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1.
The present study assesses the spatial distribution of selected land cover classes at two years (1975 and 2000) in a Mediterranean urban area (Athens, Greece) to test the hypothesis that land cover changes determine an increase in the sensitivity of landscape to forest fires on a regional scale. While urban and agricultural areas increased, although with different rates of growth, forests and semi-natural areas decreased in the study area. These changes are reflected in a significant increase of vegetation sensitivity to forest fires measured by the forest fire risk (FR) index developed in the framework of MEDALUS project. The cover classes which contributed the most to the increase of the FR index were crop mosaic, mixed agricultural-natural areas and discontinuous, low-density settlements. Results of the present study indicate that the transformation of the fringe landscape towards low-quality agricultural and pasture areas and fragmented forest patches is potentially detrimental for environmental quality and the ecological fragility of land. 相似文献
2.
In the North American upper Great Lakes region, forests dominated by the aspens (Populus grandidentata Michx. – bigtooth aspen, and P. tremuloides Michx. – trembling aspen), which established after late 19th and early 20th century logging, are maturing and succession
will create a new forest composition at landscape to regional scales. This study analyzed the capabilities of Landsat ETM+
remote sensing data combined with existing ecological land unit classifications to discriminate and quantify patterns of succession
at the landscape scale over the 4200 ha University of Michigan Biological Station (UMBS) in northern Lower Michigan. In a
hierarchical approach first multi-temporal Landsat ETM+ was used with a landscape ecosystem classification to map upland forest
cover types (overall accuracy 91.7%). Next the aspen cover type was subset and successional pathways were mapped within that
type (overall accuracy 89.8%). Results demonstrated that Landsat ETM+ may be useful for these purposes; stratification of
upland from wetland types using an ecological land unit classification eliminated confounding issues; multi-temporal methods
discriminated evergreen conifer versus deciduous understories. The Landsat ETM+ classifications were then used to quantify
succession and its relationship to landform-level ecological land units. Forests on moraine and ice contact landforms are
succeeding distinctly to northern hardwoods (95% and 88% respectively); those on outwash and other landforms show greater
diversity of successional pathways. 相似文献
3.
Fire-induced changes in northern Patagonian landscapes 总被引：4，自引：0，他引：4
In northern Patagonia, Argentina we quantify changes in fire frequency along a gradient from mesic Nothofagus dombeyi forest to xeric woodlands of Austrocedrus chilensis at the steppe ecotone, and we examine patterns of vegetation change coincident with the changes in fire regimes across a range of spatial scales. At a regional scale changes in land cover types are documented by comparing 1:250000 scale cover type maps from 1913 and 1985. Changes in landscape structure are analyzed by comparing vegetation patterns on 1:24000 scale aerial photographs taken in 1940 and 1970. Fire frequency peaked in the late nineteenth-century due to widespread burning and clearing of forests by European settlers late in the century. Subsequently, fire frequency declined dramatically about 1910 due to the cessation of intentional fires and has remained low due to increasingly effective fire exclusion. At a regional scale there has been a dramatic increase during the twentieth century in the proportion of forest cover relative to areas mapped as recent burns or shrublands in 1913. Remnant forest patches that survived the widespread late-nineteenth century burning have coalesced to form more continuous forest covers, and formerly continuous areas of shrublands have become dissected by forest. Under reduced fire frequency there has been a shift in dominance from short-lived resprouting species (mostly shrubs) towards longer-lived species and obligate seed-dispersers such as Austrocedrus chilensis and Nothofagus dombeyi. Due to limited seed dispersal of these tree species, the spatial configuration of remnant forest patches plays a key role in subsequent changes in landscape pattern. 相似文献
4.
Mirela G. Tulbure Michael C. Wimberly David P. Roy Geoffrey M. Henebry 《Landscape Ecology》2011,26(2):211-224
Agricultural burning is an important land use practice in the central U.S. but has received little attention in the literature, whereas most of the focus has been on wildfires in forested areas. Given the effects that agricultural burning can have on biodiversity and emissions of greenhouse gasses, there is a need to quantify the spatial and temporal patterns of fire in agricultural landscapes of the central U.S. Three years (2006?C2008) of the MODIS 1?km daily active fire product generated from the MODIS Terra and Aqua satellite data were used. The 2007 Cropland Data Layer developed by the U.S. Department of Agriculture was used to examine fire distribution by land cover/land use (LCLU) type. Global ordinary least square (OLS) models and local geographically weighted regression (GWR) analyses were used to explore spatial variability in relationships between fire detection density and LCLU classes. The monthly total number of fire detections peaked in April and the density of fire detections (number of fires/km2/3?years) was generally higher in areas dominated by agriculture than areas dominated by forest. Fire seasonality varied among areas dominated by different types of agriculture and land use. The effects of LCLU classes on fire detection density varied spatially, with grassland being the primary correlate of fire detection density in eastern Kansas; whereas wheat cropping was important in central Kansas, northeast North Dakota, and northwest Minnesota. 相似文献
5.
Context
Terrestrial ecosystems, including tropical forests, are hypothesized to have tipping points beyond which environmental change triggers rapid and radical shifts to novel alternative states.Objective
We explored the overarching hypothesis that fire-mediated alternative stable states exist in the semi-deciduous tropical forest zone of Ghana, and that increased fire activity has pushed some forests to a new state in which a novel ecosystem with low tree density is maintained by fire.Methods
We combined a 30-year time series of remotely-sensed data with field measurements to assess land cover trends, the effects of fire on forest vegetation, and the reciprocal effects of vegetation change on fire regimes, in four forest reserves. We analyzed precipitation trends to determine if shifts in vegetation and fire regime reflected a shift to a drier climate.Results
Two of the reserves experienced forest loss, were impacted by frequent fires, and transitioned to a vegetation community dominated by shrubs and grasses, which was maintained by fire–vegetation feedbacks. The other two reserves experienced less fire, retained higher levels of forest cover, and resisted fire encroachment from surrounding agricultural areas. Precipitation remained relatively stable, suggesting a hysteresis effect in which different vegetation states and fire regimes coexist within a similar climate.Conclusion
There is potential for human land use and fire to create novel and persistent non-forest vegetation communities in areas that are climatically suitable for tropical forests. These disturbance-mediated regime shifts should be taken into account when assessing future trajectories of forest landscape change in West Africa.6.
Intense harvesting and slash fires during the late 1800s and early 1900s led to homogenization throughout the Great Lakes region via the conversion from tamarack, pine, and spruce forests to aspen forests, which are supported by the forest products industry. Subsequently, mesophication occurred in the eastern United States due to fire suppression, transforming oak woodlands to mixed mesophytic forests. We explored both homogenization and mesophication at a regional scale by quantifying changes in community composition and density between historical General Land Office survey points and current USDA Forest Analysis and Inventory plots for Minnesota??s Laurentian Mixed and Eastern Broadleaf Forest provinces. We used the Morisita plotless density estimator and applied corrections for surveyor bias to estimate density for historical forests and we used known densities of FIA plots to predict current densities with random forests, an ensemble regression tree method, and terrain and soil predictor variables. Of the 43 ecological units used in the analysis, only one current community was similar to its historical counterpart. Within the Laurentian Mixed Forest province, forest density of primarily mature aspen stands is reduced slightly today compared to the tamarack-dominated forests of the past. Conversely, in the Eastern Broadleaf Forest province, forest densities have increased compared to historical pine and oak woodlands, due to increases of densely growing, fire-sensitive species. Ordinations of functional traits and structure showed substantial changes between current and historical communities as well as reduced differentiation among current communities compared to their historical counterparts. Homogenization in the Laurentian Mixed Forest is occurring by transition from early-successional to late-successional species, with associated changes in forest ecosystems, and homogenization and mesophication in the Eastern Broadleaf Forest are occurring by transition from disturbance-stabilized genera of open forest ecosystems to non-disturbance-dependent genera of dense forests. Despite different starting points of historical forest ecosystems in the Laurentian Mixed Forest and Eastern Broadleaf Forest, we found homogenization and mesophication to be interrelated in the convergence of composition and densities along a common trajectory to dense forests composed of late-successional species in Minnesota. 相似文献
7.
Ownership and ecosystem as sources of spatial heterogeneity in a forested landscape,Wisconsin, USA 总被引：7，自引：0，他引：7
The interaction between physical environment and land ownership in creating spatial heterogeneity was studied in largely forested landscapes of northern Wisconsin, USA. A stratified random approach was used in which 2500-ha plots representing two ownerships (National Forest and private non-industrial) were located within two regional ecosystems (extremely well-drained outwash sands and moderately well-drained moraines). Sixteen plots were established, four within each combination of ownership and ecosystem, and the land cover on the plots was classified from aerial photographs using a modified form of the Anderson (U.S. Geological Survey) land use and land cover classification system.Upland deciduous forests dominated by northern hardwoods were common on the moraines for both ownerships. On the outwash, the National Forest was dominated by pine plantations, upland deciduous forests, and upland regenerating forests (as defined by <50% canopy coverage). In contrast, a more even distribution among the classes of upland forest existed on private land/outwash. A strong interaction between ecosystem and ownership was evident for most comparisons of landscape structure. On the moraine, the National Forest ownership had a finer grain pattern with more complex patch shapes compared to private land. On the outwash, in contrast, the National Forest had a coarser grain pattern with less complex patch shapes compared to private land. When patch size and shape were compared between ecosystems within an ownership, statistically significant differences in landscape structure existed on public land but not on private land. On public land, different management practices on the moraine and outwash, primarily related to timber harvesting and road building, created very different landscape patterns. Landscape structure on different ecosystems on private land tended to be similar because ownership was fragmented in both ecosystems and because ownership boundaries often corresponded to patch boundaries on private land. A complex relationship exits between ownership, and related differences in land use, and the physical environment that ultimately constrains land use. Studies that do not consider these interactions may misinterpret the importance of either variable in explaining variation in landscape patterns. 相似文献
8.
Landscape structure in the Eastern US experienced great changes in the last century with the expansion of forest cover into
abandoned agricultural land and the clearing of secondary forest cover for urban development. In this paper, the spatial and
temporal patterns of forest cover from 1914 to 2004 in the Gwynns Falls watershed in Baltimore, Maryland were quantified from
historic maps and aerial photographs. Using a database of forest patches from six times—1914, 1938, 1957, 1971, 1999, and
2004—we found that forest cover changed, both temporally and spatially. While total forest area remained essentially constant,
turnover in forest cover was very substantial. Less than 20% of initial forest cover remained unchanged. Forest cover became
increasingly fragmented as the number, size, shape, and spatial distribution of forest patches within the watershed changed
greatly. Forest patch change was also analyzed within 3-km distance bands extending from the urban core to the more suburban
end of the watershed. This analysis showed that, over time, the location of high rates of forest cover change shifted from
urban to suburban bands which coincides with the spatial shift of urbanization. Forest cover tended to be more stable in and
near the urban center, whereas forest cover changed more in areas where urbanization was still in process. These results may
have critical implications for the ecological functioning of forest patches and underscore the need to integrate multi-temporal
data layers to investigate the spatial pattern of forest cover and the temporal variations of that spatial pattern. 相似文献
9.
The purpose of this study is to investigate if, or under what conditions, fires select given land cover types for burning.
If fires burn unselectively then the land cover composition (the proportional area of various land cover types) of individual
fires should approximate the land cover composition available in their neighborhood. In this study we test this hypothesis
by performing statistical analyses of a data set consisting of paired vectors with the proportions of land cover types present
in burned areas and in their respective surroundings. The statistical methods employed (a permutation technique and the Cmax statistic) are commonly used in resource selection studies where data is subject to a unit-sum constraint. The results of
the analysis of 506 fires that burned in Portugal in 1991 indicate that fires are selective, with small fires exhibiting stronger
land cover preferences than large fires. According to the results of a multiple comparison analysis performed for small fires,
there is a marked preference for shrubland followed by other forest cover types, while agriculture is clearly avoided. A similar
analysis is performed to test if fire selectivity is related to the ecological region where it occurs. The results obtained
in this study contribute to the discussion on the relative importance of fuels as a drivers of fire spread. 相似文献
10.
Grossinger Robin M. Striplen Charles J. Askevold Ruth A. Brewster Elise Beller Erin E. 《Landscape Ecology》2007,22(1):103-120
Historical records provide information to land managers and landscape ecologists attempting to understand current trajectories in altered landscapes. In this study, we synthesized a heterogeneous array of historical sources to reconstruct historical land cover in California’s Santa Clara Valley (a.k.a. “Silicon Valley”). To increase and assess accuracy, we used the triangulation of overlapping, independent data sources and the application of certainty level standards. The region has been subject to extensive urbanization, so we also evaluated the applicability of historical landscape reconstructions to the altered landscape. We found evidence for five major land cover types prior to significant Euro–American modification. Valley freshwater marsh, wet meadow, alkali meadow, willow grove, and valley oak savanna have all experienced extreme decline (85–100%) since Euro–American settlement. However, comparison of historical land cover patterns to contemporary land use suggested several new strategies for environmental recovery, despite the limitations of surrounding urbanization. We also observed a temporal shift in riparian habitat along the mainstem of Coyote Creek, from a relatively open mixture of riparian scrub, sycamore woodland, and unvegetated gravel bars to dense riparian forest, likely resulting from stream flow regulation. By identifying former land cover patterns we provide a basis for evaluating local landscape change and setting restoration targets, including the identification of residual features and under-recognized land cover types. These findings suggest that reliable historical landscape reconstructions can be developed in the absence of standardized historical data sources and can be of value even in highly modified regions. 相似文献
11.
Early forest dynamics in stand-replacing fire patches in the northern Sierra Nevada, California, USA 总被引：1，自引：0，他引：1
There is considerable concern over the occurrence of stand-replacing fire in forest types historically associated with low- to moderate-severity fire. The concern is largely over whether contemporary levels of stand-replacing fire are outside the historical range of variability, and what natural forest recovery is in these forest types following stand-replacing fire. In this study we quantified shrub characteristics and tree regeneration patterns in stand-replacing patches for five fires in the northern Sierra Nevada. These fires occurred between 1999 and 2008, and our field measurements were conducted in 2010. We analyzed tree regeneration patterns at two scales: patch level, in which field observations and spatial data were aggregated for a given stand-replacing patch, and plot level. Although tree regeneration densities varied considerably across sampled fires, over 50 % of the patches and approximately 80 % all plots had no tree regeneration. The percentage of patches, and to a greater extent plots, without pine regeneration was even higher, 72 and 87 %, respectively. Hardwood regeneration was present on a higher proportion of plots than either the pine or non-pine conifer groups. Shrub cover was generally high, with approximately 60 % of both patches and individual plots exceeding 60 % cover. Patch characteristics (size, perimeter-to-area ratio, distance-to-edge) appeared to have little effect on observed tree regeneration patterns. Conifer regeneration was higher in areas with post-fire management activities (salvage harvesting, planting). Our results indicate that the natural return of pine/mixed-conifer forests is uncertain in many areas affected by stand-replacing fire. 相似文献
12.
Studies dealing with community similarity are necessary to understand large scale ecological processes causing biodiversity
loss and to improve landscape and regional planning. Here, we study landscape variables influencing patterns of community
similarity in fragmented and continuous forest landscapes in the Atlantic forest of South America, isolating the effects of
forest loss, fragmentation and patterns of land use. Using a grid design, we surveyed birds in 41 square cells of 100 km2 using the point count method. We used multivariate, regression analyses and lagged predictor autoregressive models to examine
the relative influence of landscape variables on community similarity. Forest cover was the primary variable explaining patterns
of bird community similarity. Similarity showed a sudden decline between 20 and 40% of forest cover. Patterns of land use
had a second order effect; native bird communities were less affected by forest loss in landscapes dominated by tree plantations
(the most suitable habitat for native species) than in landscapes dominated by annual crops or cattle pastures. The effects
of fragmentation were inconclusive. The trade-off between local extinctions and the invasion of extra-regional species using
recently created habitats is probably the mechanism generating the observed patterns of community similarity. Limiting forest
loss to 30–40% of the landscape cover and improving the suitability of human-modified habitats will contribute to maintain
the structure and composition of the native forest bird community in the Atlantic forest. 相似文献
13.
Group selection silviculture creates canopy openings that can alter connectivity in patchy forests, thereby affecting wildlife
movement and fire behavior. We examined effects of group selection silviculture on percolation (presence of continuously forested
routes across a landscape) in Sierra Nevada East-side pine forest in northern California, USA. Four ~ 250 ha project areas
were analyzed at three map resolutions in three ways: analyzing forest cover maps for percolation before and after group-selection
treatment, placing simulated group openings in forest cover maps until fragmentation occurred, and comparing project areas
to neutral maps that varied in forest cover and self-adjacency. Two project areas were fragmented (i.e., did not percolate)
prior to treatment, one resisted fragmentation, and the other became fragmented by treatment when analyzed at 30 m cell resolution.
Median simulated openings required to create fragmentation agreed well with the actual number. There was a well-defined transition
between percolating and non-percolating neutral maps; increased aggregation of forest lowered the critical value at which
forests percolated. A logistic model based on these maps predicted percolation behavior of the project areas effectively,
but alternative generating algorithms gave slightly different predictions. A graph of this model provides a straightforward
way to visualize how close a landscape is to fragmentation based on its forest cover and aggregation. In East-side Sierran
landscape, fragmentation from group-selection openings may make the landscape less hospitable to the American marten but more
resistant to crown fire. 相似文献
14.
Frauke Ecke Pernilla Christensen Per Sandström Birger Hörnfeldt 《Landscape Ecology》2006,21(4):485-497
Several studies indicate a long-term decline in numbers of different species of voles in northern Fennoscandia. In boreal Sweden, the long-term decline is most pronounced in the grey-sided vole (Clethrionomys rufocanus). Altered forest landscape structure has been suggested as a possible cause of the decline. However, habitat responses of grey-sided voles at the landscape scale have never been studied. We analyzed such responses of this species in lowland forests in Västerbotten, northern Sweden. Cumulated spring densities representing 22 local time series from 1980–1999 were obtained by a landscape sampling design and were related to the surrounding landscape structure of 2.5×2.5 km plots centred on each of the 22 1-ha trapping plots. In accordance with general knowledge on local habitat preferences of grey-sided voles, our study supported the importance of habitat variables such as boulder fields and old-growth pine forest at the landscape scale. Densities were negatively related to clear cuts. Habitat associations were primarily those of landscape structure related to habitat fragmentation, distance between habitat patches and patch interspersion rather than habitat patch type quantity. Local densities of the grey-sided vole were positively and exponentially correlated with spatial contiguity (measured with the fragmentation index) of old-growth pine forest, indicating critical forest fragmentation thresholds. Our results indicate that altered land use might be involved in the long-term decline of the grey-sided vole in managed forest areas of Fennoscandia. We propose two further approaches to reveal and test responses of this species to changes in landscape structure. 相似文献
15.
Forest conservation and land development in Puerto Rico 总被引：4，自引：1，他引：3
In the Caribbean island of Puerto Rico, rapid land-use changes over the past century have included recent land-cover conversion to urban/built-up lands. Observations of this land development adjacent to reserves or replacing dense forest call into question how the changes relate to forests or reserved lands. Using existing maps, this study first summarizes island-wide land-cover change between 1977-78 and 1991-92. Then, using binomial logit modeling, it seeks evidence that simple forest cover attributes, reserve locations, or existing land cover influence land development locations. Finally, this study quantifies land development, reserve protection and forest cover by ecological zone. Results indicate that 1) pasture is more likely to undergo land development than shrubland plus forest with low canopy density, 2) forest condition and conservation status appear unimportant in that development locations neither distinguish between classes of forest canopy development nor relate to forest patch size or reserve proximity, and 3) most land development occurs in the least-protected ecological zones. Outside the boundaries of strictly protected forest and other reserves, accessibility, proximity to existing urban areas, and perhaps desirable natural settings, serve to increase land development. Over the coming century, opportunities to address ecological zone gaps in the islands forest reserve system could be lost more rapidly in lowland ecological zones, which are relatively unprotected.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
16.
Two ecological models have been put forward to explain the dynamics of fire-promoting and fire-sensitive vegetation in southwest
Tasmania: the alternative stable states model of Jackson (in Proc Ecol Soc Aust 3:9–16, 1968) and the sharpening switch model of Mount (in Search 10:180–186, 1979). Assessing the efficacy of these models requires high resolution spatio-temporal data on whether vegetation patterns are
stable or dynamic across landscapes. We analysed ortho-rectified sequences of aerial photography and satellite imagery from
1948, 1988 and 2010 to detect decadal scale changes in forest and non-forest vegetation cover in southwest Tasmania. There
was negligible change from forest to non-forest (<0.05%) and only a modest change from non-forest to forest over the study
period. Forest cover increased by 4.1% between 1948 and 1988, apparently due to the recovery of forest vegetation following
stand-replacing fire prior to 1948. Forest cover increased by 0.8% between 1988 and 2010, reflecting the limited ability of
forest to invade treeless areas. The two models include interactions between vegetation, fire and soil, which we investigated
by analysing the chemical (phosphorus, nitrogen) and physical properties (clay, silt) of 128 soil samples collected across
34 forest–non-forest boundaries. Phosphorus in the upper horizon was typically lower in non-forest vegetation compared to
forest vegetation, which is consistent with proposed fire–vegetation–soil feedbacks. Mineral horizons were dominated by sand,
with low levels of clay under all vegetation types. Available field evidence lends support to the Jackson (1968) alternative stable states model as the most suitable model of vegetation dynamics on nutrient poor substrates in southwest
Tasmania although modifications of the timeframes for transitions toward rainforest are required. 相似文献
17.
Patch-level based vegetation change and environmental drivers in Tarim River drainage area of West China 总被引：1，自引：0，他引：1
Weijing Kong Osbert Jianxin Sun Yaning Chen Yi Yu Ziqiang Tian 《Landscape Ecology》2010,25(9):1447-1455
Information on vegetation-related land cover change and the principle drivers is critical for environmental management and
assessment of desertification processes in arid environments. In this study, we investigated patch-level based changes in
vegetation and other major land cover types in lower Tarim River drainage area in Xinjiang, West China, and examined the impacts
of environmental factors on those changes. Patterns of land cover change were analyzed for the time sequence of 1987–1999–2004
based on satellite-derived land classification maps, and their relationships with environmental factors were determined using
Redundancy Analysis (RDA). Environmental variables used in the analysis included altitude, slope, aspect, patch shape index
(fractal dimension), patch area, distance to water body, distance to settlements, and distance to main roads. We found that
during the study period, 26% of the land experienced cover changes, much of which were the types from the natural riparian
and upland vegetation to other land covers. The natural riparian and upland vegetation patches were transformed mostly to
desert and some to farmlands, indicating expanding desertification processes of the region. A significant fraction of the
natural riparian and upland vegetation experienced a phase of alkalinity before becoming desert, suggesting that drought is
not the exclusive environmental driver of desertification in the study area. Overall, only a small proportion of the variance
in vegetation-related land cover change is explainable by environmental variables included in this study, especially during
1987–1999, indicating that patch-level based vegetation change in this region is partly attributable to environmental perturbations.
The apparent transformation from the natural riparian and upland vegetation to desert indicates an on-going process of desertification
in the region. 相似文献
18.
Recent forest cover type transitions and landscape structural changes in northeast Minnesota,USA 总被引：1，自引：0，他引：1
Landsat TM satellite data covering an approximate 5-year interval (1990–1995) were used to quantify spatial pattern and transition
rates between forest ecological states for a 2.76 million ha region in northeast Minnesota. Changes in forest cover were stratified
by Ecological Subsection, management status, and by ownership categories using a 1995 digital ownership layer. Approximately
4.2% of the 1990 mature forested area was converted to early successional types by 1995. Of this 4.2%, private lands accounted
for 33%, federal lands 31%, county lands 20% and state lands 16%. Notable conversion percentages by cover type category were
spruce-fir (−5.3%), aspen-birch(−4.7%), jack pine (−4.6%) and black spruce(−3.0%). Transition rates were also adjusted to
fit ten-year time intervals. Shannon-Weaver Eveness and edge density of cover types increased over the study period as relative
contagion and interior forest area decreased. These trends suggest both smaller patches and a more even distribution of cover
types. Area of upland conifers, lowland conifers and lowland hardwoods decreased while the area of mature upland hardwoods
increased in most patch size classes except the > 500 ha class which showed a substantial decrease in area. The area of early
successional types increased in most patch size classes. Non-industrial private forestland had the lowest proportion of interior
forest of all ownership categories -decreasing by 13.5% in five years. Smaller average cut-unit size sand uncoordinated forest
management is the likely cause since cutting rates between private and public forestland were similar.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Land use history has altered natural disturbance dynamics, causing widespread modifications of the earth’s forests. The aim of this study is to reconstruct a regional, spatially-explicit, fire and logging history for a large southern boreal forest landscape (6,050 km2) of eastern Canada. We then examined the long-term influence of land use history, fires, and physiographical gradients on the area’s disturbances regimes, present-day age structure and tree species composition. Spatially-explicit fire (1820–2005) and logging (1900–2005) histories were reconstructed from forestry maps, terrestrial forest inventories and historical records (local newspapers, travel notes, regional historical reviews). Logistic regression was used to model the occurrence of major boreal tree species at the regional scale, in relation to their disturbance history and physiographical variables. The interplay of elevation and fire history was found to explain a large part of the present-day distribution of the four species studied. We conclude that human-induced fires following the colonization activities of the nineteenth and twentieth centuries have increased fire frequency and the dominance of fire-adapted species at lower elevations. At higher elevations, the low historical fire frequency has fostered the dominance of fire-sensitive species. Twentieth-century forestry practices and escaped settlement fires have generated a forest landscape dominated by younger forest habitats than in presettlement times. The expected increase of wildfire activity in North America’s eastern boreal forest, in conjunction with continued forest management, could have significant consequences on the resilience of boreal forests. 相似文献
20.
We conducted a multi-temporal spatial analysis of forest cover for a 9600 ha landscape in northern Wisconsin, U.S.A., using data from pre-European settlement (1860s), post-settlement (1931), and current (1989) periods. Using GIS we have shown forest landscape changes and trajectories that have been generally described in aggregate for the norther Great Lake States region. We created the pre-European settlement map from the witness tree data of the original federal General Land Office survey notes. The 1931 cover was produced from the Wisconsin Land Economic Inventory, and the 1989 cover map was based on color infrared photography. We used GIS to analyze 1) land area occupied by different forest types at different dates, 2) temporal transitions between dates and their driving proceses, and 3) successional trajectories with landforms and spatial associations of forest types. Over the 120 year period, forest cover has changed from a landscape dominated by old-growth hemlock (Tsuga canadensis) and hardwood forests (Acer saccharum, Betula alleghaniensis) to largely second-growth hardwoods and conifers. The former dominant hemlock is largely eliminated from the landscape. From 1860 to 1931, large-scale disturbances associated with logging were the dominant processes on the landscape. Early successional forest types covered much of the landscape by the 1930s. From 1931 to 1989, succession was the dominant process driving forest transitions as forest types succeeded to a diverse group of upland hardwood and conifer forest types. If successional trajectories continue, a more homogeneous landscape may develop comprised of both a northern hardwood type dominated by sugar maple, and a boreal conifer/hardwood forest. 相似文献