Natural Disturbance Patterns Research Articles

Regeneration responses to gap size and coarse woody debris within natural disturbance-based silvicultural systems in northeastern Minnesota, USA

The use of silvicultural systems based on the natural disturbance patterns for a given region has been suggested as an approach for promoting late-successional forest characteristics and maintaining native biodiversity in managed forests. To this end, we examined the effectiveness of natural disturbance-based harvest gaps in maintaining and restoring native tree species diversity within second-growth northern hardwood systems in northeastern Minnesota, USA. In particular, tree regeneration and downed coarse woody debris (CWD) were measured 6- and 7-years post-treatment in 46 gaps that emulated the historic range of natural canopy opening sizes for northern hardwood forests in the upper Great Lakes region. Measurements were compared across gap size-classes (>0–0.02, >0.02–0.04, >0.04 ha) and with closed canopy portions of these systems. In addition, the factors affecting the recruitment of Betula alleghaniensis across gaps and within closed canopy were investigated due to the historical importance of this species in these forests. Seedling and sapling densities increased in harvest gaps; however, results indicated that these gaps did little to increase tree diversity, including the recruitment of shade mid-tolerant species, such as B. alleghaniensis. Gaps were dominated primarily by Acer saccharum and age distributions of dominant saplings within gaps indicated that most individuals established 10–40 years prior to gap formation. Establishment of B. alleghaniensis was strongly related to highly decayed, large coniferous pieces of CWD with little recruitment occurring on the undisturbed forest floor. Age distributions of B. alleghaniensis established on CWD suggest this species can persist on this substrate for at least a decade. Levels of CWD increased with increasing gap size; however, all gaps had lower levels of CWD compared to the surrounding intact forest. Our results suggest that management regimes based on natural canopy gap sizes within northern hardwood systems will do little to restore native tree diversity if provisions for creating the suitable seedling microsites historically generated by natural disturbance (e.g., exposed mineral soil, highly decayed wood) are not included within management prescriptions.

First decadal response to treatment in a disturbance-based silviculture experiment in Maine

Disturbance-based silvicultural systems generally seek to promote complex stand structures that are consistent with temporal and spatial patterns of natural disturbance while allowing for the sustainable harvest of timber. Gap-based harvesting systems are commonly used within this framework because they can be designed to approximate the frequencies and spatial patterns of a wide array of disturbance regimes. Patterns in stand-level growth, sapling recruitment and regeneration response were examined for one such gap-based system, the Acadian Forest Ecosystem Research Program (AFERP) in central Maine, that was designed to emulate the annual 1% disturbance frequency typical of the northeastern United States and Canada. A decade after treatment, stand-level differences in basal area growth and density between two gap-based treatments and an unharvested control were not statistically significant, largely due to low replication, but within-stand growth and regeneration responses differed strongly by spatial position relative to harvest gaps. Regeneration of shade-tolerant and intolerant species increased regardless of gap size, likely a response to increasing light availability from canopy openings due to harvesting and mortality. Further, there was evidence of gap size effects on sapling recruitment as large gaps (>1000 m 2) favored the growth and survival of mid-successional species such as red maple and white pine, while small gaps (<1000 m 2) favored late-succession species such as eastern hemlock and spruce. Overstory growth rates also differed by both species and position relative to harvest gaps with most species growing best in gaps and better along gap edges than in adjacent forest. Notably, overstory growth rates for white pine were not influenced by spatial position. These results suggest harvest gaps may have significant growth and regeneration impacts in adjacent, yet unharvested areas, which could lead to profound differences in forest development over the rotation. Obviously, longer-term studies of gap-based systems are needed to more clearly elucidate these responses.

Characterizing stand-replacing disturbance in western Alberta grizzly bear habitat, using a satellite-derived high temporal and spatial resolution change sequence

Timely and accurate mapping of anthropogenic and natural disturbance patterns can be used to better understand the nature of wildlife habitats, distributions and movements. One common approach to map forest disturbance is by using high spatial resolution satellite imagery, such as Landsat 5 Thematic Mapper (TM) or Landsat 7 Enhanced Thematic Mapper plus (ETM+) imagery acquired at a 30 m spatial resolution. However, the low revisit times of these sensors acts to limit the capability to accurately determine dates for a sequence of disturbance events, especially in regions where cloud contamination is a frequent occurrence. As wildlife habitat use can vary significantly seasonally, annual patterns of disturbance are often insufficient in assessing relationships between disturbance and foraging behaviour or movement patterns. The Spatial Temporal Adaptive Algorithm for mapping Reflectance Change (STAARCH) allows the generation of high-spatial (30 m) and -temporal (weekly or bi-weekly) resolution disturbance sequences using fusion of Landsat TM or ETM+ and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. The STAARCH algorithm is applied here to generate a disturbance sequence representing stand-replacing events (disturbances over 1 ha in area) for the period 2001–2008, over almost 6 million ha of grizzly bear habitat along the eastern slopes of the Rocky Mountains in Alberta. The STAARCH algorithm incorporates pairs of Landsat images to detect the spatial extent of disturbances; information from the bi-weekly MODIS composites is used in this study to assign a date of disturbance (DoD) to each detected disturbed area. Dates of estimated disturbances with areas over 5 ha are validated by comparison with a yearly Landsat-based change sequence, with producer's accuracies ranging between 15 and 85% (average overall accuracy 62%, kappa statistic of 0.54) depending on the size of the disturbance event. The spatial and temporal patterns of disturbances within the entire region and in smaller subsets, representative of the size of a grizzly bear annual home range, are then explored. Disturbance levels are shown to increase later in the growing season, with most disturbances occurring in late August and September. Individual events are generally small in area (<10 ha) except in the case of wildfires, with, on average, 0.4% of the total area disturbed each year. The application of STAARCH provides unique high temporal and spatial resolution disturbance information over an extensive area, with significant potential for improving understanding of wildlife habitat use.

Interactions of biological and herbicidal management of Melaleuca quinquenervia with fire: Consequences for ecosystem services

Exotic plant species invasion can alter ecosystem nutrient dynamics and natural disturbance patterns. The Australian tree Melaleuca quinquenervia has extensively invaded the Florida Everglades and is currently being suppressed using mechanical, herbicidal, and biological control management strategies. While these methods have been evaluated based on reductions in density and abundance of the target weed, other factors should be considered including consequences for ecosystem nutrient storages and interactions with natural disturbances such as fire. We hypothesized that the choice of management tactics, namely herbicidal or biological control, would differentially influence the quantity and availability of soil nutrients before and after a seasonal fire. The management of M. quinquenervia with a herbicide reduced the above- and belowground storage of nutrients both before and after a fire compared to a non-invaded area, while biological control increased storage. There were no differences in nitrogen availability between sites (non-invaded, herbicide, biological control) in the 0–5 cm or 5–15 cm soil depths before or after the fire. Pre-fire phosphorus availability was highest in the non-invaded site in the 0–5 cm soil depth and in the biological control site in the 5–15 cm soil depth. However, phosphorus availability was highest at both depths in the herbicide site post-fire. Biological control of M. quinquenervia using insect herbivores has proven to be effective at controlling plant growth and reproduction. The results of this study suggest that this method may have less of an impact on nutrient storage and cycling than herbicides.

Topographic and compositional influences on disturbance patterns in a northern Maine old-growth landscape

Disturbance patterns are strongly coupled with forest composition and structure, and patterns change through time in response to shifts in climate, anthropogenic impacts and other factors. Knowledge of the natural disturbance patterns for establishing baseline conditions for a forest type or ecosystem facilitates change detection for other elements of the biophysical system important to management and conservation. Dendrochronological reconstructions from old-growth forest remnants throughout northeastern North America document average decadal rates of disturbance of 5%–<10% over the last 150–300 years. Relatively frequent, low severity disturbance characterized by small gaps representing canopy openings made by 1–3 trees prevail in these forests dominated by varying mixtures of late-successional tree species. Few studies, though, have explicitly characterized differences related to composition or topographic setting in old-growth landscapes. We addressed this by comparing the temporal and spatial disturbance patterns reconstructed from tree rings at two spatial resolutions (0.5 ha and 200 m 2). Sites were selected to assess the influence of topography (slope) and cover type in stands where red spruce ( Picea rubens Sarg) and balsam fir ( Abies balsamea L. Mill) were key components. Low rates of disturbance (average <10% per decade) and small gap sizes (≤30 m 2) prevailed in all stands during the decades from 1850–1980. Episodic pulses of disturbance, of nearly moderate intensity in some stands, opened ca. 20–30% of the canopy area and were associated with wind events and/or insect outbreaks that differentially affected stands. We found no significant difference in the average temporal rates of disturbance related to cover type or topography in 0.5-ha plots. However, the influence of these factors was evident in comparisons of gap areas estimated for 200-m 2 plot sections. At this resolution, the largest canopy openings (≥100 m 2) occurred most frequently in slope sites, enabling pulses of canopy accession for Betula alleghaniensis (Britton). Whereas the smallest canopy openings (≤30 m 2) dominated softwood stands, favoring red spruce, balsam fir and other shade-tolerant species throughout the forest. The variable effects of common disturbance agents, regardless of topographic position and/or cover types, points to the important role of biological legacies determining stand structure and composition on subsequent disturbance events and long-term patterns.

Simulating restoration strategies for a southern boreal forest landscape with complex land ownership patterns

Restoring altered forest landscapes toward their ranges of natural variability (RNV) may enhance ecosystem sustainability and resiliency, but such efforts can be hampered by complex land ownership and management patterns. We evaluated restoration potential for southern-boreal forests in the ∼2.1millionha Border Lakes Region of northern Minnesota (U.S.A.) and Ontario (Canada), where spatially distinct timber harvest and fire suppression histories have differentially altered forest conditions (composition, age–class distribution, and landscape structure) among major management areas, effectively resulting in forest landscape “bifurcation.” We used a forest landscape simulation model to evaluate potential for four hypothetical management and two natural disturbance scenarios to restore forest conditions and reduce bifurcation, including: (1) a current management scenario that simulated timber harvest and fire suppression practices among major landowners; (2) three restoration scenarios that simulated combinations of wildland fire use and cross-boundary timber harvest designed to emulate natural disturbance patterns; (3) a historical natural disturbance scenario that simulated pre-EuroAmerican settlement fire regimes and windthrow; and (4) a contemporary fire regime that simulated fire suppression, but no timber harvest. Forest composition and landscape structure for a 200-year model period were compared among scenarios, among major land management regions within scenarios, and to six RNV benchmarks. The current management scenario met only one RNV benchmark and did not move forest composition, age–class distribution, or landscape structures toward the RNV, and it increased forest landscape bifurcation between primarily timber-managed and wilderness areas. The historical natural disturbance scenario met five RNV benchmarks and the restoration scenarios as many as five, by generally restoring forest composition, age–class distributions, and landscape structures, and reducing bifurcation of forest conditions. The contemporary natural disturbance scenario met only one benchmark and generally created a forest landscape dominated by large patches of late-successional, fire-prone forests. Some forest types (e.g., white and red pine) declined in all scenarios, despite simulated restoration strategies. It may not be possible to achieve all objectives under a single management scenario, and complications, such as fire-risk, may limit strategies. However, our model suggests that timber harvest and fire regimes that emulate natural disturbance patterns can move forest landscapes toward the RNV.

Modeling marine protected areas for threatened eiders in a climatically changing Bering Sea

Delineating protected areas for sensitive species is a growing challenge as changing climate alters the geographic pattern of habitats as well as human responses to those shifts. When human impacts are expected within projected ranges of threatened species, there is often demand to demarcate the minimum habitat required to ensure the species' persistence. Because diminished or wide-ranging populations may not occupy all viable (and needed) habitat at once, one must identify thresholds of resources that will support the species even in unoccupied areas. Long-term data on the shifting mosaic of critical resources may indicate ranges of future variability. We addressed these issues for the Spectacled Eider (Somateria fischeri), a federally threatened species that winters in pack ice of the Bering Sea. Changing climate has decreased ice cover and severely reduced the eiders' benthic prey and has increased prospects for expansion of bottom trawling that may further affect prey communities. To assess long-term changes in habitats that will support eiders, we linked data on benthic prey, sea ice, and weather from 1970 to 2001 with a spatially explicit simulation model of eider energy balance that integrated field, laboratory, and remote-sensing studies. Areas estimated to have prey densities adequate for eiders in 1970-1974 did not include most areas that were viable 20 years later (1993-1994). Unless the entire area with adequate prey in 1993-1994 had been protected, the much reduced viable area in 1999-2001 might well have been excluded. During long non-foraging periods (as at night), eiders can save much energy by resting on ice vs. floating on water; thus, loss of ice cover in the future might substantially decrease the area in which prey densities are adequate to offset the eiders' energy needs. For wide-ranging benthivores such as eiders, our results emphasize that fixed protected areas based on current conditions can be too small or inflexible to subsume long-term shifts in habitat conditions. Better knowledge of patterns of natural disturbance experienced by prey communities, and appropriate allocation of human disturbance over seasons or years, may yield alternative strategies to large-scale closures that may be politically and economically problematic.

Influence of harvest gaps and coarse woody material on click beetles (Coleoptera: Elateridae) in Maine’s Acadian forest

In order to maintain biodiversity in forests, it has been recommended that harvests be designed after patterns of natural disturbance. Using a long-term study that includes harvest treatments designed to emulate tree-fall gap disturbances in Maine’s Acadian forest, we examined how the species richness, abundance, diversity, and assemblage similarity of click beetles inhabiting coarse woody material (CWM) were affected by gap harvesting and CWM characteristics (diameter, degree of decay, and type of wood). There were few differences in beetle assemblages between 0.07 and 0.12 ha harvest gap treatments. Four of the most common species had higher abundances under a closed forest canopy than within harvest gaps. Species richness and total abundance were higher in CWM that had larger diameters and were more decayed. Species assemblages also differed with the degree of wood decomposition. Diversity was higher in CWM from softwood trees than hardwood trees. Results from this study suggest that small ( 35 cm).

STAND AND LANDSCAPE‐LEVEL DISTURBANCE DYNAMICS IN OLD‐GROWTH FORESTS IN WESTERN MASSACHUSETTS

Natural disturbances strongly influence the dynamics and developmental patterns of forest ecosystems; however, relatively little is known about the historic patterns of natural disturbance for many portions of eastern North America, such as southern New England, where human disturbance has predominated for centuries. For these regions, much of our understanding of natural disturbance dynamics comes from studies of younger second‐growth forests or isolated old‐growth stands, thus limiting the temporal and spatial resolution of our knowledge of dynamics in these regions. To address these limitations, we analyzed dendroecological data from the 18 largest remaining old‐growth stands in western Massachusetts, ranging in proximity from 1–60 km apart, in an effort to characterize the historic stand and landscape‐level patterns of natural disturbance. Our results indicate that disturbance regimes for these systems were dominated by relatively frequent, low‐intensity disturbances (average 5.0% ± 0.2% canopy area disturbed per decade) operating somewhat randomly on the landscape. Across the study areas, most decadal disturbances (86.2%) involved &lt;10% canopy loss. There was no evidence of stand‐replacing disturbances during the period examined (1700–1989), and the maximum canopy area disturbed in any given decade was 26.3%. Nonmetric multidimensional scaling demonstrated that several forests shared similar disturbance histories despite being separated by &gt;50 km. Comparisons of these patterns with model simulations of past hurricane events and historical documents suggest that broadscale disturbances, such as hurricanes and ice storms, resulted in common disturbance peaks and subsequent recruitment peaks at spatially disparate areas in the 1790s, 1870s, 1900s, and 1920s. Conversely, the lack of synchrony in proximate areas during these events highlights the patchy nature of these disturbances on the landscape. Compositional and physiographic factors influenced disturbance patterns, as stands located on northwest‐facing slopes or containing significant Picea rubens components in the forest overstory experienced the highest levels of disturbance. Our results highlight the utility of incorporating dendroecological reconstructions across numerous old‐growth stands to interpret the historic stand and landscape‐level disturbance dynamics in areas devoid of large, contiguous old‐growth landscapes.

Can natural disturbance-based forestry rescue a declining population of grizzly bears?

Forest managers are increasingly considering historic patterns of natural forest disturbance as a model for forest harvesting and as a coarse-filter ecosystem management tool. We evaluated the long-term (100-year) persistence of a grizzly bear population in Alberta, Canada using forest simulations and habitat modelling. Even with harvesting the same volume of timber, natural disturbance-based forestry resulted in a larger human footprint than traditional two-pass forestry with road densities reaching 1.39 km/km 2 or more than three times baseline conditions and suggested maximum levels of security for grizzly bears. Because bears favour young forests and edges where food resources are plentiful, a future shift to young forests and more edge habitat resulted in a 20% projected increase in habitat quality and a 10% projected increase in potential carrying capacity. Human-caused mortality risk, however, offset any projected gains in habitat and carrying capacity resulting in the loss of all secure, unprotected territories, regardless of forest harvest method, within the first 20–30 years of simulation. We suggest that natural disturbance-based forestry is an ill-suited management tool for sustaining declining populations of grizzly bears. A management model that explicitly considers road access is more likely to improve grizzly bear population persistence than changing the size of clear-cuts. In fact, large clear cuts might be counter productive for bears since a diversity of habitats within each bear’s home range is more likely to buffer against future uncertainties.

‘Ecological forestry’ and eucalypt forests managed for wood production in south-western Australia

The model of ‘ecological forestry’ has evolved as a part of the development of the concept of ecosystem management. ‘Ecological forestry’ emphasises that manipulation of a forest ecosystem should consider, and as far as practicable work within the limits of, natural disturbance patterns prior to extensive human alteration of the landscape. This paper evaluates the extent to which forest management practices in jarrah ( Eucalyptus marginata) and karri ( Eucalyptus diversicolor) forests of south-western Australia align with this view of the characteristics and appropriate silviculture of ‘ecological forestry’. Characteristics and appropriate silviculture of ‘ecological forestry’ are evaluated in relation to (i) the stand level decisions of stand structure and harvest timing and (ii) the landscape level decisions of harvest levels and age structures, and spatial patterns of harvest. Forest management in south-western Australia is found to align with appropriate silviculture under this model of ‘ecological forestry’. Additionally, the landscape triad of areas managed to ‘ecological forestry’ principles, conservation reserves and areas managed to production forestry is in place in the south-western forests of Australia. Strengths and weaknesses in the model of ‘ecological forestry’ and the ability to interpret consistency of practices in the forests of south-western Australia with the characteristics of ‘ecological forestry’ are identified.

Old-growth definitions and management: A literature review

Over the past two decades, scientific discoveries have altered how forest management is viewed, including the understanding of late-successional or old-growth forest communities. Some accept that old-growth forests should be managed, but the process of identification and management of these forests has proven to be very difficult. This review examines literature on old growth and old-growth management from a broad North American base with a focus on the special issues associated with high-frequency forest disturbance regimes. The purpose of this paper is to: examine the various old-growth definitions and management approaches; review the importance of old-growth management and conservation; and draw conclusions and make recommendations based on the information reviewed. Old-growth definitions were divided into three categories: conceptual functional, conceptual structural, and quantitative working. The relative merits and challenges of each category are discussed using examples from different forest types across North America, but the focus is on northern fire-dependent forest ecosystems. The authors recommend the establishment of landscape-level objectives for old-growth retention that include: approaching management from an ecological perspective; recognizing the importance of varied natural disturbance patterns; increasing funds for detailed inventories (especially in more contentious or ecologically sensitive areas); developing a regional old-growth attribute scoring theme or index; using a top-down approach to old-growth management; and developing a monitoring plan to determine the effectiveness of established objectives.

Structure and function of wildfire and mountain pine beetle forest boundaries

Landscape boundaries, in particular those created by natural disturbances, are fundamental structures in landscape functioning. At the stand scale, forest boundaries show a wide range of characteristics varying from sharp to diffuse, wavy to straight, enclosed areas (patches) to open ones; all of these have different effects of forest vegetation. The objectives of this study were 1) to characterize the structure of forest boundaries (width, steepness, heterogeneity) and 2) to investigate forest vegetation functional response in the boundary zones created by wildfires and mountain pine beetle (MPB) outbreaks. We studied 11 mountain pine beetle and 7 wildfire boundary zones (4–7 y since disturbance) using field‐based two‐dimensional grids in southern central British Columbia (Canada). Boundary zone delineation was determined through spatially constrained clustering algorithms at three sampling unit resolutions (5×5 m, 10×10 m, and 20×20 m). Then, to characterize boundary width and shape, we developed two new boundary indexes (maximized and minimized boundary zones). The identified boundary widths ranged from 0 to 127 m with a mean width of 51 m at the 20×20 m resolution for both fire and MPB. Although the widths were comparable between disturbance types, fires generally had steeper boundaries (more pronounced) than MPB, largely due to higher peak tree mortality within the disturbances (89 vs 43%). Most of the forest vegetation response variables (understory vegetation diversity, plot‐level species richness, evenness, and multivariate community measures) in the boundary zones tended not to be intermediate in value between the intact forest and disturbance area, in spite of intermediate tree mortality. Tree mortality heterogeneity in the boundary zones was often highest in fires and was equal to the internal heterogeneity in MPB disturbances. Using historical natural disturbance patterns as a conservation strategy, this study proposes that forest management should create boundary complexity (width and shape), thereby creating landscape heterogeneity similar to landscapes influenced primarily by natural disturbances.

A conceptual model of forest stand development based on permanent sample-plot data in Estonia

Ecosystem management assumes that management practices based on natural disturbance patterns are likely to preserve both natural biodiversity and ecosystem functions. Ecosystem management thus combines traditional natural resource management and forestry practices together with classical notions of protection that are focused on sustaining a naturally evolving ecosystem. Increased knowledge and understanding of natural disturbance dynamics in boreal forest ecosystems allow for the creation of a template for sustainable forest management that is based on mimicking disturbances that are thought to contribute to the biodiversity of the ecosystem. The observed trends of natural development are discussed in this paper. Permanent sample-plot data are used to develop a conceptual model of stand succession following natural disturbance. The distinctive characteristics of disturbances that are relevant to forest management planning are identified and modelled.

Visual-quality impacts of forest pest activity at the landscape level: A synthesis of published knowledge and research needs

Given the growing importance of forest-management strategies which seek to emulate natural disturbance patterns, and the increased incidence of pest epidemics in some parts of North America, there is surprisingly little published research on perceived visual quality of pest infestations, especially, at the landscape level (middleground viewing distance). Much of the literature that does exist focuses on the visual impact of beetles ( Dendroctonus spp.) or gypsy moth ( Lymantria dispar). This paper reviews the work published to date and distills key points and research priorities emerging from it. Visual-quality ratings generally decrease significantly as pest damage increases in the middleground landscape. Some studies have identified quite low thresholds (in terms of the area of the visible landscape affected by pest activity), below which perceived visual quality drops significantly with increasing visible pest damage, and beyond which, additional negative visual impacts of increasing damage appear to be modest. However, reductions in visual quality due to pest attack may be outweighed by high visual quality of the overall scene. Low levels of beetle damage may even enhance the visual quality of a landscape temporarily. Results are not clear on the effect of information about pest infestations on respondents’ visual-quality ratings. Some studies show that informed respondents consider visual quality of affected scenes to be lower than do uninformed respondents, but this may reflect the way in which the information was delivered. A conceptual framework is suggested which relates the existing research to knowledge gaps and future research priorities, not only on visual-quality effects of pest infestations but also on related public perceptual responses and other disturbance types.

Effects of simulated post-harvest light availability and soil compaction on deciduous forest herbs

To better understand the response of eastern deciduous forest herbs to microenvironmental changes associated with logging, the effects of experimental light and soil compaction treatments were examined in six herbaceous plant species characteristic of varying successional stages. We found severe growth reductions and increased mortality of Osmorhiza claytonii (Michx.) C.B. Clarke, a shade-tolerant forest perennial, when grown in full sun and greater soil compaction. Deeply shaded conditions, similar to those beneath regenerating forests, resulted in reduced growth of early successional species such as Galium aparine L., and Eupatorium rugosum Houtt. Growth of other species such as Geum canadense Jacq., and Elymus hystrix L. appeared to increase in the patchy, intermediate light treatment mimicking mature eastern deciduous forests. Soil compaction caused severe reductions in height and biomass of Eupatorium rugosum and O. claytonii, early- and late-successional species, respectively. While harvested stands experience relatively uniform light environments, canopy gaps and sunflecks in mature eastern deciduous forests create heterogeneous light environments often correlated with recruitment, growth, and diversity of understory herbs. Therefore, management approaches that minimize alteration of forest environments and mimic natural disturbance patterns may be important to the maintenance and regeneration of forest herbs.

Regional and National Issues for Forest Wildlife Research and Management

Abstract Biologists and managers face a broad range of issues related to research and management of forest wildlife. To assess current trends in research, I reviewed 12 scientific journals (1992–2001) that published articles on wildlife, general ecology, and forestry and summarized articles by location, topic, issue, and species. To assess management concerns and issues, I interviewed professional biologists from across the United States, asking their opinions on important forest wildlife topics, approaches to improve research design, how management differs on public versus private lands, and which species they thought were underrepresented, overrepresented, or of special concern in their region. Most scientific articles focused on habitat selection, effects of forest alteration, and demography of birds and mammals. Herpetofauna (i.e., amphibians and reptiles) and invertebrates, although the subjects of some studies, made up only 10% each of all research papers. Biologists were most concerned with the alteration of forest vegetative structure due to timber harvest and its effects on wildlife populations and communities, but also recognized other issues such as changes in natural disturbance patterns such as fire, effects of road building, and loss of early successional vegetative communities as well as fragmentation of older forests. Most biologists agreed that long-term, large-scale, experimental studies, which document the demographic response of forest wildlife to alterations in forest cover, are needed. FOR. SCI. 48(2):181–189.

Effects of forestry practices on vegetation structure and bird community of Kibale National Park, Uganda

I examined the lingering effects of past timber management practices on the vegetation structure and bird community of Kibale National Park, Uganda. I compared four forest treatments: unlogged native forest (UL), two that were selectively logged at low (LL) and high (HL) intensities in the 1960s, and a conifer plantation (PL). Forest-dependent birds were best represented at UL. LL was similar to UL in both vegetation structure and bird community composition, although some forest-dependent bird species were missing from the former. HL had significantly less canopy closure and lower tree density than other plots as a result of the combination of extensive secondary damage and natural disturbance patterns that prevented the reclosure of the forest canopy. Thirty-one percent of the forest-dependent bird species observed during the study were not detected at HL. At PL, bird species richness and bird abundance were about a third of those observed in other plots. There were significant correlations between heterogeneity of tree distribution (horizontal heterogeneity) and abundance and species richness of birds across plots. Abundance and species richness of all, forest-dependent, and forest generalist birds were highest in plots with intermediate measures of horizontal heterogeneity, which were mostly unlogged or lightly logged. If reduced-impact logging practices are not implemented during selective logging operations in tropical forests, consequent long-term changes in vegetation structure may result in significant declines in the populations of some forest-dependent species, as was observed in Kibale National Park.

Development of ecosystem management in the Pacific Northwest

ABSTRACT During the last decade, the concept of ecosystem management has increasingly influenced forestry practice, but in different ways on federal and private forests. In western Oregon, about two thirds of federal land is reserved for non-commodity use and federal forest managers follow a strict path of ecosystem management. Stands are managed to retain or develop structural complexity and species diversity while landscapes are managed to mimic natural disturbance patterns. On private lands, state and federal regulations and incentives such as Habitat Conservation Plans (HCP) and green certification influence how private forestlands are managed. Large industrial owners continue to focus on timber production within the limits of state and federal laws, with some adopting HCP's that increase landscape planning and landscape diversity. Small private forest managers are more likely to define sustainable forestry in terms of balancing ecological requirements defined in state and federal laws against their aesthetic preferences and how to derive income from their forest. Some have chosen green certification as a way to assure themselves, neighbors and perhaps wood buyers that they are practicing sustainable forestry. At a landscape level these differences are sometimes complimentary. For example, late successional wildlife species are provided for on federal lands, while early successional wildlife species are provided for on large private land. The patch size for disturbance can be large on federal (50–1000 ha) lands where large contiguous areas are designated as late successional reserves or wilderness. Patch size tends to be medium on state and large private (20–50 ha) and small on small private (2–30 ha) forestland. Because ecosystem management varies by forest type and management objectives it is unlikely that the practices adopted in the Pacific Northwest will be applicable in all regions of the world.

Modeling silviculture after natural disturbance to sustain biodiversity in the longleaf pine ( Pinus palustris) ecosystem: balancing complexity and implementation

Modeling silviculture after natural disturbance to maintain biodiversity is a popular concept, yet its application remains elusive. We discuss difficulties inherent to this idea, and suggest approaches to facilitate implementation, using longleaf pine ( Pinus palustris) as an example. Natural disturbance regimes are spatially and temporally variable. Variability leads to a range of structural outcomes, or results in different pathways leading to similar structures. In longleaf pine, lightning, hurricanes, surface fires, and windthrow all lead to similar structures, but at different rates. Consequently, a manager can select among various natural disturbance patterns when searching for an appropriate silvicultural model. This facilitates management by providing flexibility to meet a range of objectives. The outcomes of natural disturbances are inherently different from those of silviculture, for example, harvesting always removes boles. It is instructive to think of silvicultural disturbances along a gradient in structural outcomes, reflecting degree of disparity with natural disturbance. In longleaf pine this might involve managing for two-cohort structure, instead of multi-cohort structure characteristic of old growth stands. While two-cohort structure is a simplification over the old growth condition, it is an improvement over single-cohort management. Reducing structural disparity between managed and unmanaged forests is key to sustaining biodiversity because of linkages that exist between structural elements, forest biota, and ecosystem processes. Finally, interactions of frequency, severity, intensity, seasonality, and spatial pattern define a disturbance regime. These components may not have equal weight in affecting biodiversity. Some are easier to emulate with silviculture than are others. For instance, ecologists consider growing-season fire more reflective of the natural fire regime in longleaf pine and critical for maintenance of biodiversity. However, dormant season fire is easier to use and recent work with native plants suggests that seasonality of fire may be less critical to maintenance of species richness, as one component of biodiversity, than is generally believed. Science can advance the goal of modeling silviculture after natural disturbances by better illustrating cause and effect relationships among components of disturbance regimes and the structure and function of ecosystems. Wide application requires approaches that are adaptable to different operational situations and landowner objectives. A key point for managers to remember is that strict adherence to a silvicultural regime that closely parallels a natural disturbance regime may not always be necessary to maintain biodiversity. We outline examples of silvicultural systems for longleaf pine that demonstrates these ideas.