From the park:
Nowhere is there a forest like it: a product of local climate-temperate with tremendous rainfall. In this hushed, verdant world the air fairly drips, supporting epiphytes (air plants) growing in wild profusion from every vine and limb. The rare ray of sunshine finding the spongy forest floor appears as burnished green. And here are found some of the largest known trees.

From nps:
Bigleaf maple and vine maple host an abundance of epiphytes (plants growing upon other plants) that give
the rain forest its characteristic look and ethereal quality. A plethora of mosses, ferns and plants compete for space on the forest floor; grazing elk keep the understory open. Dead
and downed trees decay slowly and support new life as ‘nurselogs.' The eternal cycle of life and death is strikingly
apparent in this magnificent forest community.