Priority effects may be an important mechanism structuring biotic communities at relatively fine scales, with the random initial arrival of species impacting later community structure. In tree communities, where long-lived individuals are common, priority effects are likely maintained via niche pre-emption and competitive exclusion of similar species by those already established. In herbaceous communities, where large portions of the aboveground vegetation will die or die back each year, maintenance of priority may be less straightforward.
It seems likely that priority in herbaceous systems is in some part dependent on dispersal limitations, with species unable to overcome distance barriers to nearby communities, and/or saturation of pre-established species in local soil-seedbanks, allowing rapid, high-density recruitment. Here, we leverage data from a 10-year grassland restoration project with known initial seed applications, along with soil-seedbank surveys, to examine vegetative and soil-seedbank signals of priority effects in an herbaceous system.
Specifically, we ask the following questions: 1) Is there a signal of initial seed mixes—and thereby, priority—in the composition of grassland plots? 2) Does this signal persist across the 10-year span? And 3) Are signals of priority amplified, diluted, or approximately equivalent in the soil seedbank compared to aboveground vegetation?
Results/Conclusions:
Application of seed mixes results in clear and persistent priority effects, with grassland plots with shared initial mixes retaining compositional similarities throughout the span of the restoration. Soil-seedbanks are, as a whole, more diverse and more heterogeneous than aboveground vegetation, reflecting seedbanks’ role as a reservoir for diversity. Signals of priority are reflected in patterns of similarity among seedbanks, but to a lesser degree than in the aboveground vegetation. This suggests that, while priority is to some extent retained in the seedbank, additional mechanisms act to maintain that priority as the community is formed from the available propagules. These mechanisms may be vegetative, with perennial plants exerting an influence on their annual neighbors; alternatively, they may reflect differences in seedbank behavior such as seed dormancy rates, etc.