I visited the Chincua Monarch overwintering reserve in Michoacan,
Mexico a couple days ago and found dozens of trees (about
2 acres worth) festooned with huge clusters of monarchs:
http://www.saber.net/~monarch/chincuaoverview.jpg
I also took the following photos which I believe demonstrate
how small clear cuts and patch cuts in the overwintering forests
actually create drinking water and flower nectar habitats for the
butterflies:
http://www.saber.net/~monarch/chincuawater1.jpg
http://www.saber.net/~monarch/chincuawater3.jpg
http://www.saber.net/~monarch/chincuanectar.jpg
I also took a photo of how the overwintering monarchs in Mexico
routinely form their colonies immediately next to natural or man
made cuts / holes in the forest:
http://www.saber.net/~monarch/chincuaclearcut.jpg
Although the colonies form in moderately dense forests
http://www.saber.net/~monarch/chincuamoddense.jpg
areas of very dense forest exist right next to the cluster areas,
http://www.saber.net/~monarch/chincuatoodense.jpg
but the monarchs do not use them, perhaps because they are too
cold and shaded from the sun.
Here's a nice view of the general overwintering region in
Michoacan, Mexico
http://www.saber.net/~monarch/chincuaridgetop.jpg