Phenological response of citrus flowering to climate variability and change in Iran: 1960-2010
Date
2013-08-02
Authors
Fitchett, Jennifer Myfanwy
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Abstract
Phenology refers to “the study of the timing of recurrent biological events, the causes of their timing with regard to biotic and abiotic forces, and the interrelationship among phases of the same or different species” (Badeck et al., 2004: 295). This discipline has recently gained popularity in bio-geographical climate change studies, as it is recognized as an accurate and easily measured signature of the impact that changing temperature and precipitation over recent decades have had on plants. A five-decadal dataset (1960-2010) comprising daily temperature and rainfall records, and of the annual timing of peak flowering of five citrus types (orange, tangerine, sweet lemon, sour lemon and sour orange) was acquired for the Iranian cities of Gorgan, Kerman and Shiraz. The cities are geographically and climatically distinct, with arid Kerman located on the central Iranian plateau, humid Gorgan on the Caspian lowlands and Shiraz situated at the foot of the Zagros Mountains with a semi-arid climate. These climate data for Kerman and Shiraz reveal strong, statistically significant increases in Tmax of 0.03°C/yr, and even stronger increases in Tmin of 0.05°C/yr-0.07°C/yr, whilst Gorgan presents a statistically significant decrease in precipitation of 4.69mm/yr over the study period. Significant increases in daily sunshine hours of 7.09h/yr and 19.01h/yr are demonstrated for Gorgan and Kerman respectively. Negligible delays in the timing of peak flowering for the five citrus types in Gorgan by 0.05-0.01d/yr, and more considerable advances in the timing of flowering for Kerman (0.12-0.17d/yr) and Shiraz (0.56-0.62d/yr), occur concurrently with these climate trends. These differences in the direction of shift in flowering dates, combined with differences in climate trends, highlight the extent to which the location of the crops, and the associated abiotic forces, influence flowering dates. Significant relationships between the flowering dates of the citrus types and Tmax are demonstrated for Kerman and Shiraz, equating to advances of 1.85-3.08d/°C and 6.14-7.86d/°C respectively, with similar advances in flowering dates associated with increases in Tmin. Significant relationships between the timing of peak flowering and precipitation are demonstrated for Kerman. Across the majority of the climate variables studied, the strongest monthly relationships with flowering dates were for the month in which peak flowering occurs, suggesting a direct effect on control over this phenophase. The development of multiple regression models facilitated the simultaneous analysis of the effects of all of the climate variables, and increased the associated explanatory potential. The rate of change in peak flowering dates observed for the period 1960-2010, and the relative influence of some climate variables over others, highlight the importance of monitoring fruit tree phenology in a water scarce region such as Iran. With decreases in precipitation, increases in Tmin and Tmax and the potential for heightened frost risk by the end of the century due to the increased likelihood of late-winter flowering, citrus cultivation in Kerman is under threat. Shiraz is likely to survive continued climate variability and change throughout the 21st century, provided that sufficient water is available either naturally or through irrigation. Gorgan demonstrates the greatest capacity to continue successful citrus farming, and the greater Caspian Lowlands hold potential as a suitable location for the expansion of citrus farming required to compensate for any yields lost in the more arid areas of Iran and the Middle East.
Description
Dissertation submitted to the Faculty of Science in fulfilment of the requirements for the degree Master of Science. Johannesburg, April 2013