My training as a marine scientist takes me only so far in my journey toward becoming an environmental historian, and it is necessary to lean heavily on the wisdom assembled by others who have gone on before me.

One of their earliest messages is that of the vastness of the Chesapeake forest. The first perception of the earliest European visitors to the Bay is that of an unbroken canopy and great dark stands of colonnaded trees. And, that was in fact what some of the early visitors — notably John Smith and Maryland’s founding colonist, Father Andrew White — did see when they arrived on the necks of land which lay between the Chesapeake’s several rivers.

There are descriptions of open, parklike stands. John Smith, in particular, wrote about mammoth, individual trees, including the cypress, whose circumference at its base measured three fathoms (18 feet). He wrote about oaks from which square timbers could be hewn 2 1/2 feet on a side and 20 yards long. Extraordinary keel timber.

England, by the early 17th century, had pretty much logged off its best timber and the prospect, for a seafaring nation, of boundless new timber resources met with great enthusiasm. In the 17th century, a 74-gun ship — a thousand tons or more — required a mainmast about 39 feet in diameter and approximately 103 feet long! Building an entire warship in this class consumed almost 34,860 cubic feet — more than 414,300 board feet — of oak: clear-grained, tight-ringed, old growth oak. No chipboard here, folks.

Native Americans had already cleared small areas along the river bottoms for agriculture. Trees were girdled —a laborious process in which a band was cut through the trees’ living bark and cambium layers using a stone axe. This essentially strangled the tree, which after a few years would die and decay, opening the forest canopy for the planting of crops.

These “Indian fields” became prime opportunities for colonial agriculture and were much sought after not only because the labor of clearing was already done, but they were also often located in especially fertile alluvial soils. The Jesuit colonists, led by Father Andrew White, were careful to make what they viewed as a fair and legal purchase of lands from the original inhabitants, upon which their community and later Maryland’s first capital — St. Mary’s City — were founded.

But the nature of our pre-colonial forests inland from the coast is less clearly known. During his exploration of the Bay, John Smith met a Native American named Mosco, with whom he and his crew became friends. They asked him about the forests farther inland but Mosco said very few knew anything about these woodlands because they had not been burnt, a practice that was used to drive game and, not incidentally, clear undergrowth for easier passage.

West of the “fall lines” of the major rivers — where they tumbled as rapids down the rocky discontinuity between hilly piedmont and level coastal plain — the forests were more “trackless.” Inland tribes were hostile to the coastal Powhatans and the Piscataways, creating what appeared to be a zone of separation, where parties from both groups of tribes went to hunt seasonally.

Some of these areas were on thin soils overlying rocky outcrops. When fires were repeatedly set in these areas, they would remain as open grasslands, fragmenting the surrounding forest. Many of these mineral outcrops — chromium-bearing rock called serpentine — run southwest to northeast, paralleling the ridges of the Appalachian Mountains. Fire could run along these outcrops with ease on the prevailing winds and perpetuate the fragmentation.

Woodlands edges, where scrub vegetation is trying to colonize grasslands adjacent to forest, are good for wildlife, as they contain a lot of “mast.” Mast is new twig, bud and leaf growth on which deer, elk and the then-present Eastern woodland bison could browse. (One of the latter was reportedly shot by a colonist, within 15 miles of today’s Washington D.C.) The available food supply attracted quarry and hunters to these areas again and again.

Serpentine barrens, if we look at today’s geologic maps, occupy a small but widespread fraction — perhaps 1 percent — of the highlands. We might assume most of them were burned to drive game at one time or another. This kind and proportion of forest fragmentation was probably very attractive to wildlife, and did not in any way jeopardize the integrity of the millions of acres surrounding these openings.

As later generations of colonists explored westward in the Chesapeake’s great watershed, they found areas of grassland in the Susquehanna’s Wyoming Valley, and some accounts report much of the Shenandoah Valley — perhaps hundreds of square miles — was open land. These might have arisen from, or also been maintained by, Native American burning practices, as well.

During the American Revolution, one of the inducements for risking one’s life was the promise of a grant of farmland. Some of these parcels were inland of Baltimore and bore the name “Soldier’s Delight.” They were poor lands for farming and must have represented a real irony to the men coming to claim them.

There were other areas parceled out in Western Maryland, that Forester Dan Boone says were described in early surveys as scrub forest. Whether these were simply poor soils, or had been burned or blown down by storms, we may never know.

The role of natural disasters in fragmenting the forest is important. Hurricanes have come up the Atlantic Coast ever since the present day climate was established after the last ice age. Hurricanes occasionally do great damage and open up hundreds of acres of forest canopy. Ice storms during unusual winters can do the same.

Thunder squalls with downbursts and tornadoes, such as the severe ones experienced in Maryland this year, are also periodic features of our weather, recorded since colonial times. They carve miles-long swaths through woodland, felling or twisting off the stoutest trees.

Research in northeastern forests estimates that the return frequency over which a given parcel of woodland might experience such a disaster is about 540 years. Old growth forest can get pretty mature in 540 years. [“Coastal Wilderness to Fruited Plain” by G.G. Whitney, Cambridge University Press, 1994]

El Nino events and sunspots cause neither hurricanes nor tornadoes but their frequency is some indication how often weather cycles repeat. Sunspot cycles, for example, repeat an average of every 11 years. Hundreds of years ago, according to borings deep into corals in the Galapagos off Ecuador, El Ninos used to repeat about every 6 years, but as the 20th century comes to a close, the time between events has been compressed to something like 2.2 years. [Reported on NPR, Morning Edition WSCL 11 August 1998] This might mean a greater stress on forest integrity than was experienced in pre-colonial times.

Overall, with present understanding and ongoing research on the subject, it appears that 5 percent of the basin’s forest canopy may have been open — fragmented and deforested — at any one time during the pre-colonial period. Compared with today — where almost 43 percent of the forest cover has been removed, and essentially none of it has survived undisturbed since colonial times — fragmentation and its implications for the ecosystem are profound.