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

Tiefeng Piao,Ji Hong Kim,Liza S Comita,Guangze Jin

doi:10.1007/s00442-012-2481-y

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.

Highlights

Understanding the mechanisms of population size regulation is of vital importance in the study of species coexistence and biodiversity maintenance
We focused on the scale of 0–10 m for the analysis above, because we assume the effects from tree–tree interactions could be efficiently indicated by this scale, and changes in spatial pattern beyond a scale of 10 m could be caused by other environmental factors. dmax was the maximum strength of conspecific thinning, when d(r) takes the maximal value at the scale of 0–30 m
Adults of 12 of the 15 focal species showed increasing aggregation at scales r [ 10 m (Online Resource 4). This indicated that most of the focal species exhibited habitat preference caused by large-scale habitat heterogeneity, suggesting that we should account for habitat heterogeneity in our analysis of density dependence

Summary

Introduction

Understanding the mechanisms of population size regulation is of vital importance in the study of species coexistence and biodiversity maintenance. Recent studies have provided strong evidence that density-dependent processes play a role in shaping plant communities (Wills and Condit 1999; Harms et al 2000; Hille Ris Lambers et al 2002; Comita et al 2010). Comita and Hubbell (2009) tracked established seedlings of 235 species in the BCI 50-ha forest dynamics plot (FDP) over 3 years and found negative effects of conspecific neighbors on survival. These and additional studies (e.g. Webb and Peart 1999; Hille Ris Lambers et al 2002; Queenborough et al 2007; Pigot and Leather 2008) provide evidence for an important role of negative density dependence at early life stages

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Conclusion