The experiments are being conducted at six sites located within intact old-growth Douglas-fir-western hemlock forests. The experimental design is a split-split plot in time. Each site represents a block, and log species is the the main plot effect. Flow pathway that is, throughfall, run-off from the top, and leachate from the bottom is the subplot effect.
Overall Study
Detailed descriptions of the methods used to install the overall study were described by Harmon (1992). Logs of the four species used in the experiments (Douglas-fir, Pacific silver fir, Western red cedar, and western hemlock) were removed from four locations during September 1985. Low- standard access roads were constructed at each site during July and August 1985 to place the logs and then the roads were closed. Logs were placed on either side of the access roads after the 50 m point to reduce the microclimatic effects of stand edge on the experiment. The logs used in the experiment met specifications for diameter, length, amount of bark cover, and degree of decay. Logs that ranged in diameter between 45 and 60 cm over their length were deemed suitable. The final log length at the experimental sites was 5.5 m. Damage to the bark during the yarding, transport, and placement was minimized; however, logs with more than 10 percent of their bark missing were considered unsuitable. Logs with large decay columns, conks, or both were rejected. Enough logs of each species were placed so that destructive samples could be made at least 18 times after placement--a total of 530 logs.
A map indicating the position of logs at each site was prepared to aid relocation (maps on file in RWU- 4356, Forest Science Laboratory, Corvallis, OR). Each log was marked with an aluminum numbered tag nailed at the top of each end.
Bark coverage, length, and diameters were measured to characterize the initial condition of each log. To characterize initial density, moisture content, and volume of tissue in each log, a cross-section 8 to 10-cm thick was removed from each end. Subsequently a subset of logs has been sampled to determine the decay rate and change in nutrient content of logs. All cross-sections were wrapped in black plastic bags and stored at 2°C until they were processed. The cross-sections were photographed and these were digitized to estimate the volume of outer bark, inner bark, sapwood, and heartwood.
Wood density was sampled radially. Samples were identified as to type, log number, end, and piece by bar- code labels. The radial, longitudinal, and tangential dimensions were measured to the nearest 0.1 mm with calipers on each cross- section cut. The weight of each block before and after ovendrying was determined to the nearest 0.01 g by using an electronic digital balance linked to a microcomputer. Ovendrying was at 55°C for seven days.
Outer and inner bark were also sampled for density and moisture content for each cross-section. After recording the thickness at four points of each cross-section, a subsample of bark was removed along a 20- to 30-cm length of the circumference. The radial, longitudinal, and tangential dimensions of these pieces were recorded. For radial dimensions, at least six measurements were made to give a reasonable average. Outer and inner bark were separated by chisel for all species, except Pacific silver fir. The weight of each bark sample before and after ovendrying was determined to the nearest 0.01 g using an electronic digital balance linked to microcomputer. Ovendrying was at 55°C for seven days. Previously ovendried outer bark samples were soaked in water 48 hours, and then volume was measured to the nearest 1 cm3 by water displacement.
Each tissue type was sampled from a subset of 10 logs of each species for initial nutrient content and cell wall carbon chemistry (that is, water solubles, lignin, cellulose, acid detergent fiber). In the case of decayed samples, a pooled sample of each tissue was taken for each log that was sampled. For bark, a separate set of subsamples was removed and stored frozen until processing. Sapwood and heartwood samples were removed from the ovendried pieces. All tissues were first coarse ground, and then fine ground with a wiley mill to pass a 40-mesh screen. Nitrogen content was measured using microKjeldahl digestion. Concentration of assorted elements--including calcium , copper, iron, potassium, magnesium, manganese, phosphorus, sulfur, and zinc--were measured by inductively coupled argon spectroscopy.
Leaching Study
1986-1989.
Water collectors were installed in 1986 for one log of each species at all six of the sites. Thus a total of 24 logs were sampled. Three flows of water were measured: throughfall, run-off from the tops, and leachates from the bottom. All four species at each site had the throughfall and bottom flows measured. Top flows were measured for only one species at each site. Throughfall collectors were galvanized steel triangulars with a collection area of ?? cm squared. Bottom collectors were aluminum sheets attached to the log at the transition between the top and bottom point of the log for approximately 0.5 m. The projected areas of the bottom collectors was approximately 2500 cm squared (actual area is recorded for each log). These sheets diverted water into a galavanized triangle. The run-off collectors diverted water running off the top to a side collector that was attached above the bottom collector. Catchment area for these side traps was approx. ?? cm squared. Water collected in the samplers was stored in blue 20 liter jugs. At intervals of 2 weeks to 1 month the volume in the jugs was measured and then a subsample proportional to the volume was removed and frozen. At yearly intervals the frozen samples were thawed, filtered and then analyzed for total Kj. N, NO3, cations, DOC. These analyzes were conducted in 1986-87, and 1987-1988 until funding expired.
1989-present
In 1989 the collectors were changed. For the most part all the logs with collectors in the 1986-1989 period were used. At site 5 the THPL log was changed because it was covered by a fallen tree. For each log there was a collector for throughfall, run-off, and leachates from the bottom. The throughfall collector was a plastic funnel with an area of 317 cm squared. The side collectors for the run-off were plastic trays that had been cut in half and sampled an log length of ?? cm. Side trap collection area ranged from 488- 768 cm squared. Bottom collectors were made of flexible, corregated plastic pipe, that was cut in half and attached to the bottom of each log. The pipe diameter was ?? cm. These pipes were lined with plastic film so leachate would not collect in the corregated ridges. Water was diverted into a plastic funnel similar to those used in throughfall collections. Bottom collector area ranged from 577- 740 cm squared.
Water from all collectors was diverted through a coil of tygon tubing that contained exchange resins. These resin sinks were changed at 3-5 month intervals, and then exchangable NO3, NH4, and cations were measured. Periodically bulk collections were made to test the proportion of organic v. mineral N that was leaving the logs.
The volume of water moving through all the collectors was measured at sites 2 and 3 during 1989-1992. At the other sites only the throughfall collectors had the volume measured. The idea is the estimate the water flow through the other logs based upon the volume of throughfall hitting the logs.
This is part of the long-term log decay study (200 years). Other data sets utilizing the same logs include TD14 (log density and nutrient contnet) TD18 (nitrogen fixation), and TD20 (respiration). Data also exists for the insects attacking logs in first 3 years (contact Jack Lattin), seasonal variations in moisture content (contact Mark Harmon) and temperature (contact Tim Schowalter).
