Abundance Of Coarse Woody Debris Research Articles

The diversity of epixylic bryophytes in relation to dead wood properties and forest management in New Brunswick, Canada

Rotting wood is widely recognized as an important feature for bryophyte diversity in forest ecosystems but forest management practices, focused on high yields, have led to widespread reductions in the quantity and quality of coarse woody debris (CWD). As a result, many epixylic specialists are now uncommon or threatened throughout much of their former ranges. How much CWD is required to maintain desirable biodiversity, and which qualities of CWD do this most effectively is still to be answered. To address this, we analyzed two datasets from mid-rotation and mature plantations from the same landscape to better understand how the epixylic community varies with stand age, wetness, silvicultural treatment, and the abundance and type of CWD. Mature stands were either partially cut with a strip-cut treatment or were untreated. Mid-rotation plantations had a higher richness of non-Sphagnum mosses and liverworts than mature plantations. Both plantation types had a similar Simpson’s diversity indices, but these were lower than those of treated and untreated mature white cedar stands and untreated mature softwood stands. While composition of both plantation types was similar, only mature plantations differed significantly from other stand types. We speculate that this discrepancy between mid-rotation plantations and mature plantations was due to better soil drainage and a longer duration of intensive management in mature plantations, leading to reduced CWD abundance, and therefore to reduced bryophyte diversity. Our results revealed a clear positive relationship between total CWD surface area and liverwort richness and diversity in xeric sites while no relation was detected in mesic sites. More CWD is better in the case of xeric sites, where apparent asymptote of diversity is near the maximum total CWD detected in these stands. Because canopy composition and humidity also had a significant influence on bryophyte diversity and composition, further studies are needed to clearly identify thresholds of CWD surface area that take into account different stand types, soil moisture, fertility regimes, or with regards to the ecosystem in which the managed stands occurs.

Long-term changes in coarse woody debris abundance in three Appalachian headwater streams with differing best management practices

IntroductionTimber harvests influence coarse woody debris (CWD) dynamics both initially and long-term—contributing a significant amount of CWD as slash immediately after harvest, but also removing some or all of the mature trees necessary to produce CWD over time. Whereas shelterwood and other similar timber harvest systems retain varying amounts of the overstory, preserving CWD production after harvest, commercial clearcutting essentially eliminates sources of fresh CWD until regenerating trees are large enough to contribute CWD through fallen limbs or trunks, often decades after harvest. Forestry best management practices (BMPs) are critical for reducing the water quality impacts of timber harvest, but their effects on riparian and stream CWD are not well understood.MethodsThe current project explores CWD dynamics (surveyed in 2001, 2004, 2009, and 2020) in three eastern Kentucky watersheds receiving differing timber harvest treatments in 1983: unharvested control, BMPs (clearcut with a protected streamside management zone), and no BMPs (clearcut).ResultsAnalysis of hydrology data over the period of record demonstrated significant flooding in 2004 that likely “reset” CWD in the study watersheds. Coarse woody debris volume was higher in control (3.33 m3/ha) than no BMP (1.03 m3/ha) in 2020, with CWD accumulation rates ranging from 0.039 m3/ha in the no BMP watershed to 0.19 m3/ha in the control.DiscussionWhile not significantly different, CWD volume was nominally higher in the BMP watershed than the No BMP watershed, suggesting that, in addition to their many other benefits, streamside management zones help facilitate CWD provisioning during stand initiation after a commercial clearcut harvest. Furthermore, this study suggests that provisioning of CWD may not recover after clearcut harvesting for 100 years or more.

Ixodes scapularis density in US temperate forests shaped by deer, earthworms, and disparate factors at two scales

AbstractForest and wildlife management can help regulate the risk of human exposure to tick‐borne pathogens by influencing the population density of host‐seeking ticks and the pathogen infection prevalence in tick populations. For the blacklegged tick (Ixodes scapularis), also known as the deer tick, the overall density of host‐seeking nymphs and the density of nymphs infected with Borrelia burgdorferi sensu stricto (which causes Lyme disease) are often closely and positively correlated. We sought to identify biotic and abiotic factors influencing nymph abundance in a multiscale assessment within and across forested landscapes in northern Wisconsin. On a set of randomly located plots within each of six mesic, hardwood‐dominated forests, we collected host‐seeking and on‐host ticks, observed two common mammal hosts (white‐tailed deer and mice), and characterized the structure and composition of the forest plant community. We also surveyed activity of exotic invasive earthworms, which are altering forest structure in the region. At the broader forest‐level scale (n = 6), nymphal tick abundance was positively related to deer population density after accounting for the negative influence of forb cover. At the finer plot‐level scale (n = 87), nymph abundance was positively correlated with the abundance of coarse woody debris and negatively correlated with the density of earthworm castings, an indicator of Lumbricid (nightcrawler) activity. Thus, we identified a suite of key factors, operating at different spatial scales, that shape the suitability of forest habitat for questing immature ticks. These findings inform our basic understanding of blacklegged tick ecology and also have important implications for managing tick‐borne pathogens in forest ecosystems and landscapes.

Elevational variation in abundance of coarse woody debris in subalpine forests, central Japan

In recent years, coarse woody debris (CWD) of deadwood has attracted attention as a long-term carbon pool for global warming problems. Environmental factors such as temperature and precipitation vary greatly with elevation. Hence, it is expected that the carbon storage by CWD varies with elevation. However, few studies have examined the abundance of CWD along elevations. Therefore, we investigated the abundance and decay classes of CWD, aboveground biomass (AGB) and aboveground net primary production (ANPP) of living trees along an elevational gradient (1600–2800 m above sea level) in subalpine coniferous forests, central Japan. AGB, ANPP and CWD decreased with increasing elevation. AGB at 2800 m was about 10% of that at 1600 m a.s.l. On the other hand, CWD at 2800 m was only 2.2% of that at 1600 m a.s.l. Thus, the ratio of CWD to AGB was lower at higher elevations. The relative frequency of small CWD increased with elevation. In addition, smaller CWD tended to decay less. The lower ratio of CWD mass to AGB at higher elevations was probably caused by smaller CWD because small CWD rapidly disappears via the high decomposition rate due to its high ratio of surface area to volume. Therefore, this study suggests that the importance of CWD relative to AGB for carbon storage decreases with elevation in subalpine forests. Climate change may alter the balance between CWD and AGB by changing ANPP and decomposition rates along elevation gradients.

Elephant effects on treefall and logfall highlight the absence of megaherbivores in coarse woody debris conceptual frameworks

Despite the importance of coarse woody debris (CWD) in woody ecosystems, conceptual frameworks of its dynamics currently exclude the role of the megaherbivores, focusing instead on the role of insects, disease, fire, wind and droughts. However, recognizing the ecological roles of the megaherbivores is one of the most urgent contemporary issues, particularly as their decline will likely have unanticipated outcomes at the ecosystem-level. Here we used sites with and without elephants in a semi-arid woodland ecosystem in South Africa to test whether elephants changed the quantitative and qualitative features of the CWD profile in relation to other wood producers. We show that elephants increased the abundance of CWD, influenced its quality by toppling mostly maturing trees, and changed the distribution of large woody items along gentle hillslopes. Surprisingly, and despite the recognized importance of both CWD and elephants for biodiversity, there is almost no published data on the role of elephants in shaping wood-living communities by changing fallen woody debris dynamics. Our study contributes towards developing a broader conceptual framework of CWD dynamics that includes the role of megaherbivores and provides a novel view of the ecological consequences of the loss of the Pleistocene megaherbivores. Our findings have important implications for CWD restoration efforts in transformed systems that previously supported megaherbivores.

Hydrologic and forest management controls on dissolved organic matter characteristics in headwater streams of old-growth forests in the Oregon Cascades

Dissolved organic matter (DOM) is a critical component of the carbon cycle linking terrestrial and aquatic ecosystems. Although many factors have been identified as influencing DOM fluxes and biochemical quality in rivers with varying land cover types, controls on DOM composition in forested headwater catchments of the western U.S. are poorly understood. This study examined the effect of hydrologic patterns and forest management history on stream DOM chemistry at watersheds located in the H.J. Andrews Experimental Forest of the Oregon Cascades. Specific UV absorbance at 254nm (SUVA254), generally indicative of aromaticity, increased in streams during storms with increasing surficial soil horizon and litter DOM inputs. Fluorescence excitation and emission matrices (EEMs) with Parallel Factor Analysis (PARAFAC) identified a protein-like DOM fluorescent component as well as several other components associated with terrestrial plant material. Correlation analysis between the protein-like DOM component and hydrologic patterns, SUVA254, and DOC concentrations suggest that DOM during dry seasons represents more microbially-processed sources, such as protein-rich, deeper soil or DOM with greater in-stream microbial processing, compared to more plant-like surface soil sources observed during high flow. The base flow index (the proportion of base flow to total flow) showed a high correlation with the relative proportion of protein-like DOM indicating that deep soil water is a source of the protein-like signal. The relative proportions of the protein-like DOM and humic DOM were also influenced by the abundance of coarse woody debris (CWD), but not live tree biomass, with the proportions of protein-like DOM highest in harvested watersheds with low surficial CWD. This study shows UV and fluorescent spectroscopy is a viable finger printing method to elucidate DOM sources in pristine headwater streams at the western Cascades of Oregon.

Accumulation and Connectivity of Coarse Woody Debris in Partial Harvest and Unmanaged Relict Forests

When a tree dies, it continues to play an important ecological role within forests. Coarse woody debris (CWD), including standing deadwood (SDW) and downed deadwood (DDW), is an important functional component of forest ecosystems, particularly for many dispersal-limited saproxylic taxa and for metapopulation dynamics across landscapes. Processes, such as natural disturbance or management, modify forest composition and structure, thereby influencing CWD abundance and distribution. Many studies have compared older forests to forests managed with even-aged silvicultural systems and observed a prolonged period of low CWD occurrence after harvesting. With fine-scale spatial data, our study compares the long-term impacts of light partial harvesting on the CWD structure of eastern deciduous hardwood forests. We mapped and inventoried DDW and SDW using variable radius plots based on a 10 m×10 m grid throughout an unmanaged, structurally-complex relict forest and two nearby forests that were partially harvested over 46 years ago. The relict stand had significantly larger individual pieces and higher accumulations of DDW and SDW than both of the partially harvested stands. Connectivity of CWD was much higher in the relict stand, which had fewer, larger patches. Larger pieces and higher proportion of decay-resistant species (e.g. Quercus spp.) in the relict forest resulted in slower decomposition, greater accumulation and increased connectivity of CWD. Partial harvests, such that occur with selection forestry, are generally considered less disruptive of ecosystem services, but this study highlights the long-term impacts of even light partial harvests on CWD stocks and distribution. When planning harvesting events, forest managers should also consider alternative methods to ensure the sustainability of deadwood resources and function.

Slow Lives in the Fast Landscape: Conservation and Management of Plethodontid Salamanders in Production Forests of the United States

Intensively-managed forest (IMF) ecosystems support environmental processes, retain biodiversity and reduce pressure to extract wood products from other forests, but may affect species, such as plethodontid salamanders, that are associated with closed canopies and possess limited vagility. We describe: (1) critical aspects of IMF ecosystems; (2) effectiveness of plethodontid salamanders as barometers of forest change; (3) two case studies of relationships between salamanders and coarse woody debris (CWD); and (4) research needs for effective management of salamanders in IMF ecosystems. Although plethodontid salamanders are sensitive to microclimate changes, their role as ecological indicators rarely have been evaluated quantitatively. Our case studies of CWD and salamanders in western and eastern forests demonstrated effects of species, region and spatial scale on the existence and strength of relationships between plethodontid species and a “critical” microhabitat variable. Oregon slender salamanders (Batrachoseps wrighti) were more strongly associated with abundance of CWD in managed second growth forests than ensatina salamanders (Ensatina eschscholtzii). Similarly, CWD was not an important predictor of abundance of Appalachian salamanders in managed hardwood forest. Gaining knowledge of salamanders in IMF ecosystems is critical to reconciling ecological and economic objectives of intensive forest management, but faces challenges in design and implementation.

Wood-inhabiting fungi on pedunculate oak coarse woody debris in relation to substratum quantity and forest age

Wood-inhabiting fungi on pedunculate oak (<em>Quercus robur</em>) coarse woody debris (CWD) was investigated in 50 plots of 0.1 ha in oak stands of different ages in Lithuania. In maturing stands (50-120 years) the average volume of oak CWD was 4.7 m<sup>3</sup>/ha, and in mature stands (over 120 years) – 13.9 m3/ha. Both in maturing and mature stands, the greatest fraction of CWD consisted of fallen oak branches (81 % and 84 % respectively), whereas fallen trunks comprised about 10 % of the total units of CWD. In total 1350 records of 203 species (49 ascomycetes and 154 basidiomycetes) were collected during 2 years of investigation. Species richness and abundance increased significantly with the increase of volume and abundance of CWD. Higher species richness was detected in mature stands than in maturing ones. Wood-inhabiting species composition varied greatly at stand scale, and one third of all detected species occurred only in one plot. Red-listed fungi were found only in mature stands. We conclude that, even in managed oak stands, oak CWD maintains a rather diverse species composition of ascomycetes and basidiomycetes. However, the current practice of forestry in Lithuania of removing dying or dead wood of large volume, e.g. standing and fallen trunks, reduce the distribution of highly specialized, usually rare, and endangered fungi.

Interactions between overstorey and understorey vegetation along an overstorey compositional gradient

AbstractQuestionsWhat is the nature of the interactions between higher vegetation strata (overstorey) and lower strata (understorey vegetation) and among understorey vegetation layers in closed canopy forests? How does the abundance or richness of one vegetation layer affect the abundance or richness of the other?LocationBoreal mixed‐wood forests ofOntario andQuebec,Canada.MethodsWe sampled fire‐origin stands of varying overstorey composition from broad‐leaf‐dominated to mixed to conifer‐dominated stands on mesic sites inOntario and subhydric sites inQuebec. Overstorey tree species composition and understorey shrub, herb, bryophyte and lichen species cover and richness were estimated within 400‐m2circular plots. In addition, soil nutrients, coarse woody debris and light conditions were measured. Overstorey composition was expressed as the percentage basal area of broad‐leaf tree species. Path analysis was used to examine interactions among the forest layers.ResultsOverstorey broad‐leaf composition had positive effects on shrub and herb layer cover and herb layer richness, and negative effects on bryophyte and lichen species cover and richness. Shrub layer cover had no effect on herb layer cover, but shrub layer richness had a positive effect on herb layer richness. Herb layer cover and richness had negative effects on bryophyte species cover and richness. Bryophyte cover had no effect on lichen cover, but its richness was positively related to lichen richness. In both regions, soil pH, total nitrogen, total phosphorus and cation exchange capacity of the forest floor were positively correlated with overstorey broad‐leaf composition and with shrub layer cover and herb layer cover.ConclusionsIncreasing overstorey broad‐leaf composition, through its influence on soil nutrients, promotes shrub and herb layer species, but limits bryophyte and lichen species. In the overstorey‐controlled understorey resource environment, cover and richness of shrub and herb layers increase with resource availability, whereas bryophytes and lichens show positive associations with abundance of coarse woody debris.

Assessing and Harmonizing Lying Deadwood Volume with Regional Forest Inventory Data in Wallonia (Southern Region of Belgium)

Using lying deadwood or coarse woody debris (CWD) as an indicator of biodiversity and of sustainable forest management is on the rise among national and local forest inventories. Nevertheless choosing the most suitable sampling method is difficult as it depends mostly on CWD abundance and dimensions. In addition the CWD volume estimates of different regional inventories are rarely comparable. We therefore tested two generally recommended methods for lying deadwood: line intersect sampling and fixed area sampling. We assessed both methods in plots of the regional forest inventory of Wallonia (southern region of Belgium). Next we developed bridging functions that converts CWD volume estimates to estimates that would have been obtained with different thresholds. Results about precision and time requirement are very slightly in favour of the line intersect sampling method. Nevertheless, we have noted that this method has several drawbacks, especially in the context of a regional and multi-resource inventory. Beside the established bridging functions indicate that CWD volume estimate from the Walloon forest inventories should be reduced by 20% in order to be internationally harmonized.

Bird communities in hemiboreal old-growth forests: The roles of food supply, stand structure, and site type

Key factors causing the difference of wildlife populations in natural and managed forests are an important field of ecosystem and biodiversity research. To explore the factors contributing to bird-community features in the poorly studied European natural hemiboreal forests, we carried out a comparative study in old-growth and mature stands of five site types in Estonia. The mature stands were of clear-cut origin and managed for timber production. Old-growth hosted both more diverse and more abundant bird communities than mature stands, which does not support the putative ‘old-growth syndrome’ (high diversity at a low density) described previously in temperate Europe. Site-type specificity of bird communities was also more pronounced in old-growth, indicating a timber-harvesting induced process of biotic homogenization. In particular, natural swamp forests had characteristic bird species and those communities may be additionally sensitive to artificial drainage. In terms of invertebrate food supply, the availability of snails, rather than of insects, was related to bird-community characteristics; however, the influence of snails was due to one snail-poor forest type ( Vaccinium type pine stands), not management. The abundance of coarse woody debris was the main structural feature affecting bird communities; tree-size variation was additionally important for species richness. A significant unexplained ‘old-growth’ effect remained even after the variables describing food supply and stand structure were taken into account. Our results imply the distinct importance of old-growth of different site types for hemiboreal bird communities. However, we did not obtain any evidence of different key factors structuring the bird communities in old-growth and mature stands.

Addition of coarse woody debris – The early fungal succession on Picea abies logs in managed forests and reserves

Modern forestry practices have decreased the abundance of coarse woody debris (CWD), and as a result many species that depend on dead wood are now threatened. This implies a need to develop forestry practices that maintain biodiversity. We examined the conservation value of experimental spruce logs (control logs, logs placed in natural shade, and cut tree tops) for wood-inhabiting fungi in two forest stands, one nature reserve and one mature managed forest, in each of seven forest areas in northern Sweden. Here we report the initial findings of the experiment that was established in winter 2001–2002 and data were collected in 2002, 2003 and 2006. A pre-inventory of the local species composition in 2002 revealed a higher per area species richness, including red-listed species, in reserves than in managed forests. Ordination analyses of the experimental logs showed a significant effect of area, while not of stand type in 2003. ANOVA analysis showed no significant effect of stand type on species richness and abundance. In 2006, the species assemblage started to differentiate between the two stand types and forest age, forest site type (moisture), and distance to forest reserves, all explained part of the variation, whereas the amount of CWD, and species composition at the start of the experiment only showed a marginal effect. The early successional fungal community was dominated by two functional groups, humus-decayers and white-rot species, both characterized by a rapid, early colonization and fruit-body formation on the competition-free new substrate. A similar positive response to the new substrate was also observed for the mycorrhizal species in 2006. The high frequency and early appearance of humus-decayers and mycorrhizal species that do not primarily depend upon CWD for their nutrition suggest that their formation of fruiting bodies is limited by substrate availability. Thus some mycorrhizal fungi are apparently rare due to lack of suitable substrate for fruit-body formation. Evidence of dispersal-limitation was observed in 2006. Fomitopsis pinicola, an early colonizer in boreal forests, playing a key role for other wood-inhabiting organisms, colonized significantly more logs in the reserve stands compared with the managed stands. Our data demonstrate that lack of CWD strongly affects both species that depend upon wood for nutrition and species that depend upon wood for fruit-body formation. Thus some species may show an apparent rarity due to lack of suitable substrate. We conclude that creation of CWD appears to be a useful method to maintain or restore fungal diversity in boreal coniferous forests.

Short term effects of alternative silvicultural treatments on stand attributes in irregular balsam fir-black spruce stands

The eastern Canadian boreal forest exhibits a specific disturbance regime where forest fires are less frequent than in the western part. This particularity may explain the abundance of irregular stands with distinct ecological features. To ensure sustainable forest management, these characteristics require the implementation of an adapted silviculture regime. In this context, two selection cutting methods were developed and compared with more conventional techniques, initially designed for cutting more regular stands of the boreal forest (cutting leaving small merchantable stems, careful logging preserving advance regeneration). The comparison focused on the capacity of treatments to maintain the primary attributes of irregular boreal forests, including complex vertical structure, abundant tree cover, species composition, and an abundance of dead wood. Mortality and regeneration processes were also compared. The experiment includes three sectors dominated by irregular black spruce ( Picea mariana)-balsam fir ( Abies balsamea) stands. Treatments were replicated in each sector in 0.25 ha plots. Stand characteristics were sampled pre-harvest and monitored for 3 years after cutting. Initial results indicate an important treatment effect on residual structure. Selection cutting maintains an inverse (irregular) J-shaped structure, typical of natural stands. Also, selection cutting does not seem to produce a significant effect on tree species composition (no undesired balsam fir enrichment) and does not modify the abundance of coarse woody debris. From a sustainable forest management perspective, the selection methods tested appear efficient in maintaining the main attributes and processes of the boreal irregular stands over the short term.

On the efficiency of line intersect distance sampling

Sampling strategies commonly used for coarse woody debris (CWD) inventories, including line intersect sampling (LIS), typically require large sample sizes to estimate aggregate volume with reasonable precision. Line intersect distance sampling (LIDS) is a recently developed strategy based on a probability proportional-to-volume design and a linear sampling unit. In principle, the design augments the precision of volume estimators by increasing the intensity with which bulkier particles are sampled, while the transect-based protocol facilitates the search for qualifying particles. This study reports on the relative performances of LIDS and LIS in seven stands in Montana, USA. Particles selected by LIDS were consistently less numerous but larger in cross section than those selected at the same locations by LIS. In timed field trials, LIDS required more time than LIS, but CWD volume estimates from LIDS were generally more precise, more than offsetting the time differential. Conversely, aggregate length and abundance of CWD were generally estimated more efficiently with LIS. Results suggest that LIDS permits more efficient use of survey resources than LIS where CWD inventories focus on parameters relating to volume, biomass, or carbon. However, the constant volume factor design of LIDS is not advantageous where CWD frequency is of central interest.

HABITAT-MEDIATED VARIATION IN PREDATION RISK BY THE AMERICAN MARTEN

The probability of prey encounter, attack, capture, and kill are often hypothesized to depend on habitat structure, but field evidence in terrestrial systems is rare. We tested whether predation efficiency by the American marten (Martes americana) and fear of predation by their primary prey, the red-backed vole (Clethrionomys gapperi), differed between 20- to 50-year-old regenerating forest stands and older uncut stands. Our results showed that the frequency of prey encounter, prey attack, and prey kill were higher in old uncut forests, despite the fact that small-mammal density was similar to that in younger logged forests. These differences in predation efficiency were linked to higher abundance of coarse woody debris, which seems to offer sensory cues to martens, thereby increasing the odds of hunting success. Red-backed voles in regenerating forest stands exhibited increased wariness compared to voles living in old uncut forest, suggestive of a behavioral response to habitat-mediated variation in predation risk.

Degradation of Littoral Habitats by Residential Development: Woody Debris in Lakes of the Pacific Northwest and Midwest, United States

One of the least understood aspects of aquatic ecology is the role of riparian zones of lakes, and how these habitats and their functions are impacted by human development of lakeshores. We investigated the effects of residential lakeshore development on littoral coarse woody debris (CWD) distribution and on riparian forest characteristics by comparing 18 lakes in the U.S. Pacific Northwest with 16 previously surveyed lakes in the U.S. Upper Midwest. Residential development had a strong negative effect on CWD and riparian forest characteristics at both local and whole-lake scales. There was a strong positive correlation between riparian forest density and littoral CWD abundance in both regions. We found regional variation in CWD and riparian forest characteristics, mostly owing to differences in native forests. Our results suggest the role of local processes in determining CWD distribution and point to potential regional differences in littoral habitat structure associated with forest composition and lakeshore development that may have consequences for littoral-pelagic coupling in lakes.

Catchment disturbance and stream metabolism: patterns in ecosystem respiration and gross primary production along a gradient of upland soil and vegetation disturbance

Catchment characteristics determine the inputs of sediments and nutrients to streams. As a result, natural or anthropogenic disturbance of upland soil and vegetation can affect instream processes. The Fort Benning Military Installation (near Columbus, Georgia) exhibits a wide range of upland disturbance levels because of spatial variability in the intensity of military training. This gradient of disturbance was used to investigate the effect of upland soil and vegetation disturbance on rates of stream metabolism (ecosystem respiration rate [ER] and gross primary production rate [GPP]). Stream metabolism was measured using an open-system, single-station approach. All streams were net heterotrophic during all seasons. ER was highest in winter and spring and lowest in summer and autumn. ER was negatively correlated with catchment disturbance level in winter, spring, and summer, but not in autumn. ER was positively correlated with abundance of coarse woody debris, but not significantly related to % benthic organic matter. GPP was low in all streams and generally not significantly correlated with disturbance level. Our results suggest that the generally intact riparian zones of these streams were not sufficient to protect them from the effect of upland disturbance, and they emphasize the role of the entire catchment in determining stream structure and function.

Fuel reduction and coarse woody debris dynamics with early season and late season prescribed fire in a Sierra Nevada mixed conifer forest

Fire exclusion has led to an unnatural accumulation and greater spatial continuity of organic material on the ground in many forests. This material serves both as potential fuel for forest fires and habitat for a large array of forest species. Managers must balance fuel reduction to reduce wildfire hazard with fuel retention targets to maintain other forest functions. This study reports fuel consumption and changes to coarse woody debris attributes with prescribed burns ignited under different fuel moisture conditions. Replicated early season burn, late season burn, and unburned control plots were established in old-growth mixed conifer forest in Sequoia National Park that had not experienced fire for more than 120 years. Early season burns were ignited during June 2002 when fuels were relatively moist, and late season burns were ignited during September/October 2001 when fuels were dry. Fuel loading and coarse woody debris abundance, cover, volume, and mass were evaluated prior to and after the burns. While both types of burns reduced fuel loading, early season burns consumed significantly less of the total dead and down organic matter than late season burns (67% versus 88%). This difference in fuel consumption between burning treatments was significant for most all woody fuel components evaluated, plus the litter and duff layers. Many logs were not entirely consumed – therefore the number of logs was not significantly changed by fire – but burning did reduce log length, cover, volume, and mass. Log cover, volume, and mass were reduced to a lesser extent by early season burns than late season burns, as a result of higher wood moisture levels. Early season burns also spread over less of the ground surface within the burn perimeter (73%) than late season burns (88%), and were significantly patchier. Organic material remaining after a fire can dam sediments and reduce erosion, while unburned patches may help mitigate the impact of fire on fire-sensitive species by creating refugia from which these species can recolonize burned areas. Early season burns may be an effective means of moderating potential ecosystem damage when treating heavy and/or continuous fuels resulting from long periods of fire exclusion, if burning during this season is not detrimental to other forest functions.

Catchment disturbance and stream metabolism: patterns in ecosystem respiration and gross primary production along a gradient of upland soil and vegetation disturbance

Catchment characteristics determine the inputs of sediments and nutrients to streams. As a result, natural or anthropogenic disturbance of upland soil and vegetation can affect instream processes. The Fort Benning Military Installation (near Columbus, Georgia) exhibits a wide range of upland disturbance levels because of spatial variability in the intensity of military training. This gradient of disturbance was used to investigate the effect of upland soil and vegetation disturbance on rates of stream metabolism (ecosystem respiration rate [ER] and gross primary production rate [GPP]). Stream metabolism was measured using an open-system, single-station approach. All streams were net heterotrophic during all seasons. ER was highest in winter and spring and lowest in summer and autumn. ER was negatively correlated with catchment disturbance level in winter, spring, and summer, but not in autumn. ER was positively correlated with abundance of coarse woody debris, but not significantly related to % benthic organic matter. GPP was low in all streams and generally not significantly correlated with disturbance level. Our results suggest that the generally intact riparian zones of these streams were not sufficient to protect them from the effect of upland disturbance, and they emphasize the role of the entire catchment in determining stream structure and function.