Resin duct density and size predicts mortality in ponderosa pine trees of Northern Arizona

Abstract

In the presence of herbivores, plants must allocate a portion of their accumulated carbon towards defense to survive. For example, trees susceptible to bark beetle attack are primarily reliant on resin production for protection. Tree mortality may be reflected by individual differences in the ability of plants to produce defensive structures and compounds. We compared the radial growth rates, resin duct production, density, and size between living and dead ponderosa pine trees in northern Arizona using standard dendrochronology techniques. As a result, we found four main findings: 1) living ponderosa pines had 33% more resin ducts than dead pines (t = 2.97, P < 0.003); 2) resin duct size was 13% larger in living than in dead pines (t = 3.00, P < 0.003); 3) both resin duct density and size were predictive of mortality (Wald’s Z = 1.9, P < 0.05); and 4) resin duct production was positively correlated with growth rate. Our results suggest dendrochronology can quantify defense structure production and predict tree mortality in ponderosa pine forests in northern Arizona.