islands in the lake, and among the few large islands in 

 the Prairie Pothole landscape of northeastern Montana, 

 particularly important in reducing mammalian 

 predation. 



LAND USE HISTORY: 



The island was not previously contiguous with the 

 mainland, but livestock were brought out prior to 

 Refuge establishment. The vegetarion-altering affects of 

 grazing history compared to raised water levels and 

 colonial bird use were not evaluated. Whatever the 

 cause (s), there are areas that are covered by nothing 

 but the exotic grasses Bromus memus (smooth brome) 

 and quackgrass {Elymus repens) to the extent that 

 native communities are not identifiable. Usually where 

 these grasses have invaded native commuruties, there 

 are vestiges of the native communities. 



MANAGEMENT COMMENTS: 

 Threats are posed to this whole landscape by exotics 

 and noxious weeds. Leafy spurge (Euphorbia esula) is by 

 far the most aggressive and tenacious of noxious weeds, 

 and is well established. It has a strong presence in the 

 southern end of the island. Several species of spurge 

 fleabeetles are established on the island (Rabenberg 

 pers. commun.) Their potential for curbing seed 

 production is particularly important because the seeds 

 of leafy spurge are readily disseminated by water and 

 wildlife vectors as whitetail deer and mourning dove. 



The far north and south ends have much Canada 

 thistle (Cirsium arvense) . Smooth brome (Bromus 

 inermis), quackgrass (Elymus repens), and crested 

 wheatgrass (Agropyron cristatum) are also present 

 throughout the island. Bromis ir\ermis appears to be 

 aggressively displacing Pascopyrum smithii from 

 Symphorkarpos occiderualis- and Pascopyrum smitbii- 

 dominated communities. Other common exotic grasses 

 include cheatgrass (Bromus tectorum) , Japanese brome 

 (Bromus japonicus) , fowl bluegrass (Poa palustris) and 

 Kentucky bluegrass (Poa pratemis). 



Exceptionally high litter accumulation levels were 

 noted over most of the Island in both grassland and 

 shrubland habitat. As mentioned previously, it is 

 possible that the extensive shrub cover of 

 Symphorkarpos occidermilis is an artifact of the land 

 being left idle. This same shrubland type is present in 

 trace amounts in Tepee Hills RNA, and though the 

 two sites have different settings and substrates, they 

 have some comparative value. The management 

 options for addressing these situations depends on 

 desired vegetation structure for wildlife and the 

 framework for integrating noxious weed management. 



Bruce's Island Research Natural 

 Area 



environment: 



Unlike Big Island, which is mostly low-lying terrain, 

 Bruce's Island is a ridgeline that had once been 

 cormected to the mainland, made up of a hump and 

 toeslopes together totaling 367 acres. It has little of the 

 microtopography patterns as found on Big Island. The 

 high shores on the north are eroding in places as 

 cutbanks, and the gentle toe slopes on the south are 

 temporarily inundated. Soils are mapped as Dooley fine 

 sandy loams on the high north end, Dimmick silty clay 

 in a low-lying middle band, and Williams loam, 

 undulating at the south end (Richardson and Hanson 

 1977). The controlled lake level affects the island 

 shore, regulated at the Lake Creek oudet, with a dam 

 and spillgate to artificially maintain lake levels. The 

 semi-arid continental climate has peak precipitation in 

 June followed by July and May, and a mean annual 

 precipitation of 13.25 inches (Climate data from 

 Medicine Lake, Western Regional Climate Center, 

 1911-1997). 



Note: This area and two others in Medicine Lake are 

 part of the 11,366 acres designated as Medicine Lake 

 Wilderness Area. 



VEGETATION: 



Approximately one half of Bruce's Island on the higher 

 elevations of the north has been plowed. In this area, as 

 well as unplowed uplands, Agropyron cristatum (crested 

 wheatgrass) is the prevailing cover type. As a whole, 

 the uplands have been sufficiently altered so that they 

 no longer support intact native vegetation, instead 

 reduced to small, irregular patches of native species 

 among the exotics. The potential prevailing matrix 

 community type of the uplands is probably western 

 wheatgrass - blue grama - threadleaved sedge grassland 

 (Pascopyrum smithii - Bouteloua gracilis - Carex filifoUa 

 Herbaceous Vegetation) or western wheatgrass - 

 needle-and-thread grassland (Pascopyrum smithii - Stipa 

 comata Herbaceous Vegetation). Sample plots were not 

 established in the course of field reconnaissance of this 

 RNA because of the lack of intact vegetation. 



The lower lying terrain on the island's southern 

 portion, particularly along the shorelines, has well- 

 developed palustrine emergent vegetation. Inland 

 saltgrass (Distkhlis spkaia) is among the most extensive 

 wetland vegetation types, occurring predominantly as a 

 broad ecotone between wetter sites dominated by 

 bulrush (Scirpus spp.) or alkali cordgrass (Spartina 



45 



