Developing management strategies to enhance the recovery of horticulture from bushfires (AS19002)
What's it all about?
Severe climatic events during the summer of the 2019/20 growing season, in addition to the effects of prolonged drought, led to substantial fire damage in apple orchards and other tree crops in NSW and SA. In response, this project is assessing the short- and long-term effects of fire damage in tree crops so that growers are equipped with strategies to reduce impact in the future.
By investigating how fruit and trees respond to fire, the research team will establish the crucial knowledge needed for growers to make informed decisions on fruit marketability and tree recovery post fire-damage. Guidelines will be developed for growers to use to apply the right management options to improve production levels and meet quality standards, as soon as possible after fire damage.
Research and demonstration sites will be established in Batlow, Bilpin and the Adelaide Hills orchards, which were directly affected by bushfire in the summer of 2019-2020.
Since 2020, this project has been been collecting orchard recovery metrics from trial and monitoring sites established in orchards that suffered fire incursion during the 2019/20 bushfires. Two of the sites in Batlow, NSW were affected by radiant heat (Kanzi and Rosy Glow blowtorch sites) and fire embers from adjacent vegetation burnt an additional site (Royal Gala slow cooker site). SARDI contributes two field experiments to the AS19002 bushfire recovery program, a multi-variety cherry slow cooker site and a Rockit apple blowtorch site, both in Adelaide Hills, SA. All the sites had fully replicated pruning treatments imposed shortly after the 2019/20 bushfire event. 2022/23 represents the third season of investigations into the response of fire-affected orchards to remedial pruning treatments.
A key focus of the past six months has been communicating project outcomes to growers through orchard walks in Batlow and Adelaide Hills. Furthermore, techniques for controlled experiment, a remarkably important aspect of the project that will test relevant recovery strategies, were assessed. Assessment of these techniques provided useful and initial insights for setting up concise experiments that will assist in investigating pending fire-caused physiological disruptions in tree crops.
The project has been able to identify delayed mortality as a crucial fire-effect that can disrupt future orchard sustainability after a bushfire episode. Monitoring and trial sites in NSW and SA, that were affected by radiant heat (blowtorch sites) have demonstrated impressive levels of recovery, three years after the bushfire damage, while trees that suffered stem burnt due to dispersed fire embers or slow cooker effects are still struggling to survive. The destruction of their vascular tissues and subsequent interruption of carbohydrates to the roots has hampered their physiological state and led to delayed mortality. Controlled experiments can serve as useful methods for investigating and developing effective management responses for solving this and other issues. The project team will seek to explore solutions for reducing the economic losses that may arise from delayed mortality of trees through the controlled experiments planned.
During this reporting period, fire effects on trees in the second season after the bushfires were monitored, as well as the assessment of treatment effects on orchard recovery metrics. Project activities during this period, in NSW and SA, include root and wood sample collection from the experimental and monitoring sites for carbohydrate analysis, and leaf sampling from spring to autumn for the determination of the second season post-fire tree nutrient status. Canopy recovery was determined throughout the growing season.
In addition, flowering and crop load were assessed in monitoring and experimental sites. Finally, in the period before harvest and at harvest, fruit maturity and harvest quality attributes were determined in monitoring sites. Post-harvest assessment of harvested fruits from the monitoring site was also carried out.
The results showed that root carbohydrate concentration (post-fire) were most pronounced in the slow cooking site and lowest in severely and extremely impacted trees. This observation supports the earlier reported fire effects on vegetative and reproductive performances of trees. Some noticeable differences were found in recovery metrics based on the treatments. For instance, the total removal of fruits in the first post-fire season in the Royal Gala experimental site, recorded the highest crop load in the past growing season. This treatment also showed elevated carbohydrate root concentrations in the first season after fire damage to trees.
As part of the extension activities, a project update was presented at the biannual meeting of the Bilpin/Sydney Basin grower group and an orchard walk was conducted to assess tree recovery at one of the post-fire monitoring sites in Bilpin. Some of the project work was similarly presented at the International Horticulture Congress in Angers (France) and the conference article was submitted for publication.
At this stage it can be concluded that the blow torch sites are gradually recovering from fire damage while trees in both NSW and SA slow cooker scenario are still struggling to recover. More research will be required under controlled conditions to develop better solutions for tree recovery from smouldering fire effects that have impacted canopy and trunk functionality. This will require further understanding of the impact of trunk damage to the vascular system and the bi-directional movements of carbohydrates and nutrients.
The further assessment and evaluation of the implemented treatments aiming to enhance the recovery of the orchards from bushfires will contribute to the bushfire recovery manual scheduled to be produced towards the end of project.