Native floral strips fill seasonal resource gaps supporting pollinators in horticultural settings

Lena Alice Schmidt, Amy-Marie Gilpin, James M. Cook, Paul Rymer and Sally A. Power, Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, Australia, Paul Gibson-Roy, Kalbar Resources, Bairnsdale, VIC, Australia

Background/Question/Methods
Horticultural areas represent highly transformed systems that are heavily reliant on a single agricultural pollinator – the European honeybee (Apis mellifera). Yet, a wide range of resident native pollinators can also provide vital pollination services. Within these florally depauperate landscapes, target crops flower and provide floral resources to pollinators for only a short time-period. It is widely recognised that the provision of high quality, diverse floral resources year-round is essential for supporting and enhancing resident insect pollinator populations. Our understanding of the role targeted floral strip enhancements can play in resource provisioning has developed over the last decade in the Northern Hemisphere, however relatively little is known about this in the Southern Hemisphere. We sought to determine differences and overlaps in the pollinator assemblages visiting exotic and native floral strips in apple orchards, and how these change throughout the year. Strips comprised of either native plant species (local to the Sydney Region, Australia), or a standard commercial mix of exotic plant species (developed for Northern Hemisphere pollinators). We surveyed plant-pollinator interactions on four paired native and exotic experimental floral strips (23 species each), alongside established rows of Granny Smith apple trees, for four days per month over a one-year period.
Results/Conclusions
We observed a diverse array of native pollinators across native and exotic strips and on apple. Diversity and abundance of native pollinators was highest on native strips, with 7700 visits from 270 morphospecies across an 11-month period, compared to 1400 honeybee visits. Exotic strips recorded 3400 visits from 215 morphospecies, and 5800 honeybee visits over 9 months. We observed 50% overlap of species between natives and apples, and 40% overlap between natives and exotics. During winter months both native and exotic strips attracted high diversities and abundances of insects, but only exotic strips attracted honeybees. During apple bloom 70% of honeybee and 10% of native pollinator visits were to apple flowers. Our results suggest that exotics do provide attractive, resource-rich flowering patches, but that these are for relatively short durations, which leave a floral resource gap during late winter and most of spring (including during apple bloom). We also found that native perennial species were able to fill these ‘floral resource gaps’, while also providing resources for specialist pollinator species and encouraging a greater level of native pollinator diversity over much longer durations. Future recommendations on plant species for floral strips need to closely consider target pollinator species and seasons.