It’s been happening for more than a decade. Drought, insects and disease are recreating the landscape of western North America. A paper out of Oregon State tells the story: “A huge “migration” of trees has begun across much of the West due to global warming, insect attack, diseases and fire, and many tree species are projected to decline or die out.” These forests have been where they are (or where they once were) for millennia. Now abrupt climate change is causing a massive ecoregime change, unlike anything mankind has ever experienced.
This ecoregime change is what ecologists call it when an ecosystem changes to a different ecosystem. In its most extreme form called desertification, this can be thought of as a line of sand dunes marching across a forest, completely extinguishing all life previously known in the forest ecosystem. This may seem extreme, but in reality, the paper says that many of our forests across the North American West are at risk of being replaced by grassland. The great conservativeness of course, this study was done with the A2 scenario: one of the middle of the road scenarios. Our climate, pushed hard by our society, with decades if not generations of warming to come from already emitted greenhouse gasses, is tracking the worst-case scenario path.
Extra – Local Bulletin, Austin, Texas: The great forest die-off began in Austin with the drought of 2005/6. Our forests are not as severely impacted as those of the Rockies and the Southwestern U.S. — yet. This latest drought, the third in row, was quite likely twice as extreme as the drought of record here in Central Texas: the Drought of the 1950s. Visibly, to civilians, little has changed. That’s the trouble with outreach and forest mortality. Once a tree dies and its leaves come off, it tends to quickly disappear back into the forest. the limbs of a tree simply have much less visible mass than all those leaves. In addition, surviving neighboring trees rebound rapidly. The dead trees leaves a hole that it full of water, light and nutrients. Neighboring trees soak it up in a process that foresters call “release.” The term was coined to describe increased tree growth when a forest is selectively logged. the trees that remain are released.
Forest die-of from drought, insect infestation or disease does the same thing. the trees that survive get a growth spurt very rapidly after their neighbors die. This growth covers up
Nicholas C. Coops, Richard H. Waring. Estimating the vulnerability of fifteen tree species under changing climate in Northwest North America. Ecological Modeling, 2011; 222 (13): 2119 DOI: 10.1016/j.ecolmodel.2011.03.033 Richard H. Waring, Nicholas C. Coops, Steven W. Running. Predicting satellite-derived patterns of large-scale disturbances in forests of the Pacific Northwest Region in response to recent climatic variation. Remote Sensing of Environment, 2011; DOI: 10.1016/j.rse.2011.08.017