QUANTIFYING ORGANIZATIONAL-CHANGE AFTER FIRE IN LODGEPOLE PINE FORESTUNDERSTOREY

Temporal changes in community organization were examined in a 300+ yea r chronosequence of understorey vegetation data from lodgepole pine fo rests recovering from fire in central British Columbia. Changes betwee n six age-classes of forest were quantified as shifts in the orientati on of equal frequency ellipses depicting the main correlation structur e of the vegetation in multivariate space. Different developmental tra jectories were obtained for sites differing in soil moisture status. M esic sites displayed sharp changes in community organization within th e first 100 years following fire but only gradual changes thereafter. Ln contrast, xeric sites exhibited sharp organizational changes at the beginning and again toward the end of the chronosequence. The unantic ioated behaviour of dry sites is interpreted as reflecting a lower deg ree of integration of such communities resulting from their particular species composition and susceptibility to biotic disturbance. Analyse s of separate life-form strata indicated continuing organizational cha nges in shrubs, forbs-grasses, and lichens, but relative stability in bryophytes after 100 years. The movement through time of mesic sites t owards increasing persistence is predicted from an interpretation of e cological succession as a process of self-organization, directed by pr inciples of nonequilibrium thermodynamics.