The southern megalopolis: using the past to predict the future of urban sprawl in the Southeast U.S.

The future health of ecosystems is arguably as dependent on urban sprawl as it is on human-caused climatic warming. Urban sprawl strongly impacts the urban ecosystems it creates and the natural and agro-ecosystems that it displaces and fragments. Here, we project urban sprawl changes for the next 50 years for the fast-growing Southeast U.S. Previous studies have focused on modeling population density, but the urban extent is arguably as important as population density per se in terms of its ecological and conservation impacts. We develop simulations using the SLEUTH urban growth model that complement population-driven models but focus on spatial pattern and extent. To better capture the reach of low-density suburban development, we extend the capabilities of SLEUTH by incorporating street-network information. Our simulations point to a future in which the extent of urbanization in the Southeast is projected to increase by 101% to 192%. Our results highlight areas where ecosystem fragmentation is likely, and serve as a benchmark to explore the challenging tradeoffs between ecosystem health, economic growth and cultural desires

Examples of SLEUTH model output.

<p>Individual fifty-year model simulations (2010–2060) along with the final projection based on 200 Monte Carlo simulations for two fast-growing regions: Walton County in Georgia (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102261#pone-0102261-g004" target="_blank">Figure 4a and 4b</a>) and Wake County in North Carolina (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102261#pone-0102261-g004" target="_blank">Figure 4c and 4d</a>). Red cells in (a) and (c) correspond to new urban growth and gold cells depict 2009 classified urban areas. Cell colors in (b) and (d) are the same as color legend in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102261#pone-0102261-g001" target="_blank">Figure 1</a>.</p

Business-as-usual urbanization scenario for the Southeast US.

<p>The Southeast US region used in this study. (a) EPA Level III ecoregions and initial urban extent. The 309 sub-regions (CSAs and rural county groups) used to calibrate the SLEUTH model are outlined in black. Red areas are urban extent as classified by our hybrid NLCD-TIGER dataset method (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102261#pone.0102261.s003" target="_blank">File S1</a>). (b) Initial urban land cover in 2009. (c) projected urban land cover in 2060. (d) projected urban land cover in Piedmont ecoregion, showing connected urban landscape.</p

Land cover change metrics.

<p>(a) and (b) show time series of projected urbanization for 200 model simulations for the study region and twelve ecoregions, respectively. (c) The 95% projected range of the proportion of each land cover type converted to urban. (d) Change in patch metrics for all land cover types between 2009 and 2060. Ecoregion abbreviations in (b) are as follows: BR – Blue Ridge, CA – Central Appalachians, IP – Interior Plateau, MACP – Mid Atlantic Coastal Plain, MAP – Mississippi Alluvial Plain, MVLP – Miss. Valley Loess Plains, P – Piedmont, RV – Ridge and Valley, SP – Southeastern Plains, SCP – Southern Coastal Plains, SFC – South Florida Coastal Plain, SA – Southwest Appalachian.</p

Urban sprawl examples and their representation in the input data.

<p>Imagery in (a) and (b) document the rapid but low-density urbanization common in the Southeast US (imagery for Raleigh, NC in 1993 and 2010). (c) Road network used as basis for identifying urban areas (same area as in (a) and (b)). (d) Initial (2009) urban classification (pink shade) based on road network density and NLCD urban classification (red shade).</p

The high hydraulic conductivity of three wooded tropical peat swamps in northeast Peru: measurements and implications for hydrological function

The form and functioning of peatlands depend strongly on their hydrological status, but there are few data available on the hydraulic properties of tropical peatlands. In particular, the saturated hydraulic conductivity (K) has not previously been measured in neotropical peatlands. Piezometer slug tests were used to measure K at two depths (50 and 90 cm) in three contrasting forested peatlands in the Peruvian Amazon: Quistococha, San Jorge and Buena Vista. Measured K at 50 cm depth varies between 0.00032 and 0.11 cm s 1, and at 90 cm, it varies between 0.00027 and 0.057 cm s 1. Measurements of K taken from different areas of Quistococha showed that spatial heterogeneity accounts for ~20% of the within-site variance and that depth is a good predictor of K. However, K did not vary significantly with depth at Buena Vista and San Jorge. Statistical analysis showed that ~18% of the variance in the K data can be explained by between-site differences. Simulations using a simple hydrological model suggest that the relatively high K values could lead to lowering of the water table by >10 cm within ~48m of the peatland edge for domed peatlands, if subjected to a drought lasting 30 days. However, under current climatic conditions, even with high K, peatlands would be unable to shed the large amount of water entering the system via rainfall through subsurface flow alone. We conclude that most of the water leaves these peatlands via overland flow and/or evapotranspiration