Aspen Trees Are the Most Widely Distributed Tree in North

Aspen trees are the most widely distributed tree in North America. A forest of many aspen trees, some of which may be tens of thousands of years old, is actually one single clone. Which of the following is likely to be the greatest threat to the long-term survival of aspen forests?

A) insects, which may bore holes in the stems of trees
B) climate change, which alters aspen trees' typical environment from the usual moist and cool to dry and warm
C) a fungus that is often found associated with roots of some trees in the stand
D) lack of pollinators