Amounts and structural characteristics of coarse woody debris (CWD) were examined in relation to stand age and site moisture condition in 196 Pseudotsuga menziesii stands in western Oregon and Washington. Stands ranged from 40 to 900 yr old, and most if not all, originated after fire. In a chronosequence from the Cascade range, the amount of CWD followed a U—shaped pattern for stands <500 yr old, with moderate levels (92 Mg/ha) in stands <80 yr old, lowest levels (<50 Mg/ha) in stands 80—120 yr old, and highest levels (173 Mg/ha) in stands 400—500 yr old. After 500 yr the amounts of CWD declined to intermediate levels. In the southern Coast Range, lowest levels (32 Mg/ha) of CWD were in the youngest stands (60—80 yr), primarily because they inherited little CWD from the preceding (prefire) stands. In the Cascade Range, levels of CWD inherited from preceding stands were highest in young stands and declined to near zero by 250 yr. The overall decay rate constant (k) for snags and logs in the Cascade Range, calculated indirectly from the chronosequence, was 0.029 yr—1. Volume and biomass of CWD differed significantly in old—growth stands (>200 yr old) among site moisture classes. Dry sites averaged 72 Mg/ha moderate sites 137 Mg/ha, and moist sites 174 Mg/ha. The dynamics of CWD were modeled for three fire histories, each beginning with an initial fire in an old—growth stand but differing in number and severity of subsequent fires. All three models exhibited low values of CWD between 80 and 200 yr. The lowest and most prolonged minimum in CWD between 80 and 200 yr. The lowest and most prolonged minimum in CWD during succession occurred when additional fires burned early in succession, which probably happened preceding many stands in the southern Coast Range. The results of the study indicate that a steady—state condition in CWD may not be reached for >1000 yr, and that the nature and timing of disturbance play a key role in the dynamics of CWD in the dynamics of CWD in the region.

Little is known about the chemistry of solutions moving through old‐growth coastal temperate coniferous rain forests. The major objectives of this study were to examine precipitation, throughfall, stemflow, and soil solution chemistry in an old‐growth temperate rain forest in the Hoh River valley on the northwest Washington coast 32 km from the Pacific Ocean, and to determine mechanisms involved with changes in solution chemistry. Dominant species were Douglas‐fir (Pseudotsuga menziesii [Mirb.] Franco), western hemlock (Tsuga heterophylla [Raf.] Sarg.), western redcedar (Thuja plicata Donn), and Pacific silver fir (Abies amabilis [Dougl.] Forbes). Stemflow was more acidic (avg. pH 4.3) than throughfall (avg. pH 5.0) and precipitation (avg. pH 5.3). This precipitation pH is typical for a remote site. Organic acids were important contributors to acidity in throughfall and stemflow. Soil solution pHs were much higher as a result of acid neutralization processes, averaging 5.7 in the forest floor and 6.2 at 40‐cm depth. Sodium and Cl dominated precipitation, followed by Ca and SO4, indicating a strong oceanic influence. Throughfall and stemflow were generally enriched in cations, especially K, but concentrations in soil solutions were less than those in stemflow. Organic anions contributed greatly to cation leaching in the canopy, with a much smaller contribution from SO4. Like precipitation, Na and Cl dominated throughfall, stemflow, and soil solutions. The highest concentrations of NH4 were found in stemflow, suggesting N fixation in the canopy. Throughfall and stem‐flow under Pacific silver fir had the highest concentrations of both cations and anions. Phosphate, NH4, and NO3 concentrations were low in the soil solution, indicating strong retention of N and P in this ecosystem.

The biogeochemistry of a coastal old‐growth forested watershed in Olympic National Park, Washington, was examined. Objectives were to determine: (1) concentrations of major cations and anions and dissolved organic C (DOC) in precipitation, throughfall, stemflow, soil solution and the stream; (2) nutrient input/output budgets; and (3) nutrient retention mechanisms in the watershed. Stemilow was more acidic (pH 4.0–4.5) than throughfall (pH 5.1) and precipitation (pH 5.3). Organic acids were important contributors to acidity in throughfall and stemflow and tree species influenced pH. Soil solution pH averaged 6.2 at 40 cm depth. Stream pH was higher (7.6). Sodium (54.0 μeq L‐1) and Cl (57.6 μeq L−1) were the dominant ions in precipitation, reflecting the close proximity to the ocean. Throughfall and stemflow were generally enriched in cations, especially K. Cation concentrations in soil solutions were generally less than those in stemilow. Ion concentrations increased in the stream. Dominant ions were Ca (759.7 μeq L−1), Na (174.4 μeq L−1), HCO3 (592.0 μeq L−1), and SO4 (331.5 μeq L−1) with seasonal peaks in the fall. Bedrock weathering strongly influenced stream chemistry. Highest average NO3 concentrations were in the stream (5.2 μeq L−1) with seasonal peaks in the fall and lowest concentrations in the growing season. Nitrogen losses were similar to inputs; annual inputs were 4.8 kg/ha (not including fixation) and stream losses were 7.1 kg/ha. Despite the age and successional status of the forest, plant uptake is an important N retention mechanism in this watershed.

Tree population dynamics, growth, and mortality were determined in old-growth forested watersheds in the Hoh River valley, Olympic Peninsula, Washington: West Twin Creek (elevation 180–850 m) and Hoh Lake (elevation 1250–1525 m). Principal tree species at West Twin Creek are Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western hemlock (Tsugaheterophylla (Raf.) Sarg.), Pacific silver fir (Abiesamabilis (Dougl.) Forb.), western red cedar (Thujaplicata D. Don), and Sitka spruce (Piceasitchensis (Bong.) Carr.). At Hoh Lake they are Pacific silver fir, mountain hemlock (Tsugamertensiana (Bong.) Carr.), and Alaska cedar (Chamaecyparisnootkatensis (D. Don) Spach). In 1985 stem densities for trees >5 cm DBH averaged 476 and 489 ha−1 in the upper and lower West Twin Creek watershed, respectively, and 508 ha−1 at Hoh Lake watershed. Stem densities at both sites declined 3–5% from 1985 to 1990. Western hemlock and Pacific silver fir were the dominant species at West Twin Creek and Hoh Lake, respectively. From 1985 to 1990 the annual mortality rate was 0.8% at West Twin Creek and 0.9% at Hoh Lake. Pacific silver fir had the highest mortality rate. No Douglas-fir or western red cedar trees died. The primary causes of mortality were as follows: suppression–unknown, diseases, insects, and windthrow. In 1985 basal areas were 77, 87, and 94 m2•ha−1 in the lower and upper West Twin Creek watershed and Hoh Lake watershed, respectively. There was a 5% increase and a 1% decrease in basal area from 1985 to 1990 in the lower and upper West Twin Creek watershed, respectively, and a 4% decrease at Hoh Lake. Western red cedar, Douglas-fir, and western hemlock increased in basal area, while the other species declined.

Decomposition rates and nutrient dynamics (for N, P, K, Ca, Mg, Mn, and Na) were determined for green needles of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Pacific silver fir (Abiesamabilis (Dougl.) Forb.) in an old-growth forested watershed (58 ha West Twin Creek) in the Hoh River valley, Olympic National Park, Washington. The influence of temperature and substrate chemistry on decomposition was determined. Temperature was the dominant factor controlling decomposition rates in the first year in this watershed, with the fastest decomposition at an elevation of 275 m (lower watershed) and the slowest decomposition at 725 m (upper watershed). After 12 months mass loss averaged 36% in the lower watershed and 28% in the upper watershed. There was no significant difference in decomposition rates between species. Substrate chemistry, i.e., the lignin/N ratio, became a more important factor than temperature as decomposition proceeded. After 37 months mass loss for needles averaged 61% for western hemlock and 50% for Pacific silver fir, with no difference by watershed location. After 61 months both types of substrates appeared to be approaching similar substrate chemistry and similar decomposition rates and there were no significant differences by species or watershed location. Decomposition constants (k values) after 61 months were 0.26 and 0.20 year−1 for western hemlock needles in the lower and upper watershed, respectively, and 0.22 and 0.19 year−1 for Pacific silver fir needles in the lower and upper watershed, respectively. Nitrogen was immobilized during the first 12 months of decomposition in needles of both species and then released. No other elements were immobilized during the initial (0- to 12-month) decomposition period, except for Ca in Pacific silver fir needles. However, in the 37- to 61-month period there was a considerable immobilization of Mg and Na in both species in the upper and lower watershed and K and Mn in both species in the upper watershed.