Tree regeneration following drought- and insect-induced mortality in pinon-juniper woodlands

Widespread pinon (Pinus edulis) mortality occurred across the southwestern USA during 2002-2003 in response to drought and bark beetle infestations. Given the recent mortality and changes in regional climate over the past several decades, there is a keen interest in post-mortality regeneration dynamics in pinon-juniper woodlands. Here, we examined pinon and Utah juniper (Juniperus osteosperma) recruitment at 30 sites across southwestern Colorado, USA that spanned a gradient of adult pinon mortality levels (10-100%) to understand current regeneration dynamics. Pinon and juniper recruitment was greater at sites with more tree and shrub cover. Pinon recruitment was more strongly facilitated than juniper recruitment by trees and shrubs. New (post-mortality) pinon recruitment was negatively affected by recent mortality. However, mortality had no effect on pinon advanced regeneration (juveniles established pre-mortality) and did not shift juvenile pinon dominance. Our results highlight the importance of shrubs and juniper trees for the facilitation of pinon establishment and survival. Regardless of adult pinon mortality levels, areas with low tree and shrub cover may become increasingly juniper dominated as a result of the few suitable microsites for pinon establishment and survival. In areas with high pinon mortality and high tree and shrub cover, our results suggest that pinon is regenerating via advanced regeneration.