Seeing the Trees for the Forest: I-Tree Software Helps Communities with Tree-Canopy Analysis

By Beard, Elizabeth | Parks & Recreation, March 2013 | Go to article overview

Seeing the Trees for the Forest: I-Tree Software Helps Communities with Tree-Canopy Analysis


Beard, Elizabeth, Parks & Recreation


The Curse of the Walnut

It's a tree disease with an almost biblical name--thousand cankers. Carried by insects, this fungal disease from Mexico is wreaking havoc on black walnut trees across the western United States. Although black walnuts are actually native to the eastern U.S., they were commonly planted in many western urban and suburban communities.

The loss of entire species of trees from urban areas is not just an aesthetic concern. A recent study by the U.S. Forest Service found declining human health in areas hit hard by the emerald ash borer, which is estimated to have killed 100 million ash trees in the East and Midwest. One striking result of the study revealed that the borer infestation was associated with an additional 6,113 deaths related to illnesses of the lower respiratory system and 15,080 cardiovascular-related deaths in the 15-state study area over a period of 18 years.

Although many cities have maintained tree-inventory records for decades, tree-canopy assessments offer a wealth of new information about the beneficial effects of trees on urban areas. Boise, Idaho, known as the "City of Trees," recently participated in a canopy analysis after losing its black walnuts to thousand cankers and seeing a new mysterious decline in Norway maples.

"The tree inventory will give us an idea on a tree-by-tree or species-by-species or neighborhood-by-neighborhood basis--we know exactly where the trees are and what they are," says Brian Jorgenson, Boise city forester. "But we don't necessarily have a big picture of the city overall.... The tree canopy study is looking at the canopy overall. You'll be able to look on a broader basis--where are the trees in Boise? Where can we take advantage of the benefits that trees bring?"

i-Tree

Boise will soon be able to monitor the short- and long-term effects of tree losses and replanting efforts with the help of canopy-analysis software called i-Tree, i-Tree is a public-domain suite of software tools (www.itreetools.org) developed by the U.S. Forest Service in a cooperative partnership with the Davey Tree Expert Company, National Arbor Day Foundation, Society of Municipal Arborists, International Society of Arboriculture, and Casey Trees. The tools allow communities to assess their percentage of canopy cover by using freely available satellite-based imagery or even aerial images from Google Maps.

"We've had the idea for more than 10 years since I've been here and, honestly, I think the technology is finally catching up to our desires on this," Jorgenson says. "We can get down to where we can look at an entire city and determine what your percentage of tree canopy coverage is and even identify down to specific planting sites where you have room for more trees."

Boise, situated in a desert, has only about 15 percent tree-canopy coverage, but that overall figure is somewhat misleading, according to Jorgenson.

"Boise has undergone a huge growth explosion in the last 20 or 30 years," Jorgenson explains. "In the older parts--Boise's north end--we're looking at 30 to 40 percent tree canopy down there, but the city as a whole drops it down to 15 percent. So if you leave those old neighborhoods out, where are you at? Probably only 6 to 10 percent for the rest of the city. So that will help us determine where we want to see additional growth in the tree canopy."

Often a tree-canopy analysis is performed on several neighboring communities at the same time. In the Willamette Valley in Oregon, an American Forests tree-canopy analysis in 2001 of the entire valley, including Albany, Corvallis, Salem, and Portland, revealed that the valley's tree canopy declined from 42 percent to 24 percent from 1972 to 2000. American Forests recommends a tree-canopy cover of 40 percent for urban areas in the Willamette Valley and lower Columbia River, but Albany's current canopy cover falls well short of that level, so the city needed to set a more realistic goal. …

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