Satellite Data Track Plants’ Response to Warming Temperatures

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SAN FRANCISCO — Warming temperatures are having a significant impact on the distribution and health of plants in arctic and tropical regions, according to recent studies that rely on long-term satellite records to study the changes.

Researchers from NASA’s Goddard Space Flight Center in Greenbelt, Md., used Landsat Earth imaging satellite data to determine how plants in Northern Quebec were responding to warming temperatures.

“Most of the landscape showed an increase in greening, but that increase was not uniform across different types of land cover,” said Doug Morton, principal investigator of the study and a NASA Goddard researcher.

Grasses and shrubs exhibited the greatest gains overall, but only about half of the specific types of grasses and one-third of the shrubs showed positive results, Morton said.

The results of the NASA study offer evidence of the complex job facing scientists trying to understand how various ecosystems are responding to climate change. “Not only are different types of plants responding to the recent increase in summer temperatures in different ways, but not all shrubs and grasses are responding the same way,” Morton said.

That variation could be explained by some of the other factors influencing plant health such as the amount of water a plant receives, its placement on a slope or its exposure to sunlight, Morton added.

To conduct their research, the NASA Goddard scientists compared observations gathered during the month of July from 1986 to 2010 by U.S. government’s Landsat 5 satellite. Landsat 5, which was launched in 1984, continued to capture imagery until November 2011 when the Interior Department’s U.S. Geological Survey halted operations due to problems with an amplifier used to transmit imagery to ground stations.

That long-term data record offered researchers a unique opportunity to evaluate the impact of climate change on vegetation. The Landsat Thematic Mapper’s 30-meter spatial resolution also gave researchers a chance to compare the density and distribution of specific types of plants in Northern Quebec, where land cover varies to include small lakes, wetlands, shrubs, grasses and forests. Morton said computer models used to predict the impact of climate change suggest that warmer temperatures will encourage the growth of plants farther north than their previous habitats. Satellite data offer scientists an opportunity to monitor those changes. “The 2000s were the warmest decade on record,” Morton said. “Continuous satellite observations are needed to monitor how vegetation responds to warmer temperatures. Satellite data for the entire boreal forest and tundra region will be critical to identify the early impacts of climate change on vegetation.”

Scientists at the Woods Hole Research Center in Falmouth, Mass., are conducting similar studies to evaluate how vegetation in arctic and tropical regions is responding to climate change. Those studies show declines in productivity in the boreal forests of North America. Trees are showing signs of drought stress as a result of warmer temperatures and drier air.

“The trees in North America’s coniferous forests aren’t adapting well to hotter, drier conditions,” said Scott Goetz, deputy director and senior scientist at the research center. “That has big implications for insect infestations and fire disturbances.”

In contrast, Woods Hole research studies are noting increased productivity in tundra systems. In the past, vegetation in those regions has been constrained by the short growing season and low temperatures.

Satellite data also are being used to augment field studies of vegetation in the Amazon basin. Severe droughts in the Amazon basis in 2005 and 2010 led to the death of many of the largest trees. Nevertheless, satellite observations show increases in photosynthetic activity in those forests. That discrepancy simply may be the result of a process called leaf flushing in which new leaves are produced at the top of the forest’s canopy. The new leaves reflect more infrared light than more mature leaves. “Drought events may synchronize the production of new leaves,” Goetz said.

The way each habitat responds to climate change can have a dramatic impact on the overall amount of carbon in the Earth’s atmosphere. For example, severe fires in boreal forests may result in an increase in deciduous trees replacing coniferous trees, Goetz said. Deciduous trees absorb greater amounts of atmospheric carbon.

“We are interested in the net implications of changing vegetation patterns and what that means for the climate system,” Goetz said. “People have developed theories to explain the impact of climate change. However, researchers have not conducted enough studies to document the net effect of climate change over large areas.”

To monitor changes in vegetation pattern, Woods Hole researchers rely on satellite data drawn from a variety of sources including Landsat’s Thematic Mapper, the Advanced Very High Resolution Radiometer on the U.S. National Oceanic and Atmospheric Administration’s Polar Orbiting Environmental Satellites, the Moderate Resolution Imaging Spectrometer on NASA’s Aqua and Terra Earth Observation Satellites, and lidar data from NASA’s Ice Cloud and land Elevation Satellite.

Woods Hole scientists also track changing vegetation patterns with high-resolution imagery captured by Ikonos, a spacecraft owned by GeoEye of Dulles, Va., and Longmont, Colo.-based Digital Globe’s QuickBird satellite. “We use anything and everything available,” Goetz said.