What is the difference between a forest and woods?  A forest is a community of plants and animals, usually continuous and fairly large in area, which is made up of trees of all ages and has not been significantly disturbed in a relatively long time.  Woods are a bit different; they can develop into a forest eventually, but in the Philadelphia area, historically people have logged their woods at least every hundred years, so the forest has not been allowed to regenerate.  Small areas of woods are sometimes referred to as "wood lots", and are periodically harvested for their timber, then allowed to regenerate for a few decades, harvested again, and so on.  Woods can be viewed as forests in their teenage years; they resemble the mature forest in some respects, but they're not quite old enough to be truly called forests.

A typical wooded area in the rugged and rocky Wissahickon Valley; this photo
was taken near the intersection of Bell's Mill Road and Forbidden Drive, about
a mile from the Arboretum.  Shown are native oaks (Quercus spp.), American
beeches (Fagus grandifolia) and maples (Acer spp.).  (photo credit: Brice Dorwart)

 

The natural areas of the Arboretum that contain medium- to large-sized trees can not really be called "forest", since the entire region was denuded of trees to make room for agriculture as recently as a few generations ago.  This does not necessarily mean that the woods are inferior to the forest that would have occupied this land hundreds of years ago, but it does mean that the trees will probably not live as long, or get as large, as they did when the area was forest.  The difference has to do with the length of time that the plant community has been established.  While an area of land can become completely covered with trees that were not planted by people (i.e. they grow there from stump sprouts or naturally dispersed seeds) within only a few decades, it will not be a "mature" forest until a few hundred years have passed.  Mature forests tend to have greater plant and animal diversity, and the trees not only grow more slowly, but they live longer and reach greater sizes than the same species would in the woods.  In addition, mature forests contain trees of all different ages, while woods tend to be "even-aged stands", which means that most of the trees are the same age, because they all started growing at the same time once the land was allowed to revert to woodland.

The Arboretum is located in USDA hardiness zone 6b, meaning that the average lowest winter temperature is around 0 to -5 degrees Fahrenheit.  This hardiness zone helps to determine the kinds of trees found in the woods nearby; it is warm enough for hardwood trees to thrive, but there are some conifers as well (see the woods plant list).  In addition to the woods on the Arboretum's property, which are between the George D. Widener Education Center and the Wissahickon Creek, there are many, larger patches of protected woods nearby, mostly in parks.  Philadelphia's 9,200-acre Fairmount Park system contains thousands of acres of woods; Wissahickon Park and the Andorra Natural Area, in the northwestern section of Fairmount Park, are less than a mile from the Arboretum, and together they contain approximately 1,600 acres of woods.  To learn more about these woods and the trails that run through them, visit Fairmount Park's trail system web page.  There are also more than a dozen State Parks in the Philadelphia region, including Fort Washington State Park; to find one nearby, visit the Pennsylvania DCNR's Southeast Region web page.  To learn about local natural areas and watershed conservation issues, please visit the Wissahickon Valley Watershed Association's website.

 

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