Mature and old-growth forests are icons of the Pacific Northwest. In the parks of the North Coast and Cascades Inventory and Monitoring Network (NCCN) forests range from coastal rainforests with massive trees draped with mosses and ferns and surrounded by dense understories; to areas with drought-adapted Ponderosa pines; to high-elevation subalpine fir forests interspersed with meadows just below treeline. These forests, in turn, are the foundation for other biotic communities constituting Pacific Northwest ecosystems.
Climate change, air pollution, invasive species and other stressors threaten forest structure, species composition and abundance, thereby threatening the quality and quantity of habitat for terrestrial birds and wildlife. In particular, climate change and air pollution are expected to be the greatest threats to national parks in the Pacific Northwest. Changes in forest structure and composition will also alter the chemistry of water moving from terrestrial to aquatic systems. Consequently, forest monitoring is a fundamental part of the overall monitoring plan for the parks of NCCN. Tree recruitment, growth, and mortality are sensitive indicators of ecological change that can only be documented and understood through detailed, long-term observations. Increases in tree mortality have recently been reported for western North America, demonstrating the utility of long-term forest monitoring.