Highlights

ForWarn II maps hail damage to Midwestern crops

ForWarn's all-lands approach to monitoring provides valuable insights into crop damage caused by summer storms. In July and August of 2018, hail storms struck eastern Nebraska causing severe damage to corn and soy.

Remote sensing provides an invaluable way to track severe weather's effect on agricultural production, especially when it can be delivered soon after the event. Most storm reports of hail, for example, do not result in detectable change, suggesting that they are of limited... (read more)

Assessing defoliation in the Boise National Forest

ForWarn’s ability to accurately map defoliation comes from the high temporal frequency of the source imagery (MODIS). With any change detection, multiple disturbances are often at work in the same landscape at the same time, so careful assessment requires consideration of other stressors or disturbances.

In the Boise National Forest, defoliation from the spruce budworm and large wildfire have been recurring every year. Recently, a periodic eruption of the Douglas fir tussock moth has... (read more)

Tracking Gypsy Moth emergence and severity with magnitude and duration

Remote sensing is adept at identifying and qualifying many forest disturbances, but there remains a substantial need to further quantify actual impacts in many cases. Traditionally, vegetation change-detection approaches, such as that used by ForWarn, identify and measure disturbance severity as the magnitude of change of some measure of reflected light between two dates or periods. ForWarn tracks the percent change in NDVI relative the prior year or years, with this index falling or rising... (read more)

Pandora Moth defoliation returns to the Kaibab

The Pandora Moth (Coloradia pandora) is a native defoliator of ponderosa, Jeffrey and lodgepole pine trees of the Western US. During most years, populations and defoliation is minor, but periodic outbreaks cause widespread defoliation (Speer and others 2001). The outbreak shown here in Arizona's Kaibab National Forest first caused significant defoliation in June-July of 2013 and defoliating caterpillars have now returned in 2015.

One of the more peculiar aspects of outbreaks is that... (read more)

The typical start of greenup on agricultural lands

Understanding the normal start of greenup for croplands is important because it provides a baseline to compare year to year conditions. The date of greenup for agricultural lands varies based on year-to-year climate factors, the unique responses of the specific crop or vegetation type planted, and farmers' management practices. For areas that need to be planted in the spring, wet late winters can delay planting. Cool springs can delay growth. Either can potentially influence seasonal growth... (read more)

Autumnal Hail and Early Browndown in the Upper Midwest

It can be challenging to detect disturbances during seasonal periods of transition such as Fall or Spring in the eastern deciduous forest. The baseline conditions we use to compare with current conditions harbor a lot of normal variation that results from the onset and progression of cold temperatures. In the upper Midwest, Fall is typically reflected by a gradual drop in NDVI during September, then a more rapid decline in October. By the beginning of November during most years, this decline... (read more)

Massive hailstorm destroys Midwestern crops

During the first week of June 2014, hail caused significant damage to corn and soybean fields in eastern Nebraska and western Iowa. By June 9th, ForWarn's all-lands product was beginning to show the losses that these storms inflicted across multiple counties despite later than average crop growth in May, and when ForWarn's next product was produced for June 17th, the losses from hail were clearly visible. These maps were made by comparing current NDVI conditions to the all-year mean value... (read more)

Monitoring snow cover in near real time

ForWarn's true color product is produced every 8 days at 1km resolution to provide a quality control for ForWarn's disturbance maps. Clouds and snow cover that persists for the entire 24-day MODIS collection window can create the appearance of vegetation disturbance, when it is not. In addition, these true color images show variation in vegetation greenness seasonally and among years.

This true color product reveals how snow cover changes over time, and this is particularly... (read more)

A multi-year view of Sudden Oak Death

Sudden Oak Death (SOD) is a disease caused by the new pathogen Phytophthora ramorum (Frankel and others, 2013). This spore-producing water mold was first observed when tanoak trees began dying during the mid 1990s in California’s Marin and Santa Cruz Counties. SOD is now known to infect dozens of other species--hosts that help spread the disease--but they do not always succumb. While the SOD pathogen has been detected in nurseries throughout much of the US and in Europe the epicenter of this... (read more)

Tracking the historic Rim Fire

The 2013 Rim Fire burned over a quarter million acres of California's Sierra Nevada, including a portion of the Stanislaus National Forest and Yosemite National Park. It started in mid-August as an illegal campfire after an unusually dry winter and spring. A lower-than-average snowpack melted early, signaling that a hazardous fire season lay ahead. That early season dryness contributed to the below-average productivity in the foothills as shown on ForWarn's June departure map. Once ignited,... (read more)

Monitoring Gypsy Moth defoliation in near real time

By late 2012, forest health monitors in western New York and Pennsylvania knew that they were about to experience a severe outbreak of the non-native Gypsy Moth. Surveys showed an unusually high density of egg masses on the branches and trunks of trees, but neither egg densities, nor the distribution of primary host trees are ever perfectly known across the forest, so translating general predictions to a map remains a challenge. Using the best information available, forest managers... (read more)

Phenology is key for vegetation monitoring

Land managers in the West seek to efficiently monitor their forests and rangelands, particularly after wildfire. ForWarn's high frequency record of the Normalized Difference Vegetation Index (NDVI) provides a coarse filter means to accomplish this using two measures. First, the mean NDVI varies with vegetation composition and density such that bare ground has a low NDVI, grass is higher, shrubs and open forest stands are higher still, and dense forests are highest. Second, variation in the... (read more)

Reburning the Jemez Mountains

ForWarn's MODIS satellite-based products go back to 2000, and this allows us to observe the effects of wildfire and recovery since early in the decade. In exceptional cases, areas can reburn and this provides us with long-term monitoring insights into how vegetation is affected by a return in frequent fire. A portion of Santa Fe National Forest near Los Alamos, NM is one such area that has been reburned by wildfire in recent years. Portions of the 2000 Cerro Grande Fire were reburned in 2011... (read more)

Multiple baselines reveal short and long-term change

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... (read more)

The exceptional drought of 2011

Across Texas, 2011 will long be remembered as the year that the trees died. After over a century of weather station data, 2011 saw record breaking drought across New Mexico, Texas, Oklahoma and Louisiana; but it was west Texas in particular, that suffered the greatest and most persistent loss of greenness from drought and the numerous associated fires. In this ForWarn image for late September 2011, there are centers of drought in and around Texas and farther to the Southeast centered on... (read more)

Lake-effect snow affects spring greenup

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... (read more)

High water soaks the Atchafalaya

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... (read more)

Webworms erupt in the Allegheny

This fall 2011 webworm outbreak in the Hickory Creek Wilderness Area of the Allegheny National Forest, Pennsylvania stands out against the near normal (blue) background that dominated the state in early fall. There were minimal indications of defoliation in mid-August, but clear patterns of severity were clear by mid-September. This anomaly persisted through November, when leaflessness is the normal pre-winter condition for deciduous trees. Recognizing insect defoliations near the end of the... (read more)

Defoliation in the Wenatchee

A sizable portion of the Wenatchee National Forest, Washington shows less vegetational vigor than it did at its peak of the last decade. While such declines in NDVI often result from tree death due to wildfires in the west, no large fire has occurred here as is shown by the distribution of MODIS hotspots (shown as white triangles) between 2000 and 2011. Much of this reduction through September 13, 2011 may have been caused by the cumulative effects of defoliating insects on tree mortality,... (read more)

Yazoo tornado recovery

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... (read more)

Forest loss marks strip mines

Deforestation for strip mining is common practice in the coal regions of eastern Kentucky, Virginia and West Virginia. The image below shows areas where forests have been removed for mining over the last decade (left). Using a one-year baseline, it is possible to map areas that are both more and less vegetated on a shorter time scale. This maps where mining activity has been active, where succession or reclamation is taking place. The long term baseline reveals the cumulative effects of this... (read more)

Arizona bears the Wallow

In June, the Wallow Fire burned over half a million acres in east-central Arizona, much of it on the Apache-Sitgreaves National Forests. A substantial portion of the burn area was of high severity, killing millions of trees outright. Looking south-southwest over the Escudilla Mountain Fire Lookout Tower (upper left), the effects of the high severity fire are clear. This observed severity is consistent with the ForWarn map from July (upper right, shown with 50 percent transparency) that... (read more)

Monitoring a Pocosin fire and its recovery

The Pains Bay Fire was started by lightning on May 4, 2011 in the peaty soils of North Carolina’s coastal plain. By the end of June, the fire was contained, but the deep soils continued to smolder for weeks. The white line marks this 45,000 acre fire’s final perimeter. The center of the fire burned with low severity, allowing rapid recovery of herbs, ferns and sprouting woody species by August; yet an outer ring shows a longer lasting departure from prior years. For more information about... (read more)

Caterpillars defoliate the Pee Dee

According to climate data, coastal North and South Carolina were having a mild drought in mid May of 2011. Mean water flow for the Pee Dee River near Pee Dee, SC during the 24-days prior to May 16 was 15.9% below the 2003-2010 average for that time according to USGS statistics (http://waterdata.usgs.gov). These clues suggest that this reduction along the Waccama and Pee Dee Rivers of the Carolinas is not the result of flooding. Aerial detection... (read more)

Tracking the ephemeral in Tennessee

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... (read more)