Ascension Island’s Remarkable Ecological Transformation

Aug 18, 2021 0 comments

In the middle of the South Atlantic Ocean, thousands of miles from practically anywhere, lies an isolated volcanic island called Ascension. Two hundreds years ago, Ascension was a desert island with little appeal for passing ships except to collect giant green turtles and birds to eat as they sailed on to other regions. Today, its peaks are covered by lush green forests. This amazing transformation is the result of a remarkable ecological experiment conducted by noted British botanist Joseph Hooker with encouragement from Charles Darwin. Many scientists believe that this fantastic terraformation may hold the key to the future colonization of Mars.

Ascension Island

Photo: Ben Goode |

Ascension island is pretty young, geologically speaking, having emerged from the ocean only about a million years ago. Volcanic activity continued to shape the island as recently as a thousand years ago. As such, most of the island is covered with young volcanic soils, lava fields and cinder deposits. Small shrubs and grasses were the only thing that grew here before human intervention.

The island was first discovered in 1501 by the Portuguese navigator João da Nova on Ascension Day, hence the name of the island. For the next 300 years, the island functioned as a useful stopover point for distant journeys, allowing sailors to replenish their stock of fresh water (there is a strong water spring in the high interior of the island and a much smaller water source, lower on the mountain) and fresh meat (Ascension Island is home to giant green turtles and large seabird breeding colonies). Recognizing its strategic importance, the Royal Navy established a garrison on the island in 1815 (originally to keep watch on Napoleon Bonaparte, who was living in exile on the nearby Saint Helena island) and designated it as a stone frigate, HMS Ascension.

Location of Ascension Island

Location of Ascension Island. Image credit: Wikimedia Commons

In order to make possible for the garrison to survive, the British mariners planted a fruit and vegetable garden on the thin soil on the summit of the central mountain, known as Green Mountain, and also introduced hundreds of sheep and goats, as sources of meat, as well as cows and horses.

In 1836, the young Charles Darwin, nearing the end of his long voyage around the world aboard HMS Beagle, made a brief stop at Ascension. Coming from St Helena, Darwin did not expect much from the island. Before his departure from St Helena, its residents had joked—”We know we live on a rock, but the poor people of Ascension live on a cinder.”

When Darwin stepped on the island, he took note of the farm and marveled at the way the springs were managed “so that a single drop of water may not be lost”. Darwin was impressed by the work the British had done to make Ascension Island livable, although he noted that the island was destitute of trees. “Indeed the whole island may be compared to a huge ship kept in first-rate order,” he commented. Others shared Darwin's sentiment. The French naturalist René Primevère Lesson had remarked “that the English nation alone would have thought of making the island of Ascension a productive spot; any other people would have held it as a mere fortress in the ocean.”

View from atop Green Mountain.

View from atop Green Mountain. Photo: Lord Harris/Wikimedia Commons

Seven years later, British botanist and explorer Joseph Hooker visited the island. Edged on by Darwin, Hooker advised the British Navy that vegetating the island would help capture rain and improve the soil. Trees would capture moisture and reduce evaporation, while their roots will break down the lava rocks and create thicker and loamy soils.

Beginning in 1850 and continuing for a decade, the Royal Navy imported thousands of saplings encompassing more than 330 different species from botanical gardens in Europe, South Africa and Argentina. The plants were specifically chosen to withstand the harsh conditions of life on this volcanic desert. In twenty years, more than five thousand trees had begun to take root. They covered the crown of Green Mountain, the highest point of the island, in a lush halo of bamboo, while tall Norfolk pines flanked the slopes. These trees were planted to be used as replacement masts for sailing ships.

Lush bamboo grove on Green Mountain.

Lush bamboo grove on Green Mountain. Photo: Ben Goode |

With the change in vegetation, the climate of the island too changed. Before terraforming began hardly a cloud passed overhead and rainfall was rare. After vegetation began, settlers on the island noticed that rain storms became more frequent. Caroline Power, who visited the island in 1834, reported, that “in the last three years a considerable change in the climate has been perceived. For months together, I have been told by several who have been resident from 3 to 7 years, as well as by Captain Bateb, not a cloud would pass over the heavens, nor a drop of water fall; but since the land on the mountain has been so much cultivated, a gradual increase of rain has taken place—seldom more than a day passes over now without a shower or mist on the mountain; and during the first ten days we were here constant little showers fell.”

The development of forest on Ascension Island also caused a shift in the island’s water cycle. Previously, the biggest problem with Ascension Island was water retention. Now with forests, rainwater did not drain back into the sea but was retained by the soil and the island’s forest, taken up by roots and eventually evaporating from the leaves to put more moisture into the air. This created a humid microclimate that cooled the landscape, and increased the chances of more rain.

Mist covered forest on Ascension Island.

Mist covered forest on Ascension Island. Photo: Ben Tullis/Flickr

Green Mountain’s flora can now be divided into three distinct zones—a dry and hot zone below 330 meters with patches of grass, dry-adapted shrubs, and small thorny mesquite or tobacco trees; from 330 to 630 meters, there is more complete coverage including grasses, prickly pear, and trees such as juniper, she-oak and acacia. Above, 660 meters is the misty, wet zone that is completely forested. In addition to bamboos and Norfolk pines, there are banana, ginger, juniper, raspberry, coffee, ferns, fig trees, and Cape Yews. At the summit, there is the an open body of freshwater, the Dew Pond, replete with blue water lilies. This zone is about 7 degrees cooler than the lowlands, providing residents (the island has a population of 800 distributed in five settlements) and tourists an escape from the year-long heat of the tropics. “How glorious is the heavenly air up here!”, wrote A. C. H. Rice in 1926. “How cool and clean after the dusty dried-up lava pandemonium below!”

In 2005, Green Mountain became Ascension Island’s first National Park.

Green Mountain, Ascension Island

Green Mountain, Ascension Island. Photo: LordHarris/Wikimedia Commons

There is an important lesson to be learnt from Ascension Island. If a small forest can completely change the climate of that region by this much, imagine what the loss of plants from habitats around the world is doing to earth’s climate. Since 1990, the earth has lost an estimated 420 million hectares of forest. As the human population continue to rise, that number is only going to get bigger. The only good news is the rate of deforestation has been on a downward trend for the last couple of years.

Dr. Dave Wilkinson, an ecologist at Liverpool John Moores University, finds Ascension Island's strange ecosystem exciting. “What it tells us is that we can build a fully functioning ecosystem through a series of chance accidents or trial and error.” Wilkinson believes that Ascension Island is a great example where the aspects of ecosystem construction and function, as well as mitigation of human caused global environmental change, can be studied.

# Howard Falcon-Lang, Charles Darwin's ecological experiment on Ascension isle, BBC
# Important Lessons From Ascension Island, In Defense of Plants
# David C. Catling, Stedson Stroud, The Greening of Green Mountain, Ascension Island


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