Complicated truth of forests


Connected: As the critical factor in overall watershed health, trees should be understood and appreciated as a resource not to be wasted.

November 21, 2003|By Tom Horton | Tom Horton,SUN STAFF

TWO "facts" about Chesapeake Bay forests that I routinely hear:

We've got more trees now than we did two centuries ago.

We're losing our forests a mile a minute.

The truth is more complicated, and well worth understanding, because no landscape is more critical to bay health than the great green filter.

Just by growing, forests across the bay's 41 million-acre watershed sop up about 184 million pounds of nitrogen that otherwise would enter the bay annually from polluted air and runoff.

To put that in perspective, about 300 million pounds enter the bay from all sources. Of this total, forests contribute 10 percent, though they cover about 58 percent of the watershed.

Each acre of forest also produces more than 100 tons of oxygen each year and removes 40 tons of carbon, which retards global warming, which in turn is a factor in the sea-level rise that is rapidly submerging many bay wetlands - which filter nitrogen from the bay. So it's all connected.

A study by American Forests, a national conservation group, estimates that increasing forest cover in the Baltimore metropolitan area by about 25 percent would equal spending $100 million on physical structures to filter polluted runoff and $3 million a year spent on air pollution control equipment.

Trees, from the environment's standpoint, are as good as it gets; and this is before we even count their immense wildlife and aesthetic benefits. Ideally, cutting trees should be illegal and cruelly punished. Planting them should qualify for tax credits and sainthood.

So how is it really going with the bay's forests? More than ever, or fading fast? It depends.

Forests covered 90-some percent of the watershed 400 years ago, when Capt. John Smith wrote, "There is little grass but for that which grows in the marshes, for this country is completely overgrown with trees."

Trees covered 70 percent to 80 percent of the watershed by the mid-1700s, as more people and their favorite crop, tobacco, began usurping the landscape. (These estimates are from the Environmental Protection Agency and U.S. Forest Service.)

During the next century, bay forests shrank to about 50 percent of the bay watershed - more people and croplands, households burning 20 to 40 cords of wood a year for energy, more than 3 million miles of rail fences nationwide and railroad ties consuming forests by the millions of acres. So it is correct to say that compared to the early to mid-1800s, we've got more forests today.

Bay forests would recede to 30 percent to 40 percent of the watershed by the turn of the 20th century. Whole forest-types, such as hemlocks, were virtually removed from large regions, including the Susquehanna River Basin in Pennsylvania.

From this standpoint, bay forests, which reached about 60 percent coverage of the watershed by 1970 as old farms and clear-cuts regenerated, have been coming back like gangbusters.

And one might wonder: If forests are so critical to the health of the bay, why wasn't water quality a lot worse in 1900 than nowadays, when we complain of "historic" declines in the bay environment?

The answer is that it's not just the size of the filter that's important. It's also the nastiness of what needs filtering.

While sediment pollution from forest clearing was a problem in centuries past, the runoff in those days did not contain anything like today's brew of superabundant manures, commercial fertilizers, airborne pollutants and toxics. Nor were as many of the clearings in former centuries paved with asphalt, which maximizes the runoff of pollution.

Since the 1970s, bay forests have declined somewhat, from about 60 percent of the watershed to about 58 percent, a trend that continues.

But watershedwide statistics can be misleading. While forests are stable or increasing in the far western and northern parts of the drainage basin, declines in the Piedmont and Coastal Plain have been extensive.

These latter regions are closest to the bay and its tidal rivers, the most critical places to retain and enhance the forest filter. Forest coverage here is about 32 percent, as bad as the watershed was in 1900 at the nadir of the forest.

Recent forest loss statistics - from 1985 to 1995 - show Maryland losing about 100,000 acres, Virginia 200,000 acres, southern Pennsylvania 85,000 acres and Delaware 4,000 acres. Most of this is in the areas closest to the bay, where the filter needs to be thickest, but is thinnest.

Nor is the quantity of forest everything. "The quality of a forest matters as much, or perhaps more," said a recent EPA report.

Underscoring that is an American Forests study that compared satellite photographs over 24 years in an 11.5-million acre region closest to the bay.

It found that beyond the clearing of forest, a far larger decline had taken place in quality. Areas still green enough to qualify as "forest" were degraded enough by development to have lost much of their pollution and wildlife benefits.

The story of the bay and its forests is a complex one. But the better we understand it, the more we will realize that when we topple trees, we discover them rooted in the health of the system.

And a final note on forest quality. There are indications that if we continue bombarding forests with current levels of air pollution, they will begin losing their capacity to soak up nitrogen, and begin releasing it by the tens of millions of pounds annually - defeating much of our hard-won cleanup efforts on sewage and other fronts.

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