Distribution of forest ecosystems over two centuries in a highly urbanized landscape

Urban development often results in diminished forest cover and severely fragmented landscapes, but most research on effects of urban development has been focused on densely forested regions and has not distinguished remnant from recently established forest cover. Urban development may have different effects in heterogeneous landscapes with high pre-urban fragmentation. Our study investigated spatial and temporal distribution of remnant forest ecosystems across a large urban landscape to assess effects of landscape structure and development patterns on forest conversion. Forest ecosystem distribution within the greater Chicago region (18,822 km2) was mapped in three time periods using Public Land Survey records (1830′s) and aerial imagery (1939 and 2010). Loss of original forest between sampling periods (conversion) was related to landscape features, land use, and sociodemographic factors. In 2010 ∼17% of pre-urban forest area remained, which represented ∼40% reduction relative to 1939. Conversion did not differ greatly with urbanization, but fragmentation was greater in areas with high population density and rapid population growth. Conversion was lower in areas close to waterways, where there was less impervious surface, and also differed among land uses (highest in agricultural and industrial). Remnant forests had higher canopy cover, basal area, and native species dominance than recently established forests. Urbanization may have lower relative effects on total forest cover in naturally fragmented landscapes, but may result in extreme fragmentation. Remnant forests had characteristics consistent with high functional value, but creating connectivity among ecosystems in highly urbanized areas will require promotion of canopy cover in urban land uses.