DOI: 10.5061/dryad.0rxwdbs3r
title: Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

description: The increasing disturbances in monocultures around the world are testimony
 to their instability under global change. Many studies have claimed that
 temporal stability of productivity increase with species richness,
 although the ecological fundaments have mainly been investigated through
 diversity experiments. To adequately manage forest ecosystems, it is
 necessary to have a comprehensive understanding of the effect of mixing
 species on the temporal stability of productivity and the way in which
 this it is influenced by climate conditions across large geographical
 areas. Here, we used a unique dataset of 261 stands combining pure and
 two-species mixtures of four relevant tree species over a wide range of
 climate conditions in Europe to examine the effect of species mixing on
 the level and temporal stability of productivity. Structural equation
 modelling was employed to further explore the direct and indirect
 influence of climate, overyielding, species asynchrony and additive effect
 (i.e. temporal stability expected from the species growth in monospecific
 stands) on temporal stability in mixed forests. We showed that by adding
 only one tree species to monocultures, the level (overyielding: +6%) and
 stability (temporal stability: +12%) of stand growth increased
 significantly. We identified the key effect of temperature on
 destabilizing stand growth, which may be mitigated by mixing species. We
 further confirmed asynchrony as the main driver of temporal stability in
 mixed stands, through both the additive effect and species interactions,
 which modify between-species asynchrony in mixtures in comparison to
 monocultures. Synthesis and applications. This study highlights the
 emergent properties associated with mixing two-species, which result in
 resource efficient and temporally stable production systems. We reveal the
 negative impact of mean temperature on temporal stability of forest
 productivity and how the stabilizing effect of mixing two species can
 counterbalance this impact. The overyielding and temporal stability of
 growth addressed in this paper are essential for ecosystem services
 closely linked with the level and rhythm of forest growth. Our results
 underline that mixing two species can be a realistic and effective
 nature-based climate solution, which could contribute towards meeting EU
 climate target policies.
description: The research unit is the
 forest stand. We used data from a total of 261 forest stands belonging to
 three triplet-transects across Europe. Each triplet consists of a plot
 established in a two species mixed stands, and two plots on the respective
 monospecific stands; the three stands are located close to each other
 under similar environmental conditions. The species composition of the
 mixtures changes in the three triplet-transects. The first transect covers
 monospecific and mixed stands of <em>Fagus sylvatica</em> and
 Pinus sylvestris (32 sites, 96 stands), the second of <em>Quercus
 petraea</em> and <em>Pinus sylvestris</em> (35 sites,
 105 stands), and the third of <em>Picea abies</em> and
 <em>Pinus sylvestris</em> (20 sites, 60 stands). Plot sizes
 varies from 0-02 to 0.15 ha depending on stand density a local site
 characteristics. In each plot the diameter of all trees was
 measured, and two increment cores per tree were taken at a 1.3 m stem
 height in a sample of approximately 20 trees per species and plot. Annual
 ring widths were measured and cross-dated using standardized
 dendrochronological techniques. The studied period was 2000-2013 for the
 beech-pine transect and 2004-2017 for the oak-pine and spruce-pine
 transects (except in five triplets where the period was 2000-2013), the
 last year corresponding to triplet establishment. Using data from cored
 trees, tree diameter increment-diameter models were fitted by year,
 species and plot to estimate diameter increments of noncored trees for the
 studied period. Dead trees during the last 14 years were estimated using
 stumps, standing and lying dead trees, and their decomposition status.
 Based on measured tree diameters and annual diameter increments we
 estimated species and stand annual basal area (BA) and basal area growth
 (BAI), which conforms the dataset. 
 Annual climate data were
 obtained from meteorological weather stations located in the proximity of
 each triplet (50 triplets). When local station data were not available,
 national digital climatic atlas data (24 triplets) or more general gridded
 data (13 triplets) were used (mostly CRU gridded database). For each
 triplet mean and standard deviation of annual precipitation (P) and mean
 annual temperature (T) for the studied period were calculated.
description: The are presented in an excel-table which can be open freely in
 different ways (open office, google docs, etc.)