Wildfires are becoming more common as environmental change progresses, destroying entire landscapes and costing the American public billions of dollars annually. Wildfire frequency in many regions is intensified by the invasion of exotic grasses that are highly flammable, and which often replace native plants as burned landscapes regrow. To prevent invasive species from taking over burned landscapes, land managers are increasingly applying seeds of native plants to encourage ecosystem recovery and keep invasive plants at bay. However, there is still much to learn about the factors that determine the success of seed additions in terms of the ability of seeded species to establish, and to suppress flammable invaders. It is also unclear how previous human-caused landscape changes, such as nitrogen pollution or the removal of water-hogging shrubs (a practice common in western USA rangelands), will affect the success of native seed additions and plant recovery from fire. Moreover, it is unclear how different seed mixes repel exotic plants from invading disturbed areas. This research project addresses these issues by building on a long-term experiment investigating the effects of past nitrogen pollution and shrub removal (originally intended to improve rangeland forage) in a highly invaded sagebrush steppe ecosystem. The experimental site was entirely burned in a recent wildfire, providing a unique opportunity to evaluate how a history of nitrogen pollution and shrub removal will influence plant recovery from wildfire. The research team will develop criteria for creating seed mixes that suppress invasive plants, particularly flammable annual grasses, and will determine their effectiveness within the different long term experimental environments present across the study site. The results from this study will aid land managers in choosing native seed mixes that will help to prevent the spread of invasive plants and decrease the risks and costs of future wildfires.
This project investigates how ecological memories of nutrient enrichment and dominant plant removal impact plant re-assembly following wildfire and addresses a critical need to test the applicability of current models for creating post-fire communities that will be resistant to invasion by transformative invasive species. The research will evaluate a promising, but under-studied, trait-based model (the Community Assembly by Trait Selection model) for establishing native plant assemblages that are resistant to invasive grasses and forbs. This model will be applied in a novel experimental design to discern whether seed additions result in biotic resistance via limiting similarity, fitness hierarchies and/or trait complementarity. While much focus has been given to limiting similarity as a mechanism of resistance to invasion, experimental support has been mixed because this mechanism has been difficult to distinguish from fitness hierarchies and because ecosystems are frequently invaded by more than one exotic species simultaneously. This project will overcome these issues by using two separate seed mixes designed to convey resistance to invasive grasses and forbs, plus a high-diversity seed mix that combines these. With this experimental setup, evidence for biotic resistance within functional groups will support limiting similarity, resistance across different groups will support fitness hierarchies, and relatively greater resistance in the high diversity mix will support trait complementarity. The seed mix treatments will be nested within plots of long-term nitrogen enrichment and shrub removal, which at a microhabitat scale are characterized by environmental variation due to ecosystem engineering by shrubs and ants. This hierarchical design will enable the researchers to assess how ecological memories of landscape and microhabitat-level factors affect the success of seed additions for conveying biotic resistance to invasive plants. It also allows evaluation of how nutrient availability influences mechanism conferring resistance to invasion.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
