Sap Content and the Seasons

Despite rumors to the contrary, live trees contain the same amount of sap, summer or winter. July 28, 2012

From a web site I copied this: "Many of the chosen trees are more than 100 years old and cut during autumn or winter when the sap is low." My question is about the statement "when the sap is low." Doc?

Forum Responses
(Cabinetmaking Forum)
From contributor D:
I'm not the wood doc, but I say true. I believe that sap falls in the winter.

From contributor T:
I will take a guess that since trees grow during the spring and summer, as indicated by the rings, the sap would be more needed during the summer. But I could be completely wrong.

From contributor R:
Perhaps true, but wood is harvested when it is harvested. When I logged 30 years ago, we cut more in summer than the snowy winter.

From contributor M:
In South Georgia we are currently in the time of year when we can burn the underbrush. We do this after a period of cold and preferably before the temps get back up again. The idea being (at least in my understanding) that during the cold season the trees will not be harmed, due to the sap being down. I have often wondered how that could be, since the pines are just as green as any other time of year.

From contributor L:
So where "down" does the sap go? Do the roots bloat up? Not likely.

From contributor T:
What is the definition of low? To me they are saying there is less sap in the tree as it has been consumed in the growth process. Not that it is low in the tree.

Do you have a permit to burn that brush? You better be careful or you will be out of compliance with the bureau of compliance.

From contributor M:
Why, of course I have a permit. Not due so much to complying, but because my boss insists on it. My wife won't give me the matches until we call it in. Besides, I am surrounded by thousands of acres of dry tinderbox pine woods, that my neighbors just might not want to have burned.

From contributor J:
False. Trees need/have the higher volumes of sap in winter. In early-mid march we tap sugar maples and when the sun is higher in the sky the sap runs like a faucet. I assume most of the sap is produced in autumn/fall and then in spring, so best time may be summer. My science may be wrong. Cut on a dry spell, there will be less water in the cellulose. Cut it in summer, easier, and there's not three feet of snow in the woods.

From contributor U:
There is always sap in a tree; there is just much more of it in the summer. I used to work in a mobile home plant and in the winter the lumber would be dry and my hands would rarely get sticky, but in the summer I would have to wash them several times a day because of all the resin and it was hard to get off. I was the guy that cut all the studs, by the way.

From contributor I:
This topic has been discussed on several occasions in the Sawing and Drying forum. Around here, some folks not only believe that there is less sap in the winter, but that the sap content of a tree also varies with the moon phase, thus the almanac must be consulted prior to heading out to cut firewood.

Seasonal Moisture Content of Living Trees

From Professor Gene Wengert, forum technical advisor:
Absolutely, there is the same amount of sap, summer and winter. The sap does not fall. This is a wives' tale.

I would venture a guess as why people thought that the sap goes down a tree to the roots in the winterů They noted that in the winter and fall there was no sap stain (fungal) activity, and they reasoned that there was no sap. They did not appreciate that the sap stain fungus needs warm temperatures in order to be fully active.

Pulpwood is most often sold by weight, and pulpwood companies know for certain that the weight, or sap content, does not change seasonally. In fact, due to drying in the warm months, weights may be slightly less in the summer. Likewise, anyone involved in drying of lumber knows that the sap content is constant.

It is indeed strange how wives' tales, like this one, continue to exist and get support even today. Just think of the huge hollow reservoir that would have to exist in the roots for the trees' sap to move down and be stored. Also, when the sap begins to move in sugar maple, which is well before the leaves appear, think of where all this sap is moving from and going to. A non-scientific answer is that the sap is moving from roots to the woody stem, and that it left the stem in the fall and has been stored in the roots.

Also, if you are a bit older, you may have learned in school that the cambium layer of cells that make all wood and bark cells is a single layer, but now we know it is several layers. The cells are full size when made and die soon afterwards. Did you know that a branch in a tree that is six feet off the ground will stay that height throughout its life, unless the branch is cut off, falls off, or the ground is disturbed?

2/18 #15: True or False ...
From contributor M:
I agree with everything you are saying, Gene, but what would the criteria be for so much burning this time of year, mostly around the pine woods? I understand the benefits, and see where burning while it is cooler is more comfortable, and it does allow for the spring growth to come back in time to support the quail and other wildlife. But is there any reason from the tree perspective?

From Professor Gene Wengert, forum technical advisor:
If the ground is frozen, the tree will skid easier. Color will be better and for a check-prone species, transportation on the truck is much less likely to cause checking in the wintertime due to cooler weather.