13 



3 SOIL relationships: This species is restricted to extremely 

 sandy soils that have little or no soil development 

 tJntisols); generally characterized as "open, sandy sites" 

 (Great Plains Flora Association 1986) . 



4 CLIMATE FACTORS: The aridity of the Great Plains 



• continental climate is a central factor m ^^^f ^^^^ °^^ , 

 maintaining the early successional open quality of Annual 

 bursage habitat. 



F. POPULATION DEMOGRAPHY AND BIOLOGY 



1 PHENOLOGY: Annual bursage was barely beginning to set fruit 

 on 17 August, 1993. Flowering and fruiting activity was at 

 least two weeks delayed in the cool, wet growing season of 

 1993 The range of collection dates for this species ranges 

 from' early August to early September, taken to reflect the 

 period in which fruits can be found. 



2 POPULATION SIZE AND CONDITION: A population estimate of 

 ■ over 1000 individuals was made at the Little Muddy Creek 



site the only Montana site at which population size has 

 been noted. The plants were in patchy distribution, with 

 hundreds present or none at all. Since this species is an 

 annual, its numbers are expected to vary from year to year. 



3 REPRODUCTIVE BIOLOGY: Flowers are wind-pollinated. Seeds 

 are most effectively distributed by adhering to the fur of 

 animals . 



G. POPULATION ECOLOGY 



1. BIOLOGICAL INTERACTIONS 



a COMPETITION: This species is found only in early-succession 

 settings, indicating that it is not competitive with the 

 climax plant species. 



b. HERBIVORY: There were no signs of any browse to this species 



., ~"' ~7.'jII__ j.._T r. ,,^^^ K,, c^i-,c»or^ in -t-hf^^iT- loafina on loose 



sand, 



the Little Muddy Creek site though it occupies habitat 

 t is intensively used by sheep in their loafing on loo 

 d. 



c. OTHER: The spines of the seed are taken to represent an 



adaptation to seed dispersal by animals. Such _ spmy-seeded 

 plants are often a concern in livestock operations as 

 ^ causing injury with ingestion, but Annual bursage is not 



W) palatible and is habitat that is so sparsely vegetated that 



livestock injury is unlikely. 



