Growing Pains on the Front Range.

The Denver area struggles with too many trees in the mountains, too few on the plains, and a new dominant species: us.

In most places, human settlement has meant the loss of forest cover. Along Colorado's Front Range, however, more people has meant more trees.

Until recently.

The early eruption of trees along the fast-developing urban belt that runs from Fort Collins in the north through Boulder and Denver to Colorado Springs in the south--a distance of 100 miles--was not formally planned. Pioneers settling at the foot of the Rockies at the edge of the treeless Great Plains simply knew that trees provided shade in summer and wind protection in winter.

What they planted, though, grew up to be an urban forest of species imported from the East and nurtured by watering. The city also grew up, and today's developers seem to have forgotten their forefathers' simple logic about trees. New housing developments are mostly treeless and depend on air conditioning instead of shade. Concrete and impervious surfaces outpace cooling, green relief.

Colorado foresters are working with AMERICAN FORESTS and its CITYgreen Geographic Information System (GIS) software to document the benefits of early tree planting and pinpoint where the existing canopy is too thin.

The idea is to persuade policymakers and builders that trees are a basic, essential component of sensible development.

This close connection between development and forest may seem odd to those east of the Mississippi, where urban growth usually reduces the canopy. Out in the West's plains and deserts, however, cities can be an oasis of foliage in a largely treeless landscape.

In the intermountain region of the Rockies there are two treelines: one high, where the advance of trees is limited by cold and snow, and one low, where trees are halted by the lack of water. On the mile-high plains around the city of Denver, average precipitation is about 14 inches--several inches short of the minimum a forest needs to thrive.

When pioneers arrived at the abrupt and dramatic escarpment of the Front Range, they found the mountains' Ponderosa pine descended only to about 6,000 feet. Cottonwood grew along riverbanks, and Denver was built where three rivers met, but in large part the base of the mountains was open grassland. Today, 4 million people live in this area, shaded mostly with artificially planted trees kept alive by the hose and the sprinkler. Most are deciduous species such as maple, elm, willow, honeylocust, ash, cottonwood, Russian olive, and hackberry.

Additional development has crept into the Ponderosa pine foothills above the area's major cities. The problem there is not too few trees but too many houses in a forest ecologically programmed to regularly burn. There, AMERICAN FORESTS and Colorado officials are coupling satellite and aerial photographs with computer analysis to point the way to a balanced, sustainable future.

Two issues

"One issue is that we've created a forest we need to nurture," says Phillip Hoefer, community forest supervisor of the Colorado State Forest Service. Trees are often taken for granted and are being allowed to decline.

"Another is whether we have enough forest," adds Jennifer Sherry, a consultant with Ecosystem Analyses.

The trend in Colorado, like much of the nation, is bigger houses on smaller lots, meaning that most of the surface is impervious roofs and paving. Yet the Colorado study suggests tree planting is as essential to good development as storm sewers or well-built homes--in fact, that it is an ally of both.

Consider the region's rainfall. Much of it comes in thunderstorm downpours, resulting in the long-standing problems of retaining that water and controlling flooding. Sherry looked at the forest cover in Boulder, a university town of about 100,000 people, and found that during a 2inch rainstorm the city's trees retain 11 million cubic feet of water that would otherwise be lost to runoff.

That much water would cover a football field to a height of 20 stories.

The campus of Fort Collins City Hall has a tree canopy that covers just 28 percent of the site, and yet those trees are enough to retain 7,004 cubic feet of water in a 2-inch storm. That means only .71 inches run off.

In other words, the new forest is partially watering itself by retaining water that would otherwise be lost to evaporation and drainage on the Great Plains.

For cities that lie between 5,000 and 6,000 feet in elevation, shade trees also help to cut the intense summer sunlight and help shield against winter winds. Sherry calculated the energy savings per home in Boulder at $55 a year. The trees also absorb air pollution, store carbon that would otherwise contribute to global warming, cool parked automobiles, and add to market value.

"Realtors have told me that trees on a lot add $6,000 to $10,000 to the value of the property," says Ralph Campbell, assistant Colorado State forester in the Denver-Metro office.

"Older neighborhoods are becoming more desirable because of their trees," says Ron Stewart, chairman of the Boulder County board of commissioners.

Boulder's trees, Sherry estimates, store 112,000 tons of carbon, save $600,000 in energy costs, and act as a pollution filter valued at $644,000.

How then to explain Rock Creek, a sprawling new housing subdivision between Boulder and Denver, where developers limit tree planting to a single green ash plopped in an augered 12-inch hole in compacted soil? So cursory is the planting that some of the trees are dying even as families occupy the new homes. So short are the new trees that not a leaf breaks the angular monotony of gabled roof lines.

The problem is that the argument for trees--so obvious to pioneers with neither air conditioning or adequate insulation--is less obvious to modern home buyers seeking the most house for the least money. Trees become a frill, put off until tomorrow.

Nor are housing tracts the only offenders: Campbell said retail and office developments also have only cursory plantings.

AMERICAN FORESTS' preliminary CITYgreen analysis suggests the tree canopy cover in many newer Colorado developments is less than 6 percent, says Gary Moil, AMERICAN FORESTS' vice president for urban forestry. Boulder's commercial center, Pearl Street, has only 6 percent.

In contrast, the canopy coverage in older sections of Front Range cities as a whole averages 20 percent. Some of the most prized neighborhoods in Boulder--Mapleton is one example--may reach 30 to 40 percent because of early boulevards laid out with a central island dedicated to tree planting.

"If you put impervious surface such as roofs and parking lots over the plains, you get more runoff, more heat, and more air pollution," Moll says. "The cheapest, easiest way we know of to combat this is to use vegetation, and trees are the biggest."

The issue is immediate. The Front Range is expected to gain another million people in each of the next two decades, and the newcomers have a clear choice: Pave over the plains or forest them.

If trees are seen by planners as a vital urban component, visitors flying into Denver in 2020 could see a belt of glittering green that stretches for a hundred miles. If older trees are allowed to die without replacement, a visitor will see more roofs and asphalt, greater temperature extremes, and worsening air pollution.

"We've created an ecosystem hut now run a risk of losing it," says Hoefer. "Trees first planted a hundred years ago are beginning to deteriorate. If 70 to 80 percent of our future forest is in the hands of private developers, I'm concerned about bringing them up to speed." It is hoped the CITYgreen analysis will provide persuasive evidence.

Still, natural resource issues are never simple, and that is particularly true in Colorado. In September, for example, Fort Collins, one of the cities in the study area, was hit hard by an early snowstorm that damaged many trees. Local people now can use computer software to calculate the dollar value of this loss and adjust their planting and care programs to start rebuilding their green canopy.

Green canopy also is important in Boulder County, which has won national recognition for preserving about 100,000 of its 450,000 acres as open space. Yet an unintended consequence of that preservation has been to push newer development farther out in the Plains and farther from the existing tree cover.

Developments are hopscotching out to the cheapest land. "The kind of growth we're experiencing today is much less dense than that of the past," says Boulder's Stewart. "Colorado is losing 240 acres a day to sprawl and you no longer know where your town stops and the other begins." Houses are growing so fast that trees can't grow fast enough to keep up.

Then too, the natural ecosystem of the region is prairie, and some ecologists could argue that having too many trees threatens the native plants and animals already there.

And even as trees save water, they also consume it. Much of the Front Range water is piped under the Rockies from the western half of the state, and opposition to this liquid export is growing in that area.

An additional concern: housing development in the Rocky Mountain foothills, where the opposite situation is concerning officials. Houses built there go up in the midst of an ecosystem programmed to burn regularly, and some homeowners are reluctant to remove trees or greenery even to make the houses firesafe.

"We're not paranoid about that history but we're aware," says Jim Woodruff, who retired from Illinois to a development called Pinebrook Hills in which 300 homes climb up forested valleys to elevations as high as 6,900 feet. The lifestyle is so enticing that he and his neighbors are willing to run the risk, he says. Woodruff hesitates to cut even the pines brushing against his wood home because their shade is so beneficial in summer.

Foresters think much of this region is overdue for thinning. Yet even firewood gathering has halted because of a ban on wood stoves caused by air pollution inversions in the winter. Neighbors often disagree on how many trees to cut.

The result is a rapidly evolving ecosystem along Colorado's Front Range as a dominant new species-humans--tries to come to terms with too many trees in the mountains and too few on the plains.

There is no question they can create and sustain an effective canopy if they wish. The issue is whether they will be as conscious of the possibility as their ancestors were.

"Trees and people need each other here," Hoefer says. The challenge is to find a balance in both ecosystems that makes environmental and economic sense.

Pulitzer Prize-winner William Dietrich of Anacortes, Washington, last wrote for American Forests on "How Progress Ate America" (Autumn 1999).