Novel Weaponry in the Arsenal of an Invasive Shrub (Dahurian buckthorn)

The introduction of novel, invasive plant species can pose ecological problems for native communities. The prevalence of these invasive species have increased over the last century due to ease of international movement. The northeastern U.S. contains large swathes of abandoned agricultural fields left behind as farming moved west. Blandy Experimental Farm (BEF) is a research station and the State Arboretum of Virginia, BEF includes abandoned agricultural fields at varying periods of succession. In 1939, Dahurian buckthorn was introduced to BEF as an ornamental planting. The shrub escaped it’s original planting and has created dense thickets with little or no native woody regeneration in these abandoned fields. The mechanisms used by buckthorn to overtake the landscape are not well known but may include: changes in plant species composition, reduction of light resources, alteration of soil properties and processes, shifts in nutrient cycling, and the use of secondary compounds in allelopathy. My thesis focused on the following questions: 1.) how does Dahurian buckthorn influence plant species composition and light resource availability in secondary succession at BEF? 2.) How do Dahurian buckthorn thickets affect soil properties and nutrient cycling? 3.) Do Dahurian buckthorn leaves and berries exhibit allelopathic qualities that hinder native species germination? 4.) Has the presence of Dahurian buckthorn in dense thickets significantly altered the course of secondary succession at Blandy Experimental Farm? I used field measurements and a greenhouse study to determine the effects of the invasive shrub on the trajectory of secondary succession. In areas with high levels of buckthorn presence, soil temperature was significantly lower than areas with low levels of buckthorn (19.4 °C versus 20.5°C). Light resources at the ground level were lowest in areas with high buckthorn. Decomposition rates were significantly faster in buckthorn leaf litter than white oak litter, likely due to buckthorns higher N content (k = 0.0054 versus k = 0.0019). The greenhouse study found evidence of allelopathy in buckthorn litter and berries. Honey locust, white ash, white oak, and buckthorn had lower biomass and higher mortality when large quantities of buckthorn litter and berries were present in the soil mixture. This species is having an ecosystem level impact on the regeneration of native forests at BEF, buckthorn has these abandoned fields in arrested succession without forward movement in the plant community. Dahurian buckthorn is one of many invasive plants on the rise, they threaten our native communities and the ecosystem services we rely on. It is critical to study these invasive-native ecosystem interactions to understand their impacts and mitigate their lasting effects.