For over a decade, evidence has been growing that accumulation of green house gases in the upper atmosphere is leading to changes in climate, particularly in temperature. The average global surface temperature increased by 0.6 ± 0.2 0C over the 20th century and is projected to rise by 0.3 – 2.5 0C in the next 50 years and 1.4 – 5.8 0C in the next century.
 

Global warming changes the earth’s atmospheric circulation and is linked to changes in patterns of precipitation and the frequency and intensity of extreme climate events. The economic and ecological consequences of global warming will vary by region, but in the tropics, it will likely to threaten production of crops and may even become a major cause of species extinction.
 

Under the Kyoto protocol of the United Nations Framework convention on climate change, signatory countries must decrease emissions of carbon dioxide to the atmosphere, or increase rates of removal and storage. The Protocol’s Clean Development Mechanism (CDM) allows a country that emits C above agreed-upon limits to purchase C offsets from an entity that uses biological means to absorb or reduce greenhouse emissions. The CDM is currently offered for afforestation and reforestation projects, but it is expected that in the future it will be extended to C sequestration in agricultural soils. Markets for soil and plant C sequestration are also developing outside of the protocol in addition to those promoted by CDM.
 

The interest in C sequestration and trading as mechanism for both environmental protection and poverty alleviation in developing countries has increased considerably in the last decade. It is anticipated that the CDM could result in enhanced productivity and income as well as local conservation of natural resources in the developing world. This is of relevance to Sri Lanka.
 

Under a C trading arrangement, natural resource users who adopt and / or reintroduce land management technologies that store additional C in soils and vegetation compared to existing practices would be eligible to receive payments for the C those practices sequester. Two types of payments are anticipated, namely payments for C capture and C Storage.
 

Rubber-based cropping systems
 

Rubber based agroforestry involve complex and diversified cropping system that combines the growing of rubber and other agricultural crops in one area. A desirable rubber based cropping system would give a good economic yield while protecting the environment, conserving soil, water and nutrients.
 

Perennial tree crops as in the case of forest trees, are known to function as natural “Sponges” for absorbing corbondioxide from the atmosphere. Carbon sequestration is achieved through the uptake of carbondioxide from the atmosphere and its conversion into cellulose and organic matter.
 

The rubber tree Heva brasiliensis was first introduced as a crop for plantation agriculture several years ago from the wilderness of the Amazon Jungles. Hence, one can expect Hevea to behave as a typical tropical rain forest tree that would at least function as efficient as forest trees in C sequestration.
 

Moreover, technological practices that are known slow down soil C oxidation and increase C fixation and storage are also being adopted in rubber plantations. Such strategies include improved soil and water conservation practices such as leguminous cover cropping, application of organic manure, mulching, inter-cropping etc., which are known to have helped in the increased enrichment of soil organic C by about 30 to 50% from about 1.9% C to 2.39% C in the lower depth of soils and to 2.9 C% in the top soil.
 

Carbon accumulation within the mature Hevea ecosystem in the early years of maturity comprises mainly the carbon locked up within the mature tree through increase in dry matter accumulation, from within the interrow leguminous cover system and associated litter, decomposing Hevea leaf litter and branch material arising from self pruning and in shed reproductive parts including mature seed and fruit components and within the fertile top soil region. Annual leaf fall which includes falling branches twigs and fruit is estimated to be around 3.7 to 7.7 ton/ha.
 

Carbon trading
 

Malaysian estimates indicates that mean annual leaf litter fall for a mature Hevea rubber ecosystem which included falling branches, twigs and fruits to be around 3.7 to 7.7 ton/ha. Some preliminary studies done in Sri Lanka on biomass accumulation and crbon sequestration in rubber plantations from year 1 to year 33 when the trees are due for uprooting, indicates that total biomass accumulated in a tree at the age of 33 years is 1.8 mt which amounts is 963 mt per hectare. This value is made up of biomass accumulated in fruits, leaves and fallen branches and trees uprooted at the end of the trees’ economic life span of 33 years. The amount of Carbon sequestered in one hectare of a 33 year-old stand is 596 mt, the major portion coming from the trunks and branches. The total amount of carbon sequestered in one hectare of rubber plantation made up of tree biomass, latex produced and contribution from leguminous cover crops amount to 680 mt. The possible credit revenue entitlement per hectare at the end of 33 years at the rate of U$ 12 per mt is about U$ 8160 which is approximately equivalent to one million Sri Lankan rupees.

Consideration of additional soil C sequestration in the same land will provide additional financial benefits
 

These indicate that the economic potential for soil and plant Carbon sequestration and trading in rubber plantation appears to be vast and justifies further exploration.
Although technologies are available for the determination of carbon sequestration in soils and plant samples, development of more simpler, rapid and cost effective systems for both the technical potential to store soil organic carbon ( SOC) and the economic returns to growers who adopt practices that sequester carbon in soils and rubber plants would be an impetus for rubber growers to consider carbon trading business.
 

Institutional arrangement
 

The C market system appears to provide ample opportunities for buyers and sellers of C stock as a profit earning business but in practice however, C markets are very complex because they presuppose the existence and integration of many conditions at multiple levels. Prerequisites include the technical capacity to enhance C storage in crop production systems, the capacity for rubber growers and other resource users to collectively adopt and maintain land resource practices that sequester C, the ability for dealers or brokers to monitor C stocks at the field level, the institutional capacity to aggregate C credits at levels large enough for dealers to consider worth while and the financial mechanisms for incentive payment to reach growers. Hence, while C payments may contribute to increasing grower incomes and promoting productivity enhancement practices, they may also expose resource users to additional tension and risks.
 

Given its reliance on complex global agreements, contractual commitments and possibly subsidy programmes, C trading will not be able to function without government’s firm backing. State’s support will be instrumental in funding technology development and transfer, providing extension services, offering subsidies and incentives, regulating certification processes etc.
 

Because technical economic and institutional conditions are not yet in place to make C sequestration as a successful business venture, it is more practical for resource limited rubber industry to pursue C sequestration initially as “ long-term pilot projects” in partnership with global carbon trading professionals / ventures.
 

Ultimately, it will be the synergy of land management practices, measuring and monitoring methods, scaling up procedures and institutional mechanism that will generate and deliver a “marketable product”. Therefore, more applied research and practical experience are needed to better understand the uncertainties entailed in C sequestration and trading and to devise approaches that minimize risks and costs, create efficiencies and promote participation.
 

(The writer can be contacted at treecrops@gmail.com)