Abstract
A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Natural-enemy-mediated conspecific density dependence affects numerous tree populations, but its strength varies substantially among species. Understanding how conspecific density dependence varies with species’ traits and influences the dynamics of whole communities remains a challenge. Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. Plant-associated fungi are primarily responsible for reducing seedling recruitment near conspecific adults in ectomycorrhizal and shade-tolerant species. Insects, in contrast, primarily inhibit seedling recruitment of shade-intolerant species near conspecific adults. Our results suggest that natural enemies drive conspecific density dependence in this temperate forest and that which natural enemies are responsible depends on the mycorrhizal association and shade tolerance of tree species.
Highlights
A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density
We report on a field experiment in an old-growth temperate forest in northeast China to test for conspecific density dependence at the community scale, to identify the groups of natural enemies that may be responsible and to examine whether variation in the strength of density dependence among plant species is associated with two important plant traits: shade tolerance and type of mycorrhizal association
Seedling survival decreased with conspecific adult densities, not significantly
Summary
A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. We report on a field experiment in an old-growth temperate forest in northeast China to test for conspecific density dependence at the community scale, to identify the groups of natural enemies that may be responsible and to examine whether variation in the strength of density dependence among plant species is associated with two important plant traits: shade tolerance and type of mycorrhizal association. We test two hypotheses: (1) Plant-associated fungi and insect herbivores are critical drivers of conspecific density dependence and seedling diversity and composition in this temperate forest, and (2) Species varying in mycorrhizal association and shade-tolerance differ in their sensitivity to enemy-mediated density dependence. Seedling recruitment is more strongly inhibited by insect herbivores near conspecific adults for shade-intolerant species than shade-tolerant species
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