DOI: 10.5061/dryad.612jm64cf
title: Data from: Diversity effects and compensatory dynamics drive productivity and stability in temperate old-growth forests

description: 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.
description: The study was conducted within a 4-hectare plot (200 × 200
 meters, divided into 1,600 5 x 5 m quadrats) established in 1996 in an
 old-growth stand within the 2,715-hectare Tomakomai Experimental Forest.
 All trees exceeding a height of 1.3 meters were tagged, and their girth at
 breast height of 1.3 m (GBH) was measured in 1996, 1998, 2000, 2002, 2004,
 2006, 2009, 2012, and 2015. To comprehend their impact on average
 productivity and temporal stability, we investigated various factors,
 including taxonomic, phylogenetic, and functional (structural) diversity,
 compensatory dynamics (species asynchrony), stand density, and aboveground
 biomass. These associations were examined at a resolution of 100
 m<sup>2</sup> by dividing the 4 ha plot into 400 quadrats,
 each measuring 10 m by 10 m (local communities). The
 average productivity of community biomass in each quadrat was determined
 by analyzing changes in stand basal area increments from 1996 to 2015 (the
 sum of individual tree BAI calculated from remeasured GBH), while total
 stem density and aboveground biomass in each quadrat were estimated from
 all trees in 1996 and their stem basal area sums. We evaluated the
 temporal stability of productivity by computing the inverse of the squared
 temporal coefficient of variation (1/CV²). This metric indicates the ratio
 of the mean to the standard deviation of stand basal area growth over time
 (Wang and Loreau 2014). We quantified taxonomic, phylogenetic, and
 functional characteristics to examine the influence of multiple diversity
 facets on biomass productivity and its temporal stability directly and
 indirectly via elevated species asynchrony. Taxonomic diversity was
 assessed through species richness (tree species per quadrat). Phylogenetic
 diversity was computed from the studied tree species' phylogeny
 reconstructed from GenBank's nucleotide sequences. Functional
 diversity measures were computed for each quadrat from individually
 recorded stem girths, leaf traits, and branching patterns. Each
 tree's average relative growth rate (RGR) and its variation between
 1996-2015 were calculated for each species in each quadrat from stem basal
 area changes (RGR = ln BA<sub>2015</sub> – ln
 BA<sub>1996</sub>). Furthermore, we used
 the fast–slow leaf economics spectrum (LES) to proxy for differences in
 tree leaf adaptive strategies. Finally, productivity stability may be
 influenced by how species respond to canopy disturbances and gap dynamics.
 To explore this, species were divided into two groups: those with
 monopodial branching, where the central leader shoot continues to grow
 while lateral branches stay subordinate, and those with sympodial
 branching, featuring a bifurcating pattern where one branch dominates.
 Sympodially branching trees are expected to be more adaptable to increased
 light levels following gap formation than monopodial species, which
 generally adopt more conservative crown formation strategies.
 To assess how tree traits (mean and variance) impact community
 productivity and stability, we computed community-weighted mean (CWM) and
 functional diversity (FD) indices for each trait in every grid quadrant.
 Connections among community productivity and its temporal stability,
 species asynchrony, and diversity measures were tested by fitting a
 piecewise structural equation model to aggregate ecosystem properties in
 the 400 10 m x 10 m quadrats. We estimated a variance inflation factor
 (VIF) to assess whether multi-collinearity affected parameter estimates
 and only variables having VIF &lt; 5 were included in the model.
 Fisher's C evaluated the goodness-of-fit for the whole model, and
 Nagelkerke pseudo-R<sup>2</sup> values were reported to show
 the explained variation (Lefcheck, 2016). SEMs were
 fitted by ‘piecewiseSEM’ package version 2.3 (Lefcheck, 2016), VIF was
 computed by ‘car’ package version 3.0-12, species diversity was computed
 by ‘vegan’ package version 2.6-4, phylogenetic diversity by package
 ‘picante’ version 1.8.2, functional diversity by ‘FD’ package version
 1.0-12.1 all in R version 4.3.1.
description: # Diversity effects and compensatory dynamics drive productivity and
 stability in temperate old-growth forests
 [https://doi.org/10.5061/dryad.612jm64cf](https://doi.org/10.5061/dryad.612jm64cf) Data on multiple facets of diversity effects and compensatory dynamics on productivity and stability in temperate old-growth forests in Hokkaido, Northern Japan #### Description of the data and file structure Study site: Data were gathered in the Tomakomai Experimental Forest of Hokkaido University (established in 1904), situated in a natural mixed temperate forest in Hokkaido, northern Japan (42°43.4'N, 141°34.2'E, 99 m a.s.l.), 70 km south of Sapporo. Study area: The study was conducted within a 4-hectare plot (200 × 200 meters, divided into 1,600 5 x 5 m quadrats) established in 1996 in an old-growth stand within the 2,715-hectare Tomakomai Experimental Forest. Tree measurement: All trees exceeding 1.3 meters were tagged, and their girth at breast height of 1.3 m (GBH) was measured in 1996, 1998, 2000, 2002, 2004, 2006, 2009, 2012, and 2015. Study period: from 1996 to 2015. Forest community variables: The dataset used in this study contains variables (their z-score values) calculated from tree composition and remeasured stem sizes. To comprehend their impact on average productivity and temporal stability, we investigated various factors, including taxonomic, phylogenetic, and functional (structural) diversity, compensatory dynamics (species asynchrony), stand density, and aboveground biomass, as described below: 1\. Productivity (P, cm2): The average productivity of community biomass in each 10 by 10 m quadrat was determined by analyzing changes in stand basal area increments (BAIs) in cm2 from 1996 to 2015 (the sum of individual tree BAI calculated from remeasured stem sizes). 2\. Temporal Productivity Stability (S): The inverse of the squared temporal coefficient of variation (1/CV²). This metric indicates the ratio of the mean to the standard deviation of stand basal area growth over time. 3\. Species Asynchrony (A): the average correlation across species between the BAIs of each species and the total BAIs of all other species in each quadrat along the measured years. Species asynchrony ranges from -1, indicating maximally synchronous species' productivity, to 1, where species' productivity is maximally asynchronous. 4\. Species Richness (SR), Diversity (DI), and Evenness (EV): Taxonomic diversity was assessed through species richness (tree species counts per 10 x 10 m quadrat) and derived Shannon diversity and evenness values. 5\. Phylogenetic Diversity (PD): Phylogenetic diversity computed from the studied tree species' phylogeny reconstructed from GenBank's nucleotide sequences: internal transcribed spacer (ITS), trnT-trnL intergenic spacer, matK + trnK region, and the rubisco large subunit gene (rbcL). Sequence datasets were aligned using the L-INS-i algorithm in the online version of MAFFT 6. The resulting phylogeny was constructed using Bayesian inference with MrBayes 3.1.2 and used to calculate abundance-weighted Faith's phylogenetic diversity using the Pairwise Distance (PD) index. 6\. Stem density (D): The total number of tree individuals in each 10 x 10 m quadrat in 1996. 7\. Aboveground biomass (B, cm2): The total stem basal area of all three individuals in each quadrat in 1996. 8\. Functional Diversity Measures: community-weighted mean (CWM) and functional diversity (FD) indices for each trait in every grid quadrat computed from individually recorded stem girths, leaf traits, and branching patterns. 8A: Mean Relative Growth Rate (CWM_RGR) and its variation (FD_RGR) between 1996 and 2015 calculated for each species in each quadrat from stem basal area changes (RGR = ln BA2015—ln BA1996). 8B: Leaf economics trait spectrum (CWM_LES and FD_LES): the first PCA axis based on tree species-specific leaf area (SLA, cm2 g-1), leaf dry matter content (LDMC, mg g-1), leaf nitrogen content (LNC, %), and leaf phosphorus content (LPC, %). 8C: Tree branching pattern (BM - Monopodial branching versus BS - Sympodial branching): monopodial branching - central leader shoot continues to grow while lateral branches stay subordinate; sympodial branching, featuring a bifurcating pattern where one branch dominates.