LB 35-287 - Novel observation of resprouting following drought-induced dieback in oneseed juniper (Juniperus monosperma)

Pinyon-juniper woodlands are widespread throughout the Southwest and provide important ecological and cultural services. In recent decades, pinyon-juniper woodlands have experienced extensive tree mortality due to drought and bark beetles. In 2021, widespread juniper dieback was observed in Northern Arizona, while pinyon was relatively unaffected. Oneseed juniper (Juniperus monosperma) was the primary juniper species affected in the Flagstaff, AZ area and experienced extensive but variable dieback which we are defining as defoliation of the canopy from which trees may or may not recover. Following an above-average monsoon season in 2021, J. monosperma experiencing dieback began to resprout from defoliated branches. While some species of juniper are known to resprout following fire, J. monosperma has previously been classified as a non-resprouting species. Patterns of dieback and resprouting in J. monosperma are unclear and represent a knowledge gap in our understanding of pinyon-juniper woodland dynamics, especially as woodlands continue to experience mortality and are expected to contract. The goal of this study was to better understand the dynamics of dieback and resprouting in J. monosperma. Field data were collected at a combination of plots (n=26) and transects (n=70) in 2021-2022 on the Coconino National Forest north of Flagstaff. The 15m radius plots were established in 2021 to quantify dieback and associated variables at plot and individual tree scales. Transects were randomly generated in 2022 with the primary goal of quantifying resprouting and dieback over a greater area relative to the plots. Along each 200m transect, 10 trees were sampled and the number of resprouts, canopy dieback, and other individual-level variables were recorded. Overall, dieback data was highly bimodal, with trees experiencing either very little or very severe dieback. Mean dieback across plots and transects was 46%; 20% of seedlings, 34% of saplings, and 38% of adults experienced severe (≥70%) canopy dieback. Resprout data was zero-inflated and resprouts were found on 58% of saplings but only 23% of adults. Resprouts were present on 16% of low (0-30%) dieback trees, 44% of moderate (30-70%) dieback trees, and 35% of severe (≥70%) dieback trees. Our data suggest that adult trees experienced the most severe dieback and were also the least likely to resprout following dieback which has implications for the demographic structure of juniper populations across the Southwest.