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 from permanent plot installations are available through the web site for the HJ Andrews Long-Term Ecological Research Program:


We request that data users contact the program coordinator ( ) 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 by the HJ Andrews Experimental Forest research program, funded by the National Science Foundation's Long-Term Ecological Research Program (DEB 1440409), US Forest Service Pacific Northwest Research Station, and Oregon State University.”