State and trends
Fragmentation at the wildland-urban interface
One driver of habitat fragmentation in North America is the expansion of settled areas. From 1945 to 2007, the US population nearly doubled, but the urban land area increased at almost twice the rate of population growth (Nickerson et al. 2011). Between 1940 and 2000, 28 million housing units were built within 50 km of protected areas; 940 000 units were built within national forests (Radeloff et al. 2010). Much of this growth occurred where housing is now dense enough and close enough to wildlands – forests, grasslands, shrub lands, and wetlands – to have ecological consequences. This phenomenon is known as the wildland- urban interface (WUI) (Martinuzzi et al. 2015).
As of 2010, the WUI of the conterminous US included about 44 million houses, equivalent to one in every three houses in the country (Martinuzzi et al. 2015). Not only are the likelihood of wildfires and damage higher in the WUI (Syphard et al. 2009), the WUI also has more invasive alien plants (Gavier- Pizarro et al. 2010), more pets that disturb or prey on wildlife (Lepczyk et al. 2004), and lower quality water in streams due to contaminated storm water from pavements and lawns (Brabec et al. 2002). The increased reliance on septic tanks for waste treatment in the WUI can pose risks for groundwater contamination over time. Radeloff et al. (2010) noted that if long-term trends continue, another 17 million housing units will be built within 50 km of protected areas by 2030; 1 million within 1 km, greatly diminishing their conservation value. They concluded that housing growth poses the main threat to protected areas in the United States whereas deforestation is the main threat in developing countries. Therefore, analyzing where WUI occurs and related trends over time can shed light on the location and intensity of the consequences of development for natural resources and impacts on intactness of ecosystems and subsequent threats to sustainable provision of ecosystem services.
As urban centers grow, so do suburban and peri-urban areas. Land and housing prices rise as development intensifies, prompting real estate developers and middle-class home owners to buy further out where land prices are lower and
homes are more affordable. This development pattern requires more physical infrastructure and expanded social infrastructure, all of which disrupt intactness of natural landscapes and affect wildlife populations. Rural settings, including woodlands, are also scenic and many people prefer them over urban centers as places to live, raise families and spend their leisure time. These lifestyle preferences also influence WUI expansion.
Whether economic or social preferences are the drivers, expanded development in rural settings has an impact. One of the primary set of consequences arises from roadbuilding and expansion of shopping centers. Roads and parking lots fragment intact natural ecosystems. Their impervious surfaces create storm water runoff, often contaminated with oily residues, and require drainage structures to conduct the water into roadside ecosystems and streams. In colder climates, icy and snowy roads are often treated with chemicals which also wind up in roadside ecosystems. Adjoining utility corridors provide overhead wires where birds commonly perch and defecate, spreading seeds of weeds and other species alien to the natural area. Deer- vehicle collisions have risen 50 per cent over the past several decades as urban sprawl has encroached further into deer country (Huijser 2008). In 2000, there were over one million collisions reported in North America between vehicles and deer. Insurance experts believe that the reported collisions are perhaps only 25 – 35 per cent of the actual total. In 2000, these reported collisions caused 225 human fatalities, over 10 000 personal injuries, and over USD 1 billion in property damage.
Federal, provincial and state governments,
insurance companies, and drivers spend over USD 3 billion annually to reduce or manage the increasing number of deer-vehicle collisions. Beyond deer collisions, there are innumerable collisions with smaller animals.
Beyond the ecological consequences caused by roadways and utility corridors, there are other impacts. For example, public utilities and social services, such as schools, are costlier to provide in low-density development settings (Kramer 2013). In 2007, Baltimore County, Maryland issued the first- of-its-kind county-level “State of Our Forests” report (Outen
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