Increased resin flow in mature pine trees growing under elevated CO2 and moderate soil fertility
Warmer climates induced by elevated atmospheric CO2 (eCO2) are expected to increase damaging bark beetle activity in pine forests, yet the effect of eCO2 on resin production—the tree’s primary defense against beetle attack—remains largely unknown. Following growth-differentiation balance theory, if extra carbohydrates produced under eCO2 are not consumed by respiration or growth, resin production could increase. Here, the effect of eCO2 on resin production of mature pines is assessed. As predicted, eCO2 enhanced resin flow by an average of 140% (P = 0.03) in canopy dominants growing in low nitrogen soils, but did not affect resin flow in faster-growing fertilized canopy dominants or in carbohydrate-limited suppressed individuals. Thus, pine trees may become increasingly protected from bark beetle attacks in an eCO2 climate, except where they are fertilized or are allowed to become overcrowded.