That was a lot of fun. Thanks for that.

By the way, the discussion about color is interesting and got me to thinking and doing a little research.

I live and work in the northernmost fruit district in Michigan and have long noticed that the various fruit varieties have more color the farther north they are grown. I suspected that the longer summer photo-periods were responsible for higher levels of anthocyanin and flavanoids and other compounds associated with high coloration - reds, yellows, oranges - as compared to chlorophyll which is associated with green coloration. The same phenomenon appears to occur with leaves as well as fruit, as you suggested in your response to our friends here from the South.

I came upon this today that supports the idea:

Nature's Swiss Army Knife: The Diverse Protective Roles of Anthocyanins in Leaves
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1082902/

"When leaves receive more light energy than can be used in photochemistry, they show a characteristic decline in the quantum efficiency of photosynthesis, termed photoinhibition. Under severe conditions the chloroplasts generate reactive oxygen species, which have the potential to destroy thylakoid membranes, damage DNA, and denature proteins associated with photosynthetic electron transport. Anthocyanins have been shown in many plant species to reduce both the frequency and severity of photoinhibition, as well as to expedite photosynthetic recovery. In red-osier dogwood (Cornus stolonifera), for example, a 30-minute exposure to strong white light reduced the quantum efficiency of photosynthesis by 60% in red leaves, but by almost 100% in acyanic leaves. When the plants were returned to darkness, the red leaves recovered to their maximum potential after only 80 minutes, yet their acyanic counterparts had not achieved the pretreatment state even after six hours.

"Anthocyanins protect leaves from the stress of photoinhibitory light fluxes by absorbing the excess photons that would otherwise be intercepted by chlorophyll b. Although red leaves absorb more green light in total, their photosynthetic tissues actually receive fewer quanta than do those of acyanic leaves because the energy absorbed by the cell vacuole cannot be transferred to the chloroplasts. As a result, under light-limiting environments the photosynthetic efficiencies of red leaves are often slightly lower than those for acyanic leaves. Under strong light, however, the anthocyanins serve as a useful optical filter, diverting excess high-energy quanta away from an already saturated photosynthetic electron transport chain. Chloroplasts irradiated with light that has first passed through a red filter have been shown to generate fewer superoxide radicals, thereby reducing the propensity for structural damage to the photosystems."

I can see what seems to be Red-osier dogwood - Cornus stolonifera - in your photo, by the way, the plant that is mentioned in that excerpt from the research paper.

So, going farther north means longer days in the summer. That is certainly true. Longer days mean more light. Hard to argue with that. According to the research, more light means more anthocyanins in the leaves. More anthocyanins in the leaves means brighter red colors in the fall.

That is your reds. As for the yellows, later in the paper we find this allusion to other research on the role of flavanoids in the protection of foliage:

"Interest in the flavonoid family has increased in recent years following the observation that these compounds act as sunscreens against potentially damaging UV-B radiation. Foliar anthocyanins have generally been included with other flavonoids in this UV-B protective role."

So, going farther north means longer days in the summer. That is certainly true. Longer days mean more light. That means more UV. Hard to argue with that. According to the research, more UV means more flavanoids in the leaves. More flavanoids in the leaves means brighter yellow colors in the fall.

Mike