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.

Responsible Gardening and A Rare Lecture Opportunity

If you have read my previous posts, then you know of my personal war with one of several invasive and non-native plant or animal species in my backyard here in Chelmsford. I would like to think that I am not alone in this endeavor, either locally or regionally. So far I am not disappointed by my on-line excursions.

If you are interested in gardening for wildlife, butterfly gardens, plant or wildlife ecology or are just beginning to develop an inkling of interest in this topic I strongly recommend you take advantage of a rare opportunity to hear one of my top-list authors and a well respected scientist, Doug Tallamy (Bringing Nature Home: How You Can Sustain Wildlife with Native Plants)  lecture this Wednesday night (October 5, 2011) in Carlisle, MA.  The event is being sponsored by the Carlisle Conservation Foundation, Susan Zielinski Natural Science Fund, and Carlisle Conservation Commission and will begin at 7 pm at Corey Auditorium in the Carlisle Public School.

As many gardeners undoubtedly do, I use my garden as an expression of what is attractive to me as an individual. Also, as I have a strong interest in nature and ecology I seek to do the right thing while expressing myself in this artistic way. I want what I put in my garden to function in sync with the natural environment. Mr. Tallamy who is also a renowned entomologist (insect ecologist) at University of Delaware provides abundant scientific documentation to support that alien plant introductions generally do not have a productive ecological relationship with our environment. This is because they often have different characteristics such as leaf chemistry, time to maturity, or time to bud and flower. What this means is even though they are phisically present in our natural environment, they are not contributing or giving back energy to the system the way a native plant would (just taking it away).

We, as gardeners, do have a choice. Now, more than ever before native alternatives to invasive horticultural varieties can be found.  However, if you are not familiar with the horticulture trade or with these alternatives, it is easy to be overwhelmed and led in the wrong direction by a well-intentioned nursery worker, or even, a less than well-meaning individual who just wants to make money.

Hybrid variety of a native columbine species

For example, not all native plants are created equal. Some so-called native plants are actually naturalized alien plants from other countries.

Alien and Introduced Queen Anne's Lace - Invasive in some New England States

Some nurseries will push these plants as “native” or alternatives to invasive plants. Some plants are cultivar varieties (genetically altered) of our natives which may not possess identical or even similar traits to the native variety, depending upon what it was “crossed” with.

These plants will often be touted in their descriptions as “pest tolerant,” “a caterpillar may eat the foliage occasionally,” “deer resistant,” “disease free,” “mostly allergy free,” good for naturalizing, etc. What a description like this tells me is that the plant does not possess a substantial ecological benefit and it is not contributing much in terms of food to native insects, which are the base of our regional food chain. Any of the descriptions I listed above would be a BIG “red flag” in my book.

As an example, a lot of the statements above will often be found if you search for traits of the common butterfly bush (Buddleia davidii or Buddleia x weyeriana). Now, you are saying wait a minute, isn’t the butterfly bush good because it attracts butterflies? Well let me, and some of my favorite online sources, enlighten you. The butterfly bush is a butterfly magnet and I can often find many butterflies on it during the summer season where they seek the very abundant and nectar-rich flowers which bloom almost constantly from spring to fall. Tallamy’s research shows “not one species of butterfly in North America can use Buddleia as a larval host plant.” In particular, a large number of butterfly species are very plant-specific and will only use 1 or 2 plant types to deposit their eggs and provide food for their hatching larvae (think milkweed and the monarch butterfly folks). Without the presence of a particular plant, you cannot have a particular butterfly. Therefore, without larval host plants you cannot have any butterflies. Taken to the next logical step, if everyone is following horticulture and nursery recommendations to create a butterfly garden with the butterfly bush as its anchor plant, butterfly diversity (number and variety of butterfly species) will undoubtedly continue to decline as we raze additional natural land to build even larger suburban homes and replace these sites with sterile turf lawns.

Alien and Invasive Butterfly Bush - Buddlei Davidii

Now, here’s another little tidbit for you. The butterfly bush is considered invasive in over 25 North American states, including Massachusetts, Connecticut and Rhode Island – that is if you go by the U.S. Department of Agriculture Plants Database. I can honestly say that I personally have not had any experience with this plant’s invasive tendencies but I have heard of other wetland scientists that have. It is not currently listed on our Massachusetts Prohibited Plant list and it also has not been evaluated (as far as I know) for noxious tendencies by the Massachusetts Invasive Plant Advisory Group. Other organizations, including the National Park Service, Audubon, and other state and governmental organizations have it on their “Invasive Watch List,” or have outright banned the sale of the plant. It is considered prolifically invasive in Zones 6 and 7 (Mid-Atlantic States such as PA and VA) as well as the Northwest.  It is on the “Most Invasive” species list of the Pacific Northwest Exotic Pest Plant Council. In this region it is extremely invasive in disturbed natural areas such as burn sites and along large streams such as the Willamette River. It has been a huge problem in England, where it is considered one of the top 20 noxious weeds, infesting large tracts of disturbed land 50 years after it was introduced in those areas.

USDA Plants Database - Buddleia Invasive Representation in U.S.

You see every plant has a niche or a microhabitat which it prefers. I for one am not completely knowledgeable about this plant and what its preferred microhabitat may look like (I am NOT a botanist). But I can hazard some broad assumptions (thinking aloud folks…don’t read in more than that) based upon its noxious nature elsewhere.

For example it appears to respond well to fluctuating wet environments where it spreads predominantly by very abundant seedlings. It likes riparian corridors and floodplains, especially such sites that have experienced some level of disturbance. The fact that it likes burn sites AND wet areas could reveal an interesting relationship with nutrient cycling on low pH sites (cold, wet or acidic sites) or the timing of availability of elements critical for plant growth following a disturbance (Nitrogen or Phosphorus).  For example inorganic Nitrogen can be made available through bacterial fixation following a burn event and is often considered a valuable post-fire nutrient source. Another byproduct of fire to consider might be potash (Potassium in a water-soluble form)  The time it took to infest U.K. sites makes me wonder how long the seeds remain viable in the seed bank once they are deposited there?

Research on the Buddleia problem in the U.K. by Oregon State University has revealed that seeds from the plant require a long time to develop and release from the plant. Similarly, U.K. researchers have discovered that flower heads from a previous summer do not release seed until dry weather occurs the following spring. This could be very useful information. It is also possible that climate fluctuations or microclimate condition is sigificant. For example, does PA or VA normally have a dry spring (did we in MA have a dry spring in 2010)? In addition, practical application of this info suggests that pruning all of the spent blossoms from the butterfly bushes in the fall prior to full development of the seed could potentially limit release of the seed to native environments (possibly a best management practice?). Well at this point I am starting to ramble and very loosely hypothesizing with nothing to back it up. Needless to say, I have begun removing the butterfly bush from my gardens.

I think that Carole Sevilla-Brown in her Ecosystem Gardening Blog says it best. We have been down this road before with many of our currently-listed and most noxious invasive plants. She highlights the Bradford pear, purple loosestrife, and multi-flora rose. These are just a drop in the proverbial plant bucket. It is pretty clear that the Horticulture Trade has not learned from past mistakes. The industry’s on-going attempt to create a sterile form of butterfly bush is like déjà vu of the failed attempts at purple loosestrife sterility. If we don’t learn from our past mistakes we will be doomed to repeat them over, and over, and over again. Gee, even the mouse in the maze learns from repetition and will eventually find the cheese…

Anyway, if you have an interest and are able to find time to attend Tallamy’s lecture in Carlisle, I hope to see you there.