How do trees respond to species mixing in experimental compared to observational studies?

Stephan Kambach,Sophia Ratcliffe,Harald Auge,Bastien Castagneyrol,Sandra Müller,Julia Koricheva,Tommaso Jucker,Eric Allan,Lars Gamfeldt,Aleksi Lehtonen,Jonas Dahlgren,Fabian Roger,Gerald Kändler,Kris Verheyen,Olivier Bouriaud,Fons Van Der Plas,Alain Paquette,Quentin Ponette,Hervé Jactel,Bart Muys,Helge Bruelheide,Michael Scherer‐Lorenzen ,David A Coomes ,Paloma Ruiz‐Benito ,Charles A Nock ,Simon Bilodeau‐Gauthier ,Thomas Peer ,M Zavala ,Nuri Nurlaila Setiawan ,Georges Künstler ,Joséphine Haase

doi:10.1002/ece3.5627

Abstract

For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships.

Highlights

The provisioning of ecosystem services beneficial to human well‐ being strongly relies on plant diversity (Cardinale et al, 2012)
We provide a first comparison of the growth re‐ sponse of a large set of tree species to species mixing across three distinct research approaches
Within the framework of the European FunDivEUROPE project, the significance of forest biodiversity for ecosystem functioning across Europe was investigated with three complementary research approaches

Summary

| INTRODUCTION

The provisioning of ecosystem services beneficial to human well‐ being strongly relies on plant diversity (Cardinale et al, 2012). The relationship between tree diversity and productivity has already been studied using different research approaches (Table 1), starting with the analysis of forest inventories (Hartig, 1791; Schwappach, 1912; Wiedemann, 1943), followed by silvicul‐ tural trials and tree diversity experiments (Bruelheide et al, 2014; Koricheva, 2002; Pretzsch, 2005; Scherer‐Lorenzen et al, 2005; Tobner, Paquette, Reich, Gravel, & Messier, 2014; Verheyen et al, 2016) and more recently by the selection of comparative plots in mature forests (Baeten et al, 2013; Bruelheide et al, 2011; Fischer et al, 2010). Comparative study plots (Bruelheide et al, 2011) or “exploratories” (Fischer et al, 2010) consist of survey plots within mature forests selected to contain replicated levels of tree species diversity and compositions while at the same time controlling for differences in community structure and environmental conditions They can be regarded as an intermediate approach that combines aspects of forest inven‐ tories and tree diversity experiments. Shaded countries: national forest inventories (16,773 plots), stars: tree diversity experiments (584 plots), and black dots: forest exploratories (169 plots) this study should deepen our understanding of the species, environ‐ mental conditions, and research designs for which consistent posi‐ tive diversity‐ecosystem functioning relationships can be expected

| METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST