Question

Old growth forests are full of sick, diseased, and decadent trees.

Answer 1

That statement is misleading.

Old-growth forests do contain a lot of dead, dying, and senescent (what you call “decadent”) trees and large fallen logs — but that is a normal, healthy part of old‑growth ecology, not a sign that the forest is broadly unhealthy. Key points:

- Dead and decaying wood is an essential component. Standing dead trees (snags) and coarse woody debris provide habitat for birds, bats, insects, fungi and many plants, and they store nutrients and carbon as they decompose.
- Tree mortality creates gaps. When large trees die and fall they open the canopy, letting light in for understory and young trees. That gap dynamics drives regeneration and species diversity in old forests.
- “Senescent” does not equal “pathological.” Many very old trees are physiologically old but still performing ecological roles (seed production, habitat, structural complexity) for decades even as parts of them rot.
- Disease and insect agents are present, as in any ecosystem, and sometimes outbreaks happen. But old-growth structural and species diversity often buffer against landscape‑scale epidemics in ways that uniform, even‑aged plantations do not.
- From an ecosystem perspective, processes of decay, mortality, and renewal are signs of a functioning, resilient forest rather than failure.

If you want scientific summaries, look up work on coarse woody debris and old‑growth structure (e.g., Harmon et al. on coarse woody debris, Franklin & Spies on old‑growth forest structure, and reviews by Lindenmayer and Franklin).