DOI: 10.5061/dryad.n2z34tmtm
title: Determinants of ecosystem stability in a diverse temperate forest

description: Understanding how diversity affects ecosystem stability is crucial for
 predicting the consequences of continued habitat and biodiversity loss on
 ecosystem functions and services. Long-term productivity stability in
 plant communities is often associated with greater species, phylogenetic
 or functional diversity, more complex size and age structures, or higher
 asynchrony in species fluctuations (compensatory dynamics), all
 potentially increasing community resistance to perturbations. However, the
 relative importance of these stabilizing pathways is still poorly
 understood, especially in old-growth species-rich forests. Here we explore
 how compensatory dynamics and multiple facets of diversity underpin
 temporal stability of wood biomass production over forty years in a
 Japanese temperate forest, based on more than 45,500 stem increments from
 15 species. Whereas the effect of species richness and phylogenetic
 diversity was small, the old-growth structural attributes markedly
 increased community stability via increased asynchrony in the performance
 of co-occurring species. Greater standing tree volume, stem density and
 interspecific variation in growth rates enhanced productivity stability
 both directly and indirectly via increased asynchrony. This corroborates
 the predictions of increased compensatory dynamics with increased
 asymmetric competition for light in a more productive environment.
 Asymmetric competition in old-growth patches, between dominant oaks and
 sub-canopy shade-tolerant firs and maples, is a major driver of
 productivity stability over time via compensatory dynamics. Overall
 productivity remains relatively constant in old-growth patches, as
 abundant firs and maples in the lower canopy layers compensate for biomass
 losses in canopy oaks caused by aging, wind and snow disturbances. Younger
 forest patches, composed of fast-growing, shade-intolerant species, had a
 lower stability of productivity, with reduced stem basal area and tree
 density due to higher understory bamboo coverage preventing tree
 regeneration and growth. We provide new insights into mechanisms
 underlying the stability of ecosystem functioning in diverse forest
 ecosystems, and emphasize the importance of preserving and supporting
 old-growth forests and their structural complexity.
description: The study site is located in a
 natural mixed hardwood-conifer forest in the Uryu Experimental Forest of
 Hokkaido University (44°20´N, 142°15´E, 380 m a.s.l.; Appendix S1: Fig.
 S1) in Hokkaido, northern Japan (Takahashi et al. 2003, Dolezal et al.
 2009, Altman et al. 2016). We collected all data in a permanent 1 ha (100
 × 100 m) old-growth forest plot, established in 1982 and re-measured again
 in 1992 and 1998. The plot was homogeneous and undisturbed, lying on a
 plain with no apparent slope, without evidence of past logging and low
 natural tree mortality during the last 50 years since the last severe
 typhoon of Maria struck Hokkaido in September 1954 (Takahashi et al. 2003,
 Altman et al. 2016). In the plot, all trees taller than 1.3 m were tagged
 and their height, girth at breast height (to calculate stem basal area,
 BA), and spatial coordinates were recorded during each census.