DISCUSSION 



Anomalies 



Most of the variations in vegetation described in this report appear to be 

 related to variations ir climatic conditions. Some apparent anomalies may be 

 clarified by a few remarks . 



In the Distichlis stricta community, which is anomalous in that D^ stricta 

 productivity showed a marked increase from 1977 to 1980, D^ stricta seems to be 

 a phreatophyte, with production not closely tied to precipitation. Production 

 has tended to increase as a function of livestock exclosure. In the D^ stricta ■ 



Agropyron smithii community, D^ stricta production has varied with 

 precipitation. The D_^ stricta - Agropyron smithii community occupies a higher 

 topographic position and plants probably root above the capillary fringe. 



The Bouteloua gracilis and Andropogon scoparius communities had lower 

 production than expected in 1978 due, apparently, to cool temperatures. This 

 may have resulted in greater soil moisture availability in 1979, and 

 consequently higher production. 



High winds resulted in snow accumulation in coulees during the winter of 

 1978-79. This may have led to the unexpectedly high production of the Artemisia 

 cana / Agropyron smithii / Bouteloua gracilis community in 1979. 



Implications 



The high variability of the data presented here has many implications. The 

 plant communities studied exhibit a great deal of resiliency. Air pollution 

 impact assessments based solely on a comparative approach may fail to 

 demonstrate air pollution impacts if they occur. Classifications of vegetation 

 based upon data collected in one year may not be suitable in another phase of 

 the moisture cycle. Vegetation maps portraying actual vegetation may be subject 

 to annual changes. Range condition estimates based upon species composition 

 also may be subject to rather dramatic annual change, even in the absence of 

 livestock grazing. This point is not always considered. 



Coupland and others (1960) pointed out that climatic effects should be 

 incorporated into range condition estimates. From a long-term (1932-1945) study 

 of the effects of grazing and weather on prairie vegetation near Miles City, 

 Montana, Reed and Peterson (1961) concluded that, "Major trends in nearly all 

 vegetation characteristics were set by the major cycles of weather, and the rate 

 of change within these trends was largely influenced by intensity of grazing." 

 The Soil Conservation Service (1976) recently sanctioned more flexible range 

 condition rating procedures, which subjectively incorporate climatic effects. 

 Range condition evaluations are further complicated by the mapping of soil 

 complexes which often contain several range sites. 



To illustrate some effects of climatic conditions on range conditions, two 

 exclosures in areas mapped as soil series (not complexes) were evaluated in 

 strict accordance with the SCS Technicians' Guide to Range Sites, Condition 

 Classes and Recommended Stocking Rates in Soil Conservation Districts of the 

 Sedimentary Plains of Montana, 10-14" Precipitation Zone . 



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