Can’t see the (old) forest for the (new) trees
PLANT SUPPLANTERS
THE NEWS One of the biggest threats to the Hawaiian rainforest isn’t clear-cutting or forest fires – it’s other trees. Invasive species such as strawberry guava (introduced for agriculture) and tropical ash (for commercial forestry) are proliferating at the expense of native species. In a new study described in the Proceedings of the National Academy of Sciences, researchers from Stanford’s Carnegie Institution mapped the 3D structure of 220,000 hectares of Hawaiian forest and concluded that invasives are changing the forest at every level. Strawberry guava trees, for example, form dense canopies that prevent light from reaching the forest floor, inhibiting native ferns.
THE BUZZ “It might still be a forest full of trees, but the biodiversity will have decreased immensely,” says Gregory Asner, lead author of the study. While a native forest might contain hundreds of species, they could all be replaced by only a few types of invasives, leaving a less diverse, less resilient ecosystem behind. And it’s happening all over the globe. “We are losing regional identities,” says Dr. Asner. “This is having a fundamental effect on our society, economy, and culture as well as ecology.”
THE BOTTOM LINE Worldwide invasive species, like the cane toads in Australia or zebra mussels in Canada, can trigger huge ecological changes. And once the invasion has started, “you have to catch it early – it’s like cancer, otherwise there’s very little hope,” says Dr. Asner.
FIRE AND ICE
THE NEWS Over the coming centuries, the tundra and permafrost of the high Arctic could change to a landscape of shrubs and even periodic fires. A new study, based on analysis of sediment cores, in the journal the Public Library of Science ONE reports that at the end of the last ice age, 9,000 to 14,000 years ago, the tundra was covered in birch shrubs and experienced forest fires much more often than the infrequent blazes of modern times. “There is a precedent for high fire frequencies in the tundra, ranging from one every 75 to 150 or more years,” says Philip Higuera, lead author of the study. “This is an important component of the climate system that we haven’t considered yet.”
THE BUZZ The Arctic stores about a third of the Earth’s soil carbon at the moment. Melting permafrost and burning tundra could release huge amounts of carbon into the atmosphere. This would exacerbate global warming, accelerate the thawing of the Arctic, and possibly increase vegetation prone to periodic fires. Scientists have already documented the presence of more shrubs in the north.
THE BOTTOM LINE Nobody can predict exactly what will happen – melting permafrost, for example, might eliminate the risk of fire by keeping the tundra too wet. But one thing is certain: It’s going to warm faster than almost anywhere else on Earth, and the changes will be dramatic.
WOLF BLITZES
THE NEWS Higher numbers of wolves in the Rocky Mountains could benefit an unlikely recipient: the pronghorn antelope. A new survey from the Wildlife Conservation Society says the survival rate of pronghorn fawns is three times higher in areas of western Wyoming with high numbers of wolves and few coyotes. The reason? Wolves – unlike coyotes – seldom prey on pronghorn fawns, which are too meagre a meal for a wolf pack, but they do keep coyote numbers down, either through preying on them, or by competing them out of a region. The WCS says that pronghorn have increased by 50 per cent since wolves were reintroduced to the region in 1995.
THE BUZZ Changes in one part of the food web can have unexpected consequences, and top predators can actually be essential for maintaining biodiversity. The study follows a recent decision by the U.S. government to remove federal protection for grey wolves in Montana, Wyoming and Idaho. The government says the wolf population in Wyoming could safely be reduced from 300 to 150, but ecologists assert that such a small population would not be viable in the long term.
THE BOTTOM LINE Grey wolves used to roam most of the northern hemisphere, but today are found mainly in Kazakhstan, Russia and Canada. Thirty years ago when wolves were given federal protection in the U.S., there were almost none left to protect, and new animals (mostly from Canada) were introduced. If the wolves are hunted to near extinction again, they may once more need stock from Canada.