Thursday, September 13, 2012

New Study Benchmarks Tree Cover and Impervious Surface

The more than 50 large trees along the banks of sensitive Erwin Creek which were clear-cut this summer by an out-of-state billboard company included large cherry, elm, maple, cedar, pear and myrtle varieties.

They had been capturing, slowing and cleaning not only storm water from the impervious surface of I-77 but along the opposite bank from over and under a site long-identified as toxic.

Caring nothing about the costs they were passing along to the citizens of Charlotte, the billboard company was only interested in becoming even more visible the now-just 1 in 12 people who in the course of a year might buy something due to the messages on the huge board while avoiding the costs it was passing along to the citizens of Charlotte.

Should the outrage of Charlotteans demanding replantingErwin Creek Cuts along the banks of the creek ever be given consideration, hopefully it will be more than just plopping down some twigs or saplings from a home improvement store.

Ecolotree, based in North Liberty, Iowa is doing some amazing things with phytoremediation using hybrid poplars and willows such as that being done along hog lagoons and elsewhere.

Ecolotree’s CEO notes in a recently published book by Jim Robbins that “one willow can process fifteen gallons of waste a day, and a field of a thousand trees on an acre can treat ten gallons of toxic water per minute.”

The impervious surfaces of the highway and the parking lot which covers the toxic spill which embrace each side of Erwin Creek have long been proven to create run-off that is hazardous to human health and that is why the trees were preserved when the highway was built.

A newly released study by scientists David Nowak and Eric Greenfield, based in Syracuse, NY for the National Forest Service, has quantified both the amount of tree cover and the amount of impervious surface in each state of the United States as well as in urban and community areas.

Tree cover over the conterminous US, or what we called the “lower 48” when I was in Alaska, is now estimated at 659 million acres or 34.2% of the total acreage.  When Alaska and Hawaii are included, tree cover nationwide in urban/community areas is estimated at 35.8% or 43.7 million acres.

Tree cover in North Carolina is now estimated at only 62.6%, less than New York, South Carolina and Virginia but more than Tennessee and we’re needlessly surrendering our signature asset at no cost to things such as billboards.  North Carolina’s urban and community areas are covered with urban forest canopy by 48.2% and 50.3% respectively, about 8% of the overall statewide tree cover.

By comparison, in Durham, where I live, the county as a whole has just 51% of its tree canopy remaining and only 40% remaining in the city where urban foresters are funded to plant a net increase of only 150 trees annually, after removals for disease etc., and this amount is futile in the face of the uncounted thousands clear-cut for any single development.

Impervious surface, including roads, parking lots, buildings etc., in the lower 48 is now estimated at 45.5 million acres or 2.4%.  In urban/community areas alone it is estimated at 18 million acres or nearly 15%.

While only 4.9% of North Carolina is covered with impervious surface, more than 32% of that is in urban/community areas such as that embracing Erwin Creek along I-77 in Charlotte.  Urban and community areas in North Carolina average 18.5% and 17.3% respectively.

That average is on the low side compared to many other states but for comparison, within the city limits of Durham, the fourth most populous in the state, there are 19,176 acres of impervious surface which is 27.6% of the overall land area, a proportion more typical of the average for urban areas in about half of the other states, according to the study.

Durham is the only city in a very compact county which doesn’t track impervious surface so the comparison may not be “apples to apples.” But it is clear that in a city where only 27,780 of tree cover remain to help scrub the runoff from 19,176 acres of impervious surface, a ratio of 1.4 to 1, we must do much more to fuel urban forestry than a net 150 trees a year.

Taken statewide, the ratio of trees to impervious surface is 3.3 to 1, making it even more tragic that the new legislation that legalized the atrocity along Erwin Creek does not protect trees in communities such as Charlotte or Durham contrary to what its chief sponsor verbally assured the General Assembly from the floor.

In North Carolina the percentage of tree cover is 12.7 points less in urban/community areas while and impervious surface 12 points more in urban/community areas than in rural areas.  This tells me that compared to other states in the report, we may also be deforesting and paving over rural areas.

Interestingly, in many states such as Iowa, through which I traveled on a cross country road trip last month, the urban and community areas are forested by 24% and 18.8% respectively while the state as a whole is only 10.4%.

But even in small towns, Iowans are careful to make sure they have tree canopy, as are many farmers and ranchers around their homes and barns and equipment sheds.  One huge spread I spotted along I-80 as I returned from my trip had very deliberately planted a tree every few feet around the entire border as well as mini forests along ravines.

That is why I blogged a few months ago that maybe some in our state, which has been blessed with naturally occurring hardwood and evergreen forests, have become a bit too smug.  We take our trees and the fact that we’re aided by regeneration far too much for granted.

To sustain our state’s urban growth and still retain the scenic character and quality of life (and health) so central to our state’s economic vitality, including tourism, we need to look more seriously at a more intense and holistic approach to forest management including:

  • Reforestation and afforestation of not only urban areas but also rural areas.
  • Higher state and community standards for tree cover in and around parking lots and along roadways.
  • Manifestation by the NC Department of Transportation that it is as much in the business of managing forests for ecosystem services on behalf of the public as it is focusing attention on highways.

No comments: