Hydrologic refugia, plants, and climate change

Abstract

Climate, physical landscapes, and biota interact to generate heterogeneous hydrologic conditions in space and over time, which are reflected in spatial patterns of species distributions. As these species distributions respond to rapid climate change, microrefugia may support local species persistence in the face of deteriorating climatic suitability. Recent focus on temperature as a determinant of microrefugia insufficiently accounts for the importance of hydrologic processes and changing water availability with changing climate. Where water scarcity is a major limitation now or under future climates, hydrologic microrefugia are likely to prove essential for species persistence, particularly for sessile species and plants. Zones of high relative water availability - mesic microenvironments - are generated by a wide array of hydrologic processes, and may be loosely coupled to climatic processes and therefore buffered from climate change. Here, we review the mechanisms that generate mesic microenvironments and their likely robustness in the face of climate change. We argue that mesic microenvironments will act as species-specific refugia only if the nature and space/time variability in water availability are compatible with the ecological requirements of a target species. We illustrate this argument with case studies drawn from California oak woodland ecosystems. We posit that identification of hydrologic refugia could form a cornerstone of climate-cognizant conservation strategies, but that this would require improved understanding of climate change effects on key hydrologic processes, including frequently cryptic processes such as groundwater flow.

Detecting microrefugia in semi-arid landscapes from remotely sensed vegetation dynamics

“…Although these were not generally considered to be microrefugia in the evaluation, it is possible that they are. Large, deeply rooted trees may have access to more reliable water supplies, functioning as hydrologic microrefugia (McLaughlin et al, 2017). Further, Frey et al (2016) suggest that large trees in old growth forests (admittedly a very different system from that studied here) moderate temperature extremes because of the amount of energy required to warm their large biomass.…”

“…In arid areas, water availability is expected to drive the distribution of microrefugia. Water subsidies, such as from springs or runoff from rock outcrops and other areas with reduced infiltration, are likely to provide microrefugia from drought (McLaughlin et al, 2017;Reside et al, 2014). In addition, the moderating influence of moisture and humidity are related to the occurrence of thermal microrefugia buffering temperature extremes (Ashcroft and Gollan, 2013) and may provide microrefugia from fire disturbances as well (Ouarmim et al, 2014;Reside et al, 2014;Wilkin et al, 2016).…”

“…However, axes such as moisture availability (hydrologic refugia; Davis et al, 2013;McLaughlin et al, 2017) or disturbance (eg, fire refugia; Ouarmim et al, 2014;Wilkin et al, 2016) are equally important (Reside et al, 2014). In addition, refugia can operate over multiple time frames, determined by their size and permanence (ie, the degree to which they are decoupled from regional conditions).…”

“…There is less guidance about identifying refugia in areas of modest terrain (Reside et al, 2014). Another guideline, especially in arid systems, is that sites with access to permanent water sources are refugia McLaughlin et al, 2017;Reside et al, 2014).…”

Land Cover, Land Use, and Climate Change Impacts on Endemic Cichlid Habitats in Northern Tanzania

“…Deducing the main stressors acting upon the habitats of aquatic species may allow for the development of mitigation measures, the refinement of regional development plans, or the adoption of new paradigms in the management and protection of aquatic habitats [118]. With proper management and conservation strategies these habitats could become hydrologic refugia for endemic aquatic species [119].…”