Mean Patch Area Research Articles

Historic variability in fire-generated landscape heterogeneity of subalpine forests in the Canadian Rockies

Question: This study evaluates historical changes in landscape structure and heterogeneity in subalpine forests. We use response to severe fires in 2001 and 2003, along with historical reconstructions to examine crown-fire effects on landscape heterogeneity and to assess, comparatively, effects of fire exclusion management in the 20th century. Location: Subalpine forests of Kootenay National Park (KNP), Canadian Rockies. Methods: Using a landscape-level model based on a fire-origin stand age map, we reconstructed decadal burned areas within the landscape for 1750-2000 (forming reconstructed landscapes). Landscape pattern was analysed for each reconstructed landscape map, and we compared landscape pattern indices (total area, number of patches, mean patch area, patch area variation, largest patch index, edge density, perimeter–area ratio, landscape shape index) with those in 2005 after recent large fires. Results: After large fires in 1926, connectivity of the KNP landscape increased and its diversity was quite low. After 2001 and 2003 fires, the post-fire landscape of 2005 was highly heterogeneous in terms of size, variation, edge density and perimeter–area ratio of the remnant forest patches. Since the decline in occurrence of large fires after 1926 reflected a period of wet weather, fuel build-up resulting from landscape homogenization within the 20th century landscape could not be attributed solely to fire exclusion. This period without fires greatly enhanced connectivity of late-successional forests that finally burned in 2001/2003, but connectivity was within the historical range for these forests. The gradual increase in stand connectivity before recent large fires may indicate that fire exclusion was less responsible than often believed for fuel build-up in these fire-susceptible older forests. Conclusions: The large fires at the beginning of the 21st century are within the natural range of disturbances for this landscape, and do not stand out as “human-induced disasters” in their effects on landscape patterns. Such stochastic large disturbances contribute to maintenance of highly heterogeneous landscape structure, which is important for many taxa and natural ecological processes. Identifying future probability of such large disturbances and their ecological roles should be incorporated into management of these dynamic, disturbance-prone systems.

Colonization, Spread, and Growth of Lygodium microphyllum on Tree Islands in a Wetland in Florida

AbstractWe monitored colonization, spread, and growth of an exotic Old World climbing fern on tree islands in the interior marsh of Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida to investigate linkages between its colonization and growth and environmental factors. Number of the patches continuously increased over a 2-yr monitoring period, but mean patch area and height did not increase. Lower water depth was associated with larger number of patches whereas higher water depth was associated with higher mean patch height. Patch occurrence probability at each 3 m (9.8 ft) grid within tree islands also increased and indicated that patches spread from outer areas to interiors of tree islands over time. Patch occurrence probability was lower in sawgrass-dominated locations, which typically occur at the margin of tree islands, compared to locations dominated by woody plants. Patch occurrence probability was higher on west sides of tree islands corresponding to the side of the islands most impacted by a recent major hurricane. This study revealed that colonization and growth of Old World climbing fern are characterized by several spatial and temporal factors. A detection protocol using ground surveys that focus on the edges of tree islands could be an efficient way to identify early infestations on tree islands in the Refuge. Such a protocol also might be useful to identify new infestations on tree islands in other areas of the Everglades.

Spatial vegetation patterns as early signs of desertification: a case study of a desert steppe in Inner Mongolia, China

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.

Freshwater fish community structured more by dispersal limitation than by environmental heterogeneity

Abstract – We examined the relative contribution of environmental heterogeneity and dispersal limitation on freshwater fish community composition in 18 Greek protected lakes and reservoirs. Environmental heterogeneity was measured by spatial pattern metrics (calculated by digital map processing, e.g., patch richness density, area‐weighted mean patch area), altitude, maximum lake depth and trophic status. Dispersal limitation was measured by straight‐line distances among lake centres. Ecosystems were clustered according to species composition. We examined the correlation of similarity in species composition among ecosystems with that of environmental heterogeneity and with straight‐line distances, for the entire dataset, as well as for the occurring clusters. Fish species richness increased with ecosystem area and decreased with altitude. The clusters identified (aquatic ecosystems of Northern vs. ecosystems of Western Greece), implied an underlying biogeographical pattern as defined, with Pindus range acting as a natural barrier. Between ecosystems similarity, based on fish species composition, showed a weak to insignificant correlation with environmental heterogeneity, but was significantly correlated to dispersal limitation for the entire dataset as well as within each occurring cluster. Thus, natural barriers, species biogeography and dispersal limitation played a more significant role in shaping freshwater fish communities than environmental heterogeneity.

Landscape change in an agricultural watershed in the U.S. Midwest

Opportunities to improve the ecological functioning of agricultural landscapes in the U.S. Midwest exist, and could include the restoration of native plant communities to improve biodiversity or the modification of agricultural production systems to enhance the provisioning of ecosystem services to society. To be most effective in achieving these goals, restoration efforts require knowledge of past conditions and drivers of change. We assessed landscape change in the Clear Creek, Iowa watershed from 1940 to 2002 using five metrics derived from aerial photos: land cover composition and configuration, housing density and spatial pattern, and stream sinuosity. Major cover changes in the watershed included increases in urban (+1743.0 ha) and dense forest cover (+618.9 ha), coupled with a decline in the total area (−2773.4 ha) and mean patch area (−4.9 ha) of crops. Mean forest patch area increased (+3.7 ha), while patch number declined by 21.1% as reforestation linked small, previously isolated patches. Housing density increased dramatically, and houses were increasingly clustered across the study period. Most new houses were added in urban areas. Main stream channel sinuosity ranged between 1.49 and 1.27; mean sinuosity decreased by 0.22 from 1940 to 1963, a decline that persisted until 2002. In combination, changes in these five metrics document shifts in landscape composition and configuration that have important implications for people and the landscape. Our results indicate the dynamics of land use in the watershed, and may be used to parametrize hydrological models, in the development of future land use scenarios, and as a basis for restoration planning.

Population growth, urban sprawl and landscape integrity of Beijing City

The detailed landscape pattern of the urban area within the 6th ring road in Beijing City was identified using airborne remote sensing data acquired between 1997 and 2002. The landscape indices at landscape level were computed using Fragstats 3.3, and changes in land use/cover types in Beijing from 1997 to 2002 were examined. The results show that urban built area (UBA) and farmland changed greatly within the 6th ring road, and that farmland had been replaced by UBA. The number of patches increased by 106.6%, mean patch area decreased by 51.6%, the splitting index increased by 94.3%, and the landscape diversity index increased by 17.8%. The landscape pattern had become more fragmented and diversified in these 5 years. The main driving forces for landscape change were the increasing demand for land for construction due to the growing population, unreasonable urban growth, and improvements in housing standards. The landscape pattern change in Beijing led by rapid urbanisation has negatively influenced urban ecosystem health and has caused several environmental problems. We provide suggestions for improving urban planning and sustainable development in Beijing City.

Dynamics of wetland landscape pattern in Kaifeng City from 1987 to 2002

It is very significant for urban development and urban wetland protection and utilization to probe into the process and reasons of urban wetland landscape dynamics. Taking the information of remote sensing and detailed land survey data as the basic information sources, with the help of RS and GIS, according to the principles and methods of landscape ecology, this paper analyzed wetland landscape pattern dynamics and its reasons in Kaifeng City, Henan Province of China, from 1987 to 2002. The results show that the total wetland area in Kaifeng City firstly reduced by 20.1% from 1987 to 1990 and then increased from 1990 to 2002, with an average annual growth rate of 3.3%. At the same time, landscape fragment degree and landscape dominance degree increased, respectively from 0.64 to 0.72 and from 0.3754 to 0.5563, but mean patch area, maximum patch area, patch fractal dimension reduced. As far as single landscape element concerned, from 1987 to 2002, patch area, patch number, patch density, patch shape and patch location changed in varying degrees in all wetland types in Kaifeng City, among which rice field changed most and others relatively less. In the recent 20 years, rice fields, lake wetlands, puddles and ponds had a higher stability, but river and bottomland wetlands were mostly transformed to land use types. The change of wetland landscape pattern was the result of the combined action of the Huanghe (Yellow) River, urban expansion, wide cultivation of rice, and rapid development of fishery. Among them human activities were the main driving factors for wetland landscape changes.

Landscape spatial dynamics over 38 years under natural and anthropogenic pressures in Mount Lebanon

This research investigates spatial configuration changes of five forest types and introduces uncommon exploration of urban changes in Mount Lebanon. A forest map of 1965 and satellite images of Landsat TM (1987) and Spot 5 (2003) were used. Forest area has reduced by 7%, having low annual deforestation rate (<1%). Oak, cedar and cypress forests increased from 13% to 15%, 0.8% to 1% and 0% to 0.1% respectively; while pine and juniper forests decreased from 1% to 0.8% and 12% to 3% respectively. Grassland covered 20% of the original forest area followed by agriculture and urban. Forest patches were investigated in each 100 m distance from the edge of the old forests. Regenerated oaks were found within the first 100 m. Pine and cedar forests appeared at the 400 m distance. Urban settlements showed 4 m yr −1 moving progress toward forest patches. Landscape indices demonstrated increase in the number of forest patches (from 169 to 432) and in the mean proximity index (from 78.29 to 225.15) and decrease in mean patch area (from 219 to 70 ha) and largest patch index (from 15.45 to 10.32). The observed trends revealed major deforestation and fragmentation in 1965–1987, followed by a lesser deforestation tendency in 1987–2003. Each forest type behaves differently to deforestation and therefore requires special management practices.

Patch size, shape and orientation affect geometrical outcomes of surgical anterior ventricular restoration

To verify whether the use of a small, oval-shaped patch limits the trend toward re-dilatation compared to endoventricular circular patch plasty and leads to different geometrical and functional results in surgical anterior restoration. Thirty-seven patients with ischemic cardiomyopathy after anterior myocardial infarction end-systolic volume index of > or =45 ml/m2, ejection fraction of < or =35%, and no combined mitral procedures, underwent surgical anterior ventricular restoration between January 2000 and April 2003: 18 patients (group 1) were operated on using the endoventricular circular patch plasty technique (mean patch area 9.6 cm2) and 19 patients (group 2) received a small, obliquely oriented, oval-shaped patch (mean patch area 6.2 cm2). Ten geometrical parameters were studied preoperatively and at least 6 and 12 months after surgery. Data were analyzed using repeated-measures ANOVA, chi2, paired and unpaired Student's t-test, and binary logistic regression. Group 1 showed a worsening over time in systolic and diastolic longitudinal length, end-diastolic volume (P < 0.001), end-diastolic volume index (P = 0.006), end-systolic volume (P = 0.005), and end-systolic volume index (P = 0.03). Group 2 showed an improvement in percentage of akinesia and wall motion score index (P < 0.001) and a worsening only in end-systolic diameter (P = 0.03) and end-diastolic volume (P = 0.04). At 12-month follow-up, ANOVA revealed that the oval patch positively influenced end-diastolic volume (P = 0.03), end-systolic volume (P = 0.03), and end-systolic volume index (P = 0.05), and group 2 had a significantly higher number of patients with an end-systolic volume index of <45 ml/m2 (P = 0.01). The use of a small, narrow, obliquely oriented, oval patch may help to prevent adverse ventricular remodeling over time.

Using Penrose distance to identify potential risk of wildlife–vehicle collisions

Knowledge of the relationship between wildlife and roads is important for management of wildlife–vehicle collisions, which represent a serious threat to many wildlife populations and to human life and property. Effective reduction of these threats requires identification of variables influencing collision locations, and the use of these variables in spatially-explicit predictive models. We used Penrose distance modeling and 61 confirmed bobcat (Lynx rufus) road mortality locations in southern Illinois, USA, to demonstrate a rapid and accurate technique for the spatial mapping of wildlife–vehicle collision risk. We used the Penrose distance statistic to quantify the similarity between the mean multivariate habitat signature at bobcat-collision areas and road sections throughout the study area. Habitat variables assessed included road-related variables (e.g., traffic volume) and land cover characteristics (e.g., mean patch area of the landscape). Bobcat-collision areas were characterized by smaller, less-clustered habitat patches and more, large independent patches of grass cover than were study area roadway sections in general. As expected for a generalist carnivore in highly-suitable habitat, risk mapping indicated that large sections of the roaded landscape had high similarity to bobcat-collision areas. Unlike other modeling techniques used to identify risk of road mortality, our method requires little field data collection and relies on readily available digital spatial data. This technique can be used by wildlife managers and road planners, and may be particularly important in reduction of road mortality for species such as the Iberian lynx (Lynx pardinus), Florida panther (Puma concolor coryi), and Texas ocelot (Leopardis pardalus), which exist in small populations fragmented by development, and are limited by road mortalities.

Neighbourhood landscape effect on population kinetics of the fossorial water vole (Arvicola terrestris scherman)

This paper addresses the issue of whether landscape structure affects A. terrestris population kinetics on a neighbourhood spatial scale, and if so, at what spatial scale is that effect at its maximum. We investigated how the growth of A. terrestris populations is influenced by the landscape context of parcels used for hay production in the French Jura Mountains. Five landscape metrics (relative area of grassland, mean patch area of grassland, patch density of grassland, woodland patch density in grassland, grassland-woodland edge density) were computed over an increasing radius around each parcel (max. 3 km). Redundancy analysis showed that the extent, rate and early onset of A. terrestris population growth were favoured in open grassland areas. Landscape effects on A. terrestris populations as determined by the five metrics are scale-dependent: mean patch area of grassland, patch density of grassland and woodland patch density in grassland had an impact on a grassland parcel within a neighbourhood radius of about 800 m, while relative area of grassland and grassland-woodland edge density had an impact within a neighbourhood radius of about 400 m. Those findings corroborate earlier hypotheses about a multifactorial regulation of A. terrestris populations and a spatial hierarchy of regulating factors. They have potential implications in terms of landscape management and small mammal pest control.

Spatial correlograms of soil cover as an indicator of landscape heterogeneity

Abstract Soil cover, which is one of the most informative and integrative landscape factors, can be used for the analysis of landscape patterns. We studied the spatial autocorrelation (Moran's I ) of raster format soil maps (1:10,000; 10 m pixel size) in 35 study areas representing all landscape regions in Estonia. The carbonate concentration of soils, volumetric soil moisture (%) and the depth of the groundwater table were taken into consideration in compiling a scale of contrast of 17 soil groups. We introduce a simple characteristic based on spatial correlograms: a half-value distance lag, h I = 0.5 —a distance where Moran's I drops below 0.5. Spatial autocorrelation decreased very rapidly in the case of heights with a very heterogeneous landscape composition, showing low values of h I = 0.5 ( h I = 0.5 I did decrease slowly with increasing lag, being >200 m in all forest and bog areas with complex topographical conditions due to the variety of glacial landforms and peatlands. All of the eight FRAGSTATS landscape metrics studied demonstrated significant correlations with h I = 0.5 , whereas five of them – Contrast Weighted Edge Density (CWED); Percentage of Like Adjacencies (PLADJ), Edge Density (ED), Patch Density (PD) and Mean Patch Area Distribution (AREA_MN) – had Spearman Rank Order Correlation values higher than 0.8. Landscapes with high ED, PD, and CWED values have a low autocorrelation: PD, ED, and CWED correlated negatively with h I = 0.5 . PD, ED, and CWED decreased and PLADJ increased with the power-law relationship with increasing h I = 0.5 . Spatial autocorrelation is lower in landscapes with complex structure and high contrast. The positive relationship with PLADJ indicates the same. Thus, spatial correlograms of potential landscape structure based on soil cover analysis can be used for the characterization of human-influenced landscape (land use) structure.

Evaluation of landscape changes and ecological degradation by GIS in arid regions: a case study of the terminal oasis of the Shiyang River, northwest China

The development and utilization of water and land resources in the Shiyang River basin are the highest among the inland rivers in northwestern China. Using GIS and the landscape structure analysis program FRAGSTATS, landscape metrics of a study area in the lake-district in Minqin Oasis in the lower reaches of Shiyang River basin were calculated and analyzed based on TM images from 1987 to 2001 at class level and landscape level, respectively. Transformation matrix of the landscape mosaics was also examined. The driving forces of landscape changes were analyzed, including the dynamics of runoff and groundwater resources and their exploitation, and influences of policies and market economy. The results showed that: (1) Patch number of farmland and desert decreased, but their mean patch area increased, indicating that reclamation and desertification was very serious in the study area. Contagion index for oasis increased and edge density and landscape diversity were reduced. (2) Farmland and desert areas have enlarged by 1,520.46 and 4,941.27 hm2, respectively. This increase was at the cost of woodland and grassland, which shrank by 1,520.46 and 4,941.27 hm2, respectively. (3) The net utilization of surface water decreased by 50% in the last 10 years, and dropped to 22.3 × 106 m3 in the later 1990s. Exploitation of groundwater increased remarkably, up to 80 × 106 m3 per year in the last 5 years. (4) The capability of the economic structure to withstand pressures of the market economy has depressed distinctly because of the simplified planting pattern, which is dominated by salinity-enduring cash crops, such as cotton. Based on the above analysis, strategies of ecological reconstruction in the lake-district were suggested.

Characterizing the changes in landscape structure in the Lake Kasumigaura Basin, Japan using a high-quality GIS dataset

The changing characteristics of landscape structure in the Lake Kusumigaura Basin, Japan from 1979 to 1996 were investigated using time-series high-quality GIS datasets. We used FRAGSTATS software to calculate landscape indices to characterize the landscape structure. We found that human-modified landscapes, such as artificial fields and golf courses, increased rapidly during the study period, while forests and croplands decreased rapidly in the same period. From 1979 to 1996, forestland decreased by 8.4%, in which 44% turned into artificial fields, 37.6% turned into golf courses, and 6.8%, 6.4%, and 4.1%, turned into plowed fields, residential areas, and urban areas, respectively. Increased patch number and decreased mean patch area indicated that the most significant characteristic of land use/cover change in the Lake Kusumigaura Basin is the fragmentation of the landscape. Both Shannon's diversity and Shannon's evenness indices increased considerably during the study period, also suggesting the landscapes in the study area became more fragmented and heterogeneous. This fragmentation trend is most likely to continue due to the increasing population in the Lake Kusumigaura Basin in recent years.

Diffusion and Coalescence of the Houston Metropolitan Area: Evidence Supporting a New Urban Theory

The authors build on a recent development in urban geographic theory, providing evidence of an oscillatory behavior in spatiotemporal patterns of urban growth. With the aid of remotely sensed data, the spatial extent of urban areas in the Houston (USA) metropolitan region from 1974 to 2002 was analyzed by spatial metrics. Regularities in the spatial urban growth pattern were identified with temporal periods as short as thirty years by means of spatial metric values, including mean nearest-neighbor distance, mean patch area, total number of urban patches, and mean patch fractal dimension. Through changes in these values, a distinct oscillation between phases of diffusion and coalescence in urban growth was revealed. The results suggest that the hypothesized process of diffusion and coalescence may occur over shorter time periods than previously thought, and that the patterns are readily observable in real-world systems.

Spatial distribution of regeneration patches in an old‐growth Pinus Jeffrey‐mixed conifer forest in northwestern Mexico

AbstractQuestion:What are the shape, abundance, size, and structural characteristics of sapling patches in an old‐growth Pinus jeffreyi‐mixed conifer forest with a relatively intact disturbance regime?Location:Sierra San Pedro Martir, Baja California, Mexico.Methods:Regeneration was quantified by sampling sapling patches on seven 1200 m permanently marked line transects. For all patches intersected, tree size, species, age, and patch canopy cover were recorded. Patch structural characteristics were statistically compared to data from unbiased forest inventory plots. The minimum regeneration patch was defined as three saplings in a 49‐m2 area.Results:We sampled 54 sapling regeneration patches. Patch size varied from 6.6 to 674.8 m2. A small portion of the forest was in patches (patch fraction = 3.8%, patch abundance = 8.5 per ha). The majority of the patches were small; 64.8% were less than the mean patch area of 100.1 m2. Patches were shaped as a rhombus. For all forest characteristics, mean values inside patches were significantly different than those from the unbiased forest inventory plots.Conclusions:These forests have a fine‐grained pattern of regeneration patches. Our largest patch size of 674.8 m2 is the smallest reported in Pinus jeffreyi, P. ponderosa, and mixed conifer forests; other studies have probably had more difficulty delineating regeneration patches because of forest ingrowth from fire exclusion. Frequent fire, irregular seed crops, and seed dispersal by small mammals and birds could create this regeneration patch regime. High variation in nutrient availability after fire could also contribute to increased stand patchiness.

Spatial distribution of regeneration patches in an old-growth Pinus jeffreyi-mixed conifer forest in northwestern Mexico

Abstract Question: What are the shape, abundance, size, and structural characteristics of sapling patches in an old-growth Pinus jeffreyi-mixed conifer forest with a relatively intact disturbance regime? Location: Sierra San Pedro Martir, Baja California, Mexico. Methods: Regeneration was quantified by sampling sapling patches on seven 1200 m permanently marked line transects. For all patches intersected, tree size, species, age, and patch canopy cover were recorded. Patch structural characteristics were statistically compared to data from unbiased forest inventory plots. The minimum regeneration patch was defined as three saplings in a 49-m2 area. Results: We sampled 54 sapling regeneration patches. Patch size varied from 6.6 to 674.8 m2. A small portion of the forest was in patches (patch fraction = 3.8%, patch abundance = 8.5 per ha). The majority of the patches were small; 64.8% were less than the mean patch area of 100.1 m2. Patches were shaped as a rhombus. For all forest characteristics, mean value...

A comparison of methods for estimating the area of clipped wool patches on the mid-side of sheep

A study was conducted comparing 3 methods of measuring the skin area of a clipped patch on sheep to determine the most appropriate technique in terms of its precision, repeatability and ease of measurement. The methods were: 1) using callipers to take 3 measurements of both dimensions, 2) tracing the patch outline onto plastic, and 3) photographing the patch with an object of known area. Two clipped patches on the mid-side of 20 weaner sheep at each of 2 geographic locations were measured 2-3 times by each of the 3 methods.Linear relationships, and high correlations (0.83-0.89), between the patch area estimates by each of the methods indicate consistency between the methods in discriminating relative differences in patch size. The mean patch area was larger (P<0.01) when measured using callipers (21.0 ± 3.2 cm2) than when estimated by the tracing technique (18.5 ± 2.7) or photography (18.7 ± 2.7), although the overall coefficients of variation (CV) were similar (14.7-15.1%). The between-patch variance was also larger with callipers than tracing or photography, having between-patch CVs of 14.3, 13.6 and 13.9 %, respectively. However, the within-patch CVs of callipers and photography were lower (4.7 and 5.0%) than that for tracing (5.9%). All methods were associated with a high degree of repeatability. Callipers provided the highest level of repeatability (t=0.90), followed by photography (0.88) with tracing the least repeatable (0.84).

Chironomid responses to spatially structured, dynamic, streambed landscapes

AbstractWe used a repeated-measures factorial field experiment to ask whether the arrangement and stability of leafy debris affect the density of chironomids in leaf packs in dynamic, streambed landscapes. We replaced natural debris in 24 streambed landscapes with leaf packs suspended from wires that snagged organic debris as it moved downstream. We arranged 64 wires (each with 3 leaf packs) in each landscape so that they were distributed among 8 large (aggregated) or 64 small (fragmented) patches. We manipulated landscape stability by removing accumulated debris from 0% (stable), 50% (semi-stable), or 100% (unstable) of the patches in each landscape 3 d after a flood. We determined chironomid density in leaf packs 2 d before the flood, 3 d after the flood, and 5 d after manipulating stability (8 d after the flood). We mapped the debris in each landscape and used multiple regression to evaluate the effect of landscape characteristics on density. Mean patch area was significantly smaller, and the number of...

Change in mistbelt mixed Podocarpus forest area between 1944 and 1996 in the Midmar catchment of KwaZulu-Natal, South Africa

KwaZulu-Natal mistbelt ( Podocarpus ) forests serve as sources of firewood, structural timber, traditional food and medicinal products. Of the 3 694 km 2 of these forests in KwaZulu-Natal, only 0.45% is conserved. The extent of patches of Podocarpus forest in 1944 and 1996 within the Midmar catchment, KwaZulu-Natal, South Africa, were mapped from aerial photographs, and compared using a geographical information system. Overall, the area of Podocarpus forest was found to have increased from 784 ha to 804 ha between 1944 and 1996, as did mean patch area (km 2 ), although not significantly. Interestingly, between 1944 and 1996, the number of forest patches decreased by 50%, with many smaller patches present in 1944 having disappeared by 1996. The implications of fragmentation of patches are discussed. Linking of forest patches with corridors of grassland, and further studies on the species composition of these forest patches, is suggested.