Geology topics

Nathan Poage

Publications and source records attributed to Nathan Poage.

3 recordsLinked to original sources

USGS2005

Tree species and size structure of old-growth Douglas-fir forests in central western Oregon, USA

We characterized the structure of 91 old-growth forests dominated by Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), using inventory data from recent (1985–1991) old-growth timber sales in western Oregon. The data were complete counts (i.e., censuses) of all live trees >20 cm diameter at breast height (dbh, measured at 1.4 m above the ground) over a mean area of 17.1 ha at each site. Across all sites, Douglas-fir accounted for 79% of the total basal area (m 2 /ha) of all species. The average density of trees >100 cm dbh was 19 trees/ha and 90% of these trees were Douglas-fir. Species other than Douglas-fir constituted only about 20% of the total basal area at each old-growth site, on average, but largely accounted for the structural variation between sites. We used multivariate techniques such as cluster analysis, indicator species analysis, and ordination with non-metric multidimensional scaling (NMS) to identify and characterize six structural groups in terms of basal area in different species–diameter classes. Almost 97% of the structural information was captured by the first ( r 2 = 0.841) and second ( r 2 = 0.128) NMS ordination axis. Geographic information systems (GIS) analysis and NMS indicated that the structural differences among groups of sites were associated with moisture, temperature, and elevation gradients within the study area. This type of analysis can be used to help define differences among old-growth forests and to set local structural goals for growing forests with old-growth characteristics.

Oregon↗

USGS2003

Managed forest reserves: preserving diversity

As part of the Northwest Forest Plan, large areas have been designated on many federal forests in western Oregon to provide critical habitat for plants and animals that are associated with old-growth habitat. Some of the structural characteristics often considered typical of old forests include large-diameter overstory trees, large standing and fallen dead trees, and one or more understory layers (Figure 1). However, not all of these areas are currently in old-growth conditions. Many of them contain young (<40 years), uniformly dense Douglas-fir stands that regenerated after timber harvest. The original management goal for these stands was to produce high yields of timber and associated wood products. With implementation of the Northwest Forest Plan in 1994, the management objective shifted to accelerating development of old-growth characteristics by enhancing structural and biological diversity of these areas. A major challenge today is how to promote these structural characteristics in younger stands. Researchers have been asking if lessons can be learned from the development of our current old growth and applied to management of younger stands. Dr. John Tappeiner and his university and agency research partners are helping to answer this question by examining the differences in development between old-growth and young stands in western Oregon. Understanding how the structure of these old forests developed may provide a model for management of young stands, especially when the management goal is to provide habitat for species associated with older forests.

Fact Sheet↗

USGS2002

Long-term patterns of diameter and basal area growth of old-growth Douglas-fir trees in western Oregon

Diameter growth and age data collected from stumps of 505 recently cut old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees at 28 sample locations in western Oregon (U.S.A.) indicated that rapid early and sustained growth of old Douglas-fir trees were extremely important in terms of attaining large diameters at ages 100a??300 years. The diameters of the trees at ages 100a??300 years (D100a??D300) were strongly, positively, and linearly related to their diameters and basal area growth rates at age 50 years. Average periodic basal area increments (PAIBA) of all trees increased for the first 30a??40 years and then plateaued, remaining relatively high and constant from age 50 to 300 years. Average PAIBA of the largest trees at ages 100a??300 years were significantly greater by age 20 years than were those of smaller trees at ages 100a??300 years. The site factors province, site class, slope, aspect, elevation, and establishment year accounted for little of the variation observed in basal area growth at age 50 years and D100a??D300. The mean age range for old-growth Douglas-fir at the sample locations was wide (174 years). The hypothesis that large-diameter old-growth Douglas-fir developed at low stand densities was supported by these observations.

Canadian Journal of Forest Research↗