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 reflect individual differences in the ability of plants to produce defensive structures and compounds. We compared the radial growth rates, resin duct production, and size between living and dead ponderosa pine trees in northern Arizona using standard dendrochronology techniques. 

Results/Conclusions

As a result, we found four main findings: 1) living ponderosa pines had 45% more resin ducts per annuli than dead pines (t = 3.54, P = 0.001); 2) resin duct size was 17% larger than in dead pines (t = 2.10, P < 0.05); 3) both resin duct production and size were predictive of mortality (Wald’s Z = 2.0, 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. Recent extreme drought events may have killed trees that could not adequately defend themselves from bark beetle attack. In an era and region of rapid climate change with projected increases in drought frequency and severity, increased understanding of tree mortality causes is needed.