Wilderness housing boom challenges conservation

The housing boom may be over in the United States, but things look very different when you take a step back. Since the 1940s, housing has grown at about 20 percent each decade. And while the current recession may have slowed things down, we’ll have to start building more houses eventually if we’re to house the 120 million more people by 2050. The decades-long housing boom magnifies in intensity when you start looking around national parks, wilderness areas, and national forests, as a recent paper in the Proceedings of the National Academy of Science did. While there were just 14.9 million housing units within 50 kilometers of a protected area in 1940, there were 61.9 million units in that same buffer by 2000. And not only have the raw numbers increased, so too has their share of all American housing.

It’s no surprise that people want to live near parks. Clean air, open space, and gorgeous scenery draw people in as tourists and bring them back as prospective property buyers. Retiring Baby Boomers, freed of their work commitments, have been particularly drawn to the borders of national parks, forests, and wilderness areas. Even working-age people—many willing to suffer through a long commute to live near natural beauty—have gravitated towards protected areas.

None of this would be a big problem if we didn’t mind clustering our houses together, limiting our impact on the land around us. But the reality is no one moves to the country to live in an apartment building. People buy a handful of acres, erect a house a good distance from the road, and string in a long driveway.

Though it’s tempting to think the environmental impacts of a house stop when grass gives way to trees, the reality is that houses cast a shadow far larger than their physical footprint. Roads, utility lines, and driveways dice up the landscape. This fragmentation reduces species’ ability to travel out of the now-noosed protected areas, trapping them in reserves that may not fulfill their needs. Houses also bring hordes of exotic plants and animals, including pets, which often prey on native fauna. All of these factors—and more—create disturbances that can affect protected areas, though they may be miles away.

The authors of the study cite a few examples of how wilderness housing has already changed the habitat in and around protected areas. In the east, the Great Smoky Mountains National Park is choked with pollution. In Colorado, the number of visitors to the Mount Evans Wilderness Area has increased so much that the Forest Service now requires permits. Wildfires in Cleveland National Forest near San Diego, most of which are set by humans, have skyrocketed in number, pushing out the native coastal sage scrub and ushering in exotic grasses. In Michigan, houses peppered within the boundaries of Huron-Manistee National Forest have led to the suppression of wildfires, which has depressed reproduction of the fire-dependent Jack Pine, which has hurt populations of the Jack Pine-dependent Kirtland’s warbler.

The surge in housing near protected areas seems poised to continue apace through at least 2030. The authors of the PNAS study forecast that 17 million additional housing units will be erected within 50 kilometers of protected areas. For those of us who love to live near wilderness—myself included—this news is bittersweet. The good part is that there will be plenty of places for me to live, if I choose to move there. The bad is that nature-lovers like myself run the risk of damaging that which we admire. But not all is lost. The paper’s authors offer a few suggestions as to how we can minimize our footprint. (Really, these are suggestions that we should all follow, whether we live in the city or the country.) Push for zoning laws that clump houses closer together, leaving more open space in tact. Site and build your house with your surroundings in mind. Landscape with native plants. Keep your pets from running rampant. Don’t fertilize too much. Turn off your outside lights, and keep the noise down. And one more (this one’s mine)—keep your lawn small.

Source:

Radeloff, V., Stewart, S., Hawbaker, T., Gimmi, U., Pidgeon, A., Flather, C., Hammer, R., & Helmers, D. (2009). Housing growth in and near United States protected areas limits their conservation value Proceedings of the National Academy of Sciences, 107 (2), 940-945 DOI: 10.1073/pnas.0911131107

Photo by Kara Allyson.

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Animals seek calm seas in oceans of human influence

Habitat loss can be like death by a thousand cuts for ecosystems. Each conversion to farmland, housing, or pasture, when taken on its own, may seem a small, inconsequential nick on the surface of a vast planet. But together, and over decades and centuries, these cuts add up, leaving only tiny remnants of the original scattered across the landscape. The result can be devastating for animals and plants which depend on the original ecosystem. Yet unlike the grisly metaphor drawn from an ancient Chinese torture, the wounds of habitat loss are not entirely fatal. Farms and subdivisions may not supplant virgin forest or grasslands, but they need not be inhospitable wastelands, either.

The field of ecology typically focuses on the leftovers of habitat conversion—the bits and pieces that somehow evaded plows and bulldozers. But just as no island is truly separated from the rest of the world, habitat remnants remain connected by the fields and yards that constitute the interstitial spaces. Known as “the matrix,” such spaces are important to the continued vitality of habitat fragments. In fact, according to new research out of Australia, the qualities of the matrix may matter more to the survival of native animal species than characteristics of the remnants themselves.

The matrix in the study are primarily cattle stations prevalent in the Toowoomba Regional Shire in southern Queensland. The area has been grazed heavily since the early 1900s, and pastoral uses are still the predominant land use, though urban development has been increasing in recent years. To quantify the amount of human influence within the matrix, the researchers measured a host of variables, mostly pertaining to roads and ranging from length to width to driving surface and even road kill statistics. They also closely studied the forest patches within the matrix and surveyed their resident mammal populations.

Many previous studies have focused on remnants’ size, shape, and geographic relationship to one another. This study did that, too, but also investigated the matrix itself. Of all possible landscape characteristics, the intensity of human development and number of tall trees within the matrix exerted more influence than any other.

To see how the matrix plays a role in this case, imagine you’re part of a group of people who are stranded on one of those islands, and your island doesn’t have everything you need to survive. Other islands do, though, so you’d need to set sail from time to time, just as the animals in the forest remnants may have to cross a pasture or pass through a neighborhood. The island metaphor is often used to describe how habitat remnants and their inhabitants interact with each other. Typically, people wax lyrical about the size, shape, and distance separating the islands. In this case, however, its not just the span of open water between the islands that matters, but the qualities of that water.
Neither the sea nor the matrix are absolute barriers, but they aren’t entirely hospitable, either.

Now let’s say you had a choice of islands on which to be stranded. Which would you pick? Quite obviously you’d prefer an island close to the mainland, but let’s say that’s out of the question. In lieu of that, you’d probably pick one that’s surrounded by calm seas so that exploring nearby islands would be infinitely easier. Some shallow waters between islands might be nice, too, to anchor your boat when you needed to take a rest. And if I were you, I’d also go for one with a bit of elevation to avoid high tides or tsunamis.

If those three wishes were granted, you’d probably have a good chance of living to a ripe old age. Conveniently, those wishes mirror what mammals in the Toowoomba study seemed to prefer, too. The researchers found fewer mammals traversing heavily developed areas—analogous to rough seas—and more where tall trees provided cover from predators—calm seas. The animals also favored a matrix with more nooks to roost or hide as they travelled—similar to shallow water for anchorage. Finally, the best remnants were those where human activities didn’t encroach too often—akin to higher elevation islands that guard against tides and tsunamis.

As a stranded soul, you wouldn’t have much influence over the ocean. But as stewards of the matrix, we decide its flora, its structure, and its ease of passage for animals. The biggest difference we can make is in reducing our developed footprint. The changes don’t have to be as drastic as ripping up subdivisions or farms. They could be as simple as carving roads only where they are most needed or avoiding areas where animals frequently tread. And failing that, plant trees.

Sources:

Brady, M., McAlpine, C., Miller, C., Possingham, H., & Baxter, G. (2009). Habitat attributes of landscape mosaics along a gradient of matrix development intensity: matrix management matters Landscape Ecology, 24 (7), 879-891 DOI: 10.1007/s10980-009-9372-6

Brady, M., McAlpine, C., Possingham, H., Miller, C., & Baxter, G. (2011). Matrix is important for mammals in landscapes with small amounts of native forest habitat Landscape Ecology DOI: 10.1007/s10980-011-9602-6

Photo by Shaun Johnston.

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Plants rockin’ the suburbs, animals not so much

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Plants rockin’ the suburbs, animals not so much

Where there are more people, there’s less nature. It’s a fairly well established fact. Manhattan may have the odd hawk or falcon, but the paved island’s diversity of plants and animals just can’t compare to that of 23 square miles of pristine wilderness. What’s less known is how well biodiversity fares in human landscapes that are somewhere between the Empire State Building and Daniel Boone’s back forty.

Many scientific papers have been written about how specific types of plants and animals fare in the countryside, the city, and places in between, but few summarize the big picture. One review paper did take a wider view and surveyed 105 studies. It found that though most types of animals avoid the city, plant life seems perfectly happy living the suburban dream.

Animals, specifically mammals, reptiles, and amphibians,¹ dropped precipitously in most studies as researchers moved from the countryside to the city. In the first transition—from the countryside to the suburbs—only three studies found the same or greater numbers of mammal, reptile, and amphibian species, while 14 studies reported fewer. Invertebrate diversity rose in 14 studies, but fell in 30 others and remained the same in only three reports. These negative trends were magnified in the transition between the suburbs and the city proper. All but one study reported the same or fewer numbers of species of invertebrates in the big city as in the suburbs. As the researchers moved into the city and human population density increased, they found fewer mammal, reptile, and amphibian species.

Loss of habitat is probably behind this steady decline. Larger animals like mammals, reptiles, and amphibians need relatively large plots of land to survive. Invertebrates like insects are better off in human-dominated areas because of their smaller size—even a single tree can support dozens of different insects.

Amidst the gloom, plants were the one bright spot. In the suburb-city transition, plant diversity advanced in seven studies and retreated in seven others. It thrived when moving from the countryside to the suburbs. Plants’ success is probably due to their negligible requirements. Many only require a bit of soil, some water, and moderately clean air. On top of that, people often lend plants a helping hand by planting, watering, and fertilizing them. And while a home may have a cat and a dog, many sport dozens of different flowers, trees, and shrubs in their garden. Suburban lots are both large enough to encourage gardens yet small enough for people to support more diversity than on sprawling country lots. Even different landscaping preferences between different households fosters higher diversity.

Suburban plant diversity, though, probably comes at the expense of native flora. Most yards are beautified with species exotic to the area. Many are chosen simply based on their appearance or low maintenance. Native gardens are becoming more popular, but their numbers still pale in comparison to more traditional yards. It’s my suspicion that non-native landscaping holds down the diversity of mammals, reptiles, amphibians, and invertebrates. Native plantings would probably aid native animals, helping to offset some of the land taken by development.

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¹ This review did not include birds—there are so many studies of birds in cities that it would be another paper in and of itself.↩

McKinney, M. (2008). Effects of urbanization on species richness: A review of plants and animals Urban Ecosystems, 11 (2), 161-176 DOI: 10.1007/s11252-007-0045-4

Photo by pluckytree.

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“What if” development ran rampant in Silicon Valley?

Silicon Valley exploded in every way possible following World War II, well before it was known as Silicon Valley. The population boomed, houses were thrown up, and roads slithered out from the peninsula’s main drag, the El Camino Real. But as the strip malls started to take over, locals set about preserving much of the open space that remained.

Throughout the Bay Area, over 1,500 square miles have been protected from development. Some sprawl advocates such as Robert Bruegmann have suggested the sheer volume of protected land within the Bay Area has forced suburbs far into California’s Central Valley, and that the land closer to the city centers would be better used for housing. Silicon Valley itself holds a not-insignificant 181 square miles of the Bay Area’s protected land. Detractors claim the open space has hemmed in development too much, forcing additional housing elsewhere, increasing commute times, and reducing the amount of affordable housing in the Valley.

Even Apple engineers were enamored with the golden hills that surround Silicon Valley.

Such criticism can be difficult to deflect without ripping up woodlands and grasslands, so a group of geographers set about asking “what if” the protected land in Silicon Valley were open to development. They created a series of maps to predict where and how much development would take place by analyzing six characteristics—slope of the terrain, presence of wetlands, distance to streams, distance to railroads, and distance to historical urban centers—that would help them determine the number of additional houses each piece of land could support.

In total, they found that 51,000 additional housing units could be added in Silicon Valley if all the parks, protected watersheds, and protected wetlands were be converted to housing. For reference, the region has 790,000 units currently. Crucially, the study’s authors estimate only around 3,400 units would be on lots small enough to be considered affordable by Bay Area standards.

Topography is the main reason few affordable units would be added to the area’s housing stock. Much of the protected area in Silicon Valley is high in the hills and on steep slopes. Due to concerns over wildfires and mudslides, housing density in these areas is restricted. Existing houses built on unprotected wetlands have also been spaced far apart. Since the Valley’s large protected tracts are either up in the hills or down in the wetlands, there is little room for additional high density (and affordable) development. Over 20,000 of the additional units, they estimate, would be single family homes on large lots, around 1.6 acres each. Real estate of that size in the Bay Area is not cheap, even by Bay Area standards. Single family homes on one acre or larger lots in San Jose list for $1.5 million.

Six and a half percent more housing units might make a bit of difference in cramped Silicon Valley, but it would also do away with the open space that makes the area both livable and attractive to many. Plus, much of the gains in affordable housing would come at the expense of parks within city limits, many of which were created give residents of the surrounding high density housing a bit of fresh air and greenery. Sounds like it was a pretty good trade-off to me. Having worked with many high school students from such neighborhoods, I know many of them never made it to the Bay Area’s large regional parks. But they did spend many hours at their local neighborhood parks.

Source:

Denning, C., Mcdonald, R., & Christensen, J. (2010). Did land protection in Silicon Valley reduce the housing stock? Biological Conservation, 143 (5), 1087-1093 DOI: 10.1016/j.biocon.2010.01.025

Photo by calwhiz.

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The map that started it all

Buried in a dusty tome grandly titled Man’s Role in Changing the Face of the Earth lies a map that changed my life. Granted, my life was already headed in a direction amenable to this map’s wiles, but that lone figure’s influence cannot be understated. It is a simple map, or rather series of maps. Four panels, four dates—from left to right: 1831, 1882, 1902, and 1950. In each successive panel, the dark swaths of ink that represented forest cover in Cadiz Township, Wisconsin, grew successively smaller and more fragmented. In that one figure, John T. Curtis posthumously changed my life.

Growing up in southeastern Wisconsin, I was always peripherally aware that the forest fragments I frequented had not always been mere fragments. But Curtis’s map drove the point home. His fragments were dead ringers for my fragments. His maps were my environmental awakening, but in black-and-white.

Curtis grew up in Waukesha, Wisconsin, the same place my grandfather lives. He attended Carroll College—also in Waukesha—for his AB and then moved 65 miles west to Madison for his PhD. Curtis more or less remained in Madison till his death in 1961, proving that you don’t have to go far to accomplish big things. Curtis is best known within the ecological community for his work with Roger Bray on ordination, a statistical technique that enables botanists to make sense of the distribution, frequency, and abundance of plant species on a plot of land. His Cadiz Township maps are almost an afterthought, a minor footnote in an otherwise sweeping treatise on Wisconsin vegetation.

Unlike Bray-Curtis ordination, the Cadiz Township maps are astonishingly simple. The figure’s earliest frame depicts a wild Wisconsin, untamed by the plow and dominated by a grand deciduous forest the likes of which I sought as a kid. The scene rendered fifty-one years later in the second frame is entirely different. The smooth curve of the prairie-forest border is gone. Inky shards replace the previously continuous forest. In the third map, those bits grow smaller still. In the 1950 frame, the remaining woodlots are barely visible, like the last specks of glass from a broken platter waiting to be swept into a dustpan.

What makes Curtis’s map all the more remarkable was that he recreated the scenes from survey data and his own observations, painstakingly piecing together handwritten records of the six-by-six mile township. To my knowledge, it is one of the first visual reconstructions of fragmentation-as-it-happened, and one of the most influential—at least to me.

Photo by Ron Wiecki.

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