What Does a Longer Season Mean for Montana Forests?
by Tom Torma
Broadcast on 9.1.2015
July of 2015 was the warmest month on record in the history of our planet, 2015 is on trend to be our warmest recorded year, and in much of the American west that warmth has been coupled with moderate to extreme drought conditions.
With emissions of greenhouse gases showing no sign of decreasing, these records will probably not last long. For Montana, it means that our overall climate is likely to get warmer and drier.
As that happens, wildfires are likely to grow in both frequency and scale. Montana’s trees have a variety of adaptations to the fires. Some, such as subalpine fir and white-bark pine, escape from fire by growing at higher altitudes, where cooler temperatures and greater precipitation reduce the likelihood of fire.
Others, such as Douglas-firs, western larches, and ponderosa pines, survive in part thanks to a thick bark that protects the living tissue from fire. Perhaps the most fascinating adaptation is the serotinous cone, like those found on the lodgepole pines that dominate much of Montana’s forests.
These trees do not attempt to survive forest fires at all. Instead, they use fire for germination—their specialized cones have a waxy coating. As the coating melts in the heat of the fire, the cones open and release their seeds. Lodgepole pine seeds are thus the first to start growing after a fire, often crowding out other species.
The potential damage from a fire can continue to grow long after the burning has stopped. The above-ground vegetation that normally holds the topsoil in place is gone after some fires. The topsoil can be washed away, making plant regrowth more difficult.
Most of the fires are exterminated by early autumn rain and snow, but the water also washes the ash and loose topsoil into the streams and rivers, killing fish, insects and aquatic plants. Trees killed by the same fire mitigate much of this damage.
Even dead trees, whether fallen or still standing, serve as a buffer against the erosion, keeping the soil in place and assisting with plant regrowth the following spring. Of course, some trees fall into the streams and rivers.
As they flow downstream, they form logjams, which are effective filters against the ash that the logs on the ground were not able to block. As a result, while the brooks and streams higher in the watershed run black from the burnt materials caused by fires, downstream, the rivers still run clear.
In the first years following a fire, pioneer species like fireweed grow and help secure the soil, and the forest begins to renew itself. However, as the forests come back, dead trees continue to play a role in forest. They become a feeding ground for numerous insects – ants and termites as well as fungi and other agents of decomposition.
These in turn become food for everything from woodpeckers to bears. Woodpeckers drill nesting holes into the snags that can later become homes for squirrels, swallows and other small birds. In other words, the trees that have been killed play vital roles in the resilience and recovery of the forest.
Nevertheless, as fires become more frequent and more intense, the woodland’s ability to recover might be called into doubt. While the exact impact cannot be known, it seems likely that less time between fires means that trees will have less time to grow, so that when they are burned, they are less effective buffers against erosion and damage to streams.
Longer, hotter fire seasons also might well mean that much of the deadfall is simply burned away – thus offering little scaffolding to the ecosystem as it attempts to replenish itself. However climate change influences future weather patterns, there are bound to be some significant changes to Montana’s landscape.
Some species will thrive and others will suffer as the climate shifts and the fire season gets longer. But whether fire occurrences increase by a great deal or only a little, the trees that don’t survive the flames are certain to play a key role in whatever shape Montana’s forests take in the coming years.
Every week since 1991, Field Notes has inquired about Montana’s natural history. Field Notes are written by naturalists, students, and listeners about the puzzle-tree bark, eagle talons, woolly aphids, and giant puffballs of Western, Central and Southwestern Montana and aired weekly on Montana Public Radio.
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