Dr. Kristina Anderson-Teixeira - Forest Resilience to Imminent Ash Die-off in Shenandoah National Park.
Exotic forest insects and pathogens (EFIP) can decimate native tree populations. Temperate forests of eastern North America have been affected by numerous waves of EFIP, yet we lack long-term, regional scale perspective on their net impacts on tree mortality and ensuing impacts on forest diversity and carbon sequestration. Here, focusing on Virginia’s Blue Ridge ecoregion, we analyze three decades of forest monitoring data, including 67 plots totaling 29.4 ha, along with historical and observational records. We show that EFIP have had substantial impacts on at least eight tree genera over the past century, including chestnut (Castanea dentata), elms (Ulmus spp.), butternut (Juglans cinerea), dogwood (Cornus spp.), redbud (Cercis canadensis), oaks (Quercus spp.), hemlock (Tsuga canadensis), and ash (Fraxinus spp.). Mortality rates of EFIP-exposed taxa were elevated well above those of all other taxa. While no species were completely eliminated from the region, abundance and biomass declined steeply during EFIP outbreaks. EFIP-driven mortality resulted in modest declines in average stand-level (alpha) diversity, and several taxa disappeared from our long-term monitoring plots. Although forests of the region were carbon sinks overall, EFIP had a negative impact on carbon storage. They were associated with a loss of ~26.5 Mg ha-1 between 1987 and 2013, or an estimated 102 Mg biomass ha-1 over 100 years from the arrival of chestnut blight in the mid-1920s through the end of the current ash die-off. This implies that EFIP have increased woody mortality ~25% over “background” rates. While lost biomass has largely been recovered, biomass accumulation has been set back by several decades and likely prevented these forests from reaching the biomass of remnant old growth stands in the region. Thus, EFIP have been a major driver of Blue Ridge ecosystem forest dynamics, driving gradual declines in forest biodiversity and reducing carbon sequestration.
Ellen Frondorf - Assessing post-fire oak and pine regeneration across a burn severity gradient in Shenandoah National Park.
The study provided pine and oak regeneration data across several burned areas dating back to 2002 that span a range of burn severities. It help inform fire managers about the current state of regeneration in prescribed burn units and wildfire areas, as well as clarify the initial conditions and burn severities that are ideal for regeneration and continued growth of oak and pine.
Oaks were regenerating in all sites, whether recently burned or not, but seedling counts were higher where the canopy was opened by fire or other disturbance. Pine regeneration also depends on canopy openings, but regeneration only occurred in recently burned sites. Regeneration guidelines for Shenandoah National Park were met more often for oaks than pines. The extreme sparseness of pine seedlings may indicate that the current regime of infrequent prescribed burns or wildfire, or some other environmental condition such as climate, is not conducive to maintenance of fire-dependent pines on this landscape.
Dr. Christine May - Revealing the Current Relationship between Stream Acidification and Fish Species Richness: What is the Status after Two Decades of Recovery?
Dr. May and graduate student Pat Harmon measured Acid Neutralizing Capacity (ANC) and identified species of fish found in streams. ANC is a measure of a stream's ability to neutralize acid. Shenandoah National Park receives high amounts of acid deposition (like acid rain), which alters the park's ecosystems. This replicated a previous study by Dr. Bugler et. al. in 1995.
Changes in the relationship between fish species richness (measured in the number of different species) and minimum ANC from 1995-2016 occurred primarily in basaltic and granitic watersheds (which have medium to high ANC). The study revealed that different species of fish were found in many of the watersheds. For instance, from 1992-1995, brook trout and blacknose dace were the primary fish species found in the 13 study streams. There were four species of fish that were not found between 1992 and 1995 that were found during the 2016 survey (cutlip minnow, red belly dace, central stone roller, brook lamprey).
Dr. Jessica Rykken - Catch the buzz: pollinator diversity, distribution, and phenology in Shenandoah National Park
Sampling by J. Rykken over the course of the growing season was a combination of net and bowl collecting, and included habitats such as rock outcrops, overlooks and roadsides, meadows, and forest openings. Overall, J. Rykken and the volunteers ran 73 bee bowl transects and had 101 separate net-collecting events.
Between May 11 and October 9, 2015 the team collected approximately 3,400 bees and 415 syrphid flies throughout Shenandoah National Park. Collections were made by J. Rykken in mid-May, late July/early August, and mid-September, and by volunteers between June and October. Identifications of bees and syrphid flies are ongoing, to date we have catalogued 26 bee genera in five families, and more than 90 bee species. These include soil mining bees, twig nesting bees, mason bees, leaf-cutting bees, carpenter bees, and parasitic bees.