Klamath-Siskiyou forests

• Category: Forest Biomes.
• Geographic Location: North America.
• Summary: Among the most important temperate coniferous forests in the world, the Klamath-Siskiyou faces unprecedented threats from land-use decisions and climate disruptions.

Renowned for its extraordinary biological diversity, the Klamath-Siskiyou is among the top coniferous forests on Earth. Straddling the California-Oregon border near the Pacific Ocean and covering an area of some 9.9 million acres (4 million hectares), the region is at the junction of the uplift Coast Ranges, the volcanic Cascades, and the ancient volcanic roots of the Sierra Nevada.

The Klamath-Siskiyou tops the charts among coniferous forests globally with accolades such as Area of Global Botanical Significance, proposed World Heritage Site and International Biosphere Reserve, Global Centre of Plant Diversity, and Global 200 ecoregion as anointed by the World Conservation Union (or IUCN), scientists, and the World Wildlife Fund, respectively. More conifer species and endemic (found nowhere else) plants occur here than in nearly any other temperate conifer forest on Earth. The region’s roadless areas have been dubbed the Pacific Coastal Outback, reflecting its status as one of the wildest areas remaining near the Pacific coast of the United States.

Geography, Climate, and Threats

The region’s remarkable biological diversity is the result of the interplay of ancient, complex geology; varied but stable (long-term) climate; and natural disturbances like wildland fire. Crisscrossing mountain ranges, sometimes called the Klamath Knot, along with varied topography, allow plants with widely different environmental tolerances to persist in close proximity within this biome. Along the coast, temperate rainforests prevail, while a short way inland reveals Jeffrey pine savannas on dry slopes.

Overlapping mountain ranges allow plants from distant areas to fit together like pieces in a jigsaw puzzle. The serpentine and ultramafic bedrock geology, produced by colliding tectonic plates that uplifted mountain ranges when dinosaurs roamed, provide for unusual soils: deficient in some nutrients, but highly toxic in others. Extreme soils here have served as a barrier against weed invasions and as a maternity ward for endemic plant species specializing on them, although this is changing due to human-caused climate disruptions.

The Klamath-Siskiyou Forests biome has several properties that may aid in weathering the coming climate storm. Its central position—sandwiched between the Coastal Mountains, Shasta Valley-Sierra, and Cascades—rugged terrain, and complexity of soils and microclimates might provide habitats of refuge for some species. However, climate-related models predict hotter summers—as much as 9 degrees F (5 degrees C) warmer—and drier conditions year round by 2100. Potentially, there could be a decrease in coastal fog; this could trigger extinction of 10 percent or more of the known moisture-loving plants, invertebrates, and salamanders here, and perhaps even the loss of or heavy stress upon fog-dependent coastal redwoods.

Prior to European occupation, old forests covered up to two-thirds of the Pacific Northwest region. Today, less than 20 percent remains, due to industrial logging. Habitat fragmentation impacts many of the remaining forests, where intact forest tends to be of insufficient size and scope to provide adequately for a range of animal species. These forests generally support over 1,000 species of plants, invertebrates, and wildlife; are among the most carbon-dense ecosystems on Earth, important in ameliorating climate change; purify drinking water; and perform a myriad of life-giving services to people and wildlife.

Biodiversity

The region’s varied climate has allowed rainforests to flourish nearly undisturbed for centuries along the coast because large, severe fires occurred infrequently, while inland more frequent and severe fires allow chaparral and savannas to prevail.

The oldest stage in forest succession occurs when forests are dominated by large old trees, snags and fallen logs, and have multi-layered or fairly continuous canopies from the ground up. Precisely when this stage in forest succession occurs varies based on site productivity and disturbance conditions; however, forests show maturation generally at 80 years or so.

Much attention rightly has focused on old-growth forests, but, surprisingly, the plant assemblages immediately following fire also support high levels of biological diversity due to presence of legacy structures like big fire-resistant trees; large, dead standing trees or snags; and fallen logs that persist for decades to centuries after fire.

Such structures aid plant establishment, as the roots of even dead trees continue to anchor soils, while snags provide shade for conifer seedlings. Fallen logs in streams provide hiding cover for salmon (Oncorhynchus spp.) and those on land soak up moisture to provide to lichens, salamanders, fungi, and invertebrates, which are the pioneers of post-fire succession. When logs eventually decay, they act as living nurseries ripe with plant propagules and organic matter for new soils. Thriving in these conditions are fire-dependent specialists such as black-backed woodpeckers (Picoides arcticus) and mountain bluebirds (Sialia currucoides) that feed on destructive insects, and shrubs like various Ceanothus spp., and manzanita (Arctostaphylos spp.) that return nitrogen to soils and restore mycorrhizae—the symbiotic fungi that attach to plant roots and help them absorb nutrients—to below-ground processes necessary for new plant growth.

Klamath-Siskiyou vegetation is a highly diverse mosaic of plant communities in different stages of succession from prior disturbances. Examples of canopy trees in the mixed evergreen forest type include Douglas-fir (Pseudotsuga menziesii), white fir (Abies concolor), ponderosa pine (Pinus ponderosa), and western red cedar (Thuja plicata). These mix with understory trees of canyon live oak (Quercus chrysolepsis), Pacific madrone (Arbutus menziesii), tanoak (Lithocarpus densiflorus) and golden chinkapin (Chrysolepis chrysophylla). Endemic conifers include Brewer’s spruce (Picea breweriana) and Port Orford cedar (Chamaecyparis lawsoniana) found on serpentine soils, which typically support high levels of endemic plants. Species-rich fens contain the carnivorous cobra lily (Darlingtonia california), along with several rare plant associates.

The diversity of the biome is unparalleled, featuring approximately 3,500 plant species, including 281 endemics. The California pitcher plant or Cobra Lily, (Darlingtonia californica), is a rare carnivorous plant found in the wetlands of the forests. A relic of the pre-ice age, the Lilla Leech (kalmiopsis leachiana) is a member of the Heath family and was discovered in 1930.

Nearly two-thirds of the entire California floristic province is found here, on just 10 percent of the land mass of California. Researchers note as many as 40 conifer species, making the area one of three regions globally with such richness. A number of invertebrates dwell in the habitat. Dragonflies, flightless beetles, arthropods, and bees are also thought to be exceptionally rich—but are far less cataloged than other species. There are believed to be up to 114 species of butterflies and at least 235 mollusk taxa, including at least 60 percent that are endemic.

Almost 80 percent of all amphibian and reptile species in the Pacific Northwest can be found in the Klamath-Siskiyou Forests biome. This includes the Siskiyou Mountains salamander and the Scott Bar salamander, both endemic to the region. The Siskiyou Mountains salamander has the second smallest range of any western salamanders in its genus, and it requires specialized habitat requirements making it highly sensitive. One protected under the Survey and Manage Program, conservationists have been fighting to protect the salamanders under the Endangered Species Act. The petition was denied in 2008 and 2019.

With one of the greatest concentrations of ultramafic bedrock and serpentine geology in western North America, it is clear the Klamath-Siskiyou Forests biome is a region where the whole is greater than the sum of its parts.

Bibliography

DellaSala, Dominick, ed. Temperate and Boreal Rainforests of the World: Ecology and Conservation. Washington, DC: Island Press (2011).

Downing, William M., Garrett W. Meigs, Matthew J. Gregory, and Meg A Krawchuk. "Where and Why Do Conifer Forests Persist in Refugia Through Multiple Fire Events?" Global Change Biology, vol. 27, no. 15, 2021, pp. 3642-3656. DOI: 10.1111/gcb.15655. Accessed 12 Nov. 2024.

Olson, David, et. al. “Climate Change Refugia for Biodiversity in the Klamath-Siskiyou Ecoregion.” Natural Areas Journal 32, no. 1 (2012).

“Saving the Siskiyou Mountains Salamander.” Center for Biological Diversity, www.biologicaldiversity.org/species/amphibians/Siskiyou‗Mountains‗salamander/index.html. Accessed 12 Nov. 2024.

Strittholt, James, et. al. “Status of Mature and Old-Growth Forests in the Pacific Northwest, USA.” Conservation Biology 20, no. 1 (2006).