Canadian Forest Service Publications
Functional xylem anatomy of aspen exhibits greater change due to insect defoliation than to drought. Hillabrand, R. M., Lieffers, V. J., Hogg, E. H., Martínez-Sancho, E., Menzel, A., & Hacke, U. G. (2019). Tree physiology, 39(1), 45-54.
Issued by: Northern Forestry Centre
Catalog ID: 40417
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The study of tree rings can reveal long-term records of a tree’s response to the environment. This dendroecological approach, when supplemented with finer-scale observations of the xylem anatomy, can provide novel information about a tree’s year-to-year anatomical and hydraulic adjustments. Here we use this method in aspen (Populus tremuloides Michx.) to identify xylem response to drought and insect defoliation. Surprisingly, we found that precipitation influenced vessel diameter mostly in the trees’ youth, while this correlation was less pronounced at maturity. This is likely due to a reduction in stress the stand experiences as it ages, and reflects an ability to mediate drought stress as trees mature. Defoliation events caused consistent and profound changes in fiber anatomy likely leading to reduced structural support to vessels. We therefore expect that in years of defoliation trees may be vulnerable to drought-induced cavitation when leaf area recovers. This study highlights how the inclusion of cellular level measurements in tree ring studies provides additional information on how stress events may alter tree functioning through alterations in structure.
Plain Language Summary
Aspen is an important Canadian tree species, both ecologically and commercially. Aspen are especially susceptible to damage from droughts and from the loss of leaves (defoliation) during outbreaks of tent caterpillars. In this study, we collected samples from aspen trees and looked at microscopic changes in the tree rings that were formed during past years with either drought or defoliation by caterpillars. The results showed that the tree rings were damaged more by the caterpillars than by drought, especially in older trees. The damage included a weakening of the cells that transport water from the tree’s roots to their leaves. This suggests that aspen that have been defoliated by caterpillars will become even more susceptible to droughts in the future.