Structure and Dynamics of Red Fir Forests, Lake Tahoe Basin, Nevada
Andy Scholl
Abies magnifica (red fir) forests in the Sierra Nevada are known to demonstrate both shade tolerant and disturbance related regeneration making it difficult to understand the role of disturbances in the regeneration dynamics of the forests. We used detailed stem mapping, stand structural analysis and cross-dated fire scar samples to identify the relationships between disturbances and stand structure (i.e. age, size, and spatial patterning) in an old growth red fir forest in the Lake Tahoe Basin. All trees >5 cm dbh within four 0.5-ha plots were aged and mapped. Spatial analysis with Ripley’s K(d) statistic was used to identify clumping of seedlings and saplings at distances up to 12 m. In contrast, large, old individuals were clumped at all scales up to 25 m within plots. We used Moran’s I statistic to identify positive spatial autocorrelation between tree ages at distances up to 10m. The mean point fire return interval was 69 years (range 34-175 years) for the 100-ha study area. The lack of correspondence between fire scars on cross-dated samples suggests small, patchy burns, rather than large, widespread fires. The age structure indicated continuous recruitment with two regeneration peaks that coincide with fire dates (1610 and 1770). The spatial pattern and fire scars imply that small-scale events influence the forest structure. However, the corresponding pattern between age structure, growth suppressions, and fire occurrences suggest that regeneration in A. magnifica forests is strongly influenced by infrequent, severe fires, although continuous regeneration occurs between events.
This project was supported with funding from the National Forest Service
