BIRDS OF THE ST. CROIX RIVER VALLEY 



7 



prairie and deciduous forests. Originally, oak barrens and savannah oc- 

 curred throughout this area. 



Mississippi River Sand Plains Section. —This section includes a small por- 

 tion of northwestern Washington and southwestern Chisago counties where 

 topography is characteristic of glacial outwash plains— including broad, flat 

 areas with occasional wetland basins interspersed. Original vegetation of 

 the sand outwash soils was primarily oak forest with scattered prairie open- 

 ings and wet prairie in depressions, 



Grantshurg Section.— This section includes most of Chisago County and a 

 small part of southern Pine County. Topography is characterized by flat to 

 gently rolling glacial sediments that are frequently dissected by streams. 

 The Grantsburg section includes the bed of Glacial Lake Grantsburg, which 

 extended eastward into Burnett County, Wisconsin. Vegetation originally 

 included Jack Pine Barrens and scattered oak openings. Currently, much of 

 the land is in agricultural production. 



Mille Lacs Section.— This section includes most of southern and all of 

 northern Pine County. Topography is characterized by glacial scoured bed- 

 rock and glacial till that provide a kettle and knob topography. Forest-bor- 

 dered lakes are numerous throughout this section. Vegetation is charac- 

 terized by mixed northern hardwood and coniferous stands with conifer 

 bogs interspersed throughout. 



The classification system used in Wisconsin (Martin 1932) is based pri- 

 marily on physiographic features and bedrock geology, regardless of vegeta- 

 tion. However, the influence of physiography on vegetation is well demon- 

 strated in Wisconsin because the regions that occur in the Valley each sup- 

 port entirely different vegetative communities. Martin considered five dis- 

 tinct physiographic provinces in Wisconsin and the Valley is included in 

 three. 



Western Upland. —This region in the Valley is the northern extension of 

 the Driftless Area, a part of Wisconsin, Minnesota, and IlUnois that was not 

 covered by glacial ice. Included in the Western Upland are the highly dis- 

 sected stream valleys adjacent to the St. Croix River and the broad and 

 gently rolling glacial outwash plain of central St. Croix County. Original 

 vegetation included Southern Oak Forest in the dissected area and Tall 

 Grass Prairie associated with the outwash plain. At present, much of the 

 Western Upland is in agricultural production. Portions of central St. Croix, 

 southern Polk, and central Washington counties are dotted with numerous 

 natural basin wetlands. 



Central Plain. —This region includes northern St. Croix, southern Burnett, 

 and most of Polk counties. Topography of the Central Plain is also charac- 

 terized by broad glacial outwash plains lying over Cambrian sandstone in 

 the southern regions. Extensive areas of kettle and knob topography asso- 

 ciated with end moraines occur in the north. Numerous lakes and bogs are 

 associated with this topography. Vegetation consists of a mixture of south- 

 ern oak forest, prairie and northern mixed hardwood, and coniferous forest. 



Northern Highland.— This region, which includes northern Burnett and 

 southern Douglas counties, has topography characteristic of morainal 



