Climate Change Impacts in Alpine Meadows: Environmental Factors Correlated with the Decline of the Olympic Marmot (Marmota olympus) Population in Olympic National Park, Washington State

Abstract

Climate change is rapidly altering the environmental template globally, and detrimentally impacting the structure and function of both plant and animal communities locally. Endemic and high alpine species are especially vulnerable to these changes because of climate change impacts on the persistence of suitable habitat distribution and availability. The endemic Olympic marmot (Marmota olympus) population of Olympic National Park (ONP) has declined by ~50% in the past 30 years. Because the Olympic marmots are an ecologically important and charismatic species, it is important to determine what meadow conditions are correlated with their persistent occupancy and what conditions contribute to their decreasing population sizes and distribution range. If marmots are to be locally reintroduced into these alpine meadows, understanding what conditions cause marmots to abandon a specific meadow because it is unsuitable for their survival is also important. A rich data set on Olympic marmot distribution and natural history exists; however, information is currently lacking on the impact of climate change on the meadow conditions that may cause marmot sub-populations to disappear from meadow habitats they have historically occupied. This research project builds on occupancy monitoring and distribution data collected by the ONP- led marmot monitoring citizen science project and focused primarily on understanding which meadow characteristics were correlated to high marmot occupancy rates. The overarching research questions were: 1) Why are marmots disappearing from some meadows but not others? and 2) Specifically, are there certain habitat characteristics, or a range/threshold within each meadow that are correlated to a meadow’s suitability for occupancy by marmots? To address these research questions, an analysis of habitat characteristics was conducted. The following were the primary areas of focus: identification of variables or combination of variables (e.g., elevation, aspect, availability of food in meadows, tree encroachment rates into meadows, and predation risk--visual obstruction) that constitute habitat conditions that are correlated with high marmot abundance; and determination of habitat and/or environmental thresholds that may trigger meadow abandonment by marmots. To assess habitat differences between the abandoned meadow habitat units and those that were still occupied, a semi-randomly selected subset of alpine meadows was examined on the eastside of the Olympic mountains. The regression tree approach was used in this study to search for potential thresholds in the measured variables that relate to marmot occupancy. Multi-variant spatial analyses were used to compare the characteristics of meadows that were occupied and not occupied by marmots. Preferred habitat for marmots included meadows with a high proportion of herbs, grass and shrub as a dominant ground cover type, as well as a total meadow area of 3.5 hectares or larger in size. The highest marmot occupancy rates were found at elevation ranges between 1,676 and 1,829 meters and in meadows that had ~25% or less obstruction of the marmot’s view of the meadow (and prospective predators’ view of the marmots). This research identified environmental conditions and thresholds at which Olympic marmot subpopulations were more likely to persist and continue to occupy high alpine meadows. This research also established important baseline vegetation data and research ground plots to track habitat changes over time.