Portrait of the Oak

It’s been a while since my last post which I will write off to the “holiday hustle and bustle.” In actuality, this entry was started the day before the October snow storm which left our household with no power for an entire week. Yes, I know that is three months earlier! That, followed by getting ready for the holidays, I just couldn’t seem to get back to things as intended (we won’t even go into that I spent most of my Christmas holiday break in bed!). Hopefully, now that the holidays are behind me I can get back to a more frequent (at least monthly) writing and posting schedule.

This time of year, I often find myself thinking about northeastern forests and their benefit to wildlife. One of the reasons for this is because all of the colorful broad leaf deciduous (BLD) trees such as maple and birch have dropped their leaves, leaving the oak (and sometimes the pole-size beech trees) as the only real frequent non-coniferous contributor to color in the landscape. During the growing season the oak is usually easily over-looked. The reason it has a tendency to stand out is that it will generally hold onto its leaves much longer, often until spring. Oaks are easily identified by the common russet brown color which is a result of a natural organic compound called tannin. Once chlorophyll production ceases in the late fall, the dominance of tannin results in the characteristic brown color.  The remnant coloration makes it easy to discern this tree and also provides a great opportunity for one to learn it’s branching structure and form and to recognize its preferred habitat.

Now, don’t get me wrong most oaks (Quercus spp.) are still considered largely deciduous and do drop their leaves (which is called abscission by the way) – they just do it later. This condition of retaining dead leaves through the winter months is known as marcescence and the reason for it is commonly debated. Physiologically speaking the leaves are retained because the base of the petiole (how many of you remember your grade school botany?) retains living tissue throughout the winter. Michael Snyder, a Chittenden VT County Forester, provides an excellent summary of the varied hypotheses for the possible benefits of  marcescence in his Northern Woodlands “Woods Wise” column. Some of the theories he highlights include colonizing adaption for nutrient poor sites; a “pulse” of nutrients and mulch for the soil when it is needed most, in the spring rather than in the fall; a physical adaption to trap snow, and therefore moisture, for the root system; a way to insulate buds and new twigs over the winter from drying winter winds or to protect them from animal browse, especially voracious moose and deer. These all seem realistic and have some basis in rational scientific documentation.  Others I have heard include the relationship between acorn/nut production, both from an ecological habitat perspective (camouflage roosting/foraging for birds and small mammals) and that of species propagation. These last two appear to be somewhat common-sense driven but anecdotal so in the end the take home message is we just don’t know.

Oaks are a member of the beech tree Family (Fagaceae) and are long-lived trees. Five-hundress years is somewhat common in northern old-growth forests. In their initial years of life they will grow very slowly. I have seen oak seedlings completely browsed to nothing for several years in a row. A mature oak will produce its first good seed crop when it is 40-50 years old (imagine if we had to wait until we were that old to reproduce…) and annual acorn production varies, with trees sometimes producing very few in a given year. Large numbers of acorns are produced intermittently in what are known as “mast years,” often at intervals of three to five years.

Oak Mast aka Acorns

Especially in colder climes mammals that do not hibernate will rely on mast-producing trees as a source of necessary protein. Great, wildlife need nuts, but what does that have to do with us? It is important to recognize that the cyclic nature of mast production affects not just wildlife but the entire ecological system and every critter in it. As recently pointed out in a December 3, 2011 New York Times article the obvious shortage of acorns during the coldest winter months could result in severe population-level losses of small rodents and other mammals  which are commonly host to Lyme Disease carrying ticks. A reduction in host organisms will leave these blood-sucking insects looking for an alternate source of food (namely us).

Adult Deer Tick

This is just another example of how every living creature in the natural environment (us included) is intricately linked.

If you would ask me or any other biologist what the best tree species to plant for overall wildlife habitat purposes is, the answer you will likely get 9 out of 10 times is Oak. But why is that? One of the key aspects of any habitat management regime is to provide a healthy diversity of resources, including trees, so why do so many biologists and ecologists weigh in so heavily for one type of tree? (Hang onto this thought as it is likely that a future posting will revisit this when I discuss Forestry Management.) One critical reason is documented by a favorite researcher of mine, University of Delaware’s Doug Tallamy. It is the oak’s ecological contribution when it comes to supporting insect herbivores such as moths and butterflies (Lepidoptera). These winged creatures are the base of the food chain and are therefore critical for maintaining a healthy diversity of wildlife. In my eyes it’s the “best bang for the buck” approach. His research has demonstrated that the number one ranking woody host plant is, you guessed it, the oak (Genus Quercus). This tree alone provides host insect habitat for 532 species of native insects.

Oak Gall (egg case)

The next closest host is the Genus Prunus (cherry, chokecherry, plum, peach) which is documented to support 456 native insect species.

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