Vegetation monitoring in relation to white-tailed deer browsing in First State National Historical Park: 2021 summary report

Abstract

Baseline information on canopy regeneration and plant community composition is needed in order to better understand white-tailed deer browsing impacts at First State National Historical Park (FRST). In 2021, the Pennsylvania Natural Heritage Program (PNHP) established 20 permanent vegetation monitoring plots following methods developed by the NPS Eastern Rivers and Mountains Network (ERMN) to assess and monitor trends in vegetation (Perles et al. 2014b; Perles et al. 2017). These protocols provided an efficient method of assessing the current status of native and non-native vegetation and deer browsing impact. This report documents the methodology used to quantify the vegetative composition of natural areas at FRST and provides a summary of the data collected in the first year of monitoring. This first year’s activities (2021) included the initial baseline vegetation assessment and summary of results from the baseline data analysis. A variety of metrics used to assess the impact of deer browsing on the vegetation were calculated and are presented. A second survey is proposed for 2024. PNHP used the NPS ERMN database and analysis methods (Perles et al. 2014b) to summarize the condition in year 1 (2021). In year 4 (2024), PNHP will investigate changes in the condition of browse-sensitive understory plants and tree seedlings. Plots occurred in a variety of settings, ranging from younger successional communities to more mature forest stands. Seventy-five percent (75%) of the plots occurred in Mature or Late Successional forests. Disturbances and stressors, such as deer browsing can strongly influence future forest structure as open woodlands mature. A large population of white-tailed deer may severely impact succession from the open woodlands towards closed canopy forest. In closed canopy, later successional forests, a large deer population may inhibit canopy tree recruitment leading to regeneration failure. Given that FRST managers desire to maintain the landscape as forest, it is important to maintain an adequate number of seedlings and saplings of tree species to ensure the persistence of canopy of native tree species as Mature and Late Successional Forests continue to age. The 20 permanent sampling plots occurred within 5 plant communities described by Ebert (2016) and were classified using agglomerative hierarchical clustering (HAC analysis) and indicator species analysis. The most common plant communities within the group of sampling plots were the Mixed oak – beech forest and Mesic mixed tulip – oak-hickory-beech forest. The remaining plots were found in successional Tuliptree woodland, Successional woodland, and Thicket types. All plots were assigned to these types described in Ebert (2016) and crosswalked to the National Vegetation Classification (USNVC). A total of 128 plant species were recorded from the 20 plots at FRST. Eighteen (18) species were found in over ½ of the plots surveyed, of which eight (8) were non-native. In all, 29 plants occurring in the plots (23% of total species richness) were considered introduced (non-native). Non-native plant cover ranged from 0–98% as measured in the monitoring plot quadrats. Indicators of deer browsing varied by plant community type at FRST. In general, the drier Mixed oak – beech forests showed substantially greater impact of deer browsing and fewer seedlings of canopy species in the understory. FRST monitoring protocols focus on a few plant species considered as preferred food for white-tailed deer. Sustained browsing may be affecting long-term viability of these species within the parks. Based on the status of these regeneration metrics in FRST, we suggest that the forest in FRST are in imminent regeneration failure. We define imminent failure as parks that are experiencing severe regeneration failure and are at risk of forest loss due to very low seedling and sapling abundance, as well as species mismatches between canopy and regeneration layers. Given the poor regeneration of canopy species across all community types at FRST, managers should seek opportunities to conduct adaptive management in the park’s forests, especially mixed oak – beech forest, to experiment with and monitor the effects of fire, browse exclosures, and canopy thinning to encourage native canopy tree regeneration.