Nature News:The sap is rising.’ Arrival of maple tree taps starts the countdown to spring

03/01/2022 Special to Seacoastonline Portsmouth Herald, York Weekly, Foster’s Daily

I love winter and have been hoping for a lot more snow, which we got last week, but only after an unseasonably (record-smashing) warm spell.

Much as I love winter and want to stay in the moment, that warm spell has me looking forward to spring. I love the countdown of days marked by the varied signs of spring. A friend sent me pictures of crocuses coming up. Hopefully, they’ll survive the plunge back to cold and ice. Red-winged blackbirds hung out at my bird feeder the day of the snow storm. It was so incongruous to hear their burbling calls – one of my favorite signs of spring –  on the eve of a blizzard. And my neighbors have started tapping their trees, a sure sign that the countdown to spring has officially begun.

Maple tree tapping is a sure sign of spring to come! Sue Pike photo

Last week empty metal buckets, poly buckets and milk jugs appeared on neighborhood maple trees, looking like vampires or tick-like parasites hanging off the tree trunks, draining their blood.  If you think about it, the idea that you can just stick a tube into a tree and out comes sugary sap is quite remarkable. The blood-sucking parasite analogy is quite apt — when we stick a tube into a tree we are tapping into its vascular system, but instead of blood, this vascular system carries sap, water and nutrients throughout the tree.

High school biology comes in handy sometimes!

A tree’s vascular system is composed of tubes called xylem and phloem. Back in high school I learned that xylem carries water and nutrients up from the roots to the leaves and that phloem carries the sugars that are products of photosynthesis down from the leaves to the rest of the plant (the mnemonic I use to help me remember what phloem does is I think ‘flow’–as in flowing downhill). 

Make sure to place your tapping buckets on the south side of the tree. Big trees that are open-grown (not in a forest) will produce the most sap. Sue Pike photo

I had always assumed that the sap for maple syrup comes from the phloem, but I was wrong. When maple sugaring in the spring we are actually tapping into the xylem, the sugars in this kind of sap come from the woody parts of the tree.  This actually makes a huge amount of sense, since maple trees are not photosynthesizing in late winter/early spring- when trees are tapped the phloem isn’t actively carrying sugar down from the leaves, instead the xylem is carrying sap up and throughout the tree.  That colloquial expression “the sap is rising” also alludes to which ‘sap’ is being tapped.

Freezing nights and warm days are the best conditions for rising sap

In the winter, sugars are stored as more complex starch molecules in the woody cells that surround the xylem vessels. In the spring, as temperatures begin to rise, these starch molecules break down into sugar and are released into the xylem from the wood.  The reason we need cold nights and warm days for good maple sap flow has to do with generating enough pressure in the xylem to start pushing its contents — the water and sugars — up from the roots. 

In the early spring, the ground starts to thaw and water begins to move into the roots, generating an upward pressure in the xylem. Cold nights compress gasses in the xylem and cause water to freeze along the inside of xylem tubes.  Warm sunny days melt the ice and cause the gasses in the xylem to expand, generating enough positive pressure in the xylem to cause the sap to rise. This is why a good freeze/thaw cycle is so vital to maple sugar production … the bigger the difference in day/night temperatures, the more sap will flow.

One reason sugar maples are the most commonly tapped trees is their sap has a high sugar content compared to most trees — as much as 3 percent; most other tree sap is only 1 percent sugar.

A long boiling time produces more flavorful sap

Different maple trees and different conditions produce sap with different amounts of sugar. High sugar content at the start of the process of boiling it down to syrup produces lighter, more delicate syrup. Sap with a lower sugar content has to be boiled longer, which caramelizes more of the sugars and concentrates all the other chemicals in the sap that contribute to the maple sugar flavor — this is my favorite kind of syrup.  

There is nothing more satisfying than hearing the drip-drip-drip of sap dropping into your bucket. -Sue Pike photo

Tapping trees is incredibly easy to do!

Last year was the first year I tried tapping maple trees.  Since I only have red maples that is what I used.  I waited too long and started at the tail end of the season with just three taps.  Always an optimist, I tried boiling down my 2 gallons of maple water on the kitchen stove (something everyone says to avoid since it releases so much sticky steam into your kitchen). 

I learned that there is a point where it becomes super easy to burn your syrup–which I did and ended up with a charred, sticky, bitter tablespoon of something that had evolved beyond the deliciousness of maple syrup.  This year, having discovered how incredibly easy it is to tap a tree, I’m going to try again and start earlier  with more trees and more taps and this time, hopefully, get it right.  What better way to start the countdown to spring!

For more about red maple trees go to this article about red maples or my blog post

This article and others can be accessed in local newspapers or online at seacoastonline

Nature News: Red maple buds enjoying the last days of dormancy before budburst

published Feb 24 2021

I have a bad habit of always looking to the future, winter isn’t over yet but I’ve found myself starting to think about signs of spring to come.  As an exercise in centering myself in the here and now, especially since we are finally in the middle of a beautiful snowy winter, I wandered around my backyard appreciating what the woods had to offer.  I found animal tracks and hemlocks still encased in ice. The waterfall, covered with a blanket of snow, could be heard gurgling underneath and river ice cracked and boomed.  A hint of color, in addition to the green conifers, was provided by the brilliant red buds of the red maple trees.   

Citizen Science!!

Last March I started a 3-month bud-watch project with my students in an attempt to get them outside, doing science as we plunged into remote learning.  I participated as well.  I found a beautiful young red maple tree with some bright red buds dangling at eye level and decided to follow those, entering weekly information about the state of the buds into an online citizen science database called Project Budburst (budburst.org). While doing this, I felt like I really got to know this tree. I even (rather uncreatively) named one particular bud ‘Red’ and another ‘Rosie’.  So, I visited Red and Rosie Junior (new buds on the same twig)  this past week to see how they were getting on.  

They were both there, chilling out in the wintry weather.  I could count the number of rings around the twig that are the remnants of previous years’ terminal buds (the buds like Red and Rosie that emerge from the tip of the twig).  Using these rings I was able to figure out that the twig itself was about 3 years old and also see where this twig had added about an inch of new growth to where the buds formed last year.   

Red maple buds right now–waiting to burst in the spring Sue PIke photo

I had recently read an article (The Sex Life of the Red Maple by Richard Primack of Harvard’s Arnold Arboretum) that got me wondering what gender these buds actually are.  Red maples usually have all male or all female flowers, but some are a mix of both (called perfect flowers) and sometimes a supposedly all male tree will produce fruit.  Last spring when I named them I was more focussed on when these buds were breaking (opening up) than considering their gender.  So I checked my photos of the buds in flower from last year and found that both Red and Rosie were male flowers with the characteristic stamen composed of a long thin filament supporting the anther-a narrow disk that contains the pollen.  This doesn’t mean the whole tree is male-red maples are notorious for not following strict gender-roles.  I’m looking forward to checking later this spring to see if these still are producing male flowers or whether they’ve switched to female flowers.

Red maple buds from the same branches last spring (in April after they burst). You can see from the long stamen that these are males. Sue Pike photo

But, bud burst will happen later, right now the buds are still dormant.  Buds are wonderful structures, tough little capsules that surround and protect the embryonic flowers and leaves.  The outer part is actually made of modified leaves, called bud scales, that are tough enough to keep out insect pests and also help insulate the inner tissues. These buds formed last fall at the end of the growing season when the trees had enough food and energy to make the buds. This is a critical strategy for overwintering–trees can’t wait until the spring to make these structures–they won’t have enough leaves and there isn’t enough light.  So instead, in the fall everything the tree needs to flower and reproduce, to form its first leaves and start to photosynthesize, is packed inside those tiny buds, dormant now, waiting for warmer and longer days to burst into new growth.  I like to think that, like me, those nascent flowers and leaves are cozily wrapped up in their buds, enjoying the lazy days of winter while dreaming about spring.