Loss of horticultural pollination services from wild insects following bushfires (PH20002)
What’s it all about?
This investment is conducting a detailed case study of the impact of a major bushfire on wild pollinator communities and the pollination services they provide to an apple crop. The case study approach to this work can be extrapolated to understand the value of wild pollinators to the horticulture sector, enabling growers to better understand their reliance on wild pollinators and the potential impact of Varroa mite to their pollination security.
Extreme weather events, such as bushfires and floods, are important features of the Australian environment and are predicted to increase in frequency with climate change. However, little is known about how this may impact crop pollination.
A unique opportunity to investigate how bushfires disrupt pollination presented itself after a three-year study of apple pollination in Bilpin NSW through Hort Frontiers project Healthy bee populations for sustainable pollination in horticulture (PH15001) was followed by a major bushfire event in 2019/20. Under PH15001 the contribution of wild honeybees to orchard pollination was estimated, therefore these learnings will be combined with post-fire pollination surveys to provide a case study.
Key activities of this investment include…
- Measurement of the immediate impact of an extreme bushfire event on pollinator communities, floral resources and crop pollination services for apples, and communication of these effects to researchers, industry and growers.
- Understanding of how pollinator communities, floral resources and crop pollination services change, and hopefully recover, over three years post-fire, along with recommendations for on-ground measures to mitigate impacts for apple and other horticultural crop pollination following an extreme bushfire event.
- Estimation of the relative contribution of managed honey bees in on-farm hives versus wild honey bees to apple pollination in Bilpin as a methodological case study, using a mark-recapture survey approach on the bees from on-farm hives.
- Integration of multiple lines of evidence from this project and PH15001 to estimate the likely impact of a Varroa mite incursion (and establishment) on pollination services.
- Presentation of findings and recommendations to commercial beekeepers, growers (especially in bushfire affected areas such as Batlow, Bilpin, Adelaide Hills and Stanthorpe) and bee pollination researchers through workshops, factsheets, and online materials (e.g. short video and downloadable factsheets).
Over the past six months, the project team continued regular (6-8 weeks) monitoring of floral resources and pollinator communities on and off-farm in the bushfire affected region of Bilpin, adding to the time series of data covering pre-fire (2017-2019) and post-fire (2020-2022) periods.
The research team analysed the data from the honeybee marking experiment carried out during the 2020 apple flowering season. In this experiment, specialised apparatus was used to ensure that all bees leaving the managed honeybee hives placed in the focal study orchard were marked with fluorescent dye powders.
Honeybees visiting the crop and non-crop flowers on the orchard were then surveyed on 10 different days during the flowering season. Honeybees observed were recorded as either marked (green/red, from the managed hives) or unmarked, coming from off-farm hives in the wider landscape.
6,000 bee-flower interaction events were observed, revealing that about 50 per cent of on-farm honeybee visits are by marked bees from on-farm hives and the other 50 per cent from unmarked bees. While the latter could be from wild nests in the surrounding bush or managed hives on other properties, there is a strong implication that unmanaged wild honeybees are contributing substantially to pollination on the orchard.
This study provides a valuable proof-of-principle for this method of estimating the contribution of on-farm hives, which are often rented, versus honeybees present in the wider landscape. Such an approach can be a useful tool for understanding how pollination services are provided to a range of horticultural field crops.
Over the last six months, the research team continued regular (6-8 weeks) monitoring of floral resources and pollinator communities on and off-farm in the bushfire affected region of Bilpin, adding to the time series of data covering pre-fire (2017-2019) and post-fire (2020-2022) periods. They also carried out intensive on-crop pollinator surveys during the crop flowering period (September/October). However, due to emergency biosecurity measures to combat the Varroa outbreak, they were unable to conduct an on-farm honeybee marking experiment in this flowering season.
In the bush plots close to farms, the list of plant species in flower differs considerably between pre and post fire periods. The post-fire period shows greater incidence of plants that are known to flower post-fire and also of weedy species. Meanwhile the pollinator community using these plants throughout the year has also changed, with greater change seen in plots in areas of the greatest fire severity. A key feature of these changes is a large increase in the relative abundance of hover flies and other flies. The research team also observed post-fire changes in the pollinator community visiting non-crop flora on farms; notably, significant decreases in numbers of honeybees and stingless bees were noted, the two dominant crop pollinators during crop flowering season.
The 2022 crop pollinator surveys produced very different results to previous years. The research team recorded 3,842 insect visits to Pink Lady apple flowers with 91 per cent visits by honeybees and 8 per cent by hoverflies, while less than 1 per cent of visits were by native bees. In all previous years, there have been two dominant species – honeybees (30-75 per cent visits) and stingless bees (15-65 per cent of visits) – together making up about 90 per cent of visits. However, there were only 3 (0.1 per cent) stingless bee visits recorded in 2022. The lack of stingless (and other native) bee activity is explained well by the exceptionally cool La Nina weather. The long-term data set shows that native bee visits to apple flowers in Bilpin are very few until temperatures reach 230C, but in 2022 and daily maximum temperatures never exceeded 220C during the survey period.
Regular (6-8 weeks) monitoring of floral resources on and off-farm in the bushfire affected region of Bilpin continued, with results added to the time series of data covering pre-fire (2016-2019) and post-fire (2020 onwards) periods.
Analysis was undertaken on the vegetation patterns for 2018-2021 over a wider landscape scale using satellite photos. Major changes were found between one month before and one month after the fire event. There has since been substantial vegetation recovery, but effects are still evident two years post-fire, and vary greatly between orchards at the local scale. So far, an increase in the number of plant species in flower post-fire was recorded.
Preliminary analysis of crop pollinator data from the first post-fire crop flowering season suggests that numbers of both honey and stingless bees (the two main pollinator species) were slightly reduced following the bushfires. In contrast, hoverflies increased in abundance by an order of magnitude, suggesting that they might partially compensate for any decreases in bees. However, further data analysis is needed because (a) ambient temperature affects crop visitation rates and (b) there were considerable differences between farms that might correlate with the between-farm differences in surrounding vegetation recovery.
Apple landscape field work is underway to determine the changes in pollinators and pollination following bushfires.
Previous research in Bilpin under project, Healthy bee populations for sustainable pollination in horticulture (PH15001) provided 3-years of pre-fire data followed by a major bushfire. Project work has continued to use the same field sites and same methods to obtain 3 years post-fire data for comparison
The use of satellite imagery is also being used as another form of monitoring, with visual inspection of satellite images used before and after the bushfire event to observe the extent impact and the trajectory of vegetation recovery. Preliminary results show that native vegetation surrounding the apple orchards impacted by fire did not flower until about 7-8 months after the fire event.