Enhancing identification of whitebark and limber pines: a literature review for improving forest management

Abstract

Whitebark pine (Pinus albicaulis Engelm.) and limber pine (Pinus flexilis E. James.) are two high-elevation, five-needle pine species with overlapping ranges and numerous morphological similarities. Distinguishing these two species is challenging, but the recent listing of whitebark pine under the Endangered Species Act in 2022 emphasizes the importance of accurate identification. Therefore, I conducted a narrative literature review of identification methods and their effectiveness in distinguishing whitebark pine from limber pine. My review aims to synthesize existing literature concerning whitebark pine and limber pine identification to recommend identification methods for future researchers and discuss management implications. My literature review used search terms and research questions to identify studies. After study identification and screening, I included 16 studies in my review. I found multiple methods to distinguish whitebark pine from limber pine, including visual identification, elevational threshold, needle morphology, and genetic testing. Visual identification can be effective when seed and pollen cones are present. However,seeds and pollen cones are not always present or visible. Using needle morphology for identification is not recommended due to the limited research on this technique. When limber pine and whitebark pine co-occur, whitebark pine typically occupies higher elevation, moister sites. Considering this, an elevational threshold is another method that has been applied, with researchers assuming non-cone-bearing five-needle pines found below 2,440 m are limber pine, while those found above are whitebark pine. However, numerous studies suggest that whitebark and limber pine are found above and below these elevations. Finally, genetic testing represents a new identification method that is both effective and affordable for future researchers and natural resource managers. I conclude that genetic testing is the most reliable way to identify each species and should be used to identify non-cone-bearing trees in areas of range overlap. The suggested identification methods will help managers determine where restoration and protection are needed most and are cost-effective.