A few weeks back, I took apart a chain email about drilling in Alaska’s Arctic National Wildlife Refuge (ANWR). It was great fun, but this morning my spouse — an ecologist who studies agricultural impacts on soil carbon — made an offhand comment about climate change that made me rethink one of my claims. Yes, we are big enough nerds to talk science over breakfast.
In my post, I tried to dismantle the idea that caribou are the only reason we should care about what happens to ANWR, saying things like:
Arctic tundra like the ANWR coastal plain is ecologically important on a global scale whether or not it has caribou running around on it.
True fact, but misleading. I went on to mention the ways that Arctic tundra soils affect the global carbon cycle, and my implication was that that process is completely independent of caribou. In fact, caribou are a really important piece of the puzzle.
Grazing animals like caribou control which plants grow, and which plants die. Think about it — have you ever seen a cow pasture full of shrubs and trees? Odds are low. Grazers tend to munch fairly indiscriminately on anything small and leafy in their pasture, keeping everything except grass from taking hold. Large grasslands foraged by caribou, reindeer, elk, deer, moose, etc. are the same way — shrubs and trees aren’t going to survive the critters’ foraging. Grazers make sure that grasslands stay grasslands.
When you remove grazers, though, the vegetation changes. Shrubs start to move in, and in some places, trees will take hold. Over time, an ungrazed grassland can become a forest. This won’t happen everywhere — not all climates and geologies will support a forest — but no matter what, grazers unwittingly decide which plants survive and thrive.
When new plants move into a grassland, all of its interactions with the atmosphere change. Trees reflect sunlight differently, “breathe” carbon dioxide differently, spread across the land differently, and store carbon in their roots at different depths than grasses. All of these things change the land’s relationship to the global carbon cycle and change the way it fits into the climate change picture.
Thinking again about ANWR, scientists have turned up mixed results about whether arctic tundra soils are better at taking carbon out of the atmosphere when grazers live there or not. One recent paper found that keeping caribou and muskoxen off the land in west Greenland let it store three times as much carbon, because shrubby plants were better at sucking it out of the atmosphere than grass. Other folks get different results in slightly different ecosystems, and the general conclusion most scientists agree on is that we don’t really know enough about how it all works.
What we do know, though, is that whether they make things better or make things worse, the caribou do matter. Sorry, caribou. Didn’t mean to diss you so badly.