Forest ThreatNet

Volume 8, Issue 1 - March/April 2015

Researchers Map Seasonal Greening in U.S. Forests, Fields, and Urban Areas

With signs of spring emerging across most of the United States, Eastern Threat Center researchers are monitoring the growth and development of vegetation, signaling winter’s end and the awakening of a new growing season. Now these researchers have devised a means of characterizing and tracking this transition to help land managers plan their work and understand how the timing of this year’s greenup compares to that of the 14 previous years.

FW_SOG_All.jpgUsing nationwide satellite imagery and data collected between 2000 and 2013, researchers quantified the seasonal progression from vegetation dormancy to full greenup using a common scale from 0 to 100%. Researchers selected the median date associated with the 20th percentile at each location as a common reference point indicating a clear launch of the growing season. Three maps detailing the typical dates of seasonal greenup in forests and grasslands, agricultural lands, and urban areas are available via ForWarn.

Right: A ForWarn map shows typical dates of vegetation greenup across all lands.

ForWarn is an assessment tool that delivers weekly maps of seasonal vegetation growth and development detected by satellites, known as Land Surface Phenology (LSP), as well as national maps showing vegetation disturbances. “In contrast to field observations that track leaf emergence for particular species of trees or herbaceous plants, ForWarn's LSP map products capture the response of the mixture of natural vegetation that can be seen from space,” explains Center research ecologist Bill Hargrove.

“The start of the annual growing season is among the most important climate-sensitive measures that ForWarn can provide,” says Center research ecologist Steve Norman. Because conifer forests are evergreen, the map’s median green-up dates are particularly useful for managers of deciduous forests, grasslands, and crops. “Just as gardeners look to climate data to determine the typical last frost date, the typical green-up dates provide a baseline for land managers to establish expectations for seasonal duration and productivity,” says Norman.Managers who know more precisely when the growing season begins can better anticipate the risks and impacts of disturbances, such as those from wind, hail, frost, and fire, and can more efficiently monitor for defoliating insect pests that become active when leaves appear, for example.

A team of university and federal partners developed ForWarn, which was among the top 25 tools selected for inclusion in the White House’s U.S. Climate Resilience Toolkit in 2014. Users can see and share the maps via ForWarn’s recently upgraded Forest Change Assessment Viewer, which can also be viewed on smart phones and tablets.


Read more: The ForWarn greenup maps are generating interest from not only land management practitioners, but also among the general public. See recent media coverage from around the nation in The Washington Post, The Atlantic's CityLab, Houston Chronicle, The Buffalo News, Bring Me the News (Minnesota), and The Weather Channel.

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