Aims Litterfall is an important component of ecosystem net primary productivity, and a key link between above- and below-ground carbon processes. However, it remains unclear how biodiversity, stand factors and functional traits work together in affecting litterfall production and its temporal stability during forest succession.
Methods We measured litterfall production for three years in plots from four successional stages of broad-leaf and Korean pine (Pinus koraiensis) mixed forests, at the northern limit of Korean pine forest in the Shengshan Reserve of Heilongjiang. Functional traits (leaf carbon and nitrogen contents, specific leaf area) were measured to quantify functional diversity and community weighted mean (CWM) of traits. Tree diameter and height, total basal area (TBA) and gap fraction were measured to quantify stand structure. We used hierarchy partitioning analysis and variance partitioning to evaluate the relative effects of stand factors, community level traits, and (species, functional and phylogenetic) diversity on annual litterfall production, and its temporal stability (= 1/coefficient of variation for annual litterfall production).
Important findings Litterfall production was significantly lower in the early successional stage, but did no vary from the middle to late successional stages. The litterfall stability increased continuously with forest succession. The variable importance of multivariate models also suggest that, the litterfall production was mainly affected by stand factors (e.g. height, TBA, gap fraction) and functional traits (leaf carbon content), with species richness also playing a role. For stability of litterfall production, however, functional diversity was the strongest predictor, followed by stand factors (such as maximum tree diameter). The independent effect of biodiversity on litterfall production was only 0.41%, but was as much higher (33.12%) for temporal stability of litterfall, suggesting that biodiversity have an important influence on litterfall stability that is independent of stand factors and traits. There was also a strong joint effect (up to 53.8%) among the stand factors, biodiversity and functional traits, indicating that these factors collectively affect litterfall production and its stability. Our results suggest that forest succession not only increases forest productivity but also improves ecosystem stability. Therefore, protecting primary forests and promoting forest restoration are effective ways to improve ecosystem functions.