Research ArticleFOREST ECOLOGY

Positive biodiversity-productivity relationship predominant in global forests

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Science  14 Oct 2016:
Vol. 354, Issue 6309, aaf8957
DOI: 10.1126/science.aaf8957

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  • RE: Responses to the three eLetters below
    • Jingjing Liang, Assistant Professor of Quantatative Forest Ecology, Purdue University

    RE: Responses to the three eLetters below
    My sincere thanks to the three eLetters regarding our article entitled “Positive biodiversity-productivity relationship predominant in global forests,” and would welcome future questions, comments, criticisms, and research proposals from the authors of these eLetters!
    Please find, below, my brief response to these eLetters. For future questions, please do not hesitate to contact me at alpenbering@gmail.com, or the GFBI Steering Committee at gfbinitiative@gmail.com.

    1. Generality of biodiversity-productivity relationships in global forests
    Van de Perre et al. suggest that relationships between productivity and different components of taxonomic biodiversity, or between productivity and different dimensions biodiversity, are not necessarily positive, and that such relationships are in fact largely unknown for most clades of the tree of life.
    Taxonomic diversity has been a focus of biodiversity research, and species richness has been widely used as a proxy for all aspects of taxonomic biodiversity (e.g. evenness, dominance, dispersion, diversity) as well as for other dimensions of biodiversity (e.g. genetic, phylogenetic, functional) (Willig and Presley 2013). However, the effects of different components/dimensions of biodiversity on ecosystem functioning are indeed largely unknown.
    I thank Van de Perre et al. f...

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    Competing Interests: None declared.
  • RE: Biodiversity and forest productivity: How may tree species loss affect productivity?
    • Zhongling Guo, Professor, Beihua University, Jilin, China
    • Other Contributors:
      • Xiuli Chu, Research scientist, Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Zhejiang, China
      • Hua Yang, Professor, College of Forestry, Beijing Forestry University, Beijing, China
      • Rongzhou Man, Research scientist, Ontario Ministry of Natural Resources and Forestry
      • Pengxin Lu, Research scientist, Ontario Ministry of Natural Resources and Forestry
      • Wayne Bell, Research scientist, Ontario Ministry of Natural Resources and Forestry
      • Mahadev Sharma, Research scientist, Ontario Ministry of Natural Resources and Forestry
      • Bing Wang, Research scientist, Institute of Forest Ecology and Environmental Protection, Chinese Academy of Forestry, Beijing, China
      • Fengguo Du, Professor, Beihua University, Jilin, China
      • Chunjiang Liu, Professor, School of Agriculture and Biology and Research Center for Low-Carbon Agriculture, Shanghai Jiao Tong University, Shanghai, China
      • Jing Tao, Research scientist, Jilin Academy of Forestry, Changchun, China

    Worldwide species loss likely has negative impacts on ecosystem values and services (1). The quantitative responses of ecosystem values and services to biodiversity change, however, are not well established, especially for forests. Liang et al. (2) indicates an average of 2.1–3.1% productivity decrease with 10% tree species loss and 62–78% decrease with conversion of all natural tree mixtures to single species stands. This estimate comes from inventory data-based species richness-productivity relationships that contain confounding effects by environmental factors such as precipitation and aridity (2). The resulting species richness effect reflects influences not only from unique contribution of tree species richness, but also from shared contribution with environmental factors, and accounts for 340% productivity change on average (Fig. 3A, p5). This is apparently overestimated. The application of this estimate would lead to unrealistic expectations of increased productivity for mixed species forests and panic over possible decline of forest ecosystem values and services by species loss and potentially mislead research, industry and policy development.

    A more realistic estimate may be obtained from the findings of experimental plantations that involve more than a century of research efforts in forests. According to the pattern of experiment-based species richness-productivity relationships, forest productivity remains unchanged within a large reduction of tree speci...

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    Competing Interests: None declared.
  • Causal relationship between biodiversity and productivity
    • Rongzhou Man, Research scientist, Ontario Ministry of Natural Resources and Forestry
    • Other Contributors:
      • Pengxin Lu, Research scientist, Ontario Ministry of Natural Resources and Forestry
      • Hua Yang, Professor, Beijing Forestry University
      • Mahadev Sharma, Ontario Ministry of Natural Resources and Forestry

    Liang et al. (1) examined the relationship between forest productivity and number of tree species (richness) using permanent sample plot data worldwide. We do not question the accuracy of their findings, but we strongly caution against the interpretations of the causal relationship between biodiversity and productivity.

    Productivity and biodiversity are response variables, both strongly dependent on climate and soil conditions, and therefore positively correlated (2, 3, 4, 5, 6); more productive environments support more vigorous growth of individuals and more species populations (7). Such a correlation, however, does not suggest any causal relationship (8, 9, 10). The inclusion of species richness in productivity–climate models also adds multicollinearity. Although overall model, associated statistics, and even predictions may not be negatively affected, the estimates of model coefficients become unreliable and unstable (8). Consequently, effective information available to assess the effects of individual predictors is seriously reduced. Without separation of biodiversity effects from those of environmental variables, these observational data-based biodiversity–productivity models (1,11) would not provide a reliable indication on the unique effect of tree species richness on forest productivity or vice versa.

    Biodiversity does positively affect productivity to a certain extent (12, 13, 14), but the causal relationship can only be examined through controll...

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    Competing Interests: None declared.
  • Generality of biodiversity-productivity relationships in global forests
    • Frederik Van de Perre, PhD student, University of Antwerp
    • Other Contributors:
      • Erik Verheyen, Royal Belgian Institute for Natural Sciences
      • Luc De Bruyn, Research Institute of Nature and Forest (INBO)
      • Hans Verbeeck, Ghent University
      • Steven J. Presley, University of Connecticut
      • Michael R. Willig, University of Connecticut

    Liang et al. (1) analyzed relationships between one aspect of biodiversity, tree species richness, and productivity for a large number of forests around the globe. This was likely motivated by the considerable interest in and debate concerning this relationship, as characterized by scientific discourse from both ecological and conservation perspectives. Although we do not question the accuracy or importance of their findings, we strongly caution against generalizing from mono-trophic and unidimensional biodiversity studies to understand how all trophic levels and dimensions of biodiversity are related to productivity.
    Like others, we contend that biodiversity has many dimensions, species richness being at best an incomplete indicator of the taxonomic dimension (2–4). Liang et al. state that “because taxonomic diversity indirectly incorporates functional, phylogenetic, and genomic diversity, our results that focus on tree species richness are likely applicable to these other elements of biodiversity, all of which have been found to influence plant productivity” (p4). This statement is an assumption that is not fully justified from conceptual or empirical perspectives.
    First, variation in species richness is not always correlated with other aspects of taxonomic biodiversity (e.g. evenness and diversity) that reflect the abundances of species (5), and taxonomic diversity need not be strongly associated with phylogenetic, functional, or genetic dimensions of biodiv...

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    Competing Interests: None declared.

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