Early Warming. Nancy Lord

lighting strikes started twenty-two Kenai Peninsula fires.

      The conversion of our wetlands to a landscape of shrubs and trees is also significant for the global climate because of the major role wetlands play in the cycling of both CO₂ and methane. In the cycle that takes place everywhere on earth, trees and plants take up great quantities of carbon dioxide, release the oxygen, and store the carbon in their cells. (Wood is one-half carbon.) That carbon stays stored not just in the living vegetation but in woody debris and soil, until it’s released by decomposition or burning. Methane (CH₄) is another form of carbon, created in the absence of oxygen. (When it’s released to the atmosphere, where it’s a powerful greenhouse gas, it eventually converts to CO₂ and water.)

      Northern peatlands hold a tremendous amount of CO₂ and CH₄, equivalent to somewhere between a third and a half of that in the atmosphere. In the anaerobic (lacking oxygen) situation of wet soils, the gases stay in place. As the soils dry, the microbes get to work, decomposing the organic matter and giving off CO₂. But at the same time, the plants and trees that fill in the wetlands perform more photosynthesis, which takes in CO₂. The net result of this carbon “flux” (the transfer or rate of exchange between carbon “pools,” as between, in this case, organic matter and the atmosphere) is not yet well understood.

      A couple of months later, I returned to the refuge with a grad student, Sue Ives, helping her place a clear plastic box over vegetation plots and measure carbon flux with a gas analyzer machine. It was another example of small science steps, the necessary accumulation of place-specific data. It took most of the day to set the box over twenty plots marked out along a gradient—five very wet and mossy ones near the edge of a lake, five slightly drier ones with sedges and bog rosemary among the mosses, five dominated by brushy dwarf birches, and finally the driest, where small black spruce trees had begun to sprout up among cranberry and cloudberry plants—and to take readings with different cloud cover-imitating screens wrapped around the box.

      So far it was looking as though, at least in summer, the drier plots were both respiring and photosynthesizing more than the wetter plots—with photosynthesis significantly outpacing respiration. The drier plots were sequestering more carbon than the wet ones.

      On the surface, that seemed like a good thing—a landscape change that allowed for holding on to more carbon, keeping it out of the atmosphere. But summer measurements were, of course, not the whole story. In winter there would be little photosynthesis, but the microbes in the soil under the insulating snow would still be working, still be respiring. And there were other considerations: More plant growth would create a darker surface in winter, decreasing the albedo (surface reflectivity) and increasing the absorption of solar heat. The implications of more heat are earlier snowmelt, more drying, more plant and microbe activity, and more respiration and release of CO₂.

      And this was just one type of wetland, in one place and set of conditionos.

      In the next chapter, we’ll look more closely at the role of carbon in vegetation, soils, and permafrost—what makes a particular landscape a carbon “sink” or a carbon “source.”

      Late that day, dark rain clouds rolled in over the mountains, threatening the whole day’s work. Suddenly, we heard bugling. From the north, long skeins of sandhill cranes were coming our way, high in the sky and stretching for miles. The enormous flock—hundreds of birds—passed to our east, their calls echoing across the landscape, and I remembered the first time I saw cranes, my first fall in Alaska. I had stood then in the yard of a homestead house in the hills outside Homer and watched them spiral up into a great cloud, and I had thought they were magnificent. They were no less magnificent thirty-odd years later, flying high in their multiple twisting V formations. The two of us standing on a boardwalk in a bog stopped working to watch them pass, and then we turned to more bugling and another tremendous flock, spread out like musical notes across shifting staffs. And then, a third time—but now the birds came directly over our heads, and lower, so that we could see their long necks extended and their legs trailing, broad wings slowly flapping, the feathers on the wing tips separate and pointing like fingers. There were thousands, and the noise was deafening.

      The cranes were flying from their nesting grounds on the Yukon-Kuskokwim Delta and the tundra areas of northern Alaska and Siberia. They scatter in those places—wetland places, peat bogs and muskegs, wet tundra near water—into their nesting pairs and raise one, sometimes two, “colts” while they fatten on insects, seeds, frogs, even small rodents. They were going to wintering grounds, in the southwestern United States, Texas, Mexico, where they—birds with the longest fossil record of any bird still flying, going back perhaps ten million years—have adapted well, in recent time, to feeding on the waste grain in agricultural fields.

      I wondered where they’d settle for the night, what field or wetland they’d find, and how different that field or wetland might be in another year, ten years, within the lifetime of a long-lived crane.