Clarkia tembloriensis and "Caliente" (an undescribed Clarkia species) in a low elevation grassland habitat flower about 2 weeks earlier than sympatric or adjacent populations of C. unguiculata. At higher elevations in a woodland habitat C. exilis blooms later than the lowland populations, but about 2 and 4 weeks earlier than adjacent populations of C. unguiculata and C. xantiana, respectively. Time of flowering is differentially correlated with, and interpreted in terms of adaptation to, the onset of summer heat and drought.

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Highlight: Standing dead was clipped from clumps of bluebunch wheatgrass, with no other disturbance. Clumps without dead material, compared to those with, had less green material and shorter leaves but did not differ in height or number of flowering culms or head lengths. Standing dead appears to be beneficial to bluebunch wheatgrass. Agropyrorz spicatum (bluebunch wheatgrass), in the ungrazed condition, grows in clumps with a dense accumulation of dead culms and leaves, collectively known as standing dead. Standing dead modifies the environment of young leaves, and to a lesser degree older leaves, by intercepting sunlight and reducing air movement. Reduced light intensity may decrease photosynthetic activity. On the other hand, reduced air movement may favor a reduced vapor pressure deficit at the leaf surface and reduced water stress in plant tissues, compensating perhaps for the reduced light intensity. This report describes the effect on bluebunch wheatgrass of the removal of standing dead without the removal of live material. The results of this research are relevant to ecosystems studies focusing on the effect of standing dead on the growth of bluebunch wheatgrass. Grazing studies have dealt with the effect of removal of both live and dead material from rangeland grasses during the growing season (Rickard et al. 1975; Mueggler 1972, 1975; Wilson et al. 1966; Heady 1950). In contrast, this study addresses the effect of removing dead material early in the season before growth initiation of new leaves. Study Area and Methods The study site is the Arid Lands Ecology Reserve located on the United States Energy Research and Development Administration's Hanford Reservation in southcentral Washington. The site occupies a gently sloping, east-facing slope on the Rattlesnake Hills at an elevation of approximately 390 m (1,300 ft). The vegetation is classified as the Artemisia tridentata/Agropyron spicatum association (Daubenmire 1970). The soil is a silt loam with very few rocks in the upper 2 m of profile. Precipitation is approximately 200 mm (8 inches), most of which comes in fall, winter, andearly spring. Growth is arrested in summer by drought and in winter by cold. Most species grow in the period between January and June when soil water content and temperatures are simultaneously conducive to growth. Seventy-three clumps of bluebunch wheatgrass were randomly selected and individually identified in an area approximately 100 m by Author is research scientist, Terrestrial Ecology,

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