Re: TH: Early Spring in Baltimore ...

 Date: Sun, 23 Feb 1997 17:08:47 -0500
 From: Tom Kimmerer <tkimmer@pop.uky.edu>

Yup, it's spring.  Never mind what the calendar says, here's what the
trees know:

1.  All temperate trees have a dormant period.  They aren't able to
respond to warm temperatures until the dormancy requirement has been
satisfied by a period of cold which causes certain growth inhibitors to
disappear.  For many trees, this requirement has already been met,
meaning that the trees are no longer dormant but merely awaiting
adequate warm weather.

2.  For some species, the dormancy period for flowering is shorter than
the dormancy period for shoot growth. So, species like American elm,
slippery elm, red maple, silver maple, and a few others, will flower
during any warm period after only a few days of cold.  In Kentucky, as
of this weekend, we have the following species flowering:  red maple,
silver maple, American elm, slippery elm, rock elm, hazel alder. These
will probably pollinate successfuly, even if it gets cold again.

3.  These early-flowering trees are mostly wind-pollinated.  However,
bees and other insects visit them in profusion, for they depend on the
pollen as an important protein source for spring brood development.  The
queen bee doesn't begin laying eggs until pollen flow to the hive
begins.  [Aside: this is probably how insect pollination evolved.  Bees
and wasps were hanging about for millions of years before the invention
of the angiosperms, and many of them were pollen eaters. The evolution
from pollen eater to pollinator is obviously a simple one].

4.  Many understory plants leaf out early: they are protected from the
intense night-time radiative cold by the overstory (try standing outside
on a cold clear night with your hat off, then put it on, and you'll see
what this means).  This weekend I was out in the woods with my students,
and we saw common elder, honeysuckles and a few other plants already
breaking bud and leafing out.  Poor students: trees are impossible to
identify after the buds break and before leaves emerge.  Buckeye buds
are enormous. They are the first of our trees to leaf out, and will do
so with a few more days encouragement.

5.  Wouldn't it be wonderful if we all kept track of these changes? 
Phenology (the observation of seasonal events in plants) used to be an
important activity of the amateur naturalist, and should be an important
activity of the urban forestry guerilla. It is now mostly a lost art,
but would be easy to revive via the internet (hint, hint). Maybe we
could tell each other what we are seeing in the woods now.  Long-term
records might tell us about global warming and urban heat island
effects. Tree watching is way more fun than bird watching. And they sit
still, mostly.

6.  Watch buds as they unfold.  Magnificent.  Especially yellow-poplar. 

7.  Remember to leave your trees alone for now.  Don't prune, don't
climb in them.  This is a time of great fragility. 

Cheers and Happy Spring,

Tom Kimmerer
Forest Biologist
University of Kentucky