Study design

Plots have one of two spatial configurations: (1) a single contiguous polygon (typically square or rectangular), ranging from 0.25 ha to 4.5 ha in area; and (2) fixed-radius (circular) plots distributed systematically on transects. In all plots, trees meeting a minimum diameter threshold are tagged.

Data collection

  • Plots are measured every 5 or 6 years.
  • Live trees: At each census, we record the diameter (DBH), vigor, crown condition and stem condition of live trees and ingrowth that meet the minimum DBH threshold.
  • Mortality: 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 predisposing and proximate causes of tree death if apparent from diagnostic symptoms.
  • Many of the permanent plots are also stem-mapped, which allows for analysis of fine-scale spatial patterns of forest processes.
  • In a subset of plots we track successional development of the understory vegetation (e.g., species richness, cover and biomass).

Accessing the data

Data and data summaries from permanent plot installations are available via the PNW-PSP Data Portal:


Metadata for these data and summaries can be found here:


Data Acknowledgment

We request that data users contact the program coordinator (Andrew Bluhm, ) before initiating any data analyses. If the data are used in any reports, presentations or publications, we ask that you include the following acknowledgment: "Data were provided courtesy of the Pacific Northwest Permanent Sample Plot Program, in partnership with the HJ Andrews Experimental Forest and Long Term Ecological Research (LTER) program, which are administered cooperatively by the USDA Forest Service Pacific Northwest Research Station, Oregon State University, and the Willamette National Forest. This material is based upon work supported by the National Science Foundation under the LTER Grants: LTER8 DEB-2025755 (2020-2026) and LTER7 DEB-1440409 (2012-2020)."

this project got started in 2015, with Fox Peterson doing the initial Python scripting based on my SAS code.  Hans Luh then took on the project in 2018, thanks to Don Henshaw who made the project one of the priorities for the LTER data management team.  Hats off to Don, Hans, Suzanne and Keith for everything they’ve done to bring it to fruition.  The aims of the project were twofold: (1) for data users, we wanted to take the guesswork out of creating their own data summaries from raw data, given the various sampling designs and idiosyncrasies of our plot network; and (2) thereby reducing the workload of the PSP coordinator.