Climate Change
Climate Change is already impacting Sierra Nevada forests and the outlook for their future and its potential consequences is dire. In the future impacts could be catastrophic. Recent scientific research has shown that conifer trees in the Sierra Nevada are dying at nearly double the rate as they were two decades ago, stressed by hotter temperatures and lower precipitation. A twenty-two year study of over 21,000 trees in a variety of forests concluded that the average mortality rate increased every year by about 3 percent, leading to a near doubling of the rate by the end of the period. During the same twenty-two year period, the Sierra Nevada warmed by 1.8 degrees Fahrenheit, while the amount of snowfall and rain remained the same. Results showed that some of that precipitation evaporated as the climate warmed instead of being absorbed by the trees. Other scientific data have documented that there has been a 25% reduction in spring runoff in the central Sierra and a 10% reduction in runoff in the southern Sierra in recent years.
While climate change will affect all regions of the state, the consequences for the vegetation, wildlife, and water resources will likely be most dramatic in the Sierra Nevada. Scientists project that by the end of the century, average annual temperatures will rise between 4 and 11 degrees Fahrenheit. Winter temperatures are likely to rise 2 to 2.5 degrees F in the next fifty years. An increase in temperature in this range would substantially reduce the annual snowpack in the Sierra and by 2050 we could see a reduction in snowpack by 25 to 40 percent. When this occurs, the winter snow season will be significantly shorter, with a later average starting date and earlier onset of springtime melting. This change in both the volume of snowmelt and time of year that melting occurs will greatly impact water resources and the Sierra Nevada’s ecological systems. For instance, snowmelt beginning earlier in the year will shift streamflow regimes causing some perennial streams to become ephemeral and unable to support many aquatic species. By 2050 spring and summer stream flow is expected to decrease by as much as 25%. Streams are going to be reshaped by the change in timing and intensity of different flood events and riparian and aquatic ecosystems are going to permanently altered.
Average annual temperature is a key element in determining the presence and absence of vegetative communities found throughout the Sierra Nevada. As temperature continues to rise, plant communities in the alpine and sub-alpine zones will experience a reduction as mixed conifer communities expand into higher elevations. Oak woodlands could also expand into higher elevations, displacing some pine and fir forests. Throughout the Sierra, the higher temperatures and decreased precipitation will lead to an increase in fire frequency, further impacting the presence and abundance of certain plant communities. Shrub communities could be replaced by grasslands for example. All of these changes will have a profound affect on wildlife species as they attempt to adapt to the changing ecological systems around them.
The American pika, living at the top of the Range of Light, is likely to be threatened with extinction due to global warming. As with other species living at the tops of mountain ranges throughout the planet, the pika cannot retreat any higher up to escape the effects of climate change. Read the press release from the Center for Biological Diversity and EarthJustice, and the petition to list the pika as a threatened species, here.
The Sierra Nevada supplies over 65% of California’s developed water and the impact of climate change on our water supply will be significant. While a quick reaction by some would be to increase our water storage capacity by building new dams, it is important to remember that dams have their own destructive impact on the Sierra’s ecological systems. Dams inhibit fish passage, reduce fish survival, significantly alter riparian areas, and eliminate aquatic habitat and functions. Many fish species, including several salmon species are no longer found in the Sierra due to the current prevalence of dams. An increase in dam construction in the Sierra Nevada would have profound consequences for more aquatic species and wildlife dependent on healthy watersheds and aquatic systems.
Logging Impacts on Climate Change
The impacts of logging operations on climate change are still being analyzed in the scientific community. What is known at this point is summed up by Nick Brown, a forestry scientist at Oxford University: "The more frequently a forest is harvested, the more carbon is emitted." Land preparation, management during the growth period, and, finally, felling and logging operations all put significant amounts of CO2 into the atmosphere. The use of energy by tractors, trucks and other machinery in the actual logging operations and the transport of logged trees on each logging project add more CO2 to the atmosphere each and every day.
Some timber industry spokespersons have attempted to make a case for the role of plantation forestry in sequestering greenhouse gas emissions, thereby justifying the continuation of conversion of old growth forests into clearcuts and tree plantations on short (50-80 year) rotations between cutting. The argument is based on the theory that 1) younger trees are growing more rapidly than old growth specimens and must therefore sequester more carbon dioxide; and 2), trees which are harvested for lumber continue to store carbon when they are converted to two-by-fours and other structural components. These arguments have not stood up to scientific scrutiny.
A recent paper published in the journal Nature found that old-growth forests store large amounts of carbon dioxide from the atmosphere and can mitigate climate change for centuries. The research team, from the U.S., Belgium, Germany, Switzerland, France and the United Kingdom, reported that old-growth forests in the Northern Hemisphere alone sequester about 10 percent of net global carbon. Half of the planet’s primary forests and remaining old-growth forests are located in the boreal and temperate regions of the Northern Hemisphere, equivalent to 15 per cent of the global forest area. The paper concludes, "Because old-growth forests steadily accumulate carbon for centuries, they contain vast quantities of it. They will lose much of this carbon to the atmosphere if they are disturbed, so carbon-accounting rules for forests should give credit for leaving old-growth forest intact."
Tree plantations by contrast may take decades to overcome the effects of the major disturbance associated with clearcutting and tree planting, during which time they are net carbon emission sources.
Old forests sequester a higher volume of greenhouse gas emissions than young, uniform forests due to the size and age of the trees and the structural and biological complexity and diversity of old-growth forest communities. For example, the duff on the forest floor in old growth forests contains high volumes of fungal diversity, and a variety of associated plants and other organisms that contribute to locking up carbon and other greenhouse gases in a very efficient way. Further, old forests are extremely fire resistant and can recover their carbon storing capacity in a relatively short time after fire--unlike uniform tree plantations, which burn up with regularity in the Sierra Nevada and increase fire hazards overall.
And while structural lumber may store carbon for the lifetime of a building, much of the trees are converted to pulp and paper with a short lifetime. Overall, the long term carbon storage capacity of lumber products is a small fraction of the trees from which they came.
Finally, the industry argument fails to also account for all the myriad natural resource values that encompass a natural forest. The forest is not simply a stand of trees with commercial value, but home and habitat for species both massive--like the Giant Sequoia--or small and easily overlooked, like the bioluminescent Sequoia Glowing Millipede (Luminodesma sequoiae) that glows only in the dark in early springtime in the forest duff. These and hundreds of other species are at risk from climate change and unsustainable logging practices--including clearcutting and conversion to industrial forest plantations.
While the concept of forests serving as carbon sinks is an interesting one that is still being studied the most persuasive argument is simply to leave our existing forests alone. Limiting logging operations conserves biodiversity and natural ecological processes while minimizing the likelihood of undesirable side effects such as adding fuel to the growing climate change inferno.
Coming Soon--More on Forests, Logging, and Climate Change
As stated by Dr. Beverly Law, Science chair of the Ameriflux project, "Carbon accounting is no small task." Like most things ecological, the many variables are deeply interrelated. Sierra Forest Legacy is currently studying this complex issue in detail, through literature review, analysis, and interactions with other scientists, policy experts, and our conservation partners. Look for more information here on our website in the coming weeks.