Lessons in Hugelkultur and Nutrient Cycling - Beetle Kill harms far less than Logging

http://commons.wikimedia.org/wiki/File:Bayerischer_wald_kahlgefressen.jpg

This article shows how much natural disturbance a forest can actually take.  With an intact understory, forests can be extremely resilient.  When logging takes place, adjacent streams show up to a 400% increase in Nitrogen runoff.  However, a stand replacing beetle infestation shows very little increase in nitrogen in adjacent water ways.

Research shows that even though the entire over story may be killed off, the understory remains relatively undisturbed along with soil conditions.  Lack of competition releases understory vegetation and smaller trees left over from the initial die off.  Growth accelerates and nutrient runoff is utilized by the plants instead of washing into streams.

This all makes perfect sense and I have no arguments with their assessment.  But I think there is a larger scenario playing out here.  It is quite obvious that beetle kill leaves behind ALL woody biomass.  This wood may remain standing at first but will soon fall prey to wind throw.  Since logging removes most of the woody biomass and what remains is insignificant or burned, there is no wood left to absorb the Nitrogen.  Not only is all woody biomass removed, the understory is heavily damaged as well.

In forests affected by beetle kill, damage happens more slowly.  Structural diversity on the forest floor in unaffected.  Hillsides are stabilized and runoff patterns remain mostly unchanged.  Since this water is still moving through downed woody debris, does it not make sense that the influx of dead, woody biomass is also absorbing a portion of this Nitrogen?  If the understory is not taking up all this remaining Nitrogen, maybe the dead wood is.  Or maybe the wood is taking up the majority of the Nitrogen and releasing it to the understory as it decays.  Just as in Hugelkultur!

More information is required to make this assessment but it is an intriguing possibility.  Nutrient cycles are incredibly complex and other factors could play into it as well.  It could be that the intact soil bank is absorbing some of this Nitrogen.  Or it could be the huge increase in fungal mycelium which is likely to colonize all the newly available dead wood.  Even fungal mycelium in standing tree trunks can absorb nutrients from the ground.  But these trees won't remain standing for long and no doubt begin falling almost immediately.  All these are forms of bioremediation which are useful to ecological farmers and those working in natural resources. This information could be incredibly useful in adjusting logging practices to alleviate water quality issues.

http://phys.org/news/2013-01-beetle-outbreak-buffers-watersheds-nitrate.html