Archaeologists in Maryland's Historic St. Mary's City recently unearthed a small commemorative medal. It bore the Latin inscription which, translated, reads "Gradivus [Mars] Governs the Sword. Themis [Justice] Herself Governs the Scepter." The likeness on the obverse was that of Gustav II Adolphus, Sweden's famous warrior king.

This seemingly out-of-place artifact offers a cautionary tale of how the rise and fall of nations is often linked to their natural resources. In the Chesapeake Bay, we have lost a lot of forests, and we will be in danger of losing more if we don't pay attention to the history of other nations as well as our own.

Fourteen years ago, ecologist Howard T. Odum sent me a paper that he and three colleagues-a historian, a forester and systems ecologist-had written that demonstrated the power of forests as a renewable system for harvesting energy. Using Odum's ecological principles, they showed how natural resources had been used to further Swedish national interests during a period of wild expansionism and how exceeding the forests' replacement capacity contributed to the subsequent decline of Swedish influence.

Empire-building among European powers during the 16th and 17th centuries was terribly wasteful. The philosophy was often that "a war should feed itself." That is, the assets of a conquered or invaded people should be taken to support the military on its marches.

Swedish national aspirations began with the ascent of Gustav Eriksson, known as 'Gustav Vasa,' who ruled 1520-27. He was succeeded by Charles IX, and he in turn by Gustavus II Adolphus, third of the Vasa kings, who reigned from 1611 until 1632, when he died fighting in Germany. This period overlaps a major part of the English colonization story so often visited in this column.

Gustavus Adolphus continued to build what became an influential Swedish Empire. He was helped by Sweden's vast, boreal forests. These stood behind Sweden as well as any army in reserve as a source of energy-firewood and charcoal-for the extraction of iron, copper, silver and durable materials for shipbuilding.

Sweden, despite her Viking reputation, had historically been a weak, poor and sparsely populated nation. Gustavus Adolphus sought to overcome that, and territorial ambitions led him into wider conflicts that eventually erupted into the devastating Thirty Years' War (1618-1648). This widespread continental conflict was one of the most destructive and wasteful periods in European history.

Sweden's great forests supported what was for that time, a mobile cavalry and a modern army of pikesmen, swordsmen and archers supported by artillery and grenadiers on the flanks. Small neighbors were conquered one after the other, and a great deal of Sweden's forests were lost.

Sweden's extracted resources included bar iron and copper-much of which was exported-and a small amount of silver for domestic coinage and crafts. While the iron and copper exports were vital for funding Sweden's adventures, the extraction of each required immense amounts of firewood and charcoal to attain the high temperatures needed to refine: 25,000 cubic meters of wood and 6,000 cubic meters of charcoal annually.

Wood had other uses. "Next to God," Gustavus Adolphus said, "the welfare of the nation depends upon its navy." Sweden-and the Baltic-also exported ship timber for masts and spars.

Sweden's navy in 1570 had an aggregate displacement of 21,000 tonnes, considered at that time to be the largest sailing navy in the world. This rose temporarily to 35,000 tonnes in 1645 and in 1670. The amount of timber harvested to build a 17th-century naval fleet was astounding. Odum and his historian co-author, Jan Lindegren, drew on an amazing source for their calculations: the Swedish royal ship, Vasa.

Vasa, named after Gustav Vasa and his dynasty, was a disaster for Sweden but a gift to modern historians. In 1627, Gustavus Adolphus, jealous of a Danish warship with two superimposed decks of guns, decreed that Vasa-then under construction in Stockholm-must have these too. On its first voyage in August 1628, with flags flying and all gun ports opened, Vasa was so top-heavy that it tilted to one side not a mile from its departure point and sank within minutes to a depth of more than 100 feet. Fifty sailors and important guests drowned. Sinking into, and filling with, the soft mud of Stockholm harbor, Vasa was preserved almost intact, along with goods, provisions, decorative sculptures and even some of its sails until the ship was raised in the 1960s.

I visited Vasa, the world's only near-complete 17th century warship, in 1965, while it was still undergoing stabilization. Today, the ship is exhibited in a large museum with its lower masts and rigging set, almost intact after 400 years.

Odum and his co-authors discovered that for a ship of this size, it took about two years for shipwrights to scout out suitable oak trees, cut and season the timber, then move it (in this case) to Stockholm. It took another two years to assemble 300 skilled men and build the ship.

These vessels were launched as soon as they could float and the rest of the ship was built up while she lay alongside. Vasa, when complete, weighed 1,320 tons-2.6 million pounds-and was 227 feet long. It's calculated that for a warship with 74 guns, 4,500 cubic meters of oak and 570 cubic meters of soft woods were required at the shipyard: 7.11 million board feet per ship. Sweden, on average, built these ships at a rate of about 2.65 annually. Each ship, over a lifetime of 14-17 years, required another 40 percent more wood for repairs and maintenance.

The timber for ship masts and spars was prodigious; each ship required 20-25 masts and spars of various sizes. The average mast was about 28 inches in diameter, and at least 87 feet long. Lacking the proper bole (trunk) timber, Vasa's mainmast was built up from a squared pine log core surrounded by oak cheek pieces, and was 4.2 feet in diameter.

Many quality mast trees left Scandinavia to spar the fleets of other nations. England sent a fleet of 20 ships into the Baltic for spars in 1634, having only just begun to exploit North American forests in the New World.

Swedish forests also yielded Baltic tar, one of their most voluminous exports, and a vital naval stores commodity for shipbuilding and maintenance. It was used to saturate ships' rigging to stop solar and saltwater degradation, to prevent the "checking" or cracking of spars, to seal seams in the decks, and to topcoat and make watertight the caulking hammered into seams underwater. Rope fragments found in the English fort at Jamestown still smell of the preserving tar after more than 400 years. It is odd that despite the value of these materials, The English were slow to produce tar from North American forests.

Sweden's coniferous forests provided immense quantities of tars and pitch. Men working during slack periods on their subsistence farms cut wood near their homes and could produce, on average, a barrel of tar per man each eight to 10 days.

The trees were prepared by peeling 25 percent of the bark in a vertical strip each year. The tree, trying to heal the wounds, would saturate the trunk with resins. The logs, once cut, were stacked butts down in a fan-shaped piles on a sod-covered sloping platform called a tjŠrdal-or tar valley. These stacks were covered by layers of sod to seal out air. A slow-cooking fire ignited within caused tars to melt out and drool down to a collecting trough and then funneled it into barrels.

About 1,066 board feet of solid, resin-rich wood were required to produce each barrel of tar. "Lighter" fractions of volatile materials could be distilled from raw tree saps like tar, which with density of 1.1, was much heavier than water. The resulting product was a turpentine that was used as a solvent or for paint.

Even the barrels in which the tar was shipped were made from local spruce trees. From Sweden (and conquered Finland) yearly tar exports rose from 3,500 barrels in 1559 to 128,000 barrels from 1684-87. Annually, it is estimated that 600,000 cubic meters of wood-2.6 million board feet-was consumed by this part of Sweden's industry, representing an energy consumption equivalent to 1,400 gigawatt hours of electricity.

Taking advantage of the wars between the Dutch-who had settled what became New York and New Jersey-and England, Sweden claimed territory in the New World, both in the Caribbean and within the Delaware estuary. The ship, Kalmar Nyckel, visited a fort near today's Wilmington, DE, once at its founding, and later with a second wave of settlers.

The Swedes, while not a direct a threat to the Maryland colony, lent proxy support-muskets and training-to the warlike Susquehannock tribe, who were themselves expansionists. This tribe was embroiled in conflicts with English Marylanders as far south as the Patuxent River.

Sweden's national influence peaked while its far-flung possessions were still unstable, and began to decline as command of the underlying forest energy resource was lost. It was not for lack of trees, but the ability to transport increasingly far-flung timber to its place of use. Trees of the required size were simply inaccessible, given that local people transported them by sledges with triple axles using yokes of eight to 20 oxen. Trees of size, and trees for "compass timber"-the curved pieces that formed a ship's framing-could not be found. The energy drain became too great to support. Thus, the market for ship timber began to shift significantly to North America.

In the 1640s, Swedes disgruntled with the wars back home began emigrating from Delaware to Maryland, which was more stable. The Dutch, in 1655, overwhelmed the thinly manned Swedish fortifications near Wilmington-which had no gunpowder at one point-and renamed the area New Amstel.

In 1660, Maryland developed a legal naturalization process-denization-for New Amstel immigrants, as well as those that arrived in 1640s. While most of these records are lost, at St. Mary's City at least 16 persons filed for this status in July 1661, and are described as "Swedes, late of (Dutch) New Amstel."

Among these new Maryland arrivals was a Dutchman named Garrett Van Sweringen who moved to St. Mary's City after New Amstel was taken over by an English fleet under Sir Robert Carr about 1664. Van Sweringen and his family opened an inn at St. Mary's, which became a popular gathering place for officials. The medal featuring Gustav II Adolphus was found in his inn.

(Visitors to Historic St. Mary's City can see this "token of remembrance of the hero king. It is also possible to visit-and sail aboard-a replica Kalmar Nyckel, which often calls at Chesapeake ports.)

At that time, the exploitation of natural resources that had led to Sweden's rise and fall was just starting in the Bay watershed.

Chesapeake forests were one of the first resources to be harvested by Europeans in the 17th century. They have since become one of the most exploited and abused of all the basin's treasures, not only for ship masts, charcoal, tar and other forest-related resources-but simply by wasteful clearing.

The harvesting of North America's tall, clear-grained trees began with a shipment of masts from Jamestown in 1609.

John Smith, in his earliest accounts, extolled the massive Chesapeake timber available for shipbuilding, including straight oak for keels 30 inches square and clear-grained for 60 feet, as well as cypress with boles 18 feet around that could provide a wonderful, rot-resistant wood.

The trees were so long that the stern of the ship had to be opened to slide them into the hull for the voyage to England.

The maturation of this trade took about 100 years in North America. As ships increased in size, loggers focused on New England, where the trees were the tallest.

When England, in the 18th century, stopped exports of North American wood to competing powers in Europe, the loss of trade became one of the root causes of the American Revolution.

What has happened to our forests over centuries is one of the reasons for today's condition of Chesapeake Bay. By the early 20th century, 60-70 percent of the watershed's forests were gone, launching untold tons of sediment a journey toward the Bay-much of which is still en route-and removing one of the landscape's most valuable nutrient sponges.

Forests have recovered a bit, but less than 60 percent of the Bay's watershed is forested today, and much of it is poorer quality than the forests that early Europeans first set eyes on. The watershed loses about 100 acres a day at present.

Sweden's vast forests today are believed to be managed sustainably, but one must remember the serious consequences from using them unsustainably to fuel that nation's expansionism in those distant times. Take their lesson to heart and nurture our forests for the future.

For an overview of the importance of forests to the Chesapeake, see "Can Trees Save the Bay?" in the December 2009 issue of Chesapeake Quarterly from Maryland Sea Grant, at www.mdsg.umd.edu