No Calm after the Storm: Water Stress, Drought, and Mortality in Forest Trees in Eastern North Carolina following Hurricane Florence

by | Aug 29, 2019

It’s been almost a year since Hurricane Florence slammed our coast, yet many effects from the onslaught still linger. One of these is in our forests. Many factors can cause stress in trees, sometimes leading to their death, and in this case, the hurricane was just the beginning.

On September 14, 2018, Hurricane Florence made landfall at Wrightsville Beach as a Category 1 storm. Rainfall ranged from 15 to 35 inches throughout the southeastern coastal plain and floodwaters took some time to recede. The impacts were greatest along a line running roughly from Goldsboro east to Pamlico County.  While this was bad, things only got worse. Immediately following the storm, from late fall 2018 through early spring 2019, above average rainfall also impacted the region. Many of these events occurred at least every 5-7 days, keeping the already-saturated soils soaked over this period of time. This extended saturation led to a decrease is root mass and increase in fungal diseases such as Phytophthora root rot.

This sand post oak succumbed to the extreme weather events, which swing from excessive soil saturation to moderate drought.

However, change is the only constant. By the middle of April, the weather pattern shifted from one extreme to another and there was little measurable rainfall between then and the end of May. This, coupled with temperatures in the 90°F – 100°F range, resulted in suddenly dry soils and a “flash drought”. By June 1st, many trees were either dead or showing signs of water stress.

Much of the observed mortality was, and continues to be, on oak species on drier sites. These include southern red oak, white oak, turkey oak and sand post oak. Generally, these species are somewhat resistant to drought; however, they are not accustomed to saturated soil conditions. It is believed that because these trees lost root mass during the period of saturation, they were not able to handle the following drought-like conditions early in the growing season. Many were then attacked by secondary insect or disease organisms. Large trees weren’t the only ones affected; numerous failures of recently-planted forest stands are also occurring in the same area.

Water stress can make pine trees susceptible to secondary pests, such as Ips engraver beetles.

In addition, some areas of our coastline received a great deal of salt spray and saltwater intrusion due to the slow movement of Hurricane Florence as she tracked inland. This additional stress factor led to a larger amount of dead trees compared to many other areas. Many of the trees affected are pines but even salt-tolerant hardwoods such as live oak are showing crown damage. Ips engraver beetles, an insect attracted to weakened trees, are the leading cause of pine mortality in this region. Down East Carteret County and the Crystal Coast area appear to be most affected.

It is not unusual to see tree mortality events like this following extreme weather conditions. Similar effects occurred within the last decade following the excessively dry period from 2008 – 2011 in this same area. In addition, the maritime forests of our coastline have been shaped by similar storm events and have evolved their unique form because of these factors.  While this does not help the land or homeowner with dead trees in their landscape, it does help to understand that events like this do occur periodically. 

While not much can be done in a forested situation for individual trees experiencing the conditions described, landscape trees can be monitored and given adequate water and nutrition to aid in their recovery.  N.C. Forest Service personnel can aid in these recommendations and can be reached at your local county NC Forest Service Office.

A technical report of these ongoing water stress issues can be found in the latest N.C. Forest Service Forest Health Note.

The N.C. Forest Service can help to identify causal agents leading to tree death. Bark beetles, such as Ips engraver beetle shown here, make signature galleries beneath pine bark.