Low Shrubs on Lava.  These communities occur on basalt ridges and other areas where shallow soils overlay basalt (Figure 19).  Black sagebrush is often present, but usually not dominant.  Green rabbitbrush and broom snakeweed are common.  Wyoming big sagebrush and winterfat occur in some areas.  Native bunchgrasses and forbs typically are abundant.  Columbia goldenweed (Haplopappus acaulis, see picture below), a suffrutescent shrub, is found on patches of exposed lava. 

Sagebrush-Rabbitbrush.  Communities in this class are characterized by an abundance of green rabbitbrush, which may be the dominant shrub or a co-dominant with Wyoming big sagebrush or, occasionally, black sagebrush.  Communities in this class fall both on and off the basalt flows.  Many of these communities have a rich understory of perennial grasses and forbs.  Cheatgrass is present and sometimes very abundant where these communities occur on coarse-textured soils.  These communities variously intergrade with big sagebrush steppe.

Green rabbitbrush often is characterized in the literature as an “early successional” species.  However, it is the only shrub that consistently increased in abundance between 1950 and 1985 on the INEEL permanent vegetation plots (Anderson and Inouye 1988).  That this occurred in the absence of any major disturbances such as fire or livestock grazing indicates the “early seral” characterization is inappropriate.  It may well be an opportunistic species that can take advantage of disturbances, but the data from the INEEL does not support the view that it will be displaced by other species in later stages of vegetation development.  Green rabbitbrush can sprout vigorously following fire, so its abundance on some sites may be a consequence of fire history.

Sagebrush-Winterfat.  Communities in this class typically are dominated by Wyoming big sagebrush, but winterfat is typically abundant and may be dominant or co-dominant.  Green rabbitbrush is common, as are members of the suite of perennial grasses, especially Indian ricegrass.  This class occurs on soils derived primarily from lacustrine deposits of ancient Lake Terreton.  Cheatgrass seldom is found in these communities.  Our vegetation data suggests that these communities are intermediate between the Sagebrush/Green Rabbitbrush communities and Salt Desert Shrub communities.  This may reflect a gradient from upland loess soils to the more halomorphic lacustrine soil of the Lake Terreton basin.

Salt Desert Shrub.  Salt desert shrub communities are found on the Big Lost River and Birch Creek playas and on other playas within the Lake Terreton basin.  All are dominated by members of the chenopod family, but their composition varies considerably.  Our samples indicated the occurrence of three relatively distinct community types.  The first is dominated by suffrutescent shrubs.  Nuttall saltbush is the dominant species.  Shrubby buckwheat is a co-dominant in some areas and winterfat is often present.  The second type is dominated by shadscale.  Winterfat and green rabbitbrush are common in these communities, and Nuttall saltbush may be present.  The third type is dominated by winterfat, but four-wing saltbush (Atriplex canescens) is abundant. 

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