Minnesota moose population: using forest inventory data to assess changes in habitat

A preliminary analysis of changes in forest habitat in northeastern Minnesota suggests reduced acreage in recently disturbed and young forest as a contributing factor in moose population decline. This report also describes how available data can be used to characterize habitat conditions. Introduction: A January 2013 aerial survey of moose living in the primary habitat zone of the Arrowhead Region of northeastern Minnesota (Figure 1), suggests that numbers have declined from more than 4,230 individuals in the 2012 census to just 2,760 individuals in 2013, a 35% loss (DelGiudice 2013). The Minnesota Department of Natural Resources (MN DNR) has indicated causal factors of potential interest include disease, parasites, and habitat change. While there is no recent evidence to suggest that habitat alone has limited moose numbers in Minnesota, habitat quality and spatial arrangement can limit the population within a smaller geographic area (Moose Advisory Committee Report [MAC] 2009). This study examines the relationship between recent changes in Minnesota's moose population and changes in forest and related aquatic habitat. The literature indicates new growth in young and regenerating forests is an important summer food source contributing to the success of moose over the winter months when available food sources are typically insufficient to maintain body mass (Franzmann et al. 2007, Lenarz et al. 2011, Peek et al. 1976). Peek et al. (1976) found that the leaves of young quaking aspen, willows, and paper birch were the most important food sources for moose in northeast Minnesota from June to September; almost 60% of moose nutrition was gained from eating leaves of these three species during the summer. Other species, including aquatic vegetation and small diameter twigs and shoots, are also important at various times of the year. Figure 1: Moose Habitat Zones in northern Minnesota. Primary habitat zone data (circa 2010) courtesy of MN DNR Data Deli. Secondary habitat zone adapted from MAC (2009). Methods and Results: The US Forest Service Forest Inventory and Analysis (FIA) unit gathers data from 1,258 permanent sample plots within the primary moose habitat zone over a 5-year cycle. The current annual inventory began in 1999, with one-fifth of the field plots measured each year. The first full sampling cycle was completed for the 2003 inventory year. Thus, FIA data are an average of conditions over the reporting year plus the previous 4 years. Each FIA plot includes four subplots covering 0.0415 acres per subplot (O’Connell et. al. 2012). For the cycle ending in 2011, there were 224 FIA plots in the primary moose habitat zone with a nonforested condition code. Of these The authors are research fellow and professor, Department of Forest Resources, College of Food, Agriculture and Natural Resource Sciences, University of Minnesota. Research supported by the Department of Forest Resources and the Interagency Information Cooperative.