The Olympic Peninsula contains the finest examples of Pacific Northwest old-growth forest in North America. On its western mountain slopes and in west-facing valleys, it supports a rare temperate rain forest dominated by coniferous trees which grow to enormous size and age. Fifteen species of trees grow to heights in excess of 200 feet (the tallest approaching 400 feet high). Several species regularly reach ages of 500 to 800 years, and the oldest live to 1200 years. The Peninsula is a 6500 square mile area of land located between 47 and 48 degrees North Latitude and 123 to 124.5 degrees Longitude in the extreme northwestern part of the contiguous United States. (Connecticut is at 41-42 degrees north latitude and is comprised of 4872 square miles of land.) The Peninsula is surrounded on three sides by saltwater: the Pacific Ocean to the west, Juan de Fuca Strait to the north, and Puget Sound to the east.
There is a tremendous diversity of environments on the Olympic Peninsula, due to proximity to the ocean, prevailing winds, and topographic differences. At its center are the Olympic Mountains, dominated by Mount Olympus, which rises to 7965 feet. Other high peaks in the Olympic Range are Mount Deception (7788 feet), West Peak (7365 feet), Mount Anderson (7321 feet), Mount Mathias (7168 feet), Mount Fricaba (7100 feet), Mt. Tom (7048 feet), and Mt. Carrie (6995 feet). Most tall peaks of the range are between 5400 and nearly 8000 feet high. These mountains are significant in rising within 50 miles of the Pacific Coast, an important factor in the development of the climate of the region. The mountains are steep and rugged, and they are dissected by rivers which radiate in all directions.
The Olympic Range was formed geologically when plate tectonic activity brought sea floor shale and sandstone sediments and lava seamounts up and over the continental plate. Subsequent faulting and glaciation led to the formation of today’s sharp peaks and deep valleys. The Strait of Juan de Fuca and Puget Sound were formed by glacial advances and retreats, thereby isolating the Olympic Peninsula from the rest of the continent.
The Olympics remained glaciated or were occupied by treeless tundra until approximately 18,000 years ago. The retreat of the most recent glacial ice covering much of the northern United States occurred by about 12,000 years ago, and for at least the last 6000 years the climatic conditions of the Olympic Peninsula have been ideal for supporting a dense, coniferous, temperate rain forest.
Five major valleys occur on the Olympic Peninsula today. From north to south, they are the Soleduck Valley (which is partly in Olympic National Forest), Bogachiel River Valley, the Hoh River Valley, the Queets River Valley (these three flowing from Olympic National Park), and the Quinault River Valley (in Olympic National Park and Quinault Indian Reservation). Five large lowland, glacially formed lakes occur on the Peninsula: Ozette, Crescent, Cushman, Wynoochee, and Quinault Lakes. Many small lakes are found in the high country. No roads are found running directly through the Peninsula, due to the extremely steep, mountainous terrain of the Olympic Range. State Highway 101 is the only road which loops around the lower mountain slopes to allow travel around the peninsula.
Land ownership on the Olympic Peninsula is by federal and state agencies and private companies and individuals. Olympic National Park (managed by the U.S. Department of the Interior, National Park Service) consists of 921,000 acres, including 876,000 acres of wilderness and 600 miles of trails. Olympic National Forest (managed by the U.S. Department of Agriculture, Forest Service) consists of 632,000 acres, including 250,000 acres owned by a private timber company. The State of Washington Department of Natural Resources controls 364,000 acres and manages it primarily for timber production. Another 236,000 acres of land make up three Indian Reservations, where timber harvesting is the main commercial management strategy. Timber companies own an additional 915,000 acres and have harvested old-growth and second growth forest on these lands.
The two greatest influences on Olympic climate are the Pacific Ocean and the Olympic Mountain Range. The “Westside” of the Peninsula— west-facing mountain slopes and valleys—is the wettest part of the contiguous 48 states, averaging 70-100” of precipitation a year in most areas and reaching 130-145” in the wettest areas. The Quinault Valley in Olympic National Forest, for example, receives 133” annually. In the extreme case, the windward side of Mount Olympus and headwaters of the Quinault and Wynoochee Rivers have received 220” in a single year. These conditions are ideal for development of coniferous rain forest.
The “Eastside” of the Peninsula, however, particularly the lands northeast of the Olympic Range, is an arid rain shadow where one finds coniferous forests tolerant of dry conditions. The town of Port Angeles, where Olympic National Park Headquarters is located, receives 22” of precipitation a year. East of the Peninsula, Seattle, Washington receives 33-42” precipitation a year, slightly less than that of New Haven, Connecticut. Pacific Northwest cities farther inland—Spokane, Washington and Pendleton, Oregon—receive 17” and 12”, respectively.
There is a tremendous range in annual precipitation for Olympic Peninsula and regions to the east, and it is due to the Olympic Range intercepting moisture-laden air masses coming off the Pacific Ocean and producing extremely abundant rain to the west and arid conditions to the east. As prevailing westerlies from the Pacific Ocean pass across the Peninsula, the air is forced to rise when it reaches the mountains. For each 1000 feet the air is pushed up, it cools 5.5 degrees Fahrenheit. Less dense air at higher elevations is under less atmospheric pressure. As the air cools, it no longer can hold its water vapor, and moisture drops as clouds or fog. Water vapor which condenses extensively leads to precipitation—rain at lower elevations and snow at higher elevations. On the east side of the mountains, clouds disappear or scattered, light showers are produced.
The effects of the Pacific maritime climate, wind directions, and interaction of winds with peninsula topography change through the year. Winds blow in from the west southwest in winter and from the southwest in spring and fall. There is an extremely mild temperature regime year-round, including mild, wet winters with temperatures usually remaining above freezing, and dry summers averaging 75 degrees Fahrenheit and rarely exceeding 80 degrees. The period June through September has very little precipitation. Olympic temperature maximums during July are lower than maximums of northern Maine or Minnesota. Relative humidity is at 90% in early morning and decreases to 50-60% in the afternoon. Periodic summer winds from the northeast, called chinook winds, bring warm, dry conditions and are closely associated with the largest fires of the Peninsula.
A climatic belt running around the world at 40 to 60 degrees north latitude passes across the Pacific Northwest. During spring and summer the jet stream brings warm, subtropical air masses to this region, and in fall and winter cold polar air masses arrive. Moist polar winds reach the Pacific Northwest in December, the wettest month of the year. Winter air masses move counterclockwise in direction, and they produce cloudy, showery, or unstable weather. There is an unpredictability to both seasonal weather systems, resulting in year-to-year variation in weather conditions.
The major air masses reaching the Olympics during the year are the Pacific High of late spring and early summer, and the Aleutian Low of fall and early winter. The Pacific High is a fair weather system which moves eastward from Hawaii to North America. This high pressure system prevents most rain storms from reaching the Peninsula in spring and summer. The Aleutian Low brings winter storms down from the Gulf of Alaska. These high and low pressure systems produce an alteration between dry summers and wet winters on the Olympic Peninsula. Summer months, especially July and August, are a time of drought, when less than 10” of total precipitation reaches the Peninsula. Further south, in southwestern Oregon and northwestern California, the dry season persists for six months. Winter months are characterized by heavy precipitation, which peaks during the month of December.
In winter, freezing temperatures are reached fewer nights along coastal Washington than occur in northern Louisiana, which at 31-33 degrees north latitude is located 15 degrees to the south. This illustrates the considerable moderating influence of Pacific Northwest climate. Temperatures in lowland forests remain just above freezing most of the time. It becomes cooler further up mountain slopes, where precipitation falls as snow. With increased elevation, even more severe climatic conditions prevail. Trees are fewer, shorter, more misshapen. One hundred year old trees may be 3 feet tall. At timberline, no trees grow. Wildflowers predominate in this Arctic-alpine zone. The frost season of winter is quite short. However, there are cloudy skies many days of the year and lots of drizzle. Hurricanes and tornadoes do not occur, but winter storms may be severe.
During late summer and early fall, fog is a common feature of western mountain slopes and valleys facing perpendicular to the coast. Fogbanks develop at night along the Pacific Coast as air passing over ocean water is cooled. When the fog reaches the coast and passes over land and up mountain slopes, it warms and the fog dissipates by mid-day. Fog is believed to increase annual precipitation in the Westside by so much as 40” a year. During winter periods of high pressure, moist marine air blankets Olympic Westside valleys with low clouds and drizzle, while higher elevation peaks and slopes—those above 3000 feet—remain clear. Thus, there is a unique summer-winter split in precipitation.
The unusual feature of Olympic Peninsula climate, then, is that it is a temperate climate with dry summers and wet winters, summer droughts occurring annually and winter precipitation being very heavy. Most temperate parts of North America have precipitation distributed fairly evenly through the year. Most climates with distinct wet and dry seasons, on the other hand, are tropical, and they do not have recognizable summers and winters. The Olympic Rain Forest has a temperate climate with several of the most important seasonal and rainfall features usually associated with the tropics.
North America’s temperate rain forests are found only along a narrow band of the Pacific Coast and a short distance inland, from southeastern Alaska through British Columbia, Washington, Oregon, and to northwestern California. Outside North America, temperate rain forests are found only in southern Chile, western Scotland, portions of Norway, the northern Honshu coast of Japan, and New Zealand.
Four distinctly different habitats are found in Olympic National Park and Olympic National Forest. They are the marine and estuarine coastal areas, the temperate rain forest, the alpine meadows and unvegetated glacial peaks, and rain shadow forests and fields. The marine environment supports a tremendously rich and diverse biota, ranging from whales and dolphins to seabirds, marine invertebrates, and sea weeds and microscopic plankton. The temperate rain forest, equally diverse in its biota, is the subject of much of the discussion which ensues. It is located on lower Olympic slopes and in west-facing valleys of the Westside. Alpine meadows take over where trees no longer grow, at upper elevations of the Olympics. Rain shadow forests cover the northeastern slopes of the Olympics.
Considering only the forested regions of the Olympic Peninsula, six major vegetation zones are recognized, their distributions determined by climatic conditions including summer and winter temperatures, annual precipitation, presence of fog, and by elevation, and their names largely determined by the predominant coniferous species growing there. They are the Sitka Spruce, Western Hemlock, Silver Fir, Mountain Hemlock, Subalpine, and Douglas-fir zones. The Sitka Spruce Zone is found on the Westside, where maritime influences are greatest. It extends to just 600 feet elevation and requires in excess of 100” annual precipitation and extensive summer fog. Sitka Spruce is the dominant tree.
The Western Hemlock Zone is found above the Sitka Spruce Zone on the Westside and over an extensive area of lower slopes on the Peninsula’s north, east, and south sides. It extends to 2000 feet elevation in wetter areas of the Peninsula and to 4000 feet in drier areas. Conditions thus range from very wet to moderately dry. Fire is a common feature of this zone. In most portions of the zone Douglas-fir is the dominant tree species. The Silver Fir Zone is found on mid- and upper mountain slopes above the Western Hemlock Zone, wherever moist to moderately dry sites are found. Western Hemlock and Silver Fir are the most abundant trees.
The Mountain Hemlock Zone is on higher elevations of the Olympics, extending up to subalpine regions. Silver Fir and Mountain Hemlock are the abundant tree species, and Alaska Yellow cedar is a subdominant in some areas. This zone is distinguished from the previous one by greater elevations and deeper snowpack in winter— up to 10 feet deep. The Subalpine Fir Zone is limited to the northeastern part of the Peninsula at elevations of 4500 to 6000 feet. Snow accumulation in winter is less extensive than in the Mountain Hemlock Zone. Krummholz trees are found here (stunted trees with branches growing only on the downwind side of the trunk), growing in scattered clumps. A very restricted Douglas-fir Zone is found in the northeast where conditions are the driest. Douglas-fir dominates here. Douglas fir, while occurring in several zones mentioned above, is a far more dominant tree in old-growth forests of inland Washington and Oregon. The southernmost region of temperate rain forests, that of northern California, has Coast Redwood as the dominant tree species; these are the tallest trees in the world.