55 



It is hypothesized that this senescent period 

 could correspond with the dry summer months; 

 with new growth appearing in the fall after the 

 onset of cool, moist weather, and a shortening 

 of the photoperiod. See Appendix C, p. 70, for 

 complete details of the study. 



6. Survival and mortality: Populations of S. 

 spaldinqii . that in previous years were quite 

 large, had declined in size range-wide in 

 Montana according to monitoring studies 



(Lesica, 1988) and field surveys in 1988. This 

 change in abundance is thought to be due at 

 least in part to current drought conditions. 

 See Appendices A and B, pp. 68 and 69, for more 

 complete details. 



7. Overall assessment of taxon's reproductive 

 success: Fluctuations in population sizes have 

 been attributed to the prevailing drought 

 conditions in Montana. No juvenile plants were 

 observed in 1987; hov/ever, new adult plants 

 were observed in 1988. It is possible that 

 these plants were overlooked the first year, 

 but it is more likely that the juvenile plants 

 loose their leaves during the warm, dry summer 

 months and are thus missed when the transects 

 are read (Lesica, 1988) . Silene spaldinqii 

 appears to have good reproductive potential 

 where there is a stable native habitat, but it 

 is likely to be affected by drought conditions. 



8. Population ecology of the taxon. 



A. General summary: Silene spaldinqii occurs on north- 



to east-facing slopes and draws, in rough fescue 

 (Festuca scabrella ) grasslands. Cover of grasses at 

 these sites is generally quite high, and the species 

 thus appears to tolerate competition and some 

 shading. Much of the suitable habitat in the 

 vicinity of the Niarada populations is on private 

 land that has been heavily grazed. The result has 

 been a conversion of native grasslands to vast 

 tracts covered by stands composed of five or six 

 exotic weedy species. No S. spaldinqii populations 

 were found in these areas. Thus it mgiy be that 

 grazing alters the native habitat so as to eliminate 

 or prevent establishment of the species. 



B. Positive and neutral interactions: None known. 



C. Negative interactions. 



