Two of the most common tree failures I have seen over the years responsible for property damage are stem failures (above) or root failures (below). Stem failure typically occurs where a structural weakness is present within a tree. In Sitka spruce trees, this is often internal decay. Root failure occurs when a portion, or all of the anchoring roots of a tree fail. Stem failure is generally responsible for causing the most damage to property. Root failure can sometimes be discovered preemptively by looking for soil heaving at the base of a tree. If you question the stability of trees around your home, I recommend you have them inspected by an ISA Certified Arborist.