When Hiking Meets Science

"Why are all of these trees dead, Anne?  Did a fire come through here?"  As we pass by Lake Arnold on the shoulder of Mount Colden, one of my participants noticed the large swath of downed trees encircling the trail.  I observed the lack of burn marks on the tree trunks, and ruled out forest fire as a cause of death.  Almost all the trunks seemed to point upslope, as well, indicating either a constant flow of wind affecting forest structure or a severe storm knocking them all down at once.  On another mountain range at a lower elevation on a hike a year prior, I had hiked through a stand of mixed hardwood and softwood trees that had succumbed to the power of Hurricane Irene in 2011.  This forest that was affected by the storm was completely ravaged, with massive trees still bearing leaves perched haphazardly across one another, and there was a distinct line separating the dead from the living.   However, the forest on the slopes of Mt. Colden was comprised mainly of balsam firs and spruces, and lone trees struggling to survive were interspersed amongst the battlefield of the fallen.   

 

I did not think much past these initial observations while I was hiking — something greater than just wind was the cause of this massive tree death.  It took me until reading Peter Marchland's "Nature Guide to the Northern Forest" to realize the trees most likely fell due to a "fir wave".  This rare phenomenon is caused by over-competition amongst large stands of fir trees, as well as high winds and harsh winters which cause defoliation and tree death.  Once one tree falls to the pressing environmental factors, it creates a gap in the forest that makes the other aging trees more susceptible to wind, causing their die and fall quicker.  Firs of similar old age are particularly susceptible to the cyclic death, and a new wave wipes out old stands every 60 years or so.  These waves are restricted to the subalpine zone of 2,500 to 3,000 feet, and has only been observed in the northeastern woods of the United States in a few places in New Hampshire, Maine, and the Adirondacks of New York, as well as in Japan.

Thinking back to my hikes to Lake Arnold, and my observations of the forest composition and felled trees, the cause of death and destruction of the woods alluded me at the time.  Though fir waves seem a likely cause of the tree death, it's just one variable in the northern woods continuously shaping the ecosystem we are all lucky to hike through.  

Sources:

"Nature Guide to the Northern Forest" Peter J. Marchland 

North Woodlands Magazine: http://northernwoodlands.org/outside_story/article/doing_the_fir_wave/

SUNY Cortland: facultyweb.cortland.edu/broyles/FBIO/Firwaves.pdf