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1.
Vegetation patterns at the landscape scale are shaped by myriad processes and historical events, and understanding the relative importance of these processes aids in predicting current and future plant distributions. To quantify the influence of different environmental and anthropogenic patterns on observed vegetation patterns, we used simultaneous autoregressive modeling to analyze data collected by the Carnegie Airborne Observatory over Santa Cruz Island (SCI; California, USA). SCI is a large continental island, and its limited suite of species and well documented land use history allowed us to consider many potential determinants of vegetation patterns, such as topography, substrate, and historical grazing intensity. As a metric of vegetation heterogeneity, we used the normalized difference vegetation index (NDVI) stratified into three vegetation height classes using LiDAR (short, medium, and tall). In the SAR models topography and substrate type were important controls, together explaining 8–15 % of the total variation in NDVI, but historical grazing and spatial autocorrelation were also key components of the models, together explaining 17–21 % of the variation in NDVI. Optimal spatial autocorrelation distances in the short and medium height vegetation models (600–700 m) were similar to the home range sizes of two crucial seed dispersers on the island– the island fox (Urocyon littoralis santacruzae) and the island scrub-jay (Aphelocoma insularis)—suggesting that these animals may be important drivers of the island’s vegetation patterns. This study highlights the importance of dynamic processes like dispersal limitation and disturbance history in determining present-day vegetation patterns. 相似文献
2.
Grazing by large herbivores is a major determinant of vegetation dynamics in many semi-natural ecosystems, including ghe replacement of heather moorland by rough grassland in the British uplands. Herbivore foraging is influenced by vegetation patterns and, in turn, their grazing drives vegetation dynamics. Although vegetation impacts are local, spatially heterogeneous local impacts can have different conseqences as would the same impact distributed uniformly. We constructed a simulation model of the spatial effects of grazing by sheep on the vegetation dynamics of heather moorland, a vegetation community of international conservation importance in the UK. The model comprised three sub-models to predict (1) annual average heather utilisation, (2) spatial variation in heather utilisation (higher near the edge of grass patches) and (3) competition between heather and grass. Here we compare the predicted heather utilisation and vegetation dynamics of the spatial model, relative to those of a non-spatial model. The spatial model resulted in a reduced loss of heather cover for a given sheep stocking rate. The model demonstrtaes how spatial interactions between large herbivores and their forage drive vegetation dynamics, leading to changes in community structure and composition. Indeed, omitting spatial effects in grazing models may lead to inaccurate predictions. We have shown that ecosystem modelling, based around an iterative dialogue between developers and experienced researchers, has the potential to make a substantial contribution towards the conservation and management of vulnerable landscapes. Combining modelling with experimental studies will facilitate progress towards understanding long-term vegetation/herbivore dynamics. 相似文献
3.
Grazing by large herbivores is a major determinant of vegetation dynamics in many semi-natural ecosystems, including the replacement of heather moorland by rough grassland in the British uplands. Herbivore foraging is influenced by vegetation patterns and, in turn, their grazing drives vegetation dynamics. Although vegetation impacts are local, spatially heterogeneous local impacts can have different consequences as would the same impacts distributed uniformly. We constructed a simulation model of the spatial effects of grazing by sheep on the vegetation dynamics of heather moorland, a vegetation community of international conservation importance in the UK. The model comprised three sub-models to predict (1) annual average heather utilisation, (2) spatial variation in heather utilisation (higher near the edge of grass patches) and (3) competition between heather and grass. Here we compare the predicted heather utilisation and vegetation dynamics of the spatial model, relative to those of a non-spatial model. The spatial model resulted in a reduced loss of heather cover for a given sheep stocking rate. The model demonstrates how spatial interactions between large herbivores and their forage drive vegetation dynamics, leading to changes in community structure and composition. Indeed, omitting spatial effects in grazing models may lead to inaccurate predictions. We have shown that ecosystem modelling, based around an iterative dialogue between developers and experienced researchers, has the potential to make a substantial contribution towards the conservation and management of vulnerable landscapes. Combining modelling with experimental studies will facilitate progress towards understanding long-term vegetation/herbivore dynamics. 相似文献
4.
Grazing by large herbivores is a major determinant of vegetation dynamics in many semi-natural ecosystems, including the replacement of heather moorland by rough grassland in the British uplands. Herbivore foraging is influenced by vegetation patterns and, in turn, their grazing drives vegetation dynamics. Although vegetation impacts are local, spatially heterogeneous local impacts can have different consequences as would the same impacts distributed uniformly. We constructed a simulation model of the spatial effects of grazing by sheep on the vegetation dynamics of heather moorland, a vegetation community of international conservation importance in the UK. The model comprised three sub-models to predict (1) annual average heather utilisation, (2) spatial variation in heather utilisation (higher near the edge of grass patches) and (3) competition between heather and grass. Here we compare the predicted heather utilisation and vegetation dynamics of the spatial model, relative to those of a non-spatial model. The spatial model resulted in a reduced loss of heather cover for a given sheep stocking rate. The model demonstrates how spatial interactions between large herbivores and their forage drive vegetation dynamics, leading to changes in community structure and composition. Indeed, omitting spatial effects in grazing models may lead to inaccurate predictions. We have shown that ecosystem modelling, based around an iterative dialogue between developers and experienced researchers, has the potential to make a substantial contribution towards the conservation and management of vulnerable landscapes. Combining modelling with experimental studies will facilitate progress towards understanding long-term vegetation/herbivore dynamics. 相似文献
5.
We investigated the seasonal variability of the relationships between land surface temperature (LST) and land use/land cover (LULC) variables, and how the spatial and thematic resolutions of LULC variables affect these relationships. We derived LST data from Landsat-7 Enhanced Thematic Mapper (ETM+) images acquired from four different seasons. We used three LULC datasets: (1) 0.6 m resolution land cover data; (2) 30 m resolution land cover data (NLCD 2001); and (3) 30 m resolution Normalized Difference Vegetation Index data derived from the same ETM+ images (though from different bands) used for LST calculation. We developed ten models to evaluate effects of spatial and thematic resolution of LULC data on the observed relationships between LST and LULC variables for each season. We found that the directions of the effects of LULC variables on predicting LST were consistent across seasons, but the magnitude of effects, varied by season, providing the strongest predictive capacity during summer and the weakest during winter. Percent of imperviousness was the best predictor on LST with relatively consistent explanatory power across seasons, which alone explained approximately 50 % of the total variation in LST in winter, and up to 77.9 % for summer. Vegetation related variables, particularly tree canopy, were good predictor of LST during summer and fall. Vegetation, particularly tree canopy, can significantly reduce LST. The spatial resolution of LULC data appeared not to substantially affect relationships between LST and LULC variables. In contrast, increasing thematic resolution generally enhanced the explanatory power of LULC on LST, but not to a substantial degree. 相似文献
6.
David Christianson Robert W. Klaver Arthur Middleton Matthew Kauffman 《Landscape Ecology》2013,28(3):427-437
Annual variation in winter severity and growing season vegetation dynamics appear to influence the demography of temperate herbivores but parsing winter from spring effects requires independent metrics of environmental conditions specific to each season. We tested for independence in annual variation amongst four common metrics used to describe winter severity and early growing season vegetation dynamics across the entire spatial distribution of elk (Cervus elaphus) in Wyoming from 1989 to 2006. Winter conditions and early growing season dynamics were correlated in a specific way. Winters with snow cover that ended early tended to be followed by early, but slow, rises in the normalized difference vegetation index (NDVI), while long winters with extended periods of snow cover were often followed by late and rapid rises in NDVI. Across the 35 elk ranges, 0.4–86.8 % of the variation in the rate of increase in NDVI’s in spring was explained by the date snow cover disappeared from SNOTEL stations. Because phenoclimatological metrics are correlated across seasons and shifting due to climate change, identifying environmental constraints on herbivore fitness, particularly migratory species, is more difficult than previously recognized. 相似文献
7.
The development of forage production and utilization gradients around livestock watering points 总被引：1，自引：0，他引：1
Large herbivores can impose spatial patterns on otherwise homogeneous vegetation, but how these patterns change through time is poorly understood. Domestic livestock pastures are model systems for studying how foraging behavior influences the development of coupled grazing and vegetation patterns. We sampled forage production and utilization by cattle along distance-from-water gradients to provide a snapshot of grazing and vegetation patterns, and then evaluated the ability of simulation models to qualitatively reproduce these patterns. In the field, forage production increased with distance from water, as expected, but utilization peaked at intermediate distances from water in two of three study areas. Likewise, simulations based on a variety of foraging strategies produced gradients in forage production and, after forage availability near water declined sufficiently, peaks in utilization at intermediate distances. Distance-from-water gradients thus represent cumulative but not necessarily present day gradients in grazing intensity. The model with a foraging strategy based on time minimization produced slightly more realistic patterns in forage abundance than a model based on energy maximization, although results were sensitive to the value of the threshold for rejecting sites of low forage biomass. However, all models produced implausible thresholds in grazing and forage distribution, suggesting that factors besides resource distribution influence herbivore distributions. Moreover, different foraging rules produced similar vegetation gradients, especially on point water source landscapes, illustrating the difficulty of inferring foraging processes from vegetation patterns. 相似文献
8.
A set of structural criteria to differentiate among types of a heterogeneous woodland landscape that are shaped by goat and
cattle grazing was studied in northern Israel. The landscape was described with relation to the “human scale” of the observer,
by mapping the dimensions, basic shapes, and distribution of gaps between individual plants on sites with various grazing
management systems. The shapes of the trees and the bushes were drawn in situ and the ratio between plant height and the width
of the adjacent open space was measured in order to define the various structural profiles of the vegetation. All the structural
criteria clearly and significantly differentiated among grazing systems that created closed (no grazing), half-open (cattle
and modern goat grazing) and open (traditional goat grazing) landscapes. The diversity of plant shapes was highest under the
cattle and modern goat grazing management systems. In the ungrazed treatment, more than 60% of the gaps were defined as ‘inaccessible’
compared with only 10–15% under cattle grazing and modern goat grazing. The diversity of gap proportions was high, but their
absolute number was low. Under traditional heavy goat grazing, there were only wide and open gaps. Under cattle grazing and
modern goat-grazing management systems, a relatively large number of wide and open gaps were found, with small numbers of
narrow and closed gaps. Overall, the various grazing systems were differentiated most clearly according to their transparency,
accessibility, height of Quercus calliprinos, and gap distribution. We conclude that structural criteria provide an efficient and objective methodology for evaluating
the effects of grazing on different components of Mediterranean woodland mosaic landscapes.
Nomenclature follows Feinbrun-Dothan and Danin (1991) 相似文献
9.
Michael C. Wimberly 《Landscape Ecology》2006,21(1):35-46
Although landscape ecology emphasizes the effects of spatial pattern on ecological processes, most neutral models of species–habitat relationships have treated habitat as a static constraint. Do the working hypotheses derived from these models extend to real landscapes where disturbances create a shifting mosaic? A spatial landscape simulator incorporating vegetation dynamics and a metapopulation model was used to compare species in static and dynamic landscapes with identical habitat amounts and spatial patterns. The main drivers of vegetation dynamics were stand-replacing disturbances, followed by gradual change from early-successional to old-growth habitats. Species dynamics were based on a simple occupancy model, with dispersal simulated as a random walk. As the proportion of available habitat (p) decreased from 1.0, species occupancy generally declined more rapidly and reached extinction at higher habitat levels in dynamic than in static landscapes. However, habitat occupancy was sometimes actually higher in dynamic landscapes than in static landscapes with similar habitat amounts and patterns. This effect was most pronounced at intermediate amounts of habitat (p = 0.3?0.6) for mobile species that had high colonization rates, but were unable to cross non-habitat patches. Differences between static and dynamic landscapes were contingent upon the initial metapopulation size and the shapes of disturbances and the resulting habitat patterns. Overall, the results demonstrate that dispersal-limited species exhibit more pronounced critical behavior in dynamic landscapes than is predicted by simple neutral models based on static landscapes. Thus, caution should be exercised in extending generalizations derived from static landscape models to disturbance-driven landscape mosaics. 相似文献
10.
Spatial vegetation patterns as early signs of desertification: a case study of a desert steppe in Inner Mongolia,China 总被引：1，自引：0，他引：1
Proper assessment and early detection of land degradation and desertification is extremely important in arid and semi-arid
ecosystems. Recent research has proposed to use the characteristics of spatial vegetation patterns, such as parameters derived
from power-law modeling of vegetation patches, for detecting the early signs of desertification. However, contradictory results
have been reported regarding the suitability of those proposed indicators. We used an experiment with multiple grazing intensities
as an analog of a desertification gradient and evaluated the performance of two predictors of desertification: percent plant
cover and a transition from a patch-area distribution characterized by a power law to another portrayed by a truncated power
law, in a desert steppe in Inner Mongolia, China. We found that spatial metrics, such as the largest patch index and coefficient
of variation of mean patch area had negative linear relationships with grazing intensity, suggesting that vegetation patches
became more fragmented and homogeneous under higher grazing pressure. Using a binning-based method to analyze our dataset,
we found that the patch-area relationship deviated from a power-law to a truncated power-law model with increasing grazing
pressure, while the truncated power law was a better fit than the power law for all plots when binning was not used. These
results suggest that the selection of methodology is crucial in using power-law models to detect changes in vegetation patterns.
Plant cover was significantly correlated with stocking rate and all spatial metrics evaluated; however, the relationship between
cover and vegetation spatial pattern still deserves a thorough examination, especially in other types of ecosystems, before
using cover as a universal early sign of desertification. Our results highlight a strong connection between the vegetation
spatial pattern and the desertification associated with heavy grazing and suggest that future studies should incorporate information
about vegetation spatial pattern in monitoring desertification processes. 相似文献
11.
Context
Pasture-woodlands are semi-natural landscapes that result from the combined influences of climate, management, and intrinsic vegetation dynamics. These landscapes are sensitive to future changes in land use and climate, but our ability to predict the impact on ecosystem service provisioning is limited due to the disparate scales in time and space that govern their dynamics.Objectives
To develop a process-based model to simulate pasture-woodland landscapes and the provisioning of ecosystem services (i.e., livestock forage, woody biomass and landscape heterogeneity).Methods
We modified a dynamic forest landscape model to simulate pasture-woodland landscapes in Switzerland. This involved including an annual herbaceous layer, selective grazing from cattle, and interactions between grazing and tree recruitment. Results were evaluated within a particular pasture, and then the model was used to simulate regional vegetation patterns and livestock suitability for a ~198,000 ha landscape in the Jura Vaudois region.Results
The proportion of vegetation cover types at the pasture level (i.e., open, semi-open and closed forests) was well represented, but the spatial distribution of trees was only broadly similar. The entire Jura Vaudois region was simulated to be highly suitable for livestock, with only a small proportion being unsuitable due to steep slopes and high tree cover. High and low elevation pastures were equally suitable for livestock, as lower forage production at higher elevations was compensated by reduced tree cover.Conclusions
The modified model is valuable for assessing landscape to regional patterns in vegetation and livestock, and offers a platform to evaluate how climate and management impact ecosystem services.12.
Context
There are few detailed data for short-term (≤?monthly) fluctuations in flowering and nectar availability at relatively large spatial scales. Such information is critical for understanding the governors of variation in flowering and for the management of floral resources assisting the persistence of nectar consumers in landscapes.Objectives
To obtain monthly measurements of patterns of nectar availability in a 314,400 ha region, and to relate these patterns to potential environmental predictors.Methods
Flowering was measured at 83 sites in natural vegetation and in eight domestic gardens in subtropical, eastern Australia. A nectar-availability index was developed was based on nectarivore visitation rates and plant-specific flowering patterns. Spatial–temporal patterns were related to environmental variables using boosted regression trees.Results
The large between-year variation was due mostly to irregular flowering by several eucalypt species. There was a ‘lean season’ in the austral spring (August–September). Coastal vegetation was an important source of nectar for much of the year, including the lean season. Gardens produced prolific nectar throughout the year, peaking in August–October.Conclusions
Nectar availability was most closely associated with primary productivity over the previous 12 months, average annual solar radiation, topographic wetness, and rainfall over the previous 6 months, although some relationships seemed counter-intuitive. There were large differences in nectar availabilities among broad vegetation types (especially rainforests vs. sclerophyllous forests), which partially accounted for the unintuitive results.13.
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
14.
Disturbances such as grazing, invading species, and clear-cutting, often act at small spatial scales, and means for quantifying
their impact on fine scale vegetation patterns are generally lacking. Here we adopt a set of landscape metrics, commonly used
for quantifying coarse scale fragmentation, to quantify fine scale fragmentation, namely the fine scale vegetation structure.
At this scale, patches often consist of individual plants smaller than 1 m2, requiring the grain of the analysis to be much smaller. We used balloon aerial photographs to map fine details of Mediterranean
vegetation (pixel size <0.04 m) in experimental plots subjected to grazing and clear-cutting and in undisturbed plots. Landscape
metrics are sensitive to scale. Therefore, we aggregated the vegetation map into four coarser scales, up to a resolution of
1 m, and analyzed the effect of scale on the metrics and their ability to distinguish between different disturbances. At the
finest scale, six of the seven landscape metrics we evaluated revealed significant differences between treated and undisturbed
plots. Four metrics revealed differences between grazed and control plots, and six metrics revealed differences between cleared
and control plots. The majority of metrics exhibited scaling relations. Aggregation had mixed effects on the differences between
metric values for different disturbances. The control plots were the most sensitive to scale, followed by grazing and clearing.
We conclude that landscape metrics are useful for quantifying the very fine scale impact of disturbance on woody vegetation,
assuming that the analysis is based on sufficiently high spatial resolution data. 相似文献
15.
Moorlands perform a wide variety of roles within modern society. A vital component of these landscapes is the patterning of
vegetation, and management of this requires a thorough understanding of the drivers of vegetation change. Although there has
been a considerable body of research focussed on the processes that are important in patterning contemporary vegetation these
typically lack any significant time-depth. Long-term data, using palaeoecological techniques, offer insights into drivers
of vegetation change that are otherwise unachievable. This paper presents new palaeoecological data from Dartmoor (UK) to
test two hypotheses: (1) that vegetation character of moorland is spatially homogenous through the past 8,000 years; and (2)
that burning has a significant role in the development of open, grass-dominated, vegetation. Four peat cores spanning the
past 8,000 years were subject to pollen and microcharcoal analysis. Thirty-seven radiocarbon age estimates were obtained to
determine age-depth models for the pollen and charcoal stratigraphies. Differences within and between the pollen stratigraphies
have been used as an indirect measure of landscape heterogeneity at a coarse scale. The data reveal periods of time during
which differences in the vegetation (as sensed by pollen) around each site are small, and periods during which differences
between vegetation are large. Periods of time characterised by greater spatial difference, and by inference greater heterogeneity,
correlate with periods characterised by greater human exploitation of the landscape as revealed by archaeological evidence.
Human activities therefore promote greater spatial patterning in the landscape. Fire alone is not an important control on
long-term peatland vegetation development. The results are useful for conservation strategies by demonstrating variability
in spatial diversity of vegetation patterns in the past, and pointing towards opportunities to recreate and maintain diverse
vegetation mosaics. 相似文献
16.
We developed metrics at a landscape scale to evaluate the costs and rewards experienced by large herbivores while foraging
in natural vegetation with patchy anti-herbivore plant structures. We show an application of these metrics to the analysis
of 16,000 records of positions at successive 1 min intervals of free-ranging ewes (Ovis aries) harnessed with Global-Positioning-System (GPS) loggers, in a large paddock of the Patagonian Monte shrublands (Argentina).
Dominant shrubs in the area display numerous anti-herbivore defenses (spiny-resinous leaves, thorny stems, etc.) protecting
them from grazing and herbivore trampling. Preferred grasses and forbs constitute a minor part of aboveground plant biomass
and grow in relatively open areas among or around shrub patches. We mapped the movement speed of ewes onto high-resolution
aerial photographs of the grazed paddocks and estimated costs and rewards along their paths based on algorithms of surface
cost theory. Ewes explored areas of sparse vegetation at low speeds compatible with predominant grazing, and increased their
speed when crossing denser shrubby patches. The cost algorithm was applied to evaluate daily searching costs as well as grazing
rewards in relation to the length of daily searching paths. The observed path lengths and search speeds were consistent with
those that compensate costs and rewards of the grazing activities as estimated by the surface cost analysis. We conclude that
the technique presented here constitutes a valuable tool to quantify the effect of landscape characteristics on behavioral
traits of grazing animals in similar environments. 相似文献
17.
Hierarchical relationships between landscape structure and temperature in a managed forest landscape 总被引：10，自引：1，他引：9
Saunders Sari C. Chen Jiquan Crow Thomas R. Brosofske Kimberley D. 《Landscape Ecology》1998,13(6):381-395
Management may influence abiotic environments differently across time and spatial scale, greatly influencing perceptions of fragmentation of the landscape. It is vital to consider a priori the spatial scales that are most relevant to an investigation, and to reflect on the influence that scale may have on conclusions. While the importance of scale in understanding ecological patterns and processes has been widely recognized, few researchers have investigated how the relationships between pattern and process change across spatial and temporal scales. We used wavelet analysis to examine the multiscale structure of surface and soil temperature, measured every 5 m across a 3820 m transect within a national forest in northern Wisconsin. Temperature functioned as an indicator – or end product – of processes associated with energy budget dynamics, such as radiative inputs, evapotranspiration and convective losses across the landscape. We hoped to determine whether functional relationships between landscape structure and temperature could be generalized, by examining patterns and relationships at multiple spatial scales and time periods during the day. The pattern of temperature varied between surface and soil temperature and among daily time periods. Wavelet variances indicated that no single scale dominated the pattern in temperature at any time, though values were highest at finest scales and at midday. Using general linear models, we explained 38% to 60% of the variation in temperature along the transect. Broad categorical variables describing the vegetation patch in which a point was located and the closest vegetation patch of a different type (landscape context) were important in models of both surface and soil temperature across time periods. Variables associated with slope and microtopography were more commonly incorporated into models explaining variation in soil temperature, whereas variables associated with vegetation or ground cover explained more variation in surface temperature. We examined correlations between wavelet transforms of temperature and vegetation (i.e., structural) pattern to determine whether these associations occurred at predictable scales or were consistent across time. Correlations between transforms characteristically had two peaks; one at finer scales of 100 to 150 m and one at broader scales of >300 m. These scales differed among times of day and between surface and soil temperatures. Our results indicate that temperature structure is distinct from vegetation structure and is spatially and temporally dynamic. There did not appear to be any single scale at which it was more relevant to study temperature or this pattern-process relationship, although the strongest relationships between vegetation structure and temperature occurred within a predictable range of scales. Forest managers and conservation biologists must recognize the dynamic relationship between temperature and structure across landscapes and incorporate the landscape elements created by temperature-structure interactions into management decisions. 相似文献
18.
Interactions among fire legacies, grazing and topography predict shrub encroachment in post-agricultural páramo 总被引：1，自引：1，他引：0
Woody encroachment in grasslands is a global phenomenon driven by complex interactions between climate, grazing and fire management. Alpine shrub encroachment is of particular concern for biological conservation because high-elevation grasslands harbor high levels of biodiversity and species endemism. Páramo grasslands of the high Andes are exceptionally high in floral diversity, but traditional agricultural practices have resulted in widespread livestock grazing and anthropogenic burning. Fire suppression has frequently been identified a driver of woody expansion in other grasslands, and conservation initiatives that aim to decrease burning and grazing in páramos may inadvertently lead to shrub encroachment. We tested whether interactions among fire and grazing legacies, topography and edaphic conditions predicted the patchy distribution of encroaching shrubs in an Ecuadorian páramo 10 years after release from burning and grazing. Interviews with land-users identified proximity to roads, footpaths and riparian areas as proxies for fire frequency and grazing pressure. A recursive partitioning model of shrub cover revealed that woody abundance was generally lower at lower elevations, especially near the access road (where fire frequency and grazing pressure were high). Within the low-elevation areas, shrub cover was highest near streams (where grazing pressure was high). These results suggest that (1) the effects of fire and grazing legacies depend on the spatial patterns of grazing, and (2) legacy effects interact with topography to help explain patchy shrub encroachment. 相似文献
19.
E. J. Raynor C. D. Griffith D. Twidwell W. H. Schacht C. L. Wonkka C. P. Roberts C. L. Bielski D. M. Debinski J. R. Miller 《Landscape Ecology》2018,33(12):2103-2119
Context
Plant invasions of native ecosystems are one of the main causes of declines in biodiversity via system-simplification. Restoring native biodiversity can be particularly challenging in landscapes where invasive species have become dominant and where a new set of feedbacks reinforce an invaded state and preclude restoration actions. We lack an understanding of the response of invaded systems to landscape-level manipulations to restore pattern and process relationships and how to identify these relationships when they do not appear at the expected scale.Objectives
To better understand how fire and grazing influence landscape-level heterogeneity in invaded landscapes, we assess the scale at which grazing pressure and seasonality mediate the success of re-introducing a historical disturbance regime, grazing driven by fire (termed pyric herbivory), to an invasive plant-dominated landscape.Methods
We manipulated grazing timing and intensity in exotic grass-dominated grasslands managed for landscape heterogeneity with spring fire and grazing. In pastures under patch-burn grazing management, we evaluated the spatial and temporal variability of plant functional groups and vegetation structure among and within patches managed with separate grazing systems: season-long stocking and intensive early stocking.Results
Warm- and cool-season grasses exhibited greater among-patch variability in invasive-plant dominated grassland under intensive early grazing than traditional season-long grazing, but landscape-level heterogeneity, as measured through vegetation structure was minimal and invariable under both levels of grazing pressure, which contrasts findings in native-dominated systems. Moreover, within-patch heterogeneity for these functional groups was detected; contrasting the prediction that among-patch heterogeneity, in mesic grasslands, manifests from within-patch homogeneity.Conclusions
In invaded grasslands, manipulation of grazing pressure as a process that drives heterogeneous vegetation patterns influences native and non-native grass heterogeneity, but not heterogeneity of vegetation structure, within and among patches managed with fire. Fire and grazing-moderated heterogeneity patterns observed in native grass-dominated grasslands likely differ from invasive grass-dominated grasslands with implications for using pyric herbivory in invaded systems.20.
Matteo Garbarino Emanuele Lingua Peter J. Weisberg Alessandra Bottero Fabio Meloni Renzo Motta 《Landscape Ecology》2013,28(5):805-817
European larch (Larix decidua Mill.) forests in the Alps are cultural landscapes that have been shaped by humans for centuries through traditional management. Biological and historical data sources were employed, and a multi-scale approach was adopted to capture the influence of factors affecting the structure of these forests. Landscape and stand scale dynamics were analyzed in four watersheds (c. 13,000 ha) of the western and central Italian Alps that have experienced different land-use intensities. Observed landscape changes were generalized using path analyses developed from a common conceptual model. Stand structure and a range of environmental variables were sampled in 203 circular plots, and land use and anthropogenic variables were derived from thematic maps and aerial photographs. We used multivariate statistical analyses (ordination and SEM models) to relate forest structure, anthropogenic influences, land uses, and topography. The most commonly observed land cover transition was an expansion of forests at the expense of open areas. All studied watersheds were dominated by larch forests, but their structure and spatial pattern differed greatly. Anthropogenic variables were less important at Ventina, the least accessible site, but emerged as fundamental to explain stand structure in the other study sites. Complexity of topography and proximity to roads had influenced past human activities mainly in the most accessible sites. Regeneration density was greatest at lower elevations and closer to human settlements. Quantification of the role played by forest harvesting and cattle grazing in past centuries is critical for understanding how global change factors may influence future dynamics of mountain forests in the European Alps and similar cultural landscapes worldwide. 相似文献