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1.
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.  相似文献   

2.
Gap formation in forests can have impacts on forest ecosystems beyond the physical boundary of the canopy opening. The extent of gap influence may affect responses of many components of forest ecosystems to gap formation on stand and landscape scales. In this study, spatial extent of gap influence on understory plant communities was investigated in and around 0.1 and 0.4 ha harvested canopy gaps in four young Douglas-fir (Psuedotsuga menziesii) dominated stands in western Oregon. In larger gaps, the influence of gap creation on understory plant communities in surrounding forests was minimal. The area showing evidence of gap influence extended a maximum of 2 m beyond the edge of the canopy opening, suggesting that the area affected by gap creation did not differ greatly from the area of physical canopy removal. In smaller gaps, influence of the gap did not extend to the edge of the canopy opening. In fact, the area in which understory vegetation was influenced by gap creation was smaller than the physical canopy opening. Gap influence appears to be limited to areas where ruderal or competitor species are able to replace stress-tolerator species, likely due to elimination or reduction of these species by physical disturbance or competition. The limited gap influence extent exhibited here indicates that gap creation may not have a significant effect on understory plant communities beyond the physical canopy opening. This suggests a limited effectiveness of gaps, especially smaller gaps, as a tool for management of understory plant diversity, and perhaps biodiversity in general, on a larger scale.  相似文献   

3.
Forest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (“fluxes”) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. Silvicultural trials have been established to evaluate stand-level responses to treatments and operational aspects of the approach.  相似文献   

4.
Light is the most common limiting factor in forest plant communities,influencing species composition,stand structure,and stand productivity in closed canopy stands.Stand vertical light structure is relatively simple under a closed canopy because most light is captured by overstory trees.However,wind disturbance events create canopy openings from local to landscape scales that increase understory light intensity and vertical light structural complexity.We studied the effects of an EF-1 tornado on horizontal and vertical(i.e.three-dimensional)light structure within a Quercus stand to determine how light structure changed with increasing disturbance severity.We used a two-tiered method to collect photosynthetic photon flux density at 4.67 m and 1.37 m above the forest floor to construct three-dimensional light structure across a canopy disturbance severity gradient to see if light intensity varied with increasing tornado damage.Results indicate that increased canopy disturbance closer to the tornado track increased light penetration and light structure heterogeneity at lower forest strata.Increased light intensity correlated with increased sapling density that was more randomly distributed across the plot and had shifted light capture higher in the stand structure.Light penetration through the overstory was most strongly correlated with decreased stem density in the two most important tree species(based on relative dominance and relative density)in the stand,Quercus alba L.(r=-0.31)and Ostrya virginiana(Mill.)K.Koch(r=-0.27,p<.01),and indicated that understory light penetration was most affected by these two species.As managers are increasingly interested in patterning silvicultural entries on natural disturbances,they must understand residual stand and light structures that occur after natural disturbance events.By providing spatial light data that quantifies light structure post-disturbance,managers can use these results to improve planning required for long-term management.The study also provides comparisons with anthropogenic disturbances to the midstory that may offer useful comparisons to natural analogs for future silvicultural consideration.  相似文献   

5.
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.  相似文献   

6.

The anticipated increase in extreme disturbance events due to climate change is likely to expose Norway spruce (Picea abies (L.) Karst.) dominated forests in northern Europe to new conditions. Empirical data on the resilience of such natural (unmanaged) forests to disturbance and the long-term patterns of regeneration in its aftermath are currently scarce. We performed a quantitative assessment of natural forest stands in north–western Latvia to identify and characterise the patterns of stand structure 44 years after a stand-replacing disturbance and investigated the effects of legacies on regeneration. The spatial distribution of tree species and their dimensions were assessed in 71 circular sample plots (500 m2 each) in natural forest areas, where Norway spruce dominated prior to the windthrow and salvage logging was not carried out. Spatial indices (species mingling index, size differentiation index, and aggregation index) were used to characterise stand structure and diversity. The different initial states (age and coverage of surviving trees) of stands affected eventual tree species dominance, size differentiation, degree of mingling and aggregation. Our results demonstrate a close relationship between disturbance legacies and spatial indices. The pre-storm understory and canopy survivors decreased species mingling, whereas survivors increased size differentiation. The size differentiation increased also with a higher degree of species mingling. Leaving differential post-storm legacies untouched promotes a higher structural and species diversity and therefore supports the management approach of preserving canopy survivors.

  相似文献   

7.
Urban development typically has extensive and intensive effects on native ecosystems, including vegetation communities and their associated biota. Increasingly, urban planning strives to retain elements of native ecosystems to meet multiple social and ecological objectives. The ecological integrity of native forests in an urbanizing landscape is challenged by a myriad of impacts, such as forest management and invasive species. Environmental protection efforts in the Lake Tahoe basin, spanning the California/Nevada border in the Sierra Nevada mountains, over the past half century have resulted in the retention of thousands of parcels of remnant native forest located throughout the urbanizing landscape. The basin landscape provides an opportunity to evaluate the effects of land development on the composition and structure of remnant native forests along a gradient of urbanization. We sampled 118 sites located in remnant forests in the lower montane zone surrounded by 0–70% development. We also sampled forest structure in the landscape surrounding 75 of these sites to evaluate the contribution of remnant forests to the retention of native forest elements in the larger landscape. We characterized plant species composition and cover, vertical structure, and the density of trees, snags, and logs, as well as levels of ground disturbance and human activity. We found that remnant native forests retained much of their compositional and structural character along the development gradient, including large tree density, total canopy cover, and plant species richness. Notable exceptions were reductions in the density and decay stage of snags and logs, and the density of understory trees. We also observed increases in the richness and cover of herb and grass species and increases in the number of exotic plant species. In contrast, structural complexity was reduced in the landscape surrounding forest remnants in all measures except large tree density. We conclude that remnant native forests contribute significantly to maintaining native species in an urbanizing landscape, and that land conservation practices have an important role to play in protecting native forest ecosystems.  相似文献   

8.
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.  相似文献   

9.
The role of disturbance in structuring vegetation is widely recognized; however, we are only beginning to understand the effects of multiple interacting disturbances on ecosystem recovery and development. Of particular interest is the impact of post-disturbance management interventions, particularly in light of the global controversy surrounding the effects of salvage logging on forest ecosystem recovery. Studies of salvage logging impacts have focused on the effects of post-disturbance salvage logging within the context of a single natural disturbance event. There have been no formal evaluations of how these effects may differ when followed in short sequence by a second, high severity natural disturbance. To evaluate the impact of this management practice within the context of multiple disturbances, we examined the structural and woody plant community responses of sub-boreal Pinus banksiana systems to a rapid sequence of disturbances. Specifically, we compared responses to Blowdown (B), Fire (F), Blowdown-Fire, and Blowdown-Salvage-Fire (BSF) and compared these to undisturbed control (C) stands. Comparisons between BF and BSF indicated that the primary effect of salvage logging was a decrease in the abundance of structural legacies, such as downed woody debris and snags. Both of these compound disturbance sequences (BF and BSF), resulted in similar woody plant communities, largely dominated by Populus tremuloides; however, there was greater homogeneity in community composition in salvage logged areas. Areas experiencing solely fire (F stands) were dominated by P. banksiana regeneration, and blowdown areas (B stands) were largely characterized by regeneration from shade tolerant conifer species. Our results suggest that salvage logging impacts on woody plant communities are diminished when followed by a second high severity disturbance; however, impacts on structural legacies persist. Provisions for the retention of snags, downed logs, and surviving trees as part of salvage logging operations will minimize these structural impacts and may allow for greater ecosystem recovery following these disturbance combinations.  相似文献   

10.
Disturbance history was reconstructed across an 11300 ha managed longleaf pine (Pinus palustris Mill.) landscape in southwestern Georgia, USA. Our specific objectives were to: (i) determine forest age structure; (ii) reconstruct disturbance history through the relationship between canopy disturbance, tree recruitment and growth; and (iii) explore the relationship between canopy disturbance and climate. Age structure, canopy disturbance events and initial growth patterns at coring height were examined by randomly sampling 1260 trees in 70 1.3 ha plots. Principal component analysis was used to group plots with similar age structures to gain insight into the dynamics between canopy disturbance and recruitment. Disturbance events were detected by large and rapid increases in radial growth. We tested the following hypothesis to investigate whether these growth increases could have been triggered by improved climatic conditions: precipitation and drought are positively correlated to radial growth releases. Only four stands (comprising <6% of the study area) had an even-aged structure. Further, tree recruitment prior to European settlement indicates that longleaf pine naturally recruited into areas 1.3 ha or less, supporting early-20th century observations that the primary longleaf pine forest was uneven-aged. Contrary to our hypothesis, growing season precipitation and drought was significantly and negatively correlated with canopy disturbance (radial growth releases), which indicates that a reconstruction of disturbance history could proceed with some confidence. Most trees sampled were recruited at coring height from 1910 to 1935. Of the 67 canopy disturbances detected from 1910 to 1935, the average growth release ranged from 139 to 277% per half decade suggesting the occurrence of large canopy disturbances. Rapid initial growth patterns of young trees during these years show evidence of reduced overstory competition and support the detected disturbance intensity. Our reconstruction of stand dynamics is markedly similar to independent records of local oral and written history, which gives an additional set of evidence that the disturbance detection methodology used can be useful in open-canopied forests. Stands with multiple cohorts reveal a mix of continuous minor and major canopy disturbances leading to continual tree recruitment, suggesting their applicability as models for long-term forest management. The significant relationship between climate and disturbance in our data suggests that with the expected warming over the next 100 years, climatic impacts on stand dynamics should be incorporated into long-term longleaf pine forest restoration and management.  相似文献   

11.
The objective of this study was to examine bird communities in regenerating (5–25 years) and mature (40–100 years) jack pine (Pinus banksiana) forest in boreal Ontario. The study area was located near White River in north central Ontario with an area of 187,800 ha. We explored the response of bird community structure to stand age, and the influence of stand age on the distribution of individual species. We were interested in two principal questions. The first was how unique are the bird communities to specific age classes. If bird communities are highly specific to age classes then alterations to the age class distribution of the forest can have important impacts on the overall bird community composition and structure. The second question was how specific are individual species to age classes. Species that are highly specific to a single age class are expected to be highly sensitive to the amount and potentially the configuration of that age class on the landscape. We sampled birds for three breeding seasons. The number of bird species increased with stand age. Tree species composition did not change as stands aged, but there were distinctive changes in vegetation structure through succession. For example, the total amount of vertical vegetation structure increased significantly with age. More than half of the bird species examined were significant indicators of individual age classes. Blue-headed vireo, brown creeper, black-throated green warbler, golden-crowned kinglet, ovenbird and red-breasted nuthatch were all significant indicators of the mature age class. The bird assemblage of mature stands was significantly different from that of regenerating forest and within regenerating forest, 3–5-year-old stands contained a significantly different bird assemblage to that of 8–25-year-old regenerating forest. These results suggest that the distribution of forest age classes on the landscape is a critical element in determining habitat availability and therefore the viability of boreal bird populations in managed forests.  相似文献   

12.
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 m2) favored the growth and survival of mid-successional species such as red maple and white pine, while small gaps (<1000 m2) 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.  相似文献   

13.
A recent outbreak of spruce beetles (Dendroctonus rufipennis) in forests on the Kenai Peninsula, Alaska was met with substantial variation in response among people and communities situated within this changing landscape. Interviews and mail surveys administered to residents in six Kenai Peninsula communities revealed differences in perception of biophysical, social, and economic impacts that resulted from changing forest conditions related to the spruce beetle outbreak. Together, the qualitative and quantitative data provided evidence of collective experience and community risk perception across Kenai Peninsula communities. Fire, falling trees, declining quality of watersheds and wildlife habitat, economic fluctuations, landscape change, and emotional loss were some of the issues faced. In some communities, increased timber harvesting brought short-term, positive economic change in the wake of the spruce beetle outbreak. In other communities, the loss of a living spruce (Picea spp.) forest profoundly affected quality of life, and led to community conflict, increased risk perception of future impacts, and economic challenges. Biophysical changes were keenly felt by many residents. Communities at different stages in the spruce beetle outbreak revealed temporal and spatial variations in perceived impacts. The diverse array of perceived impacts and risks from the spruce beetle outbreak in Kenai Peninsula communities presents both opportunities and obstacles for forest management in the context of changing forest conditions.  相似文献   

14.
We studied the effects of partial cutting on understory vegetation communities within 19 mixed maple forests in an agriculture-dominated landscape in southwestern Ontario. Woodlots that had been recently harvested were grouped according to provincial silviculture guidelines (standard and heavy cuts) and compared to woodlots that had been uncut for at least 24 years (reference stands). We found significant differences in richness, diversity, and quality of understory vegetation in response to harvest indices. More intensive harvesting resulted in increased richness and diversity, but mostly through the addition of habitat generalists and weedy species. However, partial harvest does not appear to drive vegetation community composition, as ordination methods found no clear community differences between the treatments. Use of the single-tree selection system based on basal area and harvest intensity targets will have an effect on the understory plants, but other factors including past management, disturbance history, and site level microclimate features will also play an important role in shaping vegetation communities. We caution against the removal of large volumes of trees ≥38 cm in diameter, and large reductions in canopy cover, as this can reduce the presence of “conservative” (forest dependent specialist) species, despite a general increase in species richness and diversity. Furthermore, we recommend additional research to investigate the potential for incremental degradation to occur on sites with a long-term history of harvesting, as we found that richness of exotics increased on sites with a history of forest management.  相似文献   

15.
Repeated biomass harvesting for human livelihood needs can cause significant changes in forest structure, composition and diversity. Such impacts have often been associated with the distance to villages and their size, but the effects of individual villages in relation to their characteristics have been little studied. Focussing on the issues around communities’ impacts on the forest, this research aimed to understand how resource extraction by two Buffer Zone villages in Nepal's Bardia National Park affects forest structure and diversity. Tree density, basal area, diameter at breast height (DBH), species richness, two diversity indices and disturbance indices were recorded in 108 plots in 12 transects, from March till May 2005, within the park along the village boundaries, where resource extraction occurs, and in the core park area which is isolated from human disturbance. Forest subject to resource extraction had a lower density of trees, smaller DBH and lower species richness and diversity. Forest disturbance declined with distance from the villages but the two villages differed widely in their impact on the forest. Resource use was more intensive in Shivapur village and percentage of trees lopped, average lopping intensity and numbers of dung piles were statistically significant. This was mainly due to the lack of access to Buffer Zone community Forest for Shivapur households. Interviews with villagers suggested that there have been changes in species availability compared to 5 years ago. Households also underestimated the impact of their resource extraction, which may prevent them from changing their behaviour to benefit conservation. It is clear that understanding rural communities’ needs, their framing of resource extraction and utilisation, and dependence on forest resources will be very helpful for long term conservation measures.  相似文献   

16.
Catastrophic wind events, including tornado, hurricane, and linear winds, are significant disturbances in temperate forested wetlands. Information is lacking on how post-disturbance salvage logging may impact short and long-term objectives in conservation areas where natural stands are typically managed passively. Woody regeneration and herbaceous cover were assessed for three years in a bottomland hardwood forest across a gradient of damage from an F4 tornado, with and without subsequent salvage logging. Soil disturbance intensity and recovery associated with salvage logging within wind-disturbed sites were also assessed. Woody stem density and proportion of potential overstory species (species with the potential to occupy a position in the canopy) increased as a function of wind disturbance intensity. Stem density, proportion of overstory trees, or species diversity did not differ between wind + salvage and wind-disturbed-only plots. Significant dissimilarity occurred among soil disturbance classes within salvaged sites. By the third growing season, vegetation in soil disturbance classes in wind + salvage areas was converging toward undisturbed conditions and bottomland hardwood forest recovery was underway in all vegetation disturbance types and soil disturbance classes. Post-tornado salvage logging, applied judiciously, may contribute to microsite and vegetation diversity.  相似文献   

17.
Landscape structure is often regarded as an important factor that governs the distribution and abundance of species.Therefore it is critical to understand the landscapes and their dynamics.Patterns of landscape elements strongly influence the ecological characteristics.This study was designed to document and map the current status of the tropical dry deciduous forest of the Tadoba-Andhari Tiger Reserve(TATR),Central India,(using IRS P6 LISS IV data)and to describe its landscape structure at three levels of organization viz.landscape,class,and patch.The study area was classified into 10 land cover classes that include 6vegetation classes.The landscape structure was analyzed using FRAGSTATS using 12 set of indices.The TATR landscapes have a total of2,307 patches with a mean patch size of 25.67 ha and patch density of 1.7patches per km2.Amongst all land cover classes,mixed bamboo forest is dominant—it occupied maximum area(77.99%)—while riparian forest is least represented(0.32%).Mixed forest has maximum number of patches among all vegetation classes.Results have shown that despite being dominant in the area,mixed bamboo forest has low patch density(0.25/100 ha).Dominance of mixed bamboo forest is attributed to large patch sizes and not to the number of patches.This study has focussed on the approach of integrating satellite forest classification and forest inventory data for studying forest landscape patterns.  相似文献   

18.
Effective disturbance indices for Hyrcanian forests in Kheyroud,Nowshahr,Iran were determined.The study area was divided into landscape mosaics based on ecosystem parameters including profile type,slope and elevation.Co-occurrence texture indices were derived as forest disturbance factors on the first five bands of Landsat TM,ETM+and OLI images for the prevailing wood harvest disturbance regimes.These indices were screened using ten types of trend analyses and used for modeling disturbance of the harvesting regime through artificial neural networks.The results show that the selected indices can be useful in distinguishing areas with different disturbance intensities and as such,used in the context of health assessment through the health distance method.The accuracy of the health maps derived from the indices [increasing disturbance] led to give rise higher disturbance classification accuracy.  相似文献   

19.
Ecologists and foresters are becoming increasingly aware of the importance of spatial information in ecosystem analysis and resource management. An across-scale analysis of forest structure was conducted to characterize the spatial characteristics of a 2 ha spruce-fir forest located inside Changbaishan Natural Reserve (CNR), PR China. The study was designed to develop an approach for assessment of within-stand heterogeneity to increase understanding of the effects of heterogeneity on pattern–process relationships in forests. Univariate and bivariate Ripley's K functions were employed to capture stand heterogeneity in terms of intra- and inter-specific point patterns of tree distributions. Stem-mapped crowns were generated and analyzed as canopy patches within a geographic information system (GIS) to quantify patterns within the strata of the forest canopy. The dominant spruces were randomly distributed within each height class but aggregated when all height classes were analyzed. In addition, spruces had repulsive patterns to other species which exhibited clear aggregation. Canopy heterogeneity, both in terms of composition and spatial patterning, were complex – as expressed within canopy layers and among individual forest species. This across-scale complexity supports a multivariate spatial and across-scale approach to characterizing forest structure, and argues for linked pattern-process experiments. We suggest that joint field and simulation studies be conducted which relate changes in forest stand dynamics to changes in stand heterogeneity. These linked studies are needed to provide a measure of ecological significance relative to statistical significance of patterns.  相似文献   

20.
Lianas are often overlooked in temperate ecological studies even though they are important components of forest communities. While lianas have been shown to damage tropical canopy trees and reduce the growth of juvenile trees, the impact of lianas on canopy tree growth in temperate systems is largely unknown. Growth of trees ≥8 cm dbh was examined over a 9-year period within 50-year old post-agricultural secondary forests in the Piedmont region of New Jersey, USA. Five lianas, Celastrus orbiculatus, Lonicera japonica, Parthenocissus quinquefolia, Toxicodendron radicans, and Vitis species, occurred throughout the forest. Total liana basal area, number of stems, and percent cover within host trees were evaluated to assess liana burdens on 606 previously censused trees. These data were related to tree growth to assess liana impacts. Forest trees were separated based on their dominance in the canopy to determine whether lianas had the potential to influence forest composition. In general, lianas in the forests were fairly abundant, with 68% of the trees having at least one liana present. On average, each tree supported 9.7 cm2 of liana basal area and 23% of the canopy was covered by lianas. Most of the variation in tree growth was related to the dominance of trees within the canopy, with canopy dominant and co-dominant trees growing 2.5× more than suppressed trees. Liana basal area and number of lianas stems were not related to tree growth, but liana canopy cover decreased tree growth. However, not all trees were equally affected as canopy cover of lianas only reduced growth in dominant and co-dominant trees. Lianas were most influential on host tree growth in unsuppressed trees when occupying a majority of the canopy, only a minority of forest trees. This suppression was not related to differential liana colonization of canopy trees as all canopy classes supported equivalent liana burdens. Though lianas impacted only a minority of the trees in this system, some liana species, C. orbiculatus and Vitis spp., are still increasing and may pose future risks to forest growth and development.  相似文献   

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