Forests: Outrun by Climate Change

Since January 2014, Whatcom Watch has been rerunning articles from issues printed 20 years ago. The below article appeared in the April 2000 issue of Whatcom Watch.

Below is part five of a six-part series on climate change that Whatcom Watch ran from December 1999 to May 2000. The series titled “Hot Water: A Snapshot of the Northwest’s Changing Climate” was originally published by Climate Solutions, a group working to make the Northwest a leader in global warming solutions. All six parts of the series are available on the Whatch Watch website. Start at:

by Patrick Mazza

The signature forests of the Northwest are known by their longevity — they’re old growth. They are survivors, having long endured droughts, drenchings and windstorms. They have taken repeated hits from fire, disease and pests. As the Joint Institute for the Study of the Atmosphere and Ocean’s Ed Miles notes, “Mature trees tend to be long-lived and can survive long periods of marginal climate.”

As Northwest forests face global warming, “Responses will be slow and muted, especially for older forests, because they are relatively tolerant to change and can adapt somewhat to new environments,” pioneering ancient forest scientist Jerry Franklin says.

Old forests not only absorb climate change better — Northwest old-growth forests also sequester immense amounts of carbon. Some hold more carbon per acre than any other ecosystem on earth. Cutting forests on a short-rotation basis actually puts more carbon into the atmosphere than leaving the equivalent acreage in old growth.

Global warming is likely to increase the frequency and intensity of disturbances such as pest and disease outbreaks, and wildfires. This is where climate change is expected to have the greatest impact on Northwest forests, young and old. During such disturbances, the normal, slow pace of forest change drastically accelerates. Forests that otherwise might remain the same for centuries undergo dramatic shifts. Whole, new species’ communities can take root. Scientists studying pollen embedded in geologic layers have detected radical reordering of forest communities, brought on by catastrophic events that took place as climate was shifting. This is the likely scenario for future species shifts.

With warming temperatures, forests will become generally drier during summers because increased evaporation will wring out soils. Dryness will help promote fires. In a warming world, forest fires can be expected to burn more frequently and with greater intensity. For instance, large stand-replacing fires have come to the Central Washington Cascades every four centuries. Under global warming, they can be anticipated every century. One hundred years of suppressing natural fires adds to the danger. Many Northwest forests are choked with thick growth just waiting for a spark. A climate swinging between extremes sets up further troubles. Heavy rainfalls feed growth of underbrush. Then warm, dry spells turn that underbrush into a tinderbox.

A hotter climate will be more friendly for insects which infest tree stands. Some insect species might be able to birth more generations each year. Aphids could climb to elevations currently too cold for them, to attack trees with little resistance, such as subalpine fir. And trees in general, when stressed by thirst and heat, are more susceptible to pests and disease.

In many Northwest forests, such as those on the Olympic Peninsula, severe windstorms are the prime stand-replacing catastrophes. Northwesterners remember the Columbus Day 1962 windstorm as an event that downed millions of trees. Scientists as yet cannot say if global warming will promote such fierce windstorms in the region. But the southeast Alaska coast has seen gale-force wind days double in number during the warming of the past 20 years.

Every forest reflects its own particular place. Each is an adaptation to a certain pattern of temperature and precipitation. With warmer temperatures moving north, forests will find themselves in places where conditions are unlike those in which they originally grew. Tree species already living on the fringes of their range, facing global warming’s added stress and disturbances, are expected to decline or disappear across wide areas. The more dry, southern and inland the forest is, the more susceptible it will be to change.

Both Washington and Oregon could lose 15-25 percent of total forest cover, mostly conifers on the drying lower east slopes of the Cascades. They would be replaced by sagebrush steppe and grassland. For instance, one scenario shows the eastside Central Oregon Cascades, now 60 percent forested, losing half that cover in a 4.5 degree Fahrenheit warming. The east slopes of the Washington Cascades are also projected to lose half their forests in a 5 degree Fahrenheit warming. Those temperature increases are expected around 2050-80.

However, University of Oregon climate researcher Patrick Bartlein says, “The loss of forests east of the Cascades may not be a foregone conclusion.” That is due to the fertilizing effect of increased atmospheric CO2 on tree growth, he explains. Newer models that better account of this effect are giving forests stronger odds, Bartlein says.

Temperature alone is expected to impact a major Northwest tree species. Douglas fir, which requires a winter chilling, will likely vanish from the Coast Range of Southern Oregon and Northern California under expected warming.

As the geography of climate changes, forests will attempt to follow. But tree species typically migrate six-tenths of a mile each year. Climate will be moving twice as fast or faster. Forests will often be blocked by human developments. Changing ecosystems will need new kinds of seedlings, but prospective parents will be left behind. Some species adapted to special conditions, such as the Port Orford cedar, might go extinct. “Forest ecosystems are not expected to shift as intact communities, notes Miles.

Trees could find new habitat at higher elevations that are now covered by snowpack and alpine meadows. But the flowered meadows Northwesterners have come to love in places such as Paradise on Mount Rainier are at risk. Subalpine forest is already invading meadows in the Cascades and Olympics, and threatens to entirely displace them from the westside of the Cascades in Oregon.

Even though trees will find some new places to grow, the net effect of global warming in the Northwest could be forests diminished in extent, outrun by a climate changing faster than their ability to adapt.

Trouble for the Human Species
Human beings are no more exempt from global warming impacts than forests, fish and birds. A number of potential threats face us.

For urban areas, hotter temperatures mean more of those smoggy skies Seattle, Portland and other cities often encounter during hot summer days. Bright sunlight and high temperatures feed creation of ground-level ozone, a key component of smog which inflames lungs and worsens respiratory illnesses. More ozone will not only push cities further over the line — It also will hurt crops and wild plants.

Drier summers could elevate pollen counts, making life more miserable for asthma and hay fever sufferers. An increase in summer heat waves, already observed in recent decades across the United States, poses dangers to vulnerable populations, such as the elderly.

Warmer temperatures also encourage growth of disease-carrying insect populations. Lyme disease carried by ticks could increase in Oregon and forms of mosquito-born encephalitis could spread north from California. Both diseases cause long-term damage to the human nervous system.

All along the coast, warmer water could also mean an increase in health threats such as disease- carrying algal blooms, “red tides.” They appeared in Washington state waters in 1989, ‘90 and ‘91. Algal blooms, which are already reaching epidemic status around the world, cause paralytic shellfish poisoning. Ocean warming potentially menaces Northwest shellfish fisheries, particularly the valuable oyster farms of the Willapa Bay, and the people who eat their products.

Patrick Mazza was a staff writer-researcher for Climate Solutions when this article was written.