888 Million California Trees Experience Drought Related Water Losses

Summary: Since 2011, up to 888 million California trees are experiencing drought related water losses, according to a study published online Monday, Dec. 28.

mixed levels of drought stress in a forested landscape in California: Greg Asner, usage restrictions: with credit, via EurekAlert!

Current laser-guided imaging spectroscopy and historical satellite data reveal that, between 2011 and 2015, up to 888 million California trees on approximately 10.6 million hectares (40,926+ square miles) of forest are experiencing measurable, drought-related canopy water losses.

In a study published online Monday, Dec. 28, 2015, in the Proceedings of the National Academy of Sciences, six researchers in Carnegie Institution for Science’s Department of Global Ecology find that drought-driven, severe reductions in ground water, reservoir stocks, snowpack and soil moisture are impacting progressively up to 888 million California trees. Of about 10.6 million hectares of affected forests, over 1 million hectares (3,861 square miles), with up to 58 million large California trees, measure severe canopy water losses of greater than 30 percent. Up to 412 million of the 888 California trees, covering an area of 5.4 million hectares (20,849.5 square miles), show canopy water losses of at least 10 percent.

In order to distinguish drought-related water losses from fire damage losses, the researchers exclude from their measurements fire-affected forested areas reported by the US Forest Service for 2011 to 2015. Low-altitude visual mapping studies conducted by the US Forest Service yield an estimated 27 million tree deaths from forest fires for that time period.

California’s approximately 13.4 million hectares (51,737.69 square miles) of forests are critical to the state’s globally important economy and population in excess of 38 million.

The researchers note: “Forests of California are of particular interest because they include the tallest, most massive, and oldest trees on Earth, as well as provide a wide variety of goods and services to the state of California and the world.”

The Carnegie Airborne Observatory (CAO) enables the researchers to gather canopy water content (CWC) data for 1.8 million hectares (6,949.8 square miles) via 12 days of flight operations in August 2015. Canopy water content represents the total amount of liquid water in the canopy’s foliage. The canopy’s water content reveals the progressive effects of drought on the canopy and also predicts foliage flammability.

Greg Asner works on the fixed-wing Carnegie Airborne Observatory: Robin Kempster, usage restrictions: with credit, via EurekAlert!

Flown onboard a fixed-wing aircraft, the observatory uses laser-guided high-fidelity imaging spectroscopy (HiFIS), a data-fusion technique that measures canopy water content and projects the forest data in three dimensions. High-fidelity imaging spectroscopy analyzes spectral, or wavelength, radiance reflected from the land surface. The Carnegie Airborne Observatory combines high-fidelity spectral measurements with dual-laser waveform LiDAR (light + radar) scans to produce high-resolution, 3-D maps of forest biochemistry.

The researchers use statewide multivariate satellite, compiled for 2011, 2013 and 2014, to create a retrospective estimate of canopy water content changes. The historical satellite data combines with airborne observatory findings to produce a model of forest canopy physiological responses to progressive drought from 2011 to 2015.

The co-authors conclude: “If drought conditions continue or reoccur, even with temporary reprieves such as El Niño, we predict substantial future forest change.”

progressive water stress on California's forests; black areas are fire-affected forested areas reported by US Forest Service between 2011 and 2015 and are excluded from study's measurements: Greg Asner, usage restrictions: with credit, via EurekAlert!

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

drought stress image: Greg Asner, usage restrictions: with credit, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/105934.php?from=315207

Greg Asner with fixed-wing Carnegie Airborne Observatory: Robin Kempster, no usage restrictions, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/96365.php?from=302469

water stress map: Greg Asner, usage restrictions: with credit, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/105933.php?from=315207

For further information:

Asner, Gregory P., et al. "Progressive forest canopy water loss during the 2012-2015 California drought." Proceedings of the National Academy of Sciences of the United States of America, vol. 113, no. 2 (Jan. 12, 2016): E249-E255. Published online before print Dec. 28, 2015. DOI: 10.1073/pnas.1523397113
Available @ http://www.pnas.org/content/113/2/E249.full

"Tens Of Millions Of Trees In Danger From California Drought." Carnegie Institution for Science > Science News. Dec. 28, 2015.
Available @ https://carnegiescience.edu/news/tens-millions-trees-danger-california-drought