Disentangling the effects of disturbance, climate and tree age on xylem hydraulic conductivity of Betula pendula
Abstrakt
Background and Aims: Increasing frequency of disturbances in temperate forests is responsible for increasing numbers of trees with mechanically damaged cambial zones. Adjustment of wood anatomical structure to balance between safe and efficient water conductivity is one mechanism trees employ to cope with mechanical damage.
The relative role of disturbances in addition to tree age and climate in shaping xylem conduits and affecting xylem hydraulic conductivity remains unknown. Methods: We performed an experiment with five different mechanical treatments simulating natural disturbances of juvenile Betula pendula trees (stem scarring, tilting, decapitation, root exposure and stem-base burial).
After three years, trees were cut down, conduit size and density were measured, and specific hydraulic conductivity of each tree ring was calculated. Between-tree and between-year variability in xylem conductivity was decomposed into effects of tree age, climate and disturbances using linear mixed-effects models.
Key Results: Xylem specific hydraulic conductivity dropped significantly after treatment in decapitated, tilted and scarred trees. In the last treatment, wood anatomical adjustment was restricted to the area next to the callus tissue zone; in contrast, specific hydraulic conductivity declined over the entire stem circumference after tilting or decapitation.
The response of trees with buried stems and exposed roots was generally weak. The overall effect of disturbances on inter-annual variability of wood anatomical structure was greater than the contribution of tree age and climate.
Conclusions: Our results indicate that disturbances are important drivers of xylem hydraulic conductivity. Expected increase in frequency and intensity of disturbances may alter theoretical capacity of forest stands to water conductance with feedback to climate.