The 2020 bumper crop is in. As we scurry to pull taps and scrub pans, it’s good to pause, step back, and take the long view. Our crew member and guest blogger Morgan Perlman writes:
The Forest Meets the Sugarhouse
Once everything in the sugarhouse is cleaned in the morning, we get the boiling started by noon and settle into a sugaring routine. Someone stokes the fire on regular intervals. One person boils and makes syrup. Another dumps pail after pail of syrup into the filter press. The syrup density is checked for quality and it is filled into a drum and given a grade (Fancy-Delicate-Taste, Amber, Dark). We rinse and repeat each boiling day. This routine often allows for calm moments of interesting conversation with the crew in between our erratic bouts of sugaring chaos. Just recently one of our topics of conversation was the health and ecology of our sugar maple trees – the 200 acre Nebraska Knoll forest.
Sugaring is a complex network of connected parts. The sap we boil in the sugarhouse is inextricably connected to a community of individual trees that form a forest. Tubing and plumbing out in the woods connect each of our 10,000 sugar maples to our sugarhouse. The quantity and quality of the syrup sugarmakers produce is thus dependent on the health and biology of the trees and the ecology of the woods at large.
In our sugarhouse conversation, Audrey was telling me about how lately we have lost a few very large, notable maple trees – the kind of iconic trees we give affectionate names to. Max, Palace Guard, Big Foot, The Neckers, and Peek-a-boo are among the notable maples we have lost. Dave Youngbuck, The Commander, and Twin Trunks are no longer looking very healthy and will probably not be with us much longer.
The loss of these iconic trees in our sugarbush makes me think a lot about the threats facing sugar maple in our sugarbushes today. Sugar maple has for some time now been known to be declining in our northern hardwood forests, which poses future challenges to maintaining a productive sugarbush.
When ecologists talk about decline of single species like sugar maple they are not referring to a single problem like a particular disease or pest. Decline comes from many compounding factors that play a role in weakening our sugar maple trees and gradually reducing their overall abundance in the woods. Changing climate, soil chemistry, disease, insects, land management are all examples of factors collectively contributing to sugar maple decline.
Here I explain some of the many factors influencing our dear sugar maples:
A warming earth is one factor I worry about a lot both for our immediate lifetime and future generations hundreds of years from now.
One of the first stresses sugar maples will be facing with climate change is dieback that is induced by a declining snowpack in our forests. A winter snowpack insulates the ground and the roots of sugar maple. When we have major thaw events in the middle of winter followed by very severe cold snaps, the ground and shallow roots of sugar maple may freeze. Sugar maples are particularly sensitive to this with their root structure. The freezing of the soil damages their fine roots near the surface and will lead to a delay in their uptake of crucial nutrients come spring and thus reduce their overall growth and vigor. We can expect these root freezing events to become more frequent with the potential increase in snowpack-busting thaws.
A shifting climate envelope will also lead to the eventual replacement of sugar maple by trees that currently grow further south. Every trees species has a range where it is distributed in the world. The range of a species is defined by very particular climatic conditions. For the past several thousand years, Vermont has had very perfect climatic conditions for the growth of sugar maple and sugaring. That is changing. Over thousands of years our climate may be more like Virginia than today’s Vermont. Sugar maples don’t grow in climates that far south. Sugar maple’s range, over geologic time, might extend far north in what is today boreal Canada or the Arctic. We can probably expect our forests to be replaced by species like oak and hickory. Maybe someday you can tap sugar maples in Alaska where they currently tap birch. Sugarmakers will have to move north.
However, I’d worry about the loss of good sugaring weather before the loss of sugar maples. Trees, after all, can’t just get on their feet and walk North.
Luckily none of us will live long enough to witness the loss of sugaring from Vermont.
Beech Bark Disease
Beech and sugar maple coexist together in dominance in our northern hardwood forests. Where there are sugar maples, there are likely beech mixed in. These two species interact with one another in important ways, and thus the ecology of beech is fundamental to understanding the ecology of sugar maples.
Beech bark disease has been around in our forests since the 1950s. It was first brought to North America through an accidental introduction in Nova Scotia in the late 1800s. The disease has since spread to encompass the entire range of beech across North America. The disease itself is very unusual in that it is a combination of a scale insect and a fungus that work in harmony to stress beech trees by attacking their bark. Prior to BBD, our beech trees would have perfectly smooth bark. Today’s beech are speckled and scarred and don’t grow that large. The disease is thought to have changed the structure of our forests and the growth behavior of beech.
BBD promotes a unique and aggressive root-sprouting behavior in beech as a stress response to the disease. Beech are capable of sprouting vegetatively through their root system. Thus, beech are not dependent on seed dispersal for the production of new stems. This aggressive sprouting behavior can outcompete sugar maple seedlings, which are dependent on seed dispersal. In the woods, look for patches in the understory where small beech saplings form a dense thicket. These environments are very hard for the reproduction of sugar maple seedlings and may contribute to the slow and gradual decline in sugar maple dominance.
Herbivory by deer
Herbivory by deer is a significant factor in our forests today. Sugar maple seedlings are more vulnerable to deer browse than other species. Our deer populations are unsustainably high and sugar maple’s competitor, American beech, will outcompete sugar maple in forests with deer browse pressure. Deer don’t like beech.
Best thing we can do is encourage deer hunting and recover the populations of large predators we use to have here, such as wolves and mountain lions.
Ecological succession/land use legacies
To put the decline of sugar maple in context I want to remind us that forests existed long before humans settled this New England landscape and cleared more than 80% of our woods. Our uncut and virgin forests prior to the arrival of Europeans were very different. Ecological research today suggests that beech was significantly more dominant in our hardwood forests than it is today. Today, sugar maple is now more dominant than beech following the recovery of our forests since their clearing by Europeans. I’d like to think it is possible that maybe the decline of sugar maple is partly our forests following an organic successional trajectory on a timescale that is beyond human, returning to a compositional state more similar to their pre-human history. Successional trends on a landscape scale that are hard to explain may influence the dominance of sugar maple on large timescales.
Our forests are still relatively young after being so modified by human settlement. The human influence has been strong for a long time and our forests are still maturing.
Let’s watch them age.
[Morgan is a recent graduate of Middlebury College where he studied forest ecology and cultivated a particular interest in sugar maple and beech trees. He brought abundant good cheer and curiosity to the sugarhouse. -AC]