Awesome Husband and I escaped the Texas heat for a week, fleeing to Seattle and surrounding areas. One of the places we visited was the Hoh Rainforest on Washington's Olympic Peninsula, where about 80 million shades of green assault you as you walk through. Conifers like spruce, hemlock, and fir rule the area, dripping with an array of mosses, while the ground is invisible beneath ferns and oxalis.
Imagine that you're a little spruce seed, getting ready to drop from your parent tree. It's exciting to be sailing toward the ground, knowing that all you need is a fertile patch of ground that gets a little sunlight and some water, and you'll be on your way!
You look down and get a bit of a jolt.
If you're a smart youngster, you aim for a rotting log. Fallen logs can help supply two scarce resources. Rich nutrients are locked up in the decomposing wood, as well as natural fertilizer in the form of decayed leaves and animal scat that accumulates in the cracks. Not only do the downed logs provide nutrition for hungry seedlings, they rest above the layer of oxalis and ferns that block the sun from a new wannabe-tree. (See the tiny little spruce tree there?)
As the new trees grow, they send down long roots that look like sinuous legs draped over the decaying log. Because of the sometimes enormous diameter of those logs (called "nurse logs") the roots may have to be several feet long before they begin to penetrate the actual ground. The scene ends up looking as though a tree-person is straddling the log, with long legs stretching for the dirt.
As time passes, the younger tree becomes firmly anchored around the nurse log, and it's often hard to tell where one ends and the other begins. The nurse log continues to decay, a process that may take over a hundred years to complete. When it's gone, it leaves behind a hole in the twisting roots of the younger tree.
The final product is really dramatic when more than one sapling got its start on the same nurse log. When they're mature, you can see several enormous trees in a ridiculously straight line, all with the telltale hole in the buttressing root system. These groupings of trees are called "colonnades." The colonnade system is the primary way that forests in temperate rainforests renew themselves.