53 



periodic environmental fluctuaticxTS which could cause 

 Vcirying populaticHi sizes. 



b. Seed viability and longevity: No detailed quantitative 

 informatics; because H. aquatilis is an annucil species 

 which occurs in vernal wetlands, its population sizes 

 fluctuate from year to year d^aending cr\ seasoncil 

 ccnditions. For exanple, at the Swan River OidxM 

 (005) site in Montana, approximately 10,000 plants were 

 observed in 1985, but fewer than 100 plants were seen 

 in 1986 (Lesica et al. 1987). During field surveys in 

 1987, the population was very leunge again, with many 

 hundreds of plants observed. Ttjese observations 

 suggest that some seeds can remain viable for at least 

 two yeeurs. 



c. DomEincy requiranents: Unkncvni. 



d. Germinaticn requirancnts: For seeds to germinate, 

 water nust be present in the vernal ponds and wetlands. 

 In addition, H. aquatilis is found almost exclusively 

 in ponds with bottom surfaces which consist of firm, 

 consolidated clay and orgemic sediments. Only in two 

 cases in Montana were pleints found in ponds with 

 deeper, laur^gely unconsolidated bottom sediments; in 

 these situations, most tj. acfuatilis plsmts were then 

 found in shallower eureas near the shore, in more 

 consolidated portions of the ponds. Ihe texture and 

 depth of these bottom sediments may be very iiiportant 

 in relation to seed germination requirements emd early 

 growth of t}. aquatilis . Lsose, silty soil sediments 

 may lead to burial of seeds too deeply to ensure 

 efficient gemiination and establishment. 



e. Beroent germination: No quantitative information. 



5. Seedling ecology: See germination requirements described 

 above. 



6. SurvivEd and nature of mortality: No quantitative 

 information; the plants occur predomineintly in more open 

 areas within the habitat, and some seedling mortality in 

 densely vegetated areas would be expected. 



7. Overall assesanent of taxon's reproductive success: 

 R^roduction appears to be vigorous in most populaticaTS in 

 Montana, when habitat conditions aupe satisfactory. In seme 

 pc»ids the plants have been observed to produce very dense 

 mats, and the seed output in these cases is probably high. 

 Prevailing ecological conditions (especially climate) are 

 probably most iitportant in determining annual rates of seed 

 production and germination. Observations of the Idaho 

 population have revealed that Howellia aquatilis has been in 

 the same pond at the site for at least 20 years. 



