Adequacies and deficiencies of alpine and subalpine treeline studies in the national parks of the western USA

To mitigate the impact of direct human activity on treeline pattern and process, much alpine treeline research in the western USA has been conducted in nationally protected areas. The use of treeline as a proxy for climate change has been assessed in parks throughout the west but often at the expense of geology or geomorphology as controls of treeline variation. The dissimilar geology and geomorphic processes of the western national parks suggest that treeline may respond differently between national parks when subjected to disturbance. Therefore, predicted vegetation response to disturbance across the western USA may provide a limited assessment of change beyond fine-scale analysis due to data collection from a limited number of national parks containing alpine treeline. We performed a content analysis on previous research that examined alpine treeline in national parks and classified each treeline study as anthropogenic, orographic/edaphic, or climatic according to the primary factor attributed to treeline control. Results indicated that the three types of treeline are not uniformly studied. Climatic treeline is most commonly studied whereas anthropogenic and orographic/edaphic studies are often lacking. Furthermore, several western national parks are entirely devoid of anthropogenic and orographic treeline research. Similar findings exist for treeline studies in protected places worldwide. More research in protected places is required to broaden our understanding of multiple treeline processes across both regional and worldwide extents.