California forests have become net climate polluters – ‘The losses are outpacing the growth. The key element here is wildfire.’

By John Upton
29 April 2015

(Climate Central) – California introduced a world-leading carbon dioxide cap-and-trade program to drive down pollution rates after lawmakers approved an ambitious climate protection law in 2006. It also changed rules affecting utilities, spurring investments in some of the biggest solar power plants the world has yet seen. But an emerging body of research shows it’s going to take more than a clean energy blitz to help the state comply with the historic California Global Warming Solutions Act. A Californian task force has been handed the confounding task of figuring out how forestry and land management practices could be improved to prevent what scientists say are surprisingly high levels of climate pollution escaping from its forests and other wildlands. A new study has shown that greenhouse gases are billowing out of the state’s forests faster than they are being sucked back in, with unnaturally intense wildfires mostly to blame. “Ecosystems are regrowing, but not fast enough,” Patrick Gonzalez, a U.S. National Park Service climate change scientist involved with the research, said. “The losses are outpacing the growth. The key element here is wildfire.” From 2001 through 2010, the state’s wildlands were responsible for about 8 million tons of carbon pollution annually — more climate pollution than is released every year by the entire economy of Vermont. That was the conclusion of a sophisticated analysis requested and partly funded by California’s air resources board. Wildfires affecting a small portion of the state were responsible for two-thirds of the estimated losses of carbon from what had been living plants. […] “There’s a long history of discussion of using forests to sequester atmospheric carbon,” said Michael Goulden, a University of California at Irvine associate professor who studies the state’s forests, but who wasn’t involved with Gonzalez’s research. “This paper points out that any increase in forests’ carbon stock may prove ephemeral. Eventually, forests are disturbed, and then this extra carbon is released.” [more]

California’s Forests Have Become Climate Polluters

ABSTRACT: The balance between ecosystem emissions of carbon to the atmosphere and removals from the atmosphere indicates whether ecosystems are exacerbating or reducing climate change. Forest ecosystems in the State of California, USA, contain carbon that reaches the highest densities (mass per unit area) in the world, but it has been unresolved whether California ecosystems currently comprise a net sink or source of carbon. The California Global Warming Solutions Act of 2006 established greenhouse gas reduction targets for fossil fuel-burning sectors and ecosystems, underscoring the importance of tracking ecosystem carbon. Here, we conduct statewide spatial inventories of the aboveground live carbon stocks of forests and other terrestrial ecosystems of California, excluding agricultural and urban areas. We analyzed biomass data from field measurements of the Forest Inventory and Analysis program, published biomass information and remote sensing data on non-forest vegetation, and spatial distributions of vegetation types, height, and fractional cover derived by the Landfire program from Landsat remote sensing at 30 m spatial resolution. We conducted Monte Carlo analyses of the uncertainty of carbon stock change estimates from errors in tree biomass estimates, remote sensing, and estimates of the carbon fraction of biomass. The carbon stock in aboveground biomass was 850 ± 230 Tg (mean ± 95% confidence interval) in 2010. We found a net aboveground live carbon stock change of −69 ± 15 Tg from 2001 to 2010, a rate of change of −0.8 ± 0.2% y−1. Due to slow decay of some dead wood, all of the live carbon stock change does not immediately generate emissions. Wildfires on 6% of the state analysis area produced two-thirds of the live carbon stock loss. This suggests that increased tree densities from a century of fire suppression have allowed the accumulation of fuel for carbon losses in recent wildfires. Remote sensing errors in vegetation classification accounted for most of the uncertainty in the carbon stock change estimates. Improvements are also needed to track spatial patterns of growth and dead wood. Our results establish the beginning of a time series for the state greenhouse gas inventory and provide information on the role of forest conservation and management in California in mitigating global climate change.

Aboveground live carbon stock changes of California wildland ecosystems, 2001–2010