For decades, botanists have recognized that rare plants are clustered into ecological “islands”: small and isolated habitat patches produced by landscape features such as sinkholes and bedrock outcrops. Insular ecosystems often provide unusually stressful microhabitats for plant growth (due, for example, to their characteristically thin soils, high temperatures, extremepH, or limited nutrients) to which rare species are specially adapted. Climate‐driven changes to these stressors may undermine the competitive advantage of stress‐adapted species, allowing them to be displaced by competitors, or may overwhelm their coping strategies altogether. Special features of insular ecosystems – such as extreme habitat fragmentation and association with unusual landscape features – could also affect their climate sensitivity and adaptive capacity. To help predict and manage climate‐change impacts, I present a simple conceptual framework based on a synthesis of over 300 site‐level studies. Using this framework, conservation efforts can leverage existing ecological knowledge to anticipate habitat changes and design targeted strategies for conserving rare species.

Climate change is anticipated to increase the frequency and intensity of droughts, with major impacts to ecosystems globally. Broad-scale assessments of vegetation responses to drought are needed to anticipate, manage, and potentially mitigate climate-change effects on ecosystems. We quantified the drought sensitivity of vegetation in the Pacific Northwest, USA, as the percent reduction in vegetation greenness under droughts relative to baseline moisture conditions. At a regional scale, shrub-steppe ecosystems—with drier climates and lower biomass—showed greater drought sensitivity than conifer forests. However, variability in drought sensitivity was considerable within biomes and within ecosystems and was mediated by landscape topography, climate, and soil characteristics. Drought sensitivity was generally greater in areas with higher elevation, drier climate, and greater soil bulk density. Ecosystems with high drought sensitivity included dry forests along ecotones to shrublands, Rocky Mountain subalpine forests, and cold upland sagebrush communities. In forests, valley bottoms and areas with low soil bulk density and high soil available water capacity showed reduced drought sensitivity, suggesting their potential as drought refugia. These regional-scale drought-sensitivity patterns discerned from remote sensing can complement plot-scale studies of plant physiological responses to drought to help inform climate-adaptation planning as drought conditions intensify.

Natural springs in water‐limited landscapes are biodiversity hotspots and keystone ecosystems that have a disproportionate influence on surrounding landscapes despite their usually small size. Some springs served as evolutionary refugia during previous climate drying, supporting relict species in isolated habitats. Understanding whether springs will provide hydrologic refugia from future climate change is important to biodiversity conservation but is complicated by hydrologic variability among springs, data limitations, and multiple non‐climate threats to groundwater‐dependent ecosystems. We present a conceptual framework for categorizing springs as potentially stable, relative, or transient hydrologic refugia in a drying climate. Clues about the refugial capacity of springs can be assembled from various approaches, including citizen‐science‐powered ecohydrologic monitoring, remote sensing, landowner interviews, and environmental tracer analysis. Managers can integrate multiple lines of evidence to predict which springs may become future refugia for species of concern, strengthening the long‐term effectiveness of their conservation and restoration, and informing climate adaptation for terrestrial and freshwater species.

Under climate change, ecosystems are experiencing novel drought regimes, often in combination with stressors that reduce resilience and amplify drought’s impacts. Consequently, drought appears increasingly likely to push systems beyond important physiological and ecological thresholds, resulting in substantial changes in ecosystem characteristics persisting long after drought ends (i.e., ecological transformation). In the present article, we clarify how drought can lead to transformation across a wide variety of ecosystems including forests, woodlands, and grasslands. Specifically, we describe how climate change alters drought regimes and how this translates to impacts on plant population growth, either directly or through drought's interactions with factors such as land management, biotic interactions, and other disturbances. We emphasize how interactions among mechanisms can inhibit postdrought recovery and can shift trajectories toward alternate states. Providing a holistic picture of how drought initiates long-term change supports the development of risk assessments, predictive models, and management strategies, enhancing preparedness for a complex and growing challenge.

Vernal pools of the northeastern United States provide important breeding habitat for amphibians but may be sensitive to droughts and climate change. These seasonal wetlands typically fill by early spring and dry by mid‐to‐late summer. Because climate change may produce earlier and stronger growing‐season evapotranspiration combined with increasing droughts and shifts in precipitation timing, management concerns include the possibility that some pools will increasingly become dry earlier in the year, potentially interfering with amphibian life‐cycle completion. In this context, a subset of pools that continues to provide wetland habitat later into the year under relatively dry conditions might function as ecohydrologic refugia, potentially supporting species persistence even as summer conditions become warmer and droughts more frequent. We used approximately 3000 field observations of inundation from 449 pools to train machine‐learning models that predict the likelihood of pool inundation based on pool size, day of the year, climate conditions, short‐term weather patterns, and soil, geologic and landcover attributes. Models were then used to generate predictions of pool wetness across five seasonal time points, three short‐term weather scenarios and four sets of downscaled climate projections. Model outputs are available through a website allowing users to choose the inundation thresholds, time points, weather scenarios and future climate projections most relevant to their management needs. Together with long‐term monitoring of individual pools at the site scale, this regional‐scale study can support amphibian conservation by helping to identify which pools may be most likely to function as ecohydrologic refugia from droughts and climate change.

Spring‐fed wetlands are ecologically important habitats in arid and semi‐arid regions. Springs have been suggested as possible hydrologic refugia from droughts and climate change; however, springs that depend on recent precipitation or snowmelt for recharge may be vulnerable to warming and drought intensification. Springs that are expected to maintain their ecohydrologic function in a warmer, drier climate may be priorities for conservation and restoration. Identifying such springs is difficult because many springs lack hydrologic records of adequate temporal extent and resolution to assess their resilience to water cycle changes. This study demonstrates proof‐of‐concept for the assessment of certain spring types (i.e., helocrene, hypocrene, and hillslope springs) in terms of hydrologic and ecological resilience to climatic water stress using freely available remote‐sensing and climate data. We used the Normalized Difference Vegetation Index (NDVI) from 1985 through 2011 to delineate surface‐moisture zones (SMZs) associated with 39 clusters of 172 springs in a montane sage‐steppe landscape in southeastern Oregon, USA. We developed and synthesized seven NDVI‐based indicators of SMZ resilience to interannual changes in water availability: (1) mean and (2) standard deviation of July NDVI; (3) mean difference in July NDVI and (4) difference in coefficient of variation for July NDVI between each SMZ and its surrounding watershed; (5) response of SMZ July NDVI to 90‐day antecedent precipitation; (6) response of SMZ July NDVI to the previous winter's snowpack; and (7) range of NDVI values from an exceptionally wet year followed by three dry years. Because all resilience indicators were highly inter‐correlated, we derived an overall metric of SMZ resilience using principal components analysis that accounted for 66% of total variance. This overall resilience score was positively correlated with SMZ elevation, slope, mean annual precipitation, and with the number of associated springs. Resilience was greater for SMZs on topographically shaded, north‐facing slopes. Several high‐resilience SMZs were located immediately below persistent snowbanks, suggesting a possible source of steady recharge throughout the growing season. The approach presented here—if combined with field assessments of spring hydrogeology, discharge, and groundwater age—could help identify spring‐fed wetlands that are most likely to serve as hydrologic refugia from climate change.