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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



(Bouteloua curtipendula [Michx.] Torr.), vine- 

 mesquite (Panicum obtusum HBK), and switch- 

 grass (P. virgatum L.) are used in areas where 

 precipitation may exceed 350 mm. (1, 27, 30). 



Some native adapted forbs now being planted 

 in the first three types listed on page 73 are pa- 

 cific aster (Aster chUensis adscendem [Lindl.] 

 Cronq.), arrowleaf balsamroot (Balsamorhiza 

 sagittata [Pursh] Nutt.), blue flax (Linum le- 

 wisii Pursh), and sweetvetch (Hedysarum boreale 

 Nutt. ) . Introduced forbs being fairly widely used 

 are range types of alfalfa (Medicago sativa L.), 

 chickpea milkvetch (Astragalus cicer L.), sickle- 

 pod milkvetch (A. falcatus L.), and small bur- 

 netii (Sanguisorba minor Scop.). 



The shrubs in extended plantings are big sage- 

 brush, rubber rabbitbrush, antelope bitterbrush 

 (Purshia tridentata [Pursh.] DC), Stansbury 

 cliff rose (Cowania mexicana stansburiana 

 [Torr.] Jeps.), wedgeleaf ceanothus (Ceanothus 

 cuneatus [Hook] Nutt.), and winterfat (Eurotia 

 lanata [Pursh.] Moq). Fourwing saltbush (A. 

 canescens [Pursh.] Nutt.) and winterfat show 

 good adaption within most types where soils are 

 basic. 



Aspects Of Morphogenesis 



Throughout the shrublands of the West, strik- 

 ing differences are often seen in the morphology 

 of individual shrubs from place to place and 

 sometimes in the same place. Environmental fac- 

 tors such as climate, soils, light, and modifications 

 of these by elevation and latitude, are important 

 causes for differences, and are probably reasons 

 for the occurrence of what we may call regional 

 ecotypes. 



The environmental factors exerting their in- 

 fluence on sites over extended periods of time 

 were no doubt responsible for fixing climatic or 

 regional ecotypes and sometimes subspecies and 

 even species. Excellent consideration has been 

 given to this aspect through reciprocal transplant 

 studies by Clausen, Keck, and Hiesey (11)- 

 While most of their studies involved moving her- 

 baceous species from one elevation or climate into 

 another, shrubs were involved, and certainly the 

 principles developed by these investigators have 

 considerable application to woody plants. Similar, 

 but limited, transplanting of shrubs from the 



southern to the northern desert shrub type in 

 Utah, and vice versa, supports their findings (44, 

 45). 



Cropping And Grazing 



The continuing and constant use made of 

 plants over a period of time, as by grazing, has 

 temporarily altered shrub form. Over a long 

 period of time it is reasonable to expect that, 

 through the process of natural selection, a popu- 

 lation would evolve to better tolerate this use. I 

 strongly suspect this has occurred in the past 

 century of grazing by livestock. 



Commonly seen in nature are shrubs which 

 have been grazed in about the same way over a 

 period of years. As a result, they frequently as- 

 sume, a definite hedged appearance similar to or- 

 namental hedges around homes. Once shrubs of 

 some species acquire a hedged form, they persist 

 unusually well despite what appears to be heavy 

 annual cropping of the new shoots that grow 

 above the hedge line. This characteristic has been 

 noted in antelope bitterbrush. true mountain ma- 

 hogany (C ercocarpus montanus Raf.), blackbrush 

 (Coleogyne ramosissima Torr.), fourwing salt- 

 bush, rubber rabbitbrush, and others. From ob- 

 servations, it appears evident that the persistence 

 of these hedged plants is attributed to the pres- 

 ence of leaves within the strong interwoven 

 branches. Since they are not available to grazing 

 animals, the} 7 produce sufficient carbohydrate re- 

 serves to maintain vigor. New growth above the 

 hedge line is stimulated by the removal of apical 

 dominance (17, 33. 49). 



Artificial cropping of five shrub species by Gar- 

 rison (21) in Oregon showed that all were stim- 

 ulated to a considerable increased production of 

 herbage when the twig ends were removed. This 

 increased growth continued over a 4- to 5-year 

 period of cropping. The shrubs were antelope bit- 

 terbrush, rubber rabbitbrush. curlleaf mahogany 

 (Cercocarpus ledifolius Nutt,), snowbrush cean- 

 othus (Ceanothus velutinm Dough), and cream- 

 bush rockspirea (Holodiscus discolor [Pursh.] 

 Maxim.). Removal of the terminal buds resulted 

 in production of two or more twigs from lateral 

 dormant buds the next growing season. McKell 

 and Willard (35) in Utah have recently found 



