Dynamics of land use/cover changes and the analysis of landscape fragmentation in Dhaka Metropolitan, Bangladesh

Abstract

Rapid urban expansion due to large scale land use/cover change, particularly in developing countries becomes a matter of concern since urbanization drives environmental change at multiple scales. Dhaka, the capital of Bangladesh, has been experienced break-neck urban growth in the last few decades that resulted many adverse impacts on the environment. This paper was an attempt to document spatiotemporal pattern of land use/cover changes, and to quantify the landscape structures in Dhaka Metropolitan of Bangladesh. Using multi-temporal remotely sensed data with GIS, dynamics of land use/cover changes was evaluated and a transition matrix was computed to understand the rate and pattern of land use/cover change. Derived land use statistics subsequently integrated with landscape metrics to determine the impact of land use change on landscape fragmentation. Significant changes in land use/cover were noticed in Dhaka over the study period, 1975-2005. Rapid urbanization was manifested by a large reduction of agricultural land since urban built-up area increased from 5,500 ha in 1975 to 20,549 ha in 2005. At the same time, cultivated land decreased from 12,040 to 6,236 ha in the same period. Likewise, wetland and vegetation cover reduced to about 6,027 and 2,812 ha, respectively. Consequently, sharp changes in landscape pattern and composition were observed. The landscape became highly fragmented as a result of rapid increase in the built-up areas. The analysis revealed that mean patch size decreased while the number of patches increased. Landscape diversity declined, urban dominance amplified, and the overall landscape mosaics became more continuous, homogenous and clumped. In order to devise sustainable land use planning and to determine future landscape changes for sound resource management strategies, the present study is expected to have significant implications in rapidly urbanizing cities of the world in delivering baseline information about long term land use change and its impact on landscape structure.

Impacts on the Urban Environment: Land Cover Change Trajectories and Landscape Fragmentation in Post-War Western Area, Sierra Leone

“…The decrease in the LPI and PLAND metrics for forest cover is not surprising because bare land and UPA increased at the expense of natural vegetation (Figure 8). Results from the two dominance indices (LPI and PLAND) at the class level are congruent with Dewan et al's [44] argument that a positive correlation exists between increased human activities and dominance indices. The fragmentation and aggregation indices also support earlier research, which hypothesised that an increase in fragmentation will happen in areas of human habitation because of uncontrolled exploitation of forest resources, especially in settlements triggered by war [11].…”

“…A collection of classes makes up the landscape. Several studies have explored fragmentation at these scales [22,39,[44][45][46]. Exploring the relationship between LULCC, the drivers of change, and the ecological implications of such changes, Kabba and Li [45] concluded that fragmentation at the class and landscape scales in Wuhan, China was greatest in 1987-1994 but weakened in 1994-2005, leading first to species loss in the fragmented areas followed by a return of species as fragmented habitat areas re-aggregated.…”

“…Therefore, we excluded the 1976 and 2006 images from this portion of the analysis. Earlier research recommends the use of fragmentation metrics that depict distinct and meaningful fragmentation features rather than utilising metrics that are statistically redundant [3,41,44,61]. Given the complex nature of landscape disaggregation into isolated patches, several scholars have argued that a single parameter is insufficient to describe the trend and magnitude of landscape disaggregation [22,44,62].…”

“…Earlier research recommends the use of fragmentation metrics that depict distinct and meaningful fragmentation features rather than utilising metrics that are statistically redundant [3,41,44,61]. Given the complex nature of landscape disaggregation into isolated patches, several scholars have argued that a single parameter is insufficient to describe the trend and magnitude of landscape disaggregation [22,44,62]. The selected metrics for this research satisfied two criteria: they measured different parameters of the landscape (i.e., are not statistically redundant) and they are known to have played a significant role in understanding landscape fragmentation from research using data sets similar to those used in this research [44,45].…”

“…Given the complex nature of landscape disaggregation into isolated patches, several scholars have argued that a single parameter is insufficient to describe the trend and magnitude of landscape disaggregation [22,44,62]. The selected metrics for this research satisfied two criteria: they measured different parameters of the landscape (i.e., are not statistically redundant) and they are known to have played a significant role in understanding landscape fragmentation from research using data sets similar to those used in this research [44,45]. The metrics we used include number of patches (NumP), percentage of landscape (PLAND), largest patches index (LPI), landscape shape index (LSI), interspersion and juxtaposition index (IJI), contagion index (CONTAG), and Simpson's and Shannon' Diversity Indices (SDI & SHDI) [see 60 for definition and description of these metrics].…”