Are there more trees in North America now than 400 years ago, about the time the first European settlers arrived? Are any of the trees they may have planted still alive today?

If you want to know the answer right away, scroll down to the last 3 paragraphs.

Imagine you're the editor of a scientific journal on a planet in another solar system, and you're reviewing a manuscript someone has submitted about life forms on a planet called Earth. These forms are referred to as trees and are composed of cellulose husks, which are more or less vertical but have appendages which go this way and that. Earth is tilted on its axis approximately 23 degrees so that during its period of revolution (called a year) around its home star, the northern hemisphere of Earth is pointed toward the star for about half a year, after which time the southern hemisphere then faces it. The trees that happen to be in the hemisphere facing the star suddenly sprout flat, green mats as the star begins to move higher in the sky. In fact, the trees seem to take sustenance from the star, which enables them to grow and to add more of the green mats. Later, as Earth continues its sojourn about its star, the hemisphere that was cantered toward the star now points away from it, and at mid day, the star is no longer high in the sky. As a result of this change in orientation, the trees become much more colorful, and individual mats take on brilliant hues of crimson, scarlet, maroon, gold, and orange. As the daylight period continues to wane, the mats are quickly drained of their color and soon become detached from the trees, descending to the ground beneath them. The trees now stand naked for about a half year until the star again begins to climb higher in the sky. I'm guessing you'd toss such a farfetched fiction piece into the circular file.

Trees are indeed amazing. They're Earth's biggest and longest living life forms, and they've been able to eke out a living in places where there's very little soil, such as on the flank of a mountain, and where the soil is always submerged, such as in swamps. They can also survive subzero cold and searing heat. As Walt Whitman said about forest trees, "Tall and graceful, yet robust and sinewy, inimitable in hang of foliage and throwing-out of limb."

The biggest trees and some of the oldest trees are the giant redwoods (Sequoia sempervirens and Sequoia gigantea) that live along the Pacific coast of the U.S. Conditions here are nearly ideal for redwoods. From autumn through early spring as much as 60 inches (1,500 mm) of rain may fall, and although it's not rainy in summer, frequent fogs provide some moisture and prevent moisture loss (evapotranspiration). Only occasionally does the temperature dip below freezing or creep past 80 degrees F (26 degrees C). These brutes can live over 3,000 years and reach a stature of over 300 feet. Click on http://www.nps.gov/seki/shrm_pic.htm to see an image of the General Sherman Sequoia.

The oldest trees are likely the bristlecone pines (Pinus aristata) that live on the eastern slope of the Sierra Nevada Mountains, along the border of Nevada and California. These pines are puny compared to the redwoods and are even small in comparison to different species of conifers nearby. Nevertheless, some of these specimens are over 4,000 years old -- as old as the pyramids of ancient Egypt.

Apparently, the world's oldest trees are found in locations that either receive abundant rainfall or hardly any at all. In contrast to the redwoods, the bristlecones thrive high above sea level (10,000 ft or about 3,077 m) and in dry, rocky environments (< 10 inches or about 250 mm of rain annually). While these conditions prevent youthful bursts of growth, they're just right for slow growth, which can also result in extended life. With comparatively little tissue to nourish compared to their large cousins, in some years, the bristlecones add perhaps only an inch to their girth per century.

The U.S. is blessed with a profusion or tree species, especially the Mid-Atlantic and Southeastern states. The state of North Carolina may have as many species as all of Europe. In general, a longer growing season favors specimen diversity, but even more important is the geography of past ice ages. During the last ice age in North America (known as the Wisconsin Ice Age), which reached its greatest extent about 20,000 years ago, as the ice sheets inexorably pushed southward, the colder climate forced trees (actually their seeds) indigenous to northern latitudes toward more southerly locales. When the ice eventually retreated, some of the northern trees remained in the southeastern parts of the continent, having become acclimatized to their new home. In Europe, most of the ice was confined to Scandinavia, but colder temperatures across all of Europe meant that trees, which once flourished during the warmer pre-glacial period, had to migrate south in order to find conditions they could tolerate. However, the Alps, Mediterranean and Black Seas checked the southward migration of many trees. Thus, those species that weren't able to adapt to a colder climate were wiped out.

One of the most noble trees in eastern North America is the White Oak (Quercus alba), the state tree of both Maryland and Connecticut. Perhaps the most magnificent white oak in the US was the Wye Oak on Maryland's Eastern Shore (http://www.nal.usda.gov/speccoll/images1/wye.html). This behemoth stood 95 feet tall (30 m), with a girth of 28 feet (8.5 m), and its majestic crown spread out more than 125 feet (38.5 m). In recent years, it was partially supported by wires; it toppled in a wind storm last June. Based on anecdotal evidence, the Wye Oak was thought to be over 450 years old. The Charter Oak in Connecticut, which was felled by a storm in 1856, was estimated by some to be perhaps 1,000 years old.

As impressive as these trees were, they may not have been as ancient as their prodigious size would seem to entitle them. As a rule of thumb, trees that live on relatively flat ground and have roots tapping moist soil are likely not nearly as old as their dimensions might indicate, even if their girth and height are indeed awesome. Rich soil, a benign climate and a long growing season can result in phenomenal growth rates, which can lead one to over-estimate a tree's actual age. In 1984 a lower limb of the Wye Oak broke off and was dated by counting its rings to be 264 years old. Why such a limb, fairly close to the base of the tree, should be so much younger than the estimated age for the Wye Oak itself (450 years), is not easily understood. The final tally for the age of the Wye Oak is not yet in -- a complicating factor in counting the rings is a large rotten cavity in the trunk.

When the "Lincoln Tree," a large copper beech, was taken down at Soldier's Home in Washington D.C. last year, it was presumed that this was the same tree where President Lincoln sometimes sought shade at his summer home during the Civil War. However, instead of being a mature tree at the time of the War Between the States, tree rings placed its age at approximately 140 years - it would have been just a little sprout and couldn't have even shaded the president's size 13 feet. So, while there may be a few trees alive today that were standing tall when the first Europeans landed in North America, it's almost certain that any of the trees planted by the first residents of Plymouth or Jamestown are today just mulch on the forest floor.

Even though satellite views of most places east of the Mississippi River would still show a pervasion of green, it's not as green as it was before the first Europeans arrived 400 years ago. In the mid 1950s, it was estimated by the National Geographic Society that forests covered approximately 3/4 of the original acreage present when the first European settlers arrived. A good deal of additional tree loss has occurred in just the last half century. For example, according to American Forests (a conservation organization), the forest cover in the Baltimore-Washington area decreased from 51% in 1973 to 39% in 1997. Although building and construction is somewhat higher in this region than across most of the eastern US, in nearly every urban and suburban area, there are far fewer trees now than just a score ago. Not only have trees been cut down to make room for housing developments and highways, but timbering, diseases (such as Dutch Elm disease) and acid rain have all taken their toll. In the U.S. today, perhaps only 60% of the land originally in forest 400 years ago is still forested.

Many jurisdictions, recognizing the benefits of trees to their communities, have been planting saplings at a faster pace than they've had to remove diseased and dying trees. Also, a number of companies that log timber stands are now planting seedlings at a pace far surpassing removal. Nonetheless, pint-sized little fellas can't possibly provide the same sort of environmental bonuses as their full-sized brethren. With the loss of a forest or even individual mature trees, there is an irretrievable loss of shade, for cooling and reduction of evapotranspiration; leaf litter and crown, for buffering both atmospheric and water pollution; and root and trunk system, for minimizing runoff and erosion. The sylvan cathedrals that greeted the first colonists may be long gone, but fortunately, there is now an awareness that a healthy and varied ecosystem is largely dependent upon the presence of mature, vigorous forests.

For more about forest lands and state trees, see the National Geographic Magazine for November 1955 and October 1957.

I would like to acknowledge Rebecca Kidd, Manfred Owe and John Ohler for their help with this question.

This week's question is provided by Dr. James Foster. Dr. Foster originated this series and did it as a solo project for the GSFC website for SEVEN YEARS! This year Dr. Foster has decided to share the enthusiasm he has for this project with other Goddard scientists and will be posing questions on a semi-regular basis.