East of Cascade Range Crest, Oregon and Washington

Structure

The structure of the open, park-like old-growth ponderosa pine forest differs from the Pacific Coast old-growth forest that grows west of the Cascade crest. Prior to 1900, old-growth ponderosa pine forests typically had widely spaced clumps of trees, few shrubs, often grassy, with relatively few dead branches and large logs. Forest structure was the result of both the dry climate and the fire regime.

The open structure of these old-growth forests made walking within them easy. Since 1900, this openness has been replaced by a thick understory and higher tree density and tree diversity. Fire suppression has allowed shrubs to become established and allowed more shade tolerant species to encroach. Timber harvests removed the large trees thus creating gaps for shrubs and competing trees to grow. Interestingly, the arrival of timber harvests has actually increased the density of growth (although trees are rarely reaching the size and age they did in earlier times). The introduction of livestock also impacts the forest structure by the grazing of native grasses which further aid in the establishment of shrubs.

o Moisture and fire and not the only major structural forces of the ponderosa pine forests, but pathogens as well. Some common afflictions are

• The inner bark fungus, comandra blister rust, which causes growth reduction, stem deformity, and mortality of hard pines.
• Pandora moth larvae which eat the needles of ponderosa and lodgepole pine
• and western pine beetle, which is capable of killing apparently healthy Ponderosa pine trees.