Posts Tagged ‘Actinomycete’

The Forest’s Own Stimulus Package

November 21, 2009

Burnt shells of long-gone giants dot the forest.  Some trunks have blackened “fingers” that reach up from the ground toward the sky.  Forest fire, in Cappy’s Trails, must have changed this landscape at one point.

Trailhead off Holcombe and Hill Street, Cappy’s Trails, Port Townsend, Quimper Peninsula, E. Jefferson County, Washington State, USA.

From where I live, nearly in the middle of the city, I am still constantly reminded that there are still some semi-wild places in the backyard.  At night I can hear the coyotes yipping from within the acreages of undeveloped woods known as Cappy’s Trails.  These woods are bisected with numerous unmarked trails.  To the newcomer, they might seem daunting.  I usually carry a compass just in case.  There are several places to find maps of the place if you just search the internet.  I prefer to just walk and trust that Port Townsend isn’t so big that I won’t be able to find my way back home from where ever I pop out.

Today takes me hiking into the forest, walking in the tradition of the “naturalist approach”.  I haven’t been walking long when I start to recognize a pattern of burned trees among the dominant Douglas fir, Western Red cedar, Grand fir and Red Alder.  Some of the burned trees appear to have been cut prior to burning, while others were clearly still standing when the burned.  One still reaches to the sky.  The rest of the tree has been changed into the carbons and other elements that once made up the tree.  This fire must have been quite a while back for the moss covering the ground in thick blankets among the Salal and Oregon grape bushes hides any remaining evidence.

More and more, as I hike, I encounter groves of Red alder.  I have been told that Red alder are one of the first trees to come back after a disturbance.  The trees stand up to 110’ or 25 meters.  There light grey, smooth bark is encrusted with patches of whitish lichens.  The leaves that are still on the tree, have turned a pale yellow.  Most have fallen.  They are broadly elliptical with wavy “toothed” margins.  Here and there on the forest floor or on ferns fronds are the clusters of cones that make up the male parts.  Each is about 2 cm long.  Alus rubra (Red alder) have been known to have bacterial associates among their roots.  The bacteria, along with the tree, make small nodules for the bacteria to live in and then begin capturing nitrogen from the air (nitrogen fixation) and fixing it into organic compounds.  In these forests nitrogen is rare and will limit the growth of a forest- especially one that has been disturbed by fires, logging, floods, development, etc.  That would make the alder much like the Red Cross volunteers of the forest.  That was how I always remembered this interesting fact.

This forest has likely been cleared before as much of the peninsula has and might face the same fate in the future.  The land is platted for development and daily the sounds of construction encroach at the margins.  Yet, there are still some folks out there such as the Jefferson Land Trust that hope to purchase and protect parts of those woods.

I am still curious about this strange living situation that the Actinomycete bacteria have with the alder.  How does the bacteria know that it has encountered an alder and how does it stimulate the tree to grow?  Does it have to be just an alder or can it be done with other trees?  Do the alders have this associate when they are seedlings or is it later?  What process allows these bacteria to fix nitrogen, if this is such a rare process?  The small but important mysteries have captured me for the moment…

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