PS 34-224 - CANCELLED - Trait-mediated community assembly during experimental grassland restoration is altered by planting year rainfall

Abstract: Ecological restoration outcomes are highly variable. Degradation level, land-use history, restoration methods, and successional processes all imbue community assembly with variation and impact the predictability of restoration outcomes. One poorly understood source of variability is ‘year effects’ – a term describing the inter-annually variable first-year abiotic and biotic conditions. Year effects are posited to be a key control on the long-term successional trajectories of plant communities via priority effects, competitive exclusion, and plant-soil feedback, however, they are not often directly addressed or manipulated. We collected 5 years of abundance data from an experimental grassland restoration, where first-year rainfall was manipulated to low, average, and high levels. These treatments were replicated across three establishment years, to enable us to isolate the effects of precipitation during the planting year from other year effects. We use this data to test the community-weighted mean (CWM) trait response of restored communities to varying planting year rainfall. Briefly, we find that CWM specific leaf area, seed mass, and plant height all strongly relate to plot age in an expected fashion based on life-history strategies correlated with these traits. However, the relationship between CWM plant height and age was further modulated by initial water treatments, as was CWM seed mass to a lesser extent. In the low water treatments shorter-growing species also continued to increase in cover over time, comparably to taller-growing species. Our results highlight lasting effects (1–5 years) of planting year precipitation levels on plant community development. We also briefly discuss opportunities to integrate our findings into future grassland restoration.