|Abstract or Summary
- To obtain data on the decomposition of the forest floor, a battery operated electrolytic respirometer was developed making it possible to measure CO₂ evolution from field moist forest floor samples in situ independent of root respiration. Banks of four respirometers powered by two 12-volt batteries were installed in three old growth Douglas-fir-hemlock stands, two clearcuts, and one clearcut that had been broadcast burned. All sites were located on or immediately adjacent to the H. J. Andrews Experimental Forest located in the western Cascades near Blue River, Oregon. Seasonal and yearly totals of mineralized carbon were similar for the three habitat types. First year totals for the Tsuga heterophylla/Rhododendron macrophyllum/Berberis nervosa associa tion (RS 2), the Tsuga heterophylla/Castanopsis chrysophylla association (RS 6) and the Tsuga heterophylla/Polystichum munitum-Oxalis oregana association (RS 7) were 77.36, 75.67, and 78.86 mg C /g litter. Spring and fall mineralization accounted for approximately 62% of this total on all three reference stands. The lowest rates occurred during the winter months. Carbon mineralization rates for the second fall of the study were similar to those of the first year. However, carbon mineralization during the second winter of the study increased unexpectedly by 88%, 123% and 142% for reference stands 2, 6 and 7, respectively, Presumably, this was due to warmer temperatures during the second winter. Clearcutting enhanced the rate of carbon mineralization, the magnitude of the effect being greater on the older clearcut. On the 4-year-old clearcuts (plots 29 and 36), yearly totals averaged 102.97 mg C/g litter. On the 3-year-old clearcut (RS 33), total carbon mineralization was 89.49 mg C/ g litter. Part of the variation was probably related to elevational effects on temperature, RS 33 being located 330 meters higher than the other clearcut. But it is also possible that the greater reestablishment of vegetation on the older clearcut could have contributed a higher proportion of fresh litter to the residual forest floor. Clearcutting followed by broadcast burning decreased the rate of carbon mineralization. Plots were established on the site one month following a light burn. The yearly totals for carbon mineralization averaged 64.62 mg C/g litter, or 59% less than on the older clearcut (29 and 36). Nitrogen levels remained relatively high, and there appeared to be an increase in the lignin fraction of the litter. Decomposition was significantly correlated with litter moisture content or litter temperature on a seasonal basis. In general, litter moisture content was the dominant factor during the summer and fall months. Litter temperature was the dominant factor in the winter and spring months when statistically significant correlations could be obtained. Inadequate means of estimating litter temperature under snowpack may be the reason for fewer significant correlations during these periods.