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 ∼2.1 million ha 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.     

Projected long-term response of Southeastern birds to forest management

Numerous studies have explored the influence of forest management on avian communities empirically, but uncertainty about causal relationships between landscape patterns and temporal dynamics of bird communities calls into question how observed historical patterns can be projected into the future, particularly to assess consequences of differing management alternatives. We used the Habplan harvest scheduler to project forest conditions under several management scenarios mapped at 5-year time steps over a 40-year time span. We used empirical models of overall avian richness, richness of selected guilds, and probability of presence for selected species to predict avian community characteristics for each of the mapped landscapes generated for each 5-year time step for each management scenario. We then used time series analyses to quantify relationships between changes in avian community characteristics and management-induced changes to forest landscapes over time. Our models of avian community and species characteristics indicated habitat associations at multiple spatial scales, although landscape-level measures of habitat were generally more important than stand-level measures. Our projections showed overall avian richness, richness of Neotropical migrants, and the presence of Blue-gray Gnatcatchers and Eastern Wood-pewees varied little among management scenarios, corresponding closely to broad, overall landscape changes over time. By contrast, richness of canopy nesters, richness of cavity nesters, richness of scrub-successional associates, and the presence of Common Yellowthroats showed high temporal variability among management scenarios, likely corresponding to short-term, fine-scale changes in the landscape. Predicted temporal variability of both interior-forest and early successional birds was low in the unharvested landscape relative to that in the harvested landscape. Our results also suggested that early successional species can be sensitive to both availability and connectivity of habitat on the landscape. To increase or maintain the avian diversity, our projections indicate that forest managers need to consider landscape-scale configuration of stands, maintaining a spatially heterogeneous distribution of age classes. Our findings suggest which measures of richness or species presence may be appropriate indicators for monitoring effects of forest management on avian communities, depending on management objectives.     

Spatially explicit modeling of mixed-severity fire regimes and landscape dynamics

Simulation models of disturbance and succession are being increasingly applied to characterize landscape composition and dynamics under natural fire regimes, and to evaluate alternative management strategies for ecological restoration and fire hazard reduction. However, we have a limited understanding of how landscapes respond to changes in fire frequency, and about the sensitivity of model predictions to assumptions about successional pathways and fire behavior. We updated an existing landscape dynamics model (LADS) to simulate the complex interactions between forest dynamics, fire spread, and fire effects in dry forests of the interior Pacific Northwest. Experimental model runs were conducted on a hypothetical landscape at fire rotations ranging from 5 to 50 years. Three sensitivity analyses were carried out to explore the responses of landscape composition to (1) parameters characterizing succession and fire effects on vegetation, (2) the probability of fire spread into different successional stages, and (3) the size and spatial pattern of static fire refugia. The area of old open-canopy forests was highest at the shortest fire rotations, and was particularly sensitive to the probability of stand-replacement fire in open-canopy forests and to the fire-free period required for ingrowth to occur in open-canopy forests. The area of old closed-canopy forests increased with lengthening fire rotation, but always comprised a relatively small portion of the landscape (<10%). The area of old closed-canopy forests increased when fire spread was more rapid in open-canopy forests than in closed-canopy forests, and when the physical landscape incorporated large “fire refugia” with low fire spread rates. Old closed-canopy forests appear to comprise a relatively minor landscape component in mixed-severity fire regimes with fire rotations of 50 years or less. However, these results are sensitive to assumptions about the spatial interactions between fire spread, landscape vegetation patterns, and the underlying physical landscape.     

Short-term response of the herbaceous layer within leave patches after harvest

Leave patches, uncut areas in a harvested forest, may conserve herbaceous layer species that decline after forest clearcutting. They may also serve to maintain source populations for the recolonization of the harvest area. The main objective of this study is to characterize the short-term response of the herbaceous layer to clearcut harvesting disturbance within and adjacent to leave patches. Four experimental 1 ha patches and two uncut references were established. Within each patch or reference, belts of five 1 m² quadrats were placed at 50 m and 5 m outside the patch, at 0 m (edge), and at 25 m, 35 m, and 50 m (centre) inside. These belts of quadrats were replicated at all four aspects (North, South, East, and West). Ground vegetation was sampled yearly for 1 year before harvest and 3 years after harvest in the experimental patches and for 2 consecutive years in the references. Some common residual species declined significantly in the clearcuts, but remained stable inside the patches in the short term (3 years after harvest). Overall species composition changed little in the patch interior and edge after harvest. Colonizing species (those that appeared in quadrats after harvest) in the patch exterior were predominantly early-seral species, whereas colonizers in the patch interior tended to be shade-tolerant forest species. Species were grouped a priori based on two habitat preferences (amounts of canopy cover and disturbed substrate). Species characteristic of a habitat with closed canopy and undisturbed substrates that decreased significantly over time in the patch exterior were negatively correlated with the amount of exposed mineral soil and open canopy. Species characteristic of a habitat with open canopy and disturbed substrates that increased significantly at the patch exterior showed a positive correlation with the amount of exposed mineral soil and open canopy. No species’ habitat preference groups declined significantly in the patch interior or edge over time. Based on species’ responses to forest operations, it appears that at least the common forest species are maintained in the short term within leave patches.     

An Ecological Framework for Planning for Forest Health

Concerns for maintaining biodiversity have led to the adoption of ecosystem management as the paradigm for federal land management. This approach will identify desired future conditions as the goal for management, based on ecological objectives for a given landscape. Some management efforts attempt to identify desired future conditions based on existing successional stages as defined by a classification of overstory vegetation types. Such an approach ignores most of the underlying ecological parameters of the landscape, and is inadequate for identifying past disturbance regimes and future successional pathways. An assessment of desired future conditions based on an ecological classification system is essential to overcome these inadequacies. The strategy proposed in this paper uses an appropriate ecological land classification, based on either ecological land types or habitat types, included in a broader hierarchical classification system. It also uses a vegetation map of existing overstory vegetation. These two maps are overlaid to generate polygons of ecological units that can then be used to create an ecosystem diversity matrix. Each polygon (stand) can be evaluated as to its composition and structure relative to its possible placement within the ecosystem diversity matrix through comparisons with historical ranges of variability. The overall ecosystem diversity matrix can then be examined in terms of the distribution of successional stages within each habitat type or ecological land type. The goal should be to maintain at least adequate ecological representation of all successional stages within each habitat type that occurred historically, based on past disturbance regimes. Adequate ecological representation is defined as sufficient size and distribution of inherent ecosystems to maintain viable populations of all endemic species dependent on these ecosystems. This approach can maintain and enhance regional biodiversity, but also maintain flexibility in land management options.     

Modeling wildfire risk to northern spotted owl (Strix occidentalis caurina) habitat in Central Oregon,USA

Natural disturbances including wildfire, insects and disease are a growing threat to the remaining late successional forests in the Pacific Northwest, USA. These forests are a cornerstone of the region's ecological diversity and provide essential habitat to a number of rare terrestrial and aquatic species including the endangered northern spotted owl (Strix occidentalis caurina). Wildfires in particular have reduced the amount of late successional forests over the past decade, prompting land managers to expand investments in forest management in an attempt to slow losses and mitigate wildfire risk. Much of the emphasis is focused specifically on late successional reserves established under the Northwest Forest Plan to provide habitat for spotted owls. In this paper, we demonstrate a probabilistic risk analysis system for quantifying wildfire threats to spotted owl habitat and comparing the efficacy of fuel treatment scenarios. We used wildfire simulation methods to calculate spatially explicit probabilities of habitat loss for fuel treatment scenarios on a 70,245 ha study area in Central Oregon, USA. We simulated 1000 wildfires with randomly located ignitions and weather conditions that replicated a recent large fire within the study area. A flame length threshold for each spotted owl habitat stand was determined using the forest vegetation simulator and used to predict the proportion of fires that resulted in habitat loss. Wildfire modeling revealed a strong spatial pattern in burn probability created by natural fuel breaks (lakes and lava flows). We observed a non-linear decrease in the probability of habitat loss with increasing treatment area. Fuels treatments on a relatively minor percentage of the forested landscape (20%) resulted in a 44% decrease in the probability of spotted owl habitat loss averaged over all habitat stands. The modeling system advances the application of quantitative and probabilistic risk assessment for habitat and species conservation planning.     

Effects of fire disturbance on bird communities and species of mountain Serrano forest in central Argentina

In central Argentina, Serrano forest has a long history of fire disturbance; however, the impact of fire on avifauna remains unknown. We compared the avian–habitat relationships in forest patches with low, moderate, and high fire regimes using a community-level (species richness, abundance, ordination and guilds) and species-level (indicator species analysis) approach. In patches under each fire condition, we recorded bird community composition, richness and abundance, and different vegetation structure variables. The site under high-severity fire regime was structurally poor and had been converted from original forest to dense grassland. There, diversity of bird community was low, retaining approximately 30 % of the species present in the least impacted site. Avian assemblage was dominated by generalist and open area birds. Guilds were underrepresented, showing an important reduction of foliage granivorous, nectarivorous, omnivores, and foliage and bark insectivorous, and absence of fly-catchers. Moreover, low abundance of forest understory, midstory, and canopy species and of birds belonging to open and closed nesting guilds was detected. By contrast, under low and moderate-severity fire regimes highest bird diversity as well as highest representativeness of most guilds was observed. Forest bird species were strongly associated with low fire disturbance, whereas moderate fire disturbance was characterized by the presence of forest and generalist species. Given the critical conservation status of Serrano forest in Córdoba, Argentina, habitat restoration and protection of forest relicts could be suitable measures to promote avifauna preservation.     

A comparative analysis of spatial, temporal, and ecological characteristics of forest fires in seasonally dry tropical ecosystems in the Western Ghats, India

The Western Ghats in India is one of the 25 global hotspots of biodiversity, and it is the hotspot with the highest human density. This study considers variations in the regional fire regime that are related to vegetation type and past human disturbances in a landscape. Using a combination of remote sensing data and GIS techniques, burnt areas were delineated in three different vegetation types and various metrics of fire size were estimated. Belt transects were enumerated to assess the vegetation characteristics and fire effects in the landscape. Temporal trends suggest increasingly short fire-return intervals in the landscape. In the tropical dry deciduous forest, the mean fire-return interval is 6 years, in the tropical dry thorn forest mean fire-return interval is 10 years, and in the tropical moist deciduous forest mean fire-return interval is 20 years. Tropical dry deciduous forests burned more frequently and had the largest number of fires in any given year as well as the single largest fire (9900 ha). Seventy percent, 56%, and 30% of the tropical moist deciduous forests, tropical dry thorn forests, and tropical dry deciduous forests, respectively have not burned during the 7-year period of study. The model of fire-return interval as a function of distance from park boundary explained 63% of the spatial variation of fire-return interval in the landscape. Forest fires had significant impacts on species diversity and regeneration in the tropical dry deciduous forests. Species diversity declined by 50% and 60% in the moderate and high frequency classes, respectively compared to the low fire frequency class. Sapling density declined by ca. 30% in both moderate and high frequency classes compared to low frequency class. In tropical moist deciduous ecosystems, there were substantial declines in species diversity, tree density, seedling and sapling densities in burned forests compared to the unburned forests. In contrast forest fires in tropical dry thorn forests had a marginal positive effect on ecosystem diversity, structure, and regeneration.     

Predicting late-successional fire refugia pre-dating European settlement in the Wenatchee Mountains

Fires occur frequently in dry forests of the Inland West. Fire effects vary across the landscape, reflecting topography, elevation, aspect, slope, soils, and vegetation attributes. Patches minimally affected by successive fires may be thought of as ‘refugia’, islands of older forest in a younger forest matrix. Refugia support species absent within the landscape matrix. Our goal was to predict the occurrence of pre-settlement refugia using physiographic and topographic variables.We evaluated 487 plots across a 47000 ha landscape using three criteria to identify historical fire refugia: different structure from surrounding matrix; different fire regime from surrounding matrix; presence of old individuals of fire-intolerant tree species. Several combinations of aspect, elevation, and topography best predicted refugial presence.Less than 20% of the pre-settlement landscape was identified as historical fire refugia. Refugia were not connected except by younger stands within the matrix. Current management goals of increasing amounts and connectivity of old, refugia-like forests for the benefit of species associated with late-successional habitat increase the risk of insect and pathogen outbreaks and catastrophic wildfires.     

Forest cover changes in the Oregon Coast Range from 1939 to 1993

Understanding the shifts over time in the distribution and amount of forest vegetation types in relation to forest management and environmental conditions is critical for many policy and ecological questions. Our objective was to assess the influences of ownership and environment on changes in forest vegetation from post-settlement historical to recent times in the central Coast Range of Oregon. We evaluated land cover types on 1475 20 m plots, using scanned, geo-referenced historical (1939) and recent (1993) aerial photos. The amount of older conifer cover declined by 63% relative to its former amount, from 36 to 13% of the landscape, during the 54-year period. Dominant ownership of older conifer stands shifted from industrial private to Forest Service lands. Younger conifer stands showed the greatest expansion in cover, increasing more than two-fold, from 21 to 44% of the landscape. Shrub and hardwood cover declined by 16%, from 31 to 25% of the landscape. Shrubs and hardwoods occurred at lower slope positions and closer to streams at the end of the period than at the beginning. Ownership was not an important determinant of the presence of large and very large conifer cover or shrub and hardwood cover in 1939, but was a very important factor affecting the presence of these cover types in 1993. Landscape transitional pathways were distributed among many types and no single transitional pathway was dominant. Even the most stable cover types (hardwood trees and herbs) had low absolute stability, with over 65% of their plots changing to another cover type by 1993. Our research indicates that the importance of ownership as a factor affecting the type of vegetation cover present has increased greatly during this time, whereas the relative influence of environment has lessened considerably. Land owners in the Oregon Coast Range have altered the cover and distribution of vegetation in diverse ways, changing the landscape to one dominated by young conifers, shifting the distribution of younger successional shrubs and hardwoods toward streams, and restricting the location of older coniferous stands to particular ownerships and site types.     

Resting structures and resting habitat of fishers in the southern Sierra Nevada,California

The fisher (Martes pennanti) is a forest mustelid endemic to North America that has experienced range reductions in Pacific states that have led to their listing under the Endangered Species Act as warranted but precluded by higher priorities. The viability of the southern Sierra Nevada fisher population is of particular concern due to its reduced historical range, isolated nature, and low genetic variability. We located resting structures of radio-collared fishers in the southern Sierra Nevada and compared resting and available habitat to examine selection for specific features of resting sites. Resting structures provide protection from predators and unfavorable weather and are believed to be the most limiting habitat element across fisher home ranges. Resting structures were found primarily in live trees (76%) and snags (15%). Trees used by fishers for resting were among the largest available and frequently had mistletoe infestations. Ponderosa pines (Pinus ponderosa) were used more often than expected and incense cedars (Calocedrus decurrens) less than expected. Snags were also large and in fairly advanced stages of decay. Habitat at fisher resting sites had higher canopy cover, greater basal area of snags and hardwoods, and smaller and more variable tree sizes compared to random sites. Resting sites were also found on steeper slopes and closer to streams. Canopy cover was consistently the most important variable distinguishing rest and random sites. In western North America, fishers are generally associated with late-successional forests, but changes in these forests due to logging and fire suppression have resulted in a transition to forest stands characterized by fewer large trees and more small stems. These conditions are consistent with our finding that the large rest structures were surrounded by smaller than average trees. Management practices that support the growth and retention of greater numbers of large trees and snags, while maintaining a minimum of 61% (based on moosehorn) or 56% (generated via Forest Vegetation Simulator) canopy cover and a complex horizontal and vertical forest structure, can improve and provide for future fisher habitat.     

Scale effects of vegetation and topography on burn severity under prevailing fire weather conditions in boreal forest landscapes of Northeastern China

Understanding the controlling factors of burn severity requires consideration of the scale at which these factors work. This investigation explored how well topography and vegetation factors can explain variation of burn severity in a boreal forest landscape of northern China under prevailing fire weather conditions. Eight grain sizes were examined that ranged from 30 to 2500 m. A burn severity map was derived from calculating the difference between pre- and post-fire Normalized Difference Vegetation Index of two Landsat Thematic Mapper images. Results indicate that (1) burn severity in the boreal forest landscape of northern China was mainly controlled by vegetation at grain sizes smaller than 500 m. At grain sizes larger than 1000 m, topography accounted for more variation in burn severity; (2) the relative importance of topography factors was stable with increasing grain sizes and generally ranked in order of aspect, slope, and elevation; (3) stand age appeared to be more important where canopy cover and understory cover substantially fluctuated with increasing grain sizes; and (4) the linear relationships between burn severity and specific factors of topography and vegetation decreased with increasing grain sizes. Our study can help managers to design fire management plans according to vegetation characteristics that are found important in controlling burn severity and prioritize management locations based on the relative importance of vegetation and topography.     

Think globally,manage locally: The importance of steady-state forest features for a declining songbird

Changes in historical forest composition and structure may have cascading effects throughout the forest community. Perhaps nowhere is there a better example of current forests that carry a legacy from their past than in eastern North America. The Cerulean Warbler (Dendroica cerulea), a declining Neotropical migratory bird of high conservation concern, is one excellent example of a species that seems to be sensitive to both landscape configuration and subtle features of eastern forests of North America. We used the Cerulean Warbler as a model species to demonstrate how an appreciation of fine-scale structural attributes of forests may improve our ability to conserve late-successional forest species. To do this we evaluated the extent to which multiscale habitat features were associated with density, spatial distribution, and nesting success of Cerulean Warblers in 12 mature forest sites in southeast Ohio, 2004–2006. Results suggest that adjacency of regenerating clear-cuts did not influence density or nesting success of Cerulean Warblers in adjacent mature forest. Instead, variation in demographic parameters was best explained by local habitat features. Density and nesting success were positively associated with canopy openness, numbers of large-diameter trees, and number of grapevines—all of which are typical of heterogeneous steady-state phase forests. Thus, improved management for Cerulean Warblers may require creating features (e.g., large canopy gaps) that mimic old-growth forests. Although fragmentation and habitat loss remain important contributors to population declines of many mature forest species, our work provides evidence that subtle changes in forest structure, particularly to features associated with old forests, warrant additional attention from the conservation community.     

Structural and environmental characterization of old-growth temperate rainforests of northern Chiloé Island,Chile: Regional and global relevance

Old-growth forests are ecologically relevant reservoirs of biodiversity and provide valuable and unique ecosystem functions in the landscape. However, what constitutes an old-growth stand is confusing because the definition depends largely on the forest type under study. Despite the ecological importance of old-growth temperate rainforests in southern Chile in comparison to other global forests, no attempts have been made to characterize them as a way to assess their structural variability. Here, we characterized old-growth stands of Valdivian and North Patagonian rain forest types located in Chiloé Island (Chile, 42°30′S) using inventory data from 23 permanent plots (0.1 ha each) located in rural landscapes and protected areas of northern Chiloé Island. For each stand, its age (average age of the oldest trees present in each stand) and disturbance regimes (evidence of recent human impact, e.g. cuttings or fires, and tree growth rates) were used as defining old-growth criteria. We characterized the structure (tree species richness, size-density distributions, vertical stratification and presence of snags) and floristic composition of each stand. Environmental variables (i.e. temperature, distance to coastline and elevation) were related to stand structure using multivariate constrained correspondence analysis. Old-growth forests were commonly characterized by (a) tree basal areas >80 m²/ha; (b) density of shade-tolerant tree species in the emergent and dominant canopy layer >36%; (c) higher tree species richness (>7 tree species) than successional stands; (d) presence of large canopy emergents (>80 cm dbh, >25 m tall); (e) high vertical heterogeneity; and (f) minimum stand ages older than 200 years. Old-growth forests showed a distinctive structural variability and floristic diversity influenced both by stand age and disturbance history of the stands. Structural variability was also related to environmental differences among sites (e.g. air temperature, distance to coastline, soil types). Old-growth forest features described here can offer a baseline for managers interested in maintaining and restoring old-growth forest structure in southern temperate rain forests.     

Factorial analysis on forest canopy density restoration in the burned area of northern Great Xing＇an Mountains, China

The restoration of forest landscape has drawn much attention since the catastrophic fire took place on the northern slope of Great Xing‘an Mountains in 1987. Forest canopy density, which has close relation to forest productivity, was selected as a key factor to find how much the forest quality was changed 13 years after fire, and how fire severity, regeneration way and terrain factors influenced the restoration of forest canopy density, based on forest inventory data in China, and using Kendall Bivariate Correlation Analysis, and Distances Correlation Analysis. The results showed that fire severity which was inversely correlated with forest canopy density grade was an initial factor among all that selected. Regeneration way which did not remarkably affect forest canopy density restoration in short period, may shorten the cycle of forest succession and promote the forest productivity of conophorium in the future, Among the three terrain factors, the effect of slope was the strongest, the position on slope was the second and the aspect was the last.     

Ruffed grouse-habitat preference in the central and southern Appalachians

Ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians (CSA) are declining due to widespread maturation of forest cover. Effective management of this species requires a sex- and age-specific understanding of habitat preferences at multiple temporal and spatial scales. We used multivariate logistic regression models to compare habitat within 1440 grouse home ranges and 1400 equally sized buffered random points across 7 CSA study areas. On most sites, grouse home ranges were positively associated with roads and young forest (<20 years old). Sex and age status affected habitat preference. In general, males used younger forest than females, likely because of differences in habitat use during reproductive periods. Juveniles had fewer vegetation types preferred by adult grouse and more of the avoided vegetation types within their home ranges, indicative of competitive exclusion. Adult females had the greatest specificity and selectivity of habitat conditions within their home ranges. Habitat selection varied among seasons and years on most sites. Winter habitat use reflected behavior that maximized energy conservation, with open vegetation types avoided in the winter on the northernmost study areas, and topography important on all areas. Summer habitat selection reflected vegetation types associated with reproductive activities. Scale influenced habitat preference as well. Although roads and forest age predominantly influenced grouse home range location within the landscape, mesic forest types were most important in determining core area use within the home range. This was likely a result of increased food availability and favorable microclimate. Habitat management efforts should attempt to maintain ∼3–4% of the landscape in young forest cover (<20 years old), evenly distributed across management areas. Roads into these areas should be seeded as appropriate to enhance brood habitat and provide travel corridors connecting suitable forest stands.     

Planning timber harvest of residual forest stands without compromising bird and small mammal communities in boreal landscapes

Numerous efforts have been invested in designing and configuring residual forest stands in Canadian boreal forest to preserve their overall biodiversity. Now that several landscapes have been partially logged, the next issue in forest management involves the planning of residual forest stand harvesting without compromising wildlife populations. Residual stands can be cut when adjacent regeneration reaches 3 m in height according to current regulations in several Canadian provinces (e.g., Québec, Ontario, Alberta, and British-Columbia). However, little is known on whether such regenerating habitat (RE-3m) can maintain wildlife communities similar to those found in unharvested mature forest (CO). We estimated the relative abundance of small mammals and forest birds in RE-3m and CO habitats and characterized landscape and stand structures. These variables were then compared between the two contrasting successional stages and were used to build habitat use models (HUMs) for 21 species. CO and RE-3m differed with regard to several landscape characteristics and stand structure variables as a result of logging. Snowshoe Hare, Northern Flicker, Alder Flycatcher, Ruby-crowned Kinglet, White-throated Sparrow and Magnolia Warbler were more abundant in RE-3m than CO, while Red-backed Vole, Brown Creeper and Golden-crowned Kinglet exhibited lower abundances in RE-3m. No significant differences in abundance were observed for the 12 other species. Species HUMs were highly significant and explained between 64.3 and 99.1% of the total variability in abundance. Following variance partitioning, stand structure variables accounted for most of the explained variability (54.2%) while landscape characteristics accounted for only 28.7%. No difference in species richness was observed but community evenness was greater in CO than RE-3m. Our results suggest that current regulations may threaten the maintenance of 3 out of 21 censused species for which abundances were significantly lower in regenerating 3 m tall stands. As stand structure explained a large amount of variability in abundance, it should be considered during timber harvest planning in both mature and regenerating stands. Until we know more on whether the current regulations are suitable for maintaining overall biodiversity, our results suggest that some mature forest stands should be maintained within managed landscapes for a complete logging rotation period.     

Coupling of vegetation layers and environmental influences in a mature, second-growth Central Hardwood forest landscape

Forest communities across the landscape of the Central Hardwood Forest Region are experiencing a transition from dominance by oak (Quercus) and hickory (Carya) to maple (Acer) driven largely by a prolonged period of fire suppression. In many cases, this shift in community composition, structure, and function is considered undesirable as oak-hickory forests are valued for timber, wildlife habitat, and natural heritage. Considerable management and restoration efforts target the restoration of oak-hickory forest communities, yet treatments have yielded varying degrees of success. In some cases, difficulties in meeting targets may be due to ecological thresholds created by complex vegetation-environment interactions that maintain the maple-dominated community state. We examined direct and indirect interactions among vegetation layers and environmental gradients for the mature, second-growth forest communities of the Ironton Unit of the Wayne National Forest (WNF) in southeastern Ohio. Using a stratified random approach, we identified 72 study communities with trees at least 70 years old and without evidence of recent disturbance. Within these communities, we sampled all overstory vegetation on two-four 500 m² plots and recorded saplings and ground-flora species in nested sub-plots. At each plot, we also collected soil samples for physical and chemical analyses and recorded physiographic variables. Our first objective was to describe the Ironton forest landscape, where communities were likely transitioning from oak to maple. To identify such patterns, we used ordination analyses that relate species occurrence to implied environmental gradients. Our second objective was to use the relationships to develop a structural equation model (SEM) to quantify the strength of pathways among the canopy, sapling, and ground-flora vegetation layers and environmental factors (e.g., soil chemistry and physiographic position). Our results indicate that the forest landscape of the Ironton Unit of the WNF is at a transition point with communities dominated by either oak or maple, and a sapling layer dominated by maple. Maple may be most likely to replace oak and hickory in the canopies of communities at mid- and lower-slope positions with intermediate soil moisture. This transition will likely have cascading effects throughout the sapling and ground-flora layers, which SEM demonstrates are directly influenced by the canopy. We believe the simultaneous consideration of direct and indirect interactions shaping vegetation structure and composition using techniques such as SEM will advance understanding of the current transition from an oak-hickory to a maple-dominated forest landscape. This information will contribute to the continued improvement of appropriate forest management and ecosystem restoration techniques for the Central Hardwood Forest Region, including those designed to shift the dominance of forest communities from maple to oak.     

基于森林资源二类调查的仁义镇森林景观格局及破碎化分析

通过景观的观点来审视城镇化的发展,是解决城市化过程中环境问题的新方法、新思路.采用2009年广西壮族自治区贺州市八步区仁义镇森林资源二类调查数据为基础数据,以GIS和Fragstats为技术支撑,从景观的组成结构、斑块特征等方面对研究区域景观的空间分布和结构特征进行了分析.结果表明,景观要素斑块中以小斑块所占比例最大,植被景观以乔木林和灌丛景观为主要类型.由于相对强烈的人类活动影响,区域内林业用地的景观破碎化程度较高.     

Thinning and prescribed fire effects on overstory tree and snag structure in dry coniferous forests of the interior Pacific Northwest

Forest thinning and prescribed fires are practices used by managers to address concerns over ecosystem degradation and severe wildland fire potential in dry forests. There is some debate, however, about treatment effectiveness in meeting management objectives as well as their ecological consequences. The purpose of this study was to assess changes to forest stand structure following thinning and prescribed fire treatments, alone and combined, in the eastern Cascade Mountains of Washington State. Treatments were applied to 12 management units, with each treatment combination replicated three times (including untreated controls). Thinning modified forest structure by reducing overall tree density by >60% and canopy bulk density by 50%, and increased canopy base height by ∼4 m, thereby reducing susceptibility to crown fire. The prescribed fire treatment, conversely, did not appreciably reduce tree density or canopy fuel loading, but was effective at increasing the density of standing dead trees, particularly when combined with thinning (37 snags/ha increase). Prescribed fire effects were more pronounced when used in combination with thinning. Thinning was more reliable for altering stand structure, but spring burning was lower in intensity and coverage than desired and may have led to results that downplay the efficacy of fire to meet forest restoration goals.