Monitoring vegetation change in coastal marshes of Southwest Alaska, 2007–2018

Hannam, Michael; Miller, Amy; Walton, James

doi:10.36967/nrr-2280108

Coastal marshes and meadows cover a small area in Southwest Alaska Network (SWAN) parks but are heavily used by wildlife, migratory birds, and park visitors. They are of particular value to brown bears, which frequent them for early season forage, and critical mating and rearing habitat for their young. To understand how coastal marshes are changing through time, and to inform park planning and decision making in these valued habitats, the SWAN monitors vegetation composition at three sites at Katmai (KATM) and Lake Clark (LACL) national parks and preserves (Jorgenson & Miller 2010). In 2007 and 2008, we conducted baseline monitoring at these sites in LACL and KATM, respectively, and in 2018, we resurveyed the sites in our first 10-year revisit to measure change. We also added three new monitoring sites in Kenai Fjords National Park (KEFJ) in 2018. Our results from the 2018 resurveys in LACL and KATM showed that, in general, plant communities have remained relatively stable between the 2007–2008 and 2018 sampling events. However, we also recorded localized and broad-scale changes across the sites. The habitat divisions and floristic classes identified in 2007–2008 by Jorgenson et al. (2010) still capture more than half of the variation in community composition among plots. However, we measured an increase in cover of vascular plants in 2018, and isolated cases of community-level change, indicated by a change in some floristic classes between 2007–2008 and 2018. The widespread increase in vascular plant cover that we observed between 2007–2008 and 2018 may have resulted from an earlier green-up in 2018, and/or from increases in productivity during the decade between the first and second sampling dates. Although we cannot infer a trend from two points in time, the changes recorded from our field measurements between 2007–2008 and 2018 are largely consistent with the longer-term ecosystem changes reported by Jorgenson et al. (2010) in their comparison of images from the 1950s, 1980s and early-mid 2000s. These changes, interpreted from imagery (Jorgenson et al. 2010), included vegetation establishment on barren substrates (e.g., beach berms), drying and infilling of ponds, and expansion of spruce cover on outer beach ridges. Our field data from 2018 likewise showed rapid colonization of beach dunes and mudflats, increases in spruce cover, and expansion of shrubs at upper meadow margins. Our results suggest that coastal marshes have not undergone site-wide changes in the last decade but may be showing changes in localized areas, consistent with changes reported over the last half-century by Jorgenson et al. (2010).

Monitoring vegetation change in coastal marshes of Southwest Alaska, 2007–2018

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