Sites were originally selected from common and contrasting plant communities in established reference stands. The original 19 sites represent three vegetation zones and along environmental gradients of elevation and moisture. Other sites were added in the late 1970's with some original sites discontinued. The network was collapsed in the 1990's, and the current sites are primarily used for monitoring long-term changes in temperature. The following link summarizes general vegetation zones: http://andrewsforest.oregonstate.edu/data/studies/ms05/meta/veg_zones.pdf.
Zobel, D. B.; McKee, W. A.; Hawk, G. M., and Dyrness, C. T. Correlation of forest communities with environment and phenology on the H.J. Andrews Experimental Forest, Oregon. In: Waring, R. H. and Edmonds, R. L., eds. Integrated research in the coniferous forest biome. Seattle, WA: Coniferous Forest Biome; 1974; Bulletin 5 pp. 48-56.
Originally, thermographs (later replaced with data loggers and thermistors) were installed in each reference stand to continuously monitor air and soil temperature. Air temperature was generally measured at 1 meter above the forest floor and insulated originally with an A-frame shield (later replaced with pvc-constructed shields). Many of the probes were moved to 3 meter heights in winter during the 1980's above snow level, and reinstalled at 1 meter for the summer. In the late 1980's and early 1990's, probes were established permanently at 1 meter above average winter snow level. Soil temperatures were measured nearby with probes buried at 20 cm depth (later, three probes were buried at 10, 20, and 30 cm at most sites). Generally, sites are visited and charts/CR10 records collected on a monthly basis.
Other history: In 1987, Campbell Scientific CR-10 data loggers replaced 8 circular chart installations. On seven of these sites, soil temperature is now measured at three depths: 10, 20, 30 cm. On the other CR-10 site (RS13), additional air and soil probes were added in the adjacent meadow, and soil temperature is measured at 20 cm depth. In the summer of 1991, the chart installations were removed from theCR-10 sites (RS 2,4,12,13,14,20,24,26) where they were serving as a backup to the CR-10. All sites are under the forest canopy, with the exception of RS13 meadow site, and RS86, RS89, and TS38 which were clearcuts now overgrown (as of 1990's).
Mean daytime air and soil temperatures were used to calculate a temperature-growth index (TGI). This index weighs the temperature by their relative effects upon growth of pseudotsuga menziesii seedlings in a controlled environment. This is intended to provide a representation of temperature more closely related to plant growth (Zobel et al. 1974). It is used as a uniform index to compare the plant communities measured, primarily in the 1970's.
Plant moisture stress was measured until 1975 on saplings under the stand using a pressure chamber. The value (atmospheres) represents the negative of the pressure potential of the xylem sap. The value used is the greatest average stress recorded on a single date at each site. (Note: data is only available 1973-1976 and perhaps was developed by algorithm from earlier pressure bomb data).
Please follow this link to see a general description and history of air temperature measurements for these stations:
http://andrewsforest.oregonstate.edu/data/studies/ms01/meta/air.htm
Temperature data has been measured with a variety of instruments:
Probes were housed in locally designed PVC radiation shields from the 1980s until the mid 2000s. Gill radiation shields replaced the PVC shields at all of the benchmark sites after a significant concurrent comparison was made. Aspirated shields are also now in use. The original 1.5 meter Primary Met Station sensor was housed in a Cotton Region Shelter. Historical methods included Rustrak strip charts with thermister where air temperature is measured by a Yellow Springs Instruments linear thermistor in a standard Cotton Region Shelter and continuously recorded on a separate 30-day Rustrak strip chart scaled from -10 degrees C to 40 degrees C.
Data loggers are typically Campbell Scientific (CR10, CR21X, CR500, or CR23X). Early data loggers used in the 1980s are Interface Instrument models M-2, M-3, and M-4.
Please follow this link to see a general description and history of soil temperature measurements for these stations:
http://andrewsforest.oregonstate.edu/data/studies/ms05/meta/soi.htm
Starting in 1997-1998, mean six-hourly soil temperature are measured at the sites at three depths (10, 20, 30 cm). Thermocouple wire was used in the earliest measurements and were protected inside of a PVC structure. Soil temperature was digitized on a sunrise to sunrise basis. A some point in the 1980's, depending on site, a true daily summary is available due to the use of a revised digitizing program. The revised program produces output similar to the CR10 dataloggers used for thermographs. In 1997-1998, depending on site, a CR10 datalogger is installed, and additional soil depths at 10 and 30 cm are added. The Partlow chart recorder was maintained until 31 May 1990 as a backup, and then removed.
Please follow this link to see a general description and history of relative humidity measurements for these stations:
http://andrewsforest.oregonstate.edu/data/studies/ms05/meta/rel.htm
Relative humidity is output hourly and is measured at a height of 150 cm at two sites using Vaisala sensors with Campbell data loggers.
Key references of this database include:
Smith, Jonathan W. Mapping the thermal climate of the H.J. Andrews Experimental Forest, Oregon. Corvallis, OR: Oregon State University; 2002222 p. M.S. thesis.
Rosentrater, Lynn D. The thermal climate of the H.J. Andrews Experimental Forest, Oregon . Eugene, OR: University of Oregon; 1997133 p. M.S. thesis.
