Modeling the effects of forest harvesting on landscape structure and the spatial distribution of cowbird brood parasitism

Timber harvesting affects both composition and structure of the landscape and has important consequences for organisms using forest habitats. A timber harvest allocation model was constructed that allows the input of specific rules to allocate forest stands for clearcutting to generate landscape patterns reflecting the look and feel of managed landscapes. Various harvest strategies were simulated on four 237 km² study areas in Indiana, USA. For each study area, the model was applied to simulate 80 years of management activity. The resulting landscape spatial patterns were quantified using a suite of landscape pattern metrics and plotted as a function of mean harvest size and total area of forest harvested per decade to produce response surfaces. When the mean clearcut size was 1 ha, the area of forest interior remaining on the landscape was dramatically reduced and the amount of forest edge on the landscape increased dramatically. The potential consequences of the patterns produced by the model were assessed for a generalized neotropical migrant forest bird using a GIS model that generates maps showing the spatial distribution of the relative vulnerability of forest birds to brood parasitism by brown-headed cowbirds. The model incorporates the location and relative quality of cowbird feeding sites, and the relation between parasitism rates and distance of forest from edge. The response surface relating mean harvest size and total area harvested to the mean value of vulnerability to cowbird brood parasitism had a shape similar to the response surfaces showing forest edge. The results of our study suggest that it is more difficult to maintain large contiguous blocks of undisturbed forest interior when harvests are small and dispersed, especially when producing high timber volumes is a management goal. The application of the cowbird model to landscapes managed under different strategies could help managers in deciding where harvest activity will produce the least negative impact on breeding forest birds.     

Modeling and field-testing of Ovenbird (<Emphasis Type="Italic">Seiurus aurocapillus</Emphasis>) responses to boreal forest dissection by energy sector development at multiple spatial scales

Although the area disturbed by linear features in forested systems is small relative to many other human disturbances, linear features create significantly more amounts of edge per unit area. In the boreal plains of Alberta, Canada, energy sector exploration has resulted in extensive dissection of the landscape through 8 m wide seismic lines. A spatially explicit model was developed to test how bird abundance might change in response to increasing seismic line density if individuals use seismic lines as territory boundaries or actively avoid these edges. Assuming birds had fixed territory shape and size, increasing seismic line density from 0 to 8 km/km² resulted in a 38% decline and an 82% decline in bird abundance when individuals used lines as territory boundaries or avoided edges by 50 m, respectively. We tested the assumptions of our model using the Ovenbird (Seiurus aurocapillus). Based on radio-telemetry (n = 12), all Ovenbirds crossed seismic lines at some point during the breeding season. However, male Ovenbirds showed a distinct use of one side of the seismic line, suggesting lines acted as territory boundaries. In 12.25 ha plots (n = 24) spot-mapping detected no change in Ovenbird density as linear feature density increased from 0 to 8.6 km/km². In 4 km² landscapes (n = 62) sampled using a grid of nine point-counts, we also detected no changes in Ovenbird numbers across the same range of seismic line densities. Ovenbirds declined with seismic line density at the level of the individual point-count station (12 ha scale), but only when a threshold seismic line density of 8.5 km/km² was reached. Above the threshold, Ovenbirds declined 19% for each 1 km/km² increase in seismic line density. While relatively few places in Alberta’s boreal forest have local seismic line densities of 8.5 km/km², forest dissection could increasingly become an issue if current energy exploration practices continue.     

Landscape-mediated edge effect in temperate deciduous forest: implications for oak regeneration

Context

Although the edge effect is known to be an important factor influencing the recruitment of trees in temperate forests, little is known of its synergistic relationships with landscape and fragment attributes.

Objectives

We investigated how the edge effect on regeneration of oaks (Quercus spp.) varies with respect to fragment geometry, connectivity and landscape composition.

Methods

We recorded oak sapling density along edge-interior gradients in 29 forest fragments at the periphery of Mexico City and examined the data with Generalized Additive Models.

Results

A nonlinear and landscape-mediated edge effect was supported by data, including the interactions of the edge distance with patch connectivity, shape and size. Saplings were more abundant at a distance of ca. 50 m from the edge of small, large and connected patches, but large patches also exhibited reduced recruitment towards the interior of the patch. Conversely, sapling density in simple-shaped or connected patches was lower at the edge, exhibiting linear and concave-down increase trends towards the interior of patches, respectively.

Conclusions

Boundary conditions could be interacting with interior forest conditions, making regeneration more frequent at 50 m from the edge. Shady and cooler sites in large patches may be inhibiting oak regeneration. The activity of acorn-dispersing animals and oak predators may increase in unconnected patches, thus increasing the likelihood of edge effects. These results provide insights into the restoration of temperate forest patches in heterogeneous fragmented landscapes.

     

Long-term afforestation efforts increase bird species diversity in Beijing,China

Bird communities are important components of biodiversity and provide terrestrial ecosystems with multiple functions. The impact of long-term afforestation and rapid urbanization on bird species diversity (BSD) is of interest and has attracted increasing attention from biologists, government officials and the public. This study focused on patterns of BSD and changes in forest coverage in an Asian mega-city (Beijing). Forest coverage in Beijing increased moderately from 1.3% (in 1949) to 21.26% (in 2003), and rapidly from 21.26% (in 2003) to 41% (in 2014). Natural types of land cover (i.e., woodland, grassland and water) increased from 55.25% (9070.29 km²) in 1985–63.41% (10411.16 km²) in 2013, while anthropogenic types (i.e., cultivated land, construction land and unutilized land) decreased from 44.75% to 36.59% based on remote sensing data. Three sets of BSD records were obtained from the published literature, revealing a species diversity of 344 in 1987, 375 in 1994, and 430 in 2014. Approximately 15% of bird species were endemic and 80% were migratory. From 1987–2014, Beijing gained 81 bird species (37 species disappeared while 118 species appeared), which could be a result of the progressive increase in forest coverage. The changes in BSD may be affected by long-term afforestation efforts and rapid urbanization, along with meteorological factors. This study sheds some light on the effects of afforestation and urbanization on biodiversity.     

Statistical models of landscape pattern metrics,with applications to regional scale dynamic forest simulations

Forest managers in Canada need to model landscape pattern or spatial configurationoverlarge (100,000 km²) regions. This presents a scalingproblem, as landscape configuration is measured at a high spatial resolution,but a low spatial resolution is indicated for regional simulation. We present astatistical solution to this scaling problem by showing how a wide range oflandscape pattern metrics can be modelled from low resolution data. Our studyarea comprises about 75,000 km² of boreal mixedwoodforest in northeast Alberta, Canada. Within this area we gridded a sample of 84digital forest cover maps, each about 9500 ha in size, to aresolution of 1 ha and used FRAGSTATS to compute a suite oflandscape pattern metrics for each map. We then used multivariate dimensionreduction techniques and canonical correlation analysis to model therelationship between landscape pattern metrics and simpler stand table metricsthat are easily obtained from non-spatial forest inventories. These analyseswere performed on four habitat types common in boreal mixedwood forests: youngdeciduous, old deciduous, white spruce, and mixedwood types. Using only threelandscape variables obtained directly from stand attribute tables (totalhabitatarea, and the mean and standard deviation of habitat patch size), ourstatistical models explained more than 73% of the joint variation in fivelandscape pattern metrics (representing patch shape, forest interior habitat,and patch isolation). By PCA, these five indices captured much of the totalvariability in the rich set of landscape pattern metrics that FRAGSTATS cangenerate. The predictor variables and strengths of association were highlyconsistent across habitat classes. We illustrate the potential use of suchstatistical relationships by simulating the regional, cumulative effects ofwildfire and forest management on the spatial arrangement of forest patches,using non-spatial stand attribute tables.This revised version was published online in May 2005 with corrections to the Cover Date.     

Wildfires and landscape patterns in the Eastern Iberian Peninsula

The relations between disturbance regime and landscape patterns have been developed from a theoretical perspective, but few studies have tested these relations when forces promoting opposing heterogeneity patterns are simultaneously operating on a landscape. This work provides quantitative evidence of these relations in areas dominated by human activity, showing that landscape heterogeneity decreases disturbance spread. In turn, disturbance introduces a source of landscape heterogeneity, but it is not enough to counterbalance the homogeneity trend due to agricultural abandonment. Land cover changes and wildfire occurrence (fires larger than 0.3 km²) have been monitored in the Tivissa municipality (208.4 km²) (Catalonia, NE Spain) from 1956 to 1993. Land cover maps were obtained from 1956, 1978 and 1993 and they were overlaid with fire occurrence maps obtained for the 1975–1995 period from 60 m resolution remote sensing images, which allow the identification of burned areas by sudden drops in Normalized Difference Vegetation Index (NDVI). Changes in landscape patterns in relation to fire regime have been analyzed considering several parameters: patch density, mean patch size, mean distance to the nearest neighbour of the same category, edge density, and the Shannon diversity index. In the 1956–1993 period there is a trend to increasing landscape homogenization due to the expansion of shrub­lands linked to a decrease in forest surface, and to the abandonment of agricultural lands. This trend, however, is not constant along all the period. Fires are more likely to occur in woody, homogenous areas, increasing landscape heterogeneity, as observed in the 1978–1993 period. This increase in heterogeneity does not counterbalance the general trend to landscape homogenization as a consequence of agricultural abandonment and the coalescence of natural vegetation patches.This revised version was published online in May 2005 with corrections to the Cover Date.     

Modeling vegetation pattern using digital terrain data

Using a geographic information system (GIS), digital maps of environmental variables including geology, topography and calculated clear-sky solar radiation, were weighted and overlaid to predict the distribution of coast live oak (Ouercus agrifolia) forest in a 72 km² region near Lompoc, California. The predicted distribution of oak forest was overlaid on a map of actual oak forest distribution produced from remotely sensed data, and residuals were analyzed to distinguish prediction errors due to alteration of the vegetation cover from those due to defects of the statistical predictive model and due to cartographic errors. Vegetation pattern in the study area was associated most strongly with geologic substrate. Vegetation pattern was also significantly associated with slope, exposure and calculated monthlysolar radiation. The proportion of observed oak forest occurring on predicted oak forest sites was 40% overall, but varied substantially between substrates and also depended strongly on forest patch size, with a much higher rate of success for larger forest patches. Only 21% of predicted oak forest sites supported oak forest, and proportions of observed vegetation on predicted oak forest sites varied significantly between substrates. The non-random patterns of disagreement between maps of predicted and observed forest indicated additional variables that could be included to improve the predictive model, as well as the possible magnitude of forest loss due to disturbances in different parts of the landscape.     

Studying the spatial evolutionary behavior of urban forest patches from the perspective of pattern-process relationships

Urban forest dynamics can influence the provision of ecosystem services provision. Considerable research has been conducted to understand how these dynamics respond to urbanization, from individual patches to entire landscapes. However, most of these are cross-sectional studies based on landscape metrics, and research using a process-based perspective in this context is scarce. In this study, we present a “pattern-process” analytical framework to quantify the evolutionary behavior of urban forest patches. We combine this framework with land cover classification data based on high-resolution remote sensing images (< 1 m) from 2002, 2013, and 2019 to detect the dynamic characteristics of four processes of forest patches in Beijing urban areas. These dynamic characteristics include: size distribution, aggregation and fragmentation, transfer, and self-stabilization. The results showed that 1) the average size of the patches in the study area is increasing, and patches larger than 50 m² have a more positive influence on the process of patch structure evolution, 2) patch fragmentation shifts with the direction of urban sprawl, 3) transfer between urban forest and bare land is increasing, and 4) urban forest network construction positively enhances the stability of patches. This framework can provide a useful basis for understanding the spatial and temporal evolution of urban forest landscapes during urban development and contribute to the sustainable management of urban forests.     

Influence of high-resolution data on the assessment of forest fragmentation

Context

Remote sensing has been a foundation of landscape ecology. The spatial resolution (pixel size) of remotely sensed land cover products has improved since the introduction of landscape ecology in the United States. Because patterns depend on spatial resolution, emerging improvements in the spatial resolution of land cover may lead to new insights about the scaling of landscape patterns.

Objective

We compared forest fragmentation measures derived from very high resolution (1 m²) data with the same measures derived from the commonly used (30 m?×??30 m; 900 m²) Landsat-based data.

Methods

We applied area-density scaling to binary (forest; non-forest) maps for both sources to derive source-specific estimates of dominant (density ≥?60%), interior (≥?90%), and intact (100%) forest.

Results

Switching from low- to high-resolution data produced statistical and geographic shifts in forest spatial patterns. Forest and non-forest features that were “invisible” at low resolution but identifiable at high resolution resulted in higher estimates of dominant and interior forest but lower estimates of intact forest from the high-resolution source. Overall, the high-resolution data detected more forest that was more contagiously distributed even at larger spatial scales.

Conclusion

We anticipate that improvements in the spatial resolution of remotely sensed land cover products will advance landscape ecology through re-interpretations of patterns and scaling, by fostering new landscape pattern measurements, and by testing new spatial pattern-ecological process hypotheses.

     

Regional forest cover estimation via remote sensing: the calibration center concept

A method for combining Landsat Thematic Mapper (TM), Advanced Very High Resolution Radiometer (AVHRR) imagery, and other biogeographic data to estimate forest cover over large regions is applied and evaluated at two locations. In this method, TM data are used to classify a small area (calibration center) into forest/nonforest; the resulting forest cover map is then used in combination with AVHRR spectral data from the same area to develop an empirical relationship between percent forest cover and AVHRR pixel spectral signature; the resultant regression relationship between AVHRR band values and percent forest cover is then used to extrapolate forest cover for several hundred kilometers beyond the original TM calibration center. In the present study, the method was tested over two large regions in the eastern United States: areas centered on Illinois and on the Smoky Mountains on the North Carolina-Tennessee border. Estimates of percent forest cover for counties, after aggregating AVHRR pixel estimates within each county, were compared with independent ground-based estimates. County estimates were aggregated to derive estimates for states and regions. For the Illinois region, the overall correlation between county cover estimates was 0.89. Even better correlations (up to r = 0.96) resulted for the counties close to one another, in the same ecoregion, or in the same major land resource region as the calibration center. For the Smokies region, the correlations were significant but lower due to large influences of pine forests (suppressed spectral reflectance) in counties outside the hardwood-dominated calibration center. The method carries potential for estimating forest cover across the globe. It has special advantages in allowing the assessment of forest cover in highly fragmented landscapes, where individual AVHRR pixels (1 km²) are forested to varying degrees.Managed by Martin Marietta Energy Systems, Inc., under contract PE-AC05-840R21400 with the U.S. Department of Energy     

Landscape Fragmentation and Ice Storm Damage in Eastern Ontario Forests

With return times between 20 and 100 years, ice storms are a primary disturbance type for temperate forests of eastern North America. Many studies have been conducted at the forest patch and plot scales to examine relations between damage and variables describing site, composition and structure. This paper presents results from a landscape scale study of fragmentation relations with damage in eastern Ontario forests. Data previously collected for two independent and spatially non-overlapping patch level damage studies were used. A Generalized Linear Model (GLM) was used to analyse relations between damage and fragmentation metrics representing patch isolation, edge density, and the relative size and distribution of patches in the landscape. The metrics were applied using spatial extents of 1 × 1 km and 4 × 4 km, following analyses of the variability of numbers of patches and of the lacunarity of forest patterns over a range of extents. The results showed that patch isolation, as measured by the mean Euclidean distance between patches (ENN) was significantly related to damage.     

Estimating regional forest productivity and water yield using an ecosystem model linked to a GIS

We used the PnET-II model of forest carbon and water balances to estimate regional forest productivity and runoff for the northeastern United States. The model was run at 30 arc sec resolution (approximately 1 km) in conjunction with a Geographic Information System that contained monthly climate data and a satellite-derived land cover map. Predicted net primary production (NPP) ranged from 700 to 1450 g m² yr¹ with a regional mean of 1084 g m² yr¹. Validation at a number of locations within the region showed close agreement between predicted and observed values. Disagreement at two sites was proportional to differences between measured foliar N concentrations and values used in the model. Predicted runoff ranged from 24 to 150 cm yr¹with a regional mean of 63 cm yr¹. Predictions agreed well with observed values from U.S. Geologic Survey watersheds across the region although there was a slight bias towards overprediction at high elevations and underprediction at lower elevations.Spatial patterns in NPP followed patterns of precipitation and growing degree days, depending on the degree of predicted water versus energy limitation within each forest type. Randomized sensitivity analyses indicated that NPP within hardwood and pine forests was limited by variables controlling water availability (precipitation and soil water holding capacity) to a greater extent than foliar nitrogen, suggesting greater limitations by water than nitrogen for these forest types. In contrast, spruce-fir NPP was not sensitive to water availability and was highly sensitivity to foliar N, indicating greater limitation by available nitrogen. Although more work is needed to fully understand the relative importance of water versus nitrogen limitation in northeastern forests, these results suggests that spatial patterns of NPP for hardwoods and pines can be largely captured using currently available data sets, while substantial uncertainties exist for spruce-fir.     

Thresholds in landscape structure for three common deforestation patterns in the Brazilian Amazon

Although abrupt changes (i.e. thresholds) have been precisely defined in simulated landscapes, such changes in the structure of real landscapes are not well understood. We tested for threshold occurrence in three common deforestation patterns in the Brazilian Amazon: small properties regularly distributed along roads (fishbone), irregularly distributed small properties (independent settlements), and large properties. We analyzed differences between real deforestation patterns, and tested the capacity of simulated landscape with different aggregation degrees to predict threshold occurrence. Three 8×8 km sites (replicates) with more than 90% of forest in 1984 and less than 30% in 1998 were selected/simulated for each deforestation pattern. Thresholds were observed for fishbone and large property patterns, especially when considering the connectivity index, although threshold incidences were more frequently observed in simulated landscapes. The capacity of simulated landscapes to predict the exact threshold point in real landscapes was limited, even when considering highly aggregate simulations. However, the general trend in landscape structural changes was similar in real and simulated landscapes. Thresholds occurred at the beginning of the deforestation for mean patch size and at an intermediate stage, corresponding to the percolation threshold, for connectivity, isolation and fragmentation. Threshold behavior for connectivity index might suggest that the survival of strictly forest species will sharply decrease when the proportion of forest reach values <0.60, indicating that conservation efforts should be done to maintain forest cover above this limit. Significant differences observed among the real deforestation patterns, especially in patch isolation and number of fragments, can have significant consequences for conservation. The independent settlement pattern is, without a doubt, the least favorable of them, resulting in a higher level of fragmentation, whereas the large property and fishbone patterns may be less detrimental if connectivity among the remnant forest patches is preserved.     

Utility of landscape mosaics and boundaries in forest conservation decision making in the Atlantic Forest of Brazil

We evaluated changes in the Atlantic Forest landscape over the last 40 years based on changes in boundaries and mosaics, including the hypothetical landscape resulting from the application of Brazilian laws for forest protection. Mosaics were identified as sets of land-use patches with a similar pattern of boundaries. Landscapes of different years, therefore, can be distinguished by differences in mosaics. We developed a technique to identify boundaries between patches from land-use maps using ArcGis^® and to build the patch x boundary matrix required for mosaic identification by means of a factorial and cluster analysis. The mosaics were characterized by some key uses as well as by their boundaries with other land uses. The mosaics were scored for forest conservation according to five issues: landscape permeability, cover, availability, quality, and fragmentation of forest. The values were based on land use and boundary patterns. Although Brazilian laws regarding forest protection have promoted conservation and the hypothetical legal landscape has presented the highest forest habitat availability, this expansion perpetuates a boundary pattern that complicates conservation and management, thus increasing the pressure on forest patches and favoring the further fragmentation of protected forest patches. These conclusions cannot be reached by simply recording changes in land uses.     

Matrix Matters: Effects of Surrounding Land Uses on Forest Birds Near Ottawa,Canada

Matrix quality affects probability of persistence in habitat patches in landscape simulation models while empirical studies show that both urban and agricultural land uses affect forest birds. However, due to the fact that forest bird abundance and species richness can be strongly influenced by local habitat factors, it is difficult to analyze matrix effects without confounding effects from such factors. Given this, our objectives were to (1) relate human-dominated land uses to forest bird abundance and species richness without confounding effects from other factors; (2) determine the scale at which forest birds respond to the matrix; and (3) identify whether certain bird migratory strategies or habitat associations vary in richness or abundance as a function of urban and agriculture land uses. Birds were surveyed at a single point count site 100 m from the edge of 23 deciduous forest patches near Ottawa, Ontario. Land uses surrounding each patch were measured within increasingly large circles from 200 to 5000 m radius around the bird survey site. Regression results suggest that effects of urban and agricultural land uses on forest birds (1) are not uniformly positive or negative, (2) can occur at different spatial scales, and (3) differentially affect certain groups of species. In general, agriculture appeared to affect species at a broad spatial scale (within 5 km), while urban land use had an impact at both a narrower spatial scale (within 1.8 km) and at the broad scale. Neotropical and short distance migrant birds seemed to be the most sensitive to land use intensification within the matrix. Limiting urban land use within approximately 200–1800 m of forest patches would be beneficial for Neotropical migrant birds, which are species of growing conservation concern in temperate North America.     

A multi-scale assessment of human and environmental constraints on forest land cover change on the Oregon (USA) coast range

Human modification of forest habitats is a major component of global environmental change. Even areas that remain predominantly forested may be changed considerably by human alteration of historical disturbance regimes. To better understand human influences on the abundance and pattern of forest habitats, we studied forest land cover change from 1936 to 1996 in a 25000 km² landscape in the Oregon (USA) Coast Range. We integrated historical forest survey data and maps from 1936 with satellite imagery and GIS data from 1996 to quantify changes in major forest cover types. Change in the total area of closed-canopy forests was relatively minor, decreasing from 68% of the landscape in 1936 to 65% in 1996. In contrast, large-conifer forests decreased from 42% in 1936 to 17% in 1996, whereas small-conifer forests increased from 21% of the landscape in 1936 to 39% in 1996. Linear regression models were used to predict changes in the proportion of large conifer forest as a function of socioeconomic and environmental variables at scales of subbasins (mean size = 1964 km², n=13), watersheds (mean size = 302 km², n=83), and subwatersheds (mean size = 18 km², n=1325). The proportion of land in private ownership was the strongest predictor at all three spatial scales (partial R² values 0.57–0.76). The amounts of variation explained by other independent variables were comparatively minor. Results corroborate the hypothesis that differing management regimes on private and public ownerships have led to different pathways of landscape change. Furthermore, these distinctive trajectories are consistent over a broad domain of spatial scales.     

Tropical forest regeneration following land abandonment is driven by primary rainforest distribution in an old pastoral region

Context

Tropical forest regeneration is increasingly prominent as agro-pastoral lands are abandoned. Regeneration is characterised as favouring ‘marginal’ lands; however, observations of its drivers are often coarse or simple, leaving doubt as to spatial dynamics and causation.

Objectives

We quantified the spatial dynamics of forest regeneration relative to marginality and remnant forest cover in a 3000 km² pastoral region in northern tropical Australia.

Methods

Classification and regression trees related the extent and distribution of regeneration to soil agricultural potential, land-cover history, terrain slope, distance to primary forest, and primary forest fragment size, as defined by aerial photography.

Results

Secondary forest extent and distribution overwhelmingly reflect the proximity and size of primary forest fragments. Some 85 % of secondary forest area occurs <1 km of primary forest, and 86 % of secondary forest patches >50 ha are <400 m from primary forest and coincident with historic primary forest fragments. Where primary forest fragments are >8.5 ha, secondary forest area declines less rapidly with increasing distance from primary forest up to 1.5 km. Marginality inferred by soil potential and slope had no bearing on regeneration, except at the coarsest of spatial scales where regeneration is a proxy for primary forest cover.

Conclusion

Findings underline the need to conserve even modest rainforest patches as propagule reservoirs enabling regeneration. Marginality per se may have a limited role in regeneration. As most secondary forest was an extension of primary forest, its unique conservation value relative to that of primary forest may likewise merit reconsideration.

     

Spatial versus temporal variation in precipitation in a semiarid ecosystem

Spatial and temporal variations in precipitation are central features of semiarid ecosystems, influencing patterns of plant productivity and the distribution of native fauna. Although temporal variation in precipitation has been studied extensively, far less is known about the spatial scale and pattern of precipitation variability in semiarid regions. I used long-term precipitation records to examine spatial variation across the 63 km² Central Plains Experimental Range in northeastern Colorado, and across the 117,000 km² region of shortgrass steppe in eastern Colorado. Relative to temporal variation, spatial variation was low at scales <10 km, increased linearly across scales of 40–120 km, and was nearly equal in magnitude to temporal variation across distances of 120–160 km. Although I hypothesized that most spatial variation would be generated by early-summer convective thunderstorms in June, I found that the magnitude and spatial pattern of variation was similar for precipitation received in June compared to cumulative precipitation received during the full growing season. The degree of spatial autocorrelation in precipitation across all distances that I evaluated was similar for drought, dry, above-average and wet years. Across distances of 10–120 km, spatial variation within a single growing season was approximately two times greater than spatial variation in long-term mean growing-season precipitation, indicating spatial shifting in the locations of patches of high and low precipitation over multiple years. Overall, these findings suggest spatial variation at scales of 10–160 km may have been an important factor influencing vegetation patterns and migratory fauna of the shortgrass steppe, and have implications for livestock producers and future assessments of climate change.     

The impact of landscape and adjacent land cover upon linear boundary features

The condition of over 200 km of traditional drystone walls wassurveyed within 115 km² in lowland, marginal upland and uplandlandscapes in northern England. The land covers adjacent to wallswere also recorded. Of the total length of walls surveyed, 12.6%were in disrepair. The condition of the walls differed betweenlandscapes and was also related to the type of vegetation in theadjacent enclosure. Walls enclosing conifer plantations andunimproved rough grazing were in poor condition reflectinghistorical and recent changes in their roles as livestock barriersand markers of ownership. The effect of other land covers on thecondition of walls was not consistent between landscapes. Usingdrystone walls as a simple model system suggests that the conditionof linear features in general may often be determined by both theadjacent land cover and the landscape in which the features occur.