Tree diversity effects on forest productivity increase through time because of spatial partitioning

Shinichi Tatsumi

doi:10.1186/s40663-020-00238-z

Abstract

BackgroundExperimental manipulations of tree diversity have often found overyielding in mixed-species plantations. While most experiments are still in the early stages of stand development, the impacts of tree diversity are expected to accumulate over time. Here, I present findings from a 31-year-old tree diversity experiment (as of 2018) in Japan.ResultsI find that the net diversity effect on stand biomass increased linearly through time. The species mixture achieved 64% greater biomass than the average monoculture biomass 31 years after planting. The complementarity effect was positive and increased exponentially with time. The selection effect was negative and decreased exponentially with time. In the early stages (≤ 3 years), the positive complementarity effect was explained by enhanced growths of early- and mid-successional species in the mixture. Later on (≥ 15 years), it was explained by their increased survival rates owing to vertical spatial partitioning — i.e. alleviation of self-thinning via canopy stratification. The negative selection effect resulted from suppressed growths of late-successional species in the bottom layer.ConclusionsThe experiment provides pioneering evidence that the positive impacts of diversity-driven spatial partitioning on forest biomass can accumulate over multiple decades. The results indicate that forest biomass production and carbon sequestration can be enhanced by multispecies afforestation strategies.

Highlights

Experimental manipulations of tree diversity have often found overyielding in mixed-species plantations
The linear model had a lower Akaike information criterions (AIC) than the exponential model for the net diversity effect (R2 = 0.91), while the exponential models were selected over the linear models for the complementarity (R2 = 0.99) and selection effects (R2 = 1.00) (Table S2)
State space models accounting for temporal autocorrelations showed that the net diversity and complementarity effects increased over time while the selection effect decreased in negative direction (Table S3)

Summary

Introduction

Experimental manipulations of tree diversity have often found overyielding in mixed-species plantations. Species mixtures often achieve higher performance, typically measured by biomass productivity, than expected from average monoculture performance. This net biodiversity effect can be additively partitioned into complementarity and selection effects (Loreau and Hector 2001). The complementarity effect quantifies the average species overyielding which typically derive from niche partitioning, facilitation, and/or ecosystem feedbacks (Eisenhauer et al 2012; Reich et al 2012). Selection effect arises when species that produce large biomass in monocultures tend to overyield or underyield in mixtures (i.e. positive or negative selection) (Loreau and Hector 2001). Results from grassland diversity experiments have shown that the complementarity effect often becomes increasingly important with time (Fargione et al 2007; Cardinale et al 2007; Reich et al 2012)

Methods

Results

Discussion

Conclusion