Recovering from fire: what should be done first?Weather & Environment
As the clean-up continues, many growers are assessing their properties and beginning work to reinstate infrastructure to secure the current crop and the surviving trees. Many questions have been asked about what can be recovered and what support is available.
APAL has pooled experience and advice from other industries, including the wine grape industry in Australia, the citrus and avocado industries in California, and apple and pear experts in Washington State and New Zealand. While these crops are physiologically different from apple trees, some of the advice is relevant and useful.
How does fire affect the tree?
Tree damage from fire varies within and between orchards and needs to be evaluated on an individual basis. Although damage to foliage and younger shoots can be visible immediately, the full extent of damage to trees may not be known for several months. Where trees were burnt directly, the fire was very hot, or the exposure time long, the damage through the bark into the cambium may be severe and the tree is likely to die. Reports suggest that the heat of fire along tree lines can be as high as 1000-10,000oC.
It may be useful to cut back the bark to have a look and see if the tissue is pale and moist (alive) or dry and brown (dead or dying). Tissue that is black is most likely dead. Tissue may be alive on one side of the trunk and dead on the other. Where fire damage is enough to girdle the tree, the effect will be like ringbarking and the tree is unlikely to put out new growth. If nutrients and water cannot move up or down the tree because of damage to the vascular tissue, then the tree will not be productive and is likely to decline over time. If the fire was less intense, or leaves died from heat generated by nearby fire, the trees will still be alive internally. Scorched leaves may fall off, but the trees will regrow.
Tree age and physiology will also affect fire damage. Trees with thinner trunks and thinner bark are likely to have more severe damage deeper into the trunk. Damage will also vary depending on factors such as surface area and water status.
What should be done first?
Each grower needs to assess their trees and orchard for damage and make decisions that are right for them based on their individual situation and resources. While tree recovery is complex and will vary depending a range of factors, there are some general points that are applicable to most situations.
The first thing is to repair and reinstate irrigation and continue orchard management practices. As under ‘normal’ conditions, irrigation still needs to be managed to monitor how much water trees are using. Where trees do not have much foliage, they may not need as much water. Overwatering can promote anaerobic conditions that damage roots and excess moisture that encourages weed growth and soilborne pathogens such as Phytophthora. Don’t prune and don’t apply fertiliser.
When assessing trees, the key is patience and observation. Other industries report that it is often difficult to determine how much of the tree is alive. For example, in an assessment of a vineyard 10 days after a fire showed more vines were recorded as severely damaged, but after 8 weeks a proportion of these severely damaged vines had died. Trees will change over time and it may be best to wait several weeks or even months before making final decisions and quantifying impacts.
Quantifying impacts can help with decision making. Evaluating the cost-benefit of rejuvenating a mix of dead and unhealthy trees against total replant will answer the frequently asked question of ‘what to do with blocks that have a mixture of affected and less affected trees?’. Growers should also factor in the likely return on investment and cashflow of their recovery options to establish when, or if, re-establishment of damaged blocks matches their own financial and succession plans
Feedback from growers and industry members has also included the following questions:
What are the effects on fruit?
Depending on the fire intensity and heat exposure, fruit on the trees may be affected by heat or smoke. Extreme heat can affect fruit quality and may affect firmness, time to ripening and storage life.
Can trees be cut back and grafted?
There is no straight answer to this question. The first thing to consider is how much of the tree is compromised – where is the damage and how far does it extend up and down the tree? The success will depend on the variety, the need for a nurse shoot, how much of the tree tissue is compromised.
Where to get more information about fire damage to fruit trees?
When reading these keep in mind that the physiology of the tree may differ to apples trees.
Avocados Australia: https://www.avocado.org.au/public-articles/recovering-from-fire/
Australian Wine Research Institute: https://www.youtube.com/watch?v=T-_39qT80oo&feature=youtu.be
For information about financial support, mental health support and other assistance:
NSW Rural Assistance Authority – https://www.raa.nsw.gov.au/grants
- Phone: 1800 678 593
- Primary producer assistance – up to $15,000 recovery grants (33 LGAs only), concessional loans and transport subsidies for eligible primary producers
Service NSW Guide: https://www.service.nsw.gov.au/assistance-bushfire-affected-communities
Lists of support available:
Hort Innovation: https://www.horticulture.com.au/growers/bushfires/
Many thanks to Nic Finger, Horticultural Consultant, Agfirst for feedback, and to Karen Lewis, Regional Tree Fruit Specialist, Washington State University and Dr. Ben Faber, Advisor, University of California Cooperative Extension for discussions about fire effects on fruit.