Medicine Lake National Wildlife Refuge 



Big Island Research Natural 

 Area 



ENVIRONMENT: Big Island RNA is the second 

 largest of two major islands in Medicine Lake at 25 1 

 acres. It has a knoll on the south end that rises 35 ft. 

 above the lake, and two distinct wetland swales north 

 of the knoll, but most of the island is less than 10 feet 

 above lake level and gently rolling. A large bay at the 

 south end is set off by two long isthmuses that are at or 

 below the lake water level and covered mairJy by 

 robust grasses. The island is mapped as Blanchard fine 

 sand, 4-20% slope (Richardson and Hanson 1977) 

 though most of the island soils appear to be loamy 

 sands; possibly with glacial till on the knoll at the south 

 end. The controlled lake level affects the island shore, 

 regulated at the Lake Creek outlet, 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: 



The array of plant communities forms a grassland- 

 shrubland mosaic. It can be explained by both small- 

 scale relief as evidenced in height above the lake level, 

 which need vary only a fraction of a foot in order to 

 influence vegetation, and by soil texture. See Figure 2 

 for an occurrence map of Big Island vegetation types. 



Symphoricarpos occidentaUs Shrubland 



[SYMOCC] 



western snowberry shrubland 



Western snowberry shrubland constitutes the most 

 extensive vegetation type on the island and is among 

 the most common shrub communities in the Northern 

 Great Plains. Across the island it occurs on gently 

 undulating topography and swales, some of which may 

 be seasonally inundated, intermittently flooded, or 

 subirrigated via subsurface coimection to Medicine 

 Lake. It has been characterized in regional 

 classifications as a "temporarily flooded" system, but 



this is the case on Big Island only when ground thaw is 

 delayed. As noted by Hansen et al. (1995) and 

 exemplified on Big Island, it spans an environmental 

 range from mesic upland slopes to wetlands (hydric 

 soils and wetland hydrology). Almost none of the sites 

 in the RNA would qualify as jurisdictional wetlands 

 because the dominant, western snowberry 

 (Symphoricarpos occidentaUs) , and all associated species 

 including western wheatgrass (Pascopyrum smithii), 

 smooth brome (Bromus inermis), and Kentucky 

 bluegrass (Poa pratensis) are rated FACU (Facultative 

 Upland, i.e. only occurring in wedands less than 33% of 

 the time and conferring no wetland status) by the U. S. 

 Fish and Wildlife Service. 



This type has nearly continuous cover of 

 Symphoricarpos occiderualis, a shrub that produces 

 sucker shoots emanating from stout, spreading 

 rhizomes. Given the density of Symphoricarpos 

 occidentaUs, it is perhaps not surprising that the only 

 other native species found with regularity are also 

 rhizomatous (mentioned above) . Weedy species such as 

 flixweed tansymustard (Descurainia sophia) , pinnate 

 tansymustard (Descurairua pinnata) , and leafy spurge 

 (Euphorbia esula) occur in patches, perhaps areas 

 formerly disturbed. The Euphorbia esula is widespread 

 on the island in these relatively moist commuruties and 

 appears to be expanding, forming dense clones. Several 

 species of spurge fleabeetles have been introduced on 

 the island to provide leafy spurge control. 



Ordinarily Symphoricarpos occideruaUs shrubland occurs 

 in small stands rather than as a prevalent vegetation 

 feature. It is recommended that recent aerial 

 photographs of the island be compared with historic 

 photos if it is possible to determine from them whether 

 shrubland has been present since early years of Refuge 

 establishment. A literature review and dialogue with 

 other refuges of species' management responses and 

 wildlife benefits or deterrents might also be helpful in 

 applying current vegetation information to wildlife 

 management and noxious weed management matters. 



Stipa comma - Bouteloua graciiis - Carex f^oUa 



Herbaceous Vegetation 



[STICOM - BOUGRA - CARFIL) 



needle-and-thread - blue grama - threadleaved sedge 



41 



