Plant Defenses – myriad strategies

Plants, as you might imagine, devote a great deal of energy to defending themselves from predators.  We humans have a natural bias towards animals, creatures that are like us in that they are mobile and respond to stimulus on a timescale similar to ours.  Plants operate, with a few notable exceptions, on a slower timescale, but this in no way should be taken to imply that they are any less interactive vis-a-vis their surroundings.

Plants react to light and dark, sense gravity, moisture, nutrients, and toxins; some can “feel” other organisms (Venus fly traps for example) or “hear” sounds (sensitive plants).  One thing all organisms must cope with is predators and competitors, and all organisms need defenses against these threats.  Plants are no different in their needs, but they are largely immobile, so some of their defenses tend to take a different form than they do in animals.  Surprisingly, their defenses are not as different from animal defenses as one might expect.  I would break plant defenses into three broad categories: chemical, physical, and co-optive.

Chemical defenses often involve toxins of one sort or another or pungent aromas.  Some of these we assiduously avoid, such as certain members of the Sumac (Anacardiaceae) family like poison oak (Toxicodendron diversilobum) and poison ivy (Toxicodendron radicans) due to the allergen urushiol found in the sap.  Other plants using chemical defenses we consume with great relish, many of our foods and spices, for example, derive their strong flavors from the defenses the plant manufactures to deter herbivorous predators.  Mints (Lamiaceae), rosemary, cinnamon, peppers, and onions are good example of common foods we consume that utilize strong chemical defenses.  Other chemical defenses we find recreational and/or medical uses for; ephedrine from plants in the Ephedra family, THC from Cannibus, and cocaine refined from alkaloids found in the coca family (Erythroxylaceae) all have enormous economies reliant on them.

Coca cultivation in Bolivia near Coroico

Coca cultivation in Bolivia near Coroico

Chemical defenses are enormously interesting and extremely sophisticated, but they are largely hidden from us until we are affected by them.  This is part of the reason why eating unfamiliar plants is so dangerous, there are few good ways to determine if a plant is edible upon first encounter.

Physical defenses are the most obvious to us, especially when they come in the form of thorns and barbs, but those defenses barely scratch the surface of the types of physical defenses plants can employ.

An impressive but unsubtle defense - Ceiba speciosa in the Bolivian Amazon

An impressive but unsubtle defense – Ceiba speciosa in the Bolivian Amazon

Sharp pokey bits may defend plants against larger herbivores and chemicals help to protect them from insects or pathogens, but other plants themselves can be, if not predatory, at least detrimental to large trees.  Lianas and other climbing plants, epiphytes, parasitic plants, and even other large trees may need to be defended against.

Strangler fig (Ficus spp.) overwhelming a palm tree's defenses - Bolivia

Strangler fig (Ficus spp.) overwhelming a palm tree’s defenses – Bolivia

The photo above I find particular interesting as the palm tree being overwhelmed by the strangler fig usually has an effective counter to this sort of attack.  Palm trees and tree ferns both allow their old fronds to droop as they age, sheathing the trunk and providing a structure for climbing plants to adhere to.  Eventually these canny plants shed their dead fronds, and with them the uninvited plant guests that have taken up residence.  Many trees employ a similar strategy, eucalyptus and madrone have smooth bark that regularly sloughs off in strips.  The combination of smoothness and shedding makes it difficult for other plants to gain purchase.

Strangler fig is a generic term for a wide variety of tropical fig trees sharing a similar life strategy.  These are the “matapalo” or killer trees.  Rather than growing from the ground and climbing up these trees co-opt animals to carry their tiny seeds through the canopy.  A small portion of these seeds wind up in a place like the crotch of a branch or a broken limb where organic material has built up.  The young fig sends dangling roots down from the canopy in search of nutrients, eventually reaching the ground and transitioning from a vine-like life style to a more tree-like life style.  More and more ground-seeking tendrils make their way downwards, eventually ringing the host tree and strangling it.  As this happens the strangler fig uses the original host as a scaffold and sends its own canopy high enough to overshadow the unfortunate host.  The palm tree in the photo above was underneath a tree the strangler fig took root in and had the misfortune to be attacked from above rather than from below.

Color is an oft overlooked plant defense, the role of which is still being debated.  I don’t mean fruit color, that is blatant advertising and animal bribery.  The color and pattern of the leaves and trunk of plants may serve as defense against predators.

The most familiar example of this is variegation in leaves, that is the white or colored mottling seen most often in ornamental plants, but also occasionally found in the wild.

Variegated hibiscus leaf. Source

Color mottling in leaves is often a symptom of nutrient deficiency, insect predation, viral infection, or genetic chimerism (expression of more than one genetic sequence in a single organism).  In most of the above cases this indicates poor health in the plant, and a plant in poor health makes for an unappetizing meal.  Some plants seem to capitalize on this and mimic the effects of various types of poor health (eg. false leaf damage and variegation) to trick predators into avoiding what appears to a be an un-nutritious meal(1)(2).  Bark color, whether natural or as a result of mutualistic lichen growth may be a predator deterrent as well, as lighter colors may make predators more visible to other predators higher up on the food chain.

Before moving on to animal co-option I should mention one other strategy employed by some plants.  Outgrow your predators.  In this case a plant allocates few resources to defense and focuses on growth and/or reproduction.  Balsa trees follow this strategy, they grow astoundingly rapidly and produce copious numbers of seeds.  They are not long lived and have few toxins, as a result they are subject to immense amounts of predation from a wide range of species.  Some of these, such as tapirs, they avoid by growing out of their reach.  Others are more problematic.  I saw a 30 foot tall young balsa tree completely stripped of leaves by leaf cutter ants in less than two days.

Basla saplings - Bolivia

Basla saplings – Bolivia

The most interesting of the plant defenses, to my mind, is animal co-option for defense.  Ants are probably the animal most often co-opted by plants.  We don’t often think of plants as being the ones to manipulate animals, but that is more a reflection of our animal bias than of the true nature of things.  Plants are highly manipulative, in their slow manner.  Like many effective manipulators, they accomplish their ends via bribes (and in a few cases by outright lies – orchids tricking bees into trying to mate with the flowers is a classic example of vegetative duplicity).  Ants are employed as guards by a great number of plant species.

When I first arrived in the Amazon I recall thinking to myself, “Cool, I hope I get to see some of the ant/plant mutualism.”  The first plant I looked at closely was a common understory shrub in the widespread and diverse Melastomataceae family.

Melastomataceae with ant sheltering nodes at the base of the leaves - Peru

Melastomataceae with ant sheltering nodes at the base of the leaves – Peru

At the base of each leaf there was a hollow, swollen node with two small openings on the underside.  Tiny ants occupied these nodes and would rush out to defend the plant when it was bumped.  This is a surprisingly effective defense against herbivores of all sorts, insect and mammalian.  All through the Amazon (and elsewhere in the world) ants and plants have banded together.  I found arboreal ferns with hollow rootballs harboring and colonies, tall cecropia and smoke trees (“palo diablo” – devil trees) with hollow trunks harboring vast numbers of fierce and painful fire ants, and evocative single species plant stands called Chullachaqui gardens.

According to legend the Chullachaqui is a forest guardian spirit that keeps small monoculture garden plots scattered here and there in the forest.  One should be wary entering these areas, ask permission first, and be careful not to damage any of the plants the Chullachaqui grows.  This is good advice as the Chullachaqui gardens are home to a species of ant that lives underground and kills all the plants growing on the surface except for one species.  Animals that interlope are attacked also attacked and the bite and sting of the ant is painful as it contains formic acid.

One of the neatest ant-plant interactions comes in the form of hanging “ant gardens”.

Ant garden in Peru with Monstera spp.

Ant garden in Peru with Monstera spp.

The dense cluster of plants in the above photo is growing from an arboreal ant hive.  Certain plants produce seeds with fatty nodules on them that ants eat.  Ants collect the seeds and store them in their hives, clipping the edible portions off as needed.  Some of the sees sprout and send their roots into the rich material of the ant hive, reinforcing it and protecting it from rain and predators as they grow.  These hanging ant gardens are found throughout the tropics.

Ant-plant interactions are not limited to the tropics.  Some trillium species bribe ants with food to carry their seeds to good growing locations and elderberries in certain portions of North America keep a protective coterie of ants nearby by bribing them with sugar produces from nectaries grown specifically for the ants.

Co-opting an animal may well be the most sophisticated of plant strategies for its subtly, specificity, and efficiency.  Energy cost is at the root of all these strategies.  A plant only has as much energy as it can collect from the sun and soil nutrients.  It must balance its energy use amongst growth, reproduction, and defense.  Every defense a plant employs lessens the amount of energy it can devote to growth and reproduction.  Combining forces with other species can provide a relatively low-cost way for a plant to gain an aggressive, mobile, multi-pronged defense force.  Ants, for example defend their plant hosts with both physically damaging attacks and with chemicals.  That’s a two-for-one defense with an added bonus of rapid deployment for the relatively minimal investment of a home or some food.

Humans may well be mammal plants have trained best.

***

A note about the images and film vs digital in the field:

These photos (with the exception of the hibiscus leaf which is not mine) were taken in 2005 with a well used and abused Canon AE1 with a 50mm 1.4 lens and scanned from the negatives by the developing kiosks in Peru and Bolivia.  The quality of images reflects both the environmental stresses put on the camera and film and the irregular scanning quality.

For long periods of time in the field I still think that film is the better option.  I was in the jungle for months at a time, sometimes in places with no power (20+ days hiking and on a raft in Bolivia for example) and in hot, humid conditions with frequent thundering downpours and rampant mildew growth.  I love the digital camera I use now, but it would have been completely unusable for the majority of the time I spent in South America.

Film cameras do still have their place.

Things that Gall – plants and parasites

The word “galling” is particularly evocative.  In its most simple form something that galls is merely annoying or vexing, but the true definition connotes annoyance taken to an extreme level.  The sort of thing that will do you no harm but rankles tremendously; much like being forced to pay taxes to support actions you object to.

For us these annoyances are mental and emotional, for plants these galls are physical but are often merely annoyances for them as well.

Dried oak apple gall  on Scrub oak in California

Dried oak apple gall on Scrub oak in California

Many plants suffer from galls and the galls are so singular in form that they can be reliably used to identify individual parasite species.  A fantastic book on identifying plant galls for the California region is the Field Guide to Plant Galls of California and Other Western States.

Oak trees seem to be particularly susceptible to parasites of all sorts and a common manifestation is the Oak Apple Gall, most often seen as a hard, woody ball dangling from a twig.  These galls are created by the Oak Apple Gall Wasp, a common name for a variety of small wasps that inject their eggs into the midrib of a developing leaf and chemically trick the tree into growing a protective shell for the developing larvae.  Despite appearing woody when dried, this type of gall is actually a modified leaf.  The delicacy of these galls is more easily seen when they are still green.

Fresh Oak Apple Gall - Virginia

Fresh Oak Apple Gall – Virginia

The developing wasps browse on the oak tissue and are often preyed upon or parasitized by other animals, including birds, raccoons, and a whole host of insects, other wasps included.  Some insects use the gall for their own protection, sharing the space with the wasp larvae.

Oak Apple Gall with non-wasp larva inside next to a Twig Gall - California

Oak Apple Gall with non-wasp larva inside next to a Twig Gall – California

Certain Oak Apple Galls, the Iron Galls,  in Europe were collected to make ink.  For 1500 years ink make from the iron gall was the primary source of writing quality ink in the Western Hemisphere.  For anyone interested Evan Lindquest provides detailed instructions on how to make your own iron gall ink.

Like may things we have a long history with there is a great body of mythology and folk-lore that has accumulated around these galls.

Many galls are hard and woody, there is a Twig Gall I sliced in half in the photo above.  It appears to be empty, but a dark brown patch filled with frass (insect excrement) can be seen winding its way though the bloated tissue.

Oak Apple Galls often fall from the tree, but Twig Galls are a more permanent fixture of the tree.

Twig Gall on a scrub oak branch flowering from the tip - California

Twig Gall on a scrub oak branch flowering from the tip – California

Right now the Scrub Oak is blooming along the coastal mountains in Southern California.  The twig galls are uniformly clustered near the tips of the branches, with many of them crowned by small clusters of flowers.  This provides a bit of insight into the formation of these and other galls.

The gall must be grown, and while the living plant cells are constantly dividing, the true growth of a woody plant takes place at the tips of the branches and roots, or at the apical meristem of each limb.  The cells in the apical meristem are undifferentiated,having the potential to become a wide variety of plant organs, much like stem cells in animals.  The parasite, be it a wasp, bacteria, or virus, co-opts these “stem” cells and gives them new instructions.  In a way the galls are akin to a tightly controlled cancer initiated by the parasite organism.

The Twig Galls I was looking at today were insect formed and, as such, the insect needs to escape the protective structure once it is mature.  Many of the galls had little holes in them showing where the little wasps has crawled out.

Exit holes in a Twig Gall - California

Exit holes in a Twig Gall – California

The variation in galls is astounding.  I have seen leaf galls on wild roses that look like tiny sea-urchins dipped in vermillion.  There are galls that not only force the plant to grow a protective structure around it, but that trick the plant into producing nectar to attract ants which in turn protect the growing larvae from predators.  Many are extremely colorful and the shapes are widely varied.

Colorful leaf galls on a Sugar Maple leaf - Vermont

Colorful leaf galls on a Sugar Maple leaf – Vermont

The common theme is that the galls are all formed in developing tissue, leaves, new twigs, flowers, roots, or fruit.

A gall on Shadbush fruit - Vermont

A gall on Shadbush fruit – Vermont

Some of the Ichneumonidae wasps that make so many of the galls we see have developed a biological metallurgy, evolving zinc and manganese coated ovipositors which they use to inject chemicals and hormones into the plants they co-opt.

The specificity and regularity of the galls and the relationships between the plants and the gall formers speaks to a lengthy and complicated evolutionary history.

We pride ourselves (or are horrified by) our newly found ability to genetically manipulate plants and animals.  In truth, we have a long way to go before we catch up to what we often mistakenly call the “humble” insects.

California Bay Laurel – one of the scents of home

The idea of home is a strange one to me.  Moving as often as I have my version of home is more of a set of environmental conditions rather than a living space or a house.  Last week I had an opportunity to pass through the place that feels most like home.

It is a cloudy, damp, foggy portion of land on the northwest coast of California, a place where the land falls sharply into the chilly Pacific and the beaches are as often rocky as sandy.  The hills are steep sided with sensuously rounded tops, sometimes grassy, other times thickly covered in evergreen trees, and much of the region is protected open space.

West Marin, looking at Bolinas and north along the San Andreas fault. Inverness Ridge and Drake’s Bay are visible in the background.

When I was little, West Marin, more specifically the Point Reyes National Seashore, Inverness, Tomales Bay, and Mt. Tamalpais were where I spent much of my time rambling about, climbing trees, playing in shallow cold streams, swimming in the ocean, eating berries, and watching the wildlife.  Whenever I can I return to let the fog play over my skin and to breath the air flavored with the scents of California Bay Laurel (Umbellularia californica), Douglas Fir needles (Pseudotsuga menziesii), and invasive eucalyptus trees.

To the east of the San Andreas fault the land is open, primarily coastal prairie, with the trees safely nestled into the hollows or up against boulders to avoid the strong ocean winds.  The California Bay trees are particularity well adapted to this environment and form dense wind-sculpted stands, looking like glacier scoured boulders.

Low California Bay Laurel (Umbellularia californica) trees sculpted by the ever-present coastal winds

Umbellularia californica trees are tolerant of a variety of conditions and wide spread through California.  They reach into southern Oregon, but, as is true of many plants, California is their epicenter.  In stressful conditions, windy or dry, they only grow to a few feet in height, more of a resilient shrub than a tree.  Where they are protected from the wind and have a good supply of water they reach tremendous proportions, 150 feet or more tall, narrow and slender if competing with redwoods and Douglas fir trees, broad and robust when growing in the open.  Colonies of these trees will sometimes root-graft together, covering a portion of a hill in a single tangled mass of roots and trunks.  The wood decays quickly in the damp and large California bay trees often have multiple hollow trunks, providing homes to numerous animals and giving them a dark and mysterious appearance. The trunks are often covered in dense moss.

Umbellularia californica trunk with a characteristic coat of moss

Umbellularia californica is the only species within its genus and is known by a great variety of common names, Pepperwood, Spicebush, Cinnamon Bush, Peppernut, Oregon Myrtle, Mountain Laurel, Headache Tree, Balm of Heaven, and California Bay to list just a few.  The variety of names reflects its wide range of uses, uses that include medicine, food, insect repellent, timber, and, oddly, currency.  In the early 1930s the bank in the town of North Bend Oregon closed and the local currency collapsed.  The town adopted a currency of coins carved from the wood of this tree.  In North Bend, this currency is still legal tender, though few coins survive to this day.

Leaves, flower buds, and a ripe bay nut

The leaves are rich in pungent oils.  As children we used to put green leaf-covered branches on the fire to watch them flare up as the oil spat and burned.  When dried the leaves are as good for seasoning as the Mediterranean bay laurel, though much stronger and more spicy in flavor.  As with eucalyptus leaves, inhaling the steam from boiled leaves does wonders for stuffy sinuses, and the bay nuts can be roasted and eaten once the fleshy exterior is peeled off.  The fruit looks a bit like the small wild avocado fruits one finds in Central and South America, which makes sense as both the California bay laurel and avocados are in the Laurel (Lauraceae) family.

A dense understory of ferns is common where California bay trees are large

Where the California bay laurels are large and healthy a dense understory of shrubs and ferns is common, California Huckleberry (Vaccinium ovatum) and Western Sword Ferns (Polystichum munitum) are particularly abundant in West Marin.

Western Sword Ferns (Polystichum munitum) growing under a large, multi-trunked California bay laurel

These evergreen ferns grow large, individual fronds often reaching 2.5 to 3 feet in length.  The fronds are waxy and leathery studded long the edges with small teeth and points.  Most people are familiar with these ferns from the moon of Endor in Return of the Jedi, the place the Ewoks live.

Western Shield Ferns look like primordial Christmas Ferns

For those of you in New England the western sword fern will be immediately recognizable as an enormous Christmas fern.  One can easily imagine tough mouthed dinosaurs grazing on these giant ferns.  Today they are rarely eaten by anything except when the fronds are young, or an intrepid insect cuts free a chunk of leaf.

Home is the gentle drip of tangy flavored fog-born moisture dripping from the leaves of the California bay laurels falling onto glistening ferns.  The deeply textured gray of low hanging fog drifting through the forest, the salty bite of cold wind whipping down from the north Pacific, and the constant rustle of animals and water in the underbrush.

One of my homes.

Chamise – a key chaparral plant

The chaparral ecosystem in California is comprised of a dense and diverse collection of small to mid-sized woody shrubs.   It covers the hills in a shallow cloak of gray-green vegetation just thick enough to soften the contours of the land, but not to hide them.  In some places the chaparral is dense and thick, so much so that it is nearly impossible to penetrate it, other places it is sparse and low.  Animal trails riddle the chaparral and the bones of the land show through with a dramatic abruptness.

Sandstone outcrops above a chaparral covered hillside at Red Rocks State Park in Topanga

Chaparral grows primarily in dry, hot areas, as such the plants have a number of moisture saving adaptations that are most easily seen in their leaves which tend to be either small or waxy, or both in many cases.  The ecosystem is surprisngly diverse in both plants and animals, but despite this there are a small handful that are common from Mexico through most of California and that, taken together, could be considered to be the background matrix of chaparral plants.  Sage (Artemisia) and Ceanothus both are broad genus level plants with many individual members.

These plants are common in the chaparral, and taken with another extremely common plant, Chamise (Adenostoma fasciculatum), comprise what I think of as the matrix plants for the California wide chaparral.

Chamise (Adenostoma fasciculatum) flowers are small and clustered in tight bundles at the tips of the branches

Chamise, also known as greasewood, is in the rose family and produces clusters of small white flowers that look much like another rose family genus, Spiraea, which includes hardhack and meadowsweet.  The flowers set seed and dry on the branch, remaining affixed to the stalk for several seasons after blooming.

The leaves of Chamise are needle-like, clustered in little bundles called fascicles, the word the scientific name derives from.  On the whole, the plant looks something like a cross between rosemary and juniper with shredding bark, gnarled limbs, and and regularly placed leaf clusters.

Old Chamise plant on a ridge in the Santa Monica Mountains

Like many chaparral plants Chamise seeds require fire to germinate.  This ensures that the seedlings will be able to take advantage of the temporary increase of nutrients and open sunlight in the plant’s early stages of growth.  Estimates of the longevity of Chamise vary, but range from 100-200 years.

Chamise is not generally considered to be good browse for animals, but it is common to find extensive patches of heavily browsed plants.  In some places the browse is so heavy that the bushes look like sculpted hedges, in other places they look like carefully trimmed bonsai trees.

Browsed Chamise branches

When it has not been browsed Chamise produces a relatively dense growth of vertical shoots.  Over time many of these will die, with the dead stalks being retained by the plant.  Some estimates of the total volume of retained deadwood on old plants reaches 60-70%, greatly adding to the potential combustibility of the Chamise.

Young Chamise branches

California Buckwheat (Eriogonum fasciculatum) can sometimes be mistaken for Chamise by the casual eye, but the leaves are broader and flatter and the flower structure is very different.

California Buckwheat (Eriogonum fasciculatum)

Chamise is found primarily in California, though northwest Mexico and western Nevada also host populations of this plant.  Within California it is found in nearly all of the chaparral habitats as is shown on the digital Jepson Herbaria hosted by UC Berkeley.

Chaparral types with Chamise

This is a tough plant.  It grows with little water, on hard, rocky soil, and can even grow in serpentine soils, a soil type that kills many plants.  Many people do not like Chamise due to its flammability, but it is an excellent erosion control plant, provides cover for a number of birds and small animals, and serves as a last resort browse as well.

It is not the only chaparral plant by any stretch, nor even the most typical in any given area, but it is the one I have seen in the most places through California.

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.