<p>Stretching from the redwoods of California to the vast stands of spruce and hemlock in southeast Alaska, coastal temperate rain forests have been for thousands of years home to one of the highest densities of human settlements on the continent. Given its mild climate, magnificent scenery, and abundant natural resources, the region should continue to support robust economies and vibrant communities for many years to come. However, the well-being of this region is increasingly threatened by diminishing natural capital, declining employment in traditional resource-based industries, and outward migration of young people to cities.<p>The Rain Forests of Home brings together a diverse array of thinkers-conservationists, community organizers, botanists, anthropologists, zoologists, Native Americans, ecologists, and others-to present a multilayered, multidimensional portrait of the coastal temperate rain forest and its people. Joining natural and social science perspectives, the book provides readers with a valuable understanding of the region's natural and human history, along with a vision of its future and strategies for realizing that vision.<p>Authors describe the physical setting and examine the geographic and evolutionary forces that have shaped the region since the last glacial period, with individual chapters covering oceanography, climate, geologic processes, vegetation, fauna, streams and rivers, and terrestrial/marine interactions. Three chapters cover the history of human habitation, including an examination of what is known about pre-European settlement, a consideration of the traditions of local and indigenous knowledge, and a description of the environmental and cultural upheaval brought by European explorers and settlers. The book concludes with an exploration of recent economic and cultural trends, regional and local public policy, information gathering, and the need for integrating local knowledge into decision making.<p>Interspersed among the chapters are compelling profiles of community-level initiatives and programs aimed at restoring damaged ecosystems, promoting sustainable use of resources, and fostering community-based economic development. The case studies describe what coastal residents are doing to combine environmental conservation with socioeconomic development, and document some of the most innovative experiments in sustainable development now underway in North America.<p>The Rain Forests of Home offers for the first time a unified description of the characteristics, history, culture, economy, and ecology of the coastal temperate rain forest. It is essential reading for anyone who lives in or cares about the region.
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About the Author
Jerry Franklin is Professor of Ecosystem Analysis, College of Forest Resources, University of Washington, Seattle, WA. Franklin is co-author of Conserving Forest Biodiversity, Creating a Forestry for the 21st Century, Salvage Logging and Its Ecological Consequences, and Towards Forest Sustainability, all from Island Press.
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The Rain Forests of Home
Profile of a North American Bioregion
By Peter K. Schoonmaker, Bettina von Hagen, Edward C. Wolf
ISLAND PRESSCopyright © 1997 Ecotrust
All rights reserved.
Oceanography of the Eastern North Pacific
DAVID K. SALMON
The eastern North Pacific Ocean is part of a vast and continuous expanse of water that forms the oceans of the world. The ocean and atmosphere act as a strongly coupled system—transferring heat, moisture, and momentum back and forth and interacting with landmasses to create the weather and hence the climate of the earth. In this respect, the eastern North Pacific does not act in isolation. Its behavior is strongly influenced by events in tropical, subtropical, and subarctic regions.
The coastal rain forest owes its physical and ecological characteristics to the interactive processes that occur between the ocean, atmosphere, and landmasses. Physical energy is transferred back and forth extensively between them: radiative energy, winds, precipitation, ocean waves. Energy is also transferred ecologically via processes such as migrations of salmon and other anadromous species into freshwater systems.
The ocean tends to oscillate between two climatic extremes for periods that last between ten and twenty years. These oscillations manifest themselves as changes in surface ocean and air temperatures, the strength of the wind, amounts of precipitation, and numerous other processes related to climate including floods and crop failures. Fluctuations in the abundance of marine phytoplankton, zooplankton, and many fish species often closely parallel these climatic changes.
Overview of the Region
Circulation in the upper layers of the North Pacific Ocean (about the upper 1500 meters) is driven principally by the wind. The ocean surface and near-surface atmosphere transfer heat, moisture, and momentum to one another. Therefore, the principal large-scale patterns of the North Pacific Ocean's circulation have much in common with the major components of North Pacific winds (Figure 1.1). The northeast trade winds, a band of westward-flowing air, dominate the equatorial and tropical regions of the North Pacific. These trade winds extend across the entire Pacific Basin. In the subtropics the surface winds are dominated by the eastward-flowing westerlies, which extend in a band across the North Pacific. Together the trade winds and the westerlies drive a large-scale oceanic feature called the North Pacific subtropical anticyclone, which consists of a clockwise-flowing system of currents made up of the westward-flowing North Equatorial Current, the northward- and northeastward-flowing Kuroshio Current off Japan, the eastward-flowing North Pacific Current (sometimes called the West Wind Drift), and the southward-flowing California Current (Figure 1.2).
Many of the storms that traverse the North Pacific are generated in the Kuroshio Current region, where tremendous amounts of heat are lost to the atmosphere from the warm waters of tropical origin that make up the Kuroshio. Other areas where storms develop include the central Aleutian Archipelago and the eastern Gulf of Alaska, particularly in the vicinity of large glaciers that front the coastal region. These storm systems are important to the ecology of the coastal rain forest because of their direct influence on the physical environment of the eastern North Pacific. These storms affect streamflow, cloud cover, fog, ambient air, stream and upper ocean temperatures, and the amount of stored precipitation available as spring runoff. Storms are also important in the moderation of continental temperature fluctuations (and associated processes) in the coastal temperate rain forest. The region is temperate largely because of the moderating influence of the marine component of the climate system.
Between about 45 and 60 degrees north latitude, extending across the Pacific Basin is an atmospheric feature called the Aleutian Low pressure system (Figure 1.3), a region of statistically low barometric pressure, enhanced by a nearly continuous procession of storms (except during summer) that move generally northeastward after forming in the Kuroshio region, the Bering Sea, or the Gulf of Alaska. The Gulf of Alaska is one of the most active meteorological regions on earth (Wilson and Overland 1987), especially during winter, when it is not uncommon for storms to generate 15-meter-high seas and 100-knot winds. A storm moves through this region on the average of every four or five days throughout the winter months (Hartman 1974; Wilson and Overland 1987). The coastal rain forest owes many of its physical characteristics to the effects of atmospheric and oceanic processes associated with the Aleutian Low: frequent and intense coastal storms, strong and persistent winds, fog, rain, and snow. The physical morphology of the coastal region is literally shaped by the actions of wind and waves on the continental landmass.
The Aleutian Low dominates the atmospheric circulation between 45 and 60 degrees north latitude during fall, winter, and early spring. During summer the storm activity abates and the low-pressure cells are displaced (they often move over land) by a high-pressure system called the North Pacific High. The North Pacific High is statistically present year round in the subtropical Pacific region between about 20 and 45 degrees north. It is the dominant factor influencing the weather on the west coast of North America during summer, when it intensifies and expands northward over the subarctic region of the Pacific Ocean.
The winds in the Aleutian Low drive two large ocean gyres, one in the Bering Sea and the other in the Gulf of Alaska (Figure 1.2). The predominant ocean circulation in both regions is counterclockwise, as are the wind systems that drive the currents. These wind systems are directly associated with the storms that frequently form in the regions or move there after forming off eastern Asia in warm waters of tropical Pacific origin. The Alaska gyre consists of the eastward-flowing North Pacific Current (which forms the southern boundary of the gyre) and the northwestward- and westward-flowing Alaska Current. The Bering Sea and the Gulf of Alaska are extremely important to the ecology of the temperate rain forest region because they play a major role in supporting the oceanic phases of the life histories of Pacific salmon. Pacific salmon characteristically spend more than half of their lives (depending on the species) feeding on zooplankton produced in these oceanic regions. In addition these regions are economically valuable to the coastal rain forest area because they support large stocks of commercially important fishes including halibut, sablefish, walleye pollock, Dungeness, king, and tanner crab, albacore, scallops, shrimp, sea urchins, and sea cucumbers, to name just a few.
The Alaska Coastal Current flows within about 50 kilometers of the coast of the entire Gulf of Alaska. It is a westward-flowing current driven by fresh water and wind. It carries the entire load of runoff from the rivers bordering the Gulf of Alaska (Royer 1979, 1981; Schumacher and Reed 1980). The strength of the coastal current is strongly influenced by seasonal variations in both surface winds and freshwater discharge from rivers. The ecology of the nearshore regions in the subtropical and subarctic North Pacific is quite distinct from the waters of the offshore ocean gyres largely because of continental effects associated with differential precipitation and changes in the winds and ocean currents associated with the continental margins. This is particularly true in the Gulf of Alaska region, where the coastal mountain ranges ringing the gulf act as a barrier to the inland passage of storms, resulting in large amounts of precipitation (2 to 3 meters per year) in the coastal region as the storm systems are forced against the high coastal mountains in the nearshore region of the gulf. The storm systems transport tremendous amounts of heat from the ocean, as well, affecting the temperature extremes in the coastal regions. The coastal rain forest probably extends so far poleward because of these moderating effects.
Coastal upwelling and downwelling are oceanic conditions that represent the interaction between wind stress, the rotation of the earth, and frictional effects between the ocean and the continental boundary. In the Northern Hemisphere, these interactions move water to the right of the prevailing winds. Thus upwelling is associated with equatorward winds along the coast and offshore movement of surface waters, while downwelling is associated with poleward winds along the coast and onshore motion of surface waters. During fall, winter, and spring, the coastal regions of northern British Columbia and Alaska are characterized by downwelling conditions that occur in response to prevailing southeasterly and easterly winds. The coastal region of the Gulf of Alaska is characterized as a coastal temperate environment because the prevailing winds moderate the cold subarctic climate through the importation of warm moist subtropical air masses and warm subtropically derived ocean currents. The continental shelf regions of the subarctic North Pacific support high densities of economically and ecologically important marine populations.
During spring and summer, the prevailing winds blow from the north along the west coast of North America, creating an upwelling along the west coast of the United States and southern British Columbia. This upwelling greatly moderates the climate and ecology of the coastal region by bringing relatively cold nutrient-rich subsurface waters to the surface. The nutrient-rich waters support high levels of primary production, which in turn supports tremendous zooplankton and fish biomass. Coastal upwelling regions are among the most productive marine ecosystems on the planet. The ecology of coastal upwelling systems is strongly modulated regionally by seasonal and interannual variability in the winds and by more distant variability in both atmospheric and oceanic conditions in the tropical Pacific region.
The southward-flowing California Current and the northward-flowing Alaska Current relate most directly to variability in the coastal rain forest region. As the North Pacific Current nears the North American continent, it splits and becomes the Alaska Current and the California Current. The relative amounts of water that flow poleward and equatorward in these systems are thought to be closely related to the strength and size of the Aleutian Low. When the Aleutian Low is intensified, it also tends to expand its region of influence further south. It is thought that under these conditions more warm water of subtropical origin flows poleward into the Alaskan Current than during periods of a weakened Aleutian Low. A weakened and contracted Aleutian Low would result in less water moving into the Alaska Current and more cold waters with subarctic physical properties moving south into the California Current. These processes have implications for fisheries. Shifts in the position of the Aleutian Low cause shifts in the positions of the large-scale North Pacific ocean frontal systems—the boundary regions of the large current systems in terms of their physical and ecological characteristics. On time scales of several years, large-scale displacements (to the north or south) of these current systems and associated frontal systems result in the expansion or contraction of the ranges of various phytoplankton, zooplankton, and fish populations.
El Niño, La Niña, and the Southern Oscillation
The terms El Niño, La Niña, and the Southern Oscillation are often used by oceanographers and atmospheric scientists to describe processes that have their origins in the tropical Pacific and Indian oceans with profound consequences for the northeastern Pacific and the coastal rain forest zone. The Southern Oscillation is an atmospheric indicator of a process in which El Niño and La Niña events represent extremes in conditions in the tropics, including ocean temperature, strength and persistence of the trade winds, strength of the coastal upwelling off South America, and precipitation across the entire tropical Pacific. For excellent detailed treatments of the large-scale climatological, ecological, and social effects of the El Niño–Southern Oscillation, see Philander (1990) and Glantz et al. (1991).
The physical and biological characteristics of the El Niño–Southern Oscillation provide a framework for discussing climate and ecology in the North Pacific. Indeed, the cycle plays a dominant role in forcing environmental change in the ocean, in the atmosphere, and on land in the North Pacific on time scales of a few years to decades. El Niño affects the coastal rain forest in a number of ways. Variability of North Pacific marine phytoplankton, zooplankton, and fish populations, for example, can often be linked to the El Niño cycle.
El Niño Phase
How does an El Niño event occur in the tropical Pacific? Before the onset of an El Niño event, oceanic conditions are characterized by warmer surface waters in the western equatorial Pacific and colder surface waters in the eastern tropical Pacific where strong coastal upwelling brings relatively cold, nutrient-rich, deep waters to the surface. The western tropical Pacific is characterized by frequent convective activity and intense rains; the eastern tropical Pacific is much drier. The coastal upwelling marine ecosystem along the west coast of South America is highly productive—a result of nutrient-rich deep waters being brought to the surface and fostering the growth of phytoplankton. In turn, large zooplankton populations thrive on the phytoplankton and hence support higher levels of fish, seabirds, and marine mammals.
A typical El Niño warm event occurs when the northeast and southeast trade winds weaken, causing a diminished westward circulation in the equatorial ocean current system. The trade winds sometimes weaken to the extent that there are occasional westerly wind bursts along the equator. The surface waters of the upwelling regions off South America warm partly in response to the eastward flow of heat from warmer western tropical Pacific waters. As tropical atmospheric convection zones change their positions, the moisture-producing areas move eastward toward the coast of South America. The coastal desert regions of the eastern tropical Pacific receive abundant rain and the terrestrial ecosystem flourishes. The coastal upwelling is suppressed and the marine ecosystem in the eastern tropical Pacific suffers because of the absence of nutrient-rich waters in the upper layers of the ocean. These changes drastically reduce all levels of productivity.
In the eastern North Pacific, the effects of El Niño events often manifest themselves in an intensified and expanded Aleutian Low, as well as higher air and surface ocean temperatures. Animal and plant populations are affected by the changes in their environment that can be brought about by the El Niño cycle. They can also be affected by the presence of species that move poleward in conjunction with warming conditions along the west coast of North America. Numerous examples of these phenomena can be found in Wooster and Fluharty (1985). Pacific mackerel, for instance, are known to move north into British Columbia waters in response to El Niño warm events. Since mackerel can prey heavily on juvenile salmon inhabiting the coastal region, these poleward excursions of mackerel can significantly affect regional fisheries.
La Niña Phase
In the tropical Pacific, La Niña conditions are characterized by strong trade winds, by strong convective activity and precipitation in the western tropical Pacific, by low surface ocean temperatures in the eastern equatorial and coastal upwelling regions, by dry conditions in the eastern tropical atmosphere and adjacent arid continental regions, and by high productivity in the coastal upwelling ecosystems along the west coast of South America.
La Niña conditions can often be related to low surface ocean and air temperatures in the eastern subtropical and subarctic North Pacific, as well as high surface ocean temperatures far away from landmasses in the central North Pacific. Storm activity in the Aleutian Low weakens and high-pressure systems known as blocking ridges tend to prevail over the subarctic North Pacific during the winter months. These ridges are important because they deflect storm systems away from the Gulf of Alaska—either northward into the Bering Sea or southeastward toward the west coast of the continental United States. The occurrence of these ridges during the winter months declined greatly from 1976 through 1988, relative to the previous three decades, apparently because of an intensification of the Aleutian Low during that period (Salmon 1992).
Changes in the ocean occur on a variety of time scales—from fractions of seconds to thousands of years. The annual cycle of the seasons dominates many records of North Pacific atmospheric and oceanic variables including air and upper ocean temperatures, precipitation, and winds. Periods of fluctuation greater than one year are of great ecological importance. Time scales of two to three, five to seven, and ten to twenty years tend to dominate the range of year-to-year variations in both physical and biological systems (Table 1.1). The two to three and five to seven year time scales are closely related to Southern Oscillation phenomena. The ten to twenty year variability probably involves two signals—one at about fourteen years that is related to the Southern Oscillation (Quinn et al. 1987; D. Ware, pers. comm.) and one at about twenty years, which may be related to tides forced by lunar variations (Royer 1989). Variability on all of these time scales has important implications for fish populations including salmon, herring, mackerel, hake, sardines (Mysak et al. 1982; Ware 1990; Beamish and Bouillon 1993), bluefin tuna (Mysak 1986), and Pacific halibut (Parker et al. 1995).
Excerpted from The Rain Forests of Home by Peter K. Schoonmaker, Bettina von Hagen, Edward C. Wolf. Copyright © 1997 Ecotrust. Excerpted by permission of ISLAND PRESS.
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Table of Contents
ContentsAbout Island Press,
1. Oceanography of the Eastern North Pacific,
2. Climate of the Coastal Temperate Rain Forest,
3. The Influence of Geological Processes on Ecological Systems,
4. Vegetation from Ridgetop to Seashore,
5. Terrestrial Vertebrates,
6. Streams and Rivers: Their Physical and Biological Variability,
7. The Terrestrial/Marine Ecotone,
8. Pacific Salmon: Life Histories, Diversity, Productivity,
9. Environmental History,
10. Pre-European History,
11. Traditional Ecological Knowledge,
12. "The Great Raincoast": The Legacy of European Settlement,
13. Economic and Demographic Transition on the Oregon Coast,
14. From Ecosystem Dynamics to Ecosystem Management,
15. A Vision for Conservation-Based Development in the Rain Forests of Home,
Island Press Board of Directors,