Category Archives: Plants

The wise trees stand sleeping

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photo credit: Winter Forest via photopin (license)

This year, winter has come late and with a vengeance. Snow lies in piles and drifts over every available surface, and movement through this landscape is muffled, strenuous. In the forest, the deciduous trees stand bare of adornments, their spindly limbs betraying no memory of summer. I’ve lived in a temperate climate my whole life, and though I’ve seen seasons come and go, the cycling of trees through the seasons retains a familiar mystery, year after year.

In the coldest months of the year, trees survive by becoming dormant, a condition in which tissue growth or elongation is paused. When the tree is dormant, all its biological processes–metabolism, growth, and energy production–are slowed or halted for a time. Dormancy isn’t a switch that turns on and off; rather, it is a gradual process that begins long before winter, cued by shorter day length and cooler temperatures.

Length of day is sensed by a specialized pigment called phytochrome. Phytochrome is a type of photoreceptor, which means that it is sensitive to light; in this case, light waves at the red end of the spectrum. Longer nights result in the production of a chemical called abscisic acid (ABA), which signals to the tree that it’s time to begin preparations for dormancy.

As the tree responds to these stimuli and growth slows, the production of chlorophyll slows, and leaves change color (for more on the color of fall leaves, see this post). A layer of cells grows between the branch and the base of the leaf stem, essentially cutting the leaf off from the tree so that it falls away. Since no food production is necessary during the dormant phase, the leaves are not needed until spring. As William Carlos Williams’ poem, “Winter Trees,” observes so eloquently:

All the complicated details
of the attiring and
the disattiring are completed!
A liquid moon
moves gently among
the long branches.
Thus having prepared their buds
against a sure winter
the wise trees
stand sleeping in the cold.

The shortening days of fall combined with increasing cold send the tree through this pre-dormancy phase into true dormancy, which begins a few weeks after growth has stopped. Nothing now can wake the tree until a genetically-determined number of “chill-hours” has been met. During this time, trees grow even more resistant to cold through such strategies as production of antifreeze compounds from sugars, evacuation of water from cells, and addition of fatty acids to cell membranes.

Over time, deciduous trees in temperate climates have evolved responses that ensure the highest chance of survival through recurring bitter winters. When spring comes, the trees will sense the warmth and begin to return to normal functioning. But for now, the wise trees  stand, sleeping in the cold.

REFERENCES

Campbell, Eileen 2012. “How do trees survive winter?” Mother Nature Network. Link

Krulwich, Robert 2009. “Why Leaves Really Fall off Trees.” NPR. Link

Shen Li 2011. “How Do Trees Know When to Wake Up?” Outside Story: Northern Woodlands. Link

“Winter Trees” by William Carlos Williams. Read it here.

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Chemists of Air

There are so many amazing facets of nature that tend to slip by unnoticed. Think about the last time you walked in the woods. Where was your attention? Did you think about the trees, the landscape? Or maybe the organisms you either could see and hear or that you imagined might be nearby? Did your gaze ever pause on the rocks or tree trunks encrusted with the inconspicuous forms of lichens?

When you do notice lichens, their difficult, astonishing existence becomes apparent. Lichens occur in the most inhospitable places: on trees, rocks, and roof shingles; in extremely cold environments like the Arctic and Antarctic; and even as crusts on top of desert soil. How is it that this organism–is it a plant? A fungus?–can survive where so many others cannot?

Jane Hirschfield’s poem, “For the Lichens,” is a journey of awareness. The speaker knows about the trappings of cities, but the discovery of lichen opens up a world she hadn’t known existed:

Back then, what did I know?
The names of subway lines, buses.
How long it took to walk twenty blocks.

Uptown and downtown.
Not north, not south, not you.

When I saw you, later, seaweed reefed in the air,
you were gray-green, incomprehensible, old.
What you clung to, hung from: old.
Trees looking half dead, stones.

Hirschfield hints at the answer to one of our questions when she calls lichen “seaweed reefed in air.” As it turns out, lichen is often both a plant and a fungus; it is a stable association between a fungal body and a photobiont, that is, a symbiotic partner capable of photosynthesis. Most commonly, the photobiont is an alga, but sometimes that role is filled by cyanobacteria, an ancient form of photosynthesizing bacteria.

Symbiosis, in biology, is an interaction between two organisms that is beneficial to both. When the photobiont in the partnership is algae, the fungal body protects the alga, and the alga provides food through the process of photosynthesis. When, instead, the partner is cyanobacteria, it performs photosynthesis and also nitrogen fixation, taking nitrogen from the air and making it available to the fungus. These interactions greatly increase the range of both organisms, allowing them to survive in environments that neither could handle alone.

Marriage of fungi and algae,
chemists of air,
changers of nitrogen-unusable into nitrogen-usable.

Like those nameless ones
who kept painting, shaping, engraving
unseen, unread, unremembered.
Not caring if they were no good, if they were past it.

Reproduction in lichens can be as complicated as you might imagine for a body composed of two symbiotic organisms. Certain lichens can reproduce asexually, either vegetatively through broken-off pieces or with structures called soredia, little bundles of algal cells surrounded by fungal threads. A few kinds of lichen can reproduce sexually, though it should be noted that only the fungal body is actually reproducing in these cases; after germination, a suitable photobiont must be found to form a lichen. In sexual reproduction, two different kinds of spores are produced (they can be loosely thought of as “male” and “female”), which meet and combine genetic material.

The body of a lichen, called the thallus, is a combination of algal and fungal cells. General body form, determined largely by the fungus, fits into one of three classifications: crustose lichen occurs as a crust on a surface, often rocks; foliose lichen appears leafy and lobed; and fruiticose lichen has upright, branchlike structures. The final stanza of Hirschfield’s poem begins by listing images inspired by lichens:

 Rock wools, water fans, earth scale, mouse ears, dust,
ash-of-the-woods.
Transformers unvalued, uncounted.
Cell by cell, word by word, making a world they could live in.

What an incredible feat, to change the environment to make it more suitable for yourself! What organism, besides humans, can manipulate its world to such a dramatic extent? And yet, this complex interaction of fungus and algae is occurring all the time in a nondescript little package. So the next time you’re outside, look a little closer at your surroundings. Try to remember the intricacy of what is all around you, worlds within worlds.

REFERENCES

“For the Lichens” by Jane Hirschfield, published online by The Atlantic. Read it here. 

“Lichen Biology” University of Sydney’s School of Biological Sciences Online Learning Resource. Link. 

“Lichen” 15 October 2008. HowStuffWorks.com. Link.

The smallest sprouts show there is really no death

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Within Walt Whitman’s poem “Song of Myself” is a section known as “A child said, what is the grass?”  The narrator has been asked the question, and, after admitting that he does not know himself, attempts to answer anyway.

“I guess it must be the flag of my disposition, out of hopeful
          green stuff woven.
 
Or I guess it is the handkerchief of the Lord,
A scented gift and remembrance designedly dropped,
Bearing the owner’s name somewhere in the corners, that we
          may see and remark and say Whose?
 
Or I guess the grass is itself a child…the produced babe 
          of the vegetation.
 
Or I guess it is a uniform heiroglyphic, 
And it means, Sprouting alike in broad zones and narrow
          zones.
Growing among black folks as among white,
Kanuck, Tuckahoe, Congressmen, Cuff, I give them the 
same, I receive them the same.
 
And now it seems to me the beautiful uncut hair of graves.”
 

It’s as if, through presenting these guesses, the narrator is working through his thoughts out loud until arriving at the final line, the assertion that grass seems to be “the uncut hair of graves.”  He is no longer guessing; and this confident decision leads into the second half of this section, in which the link between the living and the dead is examined.

But let us go back and examine the original question for ourselves: what is grass?  What is so special about it that it is cultivated and pampered for our lawns and landscaping, and yes, our graveyards?

This nearly ubiquitous plant belongs to the Gramineae family, which contains more than 9,000 species that are the dominant vegetation in many habitats, from grassland to saltmarsh, reedswamp and steppe.  In addition, grasses have adapted to thrive in rain forests, deserts, mountains, and intertidal zones.  Humans depend on grasses for an incredible number of things: for clothes, food, beer and whiskey, paper, sugar, plastics, and food for our livestock.

The grass plant itself can be annual (living only one year), biennial (two years), or perennial (comes back every year).  Most varieties are herbaceous, with a soft stem, though some are woody, possessing a permanent hard stem.  Leaves are always basal, which means they grow directly from the bottom of the stem, which is why the grass of your lawn grows back so efficiently after being cut.  See below for a diagram of the parts of a grass plant:

Diagram of grass parts.  (HowStuffWorks.com)

Diagram of grass parts. (HowStuffWorks.com)

So what’s so great about grasses?  For one thing, they’re a main part of many people’s diet worldwide.  Grasses provide our cereal crops as well as sugar, rice, corn, and feed for both wild and domestic animals (which we eat!)  Grass also cleans the air and conserves water.  Due to its sheer volume, grass traps more than 12 million tons of dust and dirt and to absorbs hundreds of pounds of sulfur dioxide each year.  This plant also traps water in its roots and prevents soil erosion; the average grassy yard can absorb more than 6,000 gallons of rainwater.  As an added bonus, the grass in your yard helps to keep you cool: according to Oregon State University, yards with grass lower the surface temperature of the ground 30-40 degrees when compared with bare soil.

So now we can think about the function of grass, and about its parts and its uses, but do these answer Whitman’s question?  After his initial musings, Whitman decides he knows what the grass is.  The poem changes at this point to be a tender meditation on the people who have gone before us, those unknown who have left only their names on a slab, or perhaps nothing at all but the uncut hair of their graves.

“What do you think has become of the young and old men?
What do you think has become of the women and
          children?
 
They are alive and well somewhere;
The smallest sprouts show there is really no death,
And if ever there was it led forward life, and does not wait
          at the end to arrest it,
And ceased the moment life appeared.
 
All goes onward and outward…and nothing collapses,
And to die is different from what any one supposed, and
          luckier.”
 

 In this poem the existence of the grass gives Whitman hope about what happens at the end of our lives.  The people we loved are alive and well somewhere, maybe not as something we would recognize, maybe transformed by the magic of biology into something else, but not gone forever.  What I take from this poem is a reminder that life goes on, that though one’s physical body may decay, nature allows beautiful life to go on all around us every day, drawing strength and sustenance from those who have gone before.  And so birds keep singing, flowers bloom, and grass sprouts anew from a fresh-dug grave.

 REFERENCES:
 

“Family Poaceae: Grass Family.”  GoBotany.NewEnglandWild.org.  Link.

Harris, Tom. 2002.   “How Grass Works.”  Howstuffworks.com.  Link.

Henderson, Desiree.  2008.  “”What is the Grass?” The roots of Walt Whitman’s cemetary meditation.”  Walt Whitman Quarterly Review 25(3): 89-107.  Link.

Whitman, Walt.  “A child said, what is the grass?”  Read it here.

Weeds where woods once were.

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“Between forest and field, a threshold
like stepping from a cathedral into the street–
the quality of air alters, an eclipse lifts,
 
boundlessness opens, earth itself retextured
into weeds where woods once were.”
 

Ravi Shankar’s poem “Crossings” describes something quite familiar to us all: the edge of the forest.  The speaker is struck by the clear division between a forest and a field, by how different it feels, even, to step from one to the other, from the cathedral-like hush of the forest under the canopy to the wide-open world of a field.  What Shankar is describing here is, in fact, an ecological phenomenon, one called an ecotone.

An ecotone is a transition between two biomes and can be regional (such as between an entire forest and grassland ecosystems) or local (such as the line between a forest and a field).  The name comes from the Greek  words oikos, meaning household or place to live (“ecology” is the study of the place you live!) and tonos, or tension.  So an ecotone is a place where two environments are in tension.

The most interesting part of an ecotone is how it allows for blending of the different organismal communities.  On either side of the boundary, species in competition extend as far as they can before succumbing to other species.  The influence of these two communities on each other is called the edge effect.  Some species actually specialize in ecotonal regions, using this transitional area for foraging, courtship, or nesting.

Terrestrial environments are not the only ones in which we can experience Shankar’s “threshold” between biomes.  There are also land-to-water ecotones, such as marshes or wetlands, and strictly aquatic ecotones, such as estuaries, where a river meets the sea.  Perhaps in these more dramatic transitions it is easier to see how some species can thrive in this unique habitat.

Even without knowing the biology behind ecotones, it is possible to sense the tension inherent in this boundary.  When hiking on a hot summer day, when the trail leads into a forest it’s like an exhalation.  We, as animals, sense the natural world much more acutely than society would like us to believe.  Ravi Shankar, using the skills of the poet to express what the rest of us cannot verbalize, notes this feeling, writing:

Even planes of motion shift from vertical
 
navigation to horizontal quiescence:
there’s a standing invitation to lie back
as sky’s unpredictable theater proceeds.
 
Suspended in this ephemeral moment
after leaving a forest, before entering
a field, the nature of reality is revealed.  
 

REFERENCES:

“Crossings,” by Ravi Shankar.  Read it here.

“Ecotone.”  Wikipedia.  Link.

Senft, Amanda.  2009.  Species diversity patterns at ecotones.  (Master’s thesis). University of North Carolina.  Link.

Its bark papyrus, its scars calligraphy

Paper Birch in Fall  53269

As a recent resident of New England, I am still thrilled when I see a stand of birches in the forest.  I love this tree for both its beauty and its usefulness: when camping, there’s no better firestarter in wet weather than the oily paper bark of a downed birch.  But why is this tree so different from other trees?  Why is its bark not fire-resistant, its lack of color so shockingly bright against multitudes of drab trunks?  Why has it inspired so much poetry?

“Is it agony that has bleached them to such beauty?  Their stand
is at the edge of our property–white spires like fingers, through which
the deer emerge with all the tentative grace of memory.”

– Nathaniel Bellows

That pale bark is arguably the distinguishing characteristic of a birch.  To understand why it is different, we must first think about the bark of other trees.

In the most generalized sense, bark is the outer covering of woody plants, encompassing everything outside of the vascular cambium.  There are several layers that make up “bark,” which are (moving from the cambium outward): the phloem, cortex, phelloderm, cork cambium (phellogen), and cork (phellem).  In most trees, bark serves as protection against loss of water by evaporation, attacks by insects, drastic temperature changes, and disease.  In some trees, it even acts as protection against fire damage.  Except for the last, all of these functions are served by the fine, papery bark of a birch.  What makes the birch unique is what its bark contains that other trees do not.

“After a storm, one birch fell in the field, an ivory buttress collapsed across
the pasture.  Up close, there is pink skin beneath the paper, green lichen
ascending in settlements of scales.  In the dark yard it beckons you back”
-Nathaniel Bellows
 

The chemistry of birch bark is what conveys its most amazing properties, and most likely is what secured this tree’s place in folklore, mythology, and poetry.  Birch bark is white because of the presence of a phytochemical, called betulin.  The total content of betulin ranges from 15-25%, depending on the species.  Betulin is hydrophobic, meaning that it resists water.  The whiteness (protection against light damage) and the water resistance led to birch bark being used in construction of canoes by native Americans.  Both betulin and its derivative, betulinic acid, are being studied for medicinal uses against melanoma, herpes, and HIV.

“The trunks of tall birches
Revealing the rib cage of a whale
Stranded by a still stream”
-William Jay Smith
 

Throughout history, humans have found a way to use nearly all the parts of the birch, so much so that it is often referred to as the “giving tree.”  It has an amazing ability to survive harsh circumstances, and is a first successional tree, quick to repopulate areas that have succumbed to fire or clear cutting.  (Though I couldn’t find data on this, I wonder if this ability is the reason its bark is not fireproof: fire is actually advantageous to a birch because it eliminates competitors and allows a chance to recolonize).  Because of its abilities, the birch has acquired quite a bit of symbolism in different cultures.  In Celtic cultures, the birch represents growth, renewal, stability, initiation, and adaptability.  In Gaelic folklore, it is associated with the land of the dead, and appears often in Scottish, English, and Irish folklore in association with fairies, death, or returning from the grave.  A tree with such near-legendary qualities and capacity for survival–how could it fail to inspire wonder?

“its bark
papyrus, its scars calligraphy, 
a ghost story written on
 
winding sheets, the trunk bowing, dead is
my father, the birch reading the news
of the day aloud as if we hadn’t
 
heard it, the root moss lit gas,
like the veins on your ink-stained hand–
the birch all elbows, taking us in.
-Cynthia Zarin
 
 

REFERENCES:

“Birch,” by Cynthia Zarin.  Read it here.

“Birch,” Wikipedia.  Link.

Krasutsky, Pavel.  2002.  “Birch Bark Extractives.”  University of Minnesota-Duluth.  Link.

“Russian Birch,” by Nathaniel Bellows.  Read it here.

“Winter Morning,” by William Jay Smith.  Read it here.

Nothing Gold

leaves

“Nature’s first green is gold/Her hardest hue to hold”

Robert Frost had a way of describing nature that forces the reader to both take notice of the world around them and to think about their own lives, their own experiences.  The poem “Nothing Gold Can Stay” is both a meditation of the changing colors of leaves and of the brevity of beauty.  From the first bright green of a new leaf through the point when “leaf subsides to leaf,” Frost imbues this natural progression with human emotions of loss.  What do these changing colors really mean?

The different colors of leaves are due to three classes of pigments the leaves possess.  Greens are due to chlorophyll pigment, which absorbs light for use in photosynthesis, the process by which plants turn light into usable sugars.  Leaves appear green because these pigments absorb light in most of the color spectrum.  Green is the only color not absorbed, and so that wavelength is transmitted to our eyes.

Yellow, orange and brown colors are due to a class of accessory pigments called carotenoids.  Just like it sounds, these pigments also give color to carrots, as well as bananas, corn, and daffodils.  In leaves, carotenoids work to absorb pigments that chlorophyll can’t, thereby allowing the plant to use more of the sun’s energy.

Finally, the red color of autumn leaves is caused by another accessory pigment, anthocyanin.  In different plants, this pigment can appear red, purple, or blue.  Unlike chlorophyll and carotenoids, anthocyanin does not participate in photosynthesis.  Most anthocyanins are produced in the fall, in response to shortening days and less sunlight.

So the green leaves we see for most of the year actually contain several layered colors, hidden beneath the surface.  Chlorophyll is continuously produced and broken down during the growing season, but as fall approaches, production slows and stops, and finally all the chlorophyll is destroyed.  What we see in many deciduous trees are the remnants: yellows and oranges from the carotenoids that have been there all along, reds from anthocyanins appearing later in the season.  Slowly, the leaves die.

It is difficult to not have a sense of loss as the seasons change around us.  From year to year, after the bright pulse of autumn glory, leaves fall, green disappears, and it feels like an ending.  It is hard to think of the world, reborn, in the spring.  Though perhaps, as Robert Frost wrote, “nothing gold can stay,” we must remember that there will be new beauty in the world, new beginnings.

Think of this, always.

REFERENCES:

Frost, Robert and Edward Connery Lathem (ed.)  The Poetry of Robert Frost: The Collected Poems.  1969 Reed Business Information, Inc.  http://www.poets.org/viewmedia.php/prmMID/19977

Lee, David and Kevin Gould.  2002.  Why leaves turn red.  American Scientist 90(6): 524.                                        http://www.americanscientist.org/issues/feature/why-leaves-turn-red

“Why Leaves Change” USDA Forest Service. http://www.na.fs.fed.us/fhp/pubs/leaves/leaves.shtm