Tree and impervious cover change in U.S. cities

[edfrank]

Tree and impervious cover change in U.S. cities
David J. Nowak∗, Eric J. Greenfield
USDA Forest Service, Northern Research Station, 5 Moon Library, SUNY-ESF, Syracuse, NY 13210, United States

http://nrs.fs.fed.us/pubs/jrnl/2012/nrs ... ak_001.pdf

a b s t r a c t
Paired aerial photographs were interpreted to assess recent changes in tree, impervious and other cover
types in 20 U.S. cities as well as urban land within the conterminous United States. National results
indicate that tree cover in urban areas of the United States is on the decline at a rate of about 7900 ha/yr
or 4.0 million trees per year. Tree cover in 17 of the 20 analyzed cities had statistically significant declines
in tree cover, while 16 cities had statistically significant increases in impervious cover. Only one city
(Syracuse, NY) had a statistically significant increase in tree cover. City tree cover was reduced, on average,
by about 0.27 percent/yr, while impervious surfaces increased at an average rate of about 0.31 percent/yr.
As tree cover provides a simple means to assess the magnitude of the overall urban forest resource,
monitoring of tree cover changes is important to understand how tree cover and various environmental
benefits derived from the trees may be changing. Photo-interpretation of digital aerial images can provide
a simple and timely means to assess urban

Conclusion
Tree cover provides a simple means to assess the magnitude of
the overall urban forest and its environmental effects. Despite various
and likely limited tree planting and protection campaigns, tree
cover tends to be on the decline in U.S. cities while impervious cover
is on the increase. While these individual campaigns are helping to
increase or reduce the loss of urban tree cover, more widespread,
comprehensive and integrated programs that focus on sustaining
overall tree canopy may be needed to help reverse the trend of
declining tree cover in cities. Net tree cover change is the result of
the combined influences of tree planting and natural regeneration,
tree growth and tree mortality. Developing coordinated healthy
tree canopy programs across various land ownerships can help
sustain desired tree cover levels and better manage cover change.
Monitoring of tree cover changes is essential to determine current
trends and whether desired canopy levels or program effects are
being attained. Photo-interpretation of digital aerial images can
provide a simple and timely means to assess urban tree cover and
how it is changing.

.

[edfrank]

U.S. Urban Forests Losing Ground
ScienceDaily (Feb. 23, 2012)

http://www.sciencedaily.com/releases/20 ... 104023.htm

National results indicate that tree cover in urban areas of the United States is declining at a rate of about 4 million trees per year, according to a U.S. Forest Service study published recently in Urban Forestry & Urban Greening.

Tree cover in 17 of the 20 cities analyzed in the study declined while 16 cities saw increases in impervious cover, which includes pavement and rooftops. Land that lost trees was for the most part converted to either grass or ground cover, impervious cover or bare soil.

Of the 20 cities analyzed, the greatest percentage of annual loss in tree cover occurred in New Orleans, Houston and Albuquerque.

[Lee Frelich]

Ed:

For Minneapolis, my guess is that we lost tree cover due to a second round of Dutch Elm Disease and a few derechos that hit during the mid 2000s. This took out trees with very large crowns, and although a lot of smaller trees were planted to replace them, their crowns are still quite small. This analysis does not take into account last May's tornado that took out virtually all trees on an approximately 0.15 by 4 mile path through the north side of the city, so that's another 1 or 2 % loss. It also doesn't count the more recent loss of ash trees due to the rapidly invading Emerald Ash borer.

Lee

[Rand]

U.S. Urban Forests Losing Ground

Of the 20 cities analyzed, the greatest percentage of annual loss in tree cover occurred in New Orleans, Houston and Albuquerque.

I know texas had a horrific drought this summer:

(Reuters) - Some 5.6 million urban shade trees were killed by the record drought that baked Texas last year, the Texas Forest Service reported on Wednesday.

Last year was the driest year on record in the state and the second-hottest, according to the National Weather Service.

The shade tree die-off represents some 10 percent of the state's urban forest, and is in addition to as many as a half-billion rural, park and forest trees that the forest service reported in December were killed in the drought.

The impact of the drought will be visible for decades because of the loss of the trees in yards and parks and along streets of the state's cities, according to the service.

The urban tree canopy loss may be far from over, said forest service lead researcher Pete Smith. Even though the drought appears to be easing in some parts of the state, many trees have been stressed beyond repair, he said.

"This means we may be significantly undercounting the number of tees that ultimately will succumb to the drought," he said. "That number may not be known until the end of 2012, or ever."

http://www.reuters.com/article/2012/02/ ... 2W20120216