Do the fall colours predict sap flow in the spring

[Swingpure]

The fall colours have been spectacular this year with the perfect temperatures, sunshine and rainfall. The best it has been maybe in decades.

Do those perfect conditions translate into good sap flow in the spring?

You can see one of my lines in the bottom left corner.

https://share.icloud.com/photos/003SHt4cLS3bHv2q6zeYKfQ3w

[DrTimPerkins]

The answer probably ranges from NO to VERY LITTLE.

I actually have a dataset that encompasses a large number of meteorological variables (average monthly temps, precipitation, drought, snowfall, etc.) and a bunch of biological variables (seed production, tree health, etc.), which includes spring green-up and fall-color development as well as sap sugar content and sap yield for the past 40 yrs. That's one of the beauties of UVM PMRC...we have done measurements for a long period of time, and there are lots of other studies done at our site that we have access to the data for. We were one of the first sites in the National Phenology Network. I've done a little dabbling with the data, but it is a hugely complex analysis. Not sure I'll have time to actually do all the work before I retire. If not, I'll hand it off to someone else.

The initial set of results indicates that there's not a lot that influences sap yield other than weather at the time of sap flow. Temperature and moisture at that time are critical. As far as sap sugar, there are several things that have an influence, but the relationships aren't strong, with an r-squared of 0.2-0.4 (so 20-40% of the variation between something being explained by the other). Everything we've found are negative relationships, meaning that we can't really push sap sugar higher (it is probably mostly genetically controlled), but these things can act to depress sugar content. In other words, the engine size (photosynthetic capacity) of a tree is pre-determined, but things like drought, hot temperatures, stress, etc. can act to reduce the output of the photosynthetic engine or the use of the energy (sugar) that is produced.