A wide variety of invasive plants are known to reduce native plant diversity through competition for space, nutrients, pollinators or other resources. These invasive plants may also have the potential to alter the pollinator-plant bipartite network, which in turn could have cascading impacts on plant reproduction. In this study we determined the effects of the exotic weed, Genista monspessulana on pollinator activity rates (recording floral visitation rates in visits/flower/hour) and species richness on a selection of 7 native and 4 non-native plant species in 12 grassland sites in Marin County, CA invaded by G. monspessulana. We measured reproductive success of the select plant species by collecting fruits and counting seeds to determine fruit set and seed set. We observed and collected bees approximately every 3 weeks.
Our preliminary analysis suggests that there is significant variation in reproductive success of native and non-native plants as a function of density of G. monspessulana. These data suggest that land managers that are removing significant expanses of G. monspessulana will want to understand the implications of those removals for native and non-native plants in the region.