Birches of Eastern Pennsylvania

     Four species of birch trees are native to eastern Pennsylvania, including black birches, yellow birches, river or red birches and gray birches.  Each kind is adapted to a specific habitat apart from its relatives.  And being related, all these birches have characteristics in common, some of which are attractive to us, making these trees worth experiencing. 
     All birch species have wind-pollinated catkins that grow early in spring before the birches' leaves do.  Male catkins are about two inches long and pendulous, while female ones on the same tree are about one inch long and upright. 
     Birches have small, cone-like structures where the female catkins were and where tiny, winged seeds develop by autumn.  Each seed has a wing on each side, making it look like a tiny butterfly.  And those two wings together carry the seed on the wind away from parent trees for maximum dispersal. 
     Birch trees feed a variety of wildlife.  Many seeds are eaten by mice and small, seed-eating birds.  White-tailed deer, snowshoe hares and cottontail rabbits ingest buds and twigs, particularly in winter.  And beavers consume the bark and twigs of birch trees, as well as using those trees to make their dams and lodges.  
     Black birches have smooth, shiny bark, with noticeable, horizontal lenticles in that bark when they are young.  Bark on older trees, however, develops vertical cracks and irregular, scaly plates, especially on their trunks.  And chewed twigs of this species have a pleasant wintergreen fragrance and taste that can be savored when hiking over wooded hills. 
     Black birches are most common on rocky, wooded slopes where they are associates of chestnut oak trees, red oaks, sugar maples and other deciduous, upland tree species.  In fact, black birches and chestnut oaks dominate many wooded, rocky hillsides in eastern Pennsylvania, such as Governor Dick Mountain near Mt. Gretna.
     Yellow birch trees inhabit cool, wooded ravines where cold streams and brooks flow through.  They are associates of eastern hemlocks in many of those woodland valleys.  This birch has thin, pale-yellow bark that peels away from trunks and limbs in tight curls.  Those curls, even when wet, can be used to start campfires because of the resin in them.  And their twigs have a hint of wintergreen scent and taste.  Sapsuckers, which are a kind of woodpecker, punch holes in the soft bark of this birch and later come back to lap the sugary sap that drips from those wounds in the bark. 
     Some yellow birches look like they grew on "stilts", which is interesting to see.  Those birches on poles are caused by seedling yellow birches sprouting on stumps and fallen logs.  As the yellow birches grew tall and put roots into the ground, the wood of the stumps and logs rotted away, leaving those birches on stilts.
     River birches, also called red birches because of the color of their loose bark, have thin bark that peels away profusely from trunks and branches, giving the trees a shaggy, but attractive, appearance.  River birches have been planted on many lawns because of their rustic, intriguing bark.
     As their name implies, river birches are adapted to bottomlands along creeks and rivers, where they are associates of sycamores, and ash-leafed and silver maple trees.  All those tree species, and more, help hold the soil down against erosion, and feed and shelter wildlife as well.
     Gray birches have chalky-white or grayish-white bark, with dark triangles where limbs protrude from trunks, making these birches attractive.  They are so striking that gray birches are planted on some lawns. 
     Gray birches have adapted to pioneering dry, rocky, poor soil where they are associates of large-toothed aspens and scrub pines.  These three species of trees colonize land abandoned after farming or mining fails, and when fires burned down forests.  Many gray birches have pioneered slag heaps from mining along Route 81, just south of the Pocono Mountains, for example.  In fact, they seem to be the only tree on some of those waste piles from mining.  
     All the birch species are lovely trees that also provide food for wildlife.  And through divergent evolution, each kind has its own habitat, which spreads the various species into different niches, thus reducing competition for soil, rainfall and sunlight with their relatives.