Conspecific negative density dependence in American beech

Benjamin S Ramage,Isabel J Mangana

doi:10.1186/s40663-017-0094-y

Benjamin S Ramage, Isabel J Mangana

Open Access

https://doi.org/10.1186/s40663-017-0094-y

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Abstract

BackgroundOne of the most important drivers of forest biodiversity is conspecific negative density dependence (CNDD), a reduction in performance when conspecific densities are high. While the majority of CNDD research has focused on tropical forests, evidence is mounting that CNDD may also play an important role in temperate forests. To further explore the potential reach of this phenomenon, we investigated CNDD in American beech (Fagus grandifolia) in a mature mid-Atlantic forest.MethodsWe used bivariate point pattern analyses to examine spatial relationships between large beech trees and conspecific saplings, and we also contrasted these patterns with comparable patterns for heterospecifics. In addition, to address the possibility of dispersal limitation and the associated effects on spatial patterns, we analyzed seedling density as a function of adult conspecific abundance.ResultsWe found that beech saplings were more repelled from large conspecifics than large heterospecifics, despite the fact that beech seedling density was positively correlated with beech basal area. However, saplings of other canopy tree species were also repelled from adult beech trees, suggesting a general suppressive effect. Nonetheless, the discrepancy between beech seedling and sapling densities beneath adult conspecifics suggests that beech seedling survival rates were reduced in vicinity of conspecific adults.ConclusionsRegardless of the extent to which beech inhibits heterospecific trees, a negative effect on conspecific recruits may be critical for biodiversity maintenance. Without this conspecific suppression, a dense layer of shade-tolerant beech saplings could form beneath adult beech trees. If this were to occur, beech would have a substantial head-start following canopy disturbance, and this late-successional species could potentially dominate a stand in perpetuity, through repeated disturbance cycles.

Highlights

One of the most important drivers of forest biodiversity is conspecific negative density dependence (CNDD), a reduction in performance when conspecific densities are high
American beech saplings were generally less clustered around large conspecifics than they were around large trees of other canopy species (Fig. 2)
Does CNDD in beech help to limit the formation of mono-specific beech clusters? And is self-inhibition relevant to diversity maintenance if most other tree species are inhibited? We assert that the answer to both questions is “yes”, and our rationale rests on the inevitably of disturbance

Summary

Introduction

One of the most important drivers of forest biodiversity is conspecific negative density dependence (CNDD), a reduction in performance when conspecific densities are high. While the majority of CNDD research has focused on tropical forests, evidence is mounting that CNDD may play an important role in temperate forests. Most if not all forest ecosystems include at least one tree species that is highly shade-tolerant and capable of selfreplacement In most natural forests, mixed species stands are more common. One frequently invoked explanation for this diversity is disturbance, which removes established trees and creates habitat for early successional species (White and Jentsch 2001). While disturbance is undeniably important, other factors may play essential roles

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