Forest Fragmentation Metrics Research Articles

Effects of cluster plot design parameters on landscape fragmentation estimates: A case study using data from the Swedish national forest inventory

Forest fragmentation is commonly characterized using indices derived from analyses of classified land cover maps. An alternative is to use data obtained from sampling, such as those from a national forest inventory (NFI). The main objective of the current study is fill knowledge gaps on the performance of sample-based forest fragmentation metrics calculated with different cluster plot designs and under different forest conditions. A set of NFI cluster plot designs, each with different geometric properties, was created from Swedish NFI data. Each member of the set was used to calculate the fragmentation metrics mean patch size (MPS) and perimeter-area ratio (PA). Impacts of plot design parameters on metric estimates and their precision were assessed.Important differences in metric values were observed both within and between regions under different plot design scenarios; within regions, ranges of PA and MPS values were large, and confidence intervals for the minimum and maximum metric values did not overlap. Weighted least squares regression significance testing results suggest that subplot separation distance was an impactful design factor whereas number of subplots and cluster shape were less important. However, cluster plots with more and widely-separated subplots yielded estimates that were more precise (lower relative sampling errors) than smaller, more compact clusters. We suggest that care should be taken when interpreting the physical meaning of the metrics under study.

The role of the refugee crises in driving forest cover change and fragmentation in Teknaf, Bangladesh

This research has employed remotely sensed data and image classification techniques for the first time to track three decades (1989 to 2021) of forest cover change and forest fragmentation across the largest Rohingya refugee settlement in the Teknaf peninsula, in Bangladesh. Forest fragmentation was evaluated in terms of forest core, patch, perforated, and edge, to characterize forest morphological changes at the landscape level. The results revealed that the forest occupying the study area was 97,400 acres in 1989, which decreased to 92,400 acres by 2015 (5% change) due to firewood collection. However, a sharp decline in the forest was observed in 2017, when the Rohingya refugees settled in the region causing an additional loss of 600 acres of protected forest and 7500 acres of non-protected forests. Such a drastic forest cover change led by refugee settlements has altered forest morphological patterns. As a result, in 1989, the core forest area was 42% which declined to 25% in 2015, and 20% in 2017. This loss of core area greatly increased the patch, perforated and edge areas. Through the efforts of restoration activities, the area of the core forest increased to 28% in 2019 and further increased to 32% in 2021. By 2019, the 5500 acres of non-protected forest was regained, and the protected forest increased by 770 acres. Forest recovery was sustained through the end of 2021, and the total forest in the study area was estimated to be 93,300 acres by this period. This study provides detailed information on the spatial and temporal evaluation of forest change and forest fragmentation metrics intending to understand the historic and ongoing forest disturbance regime, particularly in the ecologically critical zone of the Teknaf wildlife sanctuary. This analysis should encourage managers to enact varying forest restoration and rehabilitation strategies in the region.

Deciphering the many maps of the Xingu River Basin – an assessment of land cover classifications at multiple scales

Remote sensing is an invaluable tool to objectively illustrate the rapid decline in habitat extents worldwide. The many operational Earth Observation platforms provide options for the generation of land cover maps, each with unique characteristics and considerable semantic differences in the definition of classes. As a result, differences in baseline estimates are inevitable. Here we compare forest cover and surface water estimates over four time periods spanning three decades (1989–2018) for ∼1.3 million km2 encompassing the Xingu River Basin, Brazil, from published, freely accessible remotely sensed land cover classifications. While all showed a decrease in forest extent over time, the total deforested area reported by each ranged widely for all time periods. The greatest differences ranged from 9% to 17% (116,958 to 219,778 km2) deforestation of the total area for year 2000 and 2014–2018 time period, respectively. We also show the high sensitivity of forest fragmentation metrics (entropy and foreground area density) to data quality and spatial resolution, with cloud cover and sensor artefacts resulting in errors. Surface water classifications must be chosen carefully because sources differ greatly in location and mapped area of surface water. After operationalization of the Belo Monte dam complex, the large reservoirs are notably absent from several of the classifications illustrating land cover. Freshwater ecosystem health is influenced by the land cover surrounding water bodies (e.g., riparian zones). Understanding differences between the many remotely sensed baselines is fundamentally important to avoid information misuse, and to objectively choose the most appropriate classification for ecological studies, conservation, or policy making. The differences between the classifications examined here are not a failure of the technology, but due to different interpretations of ‘forest cover’ and characteristics of the input data (e.g., spatial resolution). Our findings demonstrate the importance of transparency in the generation of remotely sensed classifications and the need for users to familiarize themselves with the characteristics and limitations of each data set.

Relationships between Riparian Forest Fragmentation and Biological Indicators of Streams

Anthropogenic activities, such as land use and land cover modifications in riparian areas, can alter the degree of fragmentation of riparian vegetation, lead to the degradation of stream habitats, and affect biological communities in the streams. The characteristics of the riparian forests can modify the condition of stream environments and the transporting mechanisms of materials, sediments, nutrients, and pollutants loaded from the watersheds. This study aimed to examine the relationships between forest fragmentation and three biological indicators of trophic diatom, benthic macroinvertebrate, and the fish assessment in the Nakdong River, Korea. Eighty-nine biological assessment sampling sites in the National Aquatic Ecological Monitoring Program of South Korea were identified. For each sampling site, riparian forest data within a 500 m radius were extracted from national LULC using GIS to compute fragmentation metrics using FRAGSTATS software. Four fragmentation metrics—number of forest patches, percentage of riparian forest cover (PLAND), largest riparian forest patch index (LPI), and riparian forest division index (DIVISION)—were correlated with the biological indicators. Also, due to severe spatial autocorrelation among observations, the fragmentation metrics and stream environmental variables were regressed to biological indicators using regression tree analysis. Our results indicate that the biological indicators were significantly associated with most forest fragmentation metrics. We found positive correlations of PLAND and LPI with biological indicators, whereas DIVISION was negatively correlated with biological indicators. Both correlation and regression tree analyses revealed that the biological conditions of streams were likely to be better if riparian forests are less fragmented. Particularly, stronger relationships were revealed between macroinvertebrates and fish with the fragmentation metrics of riparian forests than with benthic diatoms. However, these relationships varied with elevation, stream size, and slope conditions. The results of this study reinforced the importance of including riparian forests in the planning, restoration, and management of stream environments. These results also suggested that planners and managers may need to consider different strategies for different stream environments and topographic characteristics in managing riparian forests.

Impact of time on interpretations of forest fragmentation: Three-decades of fragmentation dynamics over Canada

Measures of forest fragmentation, and how fragmentation is changing through time, offer required information for understanding the status and dynamics of forest ecosystems, habitat conditions, and ecosystem functions. In this research, we investigate the multi-temporal characterization of forest fragmentation across the forested ecosystems of Canada (>650 million ha) and characterize the past three decades of forest fragmentation, providing useful context against which future analyses can be compared. Using 33 years of annual land cover maps produced from classified Landsat image best-available pixel composites (1984–2016), we describe and quantify the different forest patterns and dynamics that emerged in areas that were not disturbed in the analysis period, as well as following stand-replacing (i.e., wildfire, harvest) and non-stand-replacing (e.g., insects, water stress) disturbances. Baseline levels of fragmentation for each ecozone were determined by analyzing unchanged areas. Fragmentation dynamics by dominant forest disturbance showed that harvest activities generally lead to an increase in fragmentation related to the amount of forest cover (composition), while wildfires result in increasing fragmentation as a function of the spatial arrangement of the forest. The results presented herein also allow for characterization of the recovery of vegetation spatial patterns following various disturbance types, with areas dominated by fire presenting slower spatial recovery rates compared to harvest. By the end of the analysis period following disturbance events, forest fragmentation metrics in harvest-dominated landscapes were comparable to the pre-harvesting baseline, reaching 96% of mean pre-disturbance levels for mean forest patch size, and 83% for number of forest patches. In contrast, fire-dominated landscapes resulted in more event related fragmentation, with reduced forest cover (mean Thiel Sen slope = −0.13% year−1), mean forest patch size (−0.22 ha year−1), an increase in forest patches (0.11 year−1), and forest–non-forest join counts (0.83 year−1). By the end of the analysis period following disturbance events, mean forest patch size reached 52% of mean pre-disturbance levels and 68% the number of forest patches. Overall, non-stand replacing changes had no impact on the behaviour of the forest fragmentation metrics. The open access to Landsat's image archive combined with the analysis methods presented herein enable the systematic quantification and characterization of Canada-wide trends in forest fragmentation trends and post-disturbance spatial patterns over three decades. The results reported herein provide detailed information on the temporal evolution of spatial forest patterns, and illustrate that given an adequate time period, spatial patterns in areas where land use has not changed, recover to resemble pre-disturbance conditions.

How well does random forest analysis model deforestation and forest fragmentation in the Brazilian Atlantic forest?

We assessed the value of applying random forest analysis (RF) to relating metrics of deforestation (DF) and forest fragmentation (FF) to socioeconomic (SE) and biogeophysical (BGP) factors, in the Brazilian Atlantic Forest of Minas Gerais, Brazil. A vegetation-monitoring project provided land cover maps, from which we derived DF and FF metrics. An ecologic-economical zoning project provided more than 300 SE and BGP factors. We used RF to identify relationships between these sets of variables and compared its performance in this task to that of a more traditional multiple linear regression approach. We found that RF modelled relatively-well variance in all metrics used (the rate of deforestation, the amount of forest and the density and isolation of forest patches), presenting a better performance when compared to the classical approach. RF also identified geographical location and topographic factors as being most closely associated with patterns of DF and FF metrics. Both analyses found factors associated with economic productivity, social institutions, accessibility and exploration to have little relationship with forest metrics. RF was better at explaining variations in rates of deforestation, remaining forest and patch patterns, than the multiple linear regression approach. We conclude that RF provides a promising methodology for elucidating the relationships between land use and cover changes and potential drivers.

Sensitivity of breeding birds to the “human footprint” in western Great Lakes forest landscapes

Breeding birds in forest ecosystems are generally diverse, habitat selective, and easily sampled. Because they must integrate environmental variables over space and time, local populations of forest birds (like other animal and plant taxa) may provide meaningful signals of local forest health or degradation. We evaluated 949 breeding bird surveys in areas ranging from degraded urban/suburban forest remnants to relatively pristine old growth forests in the western Laurentian Great Lakes region of North America. The “human footprint” across this landscape was represented by a one‐dimensional numeric gradient derived from land cover variables, forest fragmentation metrics, and publicly available data on housing density and transportation corridors. We used an iterative, maximum likelihood approach to quantify species‐specific responses to this human disturbance gradient. Many species showed significant directional responses, consistent with known life history attributes. Other species were most commonly detected at intermediate levels of anthropogenic disturbance, yielding unimodal responses. Relationships between the “human footprint” and occurrences of 38 bird species were illustrated by general Gaussian functions that represented both unidirectional and unimodal patterns. These biotic response (BR) functions were combined into a bird‐based index of ecological condition (IEC) ranging from 0 (maximally degraded) to 10 (minimally degraded). We described a successful application of the IEC method at the Wild Rivers Legacy Forest (WRLF), a >260 km2 conservation landscape in northeastern Wisconsin, USA, managed primarily under a working forest conservation easement established in 2006. In general, areas within the WRLF yielded high IEC values (7.0–9.0), but nearby forest areas not under the conservation easement were characterized by significantly lower IEC values based on breeding bird assemblages.

Characterizing fragmentation of the collective forests in southern China from multitemporal Landsat imagery: A case study from Kecheng district of Zhejiang province

Tropical and subtropical forests provide important ecosystem goods and services including carbon sequestration and biodiversity conservation. These forests are facing increasing socioeconomic pressures and are rapidly being degraded and fragmented. This analysis focuses on the rate of change and patterns of fragmentation in a collective forest area in Zhejiang province, China, during the time period 1988–2005. The research consisted of two parts. The first was the development of general land cover maps and the identification of land cover changes by interpreting Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) time series imagery. The second part involved the computation and analysis of forest fragmentation metrics. For this portion of the study, fragmentation statistics were analyzed, and images were developed to depict forest fragmentation patterns and trends. Results revealed that there was a net loss of 7.8% in forest coverage, dropping from 66.8% in 1988 to 59.0% in 2005, primarily caused by agricultural expansion and poor forest management practices. An acceleration of forest fragmentation was also witnessed during the time intervals, which was evidenced by a decreasing trend in interior forest (57.2% in 1988, 55.0% in 1996 and 54.8% in 2005 respectively) coupled with the scales of the selected geospatial metrics. Continued forest loss and fragmentation are closely correlated with the existing political, educational, institutional and economic processes of contemporary China. To unlock the developmental potentials of the collective forests and to effectively mitigate the rate of forest loss and fragmentation, reforms of forest tenure and ecological immigration practices are recognized as a prospective alternative. The produced fragmentation maps further illustrates the importance of assessing landscape change history, especially the spatiotemporal patterns of forest fragments, when developing landscape level plans for biodiversity conservation, land use management and ecologically sustainable forestry.

Landscape characteristics affecting streams in urbanizing regions of the Delaware River Basin (New Jersey, New York, and Pennsylvania, U.S.)

Widespread and increasing urbanization has resulted in the need to assess, monitor, and understand its effects on stream water quality. Identifying relations between stream ecological condition and urban intensity indicators such as impervious surface provides important, but insufficient information to effectively address planning and management needs in such areas. In this study we investigate those specific landscape metrics which are functionally linked to indicators of stream ecological condition, and in particular, identify those characteristics that exacerbate or mitigate changes in ecological condition over and above impervious surface. The approach used addresses challenges associated with redundancy of landscape metrics, and links landscape pattern and composition to an indicator of stream ecological condition across a broad area of the eastern United States. Macroinvertebrate samples were collected during 2000–2001 from forty-two sites in the Delaware River Basin, and landscape data of high spatial and thematic resolution were obtained from photointerpretation of 1999 imagery. An ordination-derived ‘biotic score’ was positively correlated with assemblage tolerance, and with urban-related chemical characteristics such as chloride concentration and an index of potential pesticide toxicity. Impervious surface explained 56% of the variation in biotic score, but the variation explained increased to as high as 83% with the incorporation of a second land use, cover, or configuration metric at catchment or riparian scales. These include land use class-specific cover metrics such as percent of urban land with tree cover, forest fragmentation metrics such as aggregation index, riparian metrics such as percent tree cover, and metrics related to urban aggregation. Study results indicate that these metrics will be important to monitor in urbanizing areas in addition to impervious surface.

Forest fragmentation, structure, and age characteristics as a legacy of forest management

The combination of forest inventory and satellite-derived landscape composition and structure provides otherwise unavailable information on regional forest conditions and enables investigation of the cumulative effects of forest management over time. Forest pattern results from a range of both natural and anthropogenic factors. This study characterizes the forest pattern of Vancouver Island, British Columbia (>32,000 km 2) at the watershed scale, using new national datasets of Canadian forest composition and fragmentation, and relating these to forest inventory-derived age structure. Vancouver Island is extensively forested, possessing highly valuable and productive forests, and is managed to meet a range of stakeholder interests. Forest fragmentation metrics were derived from a satellite-derived, 25-m spatial resolution land cover map (i.e., grain) to represent patterns within 1 km analysis units (i.e., extent) for the entire forested area of Canada. We summarized forest fragmentation island-wide and compared trends between forest-dominated (>85% forest) and less-forested (<85% forest) watersheds. We also explored these patterns with partial canonical correspondence analyses to determine the independent and shared relationships of landscape composition, forest fragmentation, and spatial variables with forest age structure. Less-forested watersheds are more fragmented than forest-dominated watersheds, as indicated by more (5.6 versus 2.7 per km 2) and smaller (36 versus 63 ha) forest patches, and a greater edge density (82 versus 55 m/ha). Of the 1283 watersheds examined, 91% were forest-dominated; island-wide trends are thus similar to those of the forest-dominated watersheds. Forest age is related to landscape composition and forest fragmentation, which collectively explain 27% and 53% of the age structure of all and less-forested watersheds, respectively. In both sets of watersheds, young forest stands (1–120 years) are associated with broadleaf forests, agreeing with successional expectations, and patchy forest distributions. For all watersheds, old growth forest stands (>240 years) are associated with dense coniferous forest, but also with early successional communities, smaller patch sizes, and greater edge densities, indicating fragmentation of these forests and reflecting strategies for managing old growth on the landscape. In contrast, watersheds with an abundance of mature forest (121–240 years) are compositionally similar to watersheds with old growth, but are much less fragmented. Our results indicate that although old growth forest stands on Vancouver Island have been retained, they are not typically found within a continuous forest matrix. Medium spatial resolution Earth observation products are now available for the entire forested area of Canada, providing valuable insight into spatial and temporal forest dynamics (i.e., succession, harvesting).

Characterizing the forest fragmentation of Canada’s national parks

Characterizing the amount and configuration of forests can provide insights into habitat quality, biodiversity, and land use. The establishment of protected areas can be a mechanism for maintaining large, contiguous areas of forests, and the loss and fragmentation of forest habitat is a potential threat to Canada's national park system. Using the Earth Observation for Sustainable Development of Forests (EOSD) land cover product (EOSD LC 2000), we characterize the circa 2000 forest patterns in 26 of Canada's national parks and compare these to forest patterns in the ecological units surrounding these parks, referred to as the greater park ecosystem (GPE). Five landscape pattern metrics were analyzed: number of forest patches, mean forest patch size (hectare), standard deviation of forest patch size (hectare), mean forest patch perimeter-to-area ratio (meters per hectare), and edge density of forest patches (meters per hectare). An assumption is often made that forests within park boundaries are less fragmented than the surrounding GPE, as indicated by fewer forest patches, a larger mean forest patch size, less variability in forest patch size, a lower perimeter-to-area ratio, and lower forest edge density. Of the 26 national parks we analyzed, 58% had significantly fewer patches, 46% had a significantly larger mean forest patch size (23% were not significantly different), and 46% had a significantly smaller standard deviation of forest patch size (31% were not significantly different), relative to their GPEs. For forest patch perimeter-to-area ratio and forest edge density, equal proportions of parks had values that were significantly larger or smaller than their respective GPEs and no clear trend emerged. In summary, all the national parks we analyzed, with the exception of the Georgian Bay Islands, were found to be significantly different from their corresponding GPE for at least one of the five metrics assessed, and 50% of the 26 parks were significantly different from their respective GPEs for all of the metrics assessed. The EOSD LC 2000 provides a heretofore unavailable dataset for characterizing broad trends in forest fragmentation in Canada's national parks and in their surrounding GPEs. The interpretation of forest fragmentation metrics must be guided by the underlying land cover context, as many forested ecosystems in Canada are naturally fragmented due to wetlands and topography. Furthermore, interpretation must also consider the management context, as some parks are designed to preserve fragmented habitats. An analysis of forest pattern such as that described herein provides a baseline, from which changes in fragmentation patterns over time could be monitored, enabled by earth observation data.

Estimating Error in an Analysis of Forest Fragmentation Change Using North American Landscape Characterization (NALC) Data

We describe an approach for estimating measurement error in an analysis of forest fragmentation dynamics. We classified North American Landscape Characterization (NALC) images in four path-row locations in the Upper Midwest to characterize changing patterns of forest cover. To estimate error, we calculated the differences in values of forest fragmentation metrics for overlapping scene pairs from the same time frame (or epoch). The overlapping image areas were subdivided into landscape partitions. We tested the effects of amount of forest cover, landscape phenology, atmospheric variability (e.g., haze and clouds), and alternative processing approaches on the consistency of metric values calculated for the same place and approximate time but from different images. Two of the metrics tested (average patch size and number of patches) were more sensitive to image characteristics and contained more measurement error in a change detection analysis than the others (percent forest cover and edge density). Increasing the landscape partition size moderately reduced the amount of error in landscape change analysis, but at the cost of reduced spatial resolution. Processes used to generalize the forest map, such as small-polygon sieving and majority filtering, were not found to consistently decrease measurement error in metric values and in some cases increased error. Predictive models of error in a forest fragmentation change analysis were developed and significantly explained up to 50% of the variation in error. We demonstrate how, in a change analysis, predicted error can be used to identify locations that exhibit change substantially greater than the error in value estimation.