A Little Bit More
At the end of the summer, maples stop growing and store their excess starch throughout their sapwood; it’s not just in the roots. Initially the starch remains in “cold storage” within the tree but eventually it is changed to sugars. In late winter or early spring, as the air temperature on multiple days climbs above 0°C (32°F) with nights below freezing, these temperature fluctuations cause positive pressure changes within the tree that produces a sap flow. Although the sap has been present within the tree’s sapwood all winter long, it was stationary until now.
The mechanism that produces the pressure changes within a tree is not completely understood but it is the above-freezing daytime temperature and below-freezing nighttime temperature pressure changes that appear to initiate sap flow. Different species of trees respond differently to temperature changes so flow in one species may not herald flow in another. This process takes time but after awhile, one can see that the buds are swelling and soon a new crop of leaves will be expanding and working to produce another year’s growth.
Activities
Science – Let It Flow
Objectives: See sap flow in action
Materials: Tree or shrub branch and pruner
Sap flow occurs all around us each and every year, yet few of us have ever seen it in action. This is an opportunity to make this process “real”. I live in a temperate climate so am most aware of this during the spring but those in subtropical or tropical areas should be able to see this all year long, depending on the species.
- In late winter/early spring select a tree or shrub on school grounds or in your yard that could use a wee bit of pruning. You won’t need to do much trimming but you’ll need to cut some branches to see this process.
- Keep an eye on temperatures in the spring and note when the days are warming to above freezing in the daytime on a consistent basis. If you then watch the buds on a given shrub or tree you’ll know when to do this activity. As soon as the buds begin to swell, you’re ready.
- Take pruners and cut a branch on your “selected’ tree or shrub
- After making your cut, you’ll need to wait a bit to see if any sap begins to ooze from the wound but it should not be a long wait. If you like, you can taste the sap to see what you think.
Here are a few questions you may want to ask your students:
- What was the color of the sap?
- Did the sap have any particular flavor?
- Did the sap run out of the cut much like blood might from your veins?
- If you wiped the sap from the tip of the branch, was it quickly replaced?
- If you had cut the same branch on a day that was below freezing, do you think the sap would have flowed? Why or why not?
You may want to look at the Electronic Naturalist unit on Maple Syrup production too.
Key Concepts
Growth and Development, Structures and Functions
Questions
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Posted by Sophie Polazkowyj on June 18, 2006 at 12:47 AM
Q: I have two tall skinny evergreens (fir trees) on one side of my driveway and a very large wide one on the other side - obviously, both kinds are different species. My husband thinks that one of the skinny ones, that has more dead branches, is dropping a very hard caralized sap all over the car, which, sap remover won't remove and on the window can only be scraped off, but what about the paint on car - can't scrape there. I think that maybe, because the bottom branches of the big wide one were cut to clear a 6 ft area because a lot of the loser brances were dead, is causing the problem. Besides the skinny ones should be dropping onto the driveway and it doesnt. Maybe the wind blows it from the wide one. Help me out here. How do I get to the bottom of this problem of deciding which tree is at fault. Also, How do you remove such hardened carmalizing sap from the car, without ruing the paint job? What breaks this sap down, safely?
A: At certain times of the year, trees do drop sap and this can be upsetting if it gets on cars or other equipment. I'm guessing that your firs have put on some new growth this year and this is what is causing the excess sap dripping - it shouldn't last too long. I think your best bet is to ask at a car supply store what they'd recommend to remove this. They'll know what kind of cleaner can be used to avoid damage to the car's finish. Best of luck to you.
Posted by marybeth balog on April 20, 2006 at 12:53 PM
Q: What is sap?
A: Basically, sap is sugar water. The sap in a tree has a small amount of sugar in it as food for the tree plus some nutrients. If you've ever cut a branch from a tree or shrub and noticed that it "bled" a clear liquid - that's sap. Hope this answers your question.
Posted by chris fairbank on April 02, 2006 at 10:41 PM
Q: Do any other trees produce a sap that can be used for edible purposes?
A: Yes they do. Since all trees have sap, it's just a matter of taste which ones are used for making syrup - over time people have preferred the taste of the maple sap. However, since the Sugar Maple (Acer saccharum)has the highest sugar content of the maples, this is the one that is typically used. Other maples can be used but you'd have to remove even more water to get the sap down to the consistency you would want for syrup. It would be interesting to tap some diffeent species of trees for their sap and then make syrup to see what flavors you could come up with - some would be tasty and some would probably not be. Birch Beer, a rootbeer-like flavor, is regulary made from the Black Birch (Betula lenta) but I'm unaware of any other products made from tree sap. Thanks for asking.