ForWarn's ability to capture short and long-term change is shown by this animated image pair that provides two different temporal contexts for the same date in May of 2012. The "all year" baseline shows change since 2000. Note the patchy forest loss from strip mines in eastern Kentucky and West Virginia. Twin tornadoes also show up, and these occurred in March 2012. As expected, they also appear on the second image that shows change since May 2011, but most of the strip mine activity does not, as it took place prior to 2011.
This late April 2010 image shows a large anomaly just east of Lake Ontario on the Tug Hill Plateau of New York. A less severe area of departure from the prior year’s condition occurs to the east. Based on weather records, the 2009-10 winter at Lake Pleasant, just east of Tug Hill, was 4.5 degrees F warmer than it was during the prior winter. Continued warmth into spring explains why so much of the northeast is strongly blue in this image. Somewhat ironically, warmer winter temperatures caused more snowfall east of open water in places like the Tug Hill Plateau.
The Atchafalaya basin's forests thrive with seasonal flooding, yet high water is normally a spring phenomenon there. During the past month, unusually high water levels have inundated wetlands and forests along and near the Mississippi River basin. From space, floodwaters appear to decrease existing vegetation, as water masks low lying plant cover. According to the USGS, river discharge at Morgan City, Louisiana was 145,000 ft3/sec on January 16, 2012 compared to 84,000 ft3/sec the prior year. (See http://waterdata.usgs.gov.)
The forests of Texas continue to suffer through one of the most extreme droughts on record and a large number of trees have already died. The photo shows mortality in Memorial Park, Houston (Ron Billings, Texas Forest Service). By late August of 2011, the regional change in greenness from the prior year were extreme. Across the map, this decline was caused by the combined effects of drought and fire. By December of 2011, some recovery occurred as shown in blue, but this December condition is only with respect to conditions in December of 2010, which was also a drought.
On April 24, 2010, a lethal F4 tornado struck the forests east of Yazoo City, Mississippi. Within a few weeks the path of the storm and patterns of severity are clearly shown with this comparison of conditions relative to the same time in 2010--the year before the event (top image). After one year of recovery, that same track is shown in dark blue compared to the post-disturbance 1-year baseline. Had the long-term baseline been used for 2011, the path would still be shown as anomalously low as just one year of recovery was not enough to regain the decadal norm.
This before-after image pair shows changes associated with Hurricane Irene. Its path is shown by the bold blue line. In the pre-Irene image (left) shades of green and yellow show the effects of drought on vegetation and dark red spots are recent wildfires. Irene brought damaging winds that defoliated trees, but also much needed rain which increased greenness.
A severe tornado touched down near Springfield, Massachusetts on June 1, 2011, then carved a path through nearly 30 miles of state and private forest. The streak in red show an extreme reduction in growth compared to the prior year’s condition as of mid-June. Many of the trees damaged or destroyed were evergreen conifers that recover slowly. Always remember that many disturbed areas are salvaged after the event, so the ultimate change can involve both the disturbance and subsequent forest management.
The April 27, 2011 tornado that hit Great Smoky Mountains National Park in eastern Tennessee was a powerful EF4 storm (its direction is indicated by the black arrow). Wind storms are important natural disturbances for Southern Appalachian forests, and the ecological impacts of this event will be long-lasting as shown in the inset photograph taken by National Park staff soon after the event. Also note the forest disturbance northwest of Maryville. That was the result of strong wind and hail during the same regional event.
Full-fledged tornadoes are typically well documented, but the massive outbreak of April 2011 also had localized short-term effects that are easily overlooked. This image pair from a month after the storm (top) and two months later (bottom) shows how fast seemingly severe damage can recover, in this case a ridgeline forest southwest of Kingsport, Tennessee. While such ephemeral disturbances from wind and hail can reduce tree productivity and annual growth, it takes high frequency forest monitoring to know that these events have even occurred.
Forests across northern Mississippi, Alabama and Georgia were hard hit by tornadoes in April, 2011. Tree mortality was often severe for areas in the direct path of these storms as shown in this photo from near Lake Burton in the Chattahoochee National Forest, Georgia (top). In this forest change map from June 1 (bottom), note the parallel, northeastern yellow-red streaks that reveal the location and intensity of these storms. Blue areas have similar growth as in 2010 and were unaffected. Black areas are non-forest such as fields or developed areas.