Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

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.