Density dependence across multiple life stages in a temperate old-growth forest of northeast China

Abstract

Recent studies on species coexistence suggest that density dependence is an important mechanism regulating plant populations. However, there have been few studies of density dependence conducted for more than one life-history stage or that control for habitat heterogeneity, which may influence spatial patterns of survival and mask density dependence. We explored the prevalence of density dependence across multiple life stages, and the effects of controlling for habitat heterogeneity, in a temperate forest in northeast China. We used generalized linear mixed-effects models to test for density-dependent mortality of seedlings and spatial point pattern analysis to detect density dependence for sapling-to-juvenile transitions. Conspecific neighbors had a negative effect on survival of plants in both life stages. At the seedling stage, we found a negative effect of conspecific seedling neighbors on survival when analyzing all species combined. However, in species-level analyses, only 2 of 11 focal species were negatively impacted by conspecific neighbors, indicating wide variation among species in the strength of density dependence. Controlling for habitat heterogeneity did not alter our findings of density dependence at the seedling stage. For the sapling-to-juvenile transition stage, 11 of 15 focal species showed patterns of local scale (<10 m) conspecific thinning, consistent with negative density dependence. The results varied depending on whether we controlled for habitat heterogeneity, indicating that a failure to account for habitat heterogeneity can obscure patterns of density dependence. We conclude that density dependence may promote tree species coexistence by acting across multiple life-history stages in this temperate forest.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2481-y) contains supplementary material, which is available to authorized users.

Effects of density dependence in a temperate forest in northeastern China

“…If, for a particular species, d s (r) < 0 and d(r) > 0, we infer that conspecific density-dependent self-thinning takes place from sapling to juvenile stages10. The maximum strength of density-dependent self-thinning is d max and r max the scale when d(r) takes the maximal value at a scale between 0–30 m. The r thin reflects the scale at which density-dependent self-thinning takes place for a particular species.…”

“…For example, a species will tend to perform better and show an aggregated spatial distribution in its preferred habitat, regardless of existing negative density-dependence102627. This may result in a positive conspecific density dependence.…”

Forest tree neighborhoods are structured more by negative conspecific density dependence than by interactions among closely related species

“…Uriarte et al 2010, Paine et al 2012, Lebrija-Trejos et al 2014. The strength and relative importance of conspecific and phylogenetically-dependent interspecific interactions has been shown to vary with tree life stage (Piao et al 2013, Zhu et al 2015. Determining the degree to which these interactions structure diverse natural tree communities therefore requires integration across multiple life stages.…”

Ontogenetic shifts in trait‐mediated mechanisms of plant community assembly

“…Such trait-based ontogenetic trade-offs may equalize overall performance and promote coexistence of functionally diverse competitors. The role of species interactions, such as competition and herbivory, in driving community assembly may also be life-stage specific and thus obscured if ontogeny is overlooked (Werner and Gilliam 1984, Schiffers and Tielbo¨rger 2006, Moll and Brown 2008, Armas and Pugnaire 2009, Piao et al 2013, Baraba´s et al 2014. Niche partitioning along functional trait axes may enable species to coexist, as evidenced by better performance when surrounded by neighbors with divergent trait values (Uriarte et al 2010, Lasky et al 2014a).…”