A network of more than 130 permanent vegetation plots provides long-term information on patterns and rates of forest succession in most of the major forest zones of the Pacific Northwest. The plot network extends from the coast to the Cascades in western Oregon and Washington and east to ponderosa pine forests in the Oregon Cascades.
Most of the permanent plots were established during two intervals: from 1910 to 1948, and from 1970 to 1989. The earlier plots were established by U.S. Forest Service researchers to quantify timber growth in young stands of important commercial species and to help answer other applied forestry questions. The more recent period of plot establishment began under the Coniferous Forest Biome program of the International Biological Program during the 1970s, and continued under the Long-term Ecological Research program. A broader set of objectives motivated plot establishment since 1970, especially quantification of composition, structure, and population and ecosystem dynamics of natural forests.
Plots have one of three spatial arrangements: (1) contiguous rectangles subjectively placed within an area of homogeneous forest; (2) circular plots subjectively placed within an area of homogeneous forest; and (3) circular plots systematically located on long transects to sample an entire watershed, ridge, or reserve. Rectangular study areas are mostly 1.0 ha or 0.4 ha (1.0 ac) in size (slope-corrected). Circular plots are 0.1 ha (0.247 ac), not corrected for slope. The tree stratum is the focus of work in closed-forest study areas. All trees larger than a minimum diameter (5 cm for most areas) are permanently tagged.
Plots are censused every 5 or 6 years. Attributes measured or assessed at each census include tree diameter, tree vigor, and the condition of the crown and stem. The same attributes are recorded for trees (ingrowth) that have exceeded the minimum diameter since the previous census. In many plots tree locations are surveyed to provide a plot-specific x-y location. A mortality assessment is done for trees that have died since the previous census. The assessment characterizes rooting, stem, and crown condition, obvious signs of distress or disturbance, and the apparent predisposing and proximate causes of tree death.
Andrew Bluhm, Andrew J. Larson, C. Ted Dyrness, Charles B. Halpern, David M. Bell, David Carl Shaw, Donald L. Henshaw, Howard Bruner, James A. Freund, James A. Lutz, Janneke HilleRisLambers, Jerry F. Franklin, Julia A. Jones, Kari B. O'Connell, Kenneth J. Bible, Mark E. Harmon, Mark E. Swanson, Matthew D. Powers, Paul A. Harcombe, Richard E. Brainerd, Robert J. Pabst, Sarah E. Greene, Steven A. Acker, Suzanne M. Remillard, Thornton T. Munger, Todd M. Wilson
The study purpose is to examine long-term trends and dynamics of representative forest types in the Pacific Northwest. The study provides baseline information on long-term rates of tree growth and tree regeneration (ingrowth), causes and characteristics of tree mortality, forest productivity and biomass, and spatial patterns (demography) of ingrowth and mortality.
Long-term observations are the only direct means to document and understand the slow changes of our forests which are dominated by long-lived trees species (individuals commonly live 400 to 1000 years). Long-term observations can quantify levels and dynamics of natural forest structures to be used as guides in ecosystem management. Long-term observations provide the definitive measure of long-term productivity and, thus, sustainable harvest levels. Long-term observations also provide a basis for monitoring effects of global climatic change as well as other changes.