Peter Constabel, a professor in the biology department at the University of Victoria said that several years of repeated drought in B.C. mixed with heat stress has increased the likelihood of branches breaking off, it could even happen on a “perfectly calm day” without any breeze. The consequences can be tragic. Constabel, who specializes in tree health said, “it’s the drought that specifically causes this, and somehow it stresses the tree and drops the branch, or the branch falls. If you get cumulative droughts, of course, it weakens the tree overall”. …Dry spells can leave trees in a weakened state, Simon Fraser University biological sciences professor Jim Mattsson said, reducing photosynthesis and growth, cutting their energy or sugar reserves, and lowering production of chemical defences. All of these can cause a chain reaction increasing trees’ susceptibility to insects and fungal diseases, causing trees to rot inside, weaken and potentially topple over.