Diversity is the main driver of ecosystem stability
In contrast to biomass and productivity, we found that the relative
importance of diversity is much higher than stand factors for ecosystem
stability at different grain sizes (Table 3 and Fig. 1). In more-diverse
communities, the growth and development of coexisting species are often
asynchronous in time and space, which allows the community to
stabilize ecosystem functions
under environmental perturbations (Loreau & de Mazancourt 2013; Morinet al. 2014). The
asynchrony of coexisting species
is mainly determined by the species-specific attributes (such as
functional traits, evolutionary history, etc.), and these differences in
species attributes can be reflected by diversity indices (e.g.
taxonomic, phylogenetic and functional diversity) (Mori et al.2013; del Río et al. 2017). This may be why diversity metrics
were powerful in explaining ecosystem stability in our analysis. Hector
et al. (2010) proposed the over-yielding effect hypothesis, which
suggests that diversity may also stabilize ecosystem functions under
environmental disturbances by increasing community biomass or
productivity. However, the hypothesis was not well supported, because we
found that the influence of diversity on biomass and productivity was
weak, and thus the over-yielding effect seem not to be the main driver
for ecosystem stability. Recent studies have also shown that the
relationship between diversity and ecosystem stability is mainly shaped
by the asynchrony of species’ response to environmental fluctuation and
interactions among species, instead of the over-yielding effect (del Ríoet al. 2017).
It is also suggested that diversity can increase ecosystem stability
through species facilitation,
which was found to reduce mortality caused by climate events such as
drought (Fichtner et al. 2017; Hutchison et al. 2018;
Schnabel et al. 2019). Under disturbances or environmental
changes, the asynchrony, facilitation and species interactions may be
the main drivers of ecosystem stability, and thus the difference in
attributes among coexisting species (i.e. diversity indices) may be more
important than stand factors. Recent studies have reported that
taxonomic diversity explained forest stability better than structural
diversity (Schnabel et al. 2019), which also provided some
supports to our finding that stand factors showed weak effect on
stability. However, analyses on the relative effect of stand factors vs.
diversity on ecosystem stability are still limited till now (Mazzochiniet al. 2019; Wang et al. 2019), and the mechanisms why
stand factors are so weak predictors of ecosystem stability across grain
sizes is still largely unknown (considering the dominant effect of stand
factors on biomass and productivity per se , this is surprising).
More studies are needed to test our findings and to better understand
the underlying mechanisms.