Long‐term and year‐to‐year stability and its drivers in a Mediterranean grassland

Abstract

1. Understanding the mechanisms underlying community stability has become an urgent need to protect ecosystems from global change and resulting biodiversity loss. While community stability can be influenced by species richness, synchrony in annual fluctuations of species, species stability and functional traits, the relative contributions of these drivers to stability are still unclear. In seminatural grasslands, land-use changes such as fertilization might affect stability by decreasing richness and influencing year-to-year fluctuations. In addition, they can promote long-term directional trends, shifting community composition and influencing grassland maintenance. Thus, it is important to consider how species and community stability vary year-to-year but also in the long term.2. Using a 14-year vegetation time series of a species-rich semi-natural Mediterranean grassland, we studied the relative importance of richness, synchrony, species stability and functional traits on community stability. To assess land-use change effects on stability, we applied a fertilization treatment. To distinguish stability patterns produced by year-to-year fluctuations from those caused by long-term trends, we compared the results obtained using a detrending approach from those without detrending.3. Independently of the treatment and approach applied, the most stable communities were those composed of asynchronous species with low specific leaf area.Fertilization decreased year-to-year and long-term community stability by increasing community-weighted mean of specific leaf area, decreasing species stability or also reducing richness in the case of year-to-year stability. Additionally, traits such as seed mass had an indirect effect on stability through synchrony.Long-term trends appeared in control and fertilized plots (due to fertilization), decreasing community and species stability and leading to differences in the relationships found between community stability and some of its drivers. This reflects the importance of accounting for the effect of temporal trends on community and species stability using both a long-term and a year-to-year approach.

Increasing synchrony opposes stabilizing effects of species richness on terrestrial communities

“…The primary aim of our study was to evaluate potential differences in community variability patterns across taxonomic groups rather than a comprehensive test on the effects of diversity for different taxa. The latter requires analysing additional metrics that capture other dimensions of diversity (Olivier et al, 2020; van Klink et al, 2019), including more varying environments such that both year‐to‐year and long‐term directional variability are examined (Lepš et al, 2019; Valencia, de Bello, Lepš, et al, 2020; Valerio et al, 2022) and conducting analyses at multitrophic community levels, which is not possible with the BioTIME dataset because most time series are focussed on single taxonomic groups (Jiang & Pu, 2009; Xu et al, 2021). Particularly, asynchronous dynamics between resources and consumers (Downing et al, 2008) can be important in stabilizing natural communities, yet taxon‐specific analyses may fail to capture these processes.…”

“…An additional advantage to analysing terrestrial time series is that the environmental history of sites can be obtained through global land cover datasets. This allows for the controlling of effects of long‐term directional changes in community composition generated by other factors such as land‐use change, which is recommended for studies examining the effects of biotic variables on community variability (Lepš et al, 2019; Valencia, de Bello, Lepš, et al, 2020; Valerio et al, 2022). We only included communities that had <10% changes in agricultural, urban and forest land within the study period at the landscape scale, defined here as 96 km 2 grids the sites belong to within a global hexagonal system (Barnes & Sahr, 2017).…”

Compensatory dynamics drive grassland recovery from drought

“…These three functional groups could exhibit different responses to drought and/or during the post‐drought recovery period (Jones et al, 2016; Mackie et al, 2019; Wellstein et al, 2017). The degree of compensatory dynamics—maintenance of ecosystem function by some productive plant species or functional groups that compensate for the reduced, slow or no contribution of others at a particular time of and/or after an event (Valerio et al, 2022)—may drive the recovery of productivity after a drought spell (Zhou et al, 2022). For example, above‐ground net primary productivity (ANPP) drastically declined in a grassland via biomass losses of grasses and forbs during a 2‐year experimental drought, but completely recovered 1‐year post‐drought (Hoover et al, 2014).…”

Plant traits modulate grassland stability during drought and post‐drought periods

“…There is increasing empirical evidence that species with conservative traits (e.g. higher leaf dry matter content [LDMC], lower specific leaf area [SLA] and larger and thicker seeds) tend to be more stable than exploitative species in response to environmental change (Valerio et al, 2022; Wright et al, 2001). For example, high CWMs of SLA modulated the temporal stability of above‐ground net primary production (ANPP) by promoting species asynchrony and population stability under increased water and nitrogen availability in a semiarid grassland (Xu, Li, et al, 2022).…”