Differences in root phenology and water depletion by an invasive grass explains persistence in a Mediterranean ecosystem

Abstract

PremiseFlexible phenological responses of invasive plants under climate change may increase their ability to establish and persist. A key aspect of plant phenology is the timing of root production, how it coincides with canopy development and subsequent water‐use. The timing of these events within species and across communities could influence the invasion process. We examined above‐ and belowground phenology of two species in southern California, the native shrub, Adenostoma fasciculatum, and the invasive perennial grass, Ehrharta calycina to investigate relative differences in phenology and water use.MethodsWe used normalized difference vegetation index (NDVI) to track whole‐canopy activity across the landscape and sap flux sensors on individual chaparral shrubs to assess differences in aboveground phenology of both species. To determine differences in belowground activity, we used soil moisture sensors, minirhizotron imagery, and stable isotopes.ResultsThe invasive grass depleted soil moisture earlier in the spring and produced longer roots at multiple depths earlier in the growing season than the native shrub. However, Adenostoma fasciculatum produced longer roots in the top 10 cm of soil profile in May. Aboveground activity of the two species peaked at the same time.ConclusionsThe fact that Ehrharta calycina possessed longer roots earlier in the season suggests that invasive plants may gain a competitive edge over native plants through early activity, while also depleting soil moisture earlier in the season. Depletion of soil moisture earlier by E. calycina suggests that invasive grasses could accelerate the onset of the summer drought in chaparral systems, assuring their persistence following invasion.

Global ecosystem thresholds driven by aridity

“…During this "soil disruption" phase, vegetation shifts from grasslands and savannahs to shrublands (Fig. S5D), which are better adapted to nutrient-poor and sandy soils (23,24). We also found a steep decrease in the overall sensitivity of vegetation to climatic fluctuations (25) (Fig.…”

Are Mediterranean forest ecosystems under the threat of invasive species Solanum elaeagnifolium?

“…In forest ecosystems, invasive alien species can cause hybridization, transmission of diseases and species competition (Langmaier & Lapin 2020). The understanding of the distribution dynamics of invasive alien plant species under predicted climate change could contribute to an effective management and conservation of ecosystems in the future (Thapa et al 2018), as the response of invasive plants to climate change may increase their ability to establish and alter Mediterranean ecosystem processes and function (Phillips et al 2019, Langmaier & Lapin 2020. As invasive plants native to tropical countries can thrive under higher temperatures they could consequently displace native species under the warming climate change conditions (Adhikari et al 2019).…”

Mapping the functional connectivity of ecosystem services supply across a regional landscape

“…Both types of pollinators could be represented in a multi-ES network, and potential impacts of land use change could be addressed using modelling of future scenarios (e.g., Redhead et al 2020). In the face of climate change, increases in dryland aridity causes grasslands and savannahs to metamorphose into shrublands as the latter grow better in sandy, nutrient-poor soils (D’Odorico and Okin 2012, Phillips et al 2019). In our study area specifically, such a shift would have implications for ES coverage and value through the dependency of model variables on underlying vegetation characteristics (Field et al 2017), and thus influence future ES production and connectivity.…”