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Structure, Diversity, and Biophysical Properties of Klamath's Old-Growth Forests

Released: 2016
WERC Publication Brief: Structure, Diversity, and Biophysical Properties of Klamath's Old-Growth Forests. Updated December 2016.

This Brief Refers To: van Mantgem, P and DA Sarr. 2015. Structure, diversity, and biophysical properties of old-growth forests in the Klamath region, USA. Northwest Science 89(2): 170-181. doi:10.3955/046.089.0208

Old-growth forests are home to endangered species, provide clean water, and store massive amounts of carbon. They may also be more resistant and resilient to severe wildfires and droughts than younger forests. However, the old-growth forests of the Klamath region of northern California and southern Oregon face a wide range of stressors, including invasive species, climate change, and, in some cases, the potential for large and severe fires due to a build-up of fuels.

Researchers need information on the relationship between the Klamath region’s current physical environment and its old-growth forest structure to predict how drought and other threats will affect these forests. In a study published online with Northwest Science, researchers from the USGS and National Park Service provided present-day benchmarks for critical elements of old-growth forest structure across a climatic gradient ranging from the coast to dry interior sites. The team began by establishing 16 large (1 ha) forest plots where all trees with stems >5 cm in diameter were identified to species and mapped. Then, they estimated evapotranspiration—a measure of average precipitation and temperature—and studied elements of forest structure, like the number of distinct tree species in the landscape.

Estimates of evapotranspiration predicted many fundamental measures of forest structure, including plot basal area, stem size-class inequality, tree species diversity, and, to a lesser extent, tree species richness. Analyses of the spatial arrangement of trees indicated significant clumping at small spatial scales (0 to 10 m).

Predictions of future climate within the study area indicate changes dominated by increasing drought. By the end of this century, several of the study sites within the Klamath region may have difficulty supporting coniferous forests. While these plots provide a picture of current conditions, continued monitoring of these stands is needed to describe forest dynamics and to detect forest responses to ongoing and future stressors.

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This product is associated with the following project:
Taking the pulse of the forest: Klamath Network old-growth forest plots

Management Implications
  • Many aspects of old-growth forest structure, like stand basal area and tree species diversity, were correlated with climate.
  • With continued monitoring, the network of plots can serve as valuable benchmarks to measure changes in forest conditions.
  • Old-growth forests did not exhibit uniform tree spatial patterns like those in some forest restoration treatments, indicating a diversity of spatial arrangements in intact forests.

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