Prolonged and intense drought has occurred throughout the Southwest since 2002 resulting in high regional die-off of the dominant tree species. The pinyon-juniper woodlands have been especially sensitive to drought, heat, and associated insect attacks. Between 2002 and 2004 large amounts of pinyon pine (Pinus edulis) died as a result of extreme drought. However, since the 2002 to 2004 drought and pinyon die-off event, drought and high temperatures have continued to persist in the region, and here, we examined long-term plots established in central New Mexico to determine if additional die-off of pinyon pine or juniper (Juniperus monosperma) has occurred and to what extent. We hypothesize that continued tree die-off will trend towards a tree-less ecosystem throughout portions of the region.
Results/Conclusions
During the 2002 to 2004 drought pinyon pine died at high levels (>50%) while juniper had substantially lower levels of die-off (<2%) during this time. However, between 2012 and 2014 an area >1,100 km2 of juniper died in northern New Mexico in which 10% of juniper died from drought and heat, while 16% of junipers incurred crown die-back. While juniper die-off was high at some locations the die-off was spatially specific to a contiguous area in northern New Mexico, but remained low elsewhere throughout the region. Furthermore, recent pinyon pine die-off was 7%, suggesting that while the initial die-off event was extreme, additional die-off has continued during the persistent drought of the past decade. Future model projections of both pinyon pine and juniper indicate substantial range shifts may occur. If current trends continue large portions of the Southwest may experience continued die-off of both pinyon and juniper and low recruitment of both species. The pinyon-juniper woodland vegetation-type comprises over 40 million hectares in the western US and results indicate vast expanses of wooded lands could potentially become devoid of trees if die-off continues.