With the weather warming and the ground thawing, spring is in the air, and Vermont is waking up! Kickoff your month with flowing sap, thawing frogs, and heated flowers.
By Julia Pupko
March freeze-thaw cycles kick the sugaring season into high gear as sap flows again. Each spring, there are only a few weeks to collect all of the sap needed to produce the year’s maple syrup. While several tree species can be tapped to create syrup, Sugar Maple (Acer saccharum) is by far the most popular and well-known.
Maple syrup and sugar production have a long history in Vermont – the Abenaki have been producing these products for millennia. From the Abenaki, European colonizers in Vermont first learned of the process. Traditionally, sap was collected and then frozen so excess water could be removed before boiling to reduce cook time. The concentrated sap was then boiled in a pot. Most of the sap was turned into sugar for seasoning meats and fruits because sugar was easier to store than syrup. You can learn more about Abenaki sugaring practices from Sugaring in Wabanahkik (Land of the Dawn) by Alexander Cotnoir.
Since trees don’t have a pumping heart or circulatory system like animals, fighting gravity to move a vast amount of nutrient-rich liquid all the way up their trunks is quite a feat. Once the leaves are out, transpiration plays an integral role in pulling water and nutrients up the tree. As water evaporates from the leaves, a negative pressure gradient forms, pulling water and nutrients upwards. The small size of the tree’s capillary tubes enables water to creep up the tree, and the high surface tension of water causes it to “stick together,” creating an unbroken column up the capillary tubes. However, when the sap begins to flow, there are no leaves to aid with the process. So how do our magnificent maple trees manage it?
When trees thaw in spring, their roots release concentrated sugars and minerals into the xylem or the vascular tissue that conveys water and minerals up the tree. The concentrated sugars cause a negative pressure gradient up the tree, which pulls the sap up the trunk. However, this alone isn’t the only process, as their roots do not create a strong enough negative pressure actually to pull the sap all the way up the trunk. Trees such as maples, walnuts, and birches have another process that aids sap flow. These trees have hollow fibers lining their xylem, which contain gas. During cold nights when temperatures fall below 25 degrees F, the gas from these fibers dissolves into the liquid in the xylem. Then, ice begins to form on the outer layers of the xylem, trapping remaining undissolved gas. Attraction to the ice and, more importantly, the negative pressure in the tree draws more sap up the tree, allowing it to “recharge.” As the trunk warms during the day, any ice within the tree melts, and the gases expand, creating positive pressure. This pushes sap throughout the tree and out any tap holes in the tree. When night temperatures fall to or below freezing for an extended period, trees suck up a lot of sap, creating conditions for a good sugaring season. (Note: this process is still not fully understood, and there is still debate about the nuances of the process.)
Like many other species, Sugar Maples are threatened by climate change. Inconsistent snowfall exposes roots to drastic temperature fluctuations, reducing growth and damaging the roots. Warming temperatures, changes in precipitation, and resulting changes in the soil stress Sugar Maples and may force them to retreat to small pockets where the soil and habitat remain hospitable if climate change continues unchecked. Northern migration, even anthropogenically facilitated, is limited for Sugar Maples, as soils farther north in Canada are not compatible with Sugar Maples. Warmer, shorter winters have the potential to reduce Sugar Maple regeneration. Sugar Maple seed germination requires about three months of cold scarification at freezing temperatures.
Additionally, climate change is already affecting the sugaring season. On average, sap flow is occurring 8.2 days earlier, and the season is ending 11.4 days sooner than the average season 40 years ago. In addition to shorter seasons, warmer temperatures mean higher respiration rates during the growing season, which requires a tree to use more fuel. The result is that Sugar Maples will have lower carbohydrate levels to store, making their sap less potent. When sugaring, it will also take more sap to produce the same amount of maple syrup. Learn more about the effects of climate change on Sugar Maples and sugaring from this Audubon Vermont post.
By Julia Pupko
As trees thaw and the sap flows, others are warming up as well. Soon, Muskrats (Ondatra zibethicus) will no longer have to gnaw breathing holes through the ice and can focus on raising their young—March is the beginning of the Muskrat breeding season. This little rodent is non-monogamous, and females are the sole caretakers of their young. After a 30-day gestation period, the females birth from two to nine young who are entirely independent at one month of age. Muskrats typically have several litters each year, and dispersing young have a very low survival rate. Muskrats are a favorite meal for Mink and Racoon and frequently fall prey to Bobcat, other Mustelids, owls, hawks, Snapping Turtles, and even large fish.
By Julia Pupko
While the Muskrats can enjoy taking a breath wherever they please, Wood Frogs (Lithobates sylvaticus) may be taking their first breath of the year. Unlike many other hibernating species that merely slow their metabolism during the winter months, Wood Frogs freeze solid and internal functions cease. When the ice thaws, the frogs thaw too. Wood Frogs are one of the first amphibians that can be seen moving around in the spring. Don’t be shocked if you find them hopping across the ice as they migrate towards their vernal pool of choice! Wood Frogs rely on vernal pools for breeding, and their loud, duck-like calls will soon fill the forests. Learn more about this fascinating frog and add your sightings to the Vermont Atlas of Life on iNaturalist. Let’s find out the earliest date for their emergence. Last year it was March 23rd in the Champlain Valley.
by Kent McFarland
Following a successful recovery effort, Bald Eagle has been removed from the Vermont endangered and threatened species list. In 2002, the first Vermont eagle nest was discovered after a 60-year absence. However, it wasn’t until 2008 that the first eagle fledgling successfully left its nest. By 2020, the number of fledgling eagles had risen to 64, leading to its removal from the list.
In Vermont, Bald Eagles typically nest in tall trees with broad visibility and sturdy branches near lakes and rivers. Adults show a strong tendency for fidelity to their breeding areas and often use the same nest for many years. The nest tree requires sturdy branches to support the growing weight of the nest as materials are added each year. Nests are usually located approximately 50 to 60 feet high and 5 to 30 feet below the top of a live tree.
Egg-laying generally begins from early March through as late as early May in the Northeast. Clutch sizes range from one to three eggs. Incubation lasts about 35 days. Competition for food in the nest can be fierce, and the youngest chick often dies. Fledging occurs at 11 to 12 weeks after hatching. Parental care may continue for up to three months after leaving the nest. From courtship to fledgling independence, the entire breeding cycle takes at least six to seven months.
You can see where eagles have been sighted on Vermont eBird recently and add your sightings. If you find a nest site, please report it to the Vermont Fish & Wildlife Department or VCE. Please do not approach or disturb nesting areas.
By Julia Pupko
One of our earliest flowers in the spring is Eastern Skunk-cabbage (Symplocarpus foetidus). Skunk-cabbage lives in wetlands and can be found blooming when ice still crusts the ground around it. But how does a plant manage these freezing spring temperatures? It produces heat through a process known as thermogenesis. Powered by starch stored in its roots, this plant can average about 36 degrees F warmer than the ambient air for twelve to fourteen days. Watch for skunk-cabbage to sprout from the ground later this month and add your sightings to the Vermont Atlas of Life on iNaturalist.
By Spencer Hardy
Believe it or not, the first bees of the year will likely awaken on a warm day near the end of March—in the past few years, more than a dozen species have been recorded this month. Since flowers are few and far between, some of these early emerging bees will seek alternative sugar sources. In particular, the Frigid Miner (Andrena frigida) seems particularly attracted to sap and is often the first species recorded in the spring. Look for this species and other insects in and around sap buckets or on recently cut maples.
This is the first of our “Bee of the Month” series which will run through 2022 in these field guides. For more seasonal bee content, check out our iNaturalist project, which has weekly journal posts from 2021, and be sure to add your observations too!
by Kent McFarland
On Sunday, March 20, at 11:33 A.M., EDT spring officially arrives in the north. The equinox marks the moment the Sun crosses the celestial equator—the imaginary line in the sky above the Earth’s equator—from south to north. It is also when people worldwide can see the sun rise exactly due east and set exactly due west. While the sun may be predictable, March weather is not. In fact, March is appropriately named for the Roman war god Mars. March is a month of battles between warm and cold, between winter’s refusal to leave and spring’s insistence on coming.
Do you want to witness something you can see only twice a year? You’ll need a straight stick or yardstick, a protractor, and a compass (smartphone apps can work in place of the last two items). Find an open space before noon. Determine your GPS location. Subtract your latitude from 90. Use a protractor or an app on your smartphone to get the angle that your yardstick will be placed. Use a compass, or again, a smartphone app, and find south. Put your yardstick in the ground at the designated angle and pointed due south. Wait till noon and see how the shadow of the stick disappears—at noon, the stick will have no shadow at all! You can only do this experiment twice a year—on the March equinox and the September equinox.
Julia, thanks for your intersting article on sap flow. I wonder if there is some advantage to the maple, walnut and birch trees of having these gas containing hollow fibers lining their xylem. Is it helpful to the trees in some way or are they just being generous by providing us with sweet syrup! (I’ve seen birch syrup but did not realize there was such a thing as walnut syrup until I did a Google search. How fun.)
What a brilliant e-zine!
Thank you so much!