Short Trees Have No Reason To Live

Feb. 21, 2012 -- Climate models have previously anticipated the advance of trees to higher elevations in mountainous regions, only to have regional influences such as reindeer populations prove a greater influence. Now a new map of Earth's forest height (above) is showing that whatever is happening with the tree line - the trees themselves in the alpine regions are giving up on reaching for the stars.

BIG PIC: Poland's Mysterious Crooked Forest

In a new analysis of Earth's forest heights, geographers working with light detection and ranging (lidar) satellite imagery have found that trees in alpine zones are getting shorter. In contrast the tropical and boreal forests are getting taller compared to a previous study using the same satellite.

"Our map contains one of the best descriptions of the height of Earth's forests currently available at regional and global scales," said remote sensing engineer Marc Simard of NASA's Jet Propulsion Laboratory in Pasadena, Calif., in a statement. The Geoscience Laser Altimeter System instrument on NASA's Ice, Cloud and land Elevation Satellite (ICESat) collected the globally distributed laser pulse measurements, which NASA remote sensing scientists and colleagues at the University of Maryland in College Park and the Woods Hole Research Center in Falmouth, Mass., screened to produce the map.

They used 2.5 million measurements, which the press statement referred to as "sparse," and coupled the lidar data with "estimates of the percentage of global tree cover from NASA's Moderate Resolution Imaging Spectroradiometer on NASA's Terra satellite, elevation data from NASA's Shuttle Radar Topography Mission, and temperature and precipitation maps from NASA's Tropical Rainfall Measuring Mission and the WorldClim database," NASA reported.

The scientists caution that while the new map provides insight on global distribution, it does not distinguish why the trends in forest height are happening and the "accuracy of the new map varies across major ecological community types in the forests, and also depends on how much the forests have been disturbed by human activities and by variability in the forests' natural height."

The study was published in the Journal of Geophysical Research - Biogeosciences.

PHOTOS: Larger Than Life

--by Christina Reed

Global map of forest height produced from NASA's ICESAT/GLAS, MODIS and TRMM sensors. Credit: NASA/JPL-Caltech