The native oaks are easiest to identify by bark alone when they occur in pure stands, which, among all our indigenous deciduous tree species, the oaks are most apt to do.  Part of the difficulty in seeing and identifying oaks in a mixed forest setting comes from the prejudices we associate with certain storied species.  More often than not, the iconic tree we envision when thinking of oaks is the English oak (Quercus robur), admittedly the most visually memorable member of the genus, but still, it's a sort of ironic cultural hangover, particularly given the broad diversity of North American species of oak.  Even if we are familiar with the forms, habits, and haunts of some of our native American oaks, we usually imagine them as open-grown specimens, when, like maples, they can turn into colossal trees.  However, even the most recognizable of the oaks, the pin oak, (Quercus palustris),  whose unmistakable and efficient branching habit graces many a late twentieth-century carpark, assumes an entirely different visage given the competitive stresses of the forested setting.

Red Oak

Of course, as is the case with even the most difficult genera, the most prevalent species is always the easiest to identify.  Among the native Quercus,  red oak (Quercus rubra) plays this role predictably, but capably nonetheless, as the species that is most widely distributed throughout the varied micro-environments to be found in our ecologically diverse region.  While most often found in acidic woodlands, red oak often dominates south-facing slopes with rich soil of varied chemistry.  Red oak has dark gray bark that becomes roughly furrowed, with raised, scaly ridges.  With advanced age, the eponymous red underbark is exposed, a dead give-away of its identity for anyone who has ever struggled to light a batch of flatlander firewood.  Once again, this species provides another instance in which location, location, location, makes all the difference; for of the ten species of oak native to Berkshire County, red oak is the sole species of oak found on the Berkshire Plateau, and never at high elevation, essentially disappearing as the presence of balsam fir and red spruce increases in the landscape.

 HortTopic: Plantings Under Oaks

All trees present challenges to the shrubs and perennials that one might wish to grow under them, but several species produce conditions and issues that require customized remedies.  Maples, for instance, colonize the soil with a prodigious number of fine, shallow roots; while black walnuts secrete allelopathic compounds that suppress both germination of seeds and vegetative growth in many shrub and perennial species.

Likewise, oaks are not always overly welcoming of understory companions.  Unlike maples, oaks do not have shallow roots, but like pines, they tend to monopolize water resources and produce foliage that decomposes at a relatively slow rate, producing a slightly acidic soil environment over time.  The latter issue is not particularly significant, especially given the fact that excessive acidity is a rare complaint in our area; far more cultural problems are associated with excessive alkalinity.

For the greatest degree of success, one ought to consider native perennials that are frequently associated with oaks: Pennsylvania sedge (Carex pensylvanica), Allegheny spurge (Pachysandra procumbens), and Canadian ginger (Asarum canadense) are but a sampling.  Nearly any kind of hardy fern will thrive in an oak woodland environment, while ephemerals such as purple trillium (Trillium erectum) often establish extensive colonies in the niches created by stands of red oaks. 

Although most perennials that will thrive in dry shade will do well under oaks, one ought to further refine the plant palette with maintenance in mind.  If the space is to be largely cleaned of fallen leaves annually, one can install any plants that fit that basic requirement.  In more naturalistic areas, one needs to bear in mind that accumulating leaves will smother most perennials under a foot in height.  Exceptions to this rule include woodland ephemerals and bulbous plants that have evolved to rapidly penetrate layers of organic material in their race to flower and propagate themselves before the canopy closes, refoliated for another season.

Black Oak 

Black oak (Quercus velutina) is in the red oak group, or rather, red oak is in the black oak group - the oak groupings are more driven by lumber grading than taxonomy - but regardless, it is the third-most common oak in our area, most often found on dry hillsides.  Like red oak, its young bark is smooth and dark gray, maturing to form large blackish ridges deeply furrowed to reveal yellowish inner bark.  Where they happen to co-exist, one must rely more on variations in acorn and bud morphology to differentiate the two species.  Other members of this group that may be encountered in small populations in our area include the northern pin oak (Quercus palustris), scarlet oak (Quercus coccinea), and scrub oak (Quercus ilicifolia).

Reader Question:

Why does snow melt in expanding rings out from tree trunks?

-submitted by J.W. Thomas, Windsor, MA. 

Of course, this explanation does not exclude the contribution of minor co-factors - such as the effects of meltwater running down trunks or the heat produced by the metabolic activity of the tree itself - but the preponderance of the evidence surrounding the phenomenon clearly points to the simplest explanation: these rings occur most often around single trees or trees in woodland edges and are most common once the light strengthens after January; are most prominent around large, dark-colored trees; and although consistent in margin, are always centered on the face of the trunk that receives the greatest solar exposure.

Maples, particularly larger specimens, tend to produce larger rings and seem to do so before other trees, a red herring that might lead one to believe that the phenomenon must be produced by the heat of rising sap - after all, these rings appear right around sugaring time.  However, the difference between a maple and, for instance, a young white pine is one of surface area.  Plated bark, such as that of maples, has a far greater capacity to capture and radiate thermal energy than smooth bark, such as occurs on young pines, thus augmenting the melting of nearby snowpack.