USA — Natalie Boelman is an ecologist at Lamont-Doherty Earth Observatory who studies the effects of climate change on organisms throughout the food chain. She first visited the Alaskan Arctic in 2001, and will return to the North Slope this spring and summer to continue a wildfire-mapping project and to set up a field study that will look at how warming-induced changes are affecting migratory songbirds that breed on the tundra each summer. The bird study will include an automated network to record songbird calls over the next five breeding seasons, allowing scientists to track songbird numbers. She spoke recently with journalist Kim Martineau.
In 2007, a wildfire tore through Alaskas North Slope, burning nearly 1,000 square kilometers, an area larger than New York City. Was global warming to blame?
We think so. Arctic temperatures have been rising and the climate is becoming drier. The drier the vegetation and soils, the more flammable they become. Warming has also been linked to a tenfold increase in lightning strikes in the region, the equivalent of striking more matches. This area has seen 26 fires since 1950nearly a third of them in the last three years.
This fire set a record for the North Slope but also burned more severely than expected. Do you know why?
The summer of 2007 was extremely dry, with warmer than normal temperatures and less than normal rainfall. But climate alone does not explain why this fire burned so vigorously and for so long. The North Slopes tundra has been growing shrubbier, and most of the severely burned area included shrubby vegetation. Shrubs have woody stems and branches that burn better than other tundra vegetation like sedges, herbaceous plants, and mosses. In other words, shrubs add fuel to the fire. A recent study of ancient lake-bottom sediments found layers of charcoal next to layers of shrub pollen, suggesting a close link between shrubs and wildfire.
Youve been using a hand-held scanner and satellite imagery to map the thousand-acre burn site. What do you hope to learn?
Im using close-up scans as well as satellite images to investigate the fires ecological impacts. We want to know how much of the vegetation and soils were scorched or completely burned, how well the vegetation is recovering and generally if the fire has turned this region into a net source of carbon dioxide to the air.
Fires end up contributing to warming by releasing carbon dioxide during combustion. And by melting the tundras permafrost, fires also increase microbial activity in the soil. These microbes munch on carbon-rich soil, releasing still more carbon dioxide.
Youre also looking at how two species of songbirdthe White-crowned Sparrow and the Lapland Longspur are responding to Arctic warming.
The earlier snowmelt may benefit both species because there will be more berries, seeds, and bugs to eat early in the season when food can be scarce. And though the increase in shrubs may help both species find shelter during spring storms, we think the sparrows may have an advantage during the summer storms; they build their nests in shrubs while the Longspurs prefer open tundra. We dont know yet how these changes are affecting the birds reproductive success.
Why does it matter?
We want to start figuring out how sensitive the birds are to ongoing changes in the tundra. If the birds are being negatively affected, this not only impacts the tundra ecosystem but also the places where these birds winter. Songbirds provide humans with important ecosystem serviceseating lots of bugs for instance. With fewer songbirds, our forests could face more intense insect infestations.
You will return to the North Slope in May and July to set up a bio-acoustic network to record bird song over the next five years. What is a bioacoustic network and what will it tell us?
Our bio-acoustic network will include four stations spread out over 80 kilometers; the waterproof mikes and recorders we set out each May will record bird song over two months. It will tell us exactly when the birds arrive on the tundra each spring to breed. It will also tell us how many birds there are and what species remain through the breeding season. By comparing the recordings with other field measurements, we should learn how the birds are responding to climate-induced changes to their breeding grounds. Although the National Breeding Bird Survey does an annual census on the North Slope, they greatly underestimate songbird numbers by counting just once, at only a handful of locations and fairly late in the season, when the birds are less vocal. We hope that the automated network will become a way to monitor long-term changes in songbird communities on the North Slope.