These sites were selected to give a wide representation of different microclimates and vegetation types found at the HJA. The microclimate sites were selected along a rough N/S gradient from the top of a ridge to the North to another ridge to the South. Another set was selected along an roughly E/W gradient which gave representative sites of different elevations and aspects including sites that were hot and dry and those that are typically wet and cold. Also included were sites near streams that experience cooling. The vegetation sites included clearcut sites, and regenerated sites of different age classes. In addition, we included a Sitka alder and a broad-leave maple site. Monthly measurements of field respiration, temperature, percent moisture, moisture by volume, field respiration rate in permenant gas exchange chambers and bulk density.
This study was also designed to provide continued monitoring of soil respiration rates at these sites which were initiated in the summer of 1992. In the earlier studies, permanent chambers had not been installed and we using temporary incubation chambers installed at each sampling. The permanent chambers were installed in the summer of 1994 and used throughout this study. Between measurements, both covers and "O" rings were removed from the chambers. The only disturbance in the chambers during this study was the removal of any vegetation by cutting the stems.
There are 10 plots within each of the twenty sites. These consist of locations along a 50 meter transect 5 meters apart where permanent gas flux chambers were lcoated and soil samples taken. The depth of the chambers varied where there was a slope, The hight of the chambers above ground was about 20 cm. For each chamber, the average of the high and low sides were used to calculate the average high of the chamber wall above the forest floor surface. This was used to calcuate the volume of the headspace for each individual chamber. The inside diameter of the chambers was 27 cm. To insure an effective seal, groves were machined into the walls of the chambers to accomedate an "O" ring. The chambers were sealed with clear plexiglass. All chambers were cleared of all vegetation before respiration measurements were made.
Soil respiration was measured using indicating soda lime with a mesh of 6/12 (Fisher #S201-3). The increase in weight is directly proportional to the amount of CO2 adsorbed during the incubation period. Thirty grams of soda lime was added to 8 oz glass jars fitted with gastight metal lids. They were heated uncovered for 8 hr at 100°C to remove moisture. At time 0 the jars were placed on metal mesh stands within a incubation chambers which were permanently installed in the ground with the edges buried to a depth of 10 cm. Twenty four hours later, the lids were placed back on the jars and returned to the laboratory where they were again dried (with lid off) at 100°C for 8 hr.
At each site, there was one control jar used to determine background CO2 levels and the uptake of CO2 during drying (jar was placed in a sealed chamber sealed on both ends). Bulk density measurements were made in soils adjacent to the chambers as indicated. Soil moisture was measured in two ways; (1) either gravimeterically from bulk density cores or (2) using a Time-Domain Reflectometer (TDR). The TDR used was a Tektronix model 1502B cable tester (Textronix, Beaverton, OR). The manufacture's recommended protocol was followed.
