General Patterns of Vegetation GrowthIn general, post-fire revegetation is rapid and profuse in the Oregon Ecoregion. Fire-adapted plants are able to regenerate from natural seed sources or sprout from unburned stumps or stems. Shrubs and hardwoods that sprout tend to dominate the early post-fire environment. This early plant community can persist for 20 years or longer.
The availability of a natural seed source is critical when relying on natural regeneration for tree establishment instead of planting. In the Klamath-Siskiyou Ecoregion, a natural seed source is available in most instances even after a severe fire. Within the boundaries of the Biscuit Fire, for example, many locations experienced fire of sufficient severity to kill all the trees present. Yet, often a living conifer tree that could act as a seed source was present within 400 meters of these severely burned areas. Conifer seeds can disperse this distance, which allows for natural regeneration. In fact, natural conifer regeneration generally was profuse except in the middle of large, severely burned patches and on southern, low-altitude sites.
Soil and topography influence the success and density of regenerating conifers. In the Klamath-Siskiyou Ecoregion, coarse-grained soils support lower densities of conifer regeneration than fine-grained soils, probably because the latter have a greater capacity to retain water. Furthermore, the combined influences of altitude and the amount of heat an area potentially receives, known as heat load, affect conifer regeneration more than competitive interactions with other plant species. In a practical sense, this means that it is more difficult to achieve regeneration on low-altitude, steep, southern-facing sites than on moist, high-altitude sites. Areas dominated by pines naturally tend to be in some of the driest areas, and natural pine regeneration can be especially difficult to achieve. In fact, in managed areas where ponderosa pine have been planted, pine densities are frequently greater than pine densities in naturally regenerating unmanaged areas.
Seedling survival is as important to forest regeneration as the dispersal and germination of seeds. Many factors influence survival, including soils, precipitation, temperature, animal predation, and site disturbance. Probably none of these factors is as debated as the logging of fire-damaged trees, a practice known as salvage logging. Research provides some insights regarding effects on seedlings. For example, when researchers looked at the areas logged 2 years after the Biscuit Fire, they found conifer seedlings much less abundant in salvage-logged areas than in unlogged areas. Possibly this was because seedlings were killed by site disturbance associated with logging. If early loss does occur, it might be inconsequential over the long term because many seedlings get started after the second year (see bar graph, right). It also is known that when severely burned forests are left to naturally regenerate, successful, abundant conifer recruitment continues for years.