In last month’s article, I assigned "audible, or sound waves" to the spectrum of solar radiant, or electro-magnetic (EM), wavelengths. A tip of the hat to reader Dick Frankel, who clarifies that “sound waves are longitudinal, i.e., the vibrations are along the line of travel, while EM waves are transverse, i.e., magnetic and electric fields both perpendicular to the line of travel and to each other.” Sound waves travels at around 700 miles per hour, while EM wavelengths travel at 186,000 miles per second. Nor do sound waves travel through a vacuum, as EM wavelengths do.
This past fall, an article ran in the Washington Post about the absence of acorns in our region. Subsequent investigation by Rod Simmons, regional expert botanist, documented a narrow strip experiencing the same phenomenon, starting around D.C., and extended north along the fall line and the I-95 corridor as far as Canada. While such a complete crop failure has no recognized precedent, it is noteworthy that this was a very localized incident. For example, areas as close as Richmond, VA and the Eastern Shore had a normal masting year. It appears that heavy May rains prevented the pollen from reaching the female flowers. Unfortunately, implications from global warming will augment the occurrence of such severe rain events in the future. For more of Rod Simmons findings, go to Earthfiles.com and quick search for Rod Simmons.
The lack of acorns has serious implications to wildlife. These fruits provide the most significant wildlife food in the deciduous forests. They are the fuel that runs the eastern US forests, being eaten by literally hundreds of forest wildlife.
Over the past one hundred and fifty years or longer, the preponderance of oak trees in eastern forests has increased. With few exceptions, oak species are shade intolerant, meaning they cannot regenerate in a closed canopy forest habitat. Thus, their contribution is directly related to openings provided in the forest canopy. Logging for timber and the charcoal-fueled iron industry, along with subsequent wildfires that have occurred throughout most of eastern US, have enabled a significant regeneration of oak forests. Subsequent abandonment of agricultural fields throughout the east has further increased the population of oaks. In fact, current forest acreage in eastern North American is approaching about two-thirds of the forest areas estimated to have existed at the time of the arrival of Europeans.
However, this trend of oak recruitment throughout most of the eastern forest biome has made a dramatic decline in the last 50 years. This decline can be attributed to a number of factors including fire suppression, deer browsing, insects and diseases, and exotic plant competition.
Fire in our eastern forests is a natural part of the ecosystem. Fires set back the successional stage of development. Low temperature non-catastrophic ground fires historically occurred in this region at a 5-25 year interval. This fire regime tended to eliminate thin-barked trees, such as red maple, sugar maple, beech, birch, cherry and black gum. With the absence of such fires, these faster growing species out-compete the oaks, thus becoming a more dominant member of the forest understory. Additionally, with the increase in understory vegetation, oak reproduction is restricted, yielding to more shade tolerant species, such as maples. Formerly catastrophic fires, intense enough to induce stand replacement, occurred on a 200-500 year basis, provided widespread new habitat for the recruitment of a new population of oak species.
The inability to control deer populations “has been the biggest mistake in the history of wildlife management” in the words of former PA DER chief deer biologist Gary Alt. From less than a thousand deer in PA and even less in VA at the beginning of the last century, current populations are 1.6 million for PA and over 1 million in VA. In fact, eastern US populations are now reaching pre-European levels. Oak mast is a preferred food of deer, and it’s not surprising that the range of oaks largely overlaps that of whitetails. Intensive browsing has removed oak seedlings, enabling a conversion of forests from oak to species such as tulip poplar, maple, and birch. Considering these impacts, white-tailed deer can be considered a ‘keystone species’ in eastern forests.
Sudden Oak Death (SOD), first identified in CA in 1995, is a fungus that has killed over 100.000 oaks on the west coast. Recently, it has been imported to the east coast. While oaks are the terminal hosts of SOD, it takes other ‘foliar host’ plants to incubate the spores that infect the oaks. Unfortunately, the eastern forests have them, as well. These hosts include rhododendron and azaleas, viburnums, witch hazel, mountain laurel and other heath family members.
The US Forest Service has stated, “Based on past history, it is not a matter of "if", but "when" SOD will gain a foothold in eastern oak forests. Due to a lack of basic epidemiological research on eastern species, the range of outcomes is extremely uncertain- from innocuous to a potential chestnut blight scenario.” Under the worst-case scenario, this disease may ultimately result in an ecological disaster greater than the loss of the American chestnut.
Adding the impact from gypsy moths and invasive exotic plants, which can reduce oak recruitment through direct competition, it is apparent that the contribution of oaks to our forests in the near future may be significantly diminished. How the oak species can respond to these pressures will ultimately determine the future viability of our eastern forest communities.
With the loss of the American chestnut tree, oaks have largely taken their place, minimizing the loss of the chestnut from the energy budget of the forest. The loss of the oaks from our forest would have a tremendously more significant impact on wildlife