Quantifying organizational change after fire in lodgepole pine forest understorey

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Abstract
Temporal changes in community organization were examined in a 300+ year chronosequence of understorey vegetation data from lodgepole pine forests recovering from fire in central British Columbia. Changes between six age-classes of forest were quantified as shifts in the orientation of equal frequency ellipses depicting the main correlation structure of the vegetation in multivariate space. Different developmental trajectories were obtained for sites differing in soil moisture status. Mesic sites displayed sharp changes in community organization within the first 100 years following fire but only gradual changes thereafter. In contrast, xeric sites exhibited sharp organizational changes at the beginning and again toward the end of the chronosequence. The unanticipated behaviour of dry sites is interpreted as reflecting a lower degree of integration of such communities resulting from their particular species composition and susceptibility to biotic disturbance. Analyses of separate life-form strata indicated continuing organizational changes in shrubs, forbs–grasses, and lichens, but relative stability in bryophytes after 100 years. The movement through time of mesic sites towards increasing persistence is predicted from an interpretation of ecological succession as a process of self-organization, directed by principles of nonequilibrium thermodynamics. Keywords: postfire succession, Pinus contorta forest understorey, plant community organization, equal frequency ellipses, principal components analysis, self-organization, nonequilibrium thermodynamics.