“Why not think of the tulip poplar on the Boulevard as a metaphor” for what we’re trying to do in the woodland? asked City Forester Doug Still. This in response to the question, “How do we know how much to intervene in the Blackstone Park Conservation District?”
The “we” refers the Providence Parks Department and the Blackstone Parks Conservancy, collaborating in the care of the two Blackstone Parks. The tulip poplar metaphor means: Work with nature where possible, intervening only as much as necessary to redress the negative impacts of human interference.
The story of the great old tulip poplar on Blackstone Boulevard between Lloyd and Irving, which was toppled by Hurricane Irene in 2011, illustrates a relatively new approach to landscaping the Boulevard. A dozen or more sturdy sprouts emerged from the stump, indicating that at least part of the root system was still healthy. Earlier, a typical reaction would have been to clip off the sprouts in the interest of tidiness—in fact, this is what happened in 2011. Then, later, a replacement tree would have been planted.
But in 2012, we jointly decided to take the advice of a scientist who volunteers as a consultant to both the Conservancy and the Parks Department to try the thousand-year-old technique called coppicing. Next, a volunteer forester working at the city’s direction singled out the strongest-looking one and cut off the others to help the tree regenerate. Virtually no expense!
There are two compelling reasons for a relatively cautious approach to intervening in a conservation area, where people want to protect a natural landscape: incomplete knowledge and scarcity of resources. More and more, the idea of minimal intervention seems to be where exploratory conversations between dedicated environmentalists settle.
A good example of minimal intervention in the woodland overlooking the Seekonk River is the gradual removal of an invasive tree, the Norway maple, one of many invaders colonizing the edges of the Conservation District. If left alone, this tree, and other invasive plants such as Asian bittersweet, would eventually take over the park. Norway maples are especially prevalent in the southern section, where, four years ago, they were well on the way to edging out native trees such as red and white oaks. Then volunteers and the city intervened.
Conservancy volunteers and, once a year, girls from Lincoln School, are interfering with the Norway maple’s march toward domination of the southern section by removing saplings. While we focus on the smaller trees, the Forestry Division removes the larger ones. We all move carefully, because disturbed soil invites more invasive species to take root.
Norway maples display all the attributes that give invasive plants an advantage over native plants, enabling them to disrupt the diversity essential to long-term forest health. First, invasive plants are often imported as ornamentals–people want them for their beauty as well as their vigor. Norway maples were planted across the United States in the mid-20th century to replace dying elms.
The second reason for invasive plants’ dominance is their strength. Norway maples are more prolific than most native trees, sending out great numbers of seeds that are widely scattered by the wind. These trees are also unusually hardy, adapting readily to poor soil and urban pollution.
Norway maples compete successfully in other ways as well. Their dense canopy inhibits the growth of other trees along with undergrowth and grass. Like many invasive plants, they beat out rivals for light, water, nutrients, and space. They especially threaten sugar maples in the northeast, and their sale is banned in New Hampshire and Massachusetts.
The Providence City Forester would like to see the results of invasive tree removal in the parks monitored over time, perhaps with photographs. The Conservancy plans to participate in more monitoring of all the work in the Conservation District.
The next question is whether to replace invasive plants with natives, as is widely recommended, and if so, what kind and how? This intervention carries its own set of risks, as our leading science advisor reminds us.
Some experts think the risks are worth taking in order to hold soil in place and prevent new invasive plants from taking hold. By late spring, after more discussion, the Conservancy and its collaborators aim to make an informed decision about replanting.