Gifford Garden Notes
Is your idea of a healthy and pristine forest one where you have no difficulty looking a long way through the forest without interference from shrubs and tree seedlings?
by Brad Roeller
Is your idea of a healthy and pristine forest one where you have no difficulty looking a long way through the forest without interference from shrubs and tree seedlings? I've personally witnessed (how shall I put it?) "ignorant" landowners (yes, those transplanted urbanites) direct their staff to clear all "underbrush" within their forest to lend a "park-like" feel to their country estate. I've had all I could do to restrain myself from hurling the nearest object in their direction! A healthy forest ecosystem is one that forest ecologists would term "complex", comprised of a rich mixture of herbaceous and woody plants (and animals). Many layers of foliage, from the forest floor progressing upward through the shrub and tree seedling layer, into the young tree saplings layer, and finally culminating with the canopy trees, would typify such a forest. Unfortunately, the current abundance of deer has contributed greatly to imparting this park-like appearance to our northeastern forests. What suffers is species richness and biodiversity. It has been shown that high deer populations have the potential to change the plant and animal composition of a forest ecosystem (Tilghman et. al. 1989).
Ecosystem management is affected by what ecologists refer to as "keystone" species. These are species by which the very integrity of the whole ecosystem relies. When it comes to forest ecosystems, white-tailed deer clearly fall into this select species list. It is widely accepted that white-tailed deer, as a keystone species, impact resources within a forest ecosystem sufficient to affect its sustainability. Think about it for a minute, the look, feel, and composition of our northeastern forests may be radically different in our children and grandchildren's time unless something is done to address current deer population densities. Just how did we get to this point? A little background is in order.
Wildlife biologists figure that prior to the colonization of North America, deer density in the eastern deciduous forests was approximately 7-10 deer per square mile. The size of the herd was affected by the amount of forage available, weather conditions (predominately winter weather), and predation. Our forests were species rich and diverse. With the immigration and colonization of our country, the seemingly infinite supply of forest resources was widely and indiscriminately used. By the end of the 19th century much of the eastern deciduous forest was cut over, and the deer herd was largely eliminated through market hunting. In rural America, agriculture was king, while in the cities the industrial revolution was in full gear. Both activities consumed forests resources to support the growth of America. Unfortunately, little regard was given to the ramifications of this indiscriminate land clearing and timber harvesting. However, an unintended consequence emerged: no forests, no browse layer, no deer (well, very few deer).
After the extensive harvesting of timber, with little deer herbivory, the germination and initial regeneration of our forests began. Abundant and available browse (i.e. young woody plant seedlings), coupled with newly enacted hunting regulations (thanks T.R.!), and the elimination of large predators (wolves, coyotes, and mountain lions), caused deer populations to mushroom in the first quarter of the 20th century. It was not uncommon to have deer densities exceed 50 per square mile in those years. These expanding deer herds were quick to reduce the available food supply (i.e. those regenerating tree and shrub seedlings), and populations starting to lessen. A series of unusually harsh winters in the mid-1930's reduced previous high densities to average around 10-15 deer per square mile (survival of the fittest). This relatively low density allowed the regenerating woodlands to naturally develop into fairly diverse young forests.
Fast forward a quarter century and these young, developing woodlands that were harvested 50 to 80 years earlier, were approaching a size to be timbered again. With active (and conscientious!) timber harvesting, more light came into previously closed canopies causing a flush of woody and herbaceous plant growth. Selective and managed timbering, coupled with the surbanization of former agricultural land, translated into growing deer densities. The current white-tailed deer density in the Hudson Valley averages over 45 deer per square mile. The highest densities in New York State are in the southern and western counties where in some "hot" spots, insular deer herds approach 200 deer per square mile!
Next week: What's a forest to do??
Gifford Garden Archives, January 2003 - present
Gifford Garden Archives, July 2001 - January 2003