Abstract
Urban ecosystem assessments increasingly rely on widely available map products, such as the U.S. Geological Service (USGS) National Land Cover Database (NLCD), and datasets that use generic classification schemes to detect and model large-scale impacts of land-cover change. However, utilizing existing map products or schemes without identifying relevant urban class types such as semi-natural, yet managed land areas that account for differences in ecological functions due to their pervious surfaces may severely constrain assessments. To address this gap, we introduce the managed clearings land-cover type–semi-natural, vegetated land surfaces with varying degrees of management practices–for urbanizing landscapes. We explore the extent to which managed clearings are common and spatially distributed in three rapidly urbanizing areas of the Charlanta megaregion, USA. We visually interpreted and mapped fine-scale land cover with special attention to managed clearings using 2012 U.S. Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) images within 150 randomly selected 1-km2 blocks in the cities of Atlanta, Charlotte, and Raleigh, and compared our maps with National Land Cover Database (NLCD) data. We estimated the abundance of managed clearings relative to other land use and land cover types, and the proportion of land-cover types in the NLCD that are similar to managed clearings. Our study reveals that managed clearings are the most common land cover type in these cities, covering 28% of the total sampled land area– 6.2% higher than the total area of impervious surfaces. Managed clearings, when combined with forest cover, constitutes 69% of pervious surfaces in the sampled region. We observed variability in area estimates of managed clearings between the NAIP-derived and NLCD data. This suggests using high-resolution remote sensing imagery (e.g., NAIP) instead of modifying NLCD data for improved representation of spatial heterogeneity and mapping of managed clearings in urbanizing landscapes. Our findings also demonstrate the need to more carefully consider managed clearings and their critical ecological functions in landscape- to regional-scale studies of urbanizing ecosystems.
Highlights
Studies of human-modified ecosystems often rely on existing land use and land cover (LULC) products, such as the U.S Geological Survey (USGS) National Land Cover Database (NLCD) [1, 2], or datasets that were produced using generic LULC classification schemes [3]
Utilizing existing products or schemes are useful for many science questions related to land change, but general-purpose LULC schemes may fail to adequately represent ecological functions that are important for particular studies, and/or may altogether omit important classes
We addressed the following research questions: How abundant are managed clearings relative to other land-cover types, and how does the area of managed clearings differ between metropolitan areas? How do recreational, transportation, and public utility services in managed clearings differ in areal proportion? we compared our managed clearing mapping outcomes with NLCD data for addressing the following questions: Can we modify the NLCD data to accurately represent the amount of managed clearings in urbanizing landscapes, and if yes, how does the proportion of manually interpreted National Agriculture Imagery Program (NAIP)-derived managed clearings compare to the NLCD’s developed land-cover types?
Summary
Studies of human-modified ecosystems often rely on existing land use and land cover (LULC) products, such as the U.S Geological Survey (USGS) National Land Cover Database (NLCD) [1, 2], or datasets that were produced using generic LULC classification schemes [3]. Utilizing existing products or schemes are useful for many science questions related to land change, but general-purpose LULC schemes may fail to adequately represent ecological functions that are important for particular studies, and/or may altogether omit important classes. Land uses such as road right-of-ways and utility lines that are pervious, yet regularly managed by mechanical clearing and herbicide applications, are often labeled as ‘developed’ in many classification schemes. LULC data without meaningful land cover types that differentiate ecological functions may imperil our efforts to achieve realism in urban ecosystems studies. Our present understanding of managed clearings is insufficient and represents an under-explored opportunity that could benefit realistic assessments of urbanizing ecosystems
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