- Succession in sub-boreal forests of West-Central British Columbia - 721 Journal of Vegetation Science 14: 721-732, 2003 © IAVS; Opulus Press Uppsala. Abstract. Structural and compositional changes were ana- lysed over the course of 400+ yr of post-fire succession in the sub-boreal forests of west-central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approxi- mately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca ¥ engel- mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub-boreal forests contain few tree species, successional changes were pronounced, with struc- ture changing more than composition across the chrono- sequence. Keywords: Abies lasiocarpa; Chronosequence; Disturbance; Diversity; Multivariate Ordination; Picea; Pinus contorta; Post-fire succession; Stand structure. Abbreviations: CWD = Coarse Woody Debris; DCA = Detrended Correspondence Analysis; DBH = Diameter at Breast Height; PCA = Principal Component Analysis. Nomenclature: Douglas et al. (1989-1994). Succession in sub-boreal forests of West-Central British Columbia Clark, Donald F. 1,2* ; Antos, Joseph A. 1,3 & Bradfield, Gary E. 4 1 Department of Biology, University of Victoria, P.O. Box 3020 STN CSC, Victoria, B.C., Canada V8W 3N5; 2 Tetra Tech, Inc., Research and Development Division, 3746 Mt. Diablo Blvd, Suite 300, Lafayette, California, 94549, USA; 3 E-mail jantos@uvic.ca; 4 Department of Botany, University of British Columbia, 6270 University Blvd., Vancouver, B.C., Canada V6T 1Z4; E-mail garyb@interchange.ubc.ca; * Corresponding author; Fax +19252830780; E-mail donald.clark@tetratech.com Introduction Forest ecosystems can be characterized and evalu- ated in terms of both their structure and composition (Peet 1992). Structure is often measured by characteris- tics of trees, including basal area and density; species composition can be described by presence or abun- dance. Many studies have examined how forest struc- ture and composition are related, and how they change during succession (Shugart 1984; Pickett & White 1985; Smith & Huston 1989). In the boreal and sub-boreal forests of North America, for example, a number of studies have considered temporal changes in forest struc- ture and composition during secondary succession, of- ten by using a chronosequence approach (e.g. Brulisauer et al. 1996; Kneeshaw & Burton 1997; Bergeron 2000; De Grandpré et al. 2000; Gauthier et al. 2000). Because changes in structure and composition may be only weakly related (e.g. Arsenault & Bradfield 1995; Brulisauer et al. 1996), assessment of both simultaneously is impor- tant when evaluating successional changes. Fundamen- tal questions concern the synchrony of changes in struc- ture and composition, and the relative amounts of change in these components during secondary succession. Struc- tural changes may predominate where post-disturbance cohorts persist throughout succession, whereas compo- sitional changes have traditionally been used as the key variable during succession. However, generalizations are tenuous and further studies directly comparing struc- tural and compositional changes are needed; such stud- ies are scant in the sub-boreal forests of North America. The timing of structural and compositional changes is a key aspect of succession that is important to both the theory and management of forest ecosystems. Events early in forest development such as the establishment and growth of trees can be critical in explaining subse- quent successional changes. For example, several stud- ies have evaluated the timing of tree species recruit- ment in terms of successional stage and substrate avail- ability (e.g. Galipeau et al. 1997; Simard et al. 1998;