Propagule, or seed limitation, is a little-explored factor that may have an important role in determining the distribution of native plant species in invaded grasslands. Distribution of species is classically considered to be controlled by a combination of abiotic factors, such as soil and climate, and biotic factors, such as competitors, predators, and seed bank dynamics. However, seed limitation is an additional constraint to species distributions that is poorly understood. The charismatic native wildflower sky lupine, Lupinus nanus, is an excellent model species because it has several attributes suggestive of seed limitation and it is found in a wide range of grassland habitats. Through large-scale surveys and field experiments in grasslands at the University of California McLaughlin Natural Reserve, we will determine specifically how seed availability interacts with competition and soil properties to delineate the distribution of sky lupine across multiple scales.
This work has practical significance for grassland restoration because it will allow us to determine the characteristics of sites in which seed addition can result in recolonization by sky lupine, and potentially a more abundant and diverse native plant community. Given the limited resources available, restoration efforts should be focused on areas that are most likely to result in the establishment of long-term viable populations with minimal investment, areas in which native species absence is primarily a function of seed limitation. From our experiments, methodologies for native plant reinvasion will be developed that take into account interacting mechanisms limiting native plant distribution and pinpoint suitable sites to increase restoration success.
