Conservation of the community/ecosystem level of biological organization is a key component of a comprehensive approach to biodiversity conservation. The Conservancy and its Natural Heritage Program partners have completed a national classification of ecological communities. These types have been preliminarily ranked in terms of their rarity, using a scale from G1 (Global 1, critically imperiled globally due to rarity, endemism, and/or threats) to G5 (little to no risk of global elimination). Currently, approximately 144 G1 - G3 communities are known from the Northern Great Plains region, where a region-wide management review is underway by the Great Plains program of the Nebraska National Forest. A total of 52 G1 and G2, as well as eight G3 communities, were described in a previous report (Faber-Langendoen et al. 1997). This report serves as an addendum to the 1997 effort, providing descriptions for an additional 28 shrubland and grassland communities ranked G3-G5. These descriptions should allow for improved inventory of these types, thereby leading to a future refinement of the preliminary global rank, as well as guidance on conservation actions. Fifteen additional shrubland and grassland types were researched and tentatively described. This process brought to light classification issues that forced these types to be "archived" until additional research can resolve specific classification issues. These tentative descriptions are included as an appendix to help document the classification process and status.