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Apparent Photosynthesis of Douglas-Fir in Relation to Silvicultural Treatment

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Abstract:

A study of apparent photosynthesis of Pseudotsuga menziesii (Mirb.) Franco in its natural environment was carried out over a period of 2 1/2 years in western Washington using a Hartmann-Braun U.R.A.S. infra-red gas analyzer. For the latter part of the study, a continuous automatic recording was made of air temperature, light intensity and relative humidity inside each of the sampling cuvettes by means of a 24-line 2-millivolt recorder in conjunction with thermocouples and photo-cells as sensing elements. After a 1 1/2-year "calibration period" during which the characteristic seasonal net assimilation patterns were determined for five trees in each of the dominant, co-dominant and suppressed crown classes, severe treatments were carried out to determine their effects on the characteristic patterns previously observed. Thinning, pruning and decapitation increased photosynthetic efficiency of the foliage on a unit dry weight basis during the first year after treatment. Fertilization had no appreciable effect on the rates of apparent photosynthesis over this period. To determine whether the considerable differences in net assimilation rates observed between naturally growing trees were due to genetic variability, similar treatments were carried out on ramets of a 4-year old clone; however, no reduction in inter-tree variability in net assimilation rate was observed.

Document Type: Journal Article

Affiliations: The Staff of the Scaool of Forestry, Univ. of Calif., Berkeley

Publication date: December 1, 1964

More about this publication?
  • 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.
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