effects of hemlock wooly adelgid and beech bark disease   Kirk Johnson
  Mar 13, 2006 11:21 PST 

The recent forest disturbance question reminds me of something I've been
meaning to ask. No one wants to see pathogens like the chestnut blight,
beech bark disease, the hemlock wooly adelgid, etc. sweep through our
forests. However, I have wondered if anyone has been studying potential
ecological side benefits to these phenomenon.

For example, up until 5 years ago or so , the Hickory Creek Wilderness Area
in the Allegheny National Forest was largely a second and third-growth
even-aged forest with almost a completely closed canopy and a dearth of
coarse woody debris on the forest floor.

In recent years, however, many beech trees in the wilderness have died, and
snapped off or tipped over completely. This has created numerous canopy gaps
that allow more sunlight to reach the forest floor, and it has also injected
an "instantaneous" coarse woody debris component to the forest ecosystem.
There are also many standing beech snags.

I would be interested to find out if there is a positive ecological response
to beech bark disease and hemlock wooly adelgid (homes for cavity nesters in
the snags, homes for ground-dwelling mammals and others on the forest floor,
diversifying the fluvial geomorphology in forest streams, etc.). Is there a
silver lining to be found in all of this? Is anyone specifically studying
this in any kind of detail? I am particularly interested in the effects of
the hemlock wooly adelgid.

Thanks in advance for any help.

Kirk Johnson
Warren, PA
Re: effects of hemlock wooly adelgid and beech bark disease   Lee E. Frelich
  Mar 13, 2006 12:56 PST 


A general principle in ecology is that what is bad for one species (or
suite of species) is good for another species or group of species.
Something always benefits when new space and resources are made
available. Other species of trees will expand their niche and fill the gaps.

In this case, these pests and diseases represent a threat to all remaining
old growth that does not respond to any sort of human protection, such as
being a designated wilderness area, and old growth is already rare due to
logging. So from a diversity management point of view they are a disaster.

Re: effects of hemlock wooly adelgid and beech bark disease   Kirk Johnson
  Mar 14, 2006 06:41 PST 

Thanks Lee,

I agree with you that these phenomenon are disasters for existing old-growth
and I wish none of these non-native pathogens ever found their way to North
America. If an environmentally benign method could be developed to
completely exterminate the hemlock wooly adelgid, or somehow reduce it's
presence to mere background noise, I would personally be ecstatic.

But anecdotally, watching what's happening in the 2nd and 3rd growth
even-aged forest of the Hickory Creek Wilderness Area and other places in
the Allegheny National Forest with beech bark disease, I wonder if there
aren't subtle benefits occurring too.

For example, could these diseases provide the endangered Indiana bat with
important new roosting habitat in cavities and under bark sloughing off dead
hemlock & beech? Also, there is currently little growth in the HCWA
understory in most places. With the combined effects of the Pennsylvania
Game Commission working to reduce the state's deer herd, and beech bark
disease opening gaps in the canopy and allowing more sunlight to reach the
forest floor, maybe that will help jump-start some important new growth over
the next several years?

Anyway, just some brain-storming thoughts. I would be interested to find out
if anyone is studying this sort of thing. Maybe someone's writing a
dissertation on it somewhere.

Kirk Johnson
Re: effects of hemlock wooly adelgid and beech bark disease   adam-@forwild.umass.edu
  Mar 14, 2006 07:15 PST 


Dave Orwig and myself have been thinking about your very question quite a bit
over the past few years and are currently working on a manuscript modeling the
long-term impacts of hemlock woolly adelgid infestations on coarse woody debris
dynamics in southern New England. I will send you a copy of this manuscript
once it is completed.

-Tony D'Amato