Mixing effects on Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) productivity along a climatic gradient across Europe

Ricardo Ruiz‐Peinado ,Sandra Metslaid,Ekaterina Makrickienė,Ignacio Barbeito,Ditlev Otto Juel Reventlow,Kšištof Godvod,Michael Heym,Jorge Aldea,Arne Nothdurft,Aksel Granhus,Hans Pretzsch,Gediminas Brazaitis,Magnus Löf,Kamil Bielak,Marek Metslaid,Roman Sitko,Gintarė Stankevičienė,Āris Jansons ,Stig‐Olof Holm ,Lars Drößler ,Miren Del Rı́o

doi:10.1016/j.foreco.2020.118834

Abstract

Mixed-species stands have been found to be more productive than would be expected from the performance of their component species in monocultures due to facilitation and complementarity between species, although these interactions depend on the combination of species present. Our study focuses on monospecific and mixed-species stands of Scots pine and Norway spruce using 20 triplets established in nine countries along a climatic gradient across Europe. Differences in mean tree and stand characteristics, productivity and stand structure were assessed. Basal area increment in mixed stands was 8% higher than expected while volume increment was only 2% greater. Scots pine trees growing in mixed-species stands showed 11% larger quadratic mean diameter, 7% larger dominant diameter, 17% higher basal area and 25% higher stand volume than trees growing in monospecific stands. Norway spruce showed only a non-significant tendency to lower mean values of diameters, heights, basal area, as well standing volume in mixtures than monocultures. Stand structure indices differed between mixed stands and monocultures of Scots pine showing a greater stratification in mixed-species stands. Furthermore, the studied morphological traits showed little variability for trees growing in monospecific stands, except for diameter at breast height, crown length and crown length ratio. For trees growing in mixed stands, all the morphological traits of the trees were identified as different. Some of these morphological traits were associated with relative productivity. Nevertheless, relative productivity in mixed-species stands was not related to site conditions.

Highlights

In the context of climate change, it has been shown that mixedspecies forests can be more resistant and resilient to disturbances compared to monocultures (Bauhus et al, 2017a)
We found no significant differences when comparing the di mensions of Norway spruce trees grown in mixture with those in monocultures
Basal area increment (IBA) at stand and species level was always higher than expected for both species (Table 4), a significant effect was only detected at stand level (+7%)

Summary

Introduction

In the context of climate change, it has been shown that mixedspecies forests can be more resistant and resilient to disturbances compared to monocultures (Bauhus et al, 2017a) This reflects different growth patterns of species along with other mechanisms such as niche complementarity and facilitation (Jactel et al, 2017). Productivity has been found to be more temporally stable in mixed-species forests (Aussenac et al, 2017; del Río et al, 2017). This higher and more stable produc tivity suggests that mixed-species forests can be capable of sequestering and storing more carbon than monospecific forests (Ruiz-Benito et al, 2014; Poorter et al, 2015; Liu et al, 2018). Mixed forests can provide a wider range of ecosystem services than monospecific forests (Gamfeldt et al, 2013; Bauhus et al, 2017b)

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Results

Discussion

Conclusion