Climate dominates geographic influences on whitebark pine and limber pine trends and landscape patterns in Canada

Abstract

Limber pine (LP; Pinus flexilis) and whitebark pine (WBP; Pinus albicaulis) are classified as endangered in Canada due to rapid declines caused by the introduced pathogen causing white pine blister rust (WPBR; Cronartium ribicola), mountain pine beetle, and other stressors. A long-term monitoring study from 2003 to 2019 on 102 LP and 232 WBP permanent plots found that LP mortality decreased with increasing latitude and spring solar radiation, while WBP mortality was highest at low latitudes and elevations in areas with higher moisture and longer growing degree days. WPBR incidence in LP was associated with lower latitudes, high spring precipitation, cool/wet summers, and low solar radiation, while WBP disease incidence drivers were similar, plus increasing tree diameter and slope. Annually, mature LP and WBP mortality from all causes increased 0.4% and 0.5%, respectively, while disease incidence in live trees increased 0.6% and 0.5%. Regeneration density increased 1.3% annually on average for WBP and 2.5% for LP. Disease incidence and mortality rates have slowed compared to prior assessments, likely due to a recruitment deficit of healthy trees and some natural selection for blister rust resistance. The results support customizing landscape restoration strategies based on each species’ unique biology and local climatic factors that influence mortality and infection.