Features
Climate repair through rubber cultivation
by Dr Sunil.E Fernando
Environmental Benefit of Growing Rubber
Hevea brasiliensis, or the rubber tree, began its epic journey in 1875, when Sir Henry Wickham brought 70,000 seeds from the Rio Tapajos area, in the upper Amazon, to Kew gardens in London. Of these, 1911 seedlings were planted in the Gampaha botanical gardens, initiating an agricultural revolution in S-E Asia and an industrial revolution globally. Apart from giving 14 million tons of Natural Rubber (NR) consumed annually, worldwide, rubber trees have other attributes (listed below) as well.
* Splitting Oxygen from Carbon dioxide and water and adding it to the atmosphere while producing rubber latex.
* Yielding 2.1 cubic meters/tree of wood from Carbon dioxide as biomass in every 30-year cycle of the tree.
* Producing easily biodegradable litter, compared to monocultures like Teak.
* Requiring comparatively less chemical fertilisers, water and pesticides.
* Retaining biodiversity as a tropical plant by co-existing with other species and allowing for intercropping E.g Ginger, Turmeric, Banana, and even Coffee and Cinnamon.
* The uniqueness of the rubber tree is its ability to fix Carbon dioxide almost instantaneously into a rubber hydrocarbon on a daily basis with just water and energy from sunlight. For a similar conversion, nature took millions of years, turning biomass to a hydrocarbon, Petroleum.
Thus, the rubber tree is a natural chemical factory trapping energy from the Sun, propagating a chemical reaction giving, a hydrocarbon, while releasing Oxygen to the atmosphere and accumulating a renewable timber resource. Tapped from year five , the tree removes GHG by converting it to a useful commercial raw material, unlike any other plant species, for 11 months of the year for a minimum period of 25 years.
Why Excess Carbon Dioxide is bad?
Carbon dioxide present in the atmosphere is a double-edged sword. It is an essential prerequisite to make one of the most vital building materials, Carbohydrates, to benefit all living forms. However, its increase in the atmosphere, and in the Oceans, brings about undesirable effects of global warming. “CARBON DIOXIDE-Earth” reports that, its concentration increased from 330 Parts per million (ppm) in 1975 to 408 in September 2019, and further to 415 ppm in September 2020.
Carbon dioxide absorbs Infrared Radiation (heat radiation) from the Sun through molecular vibrations. Unlike other common gases in the atmosphere, like Nitrogen and Oxygen, it emits this absorbed energy back into the surrounding warming the location. Ozone, Methane and Nitrous Oxide are other GHG’s function in a similar manner, absorbing energy from the Sun and emitting heat thus warming the atmosphere.
However, GHG’s also performs a useful function by maintaining atmospheric temperatures, without converting Earth into an ice ball. Nevertheless, high concentration of GHG in atmosphere will emit more heat increasing atmospheric temperature beyond what is required to sustain and enhance global warming. The imbalance in CHG is created by excessive human activity like burning fossil fuels and releasing gases like Sulphur dioxide responsible for acid rain. While farming and especially raising cattle/sheep for meat as well, release large quantities of Carbon dioxide and Methane, etc. In addition, abandoned oil/gas wells and coal mines emit Methane is large quantities as well increasing CHG in the atmosphere.
Two confirmed methods to lower ill effects of GHG’s are,
a) Produce less of it, and
b) Increase plant cover
Carbon dioxide is the raw material for all forms of Carbohydrates, Proteins and Fats produced by plants providing for growth and energy in all life forms. What is alarming is the excess Carbon dioxide produced, through human interaction accumulating in the atmosphere and in Oceans. Dissolved Carbon dioxide in seawater raises temperature while forming Carbonic acid, thus increasing Ocean acidification. Ocean acidification reduces the ability of sea creatures to fix Calcium as Calcium Carbonate in bones and shells. While Calcium carbonate helps build rigid structures in their bodies it is another form of Carbon sink, besides being a valuable raw material, as well.
Carbon Dioxide Accumulation
Antoine Lavoisier said that in a chemical reaction, matter is neither created nor destroyed. Though producing GHG’s through human intervention a new matter is not created, it leads to an unsustainable imbalance in the environment. This is what causes the problem. See Figure.
In the 21st century Carbon dioxide cycle, there are less of trees and more exhausts due to auto and factory emissions leading to this imbalance. Carbon dioxide is a GHG not only produced by burning fuels and biomass. Humans exhale One Kilogram of it daily. Increase in human population does not increase Carbon dioxide as what we exhaled came from plant-based materials. But when the human population went up from 1 billion 200 years ago to seven billion as of now, increase in human activity led to an imbalance of CHG in the atmosphere and in the Oceans due to accelerated faster release of these gases. Meanwhile, excessive consumption and population pressure, led to lower forest cover that can absorb Carbon dioxide. Thus, the imbalance of accumulating gases that are capable of absorbing excessive amount of heat from the sun, and releasing it through molecular vibrations creates the global warming experienced now.
Biosynthesis of Natural Rubber (NR)
About 2000 plant species produce natural rubber as biological necessity, but Hevea brasiliensis (botanical name for normal rubber tree) produce commercially exploitable dispersion of it in water as latex. The biological reasons for production rubber latex by the rubber tree is not clear, but having a layer of latex just below the top of the bark of the tree, prevent pathogenic microorganisms entering the tree in case of an injury to it.
Latex, which contains about 30% rubber hydrocarbon, is found in horizontally arranged interconnected cells called Laticifers in the bark of the tree. Latex is commercially extracted by making careful incision or “tapping” of the bark. High yielding rubber plantations with about 400 trees per Hectare have reported a production of 2500 Kg/Rubber/Year. However, the theoretical yield potential of rubber is estimated at, 7,000 to 12,000 kg/Ha/Year. A tree giving 15 to 30 grams of rubber per day, tapping on alternative days, yield 2.6-5.2 Kg of rubber per year. According to Apollo Vredestein R and D, on average 1.9 Kg of natural rubber goes into a tire and a tree produces enough rubber to make 2 tires per year or 50 in its lifetime.
Plants take in Carbon dioxide for survival and convert it into an edible/useful form of a Carbohydrate, containing Carbon, Hydrogen and Oxygen as the first stage. Part of the Carbohydrate becomes a source of energy and the rest become precursor for Fats and Proteins, which perform vital functions of all living organisms. Plants also convert carbohydrates into other polymeric forms including Cellulose. Some Cellulose produced ends up as wood becoming a Carbon sink for a considerable period of time.
In the rubber trees, the process of Carbon Dioxide fixation extends further by converting part of Carbohydrates produced, consisting of Carbon, Hydrogen and Oxygen into a rubber containing only Carbon and Hydrogen, which is more akin to Petroleum. The wonder tree makes this hydrocarbon in a few minutes, while nature took millions of years to convert biomass derived from Carbon dioxide like cellulose to give Petroleum.
(To be continued)