The Rain Forest Atlas - page 4
Page 1: Coastal Temperate Rain Forests
Page 2: The Rain Forests of Home, A Review of the Research
Page 3: First Nations of the Coastal Temperate Rain Forest
Page 4: Original Distribution, Current Forest Status
Page 5: Watershed Condition, The Research Challenge
Page 6: Sustaining the Rain Forests of Home
Page 7: Data Sources, References
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State of the Forest Overview
North America's coastal temperate rain forest bioregion contains some of the best examples of forest unmodified by industry, and some of the only examples of fully intact forested coastal watersheds sustaining a full spectrum of native species, left in the world. Many of these areas survive because of the concern and perseverance of conservationists and Native communities; they are protected as parks, wilderness areas, or First Nations territories. Many, however, persist less by intent than by default: industrialized resource extraction has not yet reached them.
A regional picture of the North American coastal rain forest can do more than identify conservation opportunities in such pristine areas. It can also bring knowledge of natural forests to bear on the economic challenges facing coastal communities — Native and non-Native alike — that depend on resource-based livelihoods in heavily modified landscapes. Scientists and resource managers throughout the region are keenly interested in understanding ecological patterns at the landscape and regional scale. Conservationists seek clear guidance as they identify gaps in the protection of natural systems and set priorities for preservation and restoration. Residents want a sense that their livelihoods and their families have a future. The bioregional portrait presented in the following maps is intended to help all three.
This analysis of forest cover consists of three parts: an estimation of the original (pre-European settlement) distribution of coastal temperate rain forests; an appraisal of the present-day status of coastal temperate rain forests; and an assessment of the condition of forest cover within major watersheds of the coastal temperate rain forest region. Data for the development of the GIS database and analyses were collected in digital or map form from a variety of public and private sources, and integrated in the GIS. For more information about the data sets used in this analysis.
Original Distribution
The forests along the western coast of North America from the redwoods in California to Alaska's Kodiak Island contain approximately half of the remaining worldwide distribution of coastal temperate rain forest. Alaback (1991, 1995) dis tinguishes four coastal rain forest zones in North America based on temperature and precipitation distribution, which are the primary determinants of the distribution of plants and animals. This map shows the probable pre-European settlement distribution of conifer forests and associated vegetation types (bogs, muskegs, and high-elevation areas) that make up the North American coastal temperate rain forest.
Several sets of climate data (precipitation and temperature) and elevation information, augmented by land cover data, were combined to estimate the original extent of coastal temperate rain forest in the United States portion of the bioregion. For British Columbia, the coastal western hemlock biogeoclimatic zone provided a preferred indication of original distribution. The coast redwood range, a drier zone of coastal temperate rain forest, was also mapped using information on the major vegetation zones of California. The sub-polar, perhumid, and seasonal rain forest zones distinguished within the coastal temperate rain forest were delimited based on the expert knowledge of several leading ecologists.
Highlights
- Changes in climate and physiography from north to south change the character of the forest. The rugged relief of the far north creates a steep climatic gradient that confines the forest to a narrow coastal strip. The fjord-like character of southeastern Alaska and the central British Columbia coast expands the width of the forest zone, as the rain forest follows branching channels inland. From Vancouver Island south, the forest is not confined to fjords, but a marked orographic effect from the Coast and Cascade ranges limits its interior extent. At its southern extent, the zone narrows again, confined to the fog belt not by mountains but by moisture.
- Each zone supports distinct associations of dominant species. Sitka spruce and western and mountain hemlock dominate the subpolar zone. Sitka spruce, western red cedar, and western hemlock characterize the perhumid zone. Douglas-fir joins these species as a dominant in the seasonal zone. Coast redwood distinguishes the redwood zone.
Estimating Original Distribution
Different methods were used throughout the range of coastal temperate rain forest to delineate probable original extent, depending on information availability. (The fact that different data sets and methodologies were used is most apparent at the British Columbia/Washington border.) For British Columbia, the coastal western hemlock zone from the Ministry of Forest's biogeoclimatic zone classification (a scheme based on factors including vegetation, climate, and soil type) was used to determine the temperate rain forest zone. The coast redwood zone was also mapped, based on a data layer of vegetation cover types of California.
Outside British Columbia and California, areas having at least 1,400 millimeters average annual precipitation (identified using data from several state agencies) were combined with areas having a mean annual temperature range of less than 22 degrees Celsius (derived from the International Institute for Applied Systems Analysis global spatial data set of mean monthly temperatures) to distinguish temperate from wet boreal forests. The combined data set, showing wet temperate areas, was then filtered with elevation data (from the Digital Chart of the World) to exclude areas above 3,000 feet, which would be snow-dominated during the winter. Areas of permanent snow and ice at the northern end of the range and non-forest areas (barren, shrub-dominated, and rock) were filtered out using generalized land cover data (based on the Normalized Difference in Vegetation Index [INDVI] data set from the Advanced Very High Resolution Radiometer [AVHRR] satellite sensor).
The resulting data layer, combined with the coastal western hemlock biogeoclimatic zone data for British Columbia and the redwood zone for California, represents the probable pre-European settlement distribution of coastal temperate rain forest.
Current Forest Status
North America's coastal rain forests contain some of the world's most valuable commercial timber lands. They have been heavily harvested, particularly in the southern third of the bioregion. In Map 8, mature coastal forests that have not been extensively logged or disturbed by other development appear green. The red areas are those classified as "developed." Other areas within the bioregion, shown in gold, consist of undis turbed bog, muskeg, and high-elevation rain forest. The boundaries of existing protected areas larger than 250 hectares within the coastal temperate rain forest bioregion are also shown in relation to mature forest and other land cover classes.
To determine the extent of remaining natural forest, analysts created a region-wide "human development" layer, depicting areas of forest affected by logging, farming, or urban development. Undeveloped areas within the bioregion were mapped by subtracting areas affected by human activity from the map of original distribution. An overlay of areas of remaining mature forest (compiled from various sources), when superimposed on the map of undeveloped areas, distinguished forested from non-forested undeveloped habitat. Protected areas (provincial, state, and national parks, wilderness areas, etc. that conformed to the World Conservation Union [IUCN] definition of "protection") were also aggregated from various sources and mapped.
The information on this map is not static, but rather changes from year to year as more forest is harvested or protected. Some areas shown on this map as remaining mature forest may in fact now be logged, and others may have been protected.
Highlights
- Overall, 44 percent of the North American coastal temperate rain forest has been developed. The main impact of development is evident from Vancouver Island south.
- Two factors — accessibility and value — have determined the pattern of development. Low-elevation valleys proved easier to log, and the natural predominance of Douglas-fir in the seasonal rain forest zone and redwood in northern California historically provided high-quality lumber.
- Sixteen percent of the coastal temperate rain forest bioregion is protected. Over two-thirds of the protected coastal temperate rain forest is forest of the subpolar and perhumid zones in Alaska; comparatively little forest in the seasonal zone or the bioregion's southern extent is protected. Many of these protected areas are situated in alpine or other non-forested regions.
- The most important opportunities to protect large contiguous areas of coastal temperate rain forest are in Alaska and northwestern British Columbia, while restoration efforts will characterize conservation in the lower forty-eight.
Determining Current Forest Status
Analysts determined the extent of remaining undeveloped forest by subtracting a GIS layer representing areas primarily affected by human activity from the layer of original forest distribution. The "human development" layer was assembled from sources giving some indication of areas primarily affected by farming, logging, or urban development. These sources included forest and vegetation classification data sets as well as more general land use land cover data sets.
Similarly, contiguous areas of remaining mature forest were compiled in the GIS from a number of forest classification data sets for specific areas within the region, mainly at the state or provincial level. Analysts selected the data sets that offered the widest coverage for each given area, and those that best distinguished managed from unmanaged forest. Where necessary, auxiliary data sets were added to complete the geographic coverage. Again, analysts extracted from each data set just those areas indicating mature or old-growth forest (or some surrogate measure of this condition), on the assumption that these areas best represented undeveloped forest. Analysts recognized that some very old second growth might be included and areas of undeveloped forest may have been omitted. In Alaska, the non-forest undeveloped areas were taken from satellite imagery and GIS databases that distinguish forest from non-forest types. Remaining mature forest areas included those classified as forests but not shown in databases of harvested areas.
