Located in the middle of the South Atlantic, Ascension Island is probably not on the top of anyone's travel list. This bleak volcanic island doesn't have much to offer the casual tourist but what it lacks in amenities it makes up for in a rich and bizarre history. Situated about 2,200 km east of Brazil and 3,200 km west of Angola, this remote island is home to one of the most remarkable ecological experiments that is rarely talked about. The roots of this experiment stem back to a peculiar time in history and the results have so much to teach the human species about botany, climate, extinction, speciation, and much more. What follows is not a complete story; far from it actually. However, my hope is that you can take away some lessons from this and, at the very least, use it as a jumping off point for future discussions.
Ascension Island is, as land masses go, quite young. It arose from the ocean floor a mere 1 million years ago and is the result of intense volcanic activity. Estimates suggest that volcanism was still shaping this island as little as 1000 years ago. Its volcanic birth, young age, isolated conditions, and nearly non-existent soils meant that for most of its existence, Ascension Island was a depauperate place. It was essentially a desert island. Early sailors saw it as little more than a stopover point to gather turtles and birds to eat as they sailed on to other regions. It wasn't until 1815 that any permanent settlements were erected on Ascension.
Photo by Drew Avery licensed under CC BY 2.0
In looking for an inescapable place to imprison Napoleon Bonaparte, the Royal Navy claimed Ascension in the name of King George III. Because Napoleon had a penchant for being an escape artist, the British decided to build a garrison on the island in order to make sure Napoleon would not be rescued. In doing so, the limitations of the island quickly became apparent. There were scant soils in which to grow vegetables and fresh water was nearly nonexistent.
The native flora of Ascension was minimal. It is estimated that, until the island was settled, only about 25 to 30 plant species grew on the island. Of those 10 (2 grasses, 2 shrubs, and 6 ferns) were considered endemic. If the garrison was to persist, something had to be done. Thus, the Green Mountain garden was established. British marines planted this garden at an elevation of roughly 2000 feet. Here the thin soils supported a handful of different fruits and vegetables. In 1836, Ascension was visited by a man named Charles Darwin. Darwin took note of the farm that had developed and, although he admired the work that was done in making Ascension "livable" he also noted that the island was "destitute of trees."
One of Ascension Island's endemic ferns - Pteris adscensionis. Photo by Drew Avery licensed under CC BY 2.0
Others shared Darwin's sentiment. The prevailing view of this time period was that any land owned by the British empire must be transformed to support people. Thus, the wheels of 'progress' turned ever forward. Not long after Darwin's visit, a botanist by the name of Joseph Hooker paid a visit to Ascension. Hooker, who was a fan of Darwin's work, shared his sentiments on the paucity of vegetation on the island. Hooker was able to convince the British navy that vegetating the island would capture rain and improve the soil. With the support of Kew Gardens, this is exactly what happened. Thus began the terraforming of Green Mountain.
Photo by LordHarris licensed under CC BY-SA 3.0
For about a decade, Kew shipped something to the tune of 330 different species of plants to be planted on Ascension Island. The plants were specifically chosen to withstand the harsh conditions of life on this volcanic desert in the middle of the South Atlantic. It is estimated that 5,000 trees were planted on the island between 1860 and 1870. Most of these species came from places like Argentina and South Africa. Soon, more plants and seeds from botanical gardens in London and Cape Town were added to the mix. The most incredible terraforming experiment in the world was underway on this tiny volcanic rock.
By the late 1870's it was clear the the experiment was working. Trees like Norfolk pines (Araucaria heterophylla), Eucalyptus spp. and figs (Ficus spp.), as well as different species of banana and bamboo had established themselves along the slopes of Green Mountain. Where there was once little more than a few species of grass, there was now the start of a lush cloud forest. The vegetation community wasn't the only thing that started to change on Ascension. Along with it changed the climate.
Photo by Drew Avery licensed under CC BY 2.0
Estimates of rainfall prior to these terraforming efforts are sparse at best. What we have to go on are anecdotes and notes written down by early sailors and visitors. These reports, however, paint a picture of astounding change. Before terraforming began, it was said that few if any clouds ever passed overhead and rain rarely fell. Those living on the island during the decade or so of planting attested to the fact that as vegetation began to establish, the climate of the island began to change. One of the greatest changes was the rain. Settlers on the island noticed that rain storms were becoming more frequent. Also, as one captain noted "seldom more than a day passes over now without a shower or mist on the mountain." The development of forests on Ascension were causing a shift in the island's water cycle.
Plants are essentially living straws. Water taken up by the roots travels through their tissues eventually evaporating from their leaves. The increase in plant life on the island was putting more moisture into the air. The humid microclimate of the forest understory cooled the surrounding landscape. Water that would once have evaporated was now lingering. Pools were beginning to form as developed soils retained additional moisture.
Photo by Ben Tullis licensed under CC BY 2.0
Now, if you are anything like me, at this point you must be thinking to yourself "but what about the native flora?!" You have every right to be concerned. I don't want to paint the picture that everything was fine and dandy on Ascension Island. It wasn't. Even before the terraforming experiment began, humans and other trespassers left their mark on the local biota. With humans inevitably comes animals like goats, donkeys, pigs, and rats. These voracious mammals went to work on the local vegetation. The early ecology that was starting to develop on Ascension was rocked by these animals. Things were only made worse when the planting began.
Of the 10 endemic plants native to Ascension Island, 3 went extinct, having been pushed out by all of the now invasive plant species brought to the island. Another endemic, the Ascension Island parsley fern (Anogramma ascensionis) was thought to be extinct until four plants were discovered in 2010. The native flora of Ascension island was, for the most part, marginalized by the introduction of so many invasive species. This fact was not lost of Joseph Hooker. He eventually came to regret his ignorance to the impacts terraforming would have on the native vegetation stating “The consequences to the native vegetation of the peak will, I fear, be fatal, and especially to the rich carpet of ferns that clothed the top of the mountain when I visited it." Still, some plants have adapted to life among their new neighbors. Many of the ferns that once grew terrestrially, can now be found growing epiphytically among the introduced trees on Green Mountain.
The Ascension Island parsley fern (Anogramma ascensionis). Photo by Ascension Island Government Conservation Department licensed under CC BY-SA 3.0
Today Ascension Island exists as a quandary for conservation ecologists. On the one hand the effort to protect and conserve the native flora and fauna of the island is of top priority. On the other hand, the existence of possibly the greatest terraforming effort in the world begs for ecological research and understanding. A balance must be sought if both goals are to be met. Much effort is being put forth to control invasive vegetation that is getting out of hand. For instance, the relatively recent introduction of a type of mesquite called the Mexican thorn (Prosopis juliflora) threatens the breeding habitat of the green sea turtle. Efforts to remove this aggressive species are now underway. Although it is far too late to reverse what has been done to Ascension Island, it nonetheless offers us something else that may be more important in the long run: perspective.
If anything, Ascension Island stands as a perfect example of the role plants play in regulating climate. The introduction of these 330+ plant species to Ascension Island and the subsequent development of a forest was enough to completely change the weather of that region. Where there was once a volcanic desert there is a now a cloud forest. With that forest came clouds and rain. If adding plants to an island can change the climate this much, imagine what the loss of plants from habitats around the world is doing.
Each year an estimated 18 million acres of forest are lost from this planet. As human populations continue to rise, that number is only going to get bigger. It is woefully ignorant to assume that habitat destruction isn't having an influence on global climate. It is. Plants are habitat and when they go, so does pretty much everything else we hold near and dear (not to mention require for survival). If the story of Ascension does anything, I hope it serves as a reminder of the important role plants play in the function of the ecosystems of our planet.
The endemic Ascension spurge (Euphorbia origanoides). Photo by Drew Avery licensed under CC BY 2.0
Photo by DCSL licensed under CC BY-NC 2.0
