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Climate change and silk cotton trees

Nandkumar M Kamat

Known from ancient time as ‘Shalmali’ in Sanskrit, Sanvar in Konkani, silk cotton trees are scientifically known as Bombax ceiba. The best location to study the ecology, phenology, biology and microbiology of these trees is Goa University campus where only 10 per cent of the trees have survived the bulldozers of development. These trees are key stone species supporting more than 40 species of birds, several mammals, more than 500 species of insects and about 1000 microbial species.

It was unusual to see the birds perching silently on these trees this year when normally it is their noisy nectar drinking season. The confusion among the birds is due to climate change. Heavy soil moisture stress due to suboptimal rainfall, thermal inversion and other factors related to climate change have affected the natural biological clock, the flowering cycle of these trees. More than 90 per cent of the trees would flower this month, a delay of more than six weeks as compared to normal. The earliest flowering of these trees has been recorded towards the end of November and delayed flowering is seen even in April.

Since 2003, I assigned research projects on these trees to M Sc and PhD students and these led to several important discoveries. Silk cotton tree is biometeorologically important species because its fate, future and survival in the ecosystem depends on temperature, rains, and wind speed. The delayed flowering indicates two possibilities -unexpected local convective rains in coming weeks and a delay in the onset of SW monsoon.

Thousands of green floral buds are seen on all trees. Within the next few weeks these need to complete their genetic programme to develop into bright red flowers, produce ample nectar and offer it as a reward to pollinators, get pollinated, resist herbivory and infections, form the pods with hard, round black seeds and finally produce the white, silky, smooth, fibrous floss to carry the round black lipid rich seeds for dispersal by the winds.

Nikita De Silva studied the nectar and isolated wild nectarifarious yeasts which utilise glucose. Shweta Saudagar was curious to know the source of the yeasts found by Nikita and discovered that the fertilised floral ovaries of this tree hide inside the sterile tissue some unique endophytic yeasts. An exhaustive ecological, glycobiological and microbiological study was done for a full year by Priyanka Chodankar. She identified the trees as factories of carbohydrates producing not only abundant glucose in floral nectar but stores of starch in huge tuberous roots and prodigious amounts of cellulose in floss. She also discovered that the trees get energy during flowering from breakdown of starch stored in roots.

From November to May silk cotton trees are virtually leafless. Vegetative growth begins immediately after maturation of the pods. The trees regain their green crowns during the monsoon. Younger trees protect themselves with one of world’s most dangerous shield of pointed woody spicules on trunks. These can pierce skins of herbivorous mammals. So Teja Gawde got curious to know their microbiology and found that inside these woody spicules hide dangerous bacterial pathogens which we know as bacterial endophytes.  Sonashia Velho-Pereira investigated antibiotics and enzyme producing actinobacteria from the soil surrounding silk cotton tree roots and published a paper on the novel technique. Shweta Kambli followed her microbiological work and developed methods to study the structure of the silk cotton fibres and isolated fungi capable of hydrolysing the cellulose from the soil around these trees. Ecologically her important finding was higher diversity of cellulolytic fungi in unpolluted habitats as compared to locations polluted by human interference. She also confirmed that these trees may be some of the best species in the world to fix atmospheric carbon dioxide.

Anjum Sadekar was interested in the fate of the dead leaves of these trees. She found interesting biominerals of silica called phytoliths and iron called sideroliths showing the role of this tree in biogeochemical cycling of silicon and iron. Khushboo Khatun found a nematode killer mushroom on dead branches of the tree and finally we could see seven species of oyster mushrooms associated with this species. More than 20 years of silk cotton tree research work resulted in development of several novel techniques.

Near SBI circle, Goa University there was a century old giant silk cotton tree with a girth of two metres and a trunk height of ten metres. It supported a unique web of life. The forest department determined the value of this tree weighing more than 40 metric tons at just `60. To widen the district road MDR-3 , first it was uprooted at night and then cut into pieces with electric saws. Then the people from surrounding villages descended, chopped the fallen branches and stole all the timber to be used as firewood. So practically these trees which produce beautiful bright red flowers have no friends except handful of biologists.

Nobody noticed their delayed flowering this year. Nobody would notice if these majestic, self-maintaining, environmentally useful, ecologically important trees die a natural death or get sacrificed during construction of various projects. A nationally recognised visiting scientist after listening to such stories had commented in a meeting of experts at Goa University, “Don’t worry, if these trees die, you can still have many more elsewhere.” This type of logic is tearing apart the web of life as we debate rapid melting of glaciers, Greenland ice, Antarctic ice shelves while completely ignoring the tragedy of common trees in our own backyard.

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