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1.
Increasing land ownership fragmentation in the United States is causing concerns with respect to its ecological implications
for forested landscapes. This is especially relevant given that human influence is one of the most significant driving forces
affecting the forest landscape. A method for generating realistic land ownership maps is needed to evaluate the effects of
ownership fragmentation on forest landscapes in combination with other natural processes captured in forest process models.
Ownership patterns from human activities usually generate landscape boundary shapes different from those arising from natural
processes. Spatial characteristics among ownership types – e.g., private, public ownership – may also differ. To address these
issues, we developed the Fragmented Land Ownership Spatial Simulator (FLOSS) to generate ownership patterns that reflect the
Public Land Survey System (PLSS) shapes and various patch size distributions among different types of ownership (e.g., private,
public). To evaluate FLOSS performance, we compared the simulated patterns with various ownership fragmentation levels to
the actual ownership patterns in the Missouri Ozarks by using selected landscape indices. FLOSS generated landscapes with
spatial characteristics similar to actual landscapes, suggesting that it can simulate different levels of ownership fragmentation.
This will allow FLOSS to serve as a feasible tool for evaluating forest management applications by spatially allocating various
management scenarios in a realistic way. The potentials and limitations of FLOSS application are discussed. 相似文献
2.
Logging pattern and landscape changes over the last century at the boreal and deciduous forest transition in Eastern Canada 总被引:4,自引:0,他引:4
Forestry practices associated with the industrial era (since ~1900) have altered the natural disturbance regimes and greatly
impacted the world’s forests. We quantified twentieth century logging patterns and regional scale consequences in three sub-boreal
forest landscapes of Eastern Canada (117,000, 49,400 and 92,300 ha), comparing forestry maps depicting age and forest cover
types for early industrial (1930) and present-day (2000) conditions. Results were similar for the three landscapes, indicating
large-scale forest change during the twentieth century. In 1930, previous logging activities had been concentrated in the
lowlands and along the main hydrographical network, as compared to a more even distribution over the landscapes in 2000, reflecting
a decreasing influence of the environmental constraints on forest harvesting. In 1930, old-aged forests (>100 years) accounted
for more than 75% of the unlogged areas of the three landscapes, as compared to less than 15% for the present-day conditions.
Logging practices have thus inverted the stand age distribution of the landscapes that are currently dominated by young and
regenerating stands. The 1930 forest cover types showed a clear relationship with elevation, with conifers located in the
lowlands and mixed and deciduous stands restricted to the upper slopes. Between 1930 and 2000, 58–64% of the conifer areas
transformed to mixed and deciduous forests, such that no clear altitudinal relationships remained in 2000. We conclude that
twentieth century logging practices have strongly altered the preindustrial vegetation patterns in our study area, to the
point that ecosystem-based management strategies should be developed to restore conifer dominance, altitudinal gradients,
as well as the irregular structure inspired from old forest stands. 相似文献
3.
Rune H. Økland Harald Bratli Wenche E. Dramstad Anette Edvardsen Gunnar Engan Wendy Fjellstad Einar Heegaard Oddvar Pedersen Heidi Solstad 《Landscape Ecology》2006,21(7):969-987
Knowledge of variation in vascular plant species richness and species composition in modern agricultural landscapes is important
for appropriate biodiversity management. From species lists for 2201 land-type patches in 16 1-km2 plots five data sets differing in sampling-unit size from patch to plot were prepared. Variation in each data set was partitioned
into seven sources: patch geometry, patch type, geographic location, plot affiliation, habitat diversity, ecological factors,
and land-use intensity. Patch species richness was highly predictable (75% of variance explained) by patch area, within-patch
heterogeneity and patch type. Plot species richness was, however, not predictable by any explanatory variable, most likely
because all studied landscapes contained all main patch types – ploughed land, woodland, grassland and other open land – and
hence had a large core of common species. Patch species composition was explained by variation along major environmental complex
gradients but appeared nested to lower degrees in modern than in traditional agricultural landscapes because species-poor
parts of the landscape do not contain well-defined subsets of the species pool of species-rich parts. Variation in species
composition was scale dependent because the relative importance of specific complex gradients changed with increasing sampling-unit
size, and because the amount of randomness in data sets decreased with increasing sampling-unit size. Our results indicate
that broad landscape structural changes will have consequences for landscape-scale species richness that are hard or impossible
to predict by simple surrogate variables. 相似文献
4.
Creating landscape patterns by forest cutting: Ecological consequences and principles 总被引:2,自引:2,他引:0
Landscape structural characteristics, such as patch size, edge length, and configuration, are altered markedly when management regimes are imposed on primeval landscapes. The ecological consequences of clearcutting patterns were explored by using a model of the dispersed patch or checkerboard system currently practiced on federal forest lands in the western United States. Thresholds in landscape structure were observed on a gradient of percentages of landscape cutover. Probability of disturbance,e.g., wildfire and windthrow, and biotic components,e.g., species diversity and game populations, are highly sensitive to these structural changes. Altering the spatial configuration and size of clearcuts provides an opportunity to create alternative landscapes that differ significantly in their ecological characteristics. Both ecosystem and heterogeneous landscape perspectives are critical in resource management. 相似文献
5.
Fire and grazing are ecological processes that frequently interact to modify landscape patterns of vegetation. There is empirical
and theoretical evidence that response of herbivores to heterogeneity is scale-dependent however the relationship between
fire and scale of heterogeneity is not well defined. We examined the relationship between fire behavior and spatial scale
(i.e., patch grain) of fuel heterogeneity. We created four heterogeneous landscapes modeled after those created by a fire–grazing
interaction that differed in grain size of fuel patches. Fire spread was simulated through each model landscape from 80 independent,
randomly located ignition points. Burn area, burn shape complexity and the proportion of area burnt by different fire types
(headfire, backfire and flankfire) were all affected by the grain of fuel patch. The area fires burned in heterogeneous landscapes
interacted with the fuel load present in the patch where ignition occurred. Burn complexity was greater in landscapes with
small patch grain than in landscapes with large patch grain. The proportion of each fire type (backfire, flankfire and headfire)
was similar among all landscapes regardless of patch grain but the variance of burned area within each of the three fire types
differed among treatments of patch grain. Our landscape fire simulation supports the supposition that feedbacks between landscape
patterns and ecological processes are scale-dependent, in this case spatial scale of fuel loading altering fire spread through
the landscape. 相似文献
6.
Temporal change in forest fragmentation at multiple scales 总被引:1,自引:0,他引:1
Previous studies of temporal changes in fragmentation have focused almost exclusively on patch and edge statistics, which
might not detect changes in the spatial scale at which forest occurs in or dominates the landscape. We used temporal land-cover
data for the Chesapeake Bay region and the state of New Jersey to compare patch-based and area–density scaling measures of
fragmentation for detecting changes in the spatial scale of forest that may result from forest loss. For the patch-based analysis,
we examined changes in the cumulative distribution of patch sizes. For area–density scaling, we used moving windows to examine
changes in dominant forest. We defined dominant forest as a forest parcel (pixel) surrounded by a neighborhood in which forest
occupied the majority of pixels. We used >50% and ≥60% as thresholds to define majority. Moving window sizes ranged from 2.25
to 5,314.41 hectares (ha). Patch size cumulative distributions changed very little over time, providing no indication that
forest loss was changing the spatial scale of forest. Area–density scaling showed that dominant forest was sensitive to forest
loss, and the sensitivity increased nonlinearly as the spatial scale increased. The ratio of dominant forest loss to forest
loss increased nonlinearly from 1.4 to 1.8 at the smallest spatial scale to 8.3 to 11.5 at the largest spatial scale. The
nonlinear relationship between dominant forest loss and forest loss in these regions suggests that continued forest loss will
cause abrupt transitions in the scale at which forest dominates the landscape. In comparison to the Chesapeake Bay region,
dominant forest loss in New Jersey was less sensitive to forest loss, which may be attributable the protected status of the
New Jersey Pine Barrens. 相似文献
7.
This collaborative essay grows out of a debate about the relationship between aesthetics and ecology and the possibility of
an “ecological aesthetic” that affects landscape planning, design, and management. We describe our common understandings and
unresolved questions about this relationship, including the importance of aesthetics in understanding and affecting landscape
change and the ways in which aesthetics and ecology may have either complementary or contradictory implications for a landscape.
To help understand these issues, we first outline a conceptual model of the aesthetics–ecology relationship. We posit that:
1. While human and environmental phenomena occur at widely varying scales, humans engage with environmental phenomena at a
particular scale: that of human experience of our landscape surroundings. That is the human “perceptible realm.”
2. Interactions within this realm give rise to aesthetic experiences, which can lead to changes affecting humans and the landscape,
and thus ecosystems.
3. Context affects aesthetic experience of landscapes. Context includes both effects of different landscape types (wild, agricultural,
cultural, and metropolitan landscapes) and effects of different personal–social situational activities or concerns. We argue
that some contexts elicit aesthetic experiences that have traditionally been called “scenic beauty,” while other contexts
elicit different aesthetic experiences, such as perceived care, attachment, and identity.
Last, we discuss how interventions through landscape planning, design, and management; or through enhanced knowledge might
establish desirable relationships between aesthetics and ecology, and we examine the controversial characteristics of such
ecological aesthetics. While these interventions may help sustain beneficial landscape patterns and practices, they are inherently
normative, and we consider their ethical implications. 相似文献
8.
The discipline of landscape ecology recognizes the importance of measuring habitat suitability variables at spatial scales
relevant to specific organisms. This paper uses a novel multi-scale hierarchical patch delineation method, PatchMorph, to
measure landscape patch characteristics at two distinct spatial scales and statistically relate them to the presence of state-listed
endangered yellow-billed cuckoos (Coccyzus americanus occidentalis) nesting in forest patches along the Sacramento River, California, USA. The landscape patch characteristics calculated were:
patch thickness, area of cottonwood forest, area of riparian scrub, area of other mixed riparian forest, and total patch area.
A third, regional spatial variable, delineating the north and south portions of study area was also analyzed for the effect
of regional processes. Using field surveys, the landscape characteristics were related to patch occupancy by yellow-billed
cuckoos. The area of cottonwood forest measured at the finest spatial scale of patches was found to be the most important
factor determining yellow-billed cuckoo presence in the forest patches, while no patch characteristics at the larger scale
of habitat patches were important. The regional spatial variable was important in two of the three analysis techniques. Model
validation using an independent data set of surveys (conducted 1987–1990) found 76–82% model accuracy for all the statistical
techniques used. Our results show that the spatial scale at which habitat characteristics are measured influences the suitability
of forest patches. This multi-scale patch and model selection approach to habitat suitability analysis can readily be generalized
for use with other organisms and systems. 相似文献
9.
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
10.
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
11.
Frauke Ecke Pernilla Christensen Ralf Rentz Mats Nilsson Per Sandström Birger Hörnfeldt 《Landscape Ecology》2010,25(4):551-560
Changes in forest landscape structure have been suggested as a likely contributing factor behind the long-term decline in
the numbers of cyclic grey-sided voles (Clethrionomys rufocanus) in northern Fennoscandian lowland regions in contrast to mountain regions due to the absence of forest management in the
mountains. This study, for the first time, formally explored landscape structure in 29 lowland (LF) and 14 mountain forest
(MF) landscapes (each 2.5 × 2.5 km) in northern Sweden, and related the results to the cumulated spring trapping index of
the grey-sided vole in 2002–2006. The grey-sided vole showed striking contrasts in dynamics close in space and time. The MF
landscapes were characterized by larger patches and less fragmentation of preferred forest types. The grey-sided vole was
trapped in all of 14 analyzed MF landscapes but only in three out of 29 of the LF landscapes. MF and LF landscapes with grey-sided
vole occurrence were characterized by similar focal forest patch size (mean 357 ha, minimum 82 ha and mean 360 ha, minimum
79 ha, respectively). In contrast, these MF compared to the LF landscapes were characterized by larger patches of preferred
forest types and less fragmented preferred forest types and by a lower proportion of clear-cut areas. The present results
suggest that landscape structure is important for the abundance of grey-sided voles in both regions. However, in the mountains
the change from more or less seasonal dynamics to high-amplitude cycles between the mid 1990s and 2000s cannot be explained
by changes in landscape structure. 相似文献
12.
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
13.
With expansion of urban areas worldwide, migrating songbirds increasingly encounter fragmented landscapes where habitat patches
are embedded in an urban matrix, yet how migrating birds respond to urbanization is poorly understood. Our research evaluated
the relative importance of patch-level effects and body condition to movement behaviour of songbirds during migratory stopover
within an urban landscape. We experimentally relocated 91 migrant Swainson’s thrushes (Catharus ustulatus) fitted with 0.66 g radio-transmitters to seven forest patches that differed in area (0.7–38.4 ha) and degree of urbanization
within central Ohio, USA, May 2004–2007. Fine-scale movement rate of thrushes (n = 55) did not differ among urban forest sites, but birds in low energetic condition moved at higher rates, indicating an
energetically mediated influence on movement behaviour. In larger sites, Swainson’s thrushes (n = 59) had greater coarse-level movement during the first 3 days and utilized areas farther from forest edge, indicating stronger
influence by patch-level factors. Thrushes exhibited strong site tenacity, with only five individuals (7%) leaving release
patches prior to migratory departure. Movement outside the release patch only occurred at the smallest forest patches (0.7
and 4.5 ha), suggesting that these sites were too small to meet needs of some individuals. Swainson’s thrushes exhibited edge
avoidance and apparent area sensitivity within urban forest patches during stopover, implying that conservation of larger
patches within urban and other fragmented landscapes may benefit this species and other migrant forest birds. 相似文献
14.
David A. Etheridge David A. MacLean Robert G. Wagner Jeremy S. Wilson 《Landscape Ecology》2006,21(4):509-524
Historical and future projected landscape patterns and changes caused by harvesting and silviculture were evaluated for a
189,000 ha, intensively managed forest in New Brunswick, Canada. We compared changes in species composition, age classes,
and patch characteristics (area, size, density, edge, shape, and core area) between 1945, 2002, and projections to 2027 (based
on the landowner's spatial forest management plan). In 1945, the landbase was 40% softwood, 37% mixed hardwood–softwood, 10%
hardwood, and 9% softwood–cedar. From 1945 to 2002 and 2027, respectively, softwood forest area increased by 2 and 11%, mixedwood
decreased by 19 and 20%, and hardwood area increased by 15 and 14%, and softwood–cedar increased by 6% and then decreased
by 7%. In 1945, forest >70 years old comprised 85% of the landscape, but declined to 44% in 2002 and was projected to encompass
41% in 2027. Increased area harvested, decreasing harvest patch size, and protection against natural disturbances resulted
in progressively smaller mean and less variable patch sizes from 1945 to 2002. Based upon the 25-year forest management plan,
this trend was projected to continue, with the exception of nine patches >1000 ha created by 2027, eight of which were softwood
plantations. Stand type successional dynamics were highly variable in both harvested and non-harvested areas, and in some
cases were unexpected. Few of the 1945 stand types remained static by 2002, with 42 and 35% of mixedwood shifting to softwood
as a result of harvesting, and to hardwood as a result of both harvesting and spruce budworm (Choristoneura fumiferana Clem.) outbreaks in the 1950s and 1970s. This study demonstrates the strong cumulative effect of forest management on landscape
patterns, especially the socially mandated drive for smaller clearcuts resulting in the loss of large patches. 相似文献
15.
We evaluated support for four alternate hypotheses explaining the distribution of breeding Brown-headed Cowbirds (Molothrus ater) in forests at varying distances from the forest edge in three Midwestern USA landscapes with varying amounts of forest fragmentation
(core forest area ranged from 5 to 70%). We focused on breeding cowbirds’ use of forest because of the risk of nest parasitism
to forest-dwelling hosts and to identify factors affecting breeding cowbird habitat selection. We compared distances of cowbird
locations in the forest from the forest edge (“edge distances”) to distances of random forest locations in the entire landscape
or within individual cowbird home ranges. We analyzed 1322 locations of 84 cowbirds across three landscapes. We found support
for the landscape context hypothesis that breeding cowbird preference for forest edge varied with landscape context. Ninety
percent of cowbird locations were within 150–350 m of forest edge, despite the overall availability of forest at greater distances
from edge (as far as 500–1450 m) both within cowbird home ranges and the entire forested landscape. Cowbird preference for
edge varied by landscape context largely due to differences in the availability of forest edge. In a highly fragmented forest
cowbirds utilized the entire forest and likely viewed it as “all edge.” In less fragmented forests, cowbirds preferred edge.
We consider how variation in cowbird edge preference might relate to patterns in host abundance, host diversity, and host
quality because cowbird movements indicate they are capable of using forest farther from edges. 相似文献
16.
Scale questions are particularly important for organisms which range over large areas, as pelagic seabirds do. The investigations
of scale are of practical importance for describing patch size of predator and prey, determining the appropriate scale of
study and correcting survey transects. We conducted this study in order to explore a substantially wider diversity of spatial
scales than has previously been attempted in the pelagic bird literature. As an example of large monitoring datasets dealing
with seabirds, we use the PIROP (Programme intégré pour le recherche des oiseaux pélagiques) data set to investigate relevant
large scale issues for these species in the Northwestern Atlantic. We analyzed autocorrelation within selected winter and
summer transects, and for 1 degree analysis units (‘bins’) for data collected June–August 1966–1992. We also investigated
effects of the analysis unit on counting results and on the links between seabirds and their environment (depth, sea surface
salinity and temperature). We selected scales of 1, 2, 5 and 10 degrees analysis units; an ecological mapping scale (‘Banks’
not deeper than 200 m) and a political scale (management convention zones of the North Atlantic Fisheries Organization, NAFO)
were also included. Using ‘binning’ of various scales, our results show that the Coefficient of Variation for seabird abundances
varies among aggregation scales, and that seabird associations with their environment can show scale effects. Autocorrelation
of analysis units indicated some distinct larger scale patch sizes for particular species during the breeding season. 相似文献
17.
Global biodiversity scenarios and landscape ecology 总被引:1,自引:0,他引:1
Graeme S. Cumming 《Landscape Ecology》2007,22(5):671-685
The composition of ecological communities is both cause and consequence of landscape pattern. Predicting biodiversity change
involves understanding not only ecology and evolution, but also complex changes in human societies and economies. Scenarios
offer a less rigid approach to thinking about biodiversity change in a policy and management context. They shift the focus
of research and management from making singular predictions and developing single ‘best’ strategies to exploring uncertainties
and assessing the outcomes of alternative policies. The four Millennium Ecosystem Assessment (MA) biodiversity scenarios illustrate
current approaches to biodiversity estimation in global scenarios. The MA biodiversity scenarios are built around the species–area
relationship and the magnitudes of a few area-dependent processes such as nitrogen deposition and climate change. Some of
the most obvious landscape-related omissions from the MA scenarios are pattern-process feedbacks, scale dependencies, and
the role of landscape configuration. While the MA has set a new standard for biodiversity scenarios, future exercises would
benefit from a more multi-scale and more mechanistic framework. I use examples from research on the landscape ecology and
biogeography of African ticks to illustrate how a hypothesis-based approach can be used to analyse the multi-scale, multi-level
drivers of change in patterns of species occurrences. Two of the most important challenges for the future development of both
landscape ecology and biodiversity scenarios are to become more mechanistic (less pattern-based) and more general (applicable
across different landscapes). 相似文献
18.
Although the role of habitat fragmentation in species declines is well recognised, the effect of habitat quality on species
distributions is often studied using presence–absence models that ignore metapopulation dynamics. We compared three approaches
to model the presence–absence of North Island robins in 400 sites among 74 fragments of native forest in a 15,000-ha agricultural
landscape in New Zealand. The first approach only considered local habitat characteristics, the second approach only considered
metapopulation factors (patch size and isolation), and the third approach combined these two types of factors. The distribution
of North Island robins was best predicted by patch isolation, as their probability of occurrence was negatively correlated
with isolation from neighbouring patches and from the closest major forests, which probably acted as a source of immigrants.
The inclusion of habitat factors gave only a slight increase in predictive power and indicated that robins were more likely
to occur in areas with tall canopy, tall understory and low density of young trees. We modelled the effect of isolation using
an index of functional patch connectivity based on dispersal behaviour of radio-tracked juveniles, and this functional index
greatly improved the models in comparison to classical indices relying on Euclidean distances. This study highlights the need
to incorporate functional indices of isolation in presence–absence models in fragmented landscapes, as species occurrence
can otherwise be a misleading predictor of habitat quality and lead to wrong interpretations and management recommendations. 相似文献
19.
Forest cover reduction may affect movements of forest animals, but resistance to animal movements in and out of forests remains
unknown despite its importance for modelling. We tested whether ovenbird (Seiurus aurocapilla), a forest-interior songbird, responds similarly to the amount of forest cover while moving locally (~2 km) and over entire
landscapes (~25 km). We compared spatially-explicit simulations to field data to address the issue of resistance to movement
in open areas. We caught, banded and translocated 143 territorial males 0.8–27 km away from their territory early in the breeding
season. Seventy-eight percent and 50% of translocated males returned (homed) within 10 days following “local” and “landscape”
translocations respectively. Independent of translocation distance, homing times increased with decreasing forest in the landscape.
With a Geographic Information System (GIS), we simulated “least-cost” paths that homing ovenbirds would ideally take, when
resistance to movement in open areas ranged 1–1000 times the resistance to movement in forest. The length, the cumulative
cost, and variability of simulated least-cost movement paths increased with increasing resistance in open areas. With landscape
translocations, least-cost path length explained homing time better than Euclidean distance, and based on an information-theoretic
approach, resistance to movement was estimated to be 27 times greater in open areas than in forests (95% confidence interval:
16–45). However, least-cost path length did not perform better than Euclidean distance with local translocations, and the
cumulative cost of least-cost paths was not associated to homing time in either translocation scale. We conclude that resistance
to animal movements in open areas can be addressed by a combination of GIS modelling and translocation experiments, and is
between one and two orders of magnitude greater than resistance to movements in forests, in the case of ovenbirds. 相似文献
20.
Ecological processes such as plant–animal interactions have a critical role in shaping the structure and function of ecosystems,
but little is known of how such processes are modified by changes in landscape structure. We investigated the effect of landscape
change on mistletoe parasitism in fragmented agricultural environments by surveying mistletoes on eucalypt host trees in 24
landscapes, each 100 km2 in size, in south-eastern Australia. Landscapes were selected to represent a gradient in extent (from 60% to 2% cover) and
spatial pattern of remnant wooded vegetation. Mistletoes were surveyed at 15 sites in each landscape, stratified to sample
five types of wooded elements in proportion to their relative cover. The incidence per landscape of box mistletoe (Amyema miquelii), the most common species, was best explained by the extent of wooded cover (non-linear relationship) and mean annual rainfall.
Higher incidence occurred in landscapes with intermediate levels of cover (15–30%) and higher rainfall (>500 mm). Importantly,
a marked non-linear decline in the incidence of A. miquelii in low-cover landscapes implies a disproportionate loss of this species in remaining wooded vegetation, greater than that
attributable to decreasing forest cover. The most likely mechanism is the effect of landscape change on the mistletoebird
(Dicaeum hirundinaceum), the primary seed-dispersal vector for A. miquelii. Our results are consistent with observations that habitat fragmentation initially enhances mistletoe occurrence in agricultural
environments; but in this region, when wooded vegetation fell below a threshold of ~15% landscape cover, the incidence of
A. miquelii declined precipitously. Conservation management will benefit from greater understanding of the components of landscape structure
that most influence ecological processes, such as mistletoe parasitism and other plant–animal mutualisms, and the critical
stages in such relationships. This will facilitate action before critical thresholds are crossed and cascading effects extend
to other aspects of ecosystem function. 相似文献