Unravelling the mechanisms of spatial correlation between species and size diversity in forest ecosystems

Arne Pommerening,Gongqiao Zhang,Xiaohong Zhang

doi:10.1016/j.ecolind.2020.106995

Abstract

With ongoing climate change at global scale we are currently losing biodiversity at an unprecedented rate. The insurance hypothesis and associated research, however, suggest that biodiversity has a major stabilising effect in ecosystems. In this situation, it is crucial to develop a better understanding of natural processes of maintaining biodiversity for employing them in conservation practice. In forest ecosystems, spatial species and size diversity are important aspects of α-diversity at woodland community and species population level. Both aspects of spatial diversity stem from complex relationships between tree interaction, disturbances and subsequent waves of colonisation by tree seedlings of various species. Using point process statistics, particularly the mark mingling function and the mark variogram, we studied the processes causing spatial correlations of species and size diversity. We found that spatial species dispersal and conspecific size distributions are key drivers of spatial species-size correlations and that a combination of simple random size-labelling techniques applied to mark variograms is instrumental in efficiently diagnosing them. If size ranges differ between species, spatial size diversity is largely a function of spatial species mingling. The existence of these correlations is crucial to conservation because they imply that conservation efforts can be rationalised: It is possible to focus on only one of the two tree diversity aspects. Interestingly, in multi-species forest ecosystems, although general species diversity is high, spatial species-size correlations can be diluted, because some of the many species populations may have similar size distributions.

Highlights

A growing body of empirical studies has found that more diverse animal and plant communities are more stable, i.e. exhibit smaller fluctuations over time (Valone and Barber, 2008)
The point-process simulations offered valuable insights on how the mark mingling functionν(r), the mark variogramγm(r) and the associ ated tests respond to different strategies of tree species mingling
The central argument of our paper is that any difference in the envelopes resulting from the two random-labelling tests clearly indicates spatial correlations between species and size diversity

Summary

Introduction

A growing body of empirical studies has found that more diverse animal and plant communities are more stable, i.e. exhibit smaller fluctuations over time (Valone and Barber, 2008). Through niche complementarity biodiversity promotes greater insurance when communities are made up of species that are better performers (i.e. specialists) in different, localised environments and complement each other (Yachi and Loreau, 1999; Matias et al, 2013). This concept was extended by the spatial insurance hypothesis predicting that func tional complementarity of species across space and time insures the system against the impact of environmental fluctuation (Loreau et al, 2003). Similar theories and hypotheses include statistical averaging or the portfolio effect and compensatory dynamics (Shanafelt et al, 2015) and put more weight on statistical mechanisms

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Conclusion