In the past 100 years, pinyon and juniper trees have expanded their historic range, partly because wildfires have been suppressed and partly because there are fewer grasses to carry fire between trees because of grazing. These trees are using more water, out-competing other plants, and changing the ecosystem, leading to some fairly serious consequences.
Gilbert, Lael, "Expansion of Pinyon and Juniper Trees in the Great Basin (Infographic)" (2015). Presentations & Posters. Paper 1.