First, didn't anyone read the online Seminar article on urban forests and climate change - no comments yet in that sub-forum?
About this thread though, there are people studying old growth forest in the Pacific NW of the USA, using a tall crane to suspend a gondola above the forest canopy.
Local News | Trees giving bizarre clues to climate change | Seattle Times Newspaper
This should provide some interesting discussion over the next year. May even give them a chance to learn some other related facts.
Odds are, they will find that the cause is other than global warming. May just be a fertile year.
If they can say where the exact location is, we may be able to look at climate tables to see if there was any kind of mini-drought in the area previously.
Those trees hold so much water on their needles, they may even affect the soil moisture by how many needles they hold from year to year.