of small trees showed signs of regular spacing between individuals. Negative density dependence among seedlings of the same species has been attributed to proximity to larger trees due to shading and the increase in density of predators (Marchand et al 2020;Barry and Schnitzer 2021). Alternatively, this may be a relic of the scale of investigation being too large to properly evaluate the relationships between neighboring redcedar seedlings or saplings.…”

Maximum stem diameter predicts liana population demography

“…For example, tree species with a larger maximum height may have larger seeds, leaves, and leaf mass per area, as well as higher stem density and greater biomass (Diaz et al, 2016; Piponiot et al, 2022). Maximum size may also be correlated with plant metabolic rate, geographic distribution, and even the mechanism that maintain species' diversity (Barry & Schnitzer, 2021; Enquist et al, 1998; Moles et al, 2009; Rüger et al, 2018). Thus, variation in body size can signify distinct ecological strategies among plant species and may explain plant species' coexistence.…”