Above‐ and below‐ground complementarity rather than selection drive tree diversity–productivity relationships in European forests

Abstract

Biodiversity experiments have identified both complementarity and selection as important drivers of the relationship between biodiversity and ecosystem functioning. However, their relative importance in above‐ and below‐ground ecosystem compartments of mature forests remains yet to be explored. We adopted a trait‐based approach to partition biodiversity effects in above‐ and below‐ground complementarity and selection. This approach was based on canopy and root traits measured in single‐ and mixed‐species plots in mature forests across a European latitudinal gradient. We assessed the relative importance of above‐ and below‐ground selection and complementarity in driving the relationship between tree species diversity and above‐ground wood production. We used the expected values (based on the values measured in monocultures) of leaf area index (LAI) and fine root biomass as proxies for above‐ and below‐ground selection, whereas canopy packing and rooting depth variability were used as proxies for above‐ and below‐ground complementarity. Our results showed that tree species richness–wood production relationships were driven by above‐ and below‐ground complementarity (i.e. canopy packing and rooting depth variability), rather than selection. The proxies for selection were found to have a positive effect on wood production but were not affected by tree species richness. We concluded that above‐ground‐ but also the largely neglected below‐ground complementarity drives biodiversity–productivity relationships in mature forests. Our findings suggest that choosing tree species with complementary above‐ and below‐ground traits should be considered in afforestation and forest management to promote tree diversity and productivity in European forests.

Tree diversity effects on productivity depend on mycorrhizae and life strategies in a temperate forest experiment

“…As a result, selection effects decreased after four years in our experiment, while complementarity effects continued to increase. This is in line with previous findings showing that selection effects play a major role at the beginning, but are replaced by complementarity effects after some time (Fargione et al, 2007;Jing et al, 2021;Lasky et al, 2014). Overall, our results support the hypothesis that co-occurring species in high-diverse temperate forests differ in niches and competitive abilities, which leads to strong biodiversity effects and higher productivity in mixtures compared to their monospecific counterparts Huang et al, 2018;Morin et al, 2011;Urgoiti et al, 2022).…”

Effects of stand condition and root density on fine-root dynamics across root functional groups in a subtropical montane forest

“…Over-yielding reflects substantial rooting plasticity in response to neighbors (Schmid and Kazda 2005 ; Bolte and Villanueva 2006 ). Several studies have confirmed that variation in root traits as the diversity of neighbors increases leads to niche differentiation and complementary colonization of underground space, thus promoting soil resource acquisition and reducing the competitive pressure among neighbors (Brassard et al 2013 ; Mueller et al 2013 ; Ma and Chen 2017 ; Jing et al 2021 ). Studies also have revealed evidence of interactive effects between nutrients and neighbors where some plants increase their root production in the presence of competition from neighbors (Mommer et al 2010 ; Padilla et al 2013 ).…”

“…Another hypothesis is the selection probability effect, which proposes that higher species richness improves productivity by increasing the chances of possessing high-yielding species (Špaèková and Lepš 2001 ; Schmid et al 2008 ). Most research on the relationship between plant species diversity and root productivity has tended to support the complementarity effect rather than the selection probability effect (Brassard et al 2011 ; Zeng et al 2020 ; Jing et al 2021 ).…”

Climatic conditions, not above- and belowground resource availability and uptake capacity, mediate tree diversity effects on productivity and stability

“…Mean annual cloud cover was compiled from the global 1-km cloud cover project (Wilson and Jetz, 2016). The standardized residuals were then used in the SEM analyses (Desie et al, 2020;García-Palacios et al, 2018;Jing et al, 2021). In addition, plant species responses to environmental changes can shift throughout their range, and many regional ecological indicator value systems have been developed in Europe, each with a different ordinal scale, spanning different environmental gradients and their own region of application (Diekmann, 2003).…”

“…Complementarity is often considered as one of the fundamental mechanisms responsible for the positive effects of tree species diversity on forest primary productivity (a frequently measured component of ecosystem functioning) (Barry et al, 2019;Jing et al, 2021;Scherer-Lorenzen, 2014;Trogisch et al, 2017). For instance, complementarity in resource uptake ensures a higher amount of resources captured and thus a higher productivity (Forrester and Bauhus, 2016).…”