Abstract
Meta-analysis of case studies has become an important tool for synthesizing case study findings in land change. Meta-analyses of deforestation, urbanization, desertification and change in shifting cultivation systems have been published. This present study adds to this literature, with an analysis of the proximate causes and underlying forces of wetland conversion at a global scale using two complementary approaches of systematic review. Firstly, a meta-analysis of 105 case-study papers describing wetland conversion was performed, showing that different combinations of multiple-factor proximate causes, and underlying forces, drive wetland conversion. Agricultural development has been the main proximate cause of wetland conversion, and economic growth and population density are the most frequently identified underlying forces. Secondly, to add a more quantitative component to the study, a logistic meta-regression analysis was performed to estimate the likelihood of wetland conversion worldwide, using globally-consistent biophysical and socioeconomic location factor maps. Significant factors explaining wetland conversion, in order of importance, are market influence, total wetland area (lower conversion probability), mean annual temperature and cropland or built-up area. The regression analyses results support the outcomes of the meta-analysis of the processes of conversion mentioned in the individual case studies. In other meta-analyses of land change, similar factors (e.g., agricultural development, population growth, market/economic factors) are also identified as important causes of various types of land change (e.g., deforestation, desertification). Meta-analysis helps to identify commonalities across the various local case studies and identify which variables may lead to individual cases to behave differently. The meta-regression provides maps indicating the likelihood of wetland conversion worldwide based on the location factors that have determined historic conversions.
Highlights
Wetland loss and degradation occur worldwide, sometimes at extremely high rates [1]
105 case studies were found for which proximate causes and underlying driving forces of wetland conversion could be traced (Figure 1; for a full list and documentation of cases see Information S3)
This study applies the method of Geist and Lambin ([11,13]) to study conversion of wetlands at the global scale, making it comparable with meta-studies of other land use changes
Summary
Wetland loss and degradation occur worldwide, sometimes at extremely high rates [1]. Estimated wetland loss in different parts of Canada ranges between 65% and 80% [3]. Frequently-cited anthropogenic causes of wetland loss and degradation, include drainage for crop production and plantations, wetland conversion for fish production, conversion for logging, peat extraction, construction of canals, dykes, dams and levees, and commercial, residential and industrial developments, e.g., [1,2,4]. Underlying drivers of wetland loss are socio-economic and political factors, such as population growth and financial policies [1]. Most studies reporting wetland conversion are conducted for single locations. A more comprehensive analysis of the most important drivers of wetland conversion at a global scale is currently lacking
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