Montana’s Forests in an Era of Climate Change
Montana forests have seen a recent trend of major disturbance events, particularly insect infestation, fires, and drought conditions. In the near future at least, these trends will likely continue, and possibly worsen.
The most conspicuous and damaging of the insect infestations in Montana is caused by the Mountain Pine Bark Beetle (Dendroctonus ponderosae Hopkins), particularly in the state’s extensive stands of Lodgepole Pine.
The pine bark beetle is native to Montana and has served over many centuries of forest cycles to quietly influence patterns of growth and species succession. In recent decades, however, the beetle has emerged as a major killer of Lodgepole forests in Montana and throughout the West. Pondersoa pine, the state tree, is also falling victim to pine bark beetle. Climatic changes may be associated with these extensive outbreaks.
Entomologists who study the beetle believe that its recent successes are linked to several factors. Prolonged periods of cold weather in the -20 to -40 F range kill pine bark beetle larvae imbedded in the thin bark of Lodgepole trees. However, winter weather over recent decades has afforded very few of these extended cold snaps.
At the other side of the seasons, recent late summer drought conditions have stressed Lodgepole forests. Weakened individual trees have long been known to issue a biological invitation to beetle attack. During its adult mating phase in late summer, adult scout beetles identify weakened trees and issue an aggregating pheromone to other beetles to key-in and attack the tree. The apparent combination of large numbers of drought-weakened trees and the growing population of beetles perpetuates the infestations.
Forest Service data indicates that about 800,000 acres of Lodgepole pine have been killed per year in Montana during recent seasons. Well more than 1 million acres of private and public forests were under attack in 2005. These outbreaks are evidenced by the extensive stands of rust-red trees easily observed along western Montana highways and forest roads. Research also indicates that the beetles are successfully reproducing at higher altitudes and extending attacks into upper elevation species such as Whitebark Pine, a tree long thought to be nearly immune from pine beetle infestation.
On a more regional scale, researchers are concerned that pine beetle outbreaks are occurring further north than ever recorded, particularly in northern British Columbia and Alberta. The concern is whether the pine bark beetle can jump species and infest the extensive stands of jack pine that comprise much of the Northern Hemisphere’s sub-Arctic boreal forest.
Spruce budworm (Choristoneura occidentalis Freeman) is another insect of concern to western forest managers. First described in the Lower Forty-Eight in 1914, spruce budworm infestations have been almost a constant presence in the Northern Rockies since the late 1940s. Most infestations subside naturally without the widespread effects of the pine bark beetle. Spruce bud larvae feed on newly emerging needles, principally of spruce and Douglas-fir trees in Montana, effectively stunting growth and sometimes killing the trees.
Perhaps few topics in Montana generate more controversy than forest fires. Most people agree on one thing, however – fire seasons are more common these days. Many long-time residents can remember fire seasons occurring two years out ten, or even less.
Historically, some fire seasons were bigger than others, and there have certainly been big ones. The 1910 fire season in the Northern Rockies is often called “The Big Blow-Up.” Three million acres in the Idaho panhandle and western Montana burned over only a couple of days and 86 lives were reportedly lost on account of the fire. It probably rates as this country’s largest forest fire in total acreage.
Many recall the 1988 fire season that focused worldwide attention on broader ecological conditions in Yellowstone National Park. About 1 million acres burned in Yellowstone and Montana that year. The year 2000 fire season featured the 292,000-acre Valley Complex fire in the Bitterroot National Forest as well as major fires in west-central Montana. The Valley Complex fire is well remembered because some of the fire front developed along areas of semi-rural homes. The fire years of 2001 and 2003 were also fairly serious locally. The 2006 fire season witnessed a major burn in the Gallatin National Forest – the 223,000-acre Derby Fire. In 2007, about 800,000 acres burned in Montana.
Since 2000, more than 3.3 million acres have burned in Montana. About one-third of these have been forested acres, and of the forested acres, about one-third were high severity burns.
Forest fire protection in Montana is accomplished through cooperative efforts between the state, federal, and local governments. Primary response exchange agreements are routine between the agencies. The state DNRC has primary fire response duties covering about 4.5 million acres of forested land. The Forest Service responds to fire events on about 16.7 million acres of forested land. Other federal and tribal responsibilities cover about 800,000 acres of forested land outside of the national parks.
Forestry specialists trained in fire management maintain that no two forest fires are alike. In addition to the obvious weather conditions, variability in fuel load, dryness, even the age and species-mix of the living forest contribute significantly to the way a fire burns. According to one internal Forest Service report, damages by forest fires are often overstated. Most fires are “patchy,” leaving unburned areas within the fire perimeter. Mature conifers often survive fire events. And a few species, notably Lodgepole, are serotinous – their cones will only open and spread their seeds when they have been exposed to the heat of a wildfire. Fire reports consequently overstate the actual acres burned by 10 to 50 percent, depending on these local variables. Furthermore, reports typically neglect the regenerative aspects provided by individual fires.
Placing the beneficial aspects aside, Montana can probably look forward to more forest fire seasons per decade in the foreseeable future. This prospect raises serious issues for public policy makers as the cost to fight fires rises. The 2006 fire season cost federal agencies $1.5 billion to fight fires that burned about 9 million acres. The 2006-2007 fire seasons may cost the state of Montana more than $30 million.
A recent study by the DNRC Forestry Division reports that forest fires are particularly expensive to fight when they occur along the “wildland-urban interface” – areas of home development in forested and other fueled lands. Large fires along the interface cost about 50 percent more to fight than comparable fires in remote areas, probably due to costs associated with home protection and more extensive use of aerial retardants. The report notes:
More people, more houses, and more businesses are located in areas at risk from wildfire. As a result, the probability is growing that many Montana communities (PDF 273 KB) will pay a tremendous economic, social, and ecological price when wildfires occur.
In Montana and the Northern Rockies, we are also painfully aware of the personal risks of fighting forest fires. In 1949, 13 firefighters lost their lives in the Mann Gulch fire northeast of Helena. During the 2001 fire season, four firefighters died in the Thirty Six Mile Fire in Washington state. And the 1994 South Canyon Fire on Colorado’s Storm King Mountain killed 14 firefighters. According to congressional testimony on a bill to improve safety conditions for firefighters, more than 900 wildland firefighters have lost their lives in the line of duty since 1910. These firefighters represented a mix of federal and state employees, volunteers and independent contractors.
The conditions of drought are difficult to define, particularly as one is unfolding. Sunny, warm weather is almost always welcomed following a period of precipitation. And a stretch of dry weather is not usually remarkable. In his 1947 book, Drought and Its Causes and Affects, I. R. Tannehill notes:
The first rainless day in a spell of fine weather contributes as much to the drought as the last, but no one knows how serious it will be until the last dry day is gone and the rains have come again...
The Palmer Drought Severity Index (PDSI) is the most commonly used drought index in the U.S. It was developed to measure intensity, duration, and spatial extent of drought. Measurements of precipitation, air temperature, and local soil moisture, are collected and compared to prior values of these measures. Values range from -6.0 (extreme drought) to +6.0 (extreme wet conditions), and have been standardized to facilitate comparisons from region to region.
Drought conditions on Montana forestlands are a major seasonal concern. Studies show that dry weather conditions are the driving factor behind uncontrolled fire events and pine bark beetle outbreaks.
The drought years between 1928 and 1939 remain the driest on record for Montana. And the fire seasons of 1931, ‘35, and ’38 were correspondingly severe, burning more than 100,000 acres per season. Montana experienced extended drought conditions for the seven-year period from 1999 to 2006, and we may yet remain in a drought cycle, (2010 Report) perhaps one linked to global warming.