Prioritize and maintain unique sites

EASTERN:
Some sites host a higher diversity of species than adjacent sites, have many endemic species, have a sheltered topographic position, or have retained species through past periods of climate change (Keppel et al. 2012). These potential refugia are formed through spatial, geophysical, and biological variation on the landscape and may be identified as unique sites that are expected to be more resistant to change. These sites may provide the best chance to retain habitat for native species under future climate change (Anderson et al. 2012). Species at these sites are not necessarily sensitive or at-risk, although they may face increased stress under future climate on some landscape positions. Committing additional resources may be necessary to ensure that the characteristic site conditions are not degraded by invasive species, herbivory, fire, or other disturbances. (1)

WESTERN:
Some sites host a higher diversity of species than adjacent sites, have many endemic species, or have retained species through past periods of climate change (Loarie et al. 2008, Keppel et al. 2012, Comer et al. 2019). These locations of high ecological value can be identified at multiple scales and may occur as a result of many factors, including geophysical factors such as complex topography, variation in geology and soils, variation in microclimates due to vegetation differences, or variation in hydrology, including access to cold groundwater or climatic buffering from large surface waters (Beier and Brost 2010, Anderson and Ferree 2010, Klausmeyer et al. 2011, Lawler et al. 2015, Comer et al. 2019, Cartwright et al. 2020, Morelli et al. 2020). When these factors moderate exposure to climate change, they are often referred to as climate refugia. Species at these sites are not necessarily sensitive or at-risk, although they may face increased stress under future climate on some landscape positions. Committing additional resources may be necessary to ensure that the characteristic site conditions are not degraded by invasive species, herbivory, altered fire regimes, or other disturbances. (2)

Refugia are areas that have resisted ecological changes occurring elsewhere, often providing suitable habitat for relict populations of species that were previously more widespread (Millar et al. 2007, Keppel et al. 2012). Climate refugia are often formed by topography (e.g., north sides of slopes, or sheltered ravines), proximity to large water bodies, or connection to groundwater (Ashcroft 2010, Dobrowski 2011, Morelli et al. 2016, Cartwright 2018, Krosby et al. 2018, Krawchuk et al. 2020, Ebersole et al. 2020, Ackerly et al. 2020). An excellent example of this are the 75 or so giant sequoia (Sequoiadendron giganteum) groves scattered across the Sierra Nevada mountain range that have persisted in sites that are relatively more mesic and have reliable summer moisture (Holland and Keil 1995). Springs and other sites with strong connections to groundwater can provide cool water refugia (Cartwright et al. 2020), and are critical habitat for a variety of California’s threatened and endangered species (Rohde et al. 2019). During previous periods of rapid climate change, at-risk populations persisted in refugia that avoided extreme impacts (Noss 2001, Millar et al. 2007, Keppel et al. 2012, Nydick et al. 2018). These populations allowed species to persist until more favorable climatic conditions returned and species were able to expand into newly available habitats. This strategy seeks to identify and maintain habitats that: (1) are on sites that may be better buffered against climate change and short-term disturbances, and or (2) contain communities and species that are at risk across the greater landscape (Noss 2001, Millar et al. 2007).