Fall Color, Superpowers, & Chemistry

My work here in Vermont is drawing to a close and the time is coming to make a transition.  Serendipitously, this is synchronized with one of the more dramatic and beautiful changes that takes place in New England.  Fall Color, the time when the trees reveal their hidden secrets for a brief time before dropping their leaves in expectation of a prolonged period of time when photosynthesis is impractical.

Mt Elmore, Vermont – early fall color

The color is easy to capture at the level of an individual leaf, but surprisingly difficult to capture at a landscape level.   The problem is, like so many things, one of chemistry and individuality.  Not only does each species of tree respond differently to the seasonal changes, each individual tree responds differently, indeed each individual leaf responds differently.  The soil and the weather over the past year have their own influences as well.  This time of year Vermont makes quite a bit of money from tourists, “leaf peepers” they’re called locally.  As with anything that generates money there are numerous conflicting opinions as to what the best conditions are for a good fall color.  The conversations have the flavor of farmers talking about the weather or arguing over the best shape for the bottom of a fence post.

Big Toothed Aspen (Populus grandidentata) leaf against Paper Birch (Betula papyrifera) bark

There are several aspects of fall color I find particular interesting.  The first is that some of the color you see is always there, it is just hidden from view within the leaf by the photosynthesizing portions for much of the year.  I mentioned chemistry.  This is not because I am a chemist, or even particularly knowledgeable about chemistry, but because it is important for understanding much of the world around us.  Chemistry and physics.

Sunlight comes in all colors and some colors (wavelengths) carry more energy than others.  A plant needs to harvest that energy to produce sugars for growth and metabolism.  One of the difficulties the plant experiences is that energy comes in discrete packages, called quantum (quanta plural), and cannot be divided.  I realize that at this point some people will bring up the wave/particle duality issue; very loosely speaking color can be though of as wavelength and quantum can be thought of as the energy each particle carries.

In any event, plants store energy by breaking phosphorous bonds and recombining the atoms in new combinations, especially as ATP.  ATP, adenosine triphosphate, is the battery plants run upon.  Breaking apart molecular bonds takes a specific amount of energy and phosphorous is a particularly energy intensive fuel to use.  This also means that it can store a lot of energy, hence the plant’s use of it.  The degradation of ATP to ADP releases some of that stored energy and powers the plant.  The tricky part is that the light energy the plant has available to it, in the form of discrete quantum packets, does not line up exactly with the energy required to break apart and recombine phosphorus.  And, as previously mentioned, this process takes a lot of energy.

Remember, wavelength is color.  Shorter wavelengths carry more energy, quanta, and longer wavelengths carry less energy (incidentally, measuring this is one of the ways we tell if a star is moving towards or away from us).  Think of a rainbow for a minute…

Summer thunderstorms bring evening rainbows

The red light is low energy, the blue light high energy. Evolution is generally smart and not wasteful, within the limits of the resources it has to work with.  The phosphorous bonds cannot be broken down directly, the plant must convert CO2 and H2O into glucose sugars, metabolize those, and use that energy to create ATP.  All this costs energy, and plants harvest it all from the sun, using much of the red and blue light, and most of the rest of the spectrum except for green (with a few exceptions – purple leaved plants for example use green light).  Blue light causes something of a problem, it is extremely high energy, more than the plant can actually use in most cases.  Excess energy becomes heat, fine if you are in a cold climate, but the bane of existence if you are already in a hot climate.  Too much heat and plants close their stomata to avoid water loss, this also limits the plant’s ability to metabolize or photosynthesize.  One idea of why plants reflect the green light, also high energy, is to avoid overheating.  Green leaves may be a safety mechanism.

Glucose, the initial fuel and energy storage system of the plant, is a relatively relatively simple sugar and sweet to our taste buds.  During fall the plant pulls the important and complex chlorophyll compounds back into the main body, abandoning the leaf, sealing it off with brittle cork-like cells so that the leaf dies and drops away.  As the green chlorophyll leaves carotenoids in the leaves reveal some of the previously obscured color, but something else happens as well.  The glucose remaining in the leaf suffers damage from the sunlight and chemically changes, becoming anthocyanins.  The colors of anthocyanins are influenced by a complex host of factors, but the end result is that they produce fall color.

The second thing I find fascinating about fall color is due to the complexity of factors influencing anthocyanin production and the resultant colors.  Below is an ugly selection of the first Mt Elmore photo I’ve extracted and over-saturated to demonstrate this second interesting aspect of fall.

Note the distinct bands of color

The distribution and pattern of colors reveal soil types and moisture content.  Notice how the colors are not randomly distributed, there are definite bands and patterns?  Color hits first and most intensively where there is some sort of environmental stress.  The two micro-habitats I see changing color first in Vermont are wetlands and well-drained, dry soils.  The upper band of color, below the rock outcrop, is on a slight ledge with extremely shallow soil, land that stays dry and goes through more moisture fluctuations than the land surrounding it.  Each of those patches of color tells you something about the environmental conditions of that area, both seasonally and geologically.

This, to me, is fascinating, it is as though for a short time I have been granted superpowers and have Landsat-like multi-spectral vision.

This time of year in new England is magical.  The nights are cool and the days can be warm, fog rises and the colors are bright.  In the right place mornings feel like something from a fantasy novel, mysterious and beautiful, a place where knights, dragons, elves, or gods might be just around a corner.

Misty lake waters in a New England fall

As the seasons change so does my future.  I have accepted a position in Borneo and will be learning a whole new ecology, a new cycle of seasons, and a new set of environmental cues to pick-up on.  As I make the transition my posts may be a bit rocky and infrequent, and, once at my post, I will be relying on a patchy satellite up-link for a few years, but please bear with me.  Borneo is a rapidly changing place not many people have the opportunity to spend any time in and I intend to share the experience with those who are interested.

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Chickadees, survivalists extraordinaire

It seems likely that weather is the only killer so devoid of both humor and dimension as to kill a chickadee.”

Aldo Leopold wrote this line back in 1949 in his incredibly influential book, A Sand County Almanac.  He was commenting on the extraordinary longevity of chickadee 65290, a bird that had survived for at least 5 years following its banding in 1937.  Little 65290 may have been extraordinary, but a brief walk in the winter New England woods will rapidly convince you that chickadees as a group are exceptionally resilient little creatures.

Chickadee in the spring sun

Chickadees are very vocal, calling to each other throughout the year. You can hear some of their calls at the Cornell Bird Lab website.  Chickadees often travel in loose flocks, flitting about, hanging upside down from branches, stealing insects from spiders, scrounging for seeds, and chasing each other about in the forest like a group of excited 5 year old children just released from a long, boring bus ride.  Their colors are subdued, yet distinctive: black, gray, white, often with a hint of yellow or tan on their underbellies.

Chickadee acrobatics

Black-Capped Chickadees (Poecile atricapillus) are cold weather specialists with a home range extending from Alaska to New England and dipping as far south as the mountains of Arizona and New Mexico and along the spine of the southern Appalachians (map).  I find this is extraordinary.

There is a principle of physics called the square-cube theory that relates the volume of an object to its surface area.  Basically, this can be simplified to the idea that a mouse has more surface area compared to its volume than does an elephant, and that for every time you double the size of an object its mass goes up by eight times (Length x Width x Height).  In terms of survival in cold climates this is really important because smaller things lose their heat far faster than large things because of that ratio of surface area to volume.

Chickadees are tiny.  Their bodies are barely larger than a golf ball, and much of that is feathers.  All told they probably weight as much as an emaciated mouse, yet they live in a part of the world that is well below freezing for great portions of the year.  During the winter nights chickadees huddle in cavities in trees in semi-torpor, burning fat at a prodigious rate.  At first light they are up and spend the day searching for food.

Feeding Chickadee silhouette


All living things have to balance the payoff of their behavior with the potential risk that behavior carries.  Some species are extremely risk-averse, in political terms these species might be the Ron Paul’s of the world, insisting on a gold based currency.  Chickadees are the opposite, they are inquisitive, curious, bold, and fearless.  As in many animals, their willingness to take risks is dependent on availability of resources.  You see this in humans, a far greater proportion of low income people spend their money on lottery tickets than high income people, despite the abysmally low chance of getting a winning ticket.  If you have few resources you will take more risks to get a large reward.  The costs of those risks are higher for those with fewer resources as well.  For chickadees this means of food and a place away from that humorless weather.

Keeping warm in winter takes more food than in summer, and food is more difficult to find.  Chickadees take risks to get that food, they investigate new objects almost as soon as they encounter them, they come closer to humans and stay longer than many other birds, and they try new things.

Traveling in groups is one way to offset the individual risks these brave little birds take.  More companions means more eyes to watch for danger (and food as well), and chickadees have a very well developed warning system that alerts their companions not only to danger, but to the degree of danger.

The risks they take, their small size, and the harsh weather they endure takes its toll and chickadees do not live long, hence Aldo’s comments on chickadee 65290.

Chickadee and hungry young

Chickadees may not live long, but their lives seem bright and full of vibrancy.  They are a reminder of the importance of curiosity, companionship, and communication.

Bryophyta, Ancient and Tough

An ancient creature is waking up.  These creatures are small in stature but extremely tough.  They have been around longer than plants, although we often lump all green sessile things together.  Mosses are different though.

They have neither roots, nor vascular tissue, the plant equivalent of our circularity system.  They anchor to the substrate with little hold-fasts, somewhat like those giant algae, sea-weeds, and they drink though diffusion and osmosis.  They do well in places that are rich in airborne moisture.

Another things mosses lack is flowers and the associated seeds.  Like ferns, club-mosses, horsetails, and fungi mosses reproduce by spores.  By the millions.  They invest in quantity over quality and don’t pack any food or protection for their offspring before they cast them to the wind.  The spores will only germinate under perfect conditions.  Orchid growers are familiar with this problem, as orchids try the seed equivalent of this strategy.  Their dispersal strategy is like colonizing the galaxy by putting people in zip-lock bags and flinging them out of the solar system in the hopes that one of them eventually hit an earth-like planet.

This time of year the capsules that held the spores look like fossilized wind-socks.

Mosses are incredibly tough and individual stems from a colony can be very long lived.  A common way of judging the age of stair-step moss is the count the feather-like branches on a stem.  Five and seven year old moss stems are common and there are other mosses much longer lived than that.  An established moss colony may been in place for thousands of years.  Especially colonies in cold environments.

In the northern hemisphere we tend to think of plants and animals going dormant in response to cold.  If you can prevent the water in your tissues from freezing the danger for plants becomes one of dehydration.

Mosses, as I have said, are tough.  And Ancient.  They have some tricks they have learned over the hundreds of millions of years they have been around.  They learned these tricks before the ancestors of most of the things we see around us evolved.  Dinosaurs are latecomers to the party by the standards of the mosses.

Mosses dry up.  In a way the lessons learned as a spore transfer to the adults.  Most of their water evaporates, and as it does so the moss tissues curl in predictable ways.  The pores through which they breath close. Mosses can wait a long time like that.  Some mosses are so good at surviving this way that they grow in deserts.

Air in cold environments often contains less moisture than desert air.  Vermont has been even dryer than usual and many of the fir-cap mosses are still tightly furled, waiting for water.  Many look like the dry spires in the picture above.

Others have found enough water to wake up.

Like sponges, moss colonies trap water and fine debris.  The debris falls to the ground in the suddenly still water and becomes a nutrient supply for the mosses once they rehydrate.  Much like flowers they open as their tissues fill with water.

The growing tip opens as it hydrates revealing a tight furl of nascent microphylls (moss and clubmoss leaves) tinged a rosy hue.  Cold is well and good for living slowly, but growth requires warmth and the tips of the moss are shaped like little parabolic reflectors.  They trap both water and the sun’s light.  The reddish color may help them adsorb the long-wave understory light once the forest above leafs out.

From now through summer the new spore capsules will ripen, and come fall and winter they will scatter their spores across the landscape to drift with the wind, flow with the water, and run across the snow.

Unlike the poor fellows in zip-lock bags hurtling between the stars, the mosses have stacked the odds a little for their offspring.

Where water splashes moss may grow.  Where wind dies and lets drop what it carries moss may grow.  Where snow is late to melt moss may grow.

NOTE: The three close-in photos were taken though a 10x hand-lens held to the front camera of an iPhone4.