Monarch Mexican Migration and land management

[Paul Cherubini]

Pat Foley wrote:

> I will agree with Paul and Jurgen that natural forests are mosaics of 
> patches in various stages of succession. And that this heterogeneity 
> is a good thing for the biodiversity and for various ecosystem processes, 
> including insect pest and pathogen regulation.

> Next we need to determine the historical landscape heterogeneity
> pattern, and develop land management practices to imitate it.

Pat, despite the fact that monarchs have overwintered successfully in the selectively 
logged forests of Mexico for centuries, Brower's team does not believe these 
thinned forests are good habitat for the monarchs.  Their position is "logging 
not only removes roost trees, but opens the forest to wind and weather, 
dangerously exposing the monarchs."  Brower's team studied monarch clustering 
in open and closed canopy areas of the forests and found:

"Monarchs that were clustered in open areas experienced lower ambient
temperatures during the night, higher wind velocities, higher rates of water
evaporation, higher rates of lipid use and higher rates of bird predation than 
monarchs clustered in closed areas.  All of these factors contribute to earlier 
mortality in overwintering monarchs, mainly through dessication and 
starvation."

So although monarchs commonly display a clustering preference
for open canopy areas, even when closed canopy areas are available
nearby: 
http://www.saber.net/~monarch/chincuamissrie.jpg (photo lifted
from Journey North website)
http://www.saber.net/~monarch/chincuaexposed.JPG
http://www.saber.net/~monarch/chincuacar1.JPG (photo courtesy of Carol
Cullar)
http://www.saber.net/~monarch/opencan.jpg ((photo lifted
from Journey North website

Brower's team appears to believe would be better if the holes in the forest were
sealed up and the butterflies were all forced to all stay in closed canopy areas.

Mike Quinn also seems to think it's wrong to let the butterflies cluster in
open canopy areas, even if they want to, when he wrote on dplex-l in 1998:

"Paul, it is morally bankrupt to suggest that, if an animal uses a habitat 
where it will experience an increase in mortality, then it's _okay_ to create
_more_ of this habitat."

In summary, we have a situation where even though the selectively
logged forests of Mexico have sustained the monarch migration
for centuries,  and even though monarchs commonly display a clustering 
preference for areas of the forests with holes or openings of some kind in
the canopy,  not even  selective logging is allowed anymore in the "core 
[cluster] areas" of the monarch reserves.  Further, Brower's team
has designated large areas of the reserves as "degraded" not because 
they have actually been deforested, but simply because the forest canopy is
not fully closed or almost fully closed.   

Paul Cherubini

 
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