Tree species diversity impacts average radial growth of beech and oak trees in Belgium, not their long-term growth trend

Astrid Vannoppen,Kris Verheyen,Quentin Ponette,Vincent Kint,Bart Muys

doi:10.1186/s40663-019-0169-z

Abstract

BackgroundEnvironmental change has resulted in changes in forest growth in Europe during the last century. This has consequences for the products and services delivered by forest. Mixing tree species is often proposed as a strategy to deal with the consequences of climate change. Diversifying forests is believed to result in higher productivity and increased growth stability. Tree species diversity is therefore expected to affect long-term trends in tree radial growth. However, this has not yet been studied. In this paper we study the effect of diversity on the radial growth and its long-term trends for beech and oak trees growing along a gradient of tree species diversity in the loamy region of central Belgium (from monocultures to mixed forests patches up to three species).ResultsWe found that beech trees have a higher radial growth whereas oak trees have a lower one when growing in mixtures. The contrasting diversity-productivity relationship observed for beech and oak is in agreement with their ranking in shade tolerance, where oaks suffer increased competition in mixed oak patches. Overall, in monocultures and mixtures, an increasing radial growth trend of + 2% for the period 1927–2015 and 21% for the period 1899–2015 was found for beech and oak, respectively. Tree species diversity did not alter the shape of this detected long-term radial growth trend. Nevertheless, for oak a lower year-to-year variability in radial growth is found in mixtures indicating a higher resilience.ConclusionWe conclude that diversity impacts the average radial growth and its variability (only in the case of oak) but not the shape of the long-term trend in radial growth of beech and oak trees growing in the loamy region of central Belgium.

Highlights

Environmental change has resulted in changes in forest growth in Europe during the last century
Evaluation of effect of diversity on tree-ring width, forest structure and site quality A higher tree-ring widths (TRW) is found for beech trees growing in more diverse plots, the opposite is true for oak trees, which grow better in monoculture plots (Additional file 4: Table S2, Fig. 1 and Table 2)
Beech TRW is significantly different between all species composition levels except for species composition levels beech versus beech-hornbeam, beech-maple-hornbeam versus beech-oak, beech-maple-hornbeam versus beech-maple-oak, and beech-maple versus beech-oak-hornbeam (Fig. 2)

Summary

Introduction

Environmental change has resulted in changes in forest growth in Europe during the last century. Tree species diversity is expected to affect long-term trends in tree radial growth. In this paper we study the effect of diversity on the radial growth and its long-term trends for beech and oak trees growing along a gradient of tree species diversity in the loamy region of central Belgium (from monocultures to mixed forests patches up to three species). Historical long-term radial growth changes of beech and oak trees have been reported throughout Europe (Bergès et al 2000; Charru et al 2017; Boisvenue and Running 2006; Kint et al 2012). Tree species diversity could have an impact on long-term radial growth trends since diverse systems are expected to function better (Loreau et al 2001; Isbell et al 2009). More mixed forests are found to exhibit more stable growth patterns (Jucker et al 2014a; del Río et al 2017)

Methods

Results

Discussion

Conclusion