Calculating the best tapping date

[DrTimPerkins]

Like I said, I'm a meteorologist so I naturally am trying to apply some "science" to the art of sugar making. Being a maple researcher I think you do the same thing and I appreciate your insights!

No problem, but wood temperature (THE key factor) and air temperature are often quite different. Air temp is not the important factor.

Four things make this way more complicated than you assume:
1. Weather forecasts beyond about a week aren’t great, and even then tend to give a fairly broad range.
2. Wood temp forecasts don’t exist (and few places even measure this). In addition, trees are not isothermal - some parts of a tree might thaw while others can be simultaneously frozen.
3. The sap flow phenomenon relies upon a minuscule difference between freeze and thaw.
4. Microclimate in a forest is hugely variable, especially in terms of air temperature.

We understand the variables involved. We understand the processes involved. However wood temperature forecasting in a forest setting to predict a phenomenon that relies on a tiny difference in wood temperature is not yet feasible. Any forecast would be no better than looking to historical temperature averages and historical tapping dates. To aspire to that is great, but to think we are close to that point is not realistic.

Lastly, you assume we don’t have the data or haven’t made any attempts. You’d be wrong in both cases.

[DrTimPerkins]

In fact, on 9/21 and 3/21 everywhere will have an equal amount of sunlight available to them. However, on 9/21 some places will be at peak foliage and others will still have green foliage at the same time. The only difference between the two places is temperature for the most part. On 3/21 some places will be ending their maple season while other places (typically in the inverse of locations on 9/21) are just getting started. Again, the only difference is temperatures for the most part on those dates so sunlight isn't really a factor. It it is, please excuse me for not fully understanding the equinoxes.

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 ?

Sunlight/day length triggers some physiological processes along with temperature. In other cases (sap flow) day length has no effect (except as it affects wood temperature).

[Sugar Bear]

What I was implying was that they both occur around the time when available sunlight and temperatures are either decreasing or increasing. In fact, on 9/21 and 3/21 everywhere will have an equal amount of sunlight available to them. However, on 9/21 some places will be at peak foliage and others will still have green foliage at the same time. The only difference between the two places is temperature for the most part. On 3/21 some places will be ending their maple season while other places (typically in the inverse of locations on 9/21) are just getting started. Again, the only difference is temperatures for the most part on those dates so sunlight isn't really a factor. It it is, please excuse me for not fully understanding the equinoxes.

"Sunlight isn't really a factor", Unless of course sunlight just has to reach a certain level before stimulating the process of "peak" sap flow once proper warm temperatures and thawing have occurred. The season or peak season is farther out in the spring in the more boreal regions only because colder temperatures are not allowing it to come as early as the more southern regions.

My conjecture is, that the "TYPICAL POTENTIAL" for peak sap flow in any given coming season, will not come in say early or even mid-February in southwest CT or northeast VT for only one reason. The sun is too low in the sky at both latitudes at that time. The freeze thaw cycles in early February can dance like John Travolta and it will not change that. Yes, we can and do get runs at that time that make syrup and lots of it.

Otherwise, we would not hesitate to tap the great freeze thaw cycles of late November and much of December which frequently prevail across the greater Maple Range. And yes, for sure some sap flows then. But we know it's relatively weak so we don't tap them then even though temperature can be perfect. Sap flow is still not as strong even in January and into early February even when granted perfect thawing and perfect temperatures. That was clearly evident, on my taps, at my two locations, this season. And that has been evident in other seasons although not as clearly so because of colder conditions.

I am wondering. Does anybody know if sugar maples are cultivated on South America and how they do there if they do???

[Sugar Bear]

There is ZERO evidence that day length/photoperiod/light angle have ANY effect on sap flow OTHER than how they affect tree temperature. Wood temperature is the dominant driving factor in sap flow.

Sap flow, growth, leaf drop and dormancy are all physiological functions that are well understood. The drivers and interrelationships are not terribly strong among this group. Sap will flow in wood vessels whenever driving forces are present. Those driving forces are dictated almost entirely by wood temperature.

So are you saying there is no evidence that sunlight effects sap flow within the stem any other way then thermally over the course of a sap flow season. Correct?

[Swingpure]

So are you're saying there is no evidence that sunlight effects sap flow within the stem any other way then thermally over the course of a sap flow season. Correct?

Maybe another way of asking it, does sunlight affect wood temperature?

[DrTimPerkins]

So are you saying there is no evidence that sunlight effects sap flow within the stem any other way then thermally over the course of a sap flow season. Correct?

If we are talking solely about the physiology of SAP FLOW, then the vast majority of the influence is wood temperature. The vessel elements and fibers in the wood are DEAD while functional, so those other things have no way to influence SAP FLOW. Anything that affects wood temperature (sunlight, rain, snow, wind) is an indirect effect (they can influence wood temperature, which then influences sap flow). Sunlight, day length, etc. do not affect SAP FLOW except through their effects on wood temperature.

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.

[Brian]

Calculating the best tapping date

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.

[Sugar Bear]

If we are talking solely about the physiology of SAP FLOW, then the vast majority of the influence is wood temperature. The vessel elements and fibers in the wood are DEAD while functional, so those other things have no way to influence SAP FLOW. Anything that affects wood temperature (sunlight, rain, snow, wind) is an indirect effect (they can influence wood temperature, which then influences sap flow). Sunlight, day length, etc. do not affect SAP FLOW except through their effects on wood temperature.

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.

I understand and it makes sense, and it parallels my experience with my trees.

Perhaps it's that in the first two weeks of March the rays of the sun are just producing enough thermal benefit to the wood such that it always causes me to get to peak flow in that time frame.

Do you think a Red Maple might flow earlier then a Sugar Maple in the exact same aspect ( just a few feet away ) because the wood is softer and might warm up faster? I would imagine the ideal wood flow temperature is the same in both trees.

[Sugar Bear]

Calculating the best tapping date

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 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.

It would be cool if all Maple Traders were to disclose their peak flow rate date and location each year. For me it is clearly evident each year and would imagine it is for most producers.

[maple marc]

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.