Accumulation Of Coarse Woody Debris Research Articles

Unearthing the legacy of wildfires: post fire pyrogenic carbon and soil carbon persistence across complex Pacific Northwest watersheds

Wildfires have the potential to dramatically alter the carbon (C) storage potential, ecological function, and the fundamental mechanisms that control the C balance of Pacific Northwest (PNW) forested ecosystems. In this study, we explored how wildfire influences processes that control soil C stabilization and the consequent soil C persistence, and the role of previous fire history in determining soil C fire response dynamics. We collected mineral soils at four depth increments from burned (low, moderate, and high soil burn severity classes) and unburned areas and surveyed coarse woody debris (CWD) in sites within the footprint of the 2020 Holiday Farm Fire and in surrounding Willamette National Forest and the H.J. Andrews Experimental Forest. We found few changes in overall soil C pools as a function of fire severity; we instead found that unburned sites contained high levels of pyrogenic C (PyC) that were commensurate with PyC concentrations in the high severity burn sites—pointing to the high background rate of fire in these ecosystems. An analysis of historical fire events lends additional support, where increasing fire count is loosely correlated with increasing PyC concentration. An unexpected finding was that PyC concentration was lower in low soil burn severity sites than in control sites, which we attribute to fundamental ecological differences in regions that repeatedly burn at high severity compared with those that burn at low severity. Our CWD analysis showed that high mean fire return interval (decades between fire events) was strongly correlated with low annual CWD accumulation rate; whereas areas that burn frequently had a high annual CWD accumulation rate. Within the first year postfire, trends in soil density fractions demonstrated no significant response to fire for the mineral-associated organic matter pool but slight increases in the particulate pool with increasing soil burn severity—likely a function of increased charcoal additions. Overall, our results suggest that these PNW forest soils display complex responses to wildfire with feedbacks between CWD pools that provide varying fuel loads and a mosaic fire regime across the landscape. Microclimate and historic fire events are likely important determinants of soil C persistence in these systems.

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.

Effects of species and environmental factors on browsing frequency of young trees in mountain forests affected by natural disturbances

We analyzed the effects of natural disturbances on relationships between forest regeneration and ungulate browsing. Specifically, we asked if natural disturbances affect preferences of ungulate herbivores towards tree species and size classes; and how local and landscape-scale environmental factors affect spatial patterns of ungulate browsing in disturbed forest ecosystems. Our research was conducted in the Tatra National Park, a mountain range affected by large-scale intense disturbances over the last few decades. We used field data collected in a network of regularly distributed 600 circular sample plots where young trees were recorded and examined for browsing signs. Using forage ratio, the Ivlev’s electivity index and chi square tests, we found that the preferences of wild ungulates were similar to those known from undisturbed forests. Our analyses showed preference for deciduous species, especially rowan, sycamore maple and goat willow. The most common species, Norway spruce was strongly avoided by browsing ungulates. Short saplings from 0.5 m to 1.3 m tall were the most browsed size class. Effects of environmental variables on browsing were analyzed with zero-inflated negative binomial models. The occurrence of browsing was positively related to the total number of young trees and mature tree mortality. This suggests the influence of disturbances on spatial patterns of browsing pressure. The browsing frequency (number of browsed individuals per plot) was affected by mature tree mortality and densities of young palatable trees, including silver fir, sycamore maple and rowan. Elevation, geology, soil type, and potential solar radiation did not show any significant influence on the browsing frequency. Browsing frequency was also positively related to the distance to roads and hiking trails, indicating the role of human pressure upon the behaviour of ungulate herbivores. In addition, we analyzed the effects of accumulation of coarse woody debris (CWD) on browsing frequency and found this relationship to be nonlinear. Analysis for all tree species revealed that at low levels of CWD, the browsing frequency increased with CWD accumulation as a consequence of forest regeneration. However, a large amount of CWD (>25 m3) resulted in a decrease in browsing frequency, and this relationship was species-specific.

Dynamic Responses of Ground-Dwelling Invertebrate Communities to Disturbance in Forest Ecosystems.

In forest ecosystems, natural and anthropogenic disturbances alter canopy structure, understory vegetation, amount of woody debris, and the properties of litter and soil layers. The magnitude of these environmental changes is context-dependent and determined by the properties of the disturbance, such as the frequency, intensity, duration, and extent. Therefore, disturbances can dynamically impact forest communities over time, including populations of ground-dwelling invertebrates that regulate key ecosystem processes. We propose conceptual models that describe the dynamic temporal effects of canopy gap formation and coarse woody debris accumulation following disturbances caused by invasive insects, wind, and salvage logging, and their impacts on ground-dwelling invertebrate communities. Within this framework, predictions are generated, literature on ground-dwelling invertebrate communities is synthesized, and pertinent knowledge gaps identified.

Ecological Impacts of Emerald Ash Borer in Forests at the Epicenter of the Invasion in North America

We review research on ecological impacts of emerald ash borer (EAB)-induced ash mortality in the Upper Huron River watershed in southeast Michigan near the epicenter of the invasion of North America, where forests have been impacted longer than any others in North America. By 2009, mortality of green, white, and black ash exceeded 99%, and ash seed production and regeneration had ceased. This left an orphaned cohort of saplings too small to be infested, the fate of which may depend on the ability of natural enemies to regulate EAB populations at low densities. There was no relationship between patterns of ash mortality and ash density, ash importance, or community composition. Most trees died over a five-year period, resulting in relatively simultaneous, widespread gap formation. Disturbance resulting from gap formation and accumulation of coarse woody debris caused by ash mortality had cascading impacts on forest communities, including successional trajectories, growth of non-native invasive plants, soil dwelling and herbivorous arthropod communities, and bird foraging behavior, abundance, and community composition. These and other impacts on forest ecosystems are likely to be experienced elsewhere as EAB continues to spread.

Effects of Late Stages of Emerald Ash Borer (Coleoptera: Buprestidae)-Induced Ash Mortality on Forest Floor Invertebrate Communities

Emerald ash borer (EAB; Agrilus planipennis Fairmaire) is an invasive wood-borer causing rapid, widespread ash tree mortality, formation of canopy gaps, and accumulation of coarse woody debris (CWD) in forest ecosystems. The objective of this study was to quantify the effects of canopy gaps and ash CWD on forest floor invertebrate communities during late stages of EAB-induced ash mortality, when the effects of gaps are predicted to be smallest and effects of CWD are predicted to be greatest, according to the model proposed by Perry and Herms 2016a. A 2-year study was conducted in forest stands that had experienced nearly 100% ash mortality in southeastern Michigan, USA, near where EAB first established in North America. In contrast to patterns documented during early stages of the EAB invasion, effects of gaps were minimal during late stages of ash mortality, but invertebrate communities were affected by accumulation and decomposition of CWD. Invertebrate activity-abundance, evenness, and diversity were highest near minimally decayed logs (decay class 1), but diverse taxon-specific responses to CWD affected community composition. Soil moisture class emerged as an important factor structuring invertebrate communities, often mediating the strength and direction of their responses to CWD and stages of decomposition. The results of this study were consistent with the predictions that the effects of CWD on invertebrate communities would be greater than those of canopy gaps during late stages of EAB-induced ash mortality. This research contributes to understanding of the cascading and long-term ecological impacts of invasive species on native forest ecosystems.

Responses of Ground-Dwelling Invertebrates to Gap Formation and Accumulation of Woody Debris from Invasive Species, Wind, and Salvage Logging

Natural and anthropogenic disturbances alter canopy structure, understory vegetation, amount of woody debris, and the litter and soil layers in forest ecosystems. These environmental changes impact forest communities, including ground-dwelling invertebrates that are key regulators of ecosystem processes. Variation in frequency, intensity, duration, and spatial scale of disturbances affect the magnitude of these environmental changes and how forest communities and ecosystems are impacted over time. We propose conceptual models that describe the dynamic temporal effects of disturbance caused by invasive insects, wind, and salvage logging on canopy gap formation and accumulation of coarse woody debris (CWD), and their impacts on ground-dwelling invertebrate communities. In the context of this framework, predictions are generated and their implications for ground-dwelling invertebrate communities are discussed.

Long-term structural and biomass dynamics of virgin Tsuga canadensis-Pinus strobus forests after hurricane disturbance.

The development of old-growth forests in northeastern North America has largely been within the context of gap-scale disturbances given the rarity of stand-replacing disturbances. Using the 10-ha old-growth Harvard Tract and its associated 90-year history of measurements, including detailed surveys in 1989 and 2009, we document the long-term structural and biomass development of an old-growth Tsuga canadensis-Pinus strobus forest in southern New Hampshire, USA following a stand-replacing hurricane in 1938. Measurements of aboveground biomass pools were integrated with data from second- and old-growth T.canadensis forests to evaluate long-term patterns in biomass development following this disturbance. Ecosystem structure across the Tract prior to the hurricane exhibited a high degree of spatial heterogeneity with the greatest levels of live tree basal area (70-129m2 /ha) on upper west-facing slopes where P.strobus was dominant and intermixed with T.canadensis. Live-tree biomass estimates for these stratified mixtures ranged from 159 to 503Mg/ha at the localized, plot scale (100m2 ) and averaged 367Mg/ha across these portions of the landscape approaching the upper bounds for eastern forests. Live-tree biomass 71years after the hurricane is more uniform and lower in magnitude, with T.canadensis currently the dominant overstory tree species throughout much of the landscape. Despite only one living P.strobus stem in the 2009 plots (and fewer than five stems known across the entire 10-ha area), the detrital legacy of this species is pronounced with localized accumulations of coarse woody debris exceeding 237.7-404.2m3 /ha where this species once dominated the canopy. These patterns underscore the great sizes P.strobus attained in pre-European landscapes and its great decay resistance relative to its forest associates. Total aboveground biomass pools in this 71-year-old forest (255Mg/ha) are comparable to those in modern old-growth ecosystems in the region that also lack abundant white pine. Results highlight the importance of disturbance legacies in affecting forest structural conditions over extended periods following stand-replacing events and underscore that post-disturbance salvage logging can alter ecosystem development for decades. Moreover, the dominant role of old-growth P.strobus in live and detrital biomass pools before and after the hurricane, respectively, demonstrate the disproportionate influence this species likely had on carbon storage at localized scales prior to the widespread, selective harvesting of large P.strobus across the region in the 18th and 19th centuries.

Response of the forest floor invertebrate community to canopy gap formation caused by early stages of emerald ash borer-induced ash mortality

Emerald ash borer (EAB; Agrilus planipennis) is an invasive wood-boring beetle that causes rapid ash tree mortality, widespread formation of canopy gaps, and accumulation of coarse woody debris (CWD) in forests. The objective was to quantify the effects of canopy gaps, ash CWD and their interaction caused by EAB-induced ash mortality on the forest floor invertebrate community. A two-year manipulative experiment was conducted in forests at NASA Plum Brook Research Station in Ohio, USA. Canopy gaps caused by ash mortality decreased the activity-abundance of some taxa, such as Opiliones, Carabidae and several families of Collembola, as well as invertebrate richness and diversity, but had minor effects on community composition. CWD had minimal effects on the forest floor invertebrate community overall, but altered the activity-abundance of several invertebrate groups, and marginally increased taxonomic evenness in closed canopy treatments. The results of this study suggest that the effects of ash mortality on forest floor invertebrate communities change over time due to an inverse temporal relationship in magnitude effects of canopy gaps, which diminish over time, and accumulation of CWD, which increases over time. These findings contribute to our understanding of the effects of disturbance on ecosystems and the cascading ecological impacts of emerald ash borer invasions in forests.

Short-Term Responses of Ground Beetles to Forest Changes Caused by Early Stages of Emerald Ash Borer (Coleoptera: Buprestidae)-Induced Ash Mortality

Emerald ash borer (Agrilus planipennis Fairmaire), an invasive wood-boring beetle native to Asia, has killed hundreds of millions of ash trees since its accidental introduction into North America, resulting in widespread formation of canopy gaps and accumulations of coarse woody debris (CWD) in forests. The objective was to quantify effects of canopy gaps and CWD caused by early stages of emerald ash borer-induced ash mortality, and their interaction on ground beetle assemblages. The impact of canopy gaps and CWD varied, as gaps affected beetle assemblages in 2011, while effects of CWD were only observed in 2012. Gaps decreased beetle activity-abundance, and marginally decreased richness, driving changes in species composition, but evenness and diversity were unaffected. Effects of the CWD treatment alone were minimal, but CWD interacted with the canopy treatment, resulting in an increase in activity-abundance of ground beetles in canopy gaps without CWD, and a marginal increase in species richness in canopy gaps with CWD. Although there were some initial changes in species composition, these were ephemeral, suggesting that ground beetle assemblages may be resilient to disturbance caused by emerald ash borer. This study contributes to our understanding of the cascading ecological impacts of biological invasions on forest ecosystems.

The effects of topographic variation and the fire regime on coarse woody debris: Insights from a large wildfire

Coarse woody debris (CWD) is a common structural component of terrestrial ecosystems, and provides important habitat for biota. Fires modify the distribution of CWD, both spatially and temporally. Changes in fire regimes, such as those arising from prescribed burning and changing climatic conditions, make it critical to understand the response of this resource to fire. We created a conceptual model of the effects of fire on logs and dead trees in topographically diverse forests in which trees often survive severe fire. We then surveyed paired sites, in a damp gully and adjacent drier slope, ∼3.5years after a large wildfire in south-eastern Australia. Sites were stratified by fire severity (unburnt, understorey burnt and severely burnt), and fire history (burnt ⩽3years or ⩾20years prior to the wildfire). Both components of the fire regime influenced CWD availability in gullies. Severe wildfire and fire history ⩽3years reduced the volume of small logs (10–30cm diameter) in gullies, while severe wildfire increased the number of large dead trees in gullies. CWD on slopes was not affected by fire severity or history at ∼3.5years post-fire. Log volumes on slopes may recover more quickly after wildfire through rapid collapse of branches and trees. Gullies generally supported more logs than slopes, but longer inter-fire intervals in gullies may allow fuel loads to accumulate and lead to comparatively larger fire impacts. Given that fire severity and fire interval are predicted to change in many fire-prone ecosystems in coming decades, this study highlights the importance of understanding the interacting effects of multiple components of the fire regime with landscape structure. In particular, variation in fire interval and fire severity in relation to topographic position will influence the pattern of accumulation of coarse woody debris across the landscape, and therefore the structure and quality of habitats for biota.

Accumulation and decay dynamics of coarse woody debris in a Japanese old‐growth subalpine coniferous forest

AbstractFar less is known about the coarse woody debris (CWD) stock and decay process in temperate Asia compared with that in boreal and temperate Europe and North America. We estimated coniferous CWD stock (logs and snags), decay rate and process, and fungal species responsible for the decay process in a Japanese subalpine coniferous forest. The CWD mass was 42.4 Mg ha−1, which was the greatest among the previous data recorded in temperate Asia. The decay rate calculated using the annual input of CWD divided by CWD accumulation was 0.036 year−1, whereas the decay rate when measured chronosequentially was 0.020–0.023 year−1. The decay process was divided into two phases characterized by different dominant organic chemical constituents. In the first phase, both acid‐unhydrolyzable residue and holocellulose decayed simultaneously, suggestive of the white‐rot process. In the second phase, holocellulose was selectively decomposed and AUR accumulated, suggestive of the brown‐rot process. Nutrients (N, P, K, Na, Mg, and Ca) were mineralized in the first phase but immobilized in the second phase. The fruiting bodies of 26 taxa of fungi were recorded as occurring on CWD in the study area. Trichaptum abietinum and T. fuscoviolaceum, which dominated in the first phase and are known as white‐rot fungi, were assumed to be the main decomposers of lignocellulose in the first phase. Although no known strong wood decomposers dominated the second phase, Laetiporus sulphureus and Oligoporus caesius, known as brown‐rot fungi, were expected to participate in the selective decomposition of holocellulose in the second phase.

The scientific value of the largest remaining old-growth red pine forests in North America

Old growth red pine forests (Pinus resinosa) cover less than 1% of their original range in North America and are essential for maintaining biodiversity at stand and landscape scales. Despite this, the largest remaining old-growth red pine forest in the world, the Wolf Lake Forest Reserve, is currently threatened by mining claims in Northern Ontario and has been receiving considerable media and public attention in recent months. We provide a timely review of how large old growth red pine forests maintain biodiversity at several taxonomic levels (with a focus on trees and plants) through heterogeneous partitioning of limiting resources such as light and nitrogen, formation of complex habitats through increased accumulation of coarse woody debris, and the maintenance of natural disturbance-driven succession. These processes shape the overstory community, allowing for the regeneration of pines, coexistence of early-mid successional shade intolerant species and cross-ecotonal establishment of late successional tree species in response to regional warming over the past three decades. Using Wolf Lake as a case study, we review legislation and policy complexities around this issue and provide scientific arguments for the preservation of this forest. We invoke recent insights into the ecological role of refugia, the development of criteria for assessing endangered ecosystems, and the challenges of conservation in the face of climate change and disturbance regimes. These forests are ecologically important and provide a scientifically irreplaceable system for assessing baseline ecosystem function, processes and services. As the largest remaining old-growth red pine forest in the world, Wolf Lake Forest Reserve deserves intensive study, monitoring and full protection from future development.

Coarse woody debris facilitates oak recruitment in Białowieża Primeval Forest, Poland

While oaks contribute to the ecology and economy of temperate lowland forests, recruitment into larger size classes is generally scarce. Ungulate herbivory is a limiting factor for tree recruitment, thus natural structures protecting against ungulates may be important for recruitment success. We studied oak recruitment in relation to coarse woody debris (CWD) in the Białowieża National Park, Poland, one of the last remaining reference sites for undisturbed temperate lowland forests in Europe that contains the full natural assemblage of large ungulate species and their predators. We compared two contrasting management types: one that excludes all forestry activities (the strict reserve) and one where sanitary cutting and removal of bark-beetle infested Picea abies occurs to prevent further spread.We sampled 4m wide transects (19ha in total, of which 15.8ha in the strict reserve) and recorded sapling height and sapling browsing, distance from, height of and CWD encirclement, distance to and diameter of mature oaks, tree composition, distance to and diameter of nearest trees, canopy openness and cover of herbs, mosses, bare soil and litter in an equal number of plots with and without saplings. We found 161 oak saplings (8.5/ha). CWD was predominantly formed by P. abies. Sapling plots contained more often CWD than plots without saplings. Also, the distance to CWD was smaller and the CWD encirclement was higher in sapling plots, while canopy cover did not differ. Sapling height increased and sapling browsing decreased with increasing presence of CWD. Both CWD and recruitment beyond 50cm were reduced in the managed zone.Our study shows that CWD plays an essential role for the recruitment of oaks in old-growth temperate forest systems, predominantly via protection against ungulate browsing. Sanitary cutting of infested trees, a common management practice in temperate forests, prevents the natural accumulation of CWD and so can be counter-productive for the recruitment of appreciated species.

Conflicting effects of woody debris on stream fish populations: implications for management

Summary1. Coarse woody debris (CWD) in stream channels causes changes in flow, sedimentation and ratios of pool to riffle areas. There is a consensus among fishery managers and scientists that CWD is beneficial to stream fish communities because of its enhancement of habitat diversity, invertebrate production and cover. Our hypothesis was that CWD accumulation or introduction would not increase in‐stream habitat capacity for all species and their ontogenic stages at reach and stream scales.2. The study used a system of gravel‐bed streams with naturally dynamic CWD accumulations and a fish community consisting of Salmo trutta, Cotttus gobio, Phoxinus phoxinus, Lampetra cf planeri, Nemacheilus barbatulus and Anguilla anguilla. Cotttus gobio and L. cf planeri are protected by an EU Directive and S. trutta is exploited for angling. Riffles, pools and CWD matrices, considered as the basic habitat/spatial units of channel structure, were sampled separately and abundance of each fish species quantified seasonally at each spatial scale.3. Multiple‐pass electric fishing techniques were used. Capture efficiencies were calculated for species, habitat and season. Areal densities (number m−2) were compared for habitat types and season using nonparametric anova. Canonical analysis and stepwise multiple regression were used to show the most influential physical variables on fish density. Densities were also compared by unit volume (numbers m−3) for pools and CWD matrices to investigate direct three‐dimensional use for cover. Reach‐scale densities for each fish species in relation to habitat composition were made using Spearman rank correlation of habitat‐scale densities with proportionate areas of the different habitat units in the reach.4. Habitat‐scale densities of bullheads and age 0+ trout were negatively correlated with depth and CWD areas for some seasons. Densities of lampreys, older trout, eels and minnows were positively correlated with depth in some seasons. Water depth had the most consistent influence on fish abundance at the habitat unit scale. Three‐dimensional comparisons of pools and CWD matrices indicated that only trout older than 1+ may use CWD habitats as cover.5. Reach‐scale densities of 0+ trout and bullheads were significantly correlated with proportion of riffle area and negatively with CWD and combined CWD‐pool habitat area in the reach. Densities of older trout, large eels and lampreys were positively correlated with CWD area and combined CWD‐pool area in some seasons. Inundation of riffles caused by impoundment upstream of CWD accumulations reduced spawning habitat for trout, bullheads, brook lampreys, minnows and stone loach. A trade‐off was an increase in refugia for older trout, minnows and eels.6. Coarse woody debris accumulation in streams is not beneficial to all species or ontogenic stages in a mixed species population and could severely limit essential habitat areas for some species. Thus, physical manipulation of channels should be implemented only after a thorough study of the habitat relationships of all species present, especially where protected species coexist with target species. The relative importance of in‐stream morphological changes depends on the spatial and temporal scale of the species life histories.

Coarse Woody Debris in Southern United States Loblolly Pine Plantations: From Stand-Level to Regional Scales

Abstract Broad-scale estimates of coarse woody debris (CWD) yield across landscapes are somewhat rare, despite the importance of CWD in ecosystem functioning and its potential role in terrestrial carbon cycles. Yields of CWD were estimated at regional scales by linking a stand-level predictive model with regional forest inventory data for 11 states in the southern United States. We estimated that the accumulation of CWD in late-rotation loblolly pine plantations across the South totals 48.67 million metric tons of dry wood necromass, the carbon equivalent of 24.33 million metric tons. This represents annual CO2 emissions of 21 coal-fired power plants, or the amount of carbon sequestered each year in 7 million ha of pine forests. Confidence intervals for CWD dry weight per hectare generally did not exceed ±25% of the estimated values. Although county-level estimates were of higher uncertainty, the spatial pattern appeared to be relatively consistent with the extent of loblolly pine, with low yields near the extremes of the species' natural range and high yields in extensively forested portions of its range. Quantifying regional carbon stores of CWD with respect to stand-level management activities may improve accuracy of regional estimates and provide further insight into management effects on the carbon pool and the carbon cycle.

Site and stand effects on coarse woody debris in montane mixed forests of Eastern Italian Alps

The role of deadwood on biodiversity conservation of forest ecosystems is widely recognised. Interest on deadwood has increased in the last years, and forest management policy regards deadwood as indicator of sustainable forest management.This study took place in mixed montane forests in Eastern Italian Alps. The objective was to determine how past forest management, topography and forest structure influenced coarse woody debris (CWD) accumulation. 124 sampling points were established in four forest reserves, where time since active management activities ranges from 12 to more than 50 years. A multivariate analysis was performed to investigate the connections among site, stand characteristics, and CWD.Coarse woody debris volume in the reserves was similar to other forests withdrawn from regular management in last decades in central Europe. However, CWD stocking was much lower than in old-growth montane mixed forest. Both site and stand characteristics determined CWD accumulation. Elevation, basal area of living trees and human impact emerged as the most important factors. These aspects are connected with the accretion (density-dependent mortality) and the depletion (harvesting, decay) of deadwood in the stand. In the next decades we expect an increase of deadwood stocking, due to density-dependent mortality and disturbances.

Effects of increased forest productivity and warmer climates on carbon sequestration, run-off water quality and accumulation of dead wood in a boreal landscape: A modelling study

Forest productivity is expected to increase in the future owing to the use of genetically improved plant material and climate warming. Increased productivity will lead to shorter optimum rotation lengths and larger annual clear-cut areas. This study explored the likely effects of increased forest production and a warmer climate in 15 scenarios (five productivity levels and three climate conditions) on: (1) wood production, (2) carbon sequestration, (3) water quality, and (4) amounts of coarse woody debris (CWD). The effects were simulated using a set of ecosystem models incorporating the same climate and management scenarios in a hypothetical managed boreal forest landscape. Under the assumption that increased productivity is coupled to a proportional decrease in rotation length, the outputs at the landscape-level scale were briefly as follows. In each simulated climate scenario, increased productivity resulted in increases in above- and below-ground carbon sequestration, and reduced CWD accumulation, but did not have significant effects on dissolved total nitrogen (DTN) loads in run-off water. In addition, at every simulated productivity level, a warmer climate led to reductions in carbon sequestration below ground and amounts of CWD, but increases in DTN contents in run-off water. Reasons for these trends are identified and explained.

Short-term impact of post-fire salvage logging on regeneration, hazardous fuel accumulation, and understorey development in ponderosa pine forests of the Black Hills, SD, USA

We examined the impacts of post-fire salvage logging on regeneration, fuel accumulation, and understorey vegetation and assessed whether the effects of salvage logging differed between stands burned under moderate and high fire severity following the 2000 Jasper Fire in the Black Hills. In unsalvaged sites, fire-related tree mortality created a large standing pool of available fuel, resulting in a rapid increase in surface fuel loads. After 5 years, fine woody debris (FWD) and coarse woody debris (CWD) increased ~1380% and 980% in unsalvaged sites, resulting in FWD and CWD loads of 13 and 25 Mg ha–1, respectively. In contrast, salvage logging limited the rate of accumulation of FWD to ~110% over the same time period and total accumulation of CWD to 16 Mg ha–1. In moderate-severity sites, regeneration was 75% lower in salvaged sites owing to low seed-tree retention, suggesting a re-evaluation of salvage guidelines during future operations in the Black Hills. The likelihood of timely regeneration in high-severity sites, regardless of salvage treatment, is low. We found no discernible effect of salvage logging on understorey development 5 years after fire. Logging caused neither a reduction in total plant cover nor an increase in the abundance of exotic species.

THE INFLUENCE OF SUCCESSIONAL PROCESSES AND DISTURBANCE ON THE STRUCTURE OF TSUGA CANADENSIS FORESTS

Old-growth forests are valuable sources of ecological, conservation, and management information, yet these ecosystems have received little study in New England, due in large part to their regional scarcity. To increase our understanding of the structures and processes common in these rare forests, we studied the abundance of downed coarse woody debris (CWD) and snags and live-tree size-class distributions in 16 old-growth hemlock forests in western Massachusetts. Old-growth stands were compared with eight adjacent second-growth hemlock forests to gain a better understanding of the structural differences between these two classes of forests resulting from contrasting histories. In addition, we used stand-level dendroecological reconstructions to investigate the linkages between disturbance history and old-growth forest structure using an information-theoretic model selection framework. Old-growth stands exhibit a much higher degree of structural complexity than second-growth forests. In particular, old-growth stands had larger overstory trees and greater volumes of downed coarse woody debris (135.2 vs. 33.2 m3/ha) and snags (21.2 vs. 10.7 m3/ha). Second-growth stands were characterized by either skewed unimodal or reverse-J shaped diameter distributions, while old-growth forests contained bell-shaped, skewed unimodal, rotated sigmoid, and reverse J-shaped distributions. The variation in structural attributes among old-growth stands, particularly the abundance of downed CWD, was closely related to disturbance history. In particular, old-growth stands experiencing moderate levels of canopy disturbance during the last century (1930s and 1980s) had greater accumulations of CWD, highlighting the importance of gap-scale disturbances in shaping the long-term development and structural characteristics of old-growth forests. These findings are important for the development of natural disturbance-based silvicultural systems that may be used to restore important forest characteristics lacking in New England second-growth stands by integrating structural legacies of disturbance (e.g., downed CWD) and resultant tree-size distribution patterns. This silvicultural approach would emulate the often episodic nature of CWD recruitment within old-growth forests.