PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



77 



similar response from clipping mountain snow- 

 berry (Symphoricarpos oreophilus A. Gray) and 

 rubber rabbitbrush. In both of these investiga- 

 tions removal of 50 percent or more of the twigs 

 resulted in greater production than lighter crop- 

 ping, but removal of 25 to 30 percent of the 

 twigs resulted in more production than no clip- 

 ping. 



Ferguson and Basile (20) found through a 4- 

 year period that a November cropping back of 

 the main branches of antelope bitterbrush to about 

 a 1-meter height from double this height or more, 

 resulted in a nine-fold increase of new twigs as 

 compared to the checks. Somewhat in contrast, 

 when 80 percent of twig growth of big sagebrush 

 and three-tip sagebrush (Artemisia tripartita 

 Rydb.) was removed in 8 months out of the 

 year on the Snake River plains (57), there was 

 some depression of growth at all months of clip- 

 ping, as compared to nonclipped checks. The 

 greatest depression was from clipping in the ac- 

 tive growth period of July when carbohydrates 

 were at their lowest point. It is interesting that 

 sagebrush is probably more sensitive to heavy re- 

 moval of foliage than most other shrubs. In some 

 places, high removal of herbage has killed sage- 

 brush, and in others it appears that heavy graz- 

 ing has extended its lifespan. 



Curlleaf mountain mahogany, a broadleaf win- 

 ter evergreen, furnishes protective cover and for- 

 age to big game and livestock on large tracts of 

 winter range in the mountain States. On exten- 

 sive stands, it assumes a semitree form of growth 

 so that most of the twigs and leaves are not avail- 

 able to grazing animals. When Ferguson and 

 Basile (20), and later Thompson (56), cut back 

 the heavy branches of curlleaf shrubs, no new 

 twigs were produced, and all the shrubs died. 

 Most shrubs — including curlleaf's deciduous 

 counterpart, true mountain mahogany — are stim- 

 ulated by similar treatment. However, Thompson 

 discovered that a fairly good growth on curlleaf 

 was induced from terminal spurs when one or 

 more live limbs were left on the heavy branches. 

 Regrowth was stimulated on the treelike form of 

 the shrub when it was topped in the periods from 

 April 20 to May 10 or from September 10 to 30. 

 Not enough research has been done to determine 

 why topping in other periods resulted in total 

 mortality. 



Genetic Phases 



Heavy grazing over the past 125 years has re- 

 duced, and in some instances, markedly opened 

 closed stands of shrubs and herbs on expansive 

 areas in the West. Other human-related activities 

 such as clearing and fire have had sharper and 

 quicker effect, but the impacts of these have not 

 been so continuous, nor have they "affected such 

 large areas. 



The opening of closed communities of herbs 

 and shrubs has provided habitats for establish- 

 ment of new natural combinations of closely re- 

 lated species and ecotypes. Anderson (2, 3) calls 

 this "the hybridization of the habitats." ' 



Over thousands of years, climatic change and 

 the natural erosion associated with it have also 

 created conditions which have changed the struc- 

 ture of vegetation. Cottam (15) found that 

 change from a cooler to a warmer climate, be- 

 tween 7,500 and 4,500 years ago in Utah, affected 

 the structure of oakbrush. In this warm post- 

 pluvial period, Gambel oak (Quercus gambeli 

 Nutt.) and turbinella oak (Q. turbinella Greene) 

 existed together in north central Utah. In a 

 subsequent cooling period, turbinella oak receded 

 to southern Utah to the warmer temperatures to 

 which it was accustomed, and where it was more 

 at home with its true chaparral associates. How- 

 ever, Fi hybrids and some backcrosses that sur- 

 vived cooler temperatures show that it was pres- 

 ent more than 260 miles north of where it now oc- 

 curs. In its warmer climate of southern Utah and 

 northern Arizona, where turbinella oak is asso- 

 ciated with Gambel oak, similar hybrids and back- 

 crosses are found in abundance, some of them of 

 recent origin. These same crosses have been ar- 

 tificially made and validated by Cottam and his 

 associates. Since established hybrids can spread 

 and maintain themselves by root sprouting, they 

 persist indefinitely. No doubt, some clumps are 

 at least a few thousand years old. Stutz (55) sim- 

 ilarly points out the good possibility that cliffrose 

 and antelope bitterbrush were historically to- 

 gether in Montana and Idaho, and hybridizing as 

 they do where they grow together in Utah. Cool- 

 ing temperatures removed cliffrose, but the intro- 

 gressed glandular characteristics in its leaves were 

 retained in the more cold-tolerant bitterbrush. 



We have seen abundant incidence of polyploidy 



