Early secondary succession following clearcuts in red fir forests of the Sierra Nevada, California

Vegetation was quantified for clearcuts, age 4-32 yr, of Abies magnified Andr. Murray old-growth forests along the west face of the central Sierra Nevada. TWINSPAN analysis of 113 sites × 87 common taxa generated six ecofloristic units mainly related to each other on a time-since-harvest basis, but also exhibiting correlations with slope, elevation, latitude, soil depth, harvest area, and ratio of edge-to-area. Nearly half the taxa showed non-random distributions among the TWINSPAN units, but only a minority of those could be related to time since harvest. The herbs Gayophytum diffusion Torrey & A. Gray, Phacelia hydrophylloides A. Gray, and Sidalcea glaucescens E. Greene were most significantly associated with pioneer sites age 4-10 yr since harvest, whereas the shrubs Ceanothus cordu-latus Kellogg and Ribes roezlii Regel and the herb Viola pinetorum E. Greene were most significantly associated with later serai sites 16-32 yr since harvest. CCA ordination diagrams arranged the 113 sites along a continuum, rather than breaking them up into units, and this approach also revealed a strong relationship between site vegetation and time since harvest. The general path of early succession did not show dramatic floristic shifts nor was there any significant change in species richness over time. The first 32 yr of secondary succession probably represents only one-seventh the time necessary to attain old-growth status.