Soil nitrogen and carbon dynamics in a fragmented landscape experiencing forest succession

Forest fragmentation is an increasingly common feature across the globe, but few studies examine its influence on biogeochemical fluxes. We assessed the influence of differences in successional trajectory and stem density with forest patch size on biomass quantity and quality and N transformations in the soil at an experimentally fragmented landscape in Kansas, USA. We measured N-related fluxes in the laboratory, not the field, to separate effects of microclimate and fragment edges from the effects of inherent biomass differences with patch size. We measured net N mineralization and N₂O fluxes in soil incubations, gross rates of ammonification and nitrification, and microbial biomass in soils. We also measured root and litterfall biomass, C:N ratios, and δ¹³C and δ¹⁵N signatures; litterfall [cellulose] and [lignin]; and [C], [N], and δ¹³C and δ¹⁵N of soil organic matter. Rates of net N mineralization and N₂O fluxes were greater (by 113% and 156%, respectively) in small patches than in large, as were gross rates of nitrification. These differences were associated with greater quantities of root biomass in small patch soil profiles (664.2 ± 233.3 vs 192.4 ± 66.2 g m⁻² for the top 15 cm). These roots had greater N concentration than in large patches, likely generating greater root derived organic N pools in small patches. These data suggest greater rates of N cycling in small forested patches compared to large patches, and that gaseous N loss from the ecosystem may be related to forest patch size. The study indicates that the differences in successional trajectory with forest patch size can impart significant influence on soil N transformations in fragmented, aggrading woodlands.     

Environmental factors and ecological processes controlling vegetation patterns in boreal forests

An individual tree model of forest dynamics was used to examine the environmental and ecological factors controlling forest vegetation patterns in upland boreal forests of North America. Basic life history traits that characterized the regeneration, growth, and death of individual trees were combined with species-specific responses to important environmental factors. This model simulated forest structure and vegetation patterns in conifer, hardwood, and mixed conifer-hardwood forests and woodlands in several bioclimatic sub-regions of the North American boreal forest zone. Model testing identified the processes and parameters required to understand the ecology of upland boreal forests and weaknesses in our current understanding of these processes. These factors included climate, solar radiation, soil moisture, soil temperature and permafrost, the forest floor organic layer, nutrient availability, forest fires, and insect outbreaks. Model testing also identified which of these factors were important in each bioclimatic sub-region.     

Regional scale analysis of denitrification in north temperate forest soils

Large scale analyses of biogeochemical processes are necessary for understanding anthropogenic effects on global climate and environmental quality. Regional scale estimates of denitrification from forest soils in southern lower Michigan USA were produced by stratifying the region into landscape experimental units using soil texture and natural drainage classes, and extrapolating data to larger areas using a geographic information system (GIS). Previous landscape-scale research established relationships between soil texture and drainage and denitrification and quantified annual denitrification N loss in nine soil texture/drainage groups. All forest soils within the region (64 series) were assigned to one of these nine groups based on their texture and drainage characteristics and were assigned an annual denitrification N loss value. A regional estimate of denitrification was produced by multiplying the areal extent of each of the nine soil groups by their annual denitrification N loss value. Loam-textured soils underlie 47% of the regional forest and accounted for 73% of the forest denitrification. Sandy soils were found under 44% of the regional forest but produced only 5% of the regional denitrification. Clay loam soils underlie 9% of the regional forest and produced 22% of the denitrification. Annual denitrification N loss for the region was estimated as 1.4×10⁷ kg N/yr. We used denitrification enzyme activity (DEA) as a proxy for annual denitrification N loss to determine if the relationship between denitrification and soil texture and natural drainage that we observed at the landscape scale held up at the regional scale. DEA was measured in 22 soils across the region and was strongly related to soil texture and natural drainage (r²=0.61), suggesting that extrapolation of data from the landscape to the regional scale was justified.     

Rapid sampling of plant species composition for assessing vegetation patterns in rugged terrain

Detailed species composition data are rapidly collected using a high-powered telescope from remote vantage points at two scales: site level and patch level. Patches constitute areas of homogeneous vegetation composition. Multiple samples of species composition are randomly located within the patches. These data are used as site-level data and are also aggregated to provide species composition data at the patch level. The site- and patch-level data are spatially integrated with high resolution (10 m), topographically-derived fields of environmental conditions, such as solar radiation, air temperature, and topographic moisture index in order to evaluate the applicability of the sampling method for modeling relationships between species composition and environmental processes.The methodology provides a balance between sampling efficiency and the accuracy of field data. Application of the method is appropriate for environments where terrain and canopy characteristics permit open visibility of the landscape. We evaluate the nature of data resulting from an implementation of the remote sampling methodology in a steep watershed dominated by closed-canopy chaparral. Analyses indicate that there is minimal bias associated with scaling the data from the site level to the patch level, despite variable patch sizes. Analysis of variance and correlation tests show that the internal floristic and environmental variability of patches is low and stable across the entire sample of patches. Comparison of regression tree models of species cover at the two scales indicates that there is little scale-dependence in the ecological processes that govern patterns of species composition between the site level and patch level. High explanatory power of the regression tree models suggests that the vegetation data are characterized at an appropriate scale to model landscape-level patterns of species composition as driven by topographically-mediated processes. Patch-level sampling reduces the influence of local stochasticity and micro-scale processes. Comparison of models between the two scales can be useful for assessing the processes and associated scales of variability governing spatial patterns of plant species.     

Recovery dynamics and climate change effects to future New England forests

Context

Forests throughout eastern North America continue to recover from broad-scale intensive land use that peaked in the nineteenth century. These forests provide essential goods and services at local to global scales. It is uncertain how recovery dynamics, the processes by which forests respond to past forest land use, will continue to influence future forest conditions. Climate change compounds this uncertainty.

Objectives

We explored how continued forest recovery dynamics affect forest biomass and species composition and how climate change may alter this trajectory.

Methods

Using a spatially explicit landscape simulation model incorporating an ecophysiological model, we simulated forest processes in New England from 2010 to 2110. We compared forest biomass and composition from simulations that used a continuation of the current climate to those from four separate global circulation models forced by a high emission scenario (RCP 8.5).

Results

Simulated forest change in New England was driven by continued recovery dynamics; without the influence of climate change forests accumulated 34 % more biomass and succeed to more shade tolerant species; Climate change resulted in 82 % more biomass but just nominal shifts in community composition. Most tree species increased AGB under climate change.

Conclusions

Continued recovery dynamics will have larger impacts than climate change on forest composition in New England. The large increases in biomass simulated under all climate scenarios suggest that climate regulation provided by the eastern forest carbon sink has potential to continue for at least a century.

     

Comparing the role of site disturbance and landscape properties on understory species richness in fragmented periurban Mediterranean forests

We hypothesized that the spatial configuration and dynamics of periurban forest patches in Barcelona (NE of Spain) played a minor role in determining plant species richness and assemblage compared to site conditions, and particularly to both direct (measured at plot level) and potential (inferred from landscape metrics) human-associated site disturbance. The presence of all understory vascular plants was recorded on 252 plots of 100 m² randomly selected within forest patches ranging in size from 0.25 ha to 218 ha. Species were divided into 6 groups, according to their ecology and conservation status. Site condition was assessed at plot level and included physical attributes, human-induced disturbance and Quercus spp. tree cover. Landscape structure and dynamics were assessed from patch metrics and patch history. We also calculated a set of landscape metrics related to potential human accessibility to forests. Results of multiple linear regressions indicated that the variance explained for non-forest species groups was higher than for forest species richness. Most of the main correlates corresponded to site disturbance variables related to direct human alteration, or to landscape variables associated to indirect human effects on forests: Quercus tree cover (a proxy for successional status) was the most important correlate of non-forest species richness, which decreased when Quercus tree cover increased. Human-induced disturbance was an important correlate of synanthropic and total species richness, which were higher in recently managed and in highly frequented forests. Potential human accessibility also affected the richness of most species groups. In contrast, patch size, patch shape and connectivity played a minor role, as did patch history. We conclude that human influence on species richness in periurban forests takes place on a small scale, whereas large-scale effects attributable to landscape structure and fragmentation are comparatively less important. Implications of these results for the conservation of plant species in periurban forests are discussed.     

Unexpected long-range edge-to-forest interior environmental gradients

We examined the relationships between distance-to-edge and environmental factors inferred from mean plant indicator values across large distance-to-edge and patch size gradients. Floristic composition, landscape metrics and site variables (climate, soil and forest management) were collected on 19,989 plots in 1,801 forest patches in Northern France using the French National Forest Inventory. Statistical models were applied to mean plant indicator values (MIV) from Ellenberg and Ecoplant databases for soil pH, soil nitrogen (N), soil humidity (F), light (L) and air temperature (Ta) using distance-to-edge and forest patch size as predictors. The five mean indicator values significantly varied with distance-to-edge and MIV pH, N and Ta decreased over distances in excess of 500 m. Consistent very long edge-to-interior gradients were also detected for site variables. The distance-to-edge effect remained significant after controlling for site differences, especially for MIV pH and N. Significant edge-to-core gradients of MIV were detected over much larger ranges than previously recognised. Neither the presence of an ecological boundary between forest and the surrounding matrix, nor microclimate, soil or forest management heterogeneity within forest patches can fully explain this long edge-to-interior gradient observed in MIV. Two hypotheses are discussed for MIV pH and N: (1) soil eutrophication, due to atmospheric N deposition, which could occur deeper into forest-cores than previously acknowledged; (2) land use legacies, as the periphery of ancient forests is more often occupied by recent forests where former agricultural practices have irreversibly modified topsoil properties. Land use history data would help identify the drivers underlying these long-range edge gradients.     

Re-examining fire severity relations in pre-management era mixed conifer forests: inferences from landscape patterns of forest structure

For some time, ecologists have known that spatial patterns of forest structure reflected disturbance and recovery history, disturbance severity and underlying influences of environmental gradients. In spite of this awareness, historical forest structure has been little used to expand knowledge of historical fire severity. Here, we used forest structure to predict pre-management era fire severity across three biogeoclimatic zones in eastern Washington State, USA, that contained extensive mixed conifer forests. We randomly selected 10% of the subwatersheds in each zone, delineated patch boundaries, and photo-interpreted the vegetation attributes of every patch in each subwatershed using the oldest available stereo-aerial photography. We statistically reconstructed the vegetation of any patch showing evidence of early selective harvesting, and then classified them as to their most recent fire severity. Classification used published percent canopy mortality definitions and a dichotomized procedure that considered the overstory and understory canopy cover and size class attributes of a patch, and the fire tolerance of its cover type. Mixed severity fires were most prevalent, regardless of forest type. The structure of mixed conifer patches, in particular, was formed by a mix of disturbance severities. In moist mixed conifer, stand replacement effects were more widespread in patches than surface fire effects, while in dry mixed conifer, surface fire effects were more widespread by nearly 2:1. However, evidence for low severity fires as the primary influence, or of abundant old park-like patches, was lacking in both the dry and moist mixed conifer forests. The relatively low abundance of old, park-like or similar forest patches, high abundance of young and intermediate-aged patches, and widespread evidence of partial stand and stand-replacing fire suggested that variable fire severity and non-equilibrium patch dynamics were primarily at work.     

Environmental factors at different spatial scales governing soil fauna community patterns in fragmented forests

Spatial and temporal changes in community structure of soil organisms may result from a myriad of processes operating at a hierarchy of spatial scales, from small-scale habitat conditions to species movements among patches and large-sale landscape features. To disentangle the relative importance of spatial and environmental factors at different scales (plot, patch and landscape), we analyzed changes in Collembola community structure along a gradient of forest fragmentation, testing predictions of the Hierarchical Patch Dynamics Paradigm (HPDP) in different European biogeographic regions (Boreal, Continental, Atlantic, Mediterranean, Alpine). Using variance partitioning methods, based on partial CCAs, we observed that the independent effect of environmental processes was significantly explaining Collembola community variance in all regions, while the relative effect of spatial variables was not significant, due to the observed high levels of landscape heterogeneity along the gradient. Environmental factors at the patch and plot scales were generally significant and explained the larger part of community changes. Landscape variables were not significant across all study sites. Yet, at the landscape level, an increase in forest habitat and proximity of forest patches were showed to have an indirect influence on local community changes, by influencing microhabitat heterogeneity at lower spatial scales in all studied regions. In line with HPDP, large-scale landscape features influenced spatio-temporal changes in soil fauna communities by constraining small-scale environmental processes. In turn, these provided mechanistic understanding for diversity patterns operating at the patch scale, via shifts in community weighted mean of Collembola life-forms occurring in local communities along the fragmentation gradient.     

Seasonal dynamics of soil nitrogen availability and phosphorus fractions under urban forest remnants of different vegetation communities in Southern China

Urban forest remnants are a useful tool to study forest response to global change with urbanization. Soil nutrient status in urban forests has not been well understood, especially under the pressure of rapid urbanization in developing countries. In this study, ion-exchange resin bags and a modified Hedley P fractionation procedure were used to measure seasonal dynamics of soil N forms (ammonium and nitrate) and P fractions (available, labile, slow, occlude and weathered mineral P) under urban forest remnants across a successional sequence and non-forest land in the city of Nanchang, Southern China. Results showed that soil N availability varied with season and vegetation community (P < 0.05). Soil P fractions showed minimal seasonal variation except available P, while their averages generally increased with forest development from non-forest land to coniferous forest to conifer-broadleaf mixed forest to evergreen broad-leaved forest. The ratios of fresh soil N forms to P fractions generally decreased with forest development, while N forms absorbed by resins to P fractions generally increased from non-forest land to coniferous forest, then decreased from conifer-broadleaf mixed forest to evergreen broad-leaved forest. It is suggested that urban older forest remnants could easily move to N saturation status and soil P enrichment, causing urban water pollution due to the accumulative effect of elevated atmospheric N deposition and exogenous P input with urbanization.     

Early forest dynamics in stand-replacing fire patches in the northern Sierra Nevada, California, USA

There is considerable concern over the occurrence of stand-replacing fire in forest types historically associated with low- to moderate-severity fire. The concern is largely over whether contemporary levels of stand-replacing fire are outside the historical range of variability, and what natural forest recovery is in these forest types following stand-replacing fire. In this study we quantified shrub characteristics and tree regeneration patterns in stand-replacing patches for five fires in the northern Sierra Nevada. These fires occurred between 1999 and 2008, and our field measurements were conducted in 2010. We analyzed tree regeneration patterns at two scales: patch level, in which field observations and spatial data were aggregated for a given stand-replacing patch, and plot level. Although tree regeneration densities varied considerably across sampled fires, over 50 % of the patches and approximately 80 % all plots had no tree regeneration. The percentage of patches, and to a greater extent plots, without pine regeneration was even higher, 72 and 87 %, respectively. Hardwood regeneration was present on a higher proportion of plots than either the pine or non-pine conifer groups. Shrub cover was generally high, with approximately 60 % of both patches and individual plots exceeding 60 % cover. Patch characteristics (size, perimeter-to-area ratio, distance-to-edge) appeared to have little effect on observed tree regeneration patterns. Conifer regeneration was higher in areas with post-fire management activities (salvage harvesting, planting). Our results indicate that the natural return of pine/mixed-conifer forests is uncertain in many areas affected by stand-replacing fire.     

Land use dynamics within an urbanizing non-metropolitan county in New York State (USA)

Land use/land cover data for fifteen minor civil divisions (MCDs) in Ulster County, New York (USA) were interpreted from 1968 and 1985 aerial photographs. These data were combined with ancillary physiographic and demographic data as raster layers within a computerized geographic information system (GIS). Class to class changes in land use/land cover were quantified for a study area approximately 30 kilometers by 50 kilometers. The relationships between the land use/land cover variables and the ancillary variables were modeled in a series of weighted least squares regressions employing data spatially aggregated by general soil map unit (N = 44).Between 1968 and 1985, nearly one-third of the study area changed to another land use/land cover class. Land in the urban class increased from 6.7% to 17.8% of the study area, while the forest class declined from 65.0% to 55.2%, and the agriculture class declined from 12.7% to 8.9%. Gains and losses in the remaining five major (Level I) land use/land cover classes were relatively small. Land use changes primarily involved the conversion of land from the forest, agriculture, and vacant classes to the urban class, and from the agriculture class to the forest and vacant classes. Variables accounting for the variance in the land use/land cover class proportions of the soil units were population density, highway proximity, distance to urban centers, mean elevation, mean slope gradient, and soil suitability for farming and for urban development.     

Ecosystem services of regulation and support in Amazonian pioneer fronts: searching for landscape drivers

Landscape dynamics result from forestry and farming practices, both of which are expected to have diverse impacts on ecosystem services (ES). In this study, we investigated this general statement for regulating and supporting services via an assessment of ecosystem functions: climate regulation via carbon sequestration in soil and plant biomass, water cycle and soil erosion regulation via water infiltration in soil, and support for primary production via soil chemical quality and water storage. We tested the hypothesis that patterns of land-cover composition and structure significantly alter ES metrics at two different scales. We surveyed 54 farms in two Amazonian regions of Brazil and Colombia and assessed land-cover composition and structure from remote sensing data (farm scale) from 1990 to 2007. Simple and well-established methods were used to characterize soil and vegetation from five points in each farm (plot scale). Most ES metrics were significantly correlated with land-use (plot scale) and land-cover (farm scale) classifications; however, spatial variability in inherent soil properties, alone or in interaction with land-use or land-cover changes, contributed greatly to variability in ES metrics. Carbon stock in above-ground plant biomass and water infiltration rate decreased from forest to pasture land covers, whereas soil chemical quality and plant-available water storage capacity increased. Land-cover classifications based on structure metrics explained significantly less ES metric variation than those based on composition metrics. Land-cover composition dynamics explained 45 % (P < 0.001) of ES metric variance, 15 % by itself and 30 % in interaction with inherent soil properties. This study describes how ES evolve with landscape changes, specifying the contribution of spatial variability in the physical environment and highlighting trade-offs and synergies among ES.     

Scale dependence in quantification of land-cover and biomass change over Siberian boreal forest landscapes

We investigated the influence of remote sensing spatial resolution on estimates of characteristic land-cover change (LCC) and LCC-related above-ground biomass change (Δbiomass) in three study sites representative of the East Siberian boreal forest. Data included LCC estimated using an existing Landsat-derived land-cover dataset for 1990 and 2000, and above-ground standing biomass stocks simulated by the FAREAST forest succession model and applied on a pixel basis. At the base 60 m resolution, several landscape pattern metrics were derived to describe the characteristic LCC types. LCC data were progressively degraded to 240, 480, and 960 m. LCC proportions and Δbiomass were derived at each of the coarser resolutions and scale dependences of LCC and Δbiomass were analyzed. Compared to the base 60 m resolution, the Logged LCC type was highly scale dependent and was consistently underestimated at coarser resolutions. The Burned type was under- or over-estimated depending strongly on its patch size. Estimated at the base 60 m resolution, modeled biomass increased in two sites (i.e., 3.0 and 6.4 Mg C ha⁻¹ for the Tomsk and Krasnoyarsk sites, respectively) and declined slightly in one site (i.e., −0.5 Mg C ha⁻¹ for the Irkutsk site) between the two dates. At the degraded resolutions, the estimated Δbiomass increased to 3.3 and 7.0 Mg C ha⁻¹ for the Tomsk and Krasnoyarsk sites, while it declined to −0.8 Mg C ha⁻¹ for the Irkutsk site. Results indicate that LCC and Δbiomass values may be progressively amplified in either direction as resolution is degraded, depending on the mean patch size (MPS) of disturbances, and that the error of LCC and Δbiomass estimates also increases at coarser resolutions.     

不同土层深度及磷水平对番茄生物量及根系形态的影响

以番茄品种东农708为试验材料,取距地表0~15cm,15~30cm,30~45cm的土壤为栽培土壤,各层土壤以施N、P、K肥为供磷处理,以施N、K肥为对照,研究不同土层深度及供磷水平对番茄生物量及根系形态的影响。结果表明,番茄植株地上部生物量受施磷水平和土层深度共同影响,同一土层中供磷条件下的番茄株高、地上部干、鲜质量均显著高于对照;在相同施磷水平下,0~15cm土层的番茄株高、地上部鲜质量均显著高于15~30cm和30~45cm土层。番茄植株地下部干质量、总根长、根表面积、根体积及0~1.5mm直径范围内总根长受施磷水平影响较大,受土层深度影响不明显。综上,不同土层深度及磷水平对番茄地上部生物量均有影响,且表层土壤施磷更利于番茄生物量的积累;根系形态受施磷水平影响较大,受土层深度影响不显著。     

Forest loss and matrix composition are the major drivers shaping dung beetle assemblages in a fragmented rainforest

Context

Identifying the drivers shaping biological assemblages in fragmented tropical landscapes is critical for designing effective conservation strategies. It is still unclear, however, whether tropical biodiversity is more strongly affected by forest loss, by its spatial configuration or by matrix composition across different spatial scales.

Objectives

Assessing the relative influence of forest patch and landscape attributes on dung beetle assemblages in the fragmented Lacandona rainforest, Mexico.

Methods

Using a multimodel inference approach we tested the relative impact of forest patch size and landscape forest cover (measures of forest amount at the patch and landscape scales, respectively), patch shape and isolation (forest configuration indices at the patch scale), forest fragmentation (forest configuration index at the landscape scale), and matrix composition on the diversity, abundance and biomass of dung beetles.

Results

Patch size, landscape forest cover and matrix composition were the best predictors of dung beetle assemblages. Species richness, beetle abundance, and biomass decreased in smaller patches surrounded by a lower percentage of forest cover, and in landscapes dominated by open-area matrices. Community evenness also increased under these conditions due to the loss of rare species.

Conclusions

Forest loss at the patch and landscape levels and matrix composition show a larger impact on dung beetles than forest spatial configuration. To preserve dung beetle assemblages, and their key functional roles in the ecosystem, conservation initiatives should prioritize a reduction in deforestation and an increase in the heterogeneity of the matrix surrounding forest remnants.

     

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.     

Analysing land-cover changes in relation to environmental variables in Hesse,Germany

Land-use and land-cover changes affect ecological landscape functions and processes. Hence, landscape ecologists have a central interest in a comprehensive understanding of such changes. Our study focuses on the relationships between environmental conditions and agricultural land-cover changes. We present a method to (i) characterise the major spatial-temporal processes of land-cover changes, (ii) identify the correlations between environmental attributes and land-cover changes and (iii) derive potential environmental drivers of land-cover changes in a German marginal rural landscape. The method was applied to study land-cover dynamics from 1945 to 1998 in the districts of Erda, Steinbrücken and Eibelshausen, situated in the marginal rural landscape of the Lahn-Dill Highlands, Germany. We employed land-cover data gained by the interpretation of multi-temporal aerial photographs. Various environmental variables were introduced into the analyses. We identified physical landscape attributes (elevation, slope, aspect, available water capacity and soil texture) and structural landscape dimensions (patch size, patch shape and distance between patch and nearest settlement). With the aid of GIS, K-means partitioning and canonical correspondence analysis, we investigated land-cover trajectory types, land-cover transitions at individual time intervals and their relationships to these environmental variables. Our results show that, between 1945 and 1998, land-cover changes correlated with the physical attributes of the underlying landscape. On the other hand, the structural landscape dimensions correlated with land cover only in periods of minor land-cover changes (1972–98). Greater diversity of physical landscape attributes is correlated with greater land-cover dynamics. Besides the important influence of socio-economic factors, land-cover changes in the study areas took place within the relatively stable physical constraints of the underlying landscape.This revised version was published online in May 2005 with corrections to the Cover Date.