Tree Growth Response To Climate Change Across Three Conifer Species In A Navajo Forest

Abstract

Conifer forests in the Southwest are predicted to be particularly at risk from increased drought and higher temperatures projected for the region. Higher temperature in the Southwest leads to higher evaporative demand, exaggerating drought effects, and under extreme conditions can stress trees to the point of mortality. Severe droughts are also a well-documented driver of tree-killing forest disturbances, including wildfire and insect outbreaks. Regional projections of forest drought stress show heightened sensitivity of tree growth and disturbances to hotter droughts. Little is known about how future droughts might manifest at landscape and finer scales or among different species. Understanding these dynamics is crucial for management. Here we present a multi-species, multi-variate analysis of tree response to climate at two sites on the Navajo Nation where Pinus edulis, Pinus ponderosa, and Pseudotsuga menziesii are co-occurring. We tested tree growth patterns from standardized chronologies and basal area increment against a high-resolution PRISM climate dataset. We found similar responses to climate at annual and seasonal scales across species, and although species varied in growth rates, growth was synchronous in severe drought years. These findings suggest that at these sites, all three conifer species will likely respond in equivalent ways to future hotter droughts.