Mon, Aug 02, 2021:On Demand
Background/Question/Methods
Abandoned agricultural fields are target landscapes for ecosystem restoration; however, they are degraded and susceptible to plant invasion, requiring extensive management. Callery pear (Pyrus calleryana), an invasive tree in Midwest USA, has become a prominent invader after escaping ornamental plantings. The ecology of this tree is relatively unknown, but it grows in dense monocultures and outcompetes its native counterparts. This species is challenging to control due to risk of reinvasion and because Callery pear responds to disturbance with aggressive epicormic sprouts. Thus, identifying which landscapes are most vulnerable to invasion and those areas that may be more resilient may allow for targeted management and could inform land purchasing decisions by land managers. Our objective was to assess the level of invasion in restored prairies as well as their surrounding land use, plant community richness, and soil chemistry and nutrient dynamics, to determine if these metrics could predict the invasion of Callery pear. We selected two invaded and two uninvaded sites and randomly sampled 25 quadrats in each site. We measured the distance of the quadrat to land use (roads, forests, residences), Callery pear presence/absence, Callery pear abundance, total plant species richness, plant coverage, and soil moisture, pH and nutrients.
Results/Conclusions We found higher species richness (~6/quadrat) in invaded sites than uninvaded sites (~2.5/quadrat), contradicting previous studies that suggest higher species richness decreases invasion likelihood. Invaded sites were more likely to be invaded where grasses and forbs covered less area, indicating that open niche space allowed for Callery pear establishment. Soils in uninvaded sites had higher pH, organic matter, and ammonia availability by lower phosphorus, nitrate and micronutrient content. We hypothesized that higher organic matter would be present in uninvaded sites because it can alter nutrient ratios in favor of native species. The nutrient content of soils in invaded sites were similar despite the presence of Callery pear. Finally, there was more Callery pear closer to forest edges of the prairies and further from roads and residential areas. This was contrary to our hypothesis that residential areas would increase propagule pressure, but inline with our hypothesis of forest edges supplying bird perches for bird dispersal. Taken together, Callery pear is more likely to invade on forest edges, suggesting targeted restoration in those areas; however, plant species richness and soil nutrient content may not be an appropriate indicator for determining the suitability of target landscapes.
Results/Conclusions We found higher species richness (~6/quadrat) in invaded sites than uninvaded sites (~2.5/quadrat), contradicting previous studies that suggest higher species richness decreases invasion likelihood. Invaded sites were more likely to be invaded where grasses and forbs covered less area, indicating that open niche space allowed for Callery pear establishment. Soils in uninvaded sites had higher pH, organic matter, and ammonia availability by lower phosphorus, nitrate and micronutrient content. We hypothesized that higher organic matter would be present in uninvaded sites because it can alter nutrient ratios in favor of native species. The nutrient content of soils in invaded sites were similar despite the presence of Callery pear. Finally, there was more Callery pear closer to forest edges of the prairies and further from roads and residential areas. This was contrary to our hypothesis that residential areas would increase propagule pressure, but inline with our hypothesis of forest edges supplying bird perches for bird dispersal. Taken together, Callery pear is more likely to invade on forest edges, suggesting targeted restoration in those areas; however, plant species richness and soil nutrient content may not be an appropriate indicator for determining the suitability of target landscapes.