Post-fire regeneration dynamics in whitebark pine (Pinus albicaulis) forests in Wind River and Absaroka Mountains, Wyoming, USA

Abstract

Whitebark pine (Pinus albicaulis) populations are in decline across the species’ range due to historic wildfire exclusion, mountain pine beetle (Dendroctonus ponderosae, MPB) outbreaks, and an invasive fungal pathogen causing the disease white pine blister rust (Cronartium ribicola, WPBR). Despite reliance on stand-replacing fires, information on whitebark pine regeneration occurrence is limited and the trajectory of future forests is largely unknown in some areas of the range. Regeneration densities were assessed in burned and adjacent non-burned areas at six high elevation locations in northwest Wyoming where stand-replacing fires occurred 8–32 years before the surveys. In these locations at the eastern extent of the species range, we assessed what site factors were associated with regeneration success. Whitebark pine regeneration density was greater and seedlings were older in non-burned compared to burned areas. Within burns, north aspects had more regeneration than south aspects. Potential seed source densities and other species’ regeneration were positively related to whitebark pine regeneration densities in burned areas. South facing slopes or grass covered areas may have either delayed or no regeneration of whitebark pine without the help of artificial planting.