Forest health monitoring at Sleeping Bear Dunes National Lakeshore: 2018 field season

Sanders, Suzanne; Kirschbaum, Jessica

Long-term monitoring of forest health provides managers with routine updates on which to base management decisions. Long-term monitoring can also be used to tease apart impacts and elucidate causal agents when novel problems or situations arise. Perhaps more importantly, monitoring can serve as an early warning of potential issues. This is especially true in areas experiencing new and changing stressors. Sleeping Bear Dunes National Lakeshore (SLBE) protects over 27,000 ha of forests in northern lower Michigan. Here, a range of stressors, including climate change, high deer browse pressure, beech bark disease (BBD), and exotic earthworms are affecting park forests. We initiated a comprehensive forest monitoring program at Sleeping Bear Dunes National Lakeshore in 2009 with the establishment of 50 permanent plots; in 2018, we resampled these plots. Sampled and derived metrics included trees (density and basal area of live trees, seedlings, and snags), understory (frequency), browse (bite marks on woody species and presence and height of herbaceous species), richness, multivariate community change, and earthworm impacts. In 2009, we classified plots into one of four broad forest types: Red Maple-Beech-Mixed Hardwood, Sugar Maple-Beech, Balsam Fir-Mixed Conifer, and Pine. Within each of the forest types, overall tree density changed little between the sampling periods. Across all forest types, density of live F. grandifolia increased from 408 trees/ha to 459 trees/ha between the two sampling periods. Like density, basal area changed little between sampling periods for all forest types, except Pine. Here it increased from 21 ± 5 m2/ha to 25 ± 5 m2/ha. Across all forest types, basal area of F. grandifolia decreased 4.5% to 6.64 m2/ha. Basal area of standing dead F. grandifolia nearly tripled, from 0.32 m2/ha to 0.95 m2/ha. White-tailed deer browse was notable in the park. We recorded bite makes directly visible on woody species within each of 30 browse circles per plot. This occurred in greater than 30% of circles for only three species: Sambucus racemosa var. racemosa (36%), Pinus strobus (35%), and Populus grandidentata (34%). Browse on herbaceous species was assessed indirectly, by determining the frequency of presence in 30 quadrats per plot, for 16 preferred browse understory species. For each plot, we summed the frequencies of these 16 species. For sites on the mainland and on North Manitou Island, the summed frequency of presence of preferred herbaceous species decreased 30% and 15%, respectively. There was no change at sites on South Manitou Island. The only broad-scale incidence of disease was BBD with signs and/or symptoms observed on 85% of F. grandifolia individuals. Generally BBD impacts were not observed on individuals smaller than about 4 cm DBH. Of the 50 total plots, 11 did not show any evidence of earthworm invasion, while six were heavily invaded. Earthworm-free and minimally invaded plots were dispersed throughout the park. Currently, the most significant threat to SLBE forests is the impending impacts of BBD. The park is engaged in a joint beech restoration effort with Pictured Rocks National Lakeshore. While a small fraction (<1%) of naturally-occurring beech trees are resistant to the scale, the overarching goal of the program is to propagate and cross this material, so that disease-resistant stock can be outplanted into the forest. The park should make every effort to ensure continuity of this project, as this will be one of the best ways to promote overall forest integrity.

Forest health monitoring at Sleeping Bear Dunes National Lakeshore: 2018 field season

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