Technical Resource Bulletin
February 2017 (Updated December 2021)
TRB-010
Considering Long Term Drought When Prescribed Burning
Bill Pickens - Conifer Silviculturist, NC Forest Service, Raleigh, NC
Robert Lipford — Staff Forester — FM, NC Forest Service, Clay ton, NC
Robert Trickel — Forest Health Branch Head — NC Forest Service, Raleigh, NC
Updated by:
Phil Wallace — Silviculture Staff Forester — NC Forest Service, Clayton, NC
Drought
Periodic drought is common in North Carolina. The
graph below (Figure l) shows drought occurrence
from 2000 to 202 1 with yellow (DO) indicating
abnormally dry and brown (D4) noting exceptional
drought. The Y axis indicates the percentage of the
state impacted.
Figure l -NC Drought 2000 - 202 1
^)D0 Qoi R]D2 |D3 |D4
Prolonged drought adds stress to trees, weakening
the health and resiliency of forested stands. Many
management activities also add stress, including but
not limited to thinning, prescribed burning, and pine
straw raking. Prior events must be considered and
current health evaluated before conducting a pre¬
scribed bum or implementing any activity that adds
additional stress.
technique. These parameters control the intensity
and duration of heat, which if too intense, can dam¬
age valuable overstory trees. Despite responsible
planning, unintentional scorching of tree crowns is
all too common. Crown scorch (Figure 2) is often a
factor in overstory crop tree mortality following
prescribed bums.
The Effects of Drought on Trees
“Water is essential for almost every plant function.
When drought stress occurs, the plant reacts in
many ways.” (Blaedow 20 13)
Prescribed Burning — Benefit vs. Risk
The NCFS promotes understory burning for the pur¬
pose of hazard reduction, aesthetics, wildlife habitat
improvement, and for other silvicultural reasons.
Burning, while beneficial, contains elements of risk
to overstory trees. The art and science of burning
requires that bum bosses consider temperature, rela¬
tive humidity, wind speed, fuel type, fuel load, fuel
availability, season, burning history, and firing
“Transpiration is the movement of water from the
soil through the roots, stem, branches, leaves, and
finally lost to the atmosphere. It is driven by nega¬
tive pressure, like water being sucked through a
straw. The loss of water from the leaves creates a
suction that pulls water all the way through the tree
from the soil. Water travels through elongated cells
in the xylem (sapwood) that resemble straws. In
hardwoods they are called vessels, in conifers they
