Final answer:
Horses sleeping under the cover of large trees on cold, clear nights helps them keep warm by reducing heat loss, providing a source of warmth, and creating a slightly warmer microclimate.
Step-by-step explanation:
Horses sleeping under the cover of large trees on cold, clear nights helps them keep warm in a few ways. First, the tree canopy provides shelter from wind, which helps reduce heat loss. Second, trees absorb and radiate heat during the day, so sleeping near them at night can provide a source of warmth. Finally, the tree cover can help to trap heat close to the ground and create a microclimate that is slightly warmer than the surrounding environment.