Abstract
Relatively mesic environments within arid regions may be important conservation targets as ‘climate change refugia’ for species persistence in the face of worsening drought conditions. Semi-arid southern California and the relatively mesic environments of California’s Channel Islands provide a model system for examining drought responses of plants in potential climate change refugia. Most methods for detecting refugia are focused on ‘exposure’ of organisms to certain abiotic conditions, which fail to assess how local adaptation or acclimation of plant traits (i.e. ‘sensitivity’) contribute to or offset the benefits of reduced exposure. Here, we use a comparative plant hydraulics approach to characterize the vulnerability of plants to drought, providing a framework for identifying the locations and trait patterns that underlie functioning climate change refugia. Seasonal water relations, xylem hydraulic traits and remotely sensed vegetation indices of matched island and mainland field sites were used to compare the response of native plants from contrasting island and mainland sites to hotter droughts in the early 21st century. Island plants experienced more favorable water relations and resilience to recent drought. However, island plants displayed low plasticity/adaptation of hydraulic traits to local conditions, which indicates that relatively conserved traits of island plants underlie greater hydraulic safety and localized buffering from regional drought conditions. Our results provide an explanation for how California’s Channel Islands function as a regional climate refugia during past and current climate change and demonstrate a physiology-based approach for detecting potential climate change refugia in other systems.
Highlights
Plants in the 21st century are exposed to hotter and more frequent climate change-driven drought conditions (Breshears et al, 2005; Seager, 2007; Williams et al, 2013; Trenberth et al, 2014; Allen et al, 2015)
Of particular utility in this context is the characterization of traits associated with plant hydraulic function and carbon gain, which can be predictive of drought-induced plant mortality under a warmer, drier future climate (McDowell et al, 2008; Anderegg et al, 2016; Venturas et al, 2017; Choat et al, 2018)
Our research aims to (i) determine if the maritime climate of island environments is sufficient to buffer native California plants from 21st century drought conditions exacerbated by climate change and (ii) to evaluate a trait-based method for detecting the physiological mechanisms of hydrologic refugia that can be applied to other systems
Summary
Plants in the 21st century are exposed to hotter and more frequent climate change-driven drought conditions (Breshears et al, 2005; Seager, 2007; Williams et al, 2013; Trenberth et al, 2014; Allen et al, 2015). Existing methods for detecting refugia that involve modeling the persistence of abiotic conditions within the suitable range for target species or ecosystems (e.g. bioclimate envelope models) do not provide direct information on the sensitivity of Conservation Physiology Volume 8 2020. Target species due to local adaptation or acclimation (Pearson and Dawson, 2003) Assessing both the extent to which species are exposed to climate change driven droughts and how local adaptation and acclimation contribute to species sensitivity is necessary for accurately predicting the responses of ecosystems to future conditions (Williams et al, 2008a; Crausbay et al 2017). Hydraulic safety margins provide important, comparable information on the hydraulic function of plants experiencing contrasting environmental conditions that can be predictive of future drought-induced mortality (Choat et al, 2012; Skelton et al, 2015; Anderegg et al, 2016)
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