Potential Impacts of Climate Change on Coconut

By Sanathanie Ranasinghe

There is enough scientific evidence to conclude that climate change is taking place. Plantation agriculture is one of the high priority sectors where the impacts of climate change exceed tolerance limits, with implications for the livelihoods of millions of people who are dependent on this sector as well as to the national GDP contribution of coconut.  The Coconut Tree, also referred to as the “Tree of Life”, is an important part of the Sri Lankan diet with an estimated per capita fresh nut consumption of 129 nuts per year (including oil).  Coconut provides approximately 15 % of the calories in the daily diet and is the sole source of fat for much of the rural population. The annual national coconut production during 1996-2010 averaged at 2673 million nuts from which about 80 % is locally consumed and the balance, exported as desiccated coconut, copra, oil, mature nuts, milk powder and other processed products (Coconut Development Authority and Department of Census and Statistics, Sri Lanka). The coconut sector makes a substantial contribution of about 1.4% to the GDP (of 2.7% of total plantation crops) and 3.57%  of foreign exchange earnings (Central Bank, 2009) to the country. On account of the important role it plays in the country, it is imperative to identify adaptation and mitigation measures to make coconut a sustainable industry even in the event of anticipated climate change.

Coconut is cultivated in all three agro climatic zones (ACZ) of Sri Lanka (30% in the wet zone, 50% in the intermediate zone and 20% in the dry zone), and new planting programmes of coconut are underway mainly in the northern and eastern provinces of Sri Lanka. Coconut performs well under a mean annual temperature of 27 0C – 29 0C and rainfall of 1250-2500 mm/year.  Therefore, increased temperatures and the scarcity of water predicted as a result of anticipated climate change will be the most critical factors that would affect the yield of coconut. 

It has been identified that reproductive development in coconut is more sensitive to high temperature stress and water stress than vegetative development and the principal harmful effects are reported on nut set. Nut setting is the most important yield determining factor in coconut and reduced nut setting due to heat stress and long dry spells are often experienced in coconut plantations in the dry-intermediate and dry zones, even those under irrigation.  This could be either, due to unfavourable environment conditions during fertilization (pollen germination), or poor pollen quality.

Coconut palms produce approximately one inflorescence per month, leading to about 12-14 inflorescences per year.  The stages of inflorescence development such as pollen formation (one month before inflorescence opening) and button nut formation (1-2 months after inflorescence opening) can be very sensitive to prevailing climatic conditions.  Continuous exposure to heat or water stress can prevent the accumulation of starch and sucrose in the developing anthers, which is the main source of energy for pollen germination, resulting poor pollen quality.  Further, high temperatures, low relative humidity and a high vapour pressure deficit at the stage of pollination may result in pollen drying - consequently resulting in reduced nut set. This is the situation normally observed in the February / March period of each year, as shown in Fig. 1. The degree of sensitivity to high temperature can vary with the variety, depending on their tolerance to stress.  Therefore, studies are underway to identify heat tolerant cultivars based on their reproductive survivability as a major adaptation strategy to climate change.

Fig. 1: Monthly variation in nut setting (number of set nuts per palm at 2-3 months stage) of a coconut plantation in the Intermediate Zone in 2009 and 2010.

On the other hand, Coconut - as a perennial tree crop with 50-60 years of economic lifespan, has a great potential as a Carbon Sink for mitigating climate change.  The Clean Development Mechanism (CDM) is presented as an opportunity for developing countries to get certified in order to negotiate subsidies from the Carbon (C) market. Productivity and net carbon balance of types of land used for coconut are key issues for the CDM.  The potential role of coconut plantations in mitigating global warming is not adequately addressed by researchers.  The first study on carbon sequestration potential of coconut in Sri Lanka was initiated at the Coconut Research Institute (CRI) in 2009.  The preliminary information revealed that a 25-26 yr old Sri Lanka Tall (commercially grown) plantation can sequester about 17-80 MT of Carbon dioxide ha-1 yr-1 depending on the agro-climatic and soil conditions.  If the carbon is marketed at the rate of 11 US$ / unit, growers can earn about Rs 20,000 – 96,000 ha-1 yr-1 under CDM (pay for net ecosystem carbon balance of new plantations).  The same coconut plantations contain a carbon stock of about 30 - 70 MT ha-1 (plant and soil) depending on the agro-climatic and soil conditions.  The carbon sequestration potential in coconut plantations vary with the season of the year, age of plantation, variety and management and the studies at CRI are being strengthened and continue to collect information.

Therefore, it is clear that climate change will have negative effects on coconut plantations due to increased temperature and water stress.  However, coconut plantations can also be used to mitigate climate change which is an environment service by acting as C Sinks to absorb CO2 from the atmosphere and control global warming while giving an additional income to the growers through C trading.

The author Sanathanie Ranasinghe is Head, Plant Physiology Division, Coconut Research Institute in Lunuwila, Sri Lanka.