PAULA CHAMPAGNEA stand of trees in Maine’s 100-Mile Wilderness, where AMC conducted its 10-year carbon project inventory in 2021.

“There’s a witness tree,” says Dave Publicover, AMC’s assistant research director, as a tree with a red-painted stripe around its middle comes into view. We’ve been scrambling down a pretty steep descent over rough terrain in the northern portion of AMC’s Katahdin Iron Works property (KIW) in Maine’s 100-Mile Wilderness, and I’m relieved we found what we’ve been looking for. The red-striped witness tree marked the spot. It wasn’t a long hike, but being August, it is hot and humid, and two hornets stung me halfway to this very first stop on our field day to four research plots in the vast Maine Woods. I’d seen the hornet’s nest in time, but as Dave says, it’s the second person who gets stung. Leading us along, he might have disturbed the ground-nesting colony and as I began circumventing the nest, two determined critters followed me and ensured that I would spend the rest of the scramble hiking with an arm up on top of my head to keep any swelling down.

We reach forest inventory plot No. 69, a white cedar bottomland, one of my favorite forest ecosystems. I know there shouldn’t be any more hornets in the acidic, wet sphagnum soil. We drop our packs and Dave shows me the ropes of the forest inventory procedure. This is one of 74 plots scattered across the 10,000-acre KIW ecological reserve north and east of AMC’s Little Lyford Pond Camps. Dave installed and measured these plots in 2011 to determine how much carbon has been sequestered or stored in the reserve as time passes—known as carbon stocking—for AMC’s first verified carbon offset project. The plots have to be re-measured at least every 12 years—think of it as the U.S. Census for trees– and Dave has spent the summer and fall on this project, with other AMC staff serving as field assistants. Today it’s my turn to pitch in.

DR. SARAH NELSONNelson and Publicover mark each tree they inventory with blue paint for easy tracking.

We unpack our gear, which includes tubes of gummy blue paint for marking each tree with a unique number (“Nelson” brand, I get a kick out of this); a wire brush for scraping away loose bark prior to painting; Dave’s hammer, passed down from his carpenter father, for installing nails at the diameter measurement point on trees that have grown large enough over the last 10 years to be counted; some nails; a measuring tape, clipped to his belt as it’s been nearly half the summer doing this work; a digital rangefinder, which measures the height of each tree; and a clipboard with today’s field sheets and map. One of the goals for this inventory is to better monument, or upgrade the markings that define the plot’s location, to help find these same plots and trees next time around. This includes installing a steel rebar stake at plot centers to supplement the existing orange plastic stakes, which have a tendency to be dislodged by bears and other animals, and to ensure that each tree on the plot can be correctly identified when remeasured in the next inventory.

Dave walks me through the process, step by step, as every field crew leader has a sequence and style in their work. Dave’s is orderly and logical, efficient but deliberate in carefully checking every tree over 5 inches in diameter at breast height (DBH, or 4.5 feet above ground level) in the 24-foot radius circle that comprises each plot. First, I help locate all of the trees with nails in them; the nail indicates the tree was measured in 2011 and ensures that the diameter is always measured at the same point. Each tree with a nail has a number associated with it on his field sheet, which we determine by checking the azimuth, or the compass angle to the tree when you stand at the center of the plot. Re-monumenting means that I get to carefully brush any lichen or loose dirt from a small patch of bark below the nail, and paint on a number so we can more easily find each tree next round. Then Dave measures each tree’s DBH using his measuring tape, and I record the diameter on the field sheet.

I can see the measurements from the last round on my field sheet, and some trees have grown quite a bit in diameter. Depending on the species and characteristics of the site, growth rates of individual trees can vary significantly, with healthy trees putting on an inch or more of diameter growth in 10 years. Then we look for trees that were too small to measure before—less than 5 inches DBH—but have since grown enough to be part of the census, which Dave calls “ingrowth.” Within the circle of this plot, a few new trees have been included. We measure them, too, and add their new, blue numbers to the field sheet. Then, Dave measures the height of each tree, using two different metrics: the “merch,” or height at which the diameter becomes smaller than 4 inches; and the total tree height. One tree has fallen, so I make note of it and cross it off, as only standing live and dead trees are included in the tally.

PAULA CHAMPAGNEForests sequester carbon dioxide, slowing climate change. AMC researchers conduct inventories in the Maine Woods to create accurate estimates of just how much carbon the trees capture.

At this point, I become what Dave calls the “target.” It can be hard to see an individual tree through the forest at the distance he needs to measure tall trees, so I hold the clipboard next to the trunk near nail-height to provide something at which to aim the digital rangefinder. I’m not sure how still I need to be, so I flip my ponytail to try to dislodge the late-summer deerflies and mosquitoes at this boggy site. Then we locate the center of a smaller 6.8-foot radius subplot on which trees between 1 inch and 5 inches DBH—essentially small saplings–are measured. I notice that some saplings are nearing the cutoff and might graduate to be ingrowth next time around. I silently cheer them on as we start to pack up to navigate to plot No. 70, the last of the farthest-flung plots, in a week when Dave has passed the halfway point and is crossing off the most difficult access plots of a summer-long project. I silently cheer him on as well.

Each plot can take an hour or more to measure, and some take an hour or more of bushwacking to reach. Dave has spent nearly half the summer and early fall here so far, walking the woods in his own footsteps from a decade ago and revisiting these trees he has measured before. The data will serve to “true up” the estimate of carbon stocking in the project area after 10 years of growth and provide the basis for a growth model that will estimate the increase in carbon stocking over the coming decade. At the last of our four plots measured on this day, a tree has to have a “defect deduction”—part of the trunk of the tree is hollowed out, and it can’t be counted as a whole, intact tree for the carbon accounting—so Dave estimates the proportion missing in 4-foot height increments of the trunk. It’s a big red maple, and it still seems strong and vital. I’m rooting for it and the other large trees dotted along this slope that were left in a harvest more than 25 years ago, before AMC took over managing these lands. We’ll see how it fares in another decade. The witness trees will be here waiting.