The great irony is that the cold headwater streams that were believed to be most vulnerable to climate change appear to be the least vulnerable. Equally ironic is that we arrived at that insight simply by amassing, organizing and carefully analyzing large existing databases, rather than collecting new data that would have been far more expensive.
A research team led by the U.S. Forest Service drew information from huge stream-temperature and biological databases contributed by over 100 agencies and a USGS-run regional climate model to describe warming trends throughout 222,000 km of streams in the northwestern United States.
The colleagues found that over the last 40 years, stream temperatures warmed at the average rate of 0.10°C per decade. This translates to thermal habitats shifting upstream at a rate of 300-500 meters per decade in headwater mountain streams where many sensitive cold-water species currently live. The authors are quick to point out that climate change is still detrimentally affecting the habitats of those species, but at a much slower rate than earlier studies forecast. This indicates that many populations of cold-water species will continue to persist this century and mountain landscapes will play an increasingly important role in that preservation by becoming climate refugia. This also means that resource managers will have more time than previously thought to complete extensive biological surveys of ecological communities in mountain streams so that conservation planning strategies can adequately address all species.
One of the great complexities of restoring trout and salmon under a rapidly changing climate is understanding how this change plays out across the landscape. Dr. Isaak and his colleagues show that many mountain streams may be more resistant to temperature change than our models suggest and that is very good news. This provides us more time to effect the changes we need for long-term persistence of these populations.