There was a nice article in The Economist [1] a few months ago on just about this issue - how it relates to global warming, forest densification, mismanagement,

There was a nice article in The Economist [1] a few months ago on just about this issue - how it relates to global warming, forest densification, mismanagement, etc. [1] http://www.economist.com/news/briefing/21701751-stricken-trees-provide-clues-about-how-america-will-adapt-global-warmingbut-little-hope http://www.economist.com/news/briefing/21701751-stricken-tre...