Looking beyond our borders to secure the future of local agriculture: Lessons learned from 50 years of citrus cultivation in Iran

The study analysed citrus flowering dates from Kerman on the central arid plateau, Gorgan in the humid Caspian lowlands of the north and for Shiraz, situated in the semi-arid zone at the foot of the Zagros Mountains in south-western Iran. View larger version Citrus orchard south-east of Shiraz on the foot-slopes of the Zagros Mountains. Analysis of climate data revealed that both maximum and minimum temperatures for the area have been increasing steadily since 1960. (Source: www.panoramio.com) Leaf and shoot damage caused to lemon trees by frost. Advanced flower dates increase the likelihood of frost damage to flower buds and immature fruit, while the early onset of winter jeopardises the standing crop of mature fruit. (Source: www.123rf.com)

Understanding the impacts of climate change in agriculture is challenging. In some areas of the world, the potentially positive effects of a changing climate (such as the extension of the growing season) may counter expected negative impacts (such as increased drought).

However, the overall impression is that agriculture as a whole will suffer as global mean temperatures continue to rise and rainfall regimes are redefined.

The situation is further complicated as minimum temperatures are increasing at a faster rate than maximum temperatures, and high latitude temperate regions are warming faster than the tropics.

Within this uncertainty is general agreement on two issues. Firstly, the negative impacts of climate change will not be felt equally across the world, with the greatest production losses expected in developing countries due to their limited capacity to adapt. It has been estimated that in some African and Middle Eastern countries, yields from rain-fed agriculture could be reduced by as much as 50% by 2020 (sourced from the 2007 Fourth Assessment Report issued by the Intergovernmental Panel on Climate Change).

Secondly, impacts will vary between specific crops and their climate demands. Such projections mean that farmers have to be fore-warned concerning likely local and regional impacts, and be exposed to the possibility of alternative crops more suited to the new environment, or to shifting cultivation into new areas.

Understanding climate change consequences

Understanding how climate change reduces yield and profit in agriculture is vital. Depending on the crop and the severity of the changes in climate, the worst case scenario is outright plant death. However, the more likely consequences, at least in the short term, will be more subtle and could include changes in flowering dates, failure to open buds and inhibited or delayed fruit or seed maturation.

Explaining these plant-level effects, validating regional projections and detecting present impacts require region- and crop-specific studies that correlate long-term (>30 years) climate and crop (flowering, fruiting and harvest) records.

Scientists from SAEON’s Ndlovu Node in Phalaborwa and the School of Geography, Archaeology and Environmental Studies at the University of the Witwatersrand (WITS) are working to further our understanding of the timing and causes of recurrent biological events in crops.

This discipline, termed agricultural phenology, is gaining popularity in climate change studies as a means of easily and accurately recognising the signature that temperature and rainfall has had on plants, given sufficiently long and complete data records.

Analysing citrus data in Iran

SAEON and WITS researchers recently sourced (University of Golestan, Iran and the Iranian Meteorological Association) and analysed a data set for five citrus types grown between 1960 and 2010 in three climatically distinct localities in the Islamic Republic of Iran - a species group and region for which phenological research to date is scarce.

Citrus are the highest value fruit crop in international trade (UNCTAD, 2005) and are cultivated in 140 countries. For the period 2001-2010, Iran was the 8th largest citrus producer in the world, with yields accounting for 3% of the global total of 105 million tons. By comparison, South Africa contributed 2% of global production for the same period.

Figure 1: Percentage contribution of top citrus producing countries to total global annual production for the period 2000-2004. (Source: UNCTAD, 2005)

The study analysed citrus (orange, tangerine, sweet lemon, sour lemon and sour orange) flowering dates from Kerman on the central arid plateau, Gorgan in the humid Caspian lowlands of the north and for Shiraz, situated in the semi-arid zone at the foot of the Zagros Mountains in south-western Iran. Trends for five citrus types over the 51-year period demonstrated earlier (up to 31 days) peak flowering dates from Kerman and Shiraz, but delayed (up to 2.5 days) flowering in Gorgan.

Figure 2: Advancing (earlier) peak flowering dates for the five citrus types grown in Shiraz for the period 1960 to 2010. Peak flowering has advanced by approximately four weeks, from mid-April to mid-March, over the past 50 years.

Climate data for Kerman and Shiraz revealed increases in both maximum (0.03^oC/yr) and minimum temperatures (0.07^oC/yr) and a decreasing difference between the two. Gorgan revealed decreased rainfall (4.69mm/yr) over the study period. Not surprisingly the flowering dates, and in particular the shifts in flowering dates since 1960, are strongly linked to the changes in maximum and minimum temperature, and rainfall. Further, the strongest relationships between flowering dates and climate were found for the month in which peak flowering occurred, suggesting the direct control of temperature on this life stage.

Citrus typically require a period of cool temperatures or drought to initially release bud dormancy, followed by warm conditions with sufficient moisture to induce full bloom and support fruit maturation. Consequently, increased or decreased temperatures and rainfall and any shift in the timing of annually occurring plant events is of concern for the long-term survival of the industry. For example, increased maximum and minimum temperatures increase the likelihood that bud dormancy will not be released, or that a threshold suitable for citrus growth will be exceeded. Advanced flowering places the flowers and immature fruit at considerable frost risk, especially since the annual ‘last frost date’ has remained unchanged over 50 years. Both scenarios will ultimately impact negatively on fruit yield and profit.

Models of yield under extrapolated temperature and rainfall trends suggest that citrus cultivation in Kerman through to the end of the 21st century will be unlikely, given that the industry in this region currently requires irrigation to supplement the low annual precipitation.

The citrus industry in Shiraz is likely to survive continued climate variability and change through the 21st century, provided that sufficient water is available. Alternatively, Gorgan and the greater Caspian lowlands region demonstrate the potential for increased productivity and support the expansion of citrus farming which, provided that available land and resources are not limiting, would compensate for industry losses elsewhere within the country and sustain the predominantly local demand.

Importance of long-term data

This study, built on data from Iran, reinforces the absolute value of long-term data - in this case pertaining to the behaviour and performance of crops, and how these can be interpreted to inform the adaptation strategies essential for sustaining agricultural capacity and ensuring sustained economic and food security under climate change.

Further, these findings add to a growing body of scientific evidence highlighting clear species- and location-dependent climate change responses over recent decades. Unfortunately, the phenological studies necessary for underpinning adaptation strategies remain sparse for much of the Middle East, as well as central Asia, South America and Africa - including South Africa, and are limited largely by a lack of suitable and corresponding phenology and climate records.

Not only should the collection of these data from as wide a variety of species/crops and locations be encouraged moving forward, but existing data records should be aggressively pursued and interpreted.