Challenges in predicting climate change impacts on pome fruit phenology.

Climate projection data were applied to two commonly used pome fruit flowering models to investigate potential differences in predicted full bloom timing. The two methods, fixed thermal time and sequential chill-growth, produced different results for seven apple and pear varieties at two Australian locations. The fixed thermal time model predicted incremental advancement of full bloom, while results were mixed from the sequential chill-growth model. To further investigate how the sequential chill-growth model reacts under climate perturbed conditions, four simulations were created to represent a wider range of species physiological requirements. These were applied to five Australian locations covering varied climates. Lengthening of the chill period and contraction of the growth period was common to most results. The relative dominance of the chill or growth component tended to predict whether full bloom advanced, remained similar or was delayed with climate warming. The simplistic structure of the fixed thermal time model and the exclusion of winter chill conditions in this method indicate it is unlikely to be suitable for projection analyses. The sequential chill-growth model includes greater complexity; however, reservations in using this model for impact analyses remain. The results demonstrate that appropriate representation of physiological processes is essential to adequately predict changes to full bloom under climate perturbed conditions with greater model development needed.

Impact of future warming on winter chilling in Australia.

Increases in temperature as a result of anthropogenically generated greenhouse gas (GHG) emissions are likely to impact key aspects of horticultural production. The potential effect of higher temperatures on fruit and nut trees' ability to break winter dormancy, which requires exposure to winter chilling temperatures, was considered. Three chill models (the 0-7.2°C, Modified Utah, and Dynamic models) were used to investigate changes in chill accumulation at 13 sites across Australia according to localised temperature change related to 1, 2 and 3°C increases in global average temperatures. This methodology avoids reliance on outcomes of future GHG emission pathways, which vary and are likely to change. Regional impacts and rates of decline in chilling differ among the chill models, with the 0-7.2°C model indicating the greatest reduction and the Dynamic model the slowest rate of decline. Elevated and high latitude eastern Australian sites were the least affected while the three more maritime, less elevated Western Australian locations were shown to bear the greatest impact from future warming.

Evaluation of recent trends in Australian pome fruit spring phenology.

Temporal and temperature driven analyses were conducted for eight spring phenology datasets from three Australian pome fruit growing regions ranging from 24 to 43 years in length. This, the first such analysis for Australia, indicated significant temporal change in phenophase timing for only one of the datasets. To determine relationships to temperature, a sequential chill and growth method as well as mean springtime temperatures were used to estimate phenophase timing. Expected advancement of phenophase ranged from 4.1 to 7.7 days per degree Celsius increase in temperature. The sequential chill and growth approach proved superior, with coefficients of determination between 0.49 and 0.85, indicating the inclusion of chill conditions are important for spring phenology modelling. Compared to similar phenological research in the Northern Hemisphere, the changes in response variables were often shallower in Australia, although significance of observed hemispheric differences were not found.