Changing floras Through Earth's history, continents have moved, mountains have risen and eroded, lakes and rivers have filled and dried, and ice ages have brought glaciers and periods of warming have caused them to recede. As features such as the climate, soil, or topography are altered, the plants that live in an area may also need to change (a process called adaptation) or go extinct. Changing environments can also spur the migration of plants. Migration, extinction, and evolution have undoubtedly all impacted the remaining bits of native flora that we find on the Palouse today.

---

Floristic change on the Palouse

In the history of the Palouse, one of its warmest and wettest times extended from 60 to 40 million years ago. During that time, the flora of the Palouse was more like that found today far to the south in tropical and subtropical areas. With a cooling and drying of the climate from 40 to 5 million years ago, the plant communities of the region changed dramatically, and this was marked especially by the loss of tropical plants from the region. Over much of this period, temperate forests developed in the Columbia Basin, including the Palouse. Various associations of plants might have been found in different parts of the Palouse depending upon elevation, slope, and water availability in local areas. Much of the Palouse was dominated by forests of spruces (Picea) and true cedars of the genus Cedrus. Valleys would have had various deciduous plants, such as alder (Alnus), serviceberry (Amelanchier), ash (Fraxinus), elm (Ulmus), and hickory (Carya). In wet lowlands, there were swamp forests that had cypresses (Taxodium).

Taxodium: Lowlands of the Palouse once had cypress swamps such as those shown in this photograph that today are characteristic of the southeastern U.S.

After 5 million years ago, the rise of the Cascade mountains created a rain shadow that caused the Palouse climate to become drier. This was an era in which plants of temperate forests disappeared from the Palouse. Grasses and sagebrush that had entered the northern Columbia Basin as the climate dried and warmed before 5 million years ago became more and more prevalent in the flora as the rainshadow of the Cascades had greater impact on the climate of the Palouse. We know little about the flora of the Palouse during the glaciations of the Pleistocene (from about 2 million until 10,000 years ago). It was after the last major glaciation about 10,000 years ago that the vegetation of the Palouse assumed the features of its modern flora.

Synthyris missurica: Mountain kittentail found on Kamiak Butte is an isolated relict of earlier era floras.

This modern flora is dominated by grasses and other plants characteristic of grasslands. The Palouse flora, however, continues to have a mix of plants that remain from earlier historical periods. These relicts of earlier eras are among the most interesting plants of the Palouse flora. For example, the mountain kittentail (Synthyris missurica) has been suggested to be a relict of earlier cool climates that has became isolated on Kamiak Butte at the end of the Pleistocene glaciation.