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Effect of Partial Defoliation on Growth and Carbon Exchange of Two Clones of Young Populus trichocarpa Torr. & Gray

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A controlled environment study was performed to test the effect of two levels of a single partial defoliation on growth, dry weight partitioning, and gas exchange of two contrasting clones of Populus trichocarpa Torr. & Gray. One clone was from a moist habitat in western Washington and the other from a dry habitat in eastern Washington. Trees were partially defoliated (40% or 80% of leaf area removed) at the 25-leaf stage. Height, diameter, leaf area, and rates of net photosynthesis, dark respiration, transpiration, and leaf conductance were determined at the time of defoliation and 3 wk, and 5 wk after defoliation. Biomass distribution was determined following harvest 5 wk after defoliation. Defoliation caused reductions in height, diameter, and biomass in both clones compared to control plants. However, reductions were not proportional to level of defoliation, suggesting compensatory growth was occurring. Total biomass was reduced by 30% and 27% in the western and eastern Washington clones respectively by a 40% defoliation, and 43% and 35% following an 80% defoliation. A 40% defoliation caused an increase in the proportion of biomass in lateral branches of trees of the western Washington clone. An 80% defoliation caused an increase in the proportion of biomass in lateral branches of both clones. Both defoliation treatments reduced leaf area on the main stem but increased leaf area on lateral branches. Both levels of defoliation reduced root biomass of both clones. Specific leaf weight of leaves produced after defoliation in both clones increased. Partial defoliations of 40% and 80% had no effect on net photosynthesis of either clone. Rates of dark respiration in both clones were either unaffected by defoliation or slightly reduced. For. Sci. 39(3):419-431.

Keywords: Net photosynthesis; biomass; compensatory growth; respiration

Document Type: Journal Article

Affiliations: Former Graduate Research Assistant, Department of Natural Resource Sciences, Washington State University, Pullman, WA 99164-6410

Publication date: 1993-08-01

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  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
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    Average time from submission to first decision: 62.5 days*
    June 1, 2016 to Feb. 28, 2017

    Also published by SAF:
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