Saturday, March 23, 2019

Prescribed Burns Scent Princeton's Air

This past week, some in Princeton may have detected a feint scent of smoke in the air. As reported in Planet Princeton, the smoke came not from a distant burning house but from the intentional use of fire in habitats at Fort Dix, a half hour south. So-called "prescribed burns" are used to reduce fuel loads in fields and forests, making them less prone to intense, destructive wildfires. Equally beneficial is the impact of these intentional fires (I like to call them "mildfires") on the health of habitats. Many species, particularly in the coastal plain south of Princeton, are adapted to periodic fire that would have occurred in the past, particularly in pre-colonial times when American Indians used fire to manage the landscape. The lack of fire, like the lack of keystone predators, contributes to the unnatural state of our seemingly "natural" areas, and underscores the need for management to better restore healthy ecological functioning in our open spaces.

For some, the idea of intentionally lighting fires runs contrary to environmental goals, since fire releases pollutants and more CO2 into the air, leaves ash on the ground that could be washed into streams during the next rain, and violates the still prevalent notion that we should just stand back and let nature do its thing. On the other hand, periodically burning off accumulated fuels reduces the chance of a much larger conflagration, and the ash can stimulate vigorous new growth that will absorb more CO2 from the air.

The NJ State Forest Service posted information on its prescribed burning, including news of a law passed last year to better promote prescribed burning in NJ.
Back when I lived in Ann Arbor, MI, I helped conduct prescribed burns in prairie habitats in and outside of town. There'd be a fire break around the prairie--usually a 10' wide strip of mowed grass--to reduce the chance of the fire spreading from the intended area. In late winter, a prairie is full of the dead remains of last year's growth. (If you read up on fire ecology, you find out that many species of trees and grasses adapted to fire have evolved to leave behind combustible material that lingers in the landscape to expedite the next fire that comes along. Think of those decay-resistant pine needles, oak leaves, and tall stems of prairie grasses. By contrast, European grasses brought to America tend not to leave much combustible material when they die back in the fall.) We'd begin by having a couple people with drip torches start a strip of fire along the edge of the downwind side. Several of us with garden rakes and broad rubber "flappers" would snuff out any flames headed in the wrong direction. Then, when the fire along the downwind edge of the prairie was going well, the upwind side of the field would be lit on fire. The two fires would burn towards the center of the field. There'd be a dramatic converging of the two fires before they burned themselves out for lack of any more dried grass to burn. It was exciting, efficient, even elegant in the way a field could be cleared of fuel and rendered ready for the new growing season. The layer of ash on the ground looked like the fur of a bison. Freed by the fire from the smothering mulch of last year's growth, new shoots would sprout from the perennial roots, their fresh green a pretty sight against the black of the ash.

The photo above was taken at Schiff Nature Preserve, 30 miles north of Princeton, where they burn their fields and oak woodlands periodically to improve habitat. The state park service does prescribed burns at various places along the DR Canal, though not in Princeton.

It's important to emphasize that prescribed burns require some basic safety precautions, and are only done by professionals after considerable planning.

Are there any habitats in Princeton that could benefit from prescribed burns? One interesting possibility is several detention basins in Princeton's parks that we've converted to native prairie grasses. These acre-sized plantings are surrounded by turf that would serve well as a firebreak.

Similar plantings in a park in Ann Arbor are burned each spring. Families are invited to come to witness the event. First, kids collect seed from the "wet meadows", then everyone steps back to watch last year's stems get consumed by flame. After the fire burns out, the kids scatter the seeds in the ash. Some even bring a picnic lunch to enjoy as part of the event. In the photo, you can see a residential neighborhood in the distance, which is not at all threatened by this elegant horticultural method for managing the lovely grasses and wildflowers that comprise these miniature prairies.


  1. Steve, I just read that insects may still be hibernating at this time of year in hollow stems. Curious about timing, tho all for burns.

  2. I was on the management committee for Penny's Bend, a piedmont prairie remnant in Durham, NC, where we were reintroducing fire as part of management of rare plants like smooth coneflower and hoary puccoon, and there was lots of discussion of how to minimize damage to overwintering insects. One strategy is to burn some areas while leaving others unburned on any particular year.

  3. This makes sense. Good question to put to Xerces, too. Thanks, Stephen.