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. Tissue type 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 redcedar, 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.
Field Moisture Content
During 1986-1992, one log of each species was sampled in September at each of the six sites to determine changes in tissue density and moisture. In 1986-90 five cross-sections were removed along the length of each log sampled. In 1991-92, remnants from the first sampling period were resampled, with two cross-sections removed per log. For each sampling period the density and moisture content of the outer bark, inner bark, sapwood, and heartwood was measured.
Moisture content was determined monthly from one log of each species at each of the six sites between May 1986 and November 1988. This set of logs was kept intact. Samples were taken at roughly monthly intervals. Wood samples were extracted from logs using an increment corer and placing the sample in a sealed plastic straw. Two bark samples were removed from each log by pounding a 2 cm diameter corer into the log until the bark layer could be removed. The bark samples were wrapped in plastic until laboratory processing. All holes created by the sampling were sealed with silicone rubber caulking. In the laboratory wood samples were separated into sapwood and heartwood for all species. Bark samples for all species except Abies were separated into inner and outer bark layers. Abies bark was kept intact as the separation of bark into distinct layers was extremely difficult. Wet weight of the samples was determined to the nearest 0.001 g before and after drying for 4 days at 55°C.
Maximum Moisture Content
The maximum potential moisture content for undecayed and decayed tissues of each species was determined by submersing 100 cm3 samples underwater for 1 month. This extended period was required, because heartwood samples absorbed water quite slowly. As the maximum moisture content of sapwood samples was dependent upon density, we used a range of decayed samples for each log species.
Moisture content was calculated as mass of water divided by the mass of dry material in each sample. The mass of water contained within entire logs was calculated by multiplying the mass of each tissue type by the moisture content of each layer. The mass of each tissue type was calculated from the average volume of tissues for each species and the average density for each species, tissue and time of moisture sampling. As the frequency density samples did not match those of the moisture samples, we adjusted the density by assuming it declined linearly between June and September and remained constant the rest of the year. This matches the period of high respiration activity for logs in this region (Carpenter et al 1988). The maximum potential water stores was calculated by multiplying the maximum moisture content by the mass of each tissue type.
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).
The following publications have resulted from this work and explain methods in more detail:
Carpenter, S. E. 1988. Ambrodiscus: A new genus of inoperculate discomycetes from ambrosia beetle galleries. Mycologia 80:320-323.
Carpenter, S. E., M. E. Harmon, E. R. Ingham, R. G. Kelsey, J. D. Lattin, and T. D. Schowalter. 1988. Early patterns of heterotroph activity in conifer logs. Proceedings of the Royal Society of Edinburgh 94B: 33- 43. G
riffiths, R.P., M. E. Harmon, B.A. Caldwell, and S.E. Carpenter, (in press) Acetylene reduction in conifer logs in the early stages of decomposition. Plant and Soil
Harmon, M., E. 1992. Establishment of long-term studies on log decomposition at the H. J. Andrews Experimental Forest, Oregon. USDA Forest Serv. Gen. Tech. Rep. PNW-GTR-280.
Kelsey, R.G. and M.E. Harmon 1989. Total extractable phenols and tannins in the tissues of 1 year old conifer logs. Can. J. For. Res. 19:1030-1036.
Schowalter, T.D., B.A. Caldwell, S.E. Carpenter, R.P.Griffiths, M.E. Harmon, E.R. Ingham, R.G. Kelsey and J.D. Lattin. (in press) Decomposition of fallen trees: effects of initial conditions and heterotroph colonization rates. Tropical Ecology.
Zhong, H. 1988. Host selection and wood channelization by beetles in conifer logs in western Oregon. MS Thesis, Oregon State University.
Zhong H. and T.D. Schowalter. 1989. Conifer bole utilization by wood-boring beetles in western Oregon. Canadian Journal of Forest Research 19:943-947.
