Fire

Forest fires are relatively common in these mountains, and giant sequoias have adapted unusually resistant bark. In fact, fire is a necessary part of their reproductive cycle, triggering the germination of their seeds. Sequoia seedlings need full sun and lots of mineral resources, so fire has the added benefit of clearing out less resistant competing species. Sequoias are also extremely resistant to disease, so much so that pretty much the only way a mature tree dies naturally is by falling over (they have relatively shallow roots). However, humans went through a period of putting out all fires that start (we know better now), which led to build up of highly flammable undergrowth in the forests. This made fires burn more intensely, and use smaller trees as ladders to be able to reach the crowns of sequoias. The Washington tree (previously the second-largest tree in the world) had this happen, and was damaged badly enough that the upper half of the tree collapsed the following winter. Sequoia National Park, California. Taken 3.23.15.