Nature Notes

Exploring Trees in Winter

By Greg Lecker

Though the day is gray and overcast, animals are active today.  A few scattered crows caw from trees in the parking lot.  Though I had seen a hawk on a highway light pole on my drive here; the calls these birds caw seem unalarmed.  One bird carries what appears to be a cracker in its beak, and flies away before I can take its portrait.  As I climb over the rise on Three-Mile Drive, I hear chickadees in the woodland.  The drive is clear and dry; though freezing and thawing has some wood chip paths and grassy slopes a bit icy.  Overhead, a woodpecker drumming against a tree.  The call of either a northern flicker or a pileated woodpecker resonates – seemingly from the Sensory Garden.

Among my favorite trees at the Arboretum are the clustered twisted Scotch pine at the Ordway Shelter.

scotch pine bark and foliageScotch Pine Bark and Foliage

Scotch (or Scots) Pine is native to the Scottish Highlands, not America.  The most blue-green needles of all the pines, the needles are stiff and twisty.  The upper tree bark peels, flakes and glows orange.  The lower bark is found in loose plates and reddish-brown in color.  The single trunk is often crooked, spreading irregularly into crown not quite as flattened as White or Austrian Pines.  It is thought that the crooked nature comes from the seed sources preferred by early settlers who found the crooked trunks easier to climb than a straight trunk.   Here, signs admonish the visitor against climbing for the protection of human and tree.  Because of the twisty nature of its needles, trunk, and branches, the species name of “sylvestris” is especially apt – it means “wild”.

swamp and fallen treeSwamp and Fallen Tree

A now snow free path along the north side of Green Heron Pond allows easy exploration.  A pair of gray squirrels frolic and chase one another.  Another favorite sight of mine is a tree fallen within the edge of the swamp near the footbridge and boardwalk.  Frozen water and lack of snow allows closer inspection.  About half of the root system remains; and it supports the continued life and growth of the tree.  Former branches have curved from their weight.  Young sprouts seem to battle one another for dominance as they now reach skyward.

pin oak leaf and ash seedsPin Oak Leaf and Ash Seeds

Leaves and seeds are locked in the ice of a very slick frozen pond.  The points of the leaf distinguish pin oak; and the long pointed seeds are from ash trees.

red oak leaf and bubblesRed Oak Leaf and Bubbles

Near the entry of the boardwalk is a perfectly captured red oak leaf sprinkled with frozen air bubbles.  Compared with the pin oak leaf, red oak leaf sinuses are less deeply indented; and the leaf points are not quite as sharp.  (Sinus is a name for the space between leaf lobes – one way to remember the name is to think of the nose sinuses.  Sinus is the cavity or void.)  What causes the air bubbles?  Air that is dissolved in water comes out of solution as water temperature drops.  The freezing surface traps the bubbles before they can break the surface.  In some water bodies, methane produced by rotting organic matter rises in bubbles; and they too can be frozen in place.

Greg Lecker is a Minnesota Master Naturalist Volunteer.

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