Monday, November 12, 2012

When a hurricane visits a forest

One day I was walking with my mentor in the woods when he asked me ‘Why are all these trees the same age?’.  With his hands in his pockets and a silly grin on his face (as was his style), he stood facing a small clump of young sugar maple trees.  These ten trees –all roughly the same size and age— went unnoticed until Jeff drew my attention to them.  Before he asked about them, they simply merged without distinction into the rest of the forest.  Now, they stood out as a single group with an obvious common history.

What was the history of this group of trees?  What took place to result in a tidy patch of even aged trees?  The answer is in today's post...

I was reminded of that day on a recent visit to Carolin’s Grove, one of the preserves owned and managed by the Pound Ridge Land Conservancy.  Late October's Hurricane Sand visited Carolin’s Grove like she did any other place in Pound Ridge.  The preserve’s namesake—an 80 year old grove of Norway spruce—was torn to bits by the storm.  Some trees were entirely torn from the ground (roots and all), but more commonly they were left standing, splintered and shattered in half.  As I walked through the wreckage my eyes were drawn up to the sky, which now occupied large gaps in the forest canopy where spruce trees stood only a few days before.

  The following was the sequence of my thinking: 
My thought process as I gaze up through a gap in the forest canopy.  

Every so often, something comes along and kills a handful of perfectly good trees and replaces part of the forest canopy with a wide open gap.  All types of catastrophes can cause a gap in a forest canopy: hurricanes, fire, pathogens (i.e., insect, fungi), ice storms, wind storms, lightning, and let’s not forget the good old fashioned ax.  
A view from Carolin's Grove after Hurricane Sandy.  Forest all over Pound Ridge, NY were devastated by her strong winds.  

What happens once a canopy gap is produced?  Typically, trees grow to fill in the gap.  More specifically, a handful of very lucky trees get an extra dose of light and prosper…upward.  Think back to the story at the beginning of this post – could this have been the cause of the ten evenly sized maple trees?

In one sense, last week’s Hurricane Sandy was a perfectly normal forest phenomenon; forests along the eastern seaboard and in New England have been dealing with bad storms for as long as there have been forests.  Sandy represents one piece in a never ending cycle of tree death, birth and growth.  There is, however, something happening in the forest these days which may alter the cycle.  These days, our forests are experiencing a little extra pressure which affects the processes of birth and growth.  Any guesses?

A cute little white tailed deer.  In Pound Ridge, NY white tail deer are so numerous that they prevent any new trees from growing in the forest.  

The current deer density is so high that it suppresses new trees from being recruited into the forest.  For effect, I'll say it in a few different ways: new trees don’t grow in Pound Ridge; trees fall, but new ones don’t grow back; with every storm, our tree count goes down; every day, our forests are getting thinner and thinner; many new gaps go unfilled.  I'll express it in economic terms: we are only withdrawing from our bank account—there hasn’t been a deposit in years.  

Need proof?  Go to the forest behind your house and find a tree less than 5 feet tall.  You'll be lucky to find one.  This is not forests in other places look like. Most forest can replenish their toppled trees, and they do so with a forest floor full of young trees waiting for a gap to open in the canopy.      

I spent last autumn in a part of Maine where logging is the industry.  I spent endless hours exploring the logged forests, learning great lessons in forest regeneration; all places recently cut were home to fresh clumps of young trees, fighting their way to the sun.  I didn’t mind the destruction to the trees because the forest’s future grew roughly knee high and smelled of fresh spruce as I brushed past it.  

Unlike the regrowing forests of Maine, the barren forest floor of Pound Ridge lacks promise for our forest’s future...


Charlie Hohn said...

Pretty amazing that such delicious animals can become so overpopulated and cause so many problems :(

I have heard in some areas that huge piles of downed trees keep the deer out long enough for trees to be established... perhaps in that huge pile of debris a few maples will make it. Not enough to regrow a whole forest, but it's something.

Dean Zarras said...

Re: "delicious animals"... Seriously, in New Zealand, they solved their deer problem by encouraging the farming of deer. They're now one of the world's leading exporters of venison. What's to stop us from doing the same thing, other than Bambi psychology?

Here's just one article of many.

Tate Bushell said...

Dean- thank you very much for your comment. Very interesting comment and article. You are right, there is good reason to think that if a private company or public municipality were to harvest lots of deer from the forest they could make some money and feed some people. If you think about it, venison is the perfect sustainable food; deer multiply quickly to fill any reduction in their population.

Your right again with the Bambi psychology - its a powerful perspective. By loving deer so much, anti-hunting advocates are effectively choosing for harm to come to the forest.