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Bubbler in a city park

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The United States is not run by godless Communists. Neither is most of the rest of the world. In fact, the godless Communists that do remain are not all that Communist anymore. I bring that up because command and control economies can dictate what development happens where. Land conservation under such a system is technically easier, even if the actual results in Communist nations like the Soviet Union weren’t that inspiring. Land conservation in the free world is a trickier game, one played with carrots and sticks as opposed to edicts and directives. Here, money is your best friend.

Conservation organizations have focused on preserving big tracts of land, and rightfully so. Big buys are often more cost effective and easier to manage. But they’re also becoming trickier to execute in a world dominated by curving cul-du-sacs and one acre lots. If we want functioning ecosystems in these places, we need to focus on land conservation within the subdivision, not along its borders.

Luckily, the carrot seems to be working in those places. A study of subdivisions in Maryland between Washington, D.C., and Baltimore shows that developers have been incorporating more open space into their subdivisions. That’s not because they’re interested in land conservation. Part of it is a bit of command and control—Maryland’s Forest Conservation Act forces developers to conserve a modicum of forested land—but it’s also simple economics. Developers can sell lots and houses at higher prices if open space is nearby. Because proximity matters, that open space typically needs to be within the subdivision.

To developers, though, that open space is fungible. It can exist either as public parks or larger private lots—both raise prices. The Maryland study also found that minimum lot sizes—which governments typically use to preserve open space—can push developers away from shared open space toward larger lot sizes.

This poses a problem for maintaining healthy ecosystems. Like many laws, the way the Maryland Forest Conservation Act is interpreted matters. People can uphold the letter of the law—maintaining forest cover—without changing their usual habits—mowing their entire lot. The result is something that looks like a forest from above but doesn’t function like one.

In a perfect world, everyone would happily tend a few thousand square feet around their house and leave the rest to nature. But that’s not always the case. People will spend all Saturday mowing acres of grass and grumble about it afterwards. That’s because for many people owning a country manor is more alluring than owning a chunk of the great outdoors. You can fight that mentality by increasing minimum lot sizes to the point where mowing it all becomes completely unreasonable,¹but the closer you get to a metro area, the less tenable that becomes.

There’s also no guarantee that laws dictating minimum lot sizes will remain in place. As the city creeps closer, pressure to further subdivide will mount. Open space preserved in private lots could easily disappear.

Parks, on the other hand, tend to stick around. Unlike large lots, they’re seldom subdivided. Instead, they tend to become institutions. People like their parks and are loathe to lose them—no one wants to see their neighborhood park disappear. So let’s put that to use. Instead of—or in addition to—minimum forest cover and minimum lot sizes, let’s institute minimum park sizes. Everyone will benefit. Developers will be able to sell lots at higher prices. Kids will have playgrounds. Adults will have walking paths. And because big parks often have big natural areas, ecosystems will have a better chance at surviving. It’s a solution that’s a bit more command and control than current vague regulations, but everyone will benefit. It’s also more carrot than stick. Even if you don’t particularly like carrots, it’s better than getting hit with a stick.

¹ Though there will always be exceptions—near where I grew up, one guy mowed 18 acres. He had to buy a bonafide farm tractor so it wouldn’t take him all week.

Photo by JD Hancock.

Source:

Lichtenberg, E., Tra, C., & Hardie, I. (2007). Land use regulation and the provision of open space in suburban residential subdivisions Journal of Environmental Economics and Management, 54 (2), 199-213 DOI: 10.1016/j.jeem.2007.02.001

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Red-eyed Vireo

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Earlier this week I pointed out that urban areas can actually increase tree cover over time, albeit with a caveat. The two studies I cited measured tree cover and only tree cover—they made no claims about ecological function. Luckily, other studies have done just that, including one that looked at migratory bird use of greenways in urban areas.

Migratory routes are important, though most research into migratory bird decline has focused on habitat loss in their breeding and wintering grounds. That has left a large piece of the puzzle unsolved—the habitat between point A and point B. Think of it this way: If snowbirds—you know, northern (human) retirees who flock to warmer climes in the winter—started disappearing and our best solution was to look for them at their apartment in New York or their rental in Boca Raton—ignoring rest stops and motels along I-95—we’d be doing a great disservice to our older generations. Ignoring flyways is similarly foolish.

There have been studies in more recent years that aim to fill this gap, and one published in 2009 by Salina Kohut, George Hess, and Christopher Moorman picks up the trail along, well, trails. They surveyed bird species abundance and richness—how many and how varied the itinerants were—in 47 greenways in and around Raleigh, North Carolina.

Greenways are a common and convenient way for cities to conserve natural habitat. Their linear form is well suited to urban areas, and they easily double as parks or recreational trails. They also can serve as stop-over habitat for migratory birds. Kohut, Hess, and Moorman were hoping to find the right type of corridor for migrating birds, where our feathered friends can take a load off and fatten up.

It turns out that most birds were not picky and would stop at just about any greenway, regardless of vegetation, adjacent land use, or corridor width. That’s not to say all greenways were entirely equal. Overall, birds favored corridors with taller trees and lots of native shrubs teeming with fruit. And among birds that live in forest interiors far away from human development and even open fields, greenways wider than 150 meters (about 500 feet) surrounded by low-intensity development were the most popular.

None of the greenways Kohut and her colleagues studied were as good as a regular forest, though. Still, with some tweaks—including widening corridors, siting them near low-intensity development, and planting with natives—greenways can make decent stand-ins for the real thing, at least as far as migratory birds are concerned. Residential neighborhoods can even make themselves into agreeable stopover habitat by mimicking vegetation found at popular stops along the flyway.

So greenways make for good bird habitat, but let’s not forget that they’re good neighbors, too. In addition to helping migrating fauna, they boost property values, add recreational opportunities, and work well as commuting corridors for cyclists. Five benefits from one land use. Not too shabby.

Photo by qmnonic.

Source:

Kohut, S., Hess, G., & Moorman, C. (2009). Avian use of suburban greenways as stopover habitat Urban Ecosystems, 12 (4), 487-502 DOI: 10.1007/s11252-009-0099-6

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Aerial view of Carrollton, Texas

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If you think American cities are sprawling now, just wait until 2025. In that time, the U.S. population will grow by 18 percent but the amount of developed land will increase 57 percent. Up to 9.2 percent of the lower 48 could be urbanized by then. And while that number includes cities and the infrastructure to support them—roads, rail, power lines, and so on—that number does not include land impacted by farming, logging, mining, or mineral extraction.

That 10 percent of the lower 48 could be crawling with people is a stark reminder that our nation—while immense—is not immune to the pressures of development. It’s also acknowledgement that despite years of hearing about the resurgence of American cities, sprawl is still king.

Today, it feels like much of what drove the suburbanization of America since World War II has changed. Incomes aren’t rising nearly as fast as they did in the 1950s and 1960s. In fact, when adjusted for inflation, incomes have stagnated or dropped in recent decades. Soaring gas prices and congested freeways have stolen some of the automobile’s glamor, too.

Yet two studies show that while the outlook in the U.S. may have changed, our desire for suburban living has not. The study’s results differ slightly—the 2004 paper says we’ll add 25.8 million hectares (64 million acres) by 2025, the 2009 manuscript says 22.4 million hectares (55 million acres) by 2030—but their conclusions are the same. American cities will continue to sprawl, adding more land per person than in the past.

In recent decades, the locus of suburbanization has shifted from the Northeast and Midwest to the South. With its warmer weather and lower costs of living, the South has grown faster than any other region in the U.S. since 1980. Development has been fueled by flat, cheap land and abundant freeways, which has pushed land demands well above the national average in some states.

That boom also meant the South was hit hard by the housing bust in 2008. But that doesn’t mean the market for suburban housing has disappeared. Living the burbs is still cheaper than the city, and since real incomes for most Americans have suffered in recent years, development will continue to chase lower land prices. The recession and housing slump may have put a damper on suburban development, but I’m guessing it’s just a temporary blip.

Another factor that should conspire against suburban development—higher gas prices—also doesn’t seem to have much of an influence. The 2009 study suggests development rates won’t take much of a hit from high fuel costs. To simulate rising gas prices, the study’s authors reduced the forecasted development rate in states where it was highest—primarily the car-centric South. Only 5 percent less land was converted from rural to urban uses.

It’s possible things could change—perhaps fuel costs will rise even higher, or maybe the home downsizing trend that’s in its infancy will mature. But I think we should prepare for a future filled with suburbs. In the South, where most of the development is happening, land continues to be cheap and easy to access. The same warm weather that drew many people there will also keep them in their cars. Nobody likes walking in the South’s sweltering summers, even if it’s just from the steamy parking lot to the over-air conditioned mall.

The question then is, how can we make the suburbs more environmentally friendly? Encouraging compactness would be a good start, even just at the subdivision level. Hopscotch development inflicts ecological damage well beyond its immediate footprint—there are many plants and animals that cannot survive surrounded by a sea of humanity. Dispersing job and commercial centers is another option, helping to reduce the number of miles people have to drive on a day-to-day basis.

In the end, though, we’ll have to push for more ecologically integrated development. We’ve seen small steps in that direction already—most new subdivisions must deal with run-off from rainstorms on-site rather than shunting it to an overburdened creek. It’s a start, but not enough to offset America’s suburban future.

Sources:

Alig, R., Kline, J., & Lichtenstein, M. (2004). Urbanization on the US landscape: looking ahead in the 21st century Landscape and Urban Planning, 69 (2-3), 219-234 DOI: 10.1016/j.landurbplan.2003.07.004

White, E., Morzillo, A., & Alig, R. (2009). Past and projected rural land conversion in the US at state, regional, and national levels Landscape and Urban Planning, 89 (1-2), 37-48 DOI: 10.1016/j.landurbplan.2008.09.004

Photo by La Citta Vita.

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Roman mosaic

If you want a glimpse of our ecological future, take a look at present-day Europe. Continuous and intensive human habitation for millennia have crafted ecosystems that not only thrive on human disturbance, they’re dependent on it. But even in places where pastoral uses have fallen by the wayside, the ghosts of past practices linger. If you have any doubt that the changes we’re making to the earth right now will be felt thousands of years from now, these two studies should wipe those away.

This post was chosen as an Editor's Selection for ResearchBlogging.orgThe first takes place in a post-apocalyptic landscape masquerading as a charming woods, the Tronçais forest. Smack in the middle of France, Tronçais is the site of a recent discovery of 106 Roman settlements. Photographs of the settlements call to mind Mayan ruins in Yucatan jungles, with trees overtaking helpless stone walls. Tronçais was not unique in this way—following the fall of the Roman Empire, many settlements reverted to forest after the 3rd and 4th centuries CE.

Ecologists studying plant diversity in the area noticed two distinct trends. First, the soil became markedly different as they sampled further from the center of the settlements. Nearly every measure of soil nutrients declined—nitrogen, phosphorous, and charcoal were all lower at further distances. Soil acidity declined, too. Second, plant diversity dropped off as sample sites moved further into the Roman hinterland, and likely a result of changes in the soil.

The researchers suspect the direct impacts of the settlement and Roman farming practices are behind the trends. High phosphorous and nitrogen levels were probably due to manuring. The abundance of charcoal is clearly from cooking fires, while soil pH was affected by two uses of lime common in the Roman empire—mortar used in building and marling, the spreading of lime and clay as a fertilizer. The combined effects of these practices fostered plant diversity after the settlements fell into ruin, the effects of which can be seen to this day.

The second study was undertaken by another group of ecologists who canvased grasslands in northern and western Estonia. While threatened today by the usual suspects—intensive agriculture and urbanization—the calcareous grasslands of Estonia have a long history of human stewardship which helped a wide variety of grasses and herbs to flourish. They were greatly expanded by the Vikings, who settled the area between 800 and 1100 CE. Knowing this history, the researchers suspected population density may have boosted floral diversity. They sampled exhaustively, recording plant species and communities in 15 quadrats at 45 sites for a total of 675 sample plots. They also drew 20 soil samples at each site. To estimate population density during the Viking Period, they used an established model that estimated settlement size and extent based on known ruins.

Soil qualities naturally had an affect on present-day plant diversity, but human population density during and shortly after the Viking Period also emerged as a significant predictor. As with the Roman study, changes to soil nutrients because of human activities are likely behind the results. But that’s not all. The researchers point out that seed dispersal 1,000 years ago also influenced present-day diversity. When the Vikings expanded the grasslands, they connected different patches that had previously been isolated, allowing previously isolated species to germinate in new areas.

These are not the first studies to reveal a shadow of human habitation in present day ecosystems—the Amazonian rainforest is littered with evidence of agriculture before European contact, for example. But these studies show the ghosts of ecology persisting for millennia, not centuries. Not only does it bolster the notion that no landscape is pristine—an idea that has been gaining traction with the ecological community—it should underscore the persistence of any human activity.

Sources:

Dambrine, E., Dupouey, J., Laüt, L., Humbert, L., Thinon, M., Beaufils, T., & Richard, H. (2007). Present forest biodiversity patterns in France related to former Roman agriculture Ecology, 88 (6), 1430-1439 DOI: 10.1890/05-1314

PÄRTEL, M., HELM, A., REITALU, T., LIIRA, J., & ZOBEL, M. (2007). Grassland diversity related to the Late Iron Age human population density Journal of Ecology, 95 (3), 574-582 DOI: 10.1111/j.1365-2745.2007.01230.x

Photo by mharrsch.

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Farms giving way to subdivisions in Southeastern Wisconsin

If you were a squirrel living in Southeastern Wisconsin, you’d be pleasantly surprised by the state of things. In many places, there are as many—if not more—trees than there were 200 years ago. But that rosy image doesn’t tell the entire story. Comparing the forests that cover the cities and suburbs around Milwaukee—and likely in many places around the world—is like comparing Rome before and after the fall. It’s still Rome, but it’s not quite the same as it used to be.

Southern Wisconsin is a case study of the changes that were affecting much of the country in the 20th century. Most of the forests had been cleared in the 1800s by farmers, resulting in a landscape that little resembled what came before. The woodlots that remained were small and scattered. In one famous study, only 4.8 percent of the original forests remained by 1935. Milwaukee and its surrounding cities grew steadily in the run-up to World War II, but positively boomed thereafter. They needed room to grow, and since cleared land is easy to build on, farm after farm was subdivided.

The path from forest to front yard seems clear cut. A woods is cleared to make way for farmland, which is later subdivided into lots and sold off to make way for homes. But the reality is much more complex than that. Though a neighborhood may maintain its wooded appearance, it’s original character is gone.

In Wisconsin, subdivisions are invariably preceded by farms. Farming is a tough life. There’s not much money to be made with a small family farm, and an farmer’s property often doubles as his retirement fund. To maximize the investment, he’ll usually subdivide it for housing. It usually works out well for him, because land that’s good for growing crops is also good for building houses—it’s not too steep and most of it doesn’t need to be cleared.

That’s not to say farms are entirely devoid of trees. Most contain small woodlots and extensive fencerows that separated fields of corn, wheat, and soybeans. They’re relics of bygone forests, and in many places that’s all that’s left. Though the relationship is a bit one-sided, relic trees and farms have existed side-by-side for decades.

Maintaining that landscape during subdivision isn’t difficult. Building houses around trees is easy if you don’t take a cookie cutter approach, and houses with big trees in their yards tend to sell for more. But conservation rarely happens. That’s the conclusion of one study of Southeastern Wisconsin. It looked at the fate of extant vegetation as farms gave way to subdivisions between 1937 and 1975. Though the sum total of forested land didn’t drop as much as anticipated, very little of the original vegetation that made it through the transition. By 1975, the trees that dotted subdivisions and roadsides were almost entirely new.

That study reminds us that sum totals seldom tell an entire story. The relationship between forests, farms, and yards is complex and multidirectional. Forests are often cleared for farms, but abandoned farms can return to their forested state over time—much of New England underwent this process. However, urbanization can intervene along the way, removing the little remaining vegetation and replacing it with landscaped yards. But that’s not all the forest loss development is responsible for. Though many subdivisions are carved from land cleared previously for farms, they can be indirectly responsible for the loss of even more forests. Street and yard trees can’t offset this entirely. Similar patterns are well documented in developing nations. In Brazil, for example, expanding soy production has pushed cattle ranchers to clear land further into the frontier. It’s easy to forget these same processes are at work here in the United States.

Even when subdivisions spring fully formed from forested land—skipping the intermediate farm stage—their lots are often cleared of existing vegetation. Some of my research in graduate school documented the stark changes forest edges undergo when houses move in. In old black-and-white aerial photographs, the bare earth of cleared building sites stood out in stark contrast to the dark gray of the surrounding woodlands. Straight, sharp lines separated the two. In time, the edge bled back into the yards, but it wasn’t quite the same.

Suburban development isn’t going away anytime soon, but some of the structure and function of the old woodlands they replaced can be recovered. Homeowners can plant native trees. People can lobby their cities to plant native trees as well, rather than the whatever low-maintenance tree is in fashion among city foresters this year. The result won’t be the same as an intact woodland, but at least it will be similar.

Source:

Sharpe, D., Stearns, F., Leitner, L., & Dorney, J. (1986). Fate of natural vegetation during urban development of rural landscapes in Southeastern Wisconsin Urban Ecology, 9 (3-4), 267-287 DOI: 10.1016/0304-4009(86)90004-5

Photo by sierraromeo.

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City wildflowers

Tucked amidst acres of asphalt jungle are cities’ unsung environmental heroes. Yards, lawns, gardens—call them whatever you please—these bits of unpaved earth play a real role in supporting thriving urban ecosystems. And they could play the part even more eloquently if we thought of them as parts of a larger whole.

Anyone who has spent more than five minutes in a city knows they are not always welcoming to people, let alone plants and animals. It’s common to see thin, scrappy weeds straining against their concrete binders, or birds clinging to wiry utility lines in lieu of more customary branches and brambles. But behind houses, or even hidden out front in plain sight, are postage stamps of possibility. With all the clipping, prodding, and spraying these diced green patches receive, it’s easy to forget that they are part of a real ecosystem.

Cities have long been overlooked by ecologists, mostly because the logistics involved in studying them can be convoluted. Getting permission from dozens, even hundreds of landowners is one of the biggest headaches, so urban ecologists typically resort to the next best thing—parks, forest preserves, greenways, and so on. Parks can be fantastic reservoirs of habitat, but their area pales in comparison to the amount of land scattered throughout the city as yards and gardens. Real urban conservation plans needs to account for everyone’s little patch of nature.

Here’s where landscape ecology can help. Landscape ecology teaches us to look beyond—or within—the various bits and pieces, components and parts that make up an ecosystem. Scale is king in landscape ecology, be it spatial or temporal. In the context of a city, this means that each individual yard and garden—which on its own can seem hopelessly small, only able to support a salamander, some insects, and a few birds at best—is just one piece of a larger patchwork, one connected by birds that fly across town, salamanders that waddle beneath fences, bees that hum between flower beds, and seeds that disperse on the wind. Protecting them all is only possible when conservation plans cover the gamut of spatial and temporal scales.

Unfortunately, much of this potential has yet to be tapped. By and large, cities remain natural wastelands. Habitat fragmentation keeps down the abundance and diversity of species. Inspired landscaping can counter the diversity problem, but it usually does so with exotic species that are poor ecological substitutes for natives. Pets—especially cats—take a toll on native animal populations, while air, light, and sound pollution add further disruptions to an already taxed ecosystem.

Still, most cities have enough material for a solid conservation foundation. Many people are earnestly invested in their yards, carefully curating selections of grasses, trees, and shrubs, attracting musical entertainment through bird feeders, and in doing so supporting a diversity of mammals, amphibians, reptiles, and invertebrates. This has all been accomplished without significant coordination. Programs like the Audubon Society’s “Audubon at Home” or the National Wildlife Federation’s backyard certification scheme have nibbled at the edges, but lots more could be done.

A recent review of the landscape ecology of gardens suggests that to encourage habitat friendly yards and gardens a bottom up approach would be best. Top down programs can help cities meet conservation targets, but they do little to change people’s attitudes. Encouraging a “conservation ethic of the city” would probably be more successful, but also more difficult to engender. Lawn culture is heavily embedded in many Western nations, especially the U.S. and Canada. Lawns will always have their place; besides recreation, they are surprisingly productive ecosystems. Yet most are far larger than they need to be. Substituting appropriate plantings for classic Kentucky bluegrass would save people time and effort, reduce emissions from mowing, and boost habitat diversity and complexity.

Lawns are just one part of the equation. Landscape ecologists can step in to identify the driving forces behind landowner decisions. Where the conservation ethic exists, ecologists can encourage neighbors to coordinate their landscaping, clumping their native plantings so that four quarters can add up to one whole, for instance. Depending on the area’s ecology, landscape ecologists can further define optimal sizes for these native plots—for example, will it take twenty percent of four yards or six to meet the needs of a native bird? Or in other cases, water features like ponds may be more important than contiguity. Each city, even neighborhood, will have its own gestalt, and landscape ecologists can help discover it.

Sources:

Falk, J. (1976). Energetics of a Suburban Lawn Ecosystem Ecology, 57 (1) DOI: 10.2307/1936405

Goddard, M., Dougill, A., & Benton, T. (2010). Scaling up from gardens: biodiversity conservation in urban environments Trends in Ecology & Evolution, 25 (2), 90-98 DOI: 10.1016/j.tree.2009.07.016

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Houses in Keystone, CO, located in the Arapaho National Forest

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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