. Vegetation of Oregon and Washington. Botany Oregon Ecology; Botany Washington (State) Ecology. Figure 121. — The Artemisia tridentata/Agropyron spicatum association is the climatic climax in driest parts of the Columbia basin steppe region; the range pole is 4 feet tall and marked in 6-inch segments {photo courtesy Range Manage- ment, Oregon State University). of Artemisia tridentata var. tridentata and 1 to 2 meters in height — very small amounts of other shrubs such as Chrysothamnus uiscidi- florus, C. nauseosus var. albicaulis, Artemisia tripartita or Grayia spinosa may be present; (2) a
. Vegetation of Oregon and Washington. Botany Oregon Ecology; Botany Washington (State) Ecology. Figure 121. — The Artemisia tridentata/Agropyron spicatum association is the climatic climax in driest parts of the Columbia basin steppe region; the range pole is 4 feet tall and marked in 6-inch segments {photo courtesy Range Manage- ment, Oregon State University). of Artemisia tridentata var. tridentata and 1 to 2 meters in height — very small amounts of other shrubs such as Chrysothamnus uiscidi- florus, C. nauseosus var. albicaulis, Artemisia tripartita or Grayia spinosa may be present; (2) a layer of caespitose perennial grasses dominated by Agropyron spicatum — variable amounts of Stipa comata, S. thurberiana, Poa cusickii, or Sitanion hystrix may be present; (3) a layer of plants within 1 decimeter of the soil surface, including species such as Poa secunda, Bromus tectorum, and Lappula re- dowskii; (4) a surface crust typically com- posed of crustose lichens and acrocarpous mosses (, Tortula brevipes, T. princeps, and Aloida rigida). Variation of Artemisia tri- dentata coverage in this association is from 5 to 26 percent, and this variation is not be- lieved related to past grazing. Seasonal se- quences in phenology are marked with mosses, small perennials, and annuals develop- ing earliest and larger grasses and forbs flower- ing in June. Shrubs remain active all summer by tapping permanent moisture supplies in the subsoil; flowering extends from late June (Tetradymia canescens) to October {Artemisia tridentata). This association is found on a wide variety of soils including those belonging to the Siero- zem, Brown and Brown-Chestnut (inter- graded) great soil groups. Successional changes in the Artemisia/ Agropyron Zone are most often associated with grazing, fire, or cultivation. Grazing most seriously affects the larger perennial grasses since they are preferred by cattle and sheep and are not adapted to withstand grazing. Heavy grazing tends, there
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