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Publication Title:   Physiognomic development of Pseudotsuga forests in relation to initial structure and disturbance intensity

Year:  1990     Publication Type:  Journal Article

H. J. Andrews Publication Number:  1129

Citation:  Halpern, Charles B.; Franklin, Jerry F. 1990. Physiognomic development of Pseudotsuga forests in relation to initial structure and disturbance intensity. Journal of Vegetation Science. 1: 475-482.

Online PDF:  http://andrewsforest.oregonstate.edu/pubs/pdf/pub1129.pdf

Abstract:  Physiognomic patterns may vary significantlyduring succession despite a tendency for larger-growthforms to gradually replace smaller ones. Development ofunderstory structure was observed for 25 yr after harvestof Pseudotsuga forests on two sites in the western Cas-cade Range, Oregon. We examine the influences ofdisturbance intensity and initial vegetation structure onthe origin, direction, and rate of physiognomic change. Broad-scale changes in vegetation structure differedbetween sites. On Watershed 1, herbs dominated for 11yr, after which shrubs became co-dominant. In contrast,Watershed 3 never exhibited a distinct, transitional shrubphase - herbs dominated for 18 yr, after which treesassumed co-dominance. The pattern and rate of physiognomic successionalso varied among pre-disturbance plant communitiesand with disturbance intensity. Differences amongcommunities largely corresponded with initial vegeta-tion structure, reflecting the disturbance tolerance offorest herbs and shrubs. Canopy closure occurred mostrapidly in the initially depauperate, but tree-dominatedCoptis community. Along the disturbance gradient,shifts from herb to shrub dominance occurred earlier onburned than on unburned sites due to rapid developmentof invading shrubs, whose germination and establish-ment were stimulated by fire. However, subsequenttransitions to tree dominance showed no clear relationshipwith disturbance intensity. These long-term trends suggest that pre-disturbancecommunity structure and disturbance intensity are majordeterminants of physiognomic succession, but that theireffects may be modified by historical or stochastic fac-tors such as limited seed availability or local fluctuationsin weather. Keywords: Clearcut logging; Community structure; Forestunderstory; Growth-form; Seral origin; Slash burning;Succession.

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Author Links
Halpern ,  Charles   B.
Franklin ,  Jerry   F.

Clearcut logging
Community structure
Forest understory
Plant populations
Slash burning
Slash/broadcast burning

Andrews Watershed 1
Andrews Watershed 3