Recovery of native plant species after initial management of non-native plant invaders: Vegetation monitoring in an exclosure in Morristown National Historical Park

Ehrenfeld, Joan; Ross, Kristen; Patel, Manisha; Epiphan, Jean; Handel, Steven

doi:10.36967/nrr-2278124

This report summarizes research conducted in the Native Plant Demonstration Project, within a 0.8 hectare (2 acre) exclosure in the Jockey Hollow section of Morristown National Historical Park between 2002 and 2008. To establish the experiment, a 0.8 hectare area was cleared of the dense infestation of Japanese barberry (Berberis thunbergii) and other invasive shrubs. A 2.4m (8ft) deer exclosure was erected around the cleared 0.8 ha area. Canopy trees were inventoried in 2003. Percent cover of understory vegetation was monitored within the exclosure in 2003, 2004, and 2008 to determine if and how restoration would proceed without further intervention. For comparison, understory vegetation outside the exclosure was surveyed along four transects in 2004. Removal of the uniform and dense Japanese barberry population allowed other invasive species to flourish as the understory received higher light levels. In 2003–2004 Japanese stilt grass (Microstegium vimineum) formed a dense carpet across the exclosure. In July 2003, volunteers and project staff manually removed the stiltgrass and many remaining barberry resprouts. Native plant diversity increased slowly during the five years of monitoring. Even though invasive woody vegetation initially decreased, invasive plants dominated in cover after five years. Native woody plant percent cover increased slowly over time, but it was not sufficient to establish a native woody plant stratum five years after the initial management. In April 2003, soil manipulations were undertaken to determine whether restoration could be enhanced by modifying soil conditions. The soil amendment treatments were applied to sixteen 3m x 3m quadrats established within the exclosure following a Latin square design, and included: 1) removal of the top 5cm of organic-rich material (enriched by non-native earthworm casts); 2) addition of wood chips to increase organic matter, particularly of lignin-rich, recalcitrant, slowly-decomposing material; 3) addition of aluminum sulfate to reduce soil pH, in an attempt to limit N availability and alter habitat for exotic earthworms; and 4) control plots that were similarly disturbed but no soil amendments were applied. While the treatments were successful in modifying some soil properties in the directions desired, there was little evidence that these changes affected vegetation in the years samples were surveyed. In summary, removal of non-native, invasive species without further vegetation management allows other invasive species to become established when light conditions are altered and the invasives are released from intensive deer browse. However, native woody and herbaceous plants do become established after initial intensive planting efforts and manual weeding, suggesting that over time, a native understory vegetation community will re-establish in areas protected from deer browse. We found that soil manipulations were effective in altering soil properties, but these changes have little apparent effect on plant establishment in the first few years after treatment.

Recovery of native plant species after initial management of non-native plant invaders: Vegetation monitoring in an exclosure in Morristown National Historical Park

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