State botanist Dr. Robert Wernerehl, the featured speaker Thursday evening, June 13, at the third forum of the Deer Management Subcommittee, said climate change, sea level rise, invasive species, pests and pathogens, and development all pose a threat to endangered plant species, but the biggest threat is the white-tailed deer.
The deer are a threat because of their browsing habits and large appetites. Wernerehl explained that because deer have no upper incisors, plants browsed by deer are ragged at the cut, as opposed to the clean 45-degree cut when plants are eaten by animals with both upper and lower incisors, such as rabbits. This characteristic allows scientists to note and count plants that are eaten by deer and is an important tool in studying the effects of deer on the understory of the forest. Because deer can eat their favored plants up to 5 feet above ground level, observing browse at that level is another indication of the presence of deer noted by botanists.
Exclosures are fenced-in areas where deer cannot enter. If plants flourish within the exclosure but the outside areas are barren, botanists deduce that there is overbrowsing. “Boulder” experiments, wherein the plants at ground level are sparse while plants thrive on the inaccessible top of the boulder, offer information to scientists. Observations of plants on islands, before and after the introduction of deer, are also informative.
A secondary effect of deer overbrowsing is a lack of plant diversity in areas where plants not attractive to deer dominate the space, light, and water. A glade of hay-scented fern is an example of lack of diversity. Wernerehl pointed out that even though the ferns eventually die out and succession takes place, it will be a long time before diversity of plants returns.
Grasses and sedges, which grow from the base of the plant, do recover from overbrowsing, unlike those that grow from the tip, which do not grow back. The latter group includes some oaks and maples.
Additional evidence, such as scat surveys, tracks, scent, and sightings, are also observed and documented in estimating the number and effects of deer. Presenters at past forums have stated that determining the number of deer in an area is impossible.
Weston Conservation Administrator Michele Grzenda then presented the history of Weston’s deer management program, which resulted in the introduction of bow hunting on conservation land.
From October 2011 to January 2012, the town began education and research efforts to determine if there was an overpopulation of deer. That process involved a nature walk with botanist and author Tom Rawinski, reports of sightings by residents, presentations like the forums now being held in Harvard, and self-reported survey responses from residents about Lyme disease, landscape damage, and auto collisions with deer. The survey showed 73% of respondents felt there were too many deer.
By May 2012 Weston decided to implement a deer management plan. Contraception, while successful with zoo animals and necessary in urban areas, was ruled out as too expensive and time-consuming because the process would have to be repeated every two years, with sharpshooters to inject the drug. Sterilization is even more complicated as it involves capture, anesthesia, and surgery of bucks.
Therefore, in June 2012 the selectmen of Weston voted to allow bow hunting from tree stands on five selected conservation lands on the premise that deer populations would increase due to lack of hunter access.
After applications were accepted in July 2012 and proficiency tests and background checks were performed in September, hunting permits were issued.
Five years later, by the end of the 2018 hunting season that now includes 11 conservation lands, a total of 167 deer, of which 93 were does, had been killed. Grzenda was unsure how long it would take to determine the success of the hunting program.
While Grzenda was obviously enthusiastic about Weston’s deer management program on conservation lands, she pointed out that hunting is in decline due to lack of access to land and the aging population of hunters. And she said it is necessary for all surrounding communities to engage hunters and hunting on their lands for the program to be successful.
On the other hand, Wernerehl said he did not want to give the impression that deer were the sole source of the destruction of the understory, but discussing other reasons, such as acidification of the soil, Canada geese, fire suppression, or the closure of the canopy “was not the point of the presentation.”