Time‐lagged impacts of extreme, multi‐year drought on tidal salt marsh plant invasion

Abstract

Climate change is projected to increase the frequency of extreme drought events, which can have dramatic consequences for ecosystems. Extreme drought may interact with other stressors such as invasion by non-native species, yet little research has explored these dynamics. Here, we examine the physical mechanisms and temporal scale underlying a dieback of an invasive non-native plant, Lepidium latifolium, in tidal salt marshes of the San Francisco Bay, California, USA, during an extreme, multi-year drought occurring from 2012 to 2015. Using generalized additive mixed models (GAMMs), we explored the relationship between eight years of estuarine salinity data and five years of L. latifolium density data from three marshes spanning a gradient of salinity across the San Francisco Bay. We found a significant time-lagged (3 yr) effect of estuarine salinity on L. latifolium density, with high salinities preceding reductions in L. latifolium densities and low salinities preceding increases. The most dramatic change in stem density, a 54% reduction in 2015, was preceded by a salinity increase of 43% from 2011 to 2012. We found the L. latifolium decline was driven by impacts on mature, rather than young, plants. Additionally, we tested the importance of local precipitation in driving L. latifolium densities in a one-season rain exclusion experiment. We found 100% exclusion of precipitation during one rainy season (January-mid-May) did not have a significant impact on densities of mature stands of L. latifolium. Our finding that estuarine salinity was a key driver of L. latifolium invasion dynamics suggests sea level rise, like extreme drought, may hinder L. latifolium invasion, as it will also raise estuarine salinities. Further, our study highlights the importance of temporal lags in understanding climate change impacts on biological invasions, which has received very little study to date.

Phylogenetic restriction of plant invasion in drought‐stressed environments: Implications for insect‐pollinated plant communities in water‐limited ecosystems

“…In this study, the late flowering of exotic biennial and perennial Asteraceae in both dry and wet seminatural environments suggests that, within this clade, perennial life history may be an adaptive trait supporting plant invasion in undisturbed drought-stressed environments. These findings provide counter-evidence to the hypothesis that late season drought might reduce the probability of plant invasion (Alpert et al, 2000;Wigginton et al, 2020;Wolkovich & Cleland, 2014). This further suggests that life history may be a predictor of invasion success in the late season, especially insofar as life-history traits are shared among related native and exotic drought-tolerant species.…”

Climate drivers and human impacts shape 35‐year trends of coastal wetland health and composition in an urban region

“…VPD has been identified as a major contributor to recent drought‐induced mortality in terrestrial plants (Grossiord et al, 2020). In semiarid coastal wetlands, temperature increases can lead to drought conditions and hypersaline soils, which can negatively affect plant community diversity and health (Kelso et al, 2020; Wigginton et al, 2020).…”

Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability

“…Our study provides an alternative explanation for the reduced invasion of exotic species in drier habitats or periods. Some studies have shown that drier habitats are generally less invaded than wetter habitats (Haberstroh et al, 2021; Wigginton et al, 2020). Moreover, a growing body of evidence shows that exotic plants tend to be more abundant when the drought ends (Meisner et al, 2013; Puritty et al, 2019).…”