Friday, September 25, 2015

Birches are outstanding!

Birches stand out due to their smooth, shiny, bark with long, dark horizontal lenticels,* that ranges in color from the striking white of Paper Birch, through River Birch's salmon pink, to the muted yellow-gray of Yellow Birch and charcoal-gray of Sweet Birch.  Paper birch and the similar but more darkly-marked Gray Birch are the ones that jump out at you.  These are the ones found in the 'burbs.  Of the two, gray birch is the local; paper birch is typically a tree of more northern forests, but often planted.  Paper birch is the "canoe birch" of the American Indians.  (Yes, there are still folks who make them.)  After first admiring River Birch in the South, I was surprised to find a couple in this neighborhood.  I've never encountered it wild.  The remaining two birches that occur in these parts are the yellow and the Sweet (whose sweetness you may have tasted in birch beer).  Though they're handsome trees in their own right, they are forest trees I haven't seen planted; look for them locally in Blue Hill Reservation.  

Beside the characteristic bark, birches are united by their fruits.  The green, sausage-shapped cone-like clusters ripen to brown, and then come apart into hundreds of tiny samaras (or nutlets) that whirl to the ground along with the fleur-de-li-shaped scales that bore them.  River Birch released its samaras to the wind way back in mid-June, but Gray and Paper Birches are just starting to do so now. 

River Birch (Betula nigra) can become a large tree.

 River birch (Betula nigra) has faintly pink, very shreddy bark and rounded leaves.

River birch in June: ready, set, go!
 June 5th

 River Birch fruit remaining in tree June 16th,
 and tiny, double-winged samaras and scales on ground on the19th.


 Gray birch (Betula populifolia) has more angular leaves than paper birch,
and the bark is marked by black chevrons where there were once branches.
(An unripe "cone" is visible among the leaves below center.)

Looking ripe by September 6th, some cones had begun dropping samaras by the 16th.
(The skinny green things are next year's flowering catkins.)

Gray birch cones on September 26th.  Samaras and scales fall, leaving behind the central axis.

 Paper Birch (Betula papyrifera), with its paper-white bark, has more rounded leaves than gray birch.
It also is  beginning to drop seeds.

Paper Birch (Betula papyrifera) cone scales look like fleur-de-lis, while the smaller samaras
are tiny oval seeds with two tiny round wings.   (Several "large" ones are right of center).

Yellow Birch (Betula allegheniensis) is common in the woods around Ponkapoag Pond.
The yellowish-gray bark shreds into strips so thin as to be translucent. 

The dark bark of Sweet Birch (Betula lenta) is a bit like that of cherry; it is smooth in a young trunk, 
but splits vertically rather than peeling as it grows.  (I don't know when these two trees set seed.)

Birches are sun-loving, relatively fast-growing trees, and gray birch in particular is short-lived.  If you want to grow a paper birch or gray birch of your own, find one of these striking trees overhanging a street or sidewalk.  The tiny samaras--almost like little fried eggs--collect in cracks in the pavement, or lodges among detritus.  Bag a few pinches of them and throw into the back of your refrigerator, or better yet keep them outside: they needs to experience enough cold weather to break their winter dormancy, then most should sprout next season. 

*Most trees with smooth bark develop rough, porous areas called lenticels that enable the living tissue beneath to breathe.  Their size and shape can aid in tree identification. 

Tuesday, September 22, 2015

Fall Equinox

The autumnal equinox is at 4:21am tomorrow.  What does that even mean?

The earth circles the sun once each year.  The earth's axis is tilted 23 1/2 degrees out of the vertical.  (Recall every globe you've seen).  Since the direction of that tilt does not change, but the earth's position around the sun does change, the sun shines most on the northern hemisphere from late June to late September, and on the southern hemisphere from late September to late June.  At a moment between these two periods the sun shines directly on the equator, as the earth transitions from one hemisphere to the other: this is the equinox.  So tomorrow fall officially begins in the northern hemisphere, while spring officially begins in the southern hemisphere.  (Here's a satellite's eye view.)

(NOT to scale: sun is roughly 100 earth's wide, and roughly 100 suns away!)
Image by Kevin Niewood

At the equinox day and night are equal in length everywhere in the world--hence the name.  Only at the equinox does the sun REALLY rise due east and set due west.  It also roughly marks the time when sunrise and sunset are at their shortest: in takes only a few minutes at our latitude for the sun to completely appear at dawn, or disappear beneath the horizon at sunset.  Most importantly, the equinoxes are equal in the amount of solar radiation at any given place.

That means the sun is giving us the same amount of daily energy as it did on March 21st!  Why the difference in temperature?  Think of the daily solar energy input as a day's pay.  The heat held by Earth's surface (mainly in the enormous storage capacity of ocean and lake water) is your bank account.  Our income is the same, but we have a big bank balance of heat thanks to all the bonuses we got during the summer!  That is why you are probably dressed differently now than you were last March 21!

Everything you need to know is here!

Saturday, September 19, 2015

White Oaks are Having Their Babies

A few white oaks of my acquaintance have been dropping acorns since about September 4th.  I have held off declaring White Oak Season until today: more than half of the white oaks I can think of are now launching babies.  Squirrels are "rescuing" a significant fraction of these on most trees; in fact, though these kids have a low chance of survival in the paws of a squirrel, they have an even lower chance on the street, sidewalk or lawn.  Of the hundreds or thousands of acorns produced by a tree this year, perhaps one will survive to its first birthday.

At the end I'll help you tell white oak from other oaks.

Here is the development of acorns on a single branch around the corner from my house.

July 5th

July 31st

August 10th

August 31st

September 2nd

September 7th

Will a squirrels get these?  or the lawnmower?  September 9th

September 15th

What's the Difference?
Red oaks have been dropping acorns for weeks.  How are white oaks different?  White oak leaves have rounded lobes, while leaves of red, black and scarlet oaks all have pointed lobes with bristle tips.  Both white and red oaks have acorns with shallow cups covering only the end of the nut, but only white oaks have rough, corrugated caps; the others are smoothly covered with scales.  White oaks also have "sweeter" acorns that mature in the same year, while red oak acorns mature in their second year and so are very bitter due to tannin.

Rounded leaves and warty cap of white oak (Quercus alba) above; red oak (Quercus rubra),
with its pointed and bristle-tipped lobes (below),is nearly done dropping acorns.

 White oak cap (left) is sometimes described as "warty" to the red oak's "scaly."

Soon I will be experimenting with acorns as "wild" food!

Thursday, September 17, 2015

White Pine Seed Season is more than half gone!

I watched a nice crop of pine cones develop on our white pines all summer long.  There were almost no cones last year, so it was exciting to see these cones begin smallish and green in June, then gradually brown at the edges of their scales as they matured in August.  

When all the cones on all the trees in the neighborhood surprised me by opening all at once, I began an eager hunt for seeds on the ground.  Daily.  Nothing.  For weeks.  Almost nothing.  Finally I realized that white pine cones don't release all their seeds when the cones open, but gradually over a month or more.  Since a lot of seeds have already fallen, it's high time to announce White Pine Seed Season.

Why couldn't I find fallen seeds?  White pine seeds are much smaller and lighter than the samaras of maples or ashes, for example.  The slightest breeze stirs them--complicating photography.  So besides being harder to see on the ground, they fall over a wider area, "diluted" by the landscape.  (That's my story and I'm sticking to it.)

I've finally learned that I can monitor seed release only by counting seeds in the few fallen cones, or by wacking the odd cone with a stick to see what comes out.  I've done both.  A few days ago, I picked up a fallen cone from under a large neighborhood white pine.  I searched it carefully, and came up with several seeds still tucked amongst the scales.  A cone I struck today (9/17) sent half-a-dozen seeds whirling; a second cone I knocked down had fewer than twenty seeds remaining out of about a hundred it began with.
 
White pine, Pinus strobus, is the most common pine around here, and often seen from the highway.  It is dark bluish-green, has graceful, upswept branches, and long, fine, soft needles in bundles of five.  (The yellow-green, bottle-brush-like, stiff-needled pine of dry, sandy places is a different species called Pitch Pine, Pinus rigida.)

Here is the development of cones on a single branch, month by month.

June 22nd

July 1st

 July 10th

July 21st

August 4th

August 20th: cone scales beginning to separate.
 
 August 22nd: cones almost fully open.

 August 28th: notice the drops of resin hanging from the scales.  If you touch one, only a solvent
like odorless mineral spirits will get the sticky stuff off.  (I wonder that more seeds don't
become trapped as they fall from the cone.)

September 2nd: it is very hard to see them, but most of the seeds are still inside the cone.
(A good wack with a stick will send seeds flying, whirling gently to the ground.)
 
White pine is a gymnosperm, meaning "naked seed," since, unlike flowering plants,* it has no fruit to totally enclose its seeds.  But a cone, though an older "design," makes a pretty good container even so: the conifer group of gymmosperms was the Big Kahuna of dinosaur forests until the new-fangled flowering plants became prominent.  And conifers are still a close second to angiosperms ("container seed"), aka flowering plants, as king of most forests.  Flowers and cones are related by development and evolution; think of both of them as very short twigs in which the leaves are crowded together and have become adapted to other uses than photosynthesis.  In cones they become scales, which each scale hosting two seeds.  These scales press tightly together in the immature cone, so that the cone offers great protection, even if it isn't the total container of a flowering plant: the fruit.  In a flowering plant, there has been greater evolutionary change: instead of scales all more or less alike, some are sepals, some petals, some (male) stamens, and some (female) carpels.**  In addition, flowering plants show enormous range of variation in all these parts.

Now the seeds have matured and the scales have spread outward, making it possible for the baby pine trees to be "born."

Each scale has two seeds.  A cone I counted had about fifty scales,so assume about a hundred kids per cone. (A good winged seed is above center--this is what you want for planting.)

 The seeds grow two to a scale, and in the fall a thin layer 
of the inside of the scale peels loose and adheres to the seed, 
providing a wing that gives the new pine a chance of growing 
beyond its mama's shadow.

The three seeds on the left are plump and probably healthy, with good potential to germinate. 

On the scale's inside surface, you can see the hollows at the base in which
the seeds developed, and the pale scars left by the peeling off of the wings.

On August 20th, the pines I had been watching finally begun opening their cones, and in a few days they were fully open.  I expected to see seeds on the ground and pavement almost immediately; but after almost a month I've seen very few!  It may take a wind to dislodge them, or it may take a good blow from a stick!  I have been helping the pines to be born in those cones I could reach.  (Don't worry--the neighbors already know I'm weird!)

video
Pine seeds are much lighter than maple samaras, so they fly with the least breeze.  As they fall, the asymmetrical wing sends them spinning down slowly enough to allow them to go a little distance.


video
Here I show a single scale from a cone so you can see the scars of the missing wings,
and--if you look closely--the wings of the seeds themselves waiting to be dislodged and fall. 

I am saving any good pine seeds I find.  Many of the trees in my yard are old, and will need replacing.  White pine, besides being a graceful, fast-growing tree, is favored by birds looking for an evergreen to shelter in in winter.  I expect to plant at least twenty seeds, see at least ten sprout, and be able to choose among at least five to grow to maturity.  White pine doesn't transplant successfully, so if you want to plant some of your own, check fallen cones by bending back each scale, looking for delicate wings.  Keep those that have a good, plump seed.  Either do this with disposable gloves, or clean the gum off your hands afterwards with odorless mineral spirits (or turpentine or paint thinner).

*Yes: the place you did your phys-ed was a gym(nasium), named for the place where the athletes of ancient Greece competed in physical contests.  (So named because the athletes competed naked.  Yes, they were all men, and no, women were not allowed.)  Times have changed, but the name remains.
**Most land plants are either flowering plants or gymnosperms.  (The flower doesn't have to be showy--or even have petals--to count.)  Alternative groups include ferns, clubmosses and horsetails, mosses, and liverworts.  As a rule, when you touch a tree trunk you are either touching a flowering plant or a conifer (a subgroup of gymnosperms.) 
***The carpel is the basic unit of the "container," called the pistil, eventually fruit, that defines angiosperms.

Tuesday, September 15, 2015

Squirrel Depredations--the Other Side of the Coin

This is the season of seed dispersal for many plants.  Plants have a significant disadvantage compared to animals: they don't move.  But because they depend on sunlight for energy, adult plants must have a way to get their children away--out of the parents' shade.  So if the adults can't move, the children have to.*


Plants have many ways of dispersing their young.  If you've blown on a downy gray dandelion head, or pulled burs or beggars' ticks from your clothing after an autumn walk, you've seen examples of two of the most popular means of dispersal.  Many plants build their fruits so that wind can carry them away.  Dandelions and milkweeds have their silky parachutes, basswood fruits hang glide to the ground on a wing-like bract, samaras twirl to the ground slowly enough to drift a bit on the breeze.  Other plants depend on animals to move them.  Berries have a taste and appearance that attracts animals; they are typically eaten by birds and mammals, and their seeds are pooped out later in convenient fertilizer.  (The seeds inside the fruit are built to safely withstand digestive processes.)  Like a flower's offering of nectar to bees, you can think of tasty fruit as part of a business deal.  Beggars' ticks make no deal, offering animals nothing at all in return for dispersing their kids: they simply send them to hitchhike on fur or clothing.

Maples like this sugar maple are among the many fruits that are wind-dispersed.

It will be a month or more before milkweed pods split, 
each seed drifting off under its own plume. 

 Hang-gliding basswood fruits don't usually get far, but the one below landed half a block away.

Blackberry, above, and nightshade, below, attract animals with bright color and reward with sugar.


Flowering dogwood produces highly-nutritious fruit and advertises it with bright color.

Witchhazel is unusual: instead of using wind or animals, its "ballistic" seeds 
are ejected with enough force to travel up to thirty feet.


What about the acorns of oaks?  An acorn that germinates where it falls is doomed.  They are much too heavy to be wind-dispersed, and the trees make no attempt at it.  On the other hand, the oak babies are not enclosed in a tasty fruit, and are not adequately protected from digestion.

But the acorn embryo is itself a very nutritious food.

 Oaks such as the black oak above and white oak below feed many more animals--large and small--
than just the jays and squirrels principally responsible for dispersing them.

One of many dangers of urban life.  (At least the end was quick.)

In other words, the oak tree offers its children as food to animals.  A bit like Abraham offering to stab his only child!

How could oaks possibly reproduce successfully this way?

The acorn is a staple food of squirrels and jays.  Both of these animals store food for the winter by burying them in small, scattered caches to retrieve later as needed.  Both these animals have prodigious memories.  And squirrels, at least, often move their nut stores repeatedly, with the acorns getting farther and farther from the parent tree.  But their memories aren't quite perfect, and nuts are forgotten or not needed.  And sometimes a squirrel or jay does not survive to eat all its stores.  These forgotten nuts are only a few percent of all those hidden, but they are well-placed to germinate and found the next generation.

The oak may sacrifice 99% of its kids for the sake of the one percent.  And of course the babies that survive to germinate face many other risks, so their survival is still not assured.  On the other hand, of the thousands of acorns a tree produces each year, over a reproductive lifetime of many decades, only one offspring* must survive to healthy adulthood in order to continue that oak's genes in the next generation.  Only one.

Still, it's a cruel calculus for the oak.

 This squirrel scolded me for interrupting.  When I was able to imitate his raspy note,
we scolded back and forth for nearly a minute.

*Earlier in the year their sperm need to move, also, and they do this inside pollen grains.  That's another thing plants can't do the same way many animals do: sex.
**Of course, that's the rule for any living thing: if parents produce more than one surviving offspring a piece on average, the world would be overrun by that species in fairly short order.  (But "on average" covers a lot if variation in the short term!)  And of course the human species has repeatedly found ways around this rule, to the woe of most other species.