Forest Vegetation Monitoring at the St. Croix National Scenic Riverway

Sanders, Suzanne; Grochowski, Jessica

Long-term forest health monitoring programs are a valuable means of assessing the impacts of drivers and stressors and making projections about future structure and composition. A comprehensive, long-term forest monitoring program was established at the St. Croix National Scenic Riverway (SACN) in 2007, and monitoring plots were revisited in 2013. Collectively, these plots spanned six forest types. Sugar maple forests, a climax type in the region, exhibited little change in the six-year interval between sampling periods. Substantial regeneration of Acer saccharum Marsh. and associated species suggests little change is expected in this type in the near future. In upland mixed hardwood/conifer forests, encroachment of A. rubrum L. and Abies balsamea (L.) Mill. in the sapling and small tree layers was indicative of fire suppression and mesophication. Fire suppression was also evident in mixed conifer/red oak forests as plots in this forest type showed decreasing importance of Pinus sp. L. with increasing density and basal area of Quercus rubra L. These forests are in more well-drained soils than those of upland mixed hardwood/conifer forests; Q. rubra will likely become increasingly important in the coming decades. Mixed oak/aspen forests were in an earlier successional sere than the other five forest types, due to a high wind event in 2011; the high density of aspen observed here reflected clonal shoot growth in response to increased light availability. Both black ash/mixed hardwood forests and silver maple lowland forests supported a substantial amount of Fraxinus nigra Marsh. species tolerant of saturated conditions. Major recruitment of several species occurred in black ash/mixed hardwood forests in the previous five to ten years and is likely a result of infrequent flooding and relatively shorter durations of inundation. The impending arrival of the emerald ash borer poses one of the greatest threats in the riverway, not only for the forests, but for the entire aquatic-terrestrial interface. As Fraxinus sp. L. trees begin to die, reduced evapotranspiration and increased flow velocity and water yield (i.e., volume) may result. Such changes could also drive increases in the downstream transport of nutrients and alter habitat conditions for mussels, juvenile fish, and macroinvertebrates. The 50 permanent monitoring plots sampled in 2013 will be revisited in 2022. Because it will be the third visit to these plots, an assessment of trends can be made at that time.

Forest Vegetation Monitoring at the St. Croix National Scenic Riverway

Series