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.

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!)

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.

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.

Spring 3f: All the Rest

Although the number of tree species I track through the year seems big to me, I know there are many others, and sometimes these catch my attention.  

Here they are for May.

Larch, a boreal forest tree and our only deciduous conifer, on May 1st (2), 21st and 27th (2); Silverberry, an alien covered in silvery "hairs," on the 1st, 8th, 14th, & 28th (2).

A Mystery Tree growing right

 in my back yard on May 5th (2), 11th,14th (2) and 21st (2).  It's 

probably a choke cherry.

Witchhazel, whose bark make the drugstore astringent, on May 4th (2), 7th, 11th, 13th, and 28th (2).

European buckthorn, an alien invasive, and the card-carrying native, alder,
 on May 8th.

Garlic mustard, an alien invasive, violets (2) and highbush blueberry (2) on May 11th; white pine on the 11th and 23rd (3--the second with male cones ready for action, the last showing female cones pendant near ends of branches).

Mulberry on the 14th (2) and 18th;

Fox grape on the 15th.

Ginkgo, an ancient gymnosperm

(akin to pines) that is the only remaining member of its class,

on the 17th (2) and 28th (3).

Lilac on the 17th

Wild geranium, eastern red columbine,

(2) and black locust on the 23rd.

Black raspberry, oriental bittersweet (alien) and bayberry on the 30th.

And this ends the interminable Spring 3!