Sunday, March 27, 2016

Quaking aspen finally flowering

Quaking aspen (Populus tremuloides) makes one of the earliest moves in spring, producing catkins like the fuzzy things on pussy willow.  (Aspens and willows are in the same family.)  But it has taken until now for those catkins to lengthen into dangling flower clusters and get down to business.  My visit to the weedy stand of trees at the edge of the empty parking lot (beside D'Angelo's) at the top of West St. yesterday showed good many catkins shedding pollen.  This pollen drifted off on the breeze to (hopefully) female flowers on other trees, ensuring future generations of quaking aspens on the west side.  (A place to look for bigger trees is the edge of Poliseno Field at the high school.)

Many buds had opened to reveal downy catkins more than two weeks ago.

What the catkins looked like inside: each tiny green bump is a single flower; 
a catkin has many hundreds.

 Yesterday the lengthening catkins were shedding pollen as they swayed in the breeze.

Flowering catkins up close.  The buds always seem to me to look like shiny brown beetles.

I help spread the pollen!  See it drifting off?

Meanwhile, the alder at the high school pond is about done (the male catkins dried out and darkened), silver maples (Acer saccharinum) have dropped their male flowers, leaving the females to develop their winged seeds, while red maples (Acer rubrum)--including later-blooming males--are now in full flower.  I was surprised yesterday to come upon a couple of yews (bright green evergreens with broad, flat needles often pruned into yard bushes) shedding pollen from little, ball-shaped cones.  I hadn't realized any local conifer* "bloomed" this early.  

The alders on the banks of the high school pond look dried-out--not like a week or so ago.

 Fallen male silver maple flowers, and remaining female flowers.

 Red maple female flowers (above), and male flowers (below).

 Though commonly planted and pruned, yew (Taxus canadensis) is a native tree.  
The little yellow balls are male cones shedding pollen.

*If you've seen the juicy, bright red "berries" of yew in fall, you'd be entitled to doubt it was a conifer at all, but each "berry" surrounds a tiny round cone.  Another conifer that disguises its cones is juniper, which coats its tiny, berry-like cones with blue-white wax.

Saturday, March 19, 2016

Alder in Spring

 The pond shore by Brockton High School still has last year's cattails.
The new leaves will begin to emerge soon.

Look for alder (Alnus) male catkins swaying in the breeze on pond shores right now.  Alder is an early-flowering native shrub that likes having its feet in wet ground.  (These alders grow on the shore of the pond in front of Brockton High School.)  The female flower clusters are the tiny, red, upright, spiky things visible in the close-ups.  After it matures, the female flower clusters turn into things that look very much like miniature pine cones--last years' are visible in the last photo, above this year's female flower clusters. 

Friday, March 11, 2016

Red Maples in Bloom

 The flowers above are from a female tree.  The deep red finger-like stigmas emerging from the buds will receive the pollen.  But the male tree below isn't quite ready to bloom and begin releasing pollen.

Despite myself, finding red maples beginning to bloom today caught me by surprise.  Last year our red maples bloomed about April 15th, twelve days after the silver maples--earliest of the trees nearby.  But this year silver maple bloomed more than a month earlier than last (probably due to the unseasonably warm weather).  And it is now again twelve days since the silver maples bloomed!  Maples, at least, seem to be reading the same playbook.  

Red maple (Acer rubrum) is dioecious--meaning that male and female flowers are borne on separate trees.  (This is a bit unusual, since most plants combine male and female in the same plant--and most often in the same flower.)  The trees I saw just beginning to bloom were females.  A nearby male won't bloom for another day or so.  

As a school boy, I took the arrival of red maple flowers to mean that school wouldn't go on forever, even if there was still a ways to go.

Since red maple is among the commonest native trees in southern New England, look for them to brighten your neighborhood and even the highways for the next couple of weeks.  If the flowering of silver maples was the "trial balloon," the blooming of red maple is the true beginning for the growing season hereabouts.  Look for other trees to leaf out or bloom in an rapid crescendo of new growth.

Tuesday, March 1, 2016

Early Bloom

I was just about to talk about the long period of late winter and early spring when nothing much seems to be happening in the plant world, when I came upon a twig on the sidewalk.  Silver maple, I was pretty sure.  Positively packed with swelling buds, as usual.  And did I see flowers peeking out of a few?  Already?!  And in WINTER, for God's sake!  Last year silver maples didn't flower until the beginning of April, more than four weeks later!

Over the next day or two I paid a visit to every silver maple I knew about, and also a good many quaking aspens, which bloom at about the same time as silver maple.  Sure enough, silver maples are popping more than four weeks earlier than last year, and quaking aspens aren't far behind.  The prolonged warm weather we've had lately is probably to blame.  How?

 Silver maple (Acer saccharinum) on Moraine St almost in full bloom on 2/29.

Silver maple on Tuesday, 3/1.  The white filaments sticking out all over are stamens shedding pollen.

 Pussy willow at the high school.

 Some of the quaking aspen (Populus tremuloides) buds above look larger than their neighbors
because they are expanding to flower.  Below are unopened buds.

Quaking aspen at the top of my street is almost in full bloom on Tuesday 3/1.

Why the early blooming?

Trees go dormant in winter on a schedule fixed roughly by the length of uninterrupted darkness.  (By interrupting darkness, streetlights sometimes play havoc with tree life cycles.)  When nights become long enough in the fall, processes are set in motion that cause leaves to turn color and drop, and dormancy to begin.  But dormancy doesn't end according to night length: instead, the tree must experience a certain minimum number of hours of sufficiently cold temperatures.  Just how cold, typically a little above freezing, and for how long, depend on the tree species.  This cold requirement reduces the chance that a tree will become active and grow leaves and flowers during an early thaw, only to be killed by a later cold snap.  But once the tree has clocked the required number of cold hours, any prolonged warm spell can break dormancy and send the tree into action for the new growing season.  

This early flowering was caused mainly by a fluke of the weather.  But over the long term we should expect plants to flower and leaf out earlier in a warming world.  This has consequences that could prove disastrous.  For example, a British bird called the great tit depends on a good supply of winter moth caterpillars to feed their growing chicks.  The winter moths, in turn, eat the leaves of English oak. The birds have always laid their eggs at the right time so that caterpillars are at their peak just as the chicks are at their hungriest. However, warming climate has led to earlier growth for the oaks and caterpillars, while the birds have been left behind.  Laying their eggs too late, the birds fledge fewer and lighter young, putting stress on the great tit population.  It bodes ill that most species studied so far react differently to climate change than the species they depend on.

Food chain being stretched to the breaking point?
Great tit, English oak, and the winter moth and caterpillar. 
(All photos from Wikimedia Commons.)
Quercus robur.jpg

Operophtera brumata01.jpg