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The deliberate introduction of European annual glasses and forbs by the Franciscan missionaries began a transformation of the California herbaceous flora, which is an ongoing process. In explaining the transformation to modern exotic annual grassland, the scientific community is still at the first step: detailing the history of invasions and associated change in California pastures. Conceptual models on the history of California pasture are frustrated by the sparse written record from the Spanish and Mexican periods. Because the early expansion of exotic species coincided with the introduction of livestock, whose collective numbers increased to millions of animals by the nineteenth century, ecologists have also addressed the role of grazing in the early expansion of European invasives.

This chapter discusses grass height, season of growth, and longevity. There are three grass height categories: tall, mid-height, and short. These have become standard ways of describing grasslands, grass stands, and even grass species. Warm-season grasses tend to dominate at lower latitudes, while cool-season grasses occur farther north or higher in the mountains. Perennial grasses plants live ten, twenty, or more years and send down long roots that give the dark cast and lasting fertility to true prairie soils. Annual grasses live a year or less, overwinter as seeds, and colonize waste places and grain fields. The chapter also describes grass resilience to heat and drought and grass persistence under heavy grazing.

This chapter provides a historical background of Oregon's prairies followed by a list of prairies by county. Each site is briefly described, followed by symbols showing site features, a brief location, and a phone number. Oregon supports a large variety of shrub and grassland ecosystems. Its coastal prairie lies in sporadic pockets of treeless grasslands found just beyond the coastal strand from northern San Francisco Bay to Oregon. Following the conversion of coastal prairie into agricultural land, perennial coastal prairie cannot successfully compete with now-dominant annual grasses. Palouse Prairie, a bunchgrass prairie, has also been mostly converted to farmland. This prairie resembles the Great Plains shortgrass prairie but supports shrubs; its perennial bunchgrasses are distinctive. The Willamette Valley's native upland prairies and wetland prairies now cover less than 1 percent of their former area, making them among North America's rarest ecosystems.