In the remote Campbell Island, situated more than 600 km south of New Zealand’s mainland, grows a solitary Sitka spruce that has gained distinction as the loneliest tree on earth. Its nearest neighbor is over 220 km away, on the Auckland Islands, while the nearest member of its own species is on another hemisphere altogether, across the Pacific. So how did this lonely Sitka spruce come to be where it is?

Campbell Island is one of New Zealand’s most southern island. It is located in a region dominated by fierce westerly winds—the Furious Fifties— that doesn’t allow anything taller than a few feet to grow. The weather, while not freezing, is far from pleasant. Temperatures rarely climb above 10 degree centigrade. Everyday is cloudy and most days are rainy. There are only 40 rain-free days on Campbell Island, and barely 600 hours of sunshine per year—that’s an average of less than two hours a day. The only plants that survive these conditions are a kind of perennial herbs called megaherbs. They are so called because they grow unusually big with leaves as large as a sheet of printer paper—a strategy they have adopted to make the best use of whatever little sunshine they receive.

Photo credit: chsgardens.co.nz

Sitka spruce doesn’t grow anywhere around this region. In fact, there are no Sitka spruce anywhere in the southern hemisphere. The only place the tree grows natively is a narrow belt on the west coast of North America, that stretches from southern Alaska and British Columbia to northern California.

The spruce on Campbell Island is thought to have been planted by Lord Ranfurly, who was the governor general of New Zealand from 1897 to 1904. Ranfurly planted the tree while on an expedition to New Zealand’s outlying islands to collect bird specimens for the British Museum, sometime between 1901 and 1907. Although the tree survived—thanks to its natural preference to cold and wet climate—it hasn’t exactly flourished. After all these years, it’s barely 10 meters tall, according to the most recent measurement made in 2011. Back in its native land, it would have stood at least 60 meters tall. The tree, despite being over a hundred years old, has never bore a cone, suggesting it has remained in a permanently juvenile state.

The tree’s stunted growth is partly due to the oceanic climate, and partly due to the fact that its trunk was routinely chopped down by the staff of the meteorological station that operated there until 1958. There are no natural forest in Campbell Island, and the Sitka spruce was their only source of a Christmas tree.

A New Epoch

This extraordinary tree, planted far from its natural habitat, has also become a marker for the changes humans have made to the planet—the so called “golden spike”.

Over the past few decades, scientists have been proposing a new geological epoch, the controversial “Anthropocene”, that marks the commencement of significant human impact on the Earth's geology and ecosystems. Various different start dates for the Anthropocene epoch have been proposed, ranging from the beginning of the Agricultural Revolution 12-15,000 years ago, to the rise in carbon in the atmosphere that started in the mid-1800s with the Industrial Revolution, to atmospheric radiocarbon that rose with the nuclear age.

Every epoch should have a distinctive marker. For instance, to fix a date for the start of the Holocene, researchers drilled a core into the Greenland Ice Sheet and found a change in hydrogen concentration signifying global warming as the planet emerged from the last ice age. Similarly, the famous asteroid that struck 66 million years ago wiping the dinosaurs left a strong trace of the element iridium in an outcrop of rock in Tunisia, helping researchers fix the boundary between Cretaceous and Palaeogene.

To prove that atmospheric nuclear testing had an impact on the globe as massive and as far reaching as the dinosaur killer asteroid, a team of researchers led by Chris Turner from the University of New South Wales turned to Campbell Island because the island is so remote that if something shows up there, it's likely to show up everywhere.

The researchers drilled a core into the Sitka spruce and analyzed it for carbon-14, a radioactive isotope of carbon that’s released into the atmosphere by aboveground nuclear testing. Because plants take up carbon from the atmosphere as they grow, the carbon-14 isotope should be present in the tree-rings in different concentrations depending on the level of the element in that particular year. As expected, the researchers found that atmospheric carbon-14 peaked between October and December 1965, and gradually decreased as as international treaties restricted nuclear testing.

Discovering these radiocarbon markers in some of the most remote plants in the world indicates that carbon-14 is a truly global marker, Chris Turner said, especially because most nuclear tests occurred in the Northern Hemisphere, and Campbell Island is very, very far south. Based on these findings, Turner suggests that the start date of Anthropocene be fixed at 1965.

One key aspect for any golden spike chosen is that it should be long-lasting. Carbon-14 has a half-life of nearly 6,000 years, meaning the amount present decays by half approximately every 6,000 years. So even after tens of thousands of years, the amount of carbon-14 will still be in measurable quantities allowing further geologists to pinpoint the exact date the Anthropocene started.

Campbell Island. Photo credit: David/Flickr

Photo credit: Alex James/Flickr

Sources: BBC / Live Science / Radio NZ