Masters Thesis Abstract by Rhonda L. Little (1992)

Subalpine forest regeneration following fire was studied at two locations northeast of Mount Rainier, Washington, that burned around 1902. Tree establishment dates where determined by bud scars and/or tree rings. These dates were compared to local climatic records using multiple and logistic regression to identify potential relationships between seasonal climate and tree establishment. The influence of seed availability and microsite features on forest regeneration were also explored.

There was a delay in regeneration of approximately 30 years and most trees established in the 1950’s, 1977, 1983, and 1989. The dominance of trees less than l meter tall at both sites indicates that trees may still be establishing on these burns. Establishment was correlated with warm, dry springs with low snow pack. The influence of summer temperature and precipitation on establishment varied between sites, which may reflect differential moisture stress characteristic of each site. The dominance in regeneration by Abies lasiocarpa suggests that the forests above each burn composed primarily of this species supplied the primary seed source for tree establishment. Cone production may influence the magnitude of annual establishment, but only when other conditions are favorable to tree establishment. Microsite features appear to have a greater influence than seed abundance on tree establishment. More than 50% of the recently established trees (less than 50 cm tall) were found near larger trees and shrubs, and few (less than 10%) trees were found growing in mineral soil without any microsite features nearby. Older trees (greater than 50 cm tall) were often observed near woody debris. Microsites favorable to tree establishment following fire may change over time as snags fall and trees establish.

General circulation models predict a warmer climate in the future; however, the resolution of their predictions concerning changes in precipitation are not sufficient to project responses in subalpine forest regeneration following fire. The response of forest regeneration to changes in climate will depend on the magnitude and seasonality of changes in weather, especially precipitation. Tree establishment may be enhanced if less winter precipitation that falls as snow reduces spring snow depth and possibly lengthens the growing season. However, drier summers may result in seedlings experiencing moisture stress, especially on sites with high solar radiation and well-drained soils.