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Effects of climate change on apple and pear production

Weather & Environment

Australia’s climate has warmed since 1910 and is likely to continue warming, with more hot days and fewer cold days expected in future, according to State of the Climate, 2016. So how will climate change affect apple and pear production in Australia?

In some horticulture industries, like vegetables, decisions relating to new plantings such as cultivar selection and planting system design are made many times each season, giving growers flexibility to make regular changes as conditions vary. For perennial tree crops, unlike annual vegetable crops, significant investment is required to establish new orchard blocks that will be in production for between 10 and 15 years and in some cases longer. In these industries it makes sense when designing new plantings and planning strategies for tree management to consider what the performance and productivity of a block of trees might be like in future growing environments.

Predicting the impacts of future climate change on apple and pear production

Modelling and climate analogues are tools that are commonly used in climate change research to provide insight into the possible effects of changing temperatures, rainfall and sea level on the environment we live in. Both approaches are valuable for horticulture.

Models that describe relationships between plant behaviour and temperature are a useful way of understanding how warming temperatures might affect cropping systems. Analysing climate analogues involves comparing sites where the current climate of one site is similar to the projected future climate of the site of interest. Climate analogues can provide tangible and practical information by allowing growers at the test site to learn from those at the analogue site.

In the now-completed Hort Innovation Apple and Pear Fund project Understanding apple and pear production systems in a changing climate, we used modelling and climate analogues to investigate how warming temperatures might affect flowering in apples and pears, and how the increased frequency of extreme heat days might affect fruit quality. This article presents some of the findings from this work.

Warming temperatures and flowering

As the climate warms, reduced winter chill is likely to affect the timing and quality of bud dormancy release and flowering, which will in turn influence fruit set and yield. Responses will vary between growing regions and cultivars, with cultivar response depending on specific requirements for chill and heat.

Variable bud burst and flowering in apples in Applethorpe (Qld), in years with low winter chill relative to the local historical climate.

Flowering timing

The chill-overlap model describes the relationship between winter chill, heat and timing of flowering. We used the chill-overlap model for Cripps Pink apple to predict changes in the timing of full bloom in growing regions across Australia in 2030 and 2050. In Orange, NSW – a high-chill location – the average date of full bloom was calculated to be four or five days earlier in 2050. The milder winter locations showed a later full bloom date in 2030 and 2050, with the greatest impact felt at Manjimup, WA. Changes in flowering time are likely to vary between cultivars.

Shifts in flowering can reduce yields when the flowering period of polliniser trees no longer overlaps with that of the commercial cultivar.

Flowering quality

Failure to receive enough winter chill results in variable and protracted bud burst and flowering in pome fruit trees. Increased frequency of low-chill years in milder winter growing regions will likely result in these symptoms of inadequate chill in some cultivars. A climate analogue analysis using Manjimup as an analogue for Stanthorpe, Queensland, in 2030 showed that growers in the Stanthorpe region were likely to experience a more variable and protracted pattern of flowering across many apple cultivars but with no clear impact on productivity.

Variable bud burst and more protracted periods of flowering may be a greater management challenge for growers than managing changes in flowering time.

More extreme heat days and fruit quality

Extreme heat in the orchard during summer and autumn can affect fruit quality through sunburn damage, poor blush development, watercore, rapid fruit ripening and reduced fruit growth. Of particular interest in this project was the effect of heat on sunburn browning. Results from the Goulburn Valley showed that Royal Gala apples are at risk of browning when air temperatures rise above 37.9°C with net, and 34.1°C without net. These thresholds were used to investigate the risk of sunburn damage under future climates in growing regions of Australia.

The level of sunburn browning risk varied with geographical location. Shepparton (Victoria), Mount Barker (South Australia) and Manjimup were the most adversely affected by projected increases in the percentage of days with potential sunburn browning risk. The percentage of risk days in Shepparton was predicted to increase from 18 per cent at present to 28 to 36 per cent in 2050 without netting.

Most growing regions are likely to notice some increase in sunburn risk by 2030 (if they haven’t already). By 2050, growers in regions with currently milder summers, will need to have adapted their orchard practices to manage the impacts that an increased frequency of heat events will have on fruit quality.

Apples with symptoms linked to heat and radiation damage: sunburn browning (top left), sunburn necrosis (top right) and poor blush (bottom).

Some final thoughts

Climate change will add significant variability to pome fruit production systems with respect to flowering and fruit quality. Australian growers are used to dealing with some level of variability and it seems possible that impacts of climate change on flowering and fruit quality might be within the range of grower experience up to 2030, but that by 2050 growers will be operating outside current experience.

Determining exactly when the impacts of warming temperatures will affect production is difficult because of uncertainty in climate projections, seasonal climate variability and variability within orchard systems themselves. Growers can make short-term predictions about likely climate change impacts in their own orchards using seasonal climate records together with orchard data. For example, monitoring flowering dates and quality across cultivars can provide an early indication of those cultivars that might be affected by warmer winters, as well as an identification of subtle shifts in the timing of flowering between cultivars and their pollinisers.

Australian apple and pear production is, and will continue to be, affected by the warming climate, with variable impacts across growing regions and cultivars. However, the industry is well-connected nationally and has a strong extension framework through Future Orchards®, putting it in a good position to adapt. Exploiting the genetic diversity available in scions and rootstocks globally will ensure growers can select commercial cultivars that are well suited to their regional climates. Adopting new technologies to monitor orchard climate and tree performance will improve growers’ capacity to understand and manage the impacts of a changing climate.

Research gaps

There is still a lot we don’t know about the potential impacts of increasing temperatures on apple and pear production. Some important questions to consider:

  • How can we better manage periods of extreme heat in the orchard to improve post-harvest quality and storability?
  • How much chill do our commercial cultivars need?
  • How does poor bud burst and delays in ‘leafing out’ as a result of inadequate chilling, affect fruit development, tree structure and growth?
  • Does lack of winter chilling affect flower viability, and therefore pollination and fruit set?
  • Does poor winter chilling affect fruit quality?
  • Which cultivar and rootstock combinations are best suited to the different growing climates of Australia, particularly with regard to chilling requirements and tolerance to extreme heat?

More information and acknowledgments

Full details of findings from the research project Understanding apple and pear production systems in a changing climate can be found in the AP12029 final report on APAL’s website. This project was a strategic investment under the Hort Innovation Apple and Pear Fund. It was funded by Hort Innovation using the apple and pear levy and funds from the Australian Government. Additional financial support was contributed by Queensland’s Department of Agriculture and Fisheries (DAF Qld), Victoria’s Department of Economic Development, Jobs, Transport and Resources (DEDJTR), the Department of Agriculture and Food Western Australia (DAFWA), Pomewest, and the University of Tasmania.

About the authors

Dr Heidi Parkes and Neil White are from DAF Qld; Rebecca Darbyshire is from the NSW Department of Primary Industries; Susie Murphy White is from Pomewest; Ian Goodwin, Lexie McClymont and Jenny Treeby are from DEDJTR; Penny Measham is from Hort Innovation; and Susanna Turpin is from TDI Select Fruits.

Tagged:
Climate change resilience Dormancy flowering and pollination

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