Ecological dynamics

Major Successional Stages of Forestland Development:

HERBACEOUS: Vegetation is dominated by grasses and forbs under full sunlight. This stage is experienced after a major disturbance such as crown fire or tree harvest. Skeleton forest (dead trees) remaining after fire or residual trees left following harvest have little affect on the composition and production of the herbaceous vegetation.

SHRUB-HERBACEOUS: Herbaceous vegetation and woody shrubs dominate the site. Various amounts of conifer tree seedlings (less than 20 inches in height) may be present up to the point where they are obviously a major component of the vegetal structure.

SAPLING: In the absence of disturbance, the conifer seedlings develop into saplings (20 inches to 4½ feet in height) with a range in canopy cover of about 5 to 10 percent. Vegetation consists of grasses, forbs and shrubs in association with whitebark pine, western white pine, lodgepole pine, and white fir saplings.

IMMATURE FORESTLAND: The visual aspect and vegetal structure are dominated by whitebark pine greater than 4½ feet in height. Seedlings and saplings of westerh white pine, white fir and lodgepole pine are present in the understory. Understory vegetation is moderately influenced by a tree overstory canopy of about 10 to 20 percent.

MATURE FORESTLAND: The visual aspect and vegetal structure are dominated by whitebark pine that have reached or are near maximal heights for the site. Dominant trees average ten inches or greater in diameter at breast height. Tree canopy cover is about 35 percent. Understory vegetation is strongly influenced by tree competition, overstory shading, duff accumulation, etc.

OVER-MATURE FORESTLAND: In the absence of wildfire or other naturally occurring disturbances, the tree canopy on this site can become dense. This stage is dominated by whitebark pine that have reached maximal heights for the site. Dominant and codominant trees average greater than ten inches in diameter at breast height. Understory vegetation is sparse due to tree competition, overstory shading, duff accumulation, etc. Canopy cover is commonly greater than 35 percent.

Climax communities of whitebark pine are relatively open and favorable to establishment of this moderately shade-tolerant species. Clark's nutcrackers, by caching seed in forested sites, maintain climax communities of whitebark pine. Nutcrackers are attracted to open sites for seed caching and are efficient in seeding burned areas. Natural perturbations are important in shaping the structure of whitebark pine communities. Climatic factors such as damaging winds, ice storms, snowloads, summer frost, and winter desiccation prevent stand closure. This rigorous microclimate also allows competition-intolerant species like whitebark pine to coexist indefinitely with their tolerant competitors.

Whitebark pine wood is highly flammable even when green. Fire severity is low where surface fuels are sparse, and the resulting underburn kills mostly small trees and fire-susceptible overstory species, leaving live, mature whitebark pine. Whitebark pine seedlings establish on open sites created by fires. Late-successional species dominate when fire return intervals are long, but fires were historically likely to return before whitebark pine was successionally replaced. Although whitebark pine recruitment is depressed in many areas, whitebark pine seedlings were historically highly competitive with other conifer species in the postfire environment.

Fire Ecology:
Fire kills gooseberry, however, regeneration is favored by fire because scarification of soil-stored seed generally enhances germination in gooseberry. Western needlegrass is moderately damaged by fire. The recovery time is between 3 and 5 years. Ross’ sedge survives fire through buried seed with long-term viability. These seeds germinate after heat treatment. Ross’ sedge’s rhizomes survive low- to moderate-severity fires. Whitebark pine ecosystems have a mixed-severity fire regime of widely ranging fire intensities and frequencies. Prior to 1900, fire return intervals ranged from 30 to 350+ years. Lightning is the major cause of fires in most stands although accidental fires have resulted due to increased recreation activity in these forests. Mixed-severity fires create complex landscapes of dead whitebark pine stands intermingled with live stands of different ages. Whitebark pine stands also experience nonlethal surface fires and infrequent stand-replacement fires. Infrequent stand-replacement fires and small patch fires are important components of whitebark pine's fire ecology. Two strategies allow whitebark pine to survive in fire-prone ecosystems: survival of large trees, and postfire seedling establishment facilitated by Clark's nutcrackers.