Calculating the best tapping date

[DrTimPerkins]

That is similar to my concept, but mine is take your average peak flow date and tap three weeks prior to that. Give or take up to a week based on unseasonably cold or warm weather.

Whatever works for you is the way to go. The length of time to tap prior to good flows depends largely on the technology you're using (gravity vs vacuum), how many taps you have, how much labor you have, and how deep the snow is.

[DrTimPerkins]

Given the uncertainly of weather, does it make any sense to stagger your tapping, especially for producers on gravity/buckets? Dr. Tim, you hinted at this. You might call this a probabilistic approach--hedging your bets so to speak. Pick a day when that first run looks imminent and place maybe 60 to 70% of your taps? Pick a number. Then 2 weeks later place the balance.

That strategy can work well if the time between tapping and good flows is long and if you have a sufficient number of taps. Those with a huge number of taps do that as a consequence of their size. They may start tapping around the holidays, and finish just a short time before good flows are normally expected in their area. Of course, the early taps may not be as productive (they have lower sap flow rates) towards the end of the season than the trees tapped later, but that is an acceptable tradeoff given the circumstances.

[DaveB]

This entire argument totally ignores or misunderstands the physiology of trees. In your example, why wouldn’t all the leaves on the same tree change color and then drop simultaneously ?

I wouldn't expect every leaf on a tree or area to change simultaneously due to the fact that not every leaf or tree is going to be subject to the same amount of daylight and temperatures. There are microclimates that make a place warmer or cooler for a number of factors and even though the number of available daylight hours is the same, not every leaf is going to receive the same number of hours of sunlight due to shading and the movement of the sun.

Going back more directly to the thread topic...air temperatures varies a little according to height, position, location, etc. Wood temperatures vary a great deal from one side of the tree to the other, from near the ground to the upper branches, and from a small portion of the woods to the next due to really minor changes in drainage, aspect, etc. Since the entire sap flow mechanism depends upon just the tiniest change from frozen to thawed, it is not realistic to try to predict when sap flow will occur with ANY degree of accuracy, especially from the early part of the season to the end. Weather predictions for air temperature beyond about a week aren't especially precise, and tend to revert to the mean temperatures based upon historical data. If that's the case, why not just use the same historical data to predict when tapping should start, and adjust a small and reasonable amount to account for the season.
Now if we start talking about stem sap sugar levels, dormancy, growth, fall foliage coloration, and leaf drop, then other things start to be involved as well.

To be clear, that was the original intent of the thread - to look at historical data as a guide for the current season. I really wasn't trying to come up with some numerical sap flow model like we have numerical weather prediction models. My observation about the 15-day temperature average is purely anecdotal but matches up well with my sap collection record. That gives me a good average date for when the season ends and I can start looking at weather models about 8 weeks prior to that to see if it will be warm or cold going forward and decide if I should start putting the taps in or not.

I know we don't have precise air temperature prediction beyond 5-7 days, but there are tools that allow a forecaster to blend different models to at least get an understanding of where temperatures are going relative to "normal". One I use is an ensemble based model and I can see up to 16 days out. This is one of the reasons I waited on tapping in January despite the mild weather that we had. The models were consistent that the pattern was going to flip (and it did) and we had more seasonable weather. The problem was that because we missed long prolonged cold air masses, my trees were acting like it was late March and not producing as much sap as they usually do.

Here's a site that I use that shows the ensemble models along with an mean and you can see the trend relative to the historic average. You can adjust the location by clicking on the map.

https://www.wxcharts.com/?panel=defa...18&skewtstep=0

[DaveB]

My Uncle Kenny always told me to take your average end date and back up 6 weeks and that is the date you should be all tapped in by. That has worked for me.

That's pretty much what I do. In my case I've always looked at the end of March as the end of my season and backed things up 6 weeks to the middle of February and tapped then. I started averaging the dates for when my season starting winding down and going back 42 days (6 weeks) to figure out and average date of when I should be tapping. I figure that will give me an 8 week window of time since my taps are on vacuum.

The problem for me comes when we have a year like this when its so mild. Technically I could have tapped a month early but I still waited for February because I knew more seasonable weather was coming.

I think for most years making a decision +/- 2 weeks from the average tap date is fine. For mild years I would now do the tapping as soon as temperatures will following a freeze/thaw cycle. For me that would have been January.