In uplands, grasses dominate. Plants invest limited water supply into photosynthesizing tissue, don't waste it on woody supporting tissue. Precipitation maximum in summer. Wets surface soil layers during period of plant growth. Fires common, especially during drought years.
Fires favor grasses over woody plants.
Grasses will survive fires belowground, even if aboveground stems are burned off. Woody plants commonly killed by fires, especially when they are thin-barked or small in size. A Pronounced elevation gradients in vegetation 1. Colder, shorter growing season, reduced energy with increasing elevation 2. Grasslands of western Great Plains on eastern side.