Data from: Diversity effects and compensatory dynamics drive productivity and stability in temperate old-growth forests

Understanding mechanisms stabilizing ecosystem functions, such as primary
production, is crucial for forecasting global environmental responses.
While biological diversity is expected to enhance stability through
compensatory reactions to environmental changes, empirical evidence is
lacking, especially in old-growth forests vital for biodiversity
conservation and climate change mitigation. Moreover, whether increased
niche complementarity and stronger intraspecific than interspecific
competition are key mechanisms promoting compensatory dynamics and
stabilizing ecosystem functions in diverse forests remains
unexplored. This study investigates productivity and stability in
temperate old-growth forests over 20 years at community and individual
levels. Analyzing 4,380 trees in a 4-hectare plot in northern Japan with
over 35 tree species, structural equation models evaluated the effects of
biodiversity and average asynchrony in species fluctuations (compensatory
dynamics) on productivity stability across 100 m² grid quadrats.
Functional traits and taxonomic diversity represented species
complementarity and the insurance effect. Temporal growth correlations
between conspecific and heterospecific neighbors and neighborhood effects
on growth performance indicated intra- and interspecific interactions at
the individual level. Communities with greater stability
exhibited higher diversity and asynchronous species fluctuations,
suggesting that compensatory dynamics buffer community productivity
against environmental variability. The inverse relationship between tree
size variation and stability indicates that communities with less
pronounced size and abundance hierarchies have more efficient compensatory
mechanisms, ensuring stable forest functioning. The absence of
negative temporal correlations in biomass production among heterospecific
neighbors suggests the limited significance of interspecific competition
in compensatory dynamics. Conversely, positive correlations among
conspecific neighbors and their suppressed growth in dense conspecific
patches highlight the importance of conspecific negative density-dependent
mechanisms in sustaining tree species diversity and ensuring stable
productivity. The study underscores the critical role of tree species
richness in stabilizing ecosystem functioning via asynchronous growth in
one of the world’s most diverse temperate forests. Stronger intraspecific
than interspecific competition helps prevent single-species dominance,
maintaining diversity and productivity stability. Despite occasional
destabilization from size-asymmetric interspecific competition, species
trait complementarity enhances stability by promoting overall biomass
production. This study highlights the importance of overall diversity for
the stability of forest productivity, with implications for nature
conservation and ecosystem functionality.