Shrubs Of The Great Basin: A Natural History

Dwarf Sagebrush

Dwarf Sagebrush Artemisia arbuscula DWARF OR LOW SAGEBRUSH is much like big sagebrush in general appear~ ance, but, as the name implies, it is much smaller, usually no taller than half a meter and typically much less. The easiest way to separate dwarf from big sagebrush is to look at the leaves-if they are more than three times longer than they are broad, the species is big sagebrush; if they are less than three times longer than broad, it is dwarf sagebrush. There are other differences, of course. Dwarf sagebrush tends to be a darker shade of gray, so much so that the variety (or subspecies, according to some authorities) nova is fre~ quently called black sagebrush. Both black and dwarf sagebrush leaves have three lobes at the broad end, as do those of big sagebrush, but they have a much broader, wedge~shaped appearance, ranging in length from 5 to 15 millimeters. Sometimes the lobes are separated by deep divisions, so that they appear as fingerlike extensions. Generally, dwarf sagebrush grows on rockier, poorer soil than big sage~ brush. Very commonly, it will grow adjacent to big sagebrush communities, but there is typically a sharp transition from one community to the other. Quite often, what may appear to be a big sagebrush community of gradually decreasing stature will, on closer inspection, be seen to be a transition to a dwarf sagebrush community-the steeper hillsides, particularly if only a thin soil layer is present, will be covered with dwarf sagebrush. Frequently, these are degraded big sagebrush sites that have lost surface soil layers over geologic time. Ascending our desert mountain ranges, we can observe that the coldest and driest woodland sites are frequently occupied by dwarf sagebrush, while black sagebrush usually occurs in locations which appear to have somewhat intermediate temperatures. Marda L. West, studying the big, dwarf, and 256 DWARF SAGEBRUSH 257 black sagebrushes in the White Mountains of California, found that dwarf sagebrush occurred on dolomite, sandstone, and granite soils, while black sagebrush was restricted to limestone soils in pinyon,juniper woodlands. Dwarf sagebrush and big sagebrush did not appear to do well on dolomite soils. Otherwise, West found that big sagebrush was far more adaptable than either dwarf or black sagebrush. Big sagebrush in the White Mountains ranged from 6,000 to 10,800 feet through four major vegetation zones: shadscale desert, pinyon,juniper woodland, the subalpine community, and the alpine zone. Dwarfsagebrush was found between 10,000 and 12,800 feet within the two zones known as subalpine and alpine. Black sagebrush had the most restricted distribution of all-occurring only between 7,000 and 9,500 feet. Dwarf sagebrush is distributed from the Coast ranges of northern California through the Great Basin to southwestern Montana and north, western Colorado. Black sagebrush occurs from the central Sierra Nevada of California east to southern Montana and south to southern California and northern New Mexico. Big sagebrush has a considerable ability to become acclimated to a wide range of temperatures. Dwarf sagebrush also shows some ability to become acclimated, but West's studies showed no such capacity for black sagebrush. At least in the White Mountains, big sagebrush carried out photosynthesis most efficiently at 20 degrees c., while the comparable peak for dwarf sage' brush was 15 degrees C. Black sagebrush carried out food manufacture best at 25 degrees C. It is apparent that this differing efficiency at various tempera' tures is one of the major reasons, along with acclimation capacity, for the distribution patterns we have seen for these three sagebrushes. Additional research demonstrated another aspect ofbig sagebrush's adapta, bility by showing that it was more drought,tolerant than dwarf sagebrush. Where these two overlapped, dwarfsagebrush always appeared on the moister sites. Interestingly enough, the kind of plasticity demonstrated by big sage' brush with regard to photosynthesis apparently doesn't hold for water loss by transpiration from the leaves. West found that big sagebrush from the sub, alpine zone showed essentially the same pattern of water loss even when transplanted to the warmer pinyon,juniper zone. Further, watered plants of big sagebrush in the latter zone showed a doubling of water loss compared to subalpine big sagebrush. Under these same conditions, dwarf sagebrush lost even more water than big sagebrush. When water was scarce, however, the Dwarf Sagebrush DWARF SAGEBRUSH 259 lower,elevation big sagebrush lost proportionately more water than the sub...