speaking of characteristics of old-growth forests, the cycles of great old trees living and dying create effects on the landscape that cannot be fully replicated once destroyed.
there are multiple ways for a tree to die, each with their own impacts on the ecosystem. Many trees die standing, becoming starkly bare pillars of standing deadwood with increasingly fewer branches and more sharply whitened surfaces as the bark falls off and the branches break, the smaller branches first and then the larger ones. Standing deadwood is vital for housing lots and lots of bird species and it also has an undeniable sexiness and charisma
Trees broken by wind, snapping off at some point up the trunk, are often hollow in the middle from heart rot fungi. I don't think the fungi actually kill the tree, since the center of the tree (the heartwood) is dead anyways, but they do structurally weaken it.
One of the most dramatic tree deaths is windthrow. This happens to large trees that are solid all the way through and not easily broken by the forces of wind; instead, the roots are wrenched violently out of the ground, creating a bowl-shaped hole in the ground with a huge mound of twisted tree roots standing 5 or 6 feet tall next to it.
The death of a tree by windthrow feels very sad, because the tree seemed to be thriving up until that point, but the effect on the ecosystem is very fascinating. The hole in the ground where the root ball was torn up creates a shaded, sheltered area, sometimes filling with water to become a small pool. The root ball itself, right next to it, becomes a tall pile of soil and decomposing wood.
When walking in the forest, I often notice strange mounds rising from the layer of leaf litter, covered in lush carpets of moss, like bustling moss metropolises rising out of lowlands that only have scattered moss towns. Elevated from the forest floor, the moss-hills do not become covered with leaf litter. In some cases, these distinctive moss-hills are still visibly connected to the fallen trunk of a windthrown tree; in other cases, the tree trunk has almost completely decayed, and only the mound created by the root ball remains.
I read once in an article that the creation of humps and valleys by the windthrown tree roots is characteristic of old growth forests. That is, the forest has existed so long, with trees living majestically and dying violently in it, that the ground is no longer a smooth plane, but humpy and bumpy and pitted and pooled from centuries of trees dying by windthrow.
My observations seem to agree that these windthrown-tree-humps have unique ecology, particularly in terms of their thriving moss colonies that remain even after the tree that originally died has rotted away. They would create a million little variations on light and moisture level, gathering leaf litter in some places and keeping it away from others. Variations create multiplying amounts of biodiversity due to the increased amount of niches to fill.
Not to mention that hills and valleys increase the total surface area of the forest floor, creating more forest per forest.
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