Conspecific Negative Density Dependence and Forest Diversity

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Science  18 May 2012:
Vol. 336, Issue 6083, pp. 904-907
DOI: 10.1126/science.1220269

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Conspecific negative density dependence (CNDD), whereby the abundance of a species is limited by negative interactions between individuals of the same species, is thought to have an important influence on the composition and dynamics of forest communities, but studies have generally been limited to few species and small areas. Johnson et al. (p. 904) analyzed CNDD in over 200,000 plots from a database of more than 3 million individuals of 151 species spanning 4 million square kilometers across forests in the eastern United States and found that the strength of CNDD strongly predicted the relative abundance of tree species. Because tree seedlings are unlikely to become established where conspecific adults are common, CNDD may provide a general mechanism maintaining diversity in forests.


Conspecific negative density-dependent establishment, in which local abundance negatively affects establishment of conspecific seedlings through host-specific enemies, can influence species diversity of plant communities, but the generality of this process is not well understood. We tested the strength of density dependence using the United States Forest Service’s Forest Inventory and Analysis database containing 151 species from more than 200,000 forest plots spanning 4,000,000 square kilometers. We found that most species experienced conspecific negative density dependence (CNDD), but there was little effect of heterospecific density. Additionally, abundant species exhibited weaker CNDD than rarer species, and species-rich regions exhibited stronger CNDD than species-poor regions. Collectively, our results provide evidence that CNDD is a pervasive mechanism driving diversity across a gradient from boreal to subtropical forests.

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