Other Vegetation Types: In the lost portions of the 

 landscape where the water table is shallow, subirrigated 

 conditions are found. In such settings with soils that are 

 salt-affected, inland saltgrass (Distichlis spicata) forms 

 extensive and nearly pure communities or occurs in 

 various mixes with Nuttall's alkaligrass (Puccinellia 

 nuttalliana), prairie cordgrass (Spartina pectinata) or 

 scattered black greasewood (Sarcobatus vermiculatus) . 

 Another wetland association of Baltic rush - clustered 

 field sedge (Juncus balticus - Carex praegradlis) occurs 

 in alkaline habitats as stringers or small patches that 

 are a few tenths of an acre. Kentucky bluegrass (Poa 

 pratensis) often establishes and outcompetes the natives 

 in this habitat. Wet areas that are not so salt-affected 

 have Spartina pectiriata dominant, with or without an 

 abundance of common reed (Phragmites communis) . 



On the island's west shore there is a mix of woody 

 species and communities that may be more a result of 

 past, or ongoing, disturbance than any intrinsic site 

 differences. Associated with near-shoreline locations 

 and ostensibly subirrigation are several stands of 

 common chokecherry (Prunus virginiana) , some 

 serving as nesting sites and perches for black-crowned 

 night herons. They have a margin and sometimes a 

 low-shrub layer of western snowberry (Symphoricarpos 

 occidentalis) and herbs that are mainly non-native 

 grasses. Also present is a band of black greasewood 

 (Sarcobatus vermiculatus), largely dominated by 

 exotics such as Agropyron cristatum or opportunists 

 such as Hordeum jubatum and H. brachyantherum. 

 This vrgetation type is usually present only on the 

 shores of alkali lakes, perhaps reflecting the original 

 nature of Medicine Lake. 



On the sandiest substrates associated with needle-and- 

 thread (Stipa comata) -dominated communities were 

 fragments of associations codominated by prairie 

 sandreed including Calamovilfa longifolia - Carex 

 stenophylla and Calamovilfa longifolia - Pascopyrum 

 smithii plant associations. These were too small to map 

 other than noting as inclusions. The abruptness of the 

 transition between the Stipa- and these small 

 Calamovilfa-dominated communities was noted with 

 no discernible soil or other enviromental differences to 

 account for the pattern. 



Some of the most heavily-used wildlife habitat has no 

 associated native vegetation. The places of 

 concentrated nesting by the American white pelican 

 colony shifts over time, and the history of use has 

 created areas with extensive bare ground and patches 

 of annuals/biennials, often dominated by flixweeds 

 {Descurainia sophia and D. pinnata.) 



Two Montana plant species of special concern were 

 documented on Big Island. Site information is 

 presented on the Element Occurrence Records in 

 Appendix E, and annotated illustrations are in 

 Appendix F. 



Hairy four o'clock (Mirabilis hirsuta) is represented by 

 widely scattered plants in very low numbers at different 

 ends of the island, among plant associations dominated 

 by both prairie sandreed {Calamovilfa longifolia) and 

 needle-and-thread (Stipa comata). It has the lack of 

 habitat specificity on Big Island and in the Sandhills 

 that is characteristic of adventive species. While it is 

 only known from 3 different counties in Montana, 

 there have been reports that it is adventive and more 

 common than records indicate. This study lent support 

 to the case for moving it off to the watch list. 



Plains phlox (Phlox andicola) occurs on the north-facing 

 slopes of the knoll on Big Island. It is likely to be 

 scattered across most of this slope, but the species was 

 at the very end of flowering at the time of visit, so it 

 could not reliably be located to determine population 

 numbers and extent. It, too, is present on the 

 Medicine Lake Sandhills. In general, it is restricted to 

 sandy soils and was previously known in Montana only 

 from southeastern counties. The numbers of records in 

 recent years provides the basis for changing its state 

 rank from SI to S2 (potentially imperiled) ; this rank is 

 subject to review with additional fieldwork in early 

 summer. 



OVERALL BIODIVERSITY SIGNIFICANCE: 

 Big Island RN A supports a spectrum of community 

 types, from slivers of typical prairie wetlands with 

 Spartina pectinata and Distichlis stricta to dry prairie and 

 to tall shrub copses. This community diversity affords a 

 wildlife habitat diversity, even if the plant associations 

 are not rare or in noteworthy condition. The complex 

 mosaic of communities may not representative of the 

 distribution of these communities in the local landscape 

 due to the regulated 

 lake water level. 



Wildlife values were not evaluated, though it has 

 previously been noted that Big Island harbors nesting 

 subpopulations of piping plovers, federally listed as 

 threatened, a population of black-crowned night herons 

 and a large colony of American white pelicans, both of 

 which are state species of special concern. It is 

 productive for waterfowl and sharp-tailed grouse 

 nesting. Big Island directly contributes to the core 

 waterfowl production mandate, as well as providing 

 habitat for colonial nesting birds. It is one of two major 



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