Peter wrote: Wiegand says the sugar is from 1 to 5 % concentration. Not enough to prevent freezing.
Apparently, freezing is actually integral to the process:
http://blog-yard-garden-news.extension.umn.edu/2009/04/the-mystery-of-maple-sap-flow.html
Some snippets:
"Since grade school we've learned that the xylem, or wood, transports water from the roots to the aerial parts of the plant, while the phloem transports sugars and other organic materials. Though true, this has resulted in the notion that sucrose-rich maple sap is extracted from the phloem – which is wrong. The sap that drips out of a tap, or spile, in a sugar maple tree comes from the xylem. In fact, this is the only time during the year when the fluid in the xylem is rich in sucrose, and is an exception to the wisdom we garnered in grade school."
"At night, as the temperature gets colder, air bubbles in the sap contract and dissolve decreasing the pressure. This initiates a suction (tension) that draws water from adjacent cells. In turn, these cells are refilled by water absorbed from other cells and ultimately from the root. As the temperature continues to drop, water freezes inside hollow fiber cells in the xylem and in the intercellular spaces. Additional ice forms as water vaporizes from surrounding cells, much like the formation of frost on a misty winter morning. When ice formation is complete, the remaining gases in the stem are compressed and locked in ice bubbles. The next day, when the temperature warms, the ice bubbles melt and the compressed gases expand producing the pressure that pushes the sap out of the stem. Sap flow eventually slows by late afternoon when the stem pressure declines due to the evaporation of water from branches, internal leaks, and perhaps other causes."
"Why maple?
Spring sap production is a relatively rare phenomenon. It occurs in the maples, genus Acer, and just a few other species. So, what it is about maple? The critical factor appears to be related to the distribution of liquid and gas in the xylem. Xylem is comprised of several types of cells including fibers and vessel elements. Vessel elements are the main water-transport cells while fibers are longer and thinner and serve primarily to support and strengthen the wood. In species that produce sap, like sugar maple and butternut (Juglans cinerea), the fiber cells are air-filled and the vessels are water-filled. In contrast, species that do not exude sap, such as willow (Salix), aspen (Populus), elm (Ulmus), ash (Fraxinus) and oak (Quercus), have gas-filled vessels and water-filled fibers.
The mysterious process of maple sap flow likely evolved as a way that maple could provide water to the leafless canopy during a freeze-thaw cycle."
Erin's uncle has been sugaring for over 40 years an hour and change away from us in the hills of southeastern Vermont west of Brattleboro. I figured that with global climate change, he would have seen a movement to earlier and earlier spring flows. So, yesterday I called him up and asked. Surprisingly, he told me no, that it still occurs all over the map from early February to late March. He added that a while back he had asked the same question of an 'old-timer', whose experience pre-dated his by another 40 years or so, and was told that it still varied about the same, and the 'old-timer' remembered sugaring as early as January. While I have seen fall last longer (hard to believe this year, as it is -3F/-19C this morning with 12in./30cm. of snow on the ground already), spring does seem to be rather erratic in its arrival around here, maybe more so than in the past (talking with locals the consensus is that we seem to go from winter to summer with little spring in between, although I don't have data to support). I know some of the climate change models predict more severe winter weather for New England, and, perhaps, that's what we're seeing. The warmer summers extend fall, bottling up arctic cold longer. But, once it finally hits, it takes longer for the pattern to shift back come spring.
If true, what does that mean for bees? (He asked, moving the topic back to bees.) Longer, warmer falls mean the bees stay active longer, consuming more stores, since there is nothing left blooming by October. Erratic springs with frequent cold snaps mean the first bloom may come later (in the past three years I've recorded pollen coming in between 18 March and 15 April), and the bees may have more difficulty moving to stores, especially if they have started brood-rearing in response to some other signals that we still don't fully understand (the topic of this thread). So, greater chance for later winter/early spring starvation. Which I have seen - cluster frozen over a small patch of brood in March, bees head down in empty cells with plenty of stores around them, but separated by a ring of empty cells. I have sustained colonies that have chimneyed up the center by placing sugar on newspaper on the top frames, but I can't help them, when they are down inside the boxes.
Bill
Claremont, NH US
***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
|
