834 million. the number of dead standing trees in Colorado’s forests. This could increase wildfire risk and threaten the state’s water supply.
Colorado’s 24.4 million acres of forestland provide immeasurable social, economic and ecological benefits to its citizens and visitors. These forests offer a sustainable wood products industry, diverse wildlife species, fresh water and abundant recreation and tourism opportunities. But Colorado forests face numerous threats, and can present risks to citizens and visitors. Wildland fire is a prime example. Fire plays a critical role in maintaining the health of forest, shrubland and grassland ecosystems in Colorado. Lower-elevation forests rely on frequent, low-intensity fires to control regeneration and reduce understory vegetation, while some high-elevation forest types, such as lodgepole pine, rely on high-intensity fire to regenerate the forest. But a long history of fire suppression has altered historic fire cycles and led to the dangerous buildup of fuels in some areas. Population growth into the wildlandurban interface (WUI) – the area where structures and other human developments meet or intermingle with wildland fuels – presents further challenges. Colorado’s WUI population grew from 980,000 people in 2000 to more than 2 million people in 2012,
and this number is rising. According to data from Headwaters Economics, only 20 percent of the state’s WUI is currently developed.
In addition to the complications of a growing WUI, the wildfire season has lengthened due to a changing climate, resulting in wildfires that start earlier, last longer, cost more to suppress, cause more damage, and threaten more lives than ever before. As Colorado’s population increasingly grows in the WUI, human exposure to the side effects of wildfire – including post-fire erosion impacting water sources and reduction in air quality due to smoke – will become a significant public health issue.
Is Beetle-Kill Altering Wildfire Risk?
Beyond the problems of overgrown forests and an increasing WUI population, the state’s ongoing forest health concerns are due to a combination of factors, including poor stand conditions, long-term droughts and warming annual temperatures. The resulting forests are unhealthy and overly dense, and set the stage for current and future insect and disease epidemics. Colorado’s mountain pine beetle (MPB) epidemic from approximately 1996 to 2014 resulted in almost 3.4 million acres impacted, primarily in lodgepole and ponderosa pine forests. Trees that were more recently killed
are still standing; those that died from the epidemic more than a decade ago have increasingly fallen to the ground in chaotic fashion. These “jackstrawed” stands are made up of a combination of
standing, semi-fallen and downed dead wood, creating a unique arrangement and availability of fuel for future wildfire. The MPB epidemic has thus changed the fuel arrangement within Colorado’s forests, which in turn affects fire behavior and wildfire suppression tactics.
Forest Inventory and Analysis Supports Trends
Every year, the Colorado Forest Inventory and Analysis (FIA) program completes an inventory that provides objective and scientifically credible data on the extent, condition, volume, growth,
depletion and health of Colorado’s forest resources, and measures these changes over time. This information helps researchers, policymakers, private industry, landowners and natural resource professionals better understand current forest conditions and significant changes across the state. FIA data are showing an increasing trend of forests with vegetative fuel rearrangements that may be more conducive to large fire spread, such as with jackstraw stands due to beetle-killed trees. In 2008, there were an estimated 642 million dead standing trees in Colorado; by 2015, this number had increased to 834 million dead standing trees – an almost 30 percent increase over seven years. In Colorado’s sprucefir forests, approximately 1.7 million acres have been impacted by the current spruce beetle epidemic. According to FIA data, spruce-fir forests contain two to three times more coarse woody debris – fallen dead trees and large dead branches on the ground – than any other forest type. This has significant implications for fuel loading and fire behavior, as was seen in the 2013 West Fork Fire Complex that burned in the San Juan and Rio Grande National Forests and private lands in southwest Colorado. The vegetation within the West Fork Fire consisted mainly of dense spruce-fir forests, with large stands of beetle-kill representing up to 80 percent of the trees. Spruce-fir forests contain shadetolerant trees with abundant branches close to the ground. These branches, even after the dead needles have fallen off, create a dense network of “ladder fuels” that can easily carry fire up into the forest canopy and are conducive to extreme fire behavior. Similar to the Beaver Creek Fire, the complex terrain and large number of beetlekilled snags within the West Fork Fire created an unsafe working environment for firefighters. Strong winds and low relative humidity led to extreme fire behavior as winds pushed the fire into the crowns of the dead stands of spruce, with smoke plumes visible from over a hundred miles away. The winds also carried embers up to two miles ahead of the fire front, creating spot fires.
Also of concern based on FIA data is that although tree mortality has increased across Colorado, preliminary data suggest that the reduction in competition between new and older trees due to more growing space has not resulted in an increase in forest regeneration. This may be due to lack of seed source, lack of germination, changes in micro-environments or other factors.
To see the Colorado State Forest Service’s full report, click here.
Cover Photo Credit: USDA