Growing Pains on the Front Range

Article excerpt

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. …