Saturday, October 17, 2015

Everlasting Pine Needles

My wife tells stories of her Catholic education.  One that I enjoy is the high school science teacher who insisted that pine trees don't drop their needles.  Asked by observant girls how the pine needles they found on the ground got there, the nun opined that squirrels nibbled them off.

White pines of my acquaintance beg to differ.

Needles turning yellow alter the appearance of the whole tree.

I had been taught that pine needles lasted two seasons, so that each fall the previous year's needles fell,* leaving the present year's still on the tree.  That seems true of the twig above.

But the reality can be more complicated.  I have seen needles yellow and fall in spring as well.  Are these needles that lived through a second winter? or are they last year's needles falling prematurely?  I think it's the first, but I didn't mention it in my journal last spring.  I'll have to watch closely over the coming months.

I think I have also noticed these out-of-season needles yellowing and falling individually--sometimes leaving others in the same cluster alive.

Whatever the case, the needles fall.  And from a big tree, the result is drifts big enough to be obvious even to the most obtuse.  

But how are any pine needles retained through the harsh winter months, when broad-leaved trees in this climate nearly all lose theirs?  Cold is only one of the stresses, and not the chief.  Carrying leaves over the winter means losing water when liquid water is scarce.  I also suspect that carrying broad leaves risks wind damage at a season winds are strongest.  With days so short and sun angles so low, there simply isn't enough benefit from photosynthesis to be worth the cost.  

Pines, though, have needles that are adapted to drought.  Needles are thickly coated in water-proof wax.  Their stomata (pores) can be closed more tightly to limit water loss.  Also, the stiff needles don't depend on internal water pressure (as most broad leaves do)* to maintain their shape.  And needles present less resistance to wind than broad leaves.  These adaptations, plus the ability to do photosynthesis year-round whenever conditions permit, plus the huge benefit of not having to grow a full set of leaves every spring, all tip the balance in favor of pines being evergreen.

Here is a concise but wide-ranging discussion of winter adaptations of trees.

*Actually, autumn leave don't just die and fall off, they are actively shut down, some of their most valuable nutrients recycled, and then they are "deliberately" cut loose.
**Wilt is the condition of having too little internal water pressure to maintain shape; a leaf is like a football: nearly rigid when fully inflated, very floppy when not.

Monday, October 12, 2015

Subtle Colors

"Peak color" in the fall is a thing to glory in.  I have already seen announcements for tours up north to view peak color at these higher latitudes where it comes earlier, and it will be here soon enough.  But the more subtle color at this time of the season has charms of its own.  Here are a few trees to look for right now.

Sugar maples have been turning by ones and twos for quite a while.  Sadly, many of these lose their leaves even as they turn, so that you'll notice more color on the ground than in the sparse crowns above.  (Those that hold their leaves will often finally reach a brilliant flame orange that is truly breath-taking.)

Precocious show-off, September 12th.

Trees turn individually, and even by parts.  Early October.

Sugar maple leaves often fall immediately after they turn.

Foretaste of the color to come.

Red maples have been sidling (edging) into the season, first with red leaf-stems, then red leaf edges, until whole leaves begin to turn.

 "Little Mama" September 22nd  (Hey--gotta call 'em something!)

 October 3rd.

 October 11th.

White ash is quietly going bronze.  This is a fairly unusual color, and handsome rather than gaudy.  Enjoy it while you can: the imminent arrival of the alien invasive Emerald Ash Borer beetle will doom most ashes in the area, even as it has elsewhere in North America.  If you can find a female tree, you might collect a few samaras and plant a tree in your yard; they can be kept alive in spite of borers if treated with the right insecticides.

Samaras (winged seeds) hanging in a female white ash amid a few turning leaves, 
September 25th, October 3rd.

Large and small white ashes, October 10th

One thing that I never cease to marvel at is how parts of a tree will turn quite a long time before other parts.  About this time last year I explained what makes trees turn the colors they do when they do, but this is a different effect.  As animals ourselves, we are most familiar with animal life, in which there is (usually) a brain and (almost always) a nervous system to coordinate changes throughout the whole body.  Plants have neither brain nor nerves.  They also have no circulatory system (heart and blood vessels), though they do have a system of xylem to transport water and minerals from roots to tops, and a parallel system of phloem to transport sugar from leaves toward roots.  (In trees, the xylem is typically in the "sap wood," while the phloem is in a thin layer inside the bark.)  This transport system also serves to move hormones around that work a bit like animal hormones. 

 Local effects of some sort: the entire eastern side of this sugar maple has turned
while the western side is still green.  (October 5th & 10th)

But on the whole, a plant's life is much less centralized and much more "local" than that of animals.  The conditions that trigger leaves to color and then fall act only on those parts of the tree they reach; other parts of the tree must be triggered separately as the conditions vary in time and space.  I remember as a botany student at the University of Rhode Island coming upon a Norway maple tree beside the drive to the Student Union.  A street light was nestled in its branches, and when the rest of the tree was wearing its autumn tint of clear yellow, a globe of leaves around the street light was still green: the night-time glow of the streetlight having prevented the nearer leaves from responding to the longer nights of autumn.  Those leaves remained green as weeks passed and the rest of  the tree became bare, until they finally died shredded to tatters in the winter cold and wind, never really having been "aware" that fall and winter had come.

To put the idea in perspective, imagine standing in very cold water: if you were like a plant, only your feet would feel cold, and only your feet would shiver. 

Such is the diffuse, local life of a tree. 

  I sometimes try to figure out why a certain part of a tree has turned earlier or later than another; it's worth the attempt, I think, though I have never satisfied myself that I knew what subtle gradient of light or temperature from one part of the crown to another had made the difference.  

A few less subtle.

 Poison ivy is worth watching at this time of year--but not too close.  10/10

Virginia Creeper (Parthenocissus quinquefolia) and Flowering Dogwood (Cornus florida) turn partly to attract migrating birds that, here in the city, probably won't come.  9/11, 9/29

Friday, October 9, 2015

Autumn Hitchhiker

A few weeks ago I showed that, though squirrels eat a lot of acorns, they also (unintentionally) plant some.  I gave other examples of "recruiting" animals to carry their children with offerings of tasty fruit.  But fruit costs a plant resources: you have to build that fruit, furnish it with sugar or other desirable food, and then attract animals' attention.  What if plants could get animals' help on the cheap?

Walking the dogs a few days ago, I rediscovered an old friend--and an older enemy--that does just that.

As a boy I often returned from tromping the autumn woods and fields to find my clothes thick with dark, bug-like things.  At first I took them for insects and was eager to get them off!  Soon I recognized them as seeds.  The only way to remove them from a sweater was to disentangle them  one at a time.  And if I'd gone tromping with the dog, so much the worse.  Maddening. 

Yet there was also mystery.  Try as I might, I could never see where they came from.  Sometimes I would watch for their appearance in my clothes to notice where I had picked them up, but they always took me by surprise, and I never discovered their source on my own.  Only years later did I learn the identity of this one of the many Composites* that disperse their young in animal fur.  As its only concession to the need of its children to get away from home, Beggar Ticks (Bidens frondosa) produces a fruit that comes loose at a touch, and has two spines that help it cling to fur or fabric, and is smooth and hard to get hold of. 

I had watched this particular roadside weed off and on for over months.  Then I'd forgotten it.  But walking the dog I happened to glance the right way and caught the plant in the act of readying its trick: preparing to make stowaways of its children.  

I took a photo or two.  Then, on impulse, I offered a sleeve and pants leg for old time's sake.  Those shown were still hanging on when I got home.  I might come to regret this, but I tossed them into the yard.

Bidens frondosa: fall photos show a little bit of how flowers can become hitch-hiking fruits.
 September 27th, 2014

October 19th, 2015

October 10th, 2015.  This plant is a bit behind its neighbor.

The Latin name of the genus, Bidens, means "two-tooth."  
(Think about "bicycle" and "dental.")

*Composite is a venerable but unofficial name for a very large family of flowering plants that bears its flowers in tight clusters that often collectively look like giant single flowers.  Daisy and sunflower are familiar: each has a disk of many, tightly-packed flowers.  Around this are "petals" which, if examined closely, are entire flowers in themselves.  (This seems to be a strategy for attracting pollinators with flowers massed in very visible displays.)  Other Composites (family Asteraceae) you may know include asters, black-eyed Susans, goldenrods, and dandelions, and burs.  Look at one of these closely some time!

Tuesday, October 6, 2015

"Daddy, why is the sky blue?"

"Daddy, why is the sky blue?"
"For the same reason the sunset is red, and we had a blood moon the other night, Little One."

It is not, as I used to think, a result of air pollution.

The sun gives off the full rainbow* of colors that mix to make what we call "white."  Those colors--red, orange, yellow, green, blue, and violet--differ from one another in wavelength.  Visible light of the longest waves we see as red, while orange, yellow, etc., are progressively shorter wave, and violet light has the shortest waves of all.  Earth's atmosphere, made predominantly of nitrogen and oxygen gas, is fairly transparent to all of these wavelengths.  They shine through air like it was glass.

However a funny thing happens with light waves that have wavelengths similar in size to molecules in the air.  This is true of light nearer the violet end of the spectrum.  When these rays encounter molecules they sometimes scatter in random directions, so that the sky glows blue.  

Blue sky is visible wherever sunlight shines through air and scatters to our eyes.  But a byproduct of this scattering is only obvious** when the sun is low in the sky: reddened sunsets and sunrises.  At low angles sunlight is skimming through so much of the atmosphere that the bluer wavelengths lost to scattering leave the remaining light noticeably red. 

Now you have the ingredients for a gorgeous sunset.  Anything lighted by sky-glow will be blue, while anything lighted by direct sun will be red, and these colors will grow more intense as the sun drops lower in the sky so its light passes through more air, scattering more blue.

What of the "blood moon" of the the recent lunar eclipse?  In a lunar eclipse, the moon passes through Earth's shadow.  In space, unlike on Earth, shadows are typically totally dark, since there isn't a lot of reflected light around to lighten them.  So why was the shadowed moon visible at all?  

The edges of Earth's atmosphere curve to form a sort of lens; sunlight skimming this edge is bent (refracted) inward, into the shadow, to light the dark face of the  moon.  And of course with much of the blue light light scattered out of it, that light is sunset-red, resulting in the poetic blood moon.

Learn more at Science Made Simple.

 Nice graphic showing earth's shadow lighted by reddened sunlight.
[A model like this usually only explains one thing; "truth" otherwise goes by the boards.
It's fun to critique such models: how many things does this one get "wrong?"***]
(image from

Informal shot through a small telescope soon after the moon
began to emerge from Earth's shadow.  11:28pm, 9/27/15

With the all but gone, only clouds a little bit "round the bend" are still pink with direct light.
Nearer clouds are lit only by fading sky-glow.

Sometimes snow, like water, is blue with reflected sky-glow;
water itself has almost no color.

The sun is at that magical sunset angle that it lights the clouds from beneath.  
Earth rotates as the seconds pass, and the clouds so lighted recede into the distance.
Sequence shot at Nippenicket Pond, June 2014 is only two minutes long.

These last five photos were taken while sailing across Long Island Sound in September 2013.  
If I hadn't soon had night navigation to contend with, I'd have enjoyed a sunset like this
with a glass of red wine!
Refraction of light by the atmosphere has another consequence: the bending of the sun's light means we are still seeing a sun that, in reality, is probably already below the horizon!

Deja vu!  Yes, you might have seen this post a week ago.  I accidentally deleted it a day or so later, but decided to reconstruct it!

*Actually, the sun also gives off a good deal of light that is beyond the visible rainbow: much of its output is in the infrared (with wavelengths longer than red light), while some is in the ultraviolet range (waves shorter than violet).  These are invisible to our eyes, although some animals can see a little way into these ranges.

**The little blue scattered from sunlight shining more directly down through the atmosphere leave the sun appearing yellow; the astronauts see a nearly white sun.

***Now that you've come up with your own "errors,"   Here are a few I spotted.
1. Sizes are a bit out of proportion: the moon should be a little smaller, since it has a diameter about 1/4 that of Earth.
2. Distances are way out of wack: Earth and moon are about 30 earth-diameters apart.  (Of course, making everything proportional would make Earth and Moon so small as to be hard to see.)
3. Only the right-hand sides of Earth and moon should be lit.
4. Sunlight should shine from the right over the whole image, not be "aimed" only at Earth's edges.