Mangroves: A vanishing resource (1)
By Tonye Princewill
ANYONE who has flown low over Nigeria’s coastline, or plied the creeks and rivers of the Niger Delta in a boat, must surely have been struck by ubiquitous stilted-root trees, with slim trunks and evergreen crests, thickly lining the waterways.
Those are mangroves—a defining feature of tropical and sub-tropical coastlines around the world and one of the unsung heroes of the earth’s ecosystem.
The important role these unique woody plants play in helping to sustain other life-forms, including humans, is little known and even less appreciated, especially in Nigeria.
Increasingly, therefore, mangroves are becoming ecological martyrs—victims of public apathy and indifference. Our failure to adequately protect and properly manage the nation’s mangrove system threatens their survival.
A few years ago, for example, the National Space Research and Development Agency, NASRDA, in collaboration with the University of Missouri, at Kansas City (USA), carried out a satellite study of the Niger Delta and found that “between 1986 and 2003, 318 hectares of mangrove forests have been depleted”.
It has become standard, almost ritualized, procedure, to blame the destruction of Nigeria’s mangrove swamp—and almost all other environmental problems—on the oil companies. But while the NASRDA study did name dredging and other oil-extraction-related activities as very important factors, it did not stop there.
The investigators also cited rapid urbanisation–exemplified by drastic population increases in Port Harcourt and Warri–the introduction of the voracious and highly destructive Nypa palm and the felling of mangrove trees for fire-wood, construction and other purposes by indigenous peoples.
The progressive loss of mangrove acreage may be more pronounced in Nigeria than in many other countries. But it certainly is not exclusive to us. “Across the globe,” writes Natesan Balachandran et. al. in The Journal of Ecology and Natural Environment, “mangroves are threatened”.
According to the US National Aeronautics and Space Administration, NASA, the world has lost half of its mangrove acreage over the past 50 years, a third within the last two decades.
A joint study of NASA and the US Geological Survey, found that mangroves presently cover 137,760 square kilometres of the Earth’s surface in 118 different countries and territories. But 75 percent of this area is located in just 15 tropical countries, with territory on or near the equator.
Thanks to imperialist writers, such as Rudyard Kippling, Joseph Conrad and C.S. Foster, mangroves are closely associated with Africa and India. But in reality, Asia contains about 42%, Africa 21 %, North and Central America 15 %, Australia and the South Pacific 12 % and South America 11 %.
In fact, NASA reports that most of the world’s mangroves are contained on Indonesia’s 17,000 islands, with Brazil and Australia ranking second and third respectively. Other sources put Nigeria—with the bulk of Africa’s mangrove forests–in fourth position, globally.
Technically, the word “mangrove” does not refer to a plant as such, but rather to an “ecological assemblage”, as Ilka C. Feller and Marsha Sitnik of the Washington-based Smithsonian Institution, put it. The assemblage consists of shrubs and trees that have adapted to the wet, saline (salty), hot, humid and muddy conditions of tropical and sub-tropical coastlines.
In the introduction to their “Mangrove Ecology Workshop,” the authors note that there are 34 species or so of “true mangroves” and another 80 of what they term “minor components” and “mangrove associates”.
True mangroves, they observe, are not only restricted to the swamp marshes and stream-banks of the inter-tidal zones, but they have also developed several important adaptations that set them apart from other species.
One is the ability to exclude or excrete salt from their interior. This enables the true mangrove to survive and thrive in the brackish waters of the Niger Delta’s creek system and river estuaries—places where most other woody plants would perish.
Another evolutionary asset of mangroves is their distinctive aerial root system in which embryo germination begins in the tree. Shoots then extend downward from the limbs to anchor themselves in the ground or float off to a distant location and help to establish a new colony—a process called viviparity.
“The tree later drops its developed embryos called propagules,” reports the website of the conservationist Mangrove Action Project, “which may take root in the soil beneath. Viviparity may have evolved as an adaptive mechanism to prepare the propagules for long-distance dispersal, and survival and growth within a harsh saline environment”.To be continued