Tree regeneration following clearcut logging in red fir forests of California

Abstract

We sampled red fir ( Abies magnifica) clearcuts of various age to identify site factors that predict successful regeneration. During three field seasons, 113 clearcuts were sampled in five national forests along the western slope of the Sierra Nevada between 37 and 40°N latitude. They were 4–32 years old and 2028 ha in area, had slopes of 3–30° that cumulatively faced all directions, and were situated on slope faces that ranged from concave, convex, constant, to mixed. We recorded the cover of all herbs, shrubs, and tree saplings, and the density of saplings by age class. A total of 208 taxa were encountered. Both red fir regeneration (represented by sapling cover) and invasiveness (the reciprocal of clearcut age minus average red fir sapling age) were maximum on gentle, northeast-facing, concave slopes; in clearcuts with maximum edge (the ratio of perimeter to area); and a relatively high latitudes and relatively low elevations. Both shrub and herb cover were positively correlated with red fir regeneration, indicating that management suppression of these species is not necessary. Microclimate 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 deep snowpacks and/or late snow melt on north-facing slopes. In general, abundant natural red fir regeneration occurred only after a post-logging lag phase of 12 years.