Leaf color

[Someclown]

Is there any research or knowledge, if the color of the leaves are brighter in the fall that the sugar content is higher the following spring. I have memory of an old timer mention this to me years ago. Not that I'm young, and do respect my elders.
I do notice from year to year the difference in color vibrance in the leaves but don't have enough experience sapping, last fall the colors were really bright around my area.

[Brian]

That is a good qustion I have woundered that a time or two.

[Someclown]

Is there any research or knowledge, if the color of the leaves are brighter in the fall that the sugar content is higher the following spring. I have memory of an old timer mention this to me years ago. Not that I'm young, and do respect my elders.
I do notice from year to year the difference in color vibrance in the leaves but don't have enough experience sapping, last fall the colors were really bright around my area.

Sorry, after doing a second search my question is more clear to me
Thanks for the great info Dr Tim


*Originally Posted by*BreezyHill*

Does the sugar level of a tree have anything to do with its coloration of leafs in fall?

In general yes. For those leaves that turn brown and fall off....it is typically some foliage disease (anthracnose), so we're not talking about that.

Very simply and briefly (OK....brief for me anyhow)....leaves have green (chlorophyll) and yellow colors (carotenoids....ancillary pigments) that serve to "harvest" energy in the light reactions of photosynthesis (it causes the electrons to be boosted to a higher energy state....kind of like vibrations in a wine class when you ping it with your finger). This energy then pass through an electron transfer chain (ETC=a group of different compounds close together that successively "funnel" that energy down to a specialized photocenter pigment) to "fix" or convert physical energy (electron excitation stages) into chemical energy (carbohydrates). Very simply, the vibration energy is passed through the ETC to the photocenter where enzymes hold "carbon" compounds close to each other. This vibration energy provides enough of a "push" to force the carbon compounds to fuse....eventually into sugar (that is a huge simplication....the process itself if quite involved). These fused carbon compounds provide (at least part of) the building blocks for sugar. The whole process of photosynthesis is just that of a very small electro-chemical plant that uses light to fuse carbon (from carbon dioxide in the air). Put a few million of these in a*leaf....and you're really making sugar.

In the fall, an abscission layer starts to form to cut off the*leaf*from the twig. Some trees (like maple) do this very effectively -- others aren't so good at it (oaks, beech). As this happens, photosynthesis doesn't shut down.....it just keeps cranking awy, so the leaves keep making sugar. However because one of the first layers to be affected by the abscission process is the phloem (just inside the twig bark, which serves in sugar transport from the leaves to the rest of the plant), which impairs the ability of sugars to be exported to the stem (so you haven't shut down the*leaf*"machinery" forming the sugar....just slowed down or stopped the trucks taking the sugar away. Since these sugars are trapped in the*leaf*(more or less depending upon the abscission layer development), the leaves utilize some of this excess sugar to actively form new pigments, anthocyanin, which is a red-colored (usually) pigment (so kind of like the factory that can't shut down the machines...so sugars stack up....and to get rid of some of that sugar, you turn it into candy). At least in maple, it doesn't appear that these anthocyanins are playing any major functional role in terms of protecting the leaves from excess light and/or cold temperature oxidative damage (the current theory in most textbooks....at least for maple it is incorrect). In other plants, red*color*"may" have some addition function. So the red colors in maple form "just because......"

Other stresses can cause temporary or permanent red*color*to form. Look at leaves early in the spring when the buds are breaking. The leaves are red....the phloem transport system is just getting ramped up at that time so the sugars that accumulate can't be transported out.

So, the leaves that are less able to export sugars are those that tend to develop more red*color. Some years you have little export due to prevailing weather conditions, you get lots of anthocyanin production and red leaves. If they do it less (some years), they form orange (mixture of anthocyanin and carotenoids). With more export, you get yellow (carotenoids) as the chlorophylls die off and degrade. You can see this on individual portions of trees.....often the outer edges, those that get the*color*trigger cue (and the*leaf*abscission cue) early, will turn red.

Some trees naturally are better at quick*leaf*abscission.....others not so much. It also depends upon the individual year, but like the sap sugar content, trees tend to have consistent rankings of*color*development. What does this mean for sugarmakers? Probably not a great deal, although we've never really looked to see if trees that are very red also tend to have higher (or lower) sap sugar contents. Might be an interesting study.

You want to know more about this subject.....ask Dr. Abby van den Berg (at UVM PMRC). Her Ph.D. (with me as her advisor) is in anthocyanin (red pigments) in maple leaves. She still does a little work in that area.

Last edited by DrTimPerkins; 09-27-2013 at*09:33 AM.

Dr. Tim Perkins
UVM Proctor Maple Research Ctr
http://www.uvm.edu/~pmrc
https://mapleresearch.org
Timothy.Perkins@uvm.edu

[DrTimPerkins]

Is there any research or knowledge, if the color of the leaves are brighter in the fall that the sugar content is higher the following spring.

We have been working on a study for several years now looking at the relationships among sap yield and sap sugar content and a large number of environmental (meteorological) and biological variables. This is essentially a continuation of research done years ago. The difference is that we have more data now to play with.

https://mapleresearch.org/wp-content/uploads/sugarconc.pdf
https://www.uvm.edu/~uvmaple/sapsugarcontentvariation.pdf

In short, when we look at those relationships, the weather (temperature, snow, rain) DURING the season has the biggest impact on SAP FLOW or YIELD, but the weather BEFORE the season has a bigger influence on sap sugar content (SSC). We can detect significant influences as far back as the previous summer weather (hot, dry summers and hot, dry fall periods are bad) on SSC. In general, the tree tends to have a specific genetic potential to produce sap of a fairly high SSC, but all those things that can affect it tend to drive SSC downward. We can think of the trees carbon acquisition (leaves) and storage system as a car engine. Each engine has a certain size and output potential (horsepower). But if we do things like give it poor octane fuel, or tires that have poor traction, or most anything else, we are just going to lose a little bit of the engine's output, and make it run a little slower. Same sort of things with trees. If it is hot and dry, the tree engine (leaves) run a bit less efficiently. If this goes on for a while, the output drops accordingly. I have spoken about this a few times at conferences, but there is not recording of those available unfortunately.

We haven't delved a lot into the leaf color factor much, but we do have a webcam on the roof of the building at UVM PMRC. https://phenocam.sr.unh.edu/data/latest/proctor.jpg in conjunction with UNH as part of the PhenoCam network. We recently pulled together that dataset and parsed the parts of those images that look the the treetops it into red and green color values, so we can look at how fall color and timing of leaf color might influence SSC. We can also look at how the timing of spring greenup is related to spring season end date and timing.

Lots of fun things to play with...just not enough time in the day. Hopefully I'll have this completed by the time I retire.

[Someclown]

Great info Dr.Tim thanks again
I realize that SSC may or may not be something that can be proven by research as there are so many different variables from year to year, maybe day to day, tree to tree , soils, and area, etc., but the more research that is done will always help.
Keep up the good work

[DrTimPerkins]

Realistically, while it is scientifically very interesting to better understand the factors that influence SSC and by how much, the reality is that there is not a lot maple producers can do about it other than to limit stresses in your forest, which primarily comes down to reducing competition, and if necessary, soil nutrition.

[TapTapTap]

It also seems unscientific to apply a casual and subjective observation like leaf color and brightness to a theory. Since I've now experienced 59 fall foliages, I can opine that the fall colors are spectacular in a bright sunny day and sometimes downright ugly on a dreary day - regardless of the year.

At least I can measure the length of brown in a wooly caterpillar.

[DrTimPerkins]

It also seems unscientific to apply a casual and subjective observation like leaf color and brightness to a theory.

For casual observations that might be true, but if done quantitatively it is quite simple to measure the saturation value of any particular part of the spectrum. That is the basis for remote sensing (earth), planetary observations (space missions) and astronomy (stars and planets). Looking at the brightness and spectral signatures can tell us quite a bit. It is basically what your eyes do all the time, but with quantitative measurements. It really is not a lot different from what your camera/phone does when it measures light to determine the best exposure level. The only difference is that we can break it down into different wavelengths or spectral regions. This is actually what a photometer (or your eye) does when it measures light transmission through maple syrup to determine grade.

For instance, by measuring "greenness" of maple leaves, we can give a pretty good estimate of nutrition, especially nitrogen. For "red" we can infer how far along in the fall foliage season is. For "greeness" we can infer how far along the buds have opened. Lots of interesting ways to "look" at things.

Finally, we are not actually testing theories of causation. We are simply looking for "associations" or "corelations" between variables. For example, how strong is the relationship between rainfall and temperature in the fall with SSC in the spring. If an association is found, it won't tell us WHY there is a relationship, merely that there is or isn't one and, if one is found, how strong it is in terms of its predictive value.

[TapTapTap]

For casual observations that might be true, but if done quantitatively it is quite simple to measure the saturation value of any particular part of the spectrum.

Dr. Tim,

I apologize if I sounded like I was disparaging the research. I was pointing out that assessing leaf color requires a scientific approach if we (as regular sugarmakers) are to look for leaf color as an indicator of the coming season. And thanks for clarifying the nature of the research.

Ken