I found this:

"Overwintering monarchs need forests for protection from the elements, and they need very specific forests at that. The population that breeds east of the Rocky Mountains migrates to mountains in central Mexico, where they can roost in dense stands of oyamel fir trees. Unfortunately, those trees are a valuable resource, and even after the monarch wintering site was designated as a preserve, logging activities continued illegally. In the 20 years from 1986 to 2006, an estimated 10,500 hectares of forest were either lost entirely, or disturbed to a degree that they no longer provided suitable winter cover for the butterflies. Since 2006, the Mexican government has been more vigilant in enforcing the logging ban within the preserve, and thankfully, deforestation has decreased significantly in recent years".

And:

"The number of migrating monarchs is plummeting for a few reasons: widespread loss of a plant called milkweed, which their young rely on for food; extreme climate fluctuations in North America, including freezing temperatures and heavy rain; and deforestation".

I hope this helps :-)

Please check the following links.

http://www.sciencedirect.com/science/article/pii/S0006320714003589

https://www.researchgate.net/publication/256424142_Trends_in_Deforestation_and_Forest_Degradation_after_a_Decade_of_Monitoring_in_the_Monarch_Butterfly_Biosphere_Reserve_in_Mexico_Monarch_Butterflies_in_the_Biosphere_Reserve

Article Trends in Deforestation and Forest Degradation after a Decad...

Marisol:

Also have a look at this link for insights:

http://assets.worldwildlife.org/publications/845/files/original/Monarch_butterfly_-_WWF_wildlife_and_climate_change_series.pdf?1449777278

Best

Syed

Dear Marisol,

Please check these links.

Regards

SM Najim

https://www.nrdc.org/sites/default/files/wil_15040901a.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4232930/pdf/cobi0028-0177.pdf

http://academics.hamilton.edu/biology/ewilliam/publications/brower2012icd5,95.pdf

http://www.sciencedirect.com/science/article/pii/S0006320714003589

http://www.canadiangeographic.com/wildlife-nature/articles/pdfs/monarch-butterfly-winged-wonder.pdf

http://bioscience.oxfordjournals.org/content/early/2015/05/04/biosci.biv045.full