Ecological integrity of whitebark pine ecosystems in California’s national forests

Abstract

Whitebark pine (Pinus albicaulis) forest ecosystems in California are diverse and unique, yet their current status and condition are uncertain. Using a combination of geospatial and field plot data, we assessed patterns in the structure, composition, and health of whitebark pine ecosystems on national forests throughout the state of California to evaluate potential signs of declining ecosystem integrity. We found whitebark pine ecosystems to be structurally, compositionally, and functionally distinct among subregions of California, and all subregions displayed some evidence of declining ecological integrity. Whitebark pine forests in northern California exhibited signs of greater stand densification (Cascade-Klamath), potential encroachment by shade-tolerant conifer species (Cascade-Klamath and Warner Mountains), and increased tree mortality associated with mountain pine beetle outbreaks (Warner Mountains) than elsewhere in California. Whitebark pine stands in the Sierra Nevada showed signs of stand densification (central Sierra) and localized mountain pine beetle outbreaks (southern Sierra east). Notwithstanding these negative signs, much of the state’s whitebark pine ecosystems on national forestlands appear to be relatively healthy and intact compared to more northern latitudes. Active management may be required to restore whitebark pine ecosystems on national forests in California with declining integrity, including stands experiencing substantial stand densification, encroachment by shade-tolerant conifers, and mountain pine beetle outbreaks.