Network of Climate Change Risks on Forests (FoRisk)

Since the early 1990s, it has been hypothesized that the projected trajectory of climate change would have rapid consequential impacts on biotic disturbance in forests. The argument was mainly based on two points: (1) even in the absence of directional changes in climate, forests throughout the world are strongly influenced by episodic events of pestilence, and (2) insects are very responsive to climatic variation because of their short generation time, high reproductive potential, and physiological sensitivity to temperature and food quality. The most likely potential pathways of ecological change include: direct effects of temperature on insects; effects of temperature, soil moisture, or cloud cover on plant defenses, nutritional suitability, and compensatory growth; and effects of temperature on community interactions between herbivores and their predators, competitors, and mutualists. There are now numerous examples of insect populations whose distribution and abundance have changed in ways that are consistent with the expected effects of climate change. Some globally noteworthy examples of recent pestilence may be attributable to climate change during the last two decades. Presumably there have been some other impacts that are positive from the perspective of traditional forest management. Biological responses have been uneven across insect species and forest systems, and have not usually been predictable in their details. There is a need for well validated models that can predict changes in biotic disturbance within forests given specific scenarios of climate change. I offer the following suggestions to facilitate progress: (1) develop, test, and refine general qualitative hypotheses that can predict when and where impacts will be large vs. small, and positive vs. negative; (2) develop programs of focused studies in systems with high importance and a high probability of consequential impacts; and (3) conduct multi-faceted tests (including meteorology, physiology, and population ecology at least) of explicit mechanisms by which climatic variation is theoretically transduced into biotic disturbance. FoRisk, SNS Workshop, August 29, 2008 Umeå, Sweden 3 Pest insects in Finnish forests and climate change – a short note