New Research: Temperate Forests Get More Climate CreditJuly 29, 2009
As the U.S. Senate prepares to tackle historic climate legislation in the United States, scientists from Australian National University have weighed in on how to best utilize our forests in the fight against global climate change.
Forests are unique in the climate arena because of their dual ability to both absorb and emit carbon dioxide, the primary greenhouse gas. As such, forests have become a focal point in the climate debate, as policymakers and others consider how to maximize their climate benefits while minimizing the emissions associated with their disturbance.
Some studies have suggested that very old temperate forests are unimportant from a climate perspective because they are no longer sequestering more carbon than they emit. However, according to the findings published by researchers Heather Keith and her colleagues in last month's Proceedings of the National Academy of Sciences, not only are these ecosystems still sequestering carbon, but they store some of the greatest concentrations of forest carbon on earth. Using empirical data gathered from studies conducted around the world, Keith et al. identify which forests store the greatest concentrations of forest carbon—valuable knowledge for those working to stem the tide of global climate change.
A PDF of their article can be downloaded from the PNAS website.
Presumably it was with no small amount of national pride that Keith et al. reported of the forests they studied, their own Eucalyptus forests of the Central Highlands of Victoria, Australia, stored the greatest amount of carbon globally. On average, these cool, moist, temperate mountain ash (Eucalyptus regnans) forests hold a staggering 1,867 metric tons of carbon per hectare in living and dead biomass. The study analyzed data from Oregon forests—which ranked among the top carbon-storing forests globally—though did not include information about California's redwood forests.
Further analysis of data collected from forests worldwide suggests that cool, moist temperate forests—just like those of western North America—have the highest biomass carbon stocks in the world. Using this information, Keith et al. were able to develop a methodology for predicting carbon storage according to forest conditions, management and history of disturbance.
They found that, generally, precipitation and temperature were correlated with a forest's structure. Climatic influences promoting photosynthesis increased the forest ecosystems' growth, therefore enhancing its ability to absorb and store carbon.
Where cooler temperatures slow down decomposition, carbon stored in dead vegetation of temperate forests—such as downed trees—was retained for great lengths of time, vastly boosting the ecosystem's overall ability to store carbon. Because temperate forests have relatively high rates of growth and have much lower decomposition rates than tropical forests, the largest amounts of carbon accumulate in these ecosystems.
Keith et al. reported that, despite high rates of growth in the tropics, average carbon storage in cool, moist temperate forests was the highest of any eco-region, with a mean value of 642 metric tons per hectare. Temperate forests of western North America followed this trend, with those of the Pacific Northwest ranging between 568 to 794 metric tons of carbon per hectare. Subtropical forests were the next highest with an average of 498 metric tons of carbon per hectare (10,000 square meters). These were followed by moist, tropical forests, which stored an average of 248 metric tons of carbon per hectare. Finally, with a mean carbon storage of 84 metric tons per hectare, cool, dry, boreal forests stored the least carbon of any forest biome due to low rates of growth.
So, what do these findings mean for U.S. climate policy? According to Keith et al., the answer might be in our own backyards, where our temperate forests provide some of the greatest carbon storage of all forests globally. Conserving and sustaining these valuable climate defenses in western North America will be a key component of winning the battle against climate change. Upcoming domestic climate policy must not only focus on preventing deforestation abroad, but also look to preventing the loss of our own forests here at home. Doing so will play an important role in reducing emissions from deforestation, which accounts for 18 percent of all annual carbon emissions globally, as well as ensuring the future sequestration potential of these forests.