During the recent multi-year drought on the Colorado Plateau, USA there has been an extensive die-back of pinyon pine (P. edulis). Although multi-year droughts are common in the western U.S., the extent of this recent die-back has been more widespread than a similar drought in the 1950s, raising questions of whether recent increases in temperature were exacerbating drought stress across the region. In recent years there has been a clear warming trend across this region; estimates of surface air temperature increases on the Colorado Plateau over the past 200 yrs range from 0.4-0.8 °C, with evidence of accelerated warming over the last century. In this study we examined P. edulis growth responses to climate over the last century in southeastern Utah. Using dendrochronological techniques, we examined P. edulis growth responses to 20 monthly climate variables (previous October through August precipitation and temperatures) over the last century. 

Results/Conclusions

Our results suggest that early-summer temperatures are negatively influencing P. edulis growth at a number of sites across southeastern Utah over the past several decades—a trend which was not observed early in the century. The negative influence of early-summer temperatures on tree growth was most likely due to increasing early-summer drought stress before the onset of the summer monsoons. As temperatures are expected to increase across this region in the next century, we expect to observe further declines in P. edulis growth rates, which may have long-term consequences for the distribution of this dominant vegetation type across much of the semi-arid West.