Recovery from fire damage in olive groves

Although a fire-affected olive grove can look devastated, trees could have the potential to recover and be productive again if managed well.

Tree recovery depends on the:

• degree of heat damage
• tree size and age
• moisture stress before and after the event
• the presence of undamaged trunks and scaffold branches above any graft unions

If cuttings were planted, all regrowth can be used to retrain a new tree.

Recovery of olives after fire is likely to involve:

• pruning
• replace or repair of the irrigation system
• some nutrition management
• patience while the trees reshoot and indicate the percentage of recovery

Assessment is then required of the block's viability, depending on how many trees have survived.

Death of trees

Complete death of olive trees from wildfire is more likely to occur in younger plantations that have a majority of trees with a stem diameter of less than 20mm.

A 2005 study conducted in the Western Sydney foothills of a low intensity fire and its effect on a subspecies of Olea europaea showed that a low intensity fire didn't kill larger olive trees with trunks and branches larger than 20mm (von Richter et al. 2005). But 80% of younger trees with stems less than 20mm in diameter died.

It was also found that lower rainfall leading up to the fire event may have increased the death toll by reducing the ability of small plants to resprout because of water stress.

Assessment and recovery

Assess groves as soon as possible, based on the extent of damage.

Do not prune damaged trees until regrowth has been begun. If trees are grafted, ensure that the regrowth forming the new tree is occurring above the graft union.

Trees planted as cuttings can be retrained even if shoots emerge from ground level or below the soil surface.

Olives can begin resprouting within just a couple of weeks according to a study undertaken on feral Olea europaea in the Mt Lofty ranges of South Australia (Sheldon and Sinclair 2000).

Irrigation will assist the speed at which full production can be achieved, although volumes applied may need to be less. The study by Sheldon and Sinclair (2000) also demonstrated that, during the recovery period, trees undergoing simulated post-fire regrowth had lower moisture stress and higher soil moisture availability than intact trees with full canopies. Recovering trees only need half as much water because of the presence of a smaller leaf area per root zone volume.

Fertiliser will be less important than irrigation. Olive trees don't require large amounts of fertiliser according to Paul Vossen of the University of California Davis.

Because of the small leaf area of the recovering trees in relation to large root mass, regrowth should be rapid and vigorous and extra applications of nutrients may make the task of reshaping the trees more tedious.

It could also delay the return to fruiting because of excessive vigour.

Pruning

In many cases the process of pruning and reshaping trees will be similar to the setup phase of the grove. Occasionally, unless the trees were killed outright, the regrowth will occur on what was the cooler side of the tree during the fire.

Careful attention should be paid to the selection and placement of new structural limbs to prevent possible limb breakage when cropping resumes.

Long-term viability

Decisions about long-term grove viability, possible tree replacement and pruning strategies should be made in consultation with technical specialists and your insurance company.

Decisions should take into account the:

• severity of the damage and losses
• tree age
• variety
• rootstock
• planting densities

Younger trees, if not killed outright, may be easier to reshape into productive trees than older trees.

References

Lotte von Richter, Debra Little and Doug Benson (2005) Effects of low intensity fire on the resprouting of the weed African Olive (Olea europaea subsp. cuspidata) in Cumberland Plain Woodland, Western Sydney. Ecological Management & Restoration Vol 6 No 3 Dec 2005

Megan Sheldon and Russell Sinclair (2000) Water Relations of Feral Olive Trees (Olea europaea) resprouting after severe pruning. Australian Journal of Botany, 2000, 48, 639–644

Paul Vossen, Cooperative Extension Provider (2004) Fertilizing Olive Trees. UCDavis.

Riccardo Gucci and Claudio Cantini, (2000) Pruning and Training Systems for Modern Olive Growing. Collingwood, Vic : CSIRO Publishing, 2000