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

Background/Question/Methods

• Widespread piñon (Pinus edulis) mortality occurred across the southwestern USA during 2002-2003 in response to drought and bark beetle infestations. Given recent mortality and changes in regional climate over the past several decades there is a keen interest in post-mortality regeneration dynamics in piñon-juniper woodlands.
• We examined piñon and Utah juniper (Juniperus osteosperma) recruitment at 30 sites across southwestern Colorado, USA that spanned a gradient of adult piñon mortality levels (10-100%) to understand current regeneration dynamics.

Results/Conclusions

• Piñon recruitment across our study sites was highly variable and positively related to shrub and juniper cover. Additionally, new (post-mortality) piñon recruitment was strongly positively associated with live adult piñon densities and was thus negatively affected by recent mortality. However, mortality had no effect on piñon advanced regeneration (juveniles established pre-mortality) and did not shift juvenile piñon dominance.
• Our results highlight the importance of shrubs and juniper trees for facilitating piñon establishment and survival. Regardless of adult piñon mortality levels, areas with low tree and shrub cover may become increasingly juniper dominated due to few suitable microsites for piñon establishment and survival. In areas with high piñon mortality and high tree and shrub cover, our results suggest piñon is regenerating via advanced regeneration.