Ecosystems: Objectives for Sustaining Biodiversity proper functioning condition

Abstract—Recognizing the historical abundance of major vegetation cover types is the foundation for estimating the magnitude and significance of conversion from one cover type to another and the proportion of existing cover types that are in properly functioning condition. Techniques to determine desired conditions are discussed. Existing situations for the need to treat ecosystems where aspen (Populus tremuloides Michx.) occur are prioritized: highest—mixed-conifer with aspen but where conifers comprise greater than 50 % of the canopy; high—aspen/sagebrush transition; and moderate—aspen dominated landscapes. Though aspen stands are evaluated, aspen landscapes are discussed in the context of aggregations of many stands. Within aspen dominated landscapes, five risk factors help determine the need for action: (1) conifer understory and overstory cover is greater than 25%; (2) aspen regeneration (5–15 feet tall) is less than 500 stems/acre; (3) aspen canopy cover is less than 40%; (4) dominant aspen trees are greater than 100 years old; and (5) sagebrush cover is greater than 10%. Management recommendations for treatments, as well as examples of successes and failures of efforts to restore aspen ecosystems, are summarized. Actions to restore aspen ecosystems must not be taken before excessive browsing by livestock and wildlife is addressed