John Paul Schmit | USGS Science

USGS2026

Selective herbivory by white-tailed deer is associated with demographic and compositional bottlenecks across forest regeneration stages in the National Capital Region

White-tailed deer ( Odocoileus virginianus ) populations in eastern North America now exceed historical levels, imposing intense browsing pressure on forest regeneration where hunting is limited. Using National Park Service monitoring data (2013–2023) from the National Capital Region Network, we analyzed 9459 seedlings and 6015 saplings of 71 and 64 species, respectively, from 430 plots over 10 years spanning a gradient of low to very-high deer impact. Mixed-effects models that accounted for repeated sampling of plots showed that per-plot seedling richness declined substantially with deer impact ( P < 0.001), and the probability that a plot held any browsable regeneration fell to 0.78 at very-high browse impact. Browsing was species-selective, but less broadly than raw browsing rates imply. After adjustment for height, deer impact, site, and year, only a minority of species differed from the community-average browse rate, with black tupelo ( Nyssa sylvatica ) and American hornbeam ( Carpinus caroliniana ) consistently above the overall average browse rate. Height was a major driver, with a non-monotonic effect: Browse probability peaked near 80 cm and declined in taller stems ( P < 0.001), defining a structural browse window. The sapling:seedling ratios varied among impact levels ( P < 0.001) but were unrelated to browse intensity; ratios for palatable species such as sweet birch ( Betula lenta ) and white ash ( Fraxinus americana ) approached 0 at the seedling-to-sapling transition, whereas the ratio for browse-resistant American beech ( Fagus grandifolia ) exceeded 6. Browsing was associated with reduced sapling vigor (odds ratio 1.34, P = 0.010). Community composition shifted toward browse-tolerant, shade-tolerant species, with American beech rising from 2.7% of seedlings to 25.2% of saplings, an observation of particular concern given the spread of beech leaf disease ( Litylenchus crenatae mccannii ). Our results suggest that chronic deer browsing is a significant component of the cascading constraints on forest regeneration in the region.

Maryland, Virginia, West Virginia↗

USGS2018

Evaluating the relationship among wetland vertical development, elevation capital, sea-level rise and tidal marsh sustainability

Accelerating sea-level rise and human impacts to the coast (e.g., altered sediment supply and hydrology, nutrient loading) influence the accumulation of sediment and organic matter, and thereby impact the ability of coastal tidal wetlands to maintain an elevation consistently within the vegetation growth range. Critical components of marsh sustainability are the marsh elevation within the vegetation growth range (elevation capital) and the rates of marsh surface elevation change and relative sea-level rise. The relationship among these factors and their combined influence on marsh integrity were evaluated by comparing trends in surface elevation change on five salt marsh sites located on three marsh islands in Jamaica Bay, NY, USA. All marsh sites were located in a similar physical setting (i.e., tidal range, sea-level rise rate, sediment supply). The structural integrity of the marshes ranged from densely vegetated (high integrity) to severely deteriorated (low integrity) with elevation capital ranging from high to low, respectively, and included a deteriorating marsh site that was partially restored. Two marshes with high elevation capital maintained their relative position high within the tidal range through a combination of surface sediment deposition and shallow subsurface expansion, and kept pace with local sea-level rise. A marsh with moderate elevation capital showed signs of flooding stress and was deteriorating, but managed to keep pace with local sea-level rise. The deteriorated marsh gained no elevation over the 14-year study and was located too low within the tidal range to support continuous coverage of salt marsh vegetation. Elevation gain in the restored marsh initially lagged behind sea-level rise for 8 years, but the elevation trend recovered and kept pace with sea-level rise for the last 5 years. A conceptual model is presented that describes the relationship among elevation capital, and rates of marsh elevation gain and sea-level rise. Note that a search for factors influencing wetland loss should focus on process changes to marsh vertical development (e.g., sediment supply, vegetation growth) and climate change effects (e.g., sea-level and temperature rise) that can cause elevation gain to lag behind sea-level rise, and these occur prior to the onset of marsh deterioration.

New York↗