Resin ducts and bark thickness influence pine resistance to bark beetles after prescribed fire

Document Type

Article

Journal/Book Title/Conference

Forest Ecology and Management

Publication Date

Spring 2021

Volume

494

Abstract

After fire, bark beetles pose a significant threat to trees. Resin duct characteristics in trees can increase resistance to bark beetles. However, little is known about how intra- and interspecific variations in resin ducts due to tree characteristics, fire-caused tree injury and life history traits contribute to resistance. In fall 2013, a mixed-stand of Pinus sylvestris and P. nigra was underburned, with some trees subsequently attacked and killed by bark beetles (Ips sexdentatus) during the following two years. We investigated whether inter- or intraspecific differences in constitutive defenses (i.e. bark thickness, tree size and growth, resin ducts) or fire-caused tree injury could explain tree resistance to bark beetles. Beetles preferentially attacked P. sylvestris over the more fire-resistant P. nigra subsp. salzmannii. In P. nigra, attacks were limited to smaller trees, whereas the probability of mortality from I. sexdentatus increased with diameter in P. sylvestris. The decrease in bark thickness along the stem significantly affected the probability of mortality in P. sylvestris but not in P. nigra. As tree size increased, bark thickness and resin duct area investment were lower in P. sylvestris than P. nigra, suggesting reduced defences in P. sylvestris. For both species, pines that survived had faster growth, higher resin duct area, and fewer but larger ducts than pines that died after the attack. However, resin duct area and density rather than growth or fire-caused injury were better predictors of tree resistance. Moreover, in unattacked trees resin duct area increased with diameter in P. nigra. Our study showed that bark beetles attacks were tree species and size specific, but ultimately resin duct characteristics determined host colonization. Our findings suggest managers can expect higher delayed mortality from bark beetles in P. sylvestris after burning; however, actions that encourage faster growth may increase resin duct-related defences in both pine species.

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