Over the 5 years, differences between the shortest and longest periods of active 

 growth averaged 28 days for forbs and 43 days for the grasses. Generally, the period 

 of active growth varied least between years for those species that have short growth 

 periods; it varied most for those species that have long growth periods. 



Although most species apparently became dormant for the remainder of the year 

 following drying, several produced new leaves again in the fall. Geum, Saxifvaga, 

 Cerastiim, and the five grasses shown in figure 2 had this habit. Fall regowth in Geum 

 and Saxifraga was in the form of a small rosette of new leaves within the outer rosette 

 of dried leaves. Holway and Ward (1965) noted this characteristic on Saxifraga 

 rhomboidea growing in alpine tundra. Regrowth of Cerastium was in the form of small 

 leaves in the axils of the dried leaves distributed along the stems. This regrowth 

 usually persisted over winter and appeared to become active again when growth resumed 

 the following spring. 



Plant development was delayed on northeast exposures and at the higher elevation 

 (table 4). Some species were affected by these environmental differences much more than 

 others. Depending on species, the start of growth averaged 3 to 12 days later on north- 

 east exposures than on southwest exposures. Oxytropis was an exception; start of 

 growth for this species was delayed an average of 18 days. The general trend was for 

 plants to develop about 1 week later on northeast exposures than on southwest exposures. 

 This difference persisted throughout the growing season. Costello and Price (1939) 

 observed that development on north exposures lagged about 10 days behind that on south 

 exposures on mountain herblands in Utah, whereas Bliss (1956) found only a 2- to 4-day 

 lag on north exposures in the alpine tundra of southern Wyoming. 



For individual species, a 1,100-ft. elevational difference delayed beginning of 

 growth from 19 to 37 days (table 4), an average delay of 28 days for all species. 

 Plants at the higher elevation generally developed more rapidly than those at the 

 lower; by the time of flowering, this delay was reduced to an overall average of only 

 21 days. At the 8,200-ft. elevation, plants dried an average of only 16 days later 

 than at 7,100 ft. The lag in plant development attributed to elevational rise in this 

 study is considerably greater than the 10 days per 1,000 ft. suggested by Hopkins' 

 Bioclimatic Law (Hopkins 1938). It is also greater than the average 12 days per 1,000 

 ft. observed by Costello and Price (1939) in the mountains of Utah and the average 

 10-day delay in lilac bloom for each 1,000-ft. elevational rise in Montana (Caprio 

 1966). This difference in findings might be the result of unusually late snowmelt at 

 the higher elevations on this study area in southwestern Montana. Costello and Price 

 (1939) found that date of snowmelt and onset of growth were closely related, and Holway 

 and Ward (1965) considered snow cover the primary factor influencing phenology of 

 alpine tundra. The response of individual species to elevational differences varied 

 considerably, as Costello and Price (1939) also observed. Growth of Antennaria and 

 Stipa appeared least affected by elevational differences. The beginning of growth for 

 these two species was delayed only about 20 days; flowering of Stipa, 15 days, and of 

 Antennaria , 11 days. Growth of Lomatium appeared to be most affected by elevation; 

 both the start of growth and flowering of this species were delayed an average of 37 

 days by the 1,100-ft. increase in elevation. 



Differences between exposures in the duration of plant growth varied greatly among 

 both species and years. This was also true for differences between elevation. No 

 consistent overall difference in growth duration was apparent between exposures; 

 however, the growth period was generally about 1 week shorter at 8,200-ft. than at 

 7,100-ft. elevation. For species common to both elevations, the growth period averaged 

 94 days at 8,200 ft. and 103 days at 7,100 ft. 



12 



