August 2, 2012
Drought Impacts on Forest Health and Wildland Fire Activity
by Jason Jacobson, Resource Forester Missouri Dept of Conservation
Pre-Existing Forest Conditions
Missouri forests began 2012 already stressed by multiple factors that have had lingering effects on forest health for several years.
A severe freeze event (April 2007), derecho wind storm (2009), and multiple ice storms
Above normal precipitation across much of Missouri in the summers of 2008 to 2010 and the spring of 2011, during which many plants adapted to wetter growing conditions, was followed by an abrupt shift to extreme heat and drought in summer 2011
Insect outbreaks: periodical cicadas, jumping oak gall, defoliators
Areas with recent severe drought impacts (southeast Missouri in 2010 and southwest and northeast Missouri in 2011) are most at risk for significant impacts from continued drought.
Current Drought Conditions
May-June 2012 was the 6th driest on record for Missouri and the driest since 1988. The last influential precipitation was approximately May 7, 2012.
The last time Missouri experienced 100-plus degree heat in June was 1988.
Coupled with heat and drought, Missouri also experienced unusually low relative humidity of single digits and low teens for several days in late June and early July which have contributed to heat stress affecting trees and increased wildland fire danger.
Drought impacts are occurring statewide, but by late June were most severe in southeast Missouri.
By the end of June, 97% and 93% of Missouri topsoil and subsoil moisture supplies, respectively, were in short to very short condition (Missouri Agricultural Statistics Service). Ground moisture was also a contributing factor to fire spread. We use a drought measure called Keetch-Byram Drought Index (KBDI). This is a measure of how far down one must dig before hitting any moisture in the soil. The majority of the state has been experiencing KBDI's of 5-6 inches with portions of the Southeast at 6-7 inches.
Impacts on Forest Health
Tree mortality has already been observed on trees poorly adapted to sites or otherwise previously stressed: White oaks in several areas of the state, black oaks on droughty sites in southwestern Missouri, urban trees, and exotic pines.
Leaf scorch and canopy browning is present on marginal sites (dry sites, S and W-facing slopes, urban locations) and on newly planted trees.
Leaf drop is occurring on some species (willow, cottonwood, yellow-poplar, black walnut, etc.)
Decreases in fruit/mast production (acorns, hickory nuts, walnuts, pecans etc.) can be expected, with concerns for wildlife and the nut industry.
Private landowners and the general public can be expected to make increasing demands on MDC Foresters and Forest Health staff for advice on responding to drought impacts on trees.
Oak decline has been a chronic problem in aging Ozark forest stands since the 1970s, but has worsened after severe drought episodes, most recently in the late 1980s and late 1990s.
Stands with advanced age, higher density, and lower site quality are expected to suffer greater forest health impacts.
Drought-stressed trees become more susceptible to other insect and disease attacks which may result in significant impacts several years later.
Increasing mortality increases the forest fuel load and wildfire risk.
Mortality of mast producing species may be detrimental to wildlife.
Increased Fire Activity
From May 1, 2012 - July 8, 2012 fire activity was significantly above average. The number of fires increased by 150%, the total acres burned tripled and the average acres burned per fire doubled.
Fire occurrence reporting is not yet complete as we await reports from multiple rural fire departments. However, we are projecting a total somewhere between 7,000 - 10,000 acres of natural cover fire during this two month period. Considering the yearly average for Missouri to be roughly 40,000 acres of natural cover fire, having close to 10,000 acres burn in a two month period that normally experiences minimal occurrence of wildland fire is significant.
This increase in fire activity and acres consumed can be directly contributed to the drought conditions and extreme temperatures with low humidity.
MDC staff has been working diligently with the US Forest Service and Volunteer Fire Departments throughout the state to suppress wildland fires as they occur.
Through this mutual aid assistance, it is very evident that the Excess Property Programs offered by the MDC play a crucial role in the wildland fire suppression capabilities of these Volunteer Fire Departments. MDC personnel reported that at nearly every wildland fire in which we responded, local rural fire departments were present and effectively using vehicles and other equipment that have been issued through the MDC Federal Excess Property Center for initial attack and containment of the fire.