TREE REGENERATION FOLLOWING CLEAR-CUT LOGGING IN RED FIR FORESTS OF CALIFORNIA

We sampled red fir (Abies magnifica) clearcuts of various age to ident ify site factors that predict successful regeneration. During three fi eld seasons, 113 clearcuts were sampled in five national forests along the western slope of the Sierra Nevada between 37 and 40 degrees N la titude. They were 4-32 years old and 2028 ha in area, had slopes of 3- 30 degrees that cumulatively faced all directions, and were situated o n slope faces that ranged from concave, convex, constant, to mixed. We recorded the cover of all herbs, shrubs, and tree saplings, and the d ensity of saplings by age class. A total of 208 taxa were encountered. Both red fir regeneration (represented by sapling cover) and invasive ness (the reciprocal of clearcut age minus average red fir sapling age ) were maximum on gentle, northeast-facing, concave slopes; in clearcu ts with maximum edge (the ratio of perimeter to area); and a relativel y high latitudes and relatively low elevations: Both shrub and herb co ver were positively correlated with red fir regeneration, indicating t hat management suppression of these species is not necessary. Microcli mate models showed that regeneration, invasiveness, and canopy growth were most negatively correlated with daily summer insolation and most positively correlated with late snow melt, the latter resulting from d eep snowpacks and/or late snow melt on north-facing slopes. In general , abundant natural red fir regeneration occurred only after a post-log ging lag phase of 12 years. (C) 1998 Elsevier Science B.V.