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)
The Forest Tent Caterpillar (Malacosoma disstria) is a widespread native defoliator of deciduous forests in the Eastern US. While host trees differ regionally, the insect prefers sweet gum (Liquidambar styraciflua), tupelo gum, black gum (Nyssa spp.) and species of oak (Quercus spp.) in the bottomland forests of North Carolina's Coastal Plain.
The larvae hatch in early spring as the tree buds swell, then larvae defoliate emerging and growing leaves in April and early May. After a few... (read more)
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)
Urban areas are renowned for their admixture of species and vegetation types that can change from one parcel to the next. Yards and woodland parks intermix with road medians--all of which may be dominated by an irregular mix of native and exotic trees, shrubs, herbs and grasses. In cities, the vegetation of nearly every block is compositionally complex.
These species green up at different times and at different rates. Because of this, it can be difficult to decide when spring occurs... (read more)
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)
The start of the annual growing season is among the most important climate-sensitive measures that Land Surface Phenology (LSP) products like ForWarn can provide. Warm temperatures can accelerate bud burst, and this can increase exposure to damaging spring frosts, as it did across the Southeastern US in 2007 and 2012. In natural areas, the timing of spring greenup can affect growing season duration and productivity. It can also affect the risk and impacts of disturbances, such as those from... (read more)
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)
Coastal forests and shrublands can be vulnerable to climate-associated disturbances such as the strong winds and storm surges associated with hurricanes. Because of its extension into the Atlantic, eastern North Carolina is especially vulnerable to such storms, having been hit by several hurricanes during the MODIS period of record (i.e., since 2000). In 2014, Hurricane Arthur struck causing relatively minor damage to forests compared to two earlier events, namely 2003's Hurricane Isabel and... (read more)
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)
Across the Southern Appalachians, Eastern Hemlock has long created an important ecological niche. As these trees are evergreen, they provide year-long cover for wildlife and they cool riparian areas where they tend to grow. Since the mid 2000s, these forests have been in decline due to a lethal non-native insect known as the Hemlock Woolly Adelgid. Like its kin that devastated Fraser Fir forests at higher elevations during the 1960s and 1970s, the Hemlock Woolly Adelgid has been... (read more)