Distinctly Montana Magazine

W W W. D I S T I N C T LY M O N TA N A . C O M 77 INTERVIEW WITH ANDREW LARSON, PH.D Associate Professor of Forest Ecology at the University of Montana. Dr. Andrew J. Larson is Associate Professor of For- est Ecology at the University of Montana. His research examines disturbances and dynamics of natural forest ecosystems. He currently serves as Associate Editor for the journal Fire Ecology, and his fire ecology research in the Bob Marshall Wilderness was recently recognized with the USDA Forest Service National Award for Wilderness Stew- ardship Research. BEFORE WE TAKE A LOOK AT 2045, WHAT KIND OF SHAPE ARE OUR FORESTS IN RIGHT NOW, AND WHAT ARE THEIR STRENGTHS AND WEAKNESSES? Forestland in Montana has one very important thing going for it — there is still a lot of it. We have not lost our forest landscape to shopping malls, highways, and subdivisions, in contrast to so many other places across the country, such as the Puget Sound country of western Washington, the Colorado Front Range, or the once great deciduous forests of the eastern states. As long as Montana's forests are not fragmented by development they will remain in a strong position to survive future threats. However, forests in our state are by no means pristine. Our low el- evation, dry forests suffer from the long exclusion of fire. e health and function of ponderosa pine forests in particular depend on re- current low-severity surface fires. If these dry forests are not burned every 5 to 50 years they accumulate heavy fuel loads and develop unnaturally dense canopies, making them susceptible to extreme fire. e long-standing policies of the US Forest Service and other agencies have been to suppress fire, leading to a great environmental disaster in these dry forests. Smokey Bear got it wrong. e more productive moist forests of northwest Montana have not been as affected by fire exclusion. In cool and moist forests fires naturally burn less frequently, but with higher severity, killing most trees. Our moist, productive forests are doing fine with respect to fire, but have been subject to more intense harvesting and road building. In both our dry and moist forests the number of large, old trees is greatly diminished compared to historical conditions because of high-grade harvesting. Large diameter trees, which are disproportionately important for wildlife habitat, are much rarer than they were just 50 years ago. WHAT ARE THE GREATEST THREATS TO ALL MONTANA WOODLANDS OVER THE NEXT 30 YEARS, AND WHICH ARE OF MOST LONG-TERM CONCERN? Probably the single greatest threat to Montana forests is the future introduction of non-native insects and diseases. We have already seen the decimation of the five-needle pine forests throughout Montana and the rest of the West due to white pine blister rust, an introduced disease. Global trade and travel makes the introduction of non-native diseases and tree-killing insects from other parts of the world very likely. My worst case scenario would be the introduction of a non-native disease that kills off one of our major tree species, such as the iconic western larch, much in the way that the non-native chestnut blight disease eliminated the once widespread American chestnut from forests of the eastern United States. Another major threat to Montana forests is climate change. Over the next 30 years, I expect to see things like increasingly severe and frequent droughts, which will result in widespread tree mortal- ity. But, except for the lower margins of forest cover — the hottest and driest habitats where trees can barely survive now — trees will regenerate and forest cover will persist through at least the initial de- cades and centuries of climate change. Forests of the future will look very different. Forests will reorganize in response to climate change. Species' ranges will shift as trees establish in new habitats. IS THERE A DIFFERENCE IN SENSITIVITY TO CHANGE AND MORTALITY WHEN IT COMES TO OLD GROWTH VS. NEW GROWTH TREES OR DIFFER- ENT TREE SPECIES IN FORESTED AREAS? First, it is important to recognize that tree mortality is a natural, and essential, part of forest dynamics. Dead trees, called snags, provide crucial habitat for wildlife. A forest is only healthy when it has an abundance of snags, and ongoing mortality to supply new snags as the old ones decompose. Different tree species abso- lutely have different mortality rates. For example, western larch has very low mortal- ity once it reaches middle age (which for a tree means about 100 years old). Western larch has few natural enemies. Consequently, western larch mortality rates are typically one half to one quarter those of co- occurring tree species such as Douglas-fir or subalpine fir. Smaller and younger trees typically have higher rates of mortality than large old trees of the same species. is fact often surprises people, as the assumption is that old trees are more likely to die. But, in reality, small and young trees are almost always more likely to die than their older and larger neighbors. One twist to this story is that, in extreme droughts, the oldest and largest trees are more likely to die first. CONTINUED

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