Forestry research can help prevent a rare ecosystem from disappearing.
But if land managers don’t act now, it could all be lost.
Written by Sonya Kaufman
Pine needles give off a sweet, toasted smell, and scrub oak leaves glow in the July sunlight. Hiking into the first plot of the day, the ground is soft – sand the color of breakfast cereal stretches in all directions. I’m collecting data to prevent globally imperiled pitch pine barrens from being destroyed by an aggressive insect, the Southern pine beetle (SPB). The good news: a combination of prescribed fire and mechanical harvesting creates the best conditions for healthy pine barrens. If land managers act now, they can prevent future destruction.
“This looks like a good spot for a plot,” I call out to Ryan, my field assistant. We’ve been hiking for about twenty minutes. Ryan places a stake in the ground and we start our well-practiced dance of measuring, counting, labelling, reciting, and double-checking information. We’re part of a team of researchers from the University of Vermont and the United States Forest Service assessing pitch pine barrens health across the Northeast. With climate change causing increasingly warm winters, the Southern pine beetle is expanding its range north.
In their native range of the southeastern U.S. and in healthy forests, Southern pine beetles help naturally regulate forests. Yes, they kill trees. But death is necessary – it allows more light to the understory, creates patches of mineral soil for seedlings to grow, and returns nutrients to the soil. In forests where fire exclusion and lack of management have resulted in dense, overstocked thickets of trees, Southern pine beetles wreak havoc.
Today, I’m working in the Waterboro Barrens, a preserve managed by The Nature Conservancy in southern Maine. Waterboro sits on 90 feet of sandy soils that were deposited by glaciers more than 12,000 years ago. Growing on top of the sand is the largest intact pitch pine barrens in Maine – 2,475 acres of pitch pines, scrub oak thickets, carpets of lowbush blueberry, globally rare Pine Barrens Zale moths and regionally rare populations of Whip-poor-wills and Common Nighthawks. “Hey, come look at all of these pitch pine seedlings,” Ryan calls. I jog over, excited to see what he’s found. We’ve hardly seen any all summer.
Pitch pine seeds require bare mineral soil for germination. They are adapted to fire and disturbance – the most common ways to expose mineral soil. A clump of miniature pine sprouts glows green in the sunlight. When I peer closely, I see that the needles are in bunches of three, an identifying feature. We’re in a stand managed with mechanical harvesting and prescribed fire, a combination that creates the best growing conditions for pitch pine seedling recruitment. Our data backs it up – out of 177 pitch pine seedlings we found in the preserve, 133 were in areas managed with harvesting and fire.
I crouch down at the first tree of the plot – a pitch pine with two trunks, its branches twisted and gnarled. Its bark is a deep reddish brown, with wide plates and dark furrows. A tuft of needles sprouts directly from the trunk, an epicormic sprout that would make any forester cringe. Pitch pines have low value as a timber species, and have been selectively cut down since European colonization, in favor of straight-trunked, fast-growing white pines. I position an increment borer against the tree. The borer is shaped like a “T,” a black metal rod with a razor-sharp drill bit at one end and a perpendicular blue plastic handle. I lean into the borer and turn the handle to the right. After a few turns, I feel it bite into the tree.
Tree core analysis reveals patterns in forest development and connections to climate history. In our case, we want to understand how patterns in land management, wildfires, and fire suppression affect forest composition and structure. After drying, mounting, sanding, and counting rings from the 1,024 tree cores we collected, the patterns are clear: stands lacking forest management start to mesify, or transition from open, sunny, fire-tolerant forests to closed, shade-tolerant, fire sensitive forests. A combination of harvesting and fire, in contrast, creates healthy pine barrens with higher amounts of pitch pine regeneration and restores the spatially-variable woodland structure that was historically maintained by Tribes with frequent burning. I remove an intact tree core and place it into a labelled straw. I fold over the end, secure it with tape, and place the straw in my bag.
Warming winter temperatures means that by 2080, the Southern pine beetle will have expanded its range through the entire northeastern U.S. and into southeastern Canada. Temperatures below 3ºF kill beetles. During outbreak years, they destroy millions of acres of forests. In healthy, managed forests, populations are kept in check by a large network of invertebrate predators and woodpeckers that feed on larvae and adult beetles. In the Northeast, dense, unmanaged pitch pine barrens provide the beetle with an appetizing meal. Beetles use sophisticated chemical communication to coordinate their attacks – and the closer the trees, the more easily they coordinate.
The next pine in our plot oozes resin from its bark in several places. I peel a resin chunk from the tree and see a small, round hole. The hole was made by an insect exiting the tree, and the tree’s protective response was to produce extra resin to fill that hole. Entomologists can tell what bug was in the tree based on patterns in resin color, exit hole size, and larval galleries. I’m not an entomologist, but I’ve learned enough to know that this isn’t the sign of a Southern pine beetle attack. Pitch pines affected by Southern pine beetle produce popcorn-like clumps of pitch that range in color from white to pink to red, as an attempt to expel the beetles. Beetles usually attack trees at heights greater than 10 feet, and the tree in front of me has resin oozing from the base of the trunk. But the best diagnostic feature is what happens under the bark.
I walk around the tree, looking for other signs of insects or disease. Once Southern pine beetles enter a tree, they carve out galleries in which to lay their eggs. These galleries are curved, or S-shaped, and have short larval tunnels ending in feeding chambers. Galleries eventually kill the tree by girdling it, cutting off necessary nutrient flow through xylem and phloem. Beetles can kill a tree in 2-4 months. Once their attacks begin, their populations grow exponentially and stopping them requires clearcutting strips of forest. Ryan and I continue our data collection in silence, with the focus that comes from a summer of repetition and creative efficiency.
Sonya Kaufman is a graduate student in the Field Naturalist Program at the University of Vermont and has worked as a wildland firefighter and prescribed fire practitioner. A team of people made this research possible, including Tony D'Amato, Kevin Dodds, Ryan Hawley, Jon Bailey, and Jeff Lougee. This research is part of a regional assessment of pitch pine barrens health across the Northeast, in a collaboration between the University of Vermont, the United States Forest Service, The Nature Conservancy – New Hampshire, and The Nature Conservancy – Maine. Funding for this project was provided by the Northeastern Forest Fire Protection Compact.