Forest trends in Acadia National Park

Bietsch, Sam; Miller, Kate; Weed, Aaron; Seirup, Camilla

From the abstract: "The Northeast Temperate Network Inventory & Monitoring Program (NETN) has been monitoring forest health annually in Acadia National Park since 2006. NETN monitors a suite of site and vegetation measures across a network of 176 randomly located permanent plots in Acadia. Plots are sampled on a 4-year rotating panel, such that one quarter of plots are sampled every year, and each plot is sampled every 4 years. Currently each plot has been sampled at least 3 times, allowing us to begin examining forest trends in Acadia. Overall patterns indicate that forests are succeeding to older successional stages. While this pattern is most apparent on the east side of Mount Desert Island, signals of succession are evident park-wide. Shade tolerant species are increasing in abundance, while early successional species like paper birch (Betula papyrifera) are declining. Most notably, red spruce (Picea rubens) is increasing in abundance across all strata in the forest, including seedlings, saplings, and canopy trees. Red spruce is also the most abundant understory species, occupying nearly double the percent cover of the next most abundant species of black huckleberry (Gaylussacia baccata) and lowbush blueberry (Vaccinium angustifolium). Invasive species continue to be at low levels, with invasive species documented in only 5 out of 176 plots. Red pine (Pinus resinosa) mortality from red pine scale (Matsucoccus resinosae) has been observed in the most recent 4-year cycle, although less than 1% of trees monitored by NETN in ACAD are red pine. As long as forest composition metrics remain stable (e.g., no new invasive species, stable tree condition/ forest pests, and continued regeneration), late-successional structure is expected to continue developing over time."