Sap Run 101

 Or, Are The Trees Just Over It?

Chief of Operations writes:

I really shouldn’t be trying to instruct this course, as after forty years of trying to predict the strength of sap runs, I am still only vaguely successful.

April 12/16 This week the weather seems so perfect for sap runs. Why, then, is their vigor so diminished? This same weather earlier in the season would have meant being inundated with sap. Trying to nail down what makes trees run well or not is somewhat futile, but here is my best attempt at listing some of the main ingredients.

1) Oscillating temperatures above and below freezing.
2) Other environmental factors including wind direction and amount of sunshine. North and West winds are regarded as the best, and early morning sunshine, especially after a hard freeze, is good.

3) Hard rain usually tends to slow a run, and, surprisingly, snow with the temperature above freezing often tends to invigorate it.
4) Age of taps (i.e. how long ago tap holes were drilled in the trees). Fresh taps always run the best.
5) A long period of very cold temperatures will usually cause a delay in the time it takes for the run to get going when the freeze finally ends.
6) Multiple days of warm weather with no freezing nights will gradually lower sap volume and quality. Each extended warm spell will have an accumulative negative impact on future runs.

7) Temperatures into the upper sixties and higher will severely curtail a run and extended days of this warmth will end the season regardless of what happens after.
8) Solar cycle. As April progresses, the longer days and warmer temperatures promote bud development, which ends the possibility of collecting quality sap.

 

Early in the season with fresh taps, oscillating temperatures are really all that’s needed for a good run. As tap holes age and are exposed to warm weather, contamination builds and the trees start compartmentalizing the wound, which closes off the sap loss. Check valve taps have been developed to counteract this problem, though I believe their effectiveness is limited.

Late in the season all the problems associated with old taps come into play, which diminishes sap run vitality regardless of how ideal the immediate weather may be. Aging taps, like people, become susceptible to decline in vigor.

-LC