Canopy light transmittance in Douglas-fir-western hemlock stands

Geoffrey G. Parker, Melinda Davis, Saharah Moon Chapotin

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

We measured vertical and horizontal variation in canopy transmittance of photosynthetically active radiation in five Pseudotsuga menziesii (Mirb.) Franco-Tsuga heterophylla (Raf.) Sarg. (Douglas-fir-western hemlock) stands in the central Cascades of southern Washington to determine how stand structure and age affect the forest light environment. The shape of the mean transmittance profile was related to stand height, but height of mean maximum transmittance was progressively lower than maximum tree height in older stands. The vertical rate of attenuation declined with stand age in both the overstory and understory. A classification of vertical light zones based on the mean and variance of transmittance showed a progressive widening of the bright (low variance and high mean) and transition (high variance and rapid vertical change) zones in older stands, whereas the dim zone (low variance and mean) narrowed. The zone of maximum canopy surface area in height profiles, estimated by inversion of transmittance profiles, changed from relatively high in the canopy in most young stands ("top-heavy") to lower in the canopy in older stands ("bottom-heavy"). In the understory, all stands had similar mean transmittances, but the spatial scale of variation increased with stand age and increasing crown size. The angular distribution of openness was similar in all stands, though the older stands were less open at all angles than the younger stands. Understory openness was generally unrelated to transmittance in the canopy above. Whole-canopy leaf area indices, estimated using three methods of inverting light measurements, showed little correspondence across methods. The observed patterns in light environment are consistent with structural changes occurring during stand development, particularly the diversification of crowns, the creation of openings of various sizes and the elaboration of the outer canopy surface. The ensemble of measurements has potential use in distinguishing forests of differing ages that have similar stature.

Original languageEnglish (US)
Pages (from-to)147-157
Number of pages11
JournalTree Physiology
Volume22
Issue number2-3
StatePublished - 2002
Externally publishedYes

Fingerprint

Hemlock
Pseudotsuga
transmittance
Pseudotsuga menziesii
canopy
Light
Crowns
Tsuga
understory
tree crown
Cascade Mountain region
Tsuga heterophylla
Radiation
stand structure
overstory
photosynthetically active radiation
structural change
leaf area index
surface area
taxonomy

Keywords

  • Attenuation
  • Canopy structure
  • LAI
  • Old-growth
  • PAR
  • Spatial variation

ASJC Scopus subject areas

  • Forestry
  • Plant Science

Cite this

Parker, G. G., Davis, M., & Chapotin, S. M. (2002). Canopy light transmittance in Douglas-fir-western hemlock stands. Tree Physiology, 22(2-3), 147-157.

Canopy light transmittance in Douglas-fir-western hemlock stands. / Parker, Geoffrey G.; Davis, Melinda; Chapotin, Saharah Moon.

In: Tree Physiology, Vol. 22, No. 2-3, 2002, p. 147-157.

Research output: Contribution to journalArticle

Parker, GG, Davis, M & Chapotin, SM 2002, 'Canopy light transmittance in Douglas-fir-western hemlock stands', Tree Physiology, vol. 22, no. 2-3, pp. 147-157.
Parker, Geoffrey G. ; Davis, Melinda ; Chapotin, Saharah Moon. / Canopy light transmittance in Douglas-fir-western hemlock stands. In: Tree Physiology. 2002 ; Vol. 22, No. 2-3. pp. 147-157.
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