Ostlie, W.R. 1990. Completion of the algific slope/maderate cliff landsnail survey in Minnesota. Final report submitted to the Minnesota Department of Natural Resources. Unpaged.
Algific (cold-producing) talus slopes and maderate (cold-water) cliffs are the two most important natural communities in central North America in terms of biological diversity. Among the inhabitants of these communities are many glacial relict plant and landsnail species, left-overs from the Wisconsinan glaciation (14,000 YBP). Some of the snail species (e.g. Vertigo hubrichtii and Discus macclintockii) were believed to be extinct prior to the discovery of live counterparts on these communities. Also located in these isolated cold-air pockets are several additional elements that are candidates for federal listing, all requiring the equably cool summer/winter temperatures that were widespread during the Pleistocene. Algific slopes and maderate cliffs which mimic the equably cool summer/winter temperatures of the Wisconsin glaciation, provide the only remaining suitable habitat for these rare species.