Non-native plants and nitrogen addition have little effect on pollination and seed set in 3-year-old restored woodland.
Human activities can disrupt the insect pollination process, which can trigger a decline in pollination and plant reproductive output. Floral visitors are not equally effective pollinators, and it is unknown how multiple changes to an environment further change the effectiveness of insect pollination for native plants. We investigated how herbicide treatment, the presence of non-native plants and addition of nitrogen fertiliser change the relative importance of different species of floral visitors to four native plant species: Callistemon phoeniceus, Calothamnus quadrifidus, Hakea lissocarpha and Banksia sessilis. Our field site was a large-scale revegetation site in south-west Western Australia in which the presence of non-native plants and nitrogen deposition were experimentally manipulated. Experimental exclusion of floral visitors revealed pollinators were likely required for the seed set of three of the native species, and none of the four plant species were pollen-limited. We observed 8936 floral visitors of 249 morphospecies from 14 insect orders on four native and two non-native plant species. From PIV calculations, 57% of floral visitors were potential pollinators, with the remainder considered just visitors due to their low Pollinator Importance Value (PIV). The introduced Apis mellifera (European honey bee, Apidae) was the most frequent floral visitor and the most effective pollinator of all four native plant species. The presence of two non-native plant species and addition of nitrogen fertiliser did not affect the effectiveness of the potential pollinators, or the viable seeds produced by the four native plant species.