Vegetation community monitoring at Pea Ridge National Military Park, Arkansas: 2007–2021

Abstract

Resource managers at Pea Ridge National Military Park manage the natural communities of the park as a backdrop for interpreting the civil war battle that occurred on March 7–8, 1862. Restoration of the landscape to the vegetation communities that were present at the time of the battle is ongoing. Priorities for restoration include density, form, and vegetation structure, but native representative species are also desired. Heartland Inventory and Monitoring Network ecologists observed plant community sites in park woodlands in 2007, 2012, 2016, and 2021. Climate may influence vegetation and other park natural resources. Temperatures have been increasing at the park, but precipitation and drought indices did not demonstrate significant trends. There was a great degree of interannual variability in precipitation and drought metrics. Phenological data indicated earlier first bloom and leaf-out dates. Overstory canopy, basal area, density, and tree stocking were similar through time, but class 1, midstory trees increased in basal area and density after 2007. The overstory structure remained that of a closed woodland despite prescribed fires and cedar thinning that occurred at the park. Our monitoring data show that fire management goals for overstory reduction have not yet been met. Ground cover was similar through time except for bare soil and deciduous leaf litter. Bare soil and leaf litter experienced a pulse in variability in 2012 and 2021, presumably in response to heterogeneous prescribed fires. Maintaining heterogeneous ground cover may best support biodiversity across the landscape. Ground flora cover (excluding tree regeneration) increased by 88% from 2007 to 2021, meeting a fire management goal. However, ground flora cover was heterogeneous across the sites. Concomitant with the increase in ground flora cover, we observed notable increases in alpha diversity (mean site species richness) and gamma diversity (parkwide species richness) across the monitoring period. Although increases may have been related to treatments and environmental factors, we also improved our botanical sampling preparation and included an expert botanist on the crew in 2021. Species composition of the ground flora was assessed via guilds and indicator species. Although tree regeneration was not included in estimates of total ground flora cover, it was highly variable through time. The seedling class comprised the majority of the regeneration stems observed. Although mean small sapling density values increased by 535% over 2007 levels, there was a great deal of variability among the sites, indicating small sapling estimates were contained within the confidence intervals and not truly different through time. Forbs comprised the greatest abundance of the ground flora guilds through time, except in 2012. Forbs also exhibited the greatest variability in all years except for 2012. Woody species increased over our monitoring record but remained low in cover. We analyzed a set of 50 indicator species for Ozark highlands woodlands to understand changes in the ground flora. The number of woodland indicator species observed in each monitoring event was low (ranged from 7–14 species) with the highest number of species observed in 2021. We also calculated invasive species metrics and found the number of invasive species increased from 2 to 11 over the monitoring record. Nepalese browntop (Microstegium vimineum) was the most abundant of these species. Our confidence in the 2021 ground flora observations was high. We found our observer error to be within standard levels, including agreement on species cover estimates. Not all sites have received the number of burns described in the park’s ecological fire management goals. Our monitoring data show that one of the fire management goals, increased ground flora cover, has been met, but the other two goals for overstory density reduction and seedling density have not yet been met. Further analysis of species composition of the overstory and tree regeneration will be needed after the fire treatments have been completed to determine if all fire management goals are being met.