Woody Debris Inputs Research Articles

Denitrification Hotspots and N20 Flux in Fluvial Systems

Abstract Background/Question/Methods Watersheds have a profound capacity to retain and remove nitrogen (N) inputs before entering coastal waters thereby minimizing eutrophication and hypoxia in estuarine waters. Research suggests that much of this N cycling occurs within aquatic ecosystems, e.g., lakes, streams and wetlands, which may become “hotspots” of nitrous oxide (N2O) production. We examined the effects of woody debris on nitrate removal and denitrification rates in streams of different N enrichment levels. Three different standardized substrates (fresh wood blocks, bundles of naturally occurring streambed wood, and clay‐fired blocks) that were expected to vary in their pool of labile carbon were incubated for 8‐10 weeks in each stream - a high nitrate agricultural stream in Pennsylvania and a low nitrate forested stream in Rhode Island. Substrates were collected and subjected to a series of lab‐based mesocosm assays in stream water amended with 15N-labeled nitrate-N. Nitrate removal rates were determined by mass balance techniques and denitrification rates were estimated by 15N gas generation over 18 hours. The 15N2:15N2O ratios were calculated and the mass of biofilm growth during in-situ incubation was obtained for all substrates.b) Results/Conclusions Wood block mesocosms had mean N removal and denitrification potential rates of 0.14 and 0.038 ug N/cm2 hr, respectively, for RI and 0.48 and 0.011 ug N/cm2 hr, respectively, for PA. Natural wood mesocosms from RI had 76% higher N removal (0.039 ug N/cm2 hr) than denitrification. The PA natural wood mesocosms had mean N removal (0.169 ug N/cm2 hr) an order of magnitude above the mean denitrification potential. Clay block mesocosms had negligible N removal and denitrification in RI. PA clay mesocosms had N removal rates of 0.2 ug N/cm2 hr and denitrification potential rates of 0.01 ug N/cm2 hr, likely due to the biofilms that had developed while incubating in the high nitrate stream. These results suggest that fresh inputs of natural woody debris may be an important nitrate sink in streams. High variability was observed and there were numerous cases of negligible N2O production at both sites. As a result, the differences in N removal and denitrification potential rates between sites were not significant. The mesocosms from the high nitrate PA stream generally released more N2O. The wood substrates in these mesocosms acted as significant N sinks, but are not necessarily hotspots for N2O generation.

Fire, floods and woody debris: Interactions between biotic and geomorphic processes

Fire and floods interact in the riparian zone as processes that structure plant communities and landforms. Although much of the immediate impact of fire is on the vegetation, fire-related changes in runoff, sediment supply, riparian vegetation, and woody debris volume have ongoing geomorphic impacts on the valley floor. Consequent hydrogeomorphic changes, in turn, affect the composition and distribution of vegetation. This paper reviews these interactions, and provides an example of how fires and floods intersect to supply burnt trees as woody debris. Because the temporal and spatial distribution of woody debris is initially controlled by patterns of tree mortality, ecological disturbances, like fire, can be an important source for pulses of woody debris in riparian systems. To understand these interactions, we examine woody debris inputs 3 years after a wildfire in the riparian gallery forests of the western Transverse Ranges, California. Within our sample of 339 burned stems, snags fell in distinctive patterns: species were variable in susceptibility to falling, and fell at greater rates at sites with greater subsequent flooding. Discordance between the species composition of fallen snags and that of overall burned stems indicates that variability in forest composition must be considered in predicting post-disturbance inputs of woody debris. Variation in snagfall timing among species suggests that woody debris inputs are likely to occur in multiple, sequential pulses after wildfire. The role of flooding is superimposed on this ecological influence, as the timing and spatial variability of floods affect the recruitment of woody debris from the supply of snags created by fire.

Oribatid mite communities and foliar litter decomposition in canopy suspended soils and forest floor habitats of western redcedar forests, Vancouver Island, Canada

Litter decomposition and changes in oribatid mite community composition were studied for 2 years in litterbags collected from arboreal organic matter accumulations (canopy suspended soils) and forest floors associated with western redcedar trees on Vancouver Island, British Columbia. We tested the hypotheses that lower rates of mass loss, higher nutrient levels, and different patterns of oribatid mite richness and abundance in decomposing western redcedar litter would be observed in litterbags associated with canopy suspended soils compared to forest floors. Decomposition, measured by mass loss of cedar litter in litterbags, was not significantly different in canopy and forest floor habitats, although reduced in the canopy. Abundance and richness of oribatid mites inhabiting litterbags were significantly greater on the forest floor compared to the canopy suspended soils. Canopy suspended soils had higher levels of total nitrogen, available phosphorus and potassium than the forest floor, but moisture content was significantly lower in the suspended soils. Higher nutrient levels in the canopy system are attributed to differences in coarse woody debris input (but not foliar litter), combined with reduced nutrient uptake by roots and lower mobilisation rates of nutrients by detritivorous and fungivorous microarthropods. Moisture limitation in the canopy system possibly contributed to lower mass loss in litterbags, and lower abundance and richness of oribatid mites in litterbags placed on canopy suspended soils. Patterns of oribatid mite community composition were related to mite communities associated with the underlying substrate (forest floor or canopy suspended soil) which act as source pools for individuals colonising litterbags. Successional and seasonal trends in oribatid mite communities were confounded by moisture limitation at 24 months, particularly within the canopy habitat.

Woody debris stocks and fluxes during succession in a dry tropical forest

In Southern Mexico, shifting cultivation is creating a mosaic of agricultural lands, secondary forests, and disturbed mature forests (montañas). Increased land-use change, due to population and market pressures has changed the structure and function of these forests. This study investigates the stocks and fluxes of woody debris during the course of secondary succession. We inventoried fine (≥1.8 cm to ≤10 cm diameter) and coarse woody debris (≥10 cm diameter) stocks in 28 stands. In a subset of montañas and secondary forest fallows, we monitored inputs and decomposition over a 2-year period. Total woody debris stocks were largest in montañas (37.46 Mg/ha) and in the first year after clearing (milpa, 51.62 Mg/ha). Woody debris was 22% of the total aboveground biomass in montañas and 88% in milpas. Although stocks were highly variable in secondary forest, coarse woody debris stocks were roughly three times larger than fine woody debris stocks. Coarse woody debris stocks decreased following cultivation for 10–15 years, until inputs exceeded losses to decomposition. Inputs were higher in montaña (0.91 Mg ha −1 year −1) than in secondary forest (0.11 Mg ha −1 year −1). Coarse woody debris inputs were higher during the dry season, while fine woody debris inputs tended to be higher during the wet season. Decomposition varied significantly among tree species, with decomposition rate constants from 0.124 to 0.643 year −1 for coarse woody debris and 0.368–0.857 year −1 for fine woody debris. In young forests, when woody debris stocks are largest, cultivation history is the most important factor in predicting stocks of woody debris. As forest age increases woody debris processes, both inputs and decomposition, become increasingly important factors in regulating woody debris stocks, and therefore age is a better predictor of woody debris stocks in older forests.

Detrital Controls on Soil Solution N and Dissolved Organic Matter in Soils: A Field Experiment

We established a long-term field study in an old growth coniferous forest at the H.J. Andrews Experimental Forest, OR, USA, to address how detrital quality and quantity control soil organic matter accumulation and stabilization. The Detritus Input and Removal Treatments (DIRT) plots consist of treatments that double leaf litter, double woody debris inputs, exclude litter inputs, or remove root inputs via trenching. We measured changes in soil solution chemistry with depth, and conducted long-term incubations of bulk soils from different treat- ments in order to elucidate effects of detrital inputs on the relative amounts and lability of different soil C pools. In the field, the addition of woody debris increased dissolved organic carbon (DOC) concentrations in O-horizon leachate and at 30 cm, but not at 100 cm, compared to control plots, suggesting increased rates of DOC retention with added woody debris. DOC concentrations decreased through the soil profile in all plots to a greater degree than did dissolved organic nitrogen (DON), most likely due to preferential sorption of high C:N hydrophobic dissolved organic matter (DOM) in upper horizons; percent hydrophobic DOM decreased significantly with depth, and hydrophilic DOM had a much lower and less variable C:N ratio. Although laboratory extracts of different litter types showed differences in DOM chemistry, percent hydrophobic DOM did not differ among soil solutions from different detrital treatments in the field, suggesting that microbial processing of DOM leachate in the field consumed easily degradable components, thus equalizing leachate chemistry among treatments. Total dissolved N leaching from plots with intact roots was very low (0.17 g m 2 year 1 ), slightly less than measured deposition to this very unpolluted forest (0.2 g m 2 year 1 ). Total dissolved N losses showed significant increases in the two treatments without roots whereas concentrations of DOC decreased. In these plots, N losses were less than half of estimated plant uptake, suggesting that other mechanisms, such as increased microbial immobilization of N, accounted for retention of N in deep soils. In long-term laboratory incubations, soils from plots that had both above- and below-ground litter inputs excluded for 5 years showed a trend towards lower DOC loss rates, but not lower respiration rates. Soils from plots with added wood had similar respiration and DOC loss rates as control soils, suggesting that the additional DOC sorption observed in the field in these soils was stabilized in the soil and not readily lost upon incubation.

Deforesting the riverscape: the effects of wood on fish diversity in a Venezuelan piedmont stream

While deforestation of tropical ecosystems has been shown to have significant impacts on terrestrial habitats, its effects on aquatic habitats are poorly studied. Deforestation dramatically reduces the input of woody debris to streams, and given the importance of large woody debris to fish communities in temperate streams, this might be one mechanism by which logging could affect aquatic ecosystems in the tropics. To examine the effects of large woody debris on the diverse fish assemblage of a tropical stream, we surveyed pools with and without wood at Rio Las Marias, Venezuela. Pools containing wood contained greater numbers of individuals and more species of fish than pools without wood, and the two types of pools differed in their composition. To test whether these results were due to the presence of woody debris, we conducted an experimental wood addition. Pools to which wood was added showed marked increases in both fish abundance and species richness relative to wood-free pools, and the composition of the fish assemblage in experimental pools approached that of pools with naturally occurring woody debris. These results demonstrate that large woody debris plays a major role in structuring fish communities in tropical streams. As a consequence, logging practices that reduce the input of woody debris to tropical streams or directly remove wood from streams could have serious impacts on aquatic habitats, affecting both the diverse fish communities and local economies dependent on stream fisheries.

Decay and nutrient dynamics of coarse woody debris in northern coniferous forests: a synthesis

We synthesize current information on input, accumulation, and decay of coarse woody debris (CWD) compared with other aboveground litter to assess the role of CWD in the nutrient cycles of northern coniferous forests. CWD contributes between 3% and 73% of aboveground litter input, but <20% of N, P, K, and Ca. Although CWD accounts for up to 54% of accumulated organic matter (including forest floor and soil), it contributes <5% of the N, <10% of the P, and <25% of the K, Ca, and Mg. Decay rates of CWD in northern forests range from 0.0025 to 0.071 year-1. Nitrogen or P concentrations in CWD increase during decay, depending on the initial N/P ratio, which eventually converges at about 20. CWD is initially a sink for N and (or) P, whichever is least available, but becomes a source later in decay. CWD contributes <5% of the N released annually. There is little evidence that CWD retains significant amounts of excess N following disturbance. We conclude that CWD is of minor importance in the nutrient cycles of northern coniferous forests, and that guidelines for CWD retention should be based on other perceived benefits of CWD.

Overstory litter inputs and nutrient returns in an old-growth temperate forest ecosystem, Olympic National Park, Washington

Overstory litterfall rates and nutrient returns were determined in an old-growth temperate rainforest watershed in the Hoh River valley, Olympic National Park, Washington. Litter was sorted into green needles, senescent needles, fine wood, reproductive, and miscellaneous litter (mostly arboreal lichens and mosses). Understory and coarse woody debris inputs were not determined. Total annual overstory litterfall averaged 3594 kg·ha–1 and varied among the six plant communities in the watershed. There was a trend for litterfall to be higher in the upper watershed; elevations ranged from 180 to 850 m. Needles provided the greatest amount of litterfall (60%) with woody litter and other material averaging 18 and 22%, respectively. Highest senescent needle litterfall occurred from July to October, but highest woody litterfall was from January to April. Green needles provided only 3% of annual needle litterfall. Green and senescent needle litterfall were related to western hemlock (Tsuga heterophylla (Raf.) Sarg.) basal area, suggesting that this shade-tolerant species was the greatest contributor to needle litterfall. The following quantities (kg·ha–1) of nutrients were returned to the forest floor annually: Ca, 26.8; N, 24.6; K, 4.0; Mg, 3.0; P, 2.9; Mn, 1.7; and Na, 1.2.

Harvesting and Climate Effects on Organic Matter Characteristics in British Columbia Coastal Forests

As part of investigations into the effects of harvesting old-growth forest, we characterized carbon in five organic matter pools in eight forest chronosequences of coastal British Columbia. Each chronosequence comprised stands in four seral stages from regeneration (3-8 yr) to old-growth (>250 yr), with second-growth stands mostly of harvest origin. Stands were located in two biogeoclimatic subzones with contrasting climate (wetter, slightly cooler conditions on the west coast of Vancouver Island than on the east). Carbon concentrations in fine woody debris (FWD), forest floor (LFH), fine roots from LFH, and two water-floatable fractions from 10 to 30 cm mineral soil (MIN-ROOT, 2-8 mm and MIN-FLOAT, <2 mm) showed no significant effects due to climate, seral stage, or site. There were some significant differences in N concentrations, but none related to seral stage. Carbon-13 cross-polarization with magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra with principal component analysis of relative areas also showed little harvesting effect, but greater variation related to input of coarse woody debris (CWD) vs. roots high in tannin. Overall, there tended to be more spectral features associated with wood and lignin in the west; whereas some MIN-ROOT samples from the drier east side had aromatic intensity attributed to charcoal. The minimal effects of one harvest on organic matter are most likely due to the large legacy effect; however, more intensive management will probably result in less CWD retention, less charcoal input, and less microsite variability in these pools of poorly decomposed organic matter.

Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south‐west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years.2. The average concentration of fungal spores in reference sections was nearly 10× greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams.3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams.4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones.5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production.

Input, storage and distribution of large woody debris along a mountain river continuum, the Drôme River, France

Large woody debris (LWD) input, storage and distribution were studied along the Drôme River, a French Alpine river with an active shifting channel and a well-developed riparian forest. LWD input from the floodplain is low: 669.6 mg year −1 between 1948 and 1971 and 569.3 mg year −1 between 1971 and 1991. Based on estimates of average LWD mass per study plot, a range of 766–2122 mg year −1 of LWD were stored within the active channel (e.g., unvegetated bars and low-flow channel; 60 km course covering 492 ha). LWD accumulations are mainly observed on gravel bars at a limited number of preferential sites. They are relatively rare and are randomly distributed in the low-flow channel. Consequently, LWD location is mainly associated with the decrease of flow level in shallow sectors. In the low-flow channel, LWD stop-en-route is primarily caused by in-channel structures such as boulders or vegetated islets. General geomorphological factors (e.g., pattern, slope, etc.) provide less explanation of LWD distribution. Moreover, the residence time of LWD accumulations on the Drôme River is short (LWD storage=1.3–3.7 times the annual LWD input from the floodplain) and their morphogenic role is negligible: few of the accumulations are buried or characterized by vegetation shoots and associated pools.

Age characteristics of coarse woody debris (Pinus strobus) in a lake littoral zone

Littoral coarse woody debris (CWD) is a persistent class of aquatic habitat that accumulates over many centuries and provides habitat for diverse floral and faunal communities. We used dendrochronological methods to analyze residence times and age-related characteristics of eastern white pine (Pinus strobus) CWD in the littoral zone of Swan Lake in Algonquin Provincial Park, Ontario. The mean calendar date of all the annual rings in CWD samples was 1551. Annual rings dated from calendar year 1893 to 982. The mean time from carbon assimilation in a live tree to carbon loss from littoral woody debris was 443 years. Outside ring dates of the woody debris were significantly correlated with the bole's maximum and minimum diameter ratio, mass, specific gravity, length, and submergence. Negative exponential functions described the temporal structure of the CWD mass and abundance. Accelerated inputs of woody debris resulted from late nineteenth century logging and a disturbance circa 1500. No mature eastern white pine have fallen into the lake over the last 100 years.

Macroinvertebrate Colonization of Woody Debris in Canadian Shield Lakes following Riparian Clearcutting

Deployment of litterfall traps revealed that clearcut logging of boreal riparian forests in northwestern Ontario, Canada resulted in a dramatic shift from once dominant conifers to regrowth composed largely of deciduous trees and reduced the allochthonous inputs of small woody debris to lake littoral zones by over 90%. Due to the rarity of macrophytes in these oligotrophic lakes, littoral macroinvertebrates were found to actively colonize woody debris placed within mesh litter bags. The recalcitrant nature of small woody debris in these lakes (average median persistence time of about 5 years estimated from mass loss data) indicates, however, that this important habitat resource will probably never completely disappear in relation to its projected rate of resupply during post‐disturbance forest regeneration. Colonization rates of twigs and bark contained within the litter bags were not found to differ between coniferous and deciduous species. This indicates that macroinvertebrates in these boreal lakes are merely opportunistic colonizers of woody debris, probably for its use as either a biofilm substrate or a predation refuge. As a result, shifts in tree species composition following riparian clearcutting should not detrimentally affect the taxa richness or organism abundance of aquatic macroinvertebrates in these lakes.

Ice Storm Damage to an Old-growth Oak-hickory Forest in Missouri

-On 6 December 1994 a severe ice storm hit several midwestern states. We inventoried damage and woody debris input from the storm in 30 0.1-ha permanent plots in an old-growth oak-hickory forest in northern Missouri. Twenty-seven percent of 1386 live trees 22 cm dbh were damaged but only 7% were severely damaged. Basswood (Tilia americana) and American elm (Ulmus americana) were the most susceptible species; white oak (Quercus alba), eastern hophornbeam (Ostrya virginiana) and shagbark hickory (Carya ovata) were among the least susceptible. Damage levels increased with stem diameter, and trees occupying dominant crown positions were more heavily damaged than suppressed trees. Damage severity was highly variable across the landscape, but trees on lower slopes and mesic aspects tended to have more damage, even for a given species. Coarse woody debris input from the storm averaged 5.1 m3/ha, 27% of the prestorm volume, with northern red oak (Q. rubra) and white oak contributing 79% of the total. This single event will probably have minimal impact on stand composition and structure, but repeated ice storms at 20-yr intervals likely influence forest dynamics in midwest oak-hickory forests.

Woody Detritus Inputs and Decomposition Kinetics in a Southern Temperate Deciduous Forest

ONEGA, T. L. AND W. G. EICKMEIER (Department of Biology, Vanderbilt University, Nashville, TN 37235). Woody detritus inputs and decomposition kinetics in a southern temperate deciduous forest. Bull. Torrey Bot. Club 118: 52-57. 1991.-The dynamics of woody debris input and decomposition in temperate forest ecosystems are rarely examined. Woody detritus inputs in a mesic deciduous forest in Tennessee were followed from 1976 to 1988. Annual inputs were highly variable with a mean of 3.97 Mg ha-' yr-1, with a range from 0.55 to 16.00 Mg ha-' yr-'. The woody detritus pool in 1989 was 19.26 Mg ha-'. The stand-level decomposition constant, based on the input/biomass ratio, was 0.21 yr-1 for a half-life of 3.4 years. The decomposition of 14 standing dead and 39 fallen boles of known age since death was also examined. The decomposition rate constant based on a single-exponential decay model was 0.110 yr-1, with a half-life of 6.3 years, for fallen logs and 0.062 yr-1, with a half-life of 11.2 years, for standing dead boles. Detrital turnover is thus rapid and woody debris is not a longterm energy and nutrient sink in this forest.

Modeling inputs of large woody debris to streams from falling trees

A probabilistic model predicts means and variances of the total number and volume of large woody debris pieces falling into a stream reach per unit time. The estimates of debris input are based on the density (trees/area), tree size distribution, and tree-fall probability of the riparian stand adjacent to the reach. Distributions of volume, length, and orientation of delivered debris pieces are also predicted. The model is applied to an old-growth coniferous stand in Oregon's Cascade Mountains. Observed debris inputs from the riparian stand exceeded the inputs predicted from tree mortality rates typical of similar nonriparian stands. Debris pieces observed in the stream were generally shorter, with less volume per piece, than those predicted by the model, probably because of bole breakage during tree fall. As a second application, predicted debris inputs from riparian management zones of various widths are compared with the input expected from an unharvested stand.

Input and Depletion of Woody Debris in Alaska Streams and Implications for Streamside Management

Abstract Natural rates of input and depletion of large woody debris (LWD) in southeast Alaska streams were studied to provide a basis for managing streamside zones to maintain LWD for fish habitat after timber harvest. Debris was inventoried in a variety of stream types in undisturbed old-growth forest; 252 pieces of LWD were dated from the age of trees growing on them. Longevity of LWD was directly related to bole diameter: small LWD (10–30 cm in diameter) was less than 110 years old, whereas large LWD (>60 cm in diameter) was up to 226 years old. Assuming equilibrium between input and depletion of LWD in streams in old-growth forests and exponential decay of LWD, we calculated input and depletion rates from mean age of LWD. Input and depletion rates were inversely proportional to LWD diameter and ranged from 1%/year for large LWD in all stream types to 3%/year for small LWD in large, high-energy, bedrock-controlled streams. A model of changes in LWD after timber harvest (which accounted for depletion of...

Salmonid colonization of new streams in Glacier Bay National Park, Alaska

Abstract. Following the rapid recession of a neoglacial ice sheet within the last 250 years, colonization of recently deglaciated streams by salmonid fishes was investigated in Glacier Bay National Park, south-eastern Alaska. The primary factors governing the establishment, species diversity composition and abundance of salmonids in Glacier Bay streams were water temperature, sediment loading and stream discharge. No salmonids were found in the turbid meltwater streams emerging from retreating ice. Coho, Oncorhynchus kisutch (Walbaum), and sockeye, Oncorhynchus nerka (Walbaum). salmon and Dolly Vardcn, Salvelinus malma (Walbaum), charr were the first salmonids to colonize the youngest clearwater stream. Juvenile Dolly Varden were more abundant than juvenile coho salmon in the most recently formed clearwater stream because of the characteristic absence of pool habital. Densities of juvenile coho salmon were six times greater in a stream with a series of lakes compared with a stream of similar age without lakes. Future advancement of salmonid stocks will probably depend upon the rate and extent of the development of riparian vegetation and inputs of large woody debris from the developing forest to provide further instream cover, habitat variation and channel stabilization.

Input and decay of coarse woody debris in coniferous stands in western Oregon and Washington

At 10 locations in Oregon and Washington, tree mortality resulted in dry-matter transfer of 1.5–4.5 Mg•ha−1•year−1 of boles and branches to the forest floor and 0.3–1.3 Mg•ha−1•year−1 of large-diameter roots directly to the mineral soil. The first value is about the same as that reported for leaf fall in similar stands; the second value generally is smaller than that reported for fine root turnover. Results are based on measurements by the U.S. Forest Service spanning 16–46 years and areas as large as 42 ha. Values based on intervals &lt; 10 years were highly variable and potentially misleading.At an old-growth Douglas-fir stand in Washington, fallen boles accounted for 81 Mg/ha, standing dead for 54 Mg/ha. Density of fallen boles averaged from 0.14 to 0.27 g/cm3 depending on decay state. Values were lower than some previously reported because (1) our sample included small-diameter fallen boles that tend to decay rapidly, and (2) we measured density with techniques that minimized compaction and shrinkage.The decay rate at the old-growth stand, calculated indirectly by dividing bole mortality (megagrams per hectare per year) by the amount (megagrams per hectare) of fallen and standing dead woody material, was 0.028 year−1. This rate, three to five times those previously calculated directly from change in density alone, was almost identical to values calculated elsewhere from change in both volume and density. Decay rates based on change in density alone include only respired and leached material and exclude the large amount of material lost in fragmentation. This study shows the value of permanent plots, undisturbed by salvage logging, for retrospective studies of decomposition, nutrient cycling, and productivity.

The Geomorphic Significance of Log Steps in Forest Streams1

Abstract A functional account of log steps in forest streams is provided by field surveys of 163 kilometers of streams in the central Oregon Coast Range. Natural treefall, rather than silvicultural activities, accounts for the majority of log steps. During low-flow conditions, dissipation of potential stream energy by log steps amounts to 6 percent, approximately equal to that by falls. There are no statistically significant differences regarding spatial distribution of log steps between study basins with contrasting silvicultural and natural stream inputs of large woody debris. However, significant spatial differences are revealed between streams of various orders, a finding that points to channel flushing capacity and stream-adjacent topography as dominant controls on log step development. Application of thermodynamic principles to stream systems demonstrates that neither falls nor log steps cause a statistically significant difference in equilibrium conditions of stream networks. The volume of sediment...