An online resource based on the award-winning nature guide –

Posts tagged “Bark

Porcupines and Hollow Tree Dens

Porcupines leave plenty of signs where they have eaten the inner bark, or cambium layer, of a tree. Bark is missing on the trunk of the tree, leaving fresh, yellow wood exposed, which often bears incisor marks.  An observation I have made over the years is that porcupines often de-bark around or near their hollow tree dens.  Typically, if a tree den is used year after year, they gnaw off bark each year, sometimes eating the old, scarred portion which, due to previous chewing, lacks cambium cells. This has led me to wonder whether fresh de-barking in the vicinity of their tree den entrance might have more, or as much, to do with a  porcupine’s staking out a claim on that tree than with its sustenance.  I have never come across any research that even mentions this phenomenon, and would welcome feedback from anyone who has.

White Pine Blister Rust Attracts Rodents

When a white pine has been infected with white pine blister rust (a fungus), cankers appear on the branches and sometimes the trunk of the tree.  A large amount of sap-like ooze flows from the cankered areas, sometime drying and resembling a sugary-looking crust or film.  These areas are, in fact, high in sugar content, and rodents frequently chew them.  It’s likely that a red squirrel visited and sampled the infected white pine in the photograph, leaving a freshly-gnawed patch in the bark.

Black Walnut – Identification in Winter

This slideshow requires JavaScript.

Black walnut (Juglans nigra) is a relatively easy tree to identify, as it has so many distinctive qualities. In the summer there are round, tennis-ball-sized nuts, which have a delightful smell.  The bark of black walnut is dark and deeply furrowed.  Best of all are the twigs and buds.  If you cut a twig at an angle, you will see the central portion, or pith, is chambered.  It is also brown.  The only other tree that is chambered (not solid) like this is its relative, butternut (Juglans  cinerea), and butternut’s pith is buff colored.  The buds of black walnut are greyish and fuzzy – lacking bud scales.  By far the most amusing thing about black walnut (and butternut) is its leaf scars – the scar left when a leaf falls off.  The vessels that transport food and water, called vascular bundles, are darker than the rest of the scar, and are shaped in such a way that the leaf scar resembles nothing more than the smiling face of a monkey!  (Butternut leaf scars also look like monkeys, but they have a “furrowed brow” of fuzz on the top edge of the leaf scar.)


Yellow Birch (Betula alleghaniensis)

This slideshow requires JavaScript.

Yellow birch (Betula alleghaniensis) buds are oval and pointed, and there are two shades of brown on each of their 3 – 5 bud scales.  The buds and twigs of yellow birch taste like wintergreen.  In the early morning and late afternoon, look for ruffed grouse filling their crops (“budding”) in yellow birch trees, as these buds are one of their favorite foods.  The thin bark of a mature yellow birch is a very distinctive yellow-bronze color (the bark of saplings is a shiny red-brown color), and curls when it separates from the trunk.

Northern Red Oak Identification in Winter

This slideshow requires JavaScript.

While identifying an oak species by the shape of its leaf is fairly easy, there are other characteristics in winter, when leaves aren’t available (except under the snow), that serve as clues to an oak’s identity.  A mature northern red oak can be readily recognized by its bark — its ridges appear to have shiny stripes down the center.  The buds of northern red oak are also distinctive.  Like most oaks, red oak’s terminal (located at tip of twigs) buds occur in clusters.  Northern red oak’s terminal buds are conical, and are a reddish-brown color.

Beech Bark Disease

 Anyone familiar with the beautiful, smooth, gray bark of American beech is well aware that the forest landscape is changing, in part due to the disease that is affecting American beeches. Beech bark disease is caused by not one, but two, agents – an insect and a fungus.  The bark of an American beech is initially attacked and altered by the soft-bodied scale insect, Cryptococcus fagisuga, after which it is invaded and killed by fungi, usually Nectria coccinea var. faginata or N. gallegina. This scale insect was accidentally introduced to Nova Scotia around 1890 and since then has spread far and wide, affecting large American beech trees (over 8 inches) the most.  Pale yellow eggs are laid by the yellow female scale insects (there are no males – they reproduce through parthenogenesis) on the bark of beech trees in mid-summer and hatch in the late summer or fall.  Larvae begin to feed on the bark until winter when they transform into a stage that has no legs and is covered with wool-like wax. The white wax secreted by beech scale insects is the first sign of the disease – heavy infestations of beech scale can cover tree trunks with white wax. Serious damage results only after the invasion of the bark by either one of the fungi mentioned, presumably through injuries made by scale feeding activity.