Forest health monitoring at Voyageurs National Park: 2015–2016 field seasons

Sanders, Suzanne; Kirschbaum, Jessica

Forest health monitoring programs can provide routine feedback of key indices, such as forest structure and species richness, and provide managers with periodic updates of ecosystem health. This is particularly relevant within the southern boreal forest where many species are near their southern range limits, and compositional change is expected to be great. Voyageurs National Park is situated within the southern boreal forest and the suitable habitat for most of its common overstory species is expected to shift northward and out of the park as environmental variation progresses. A comprehensive forest monitoring program was initiated at Voyageurs National Park in 2008 with the establishment of 37 permanent plots; between 2015 and 2016 we resampled the original 37 plots and installed 16 more, bringing the total to 53. We classified plots into one of five broad forest types, and present the current status, and short-term change, of multiple metrics of forest health. Forests in 2015/16 forests are dominated by Abies balsamea (L.) Mill (balsam fir) in all five forest types, with Acer rubrum L. (red maple) generally being the most abundant hardwood. Fire-adapted species, Pinus banksiana Lamb. (Jack pine) and P. resinosa Aiton (red pine) were only present as a few scattered individuals throughout the park, except in Red Pine/Jack Pine forests. Here, P. banksiana existed primarily as large individuals 20–40 cm diameter at breast height (DBH), while Pinus resinosa was present throughout a wider range of size classes (2.5–45 cm DBH), but at low densities throughout. Quercus spp. L. (oaks) were only common in Red Pine/Jack Pine forests, and were present across a range of size classes. Fraxinus nigra Marsh. (black ash) was only abundant in Black Ash/mixed hardwood forests, which supported it across all size classes. Overall tree density was higher in 2015/16 (2,461/ha ± 113) than in 2008 (2,223/ha ± 132), although basal area varied little between time periods. Sapling density was also higher during the second sampling period (18,317 ± 1,923 saplings/ha vs. 12,081 ± 1,753 saplings/ha) and also varied greatly among forest types. This was higher in Black Ash/Mixed Hardwood forests than the other four forest types. The collective results of several indices suggest there was reduced deer browse pressure between the two sampling periods. In addition to higher sapling density during the second sampling event, the summed frequencies of eight preferred browse species were also higher during the later sampling period, as was height of two target browse species, on which we collected additional data. The impacts of earthworms on soils varied although 17 of the 51 plots assessed did not show any evidence of earthworm invasion. These were generally located in the vicinity of the inland lake chain, and in the land between Namakan and Mukooda lakes. Organic horizon thickness was highest (7.90 cm) in Black Ash/Mixed Hardwood forests and lowest in Red Pine/Jack Pine forests. Our work demonstrates the dominance of A. balsamea, a species whose suitable habitat is projected to ultimately shift out of the region as environmental variation continues. We also demonstrate the regeneration failure of fire-adapted species, many of which occupy habitat that is anticipated to remain in the area of the park, despite ongoing environmental variation. Mesophication is now occurring, as this shift to species with fire dampening properties continues. If park managers wish to retain resilient forests into the next several decades, active management is needed. If the park is able to stem mesophication, and promote Pinus spp., as well as Quercus spp., it will likely be more resilient as species migration continues. Species from these two groups share many functional characteristics with both Carya spp. (Nutt., hickories) as well as other Quercus spp. These characteristics include aboveground linkages, such as wildlife with nesting and denning habitat and with food........

Forest health monitoring at Voyageurs National Park: 2015–2016 field seasons

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