On 3% of the Earth's surface, the rain forest is the habitat for half our animal species, even 80% of insects. So its wildlife is most competitive, like the birds of paradise's mating, and specialized with unique relationships of predation, parasitism etc. For plants, the quest for light is key to stratification, paralleled by interacting animals eating fruits, leaves and other animals. Even the jungle cacophony is stratified. On the soil, recycling specialist like fungi restart the cycle of life.
Trees are earth's largest organisms and are also one of the planet's oldest inhabitants. Seasonal forests (unlike tropical rain-forest) the largest land habitats. A third of all trees grow in the endless taiga of the Arctic north. Northern America has forests that include California's sequoia's, the earth's largest trees. There and elsewhere, their vast production of photosynthesis and shade presides over a seasonal cycle of life and involves countless plant and animal species.
The polar caps have the most extreme seasonal contrasts, growing and melting vast ice masses, so wildlife adapts by annual migrations. The majority of Antartica is a vast barren permafrost. Only 3% of the coast and peninsular peaks are where life migrates to in the spring, for a short fertile summer, attracted by rich supplies of krill and fish. Only the Emperor penguin males breed 4 months in winter 100 miles inland. The Arctic has a more complete fauna which migrates back North from the continent.