Mountain Hemlock
Encyclopedia
Tsuga mertensiana, known as Mountain Hemlock, is a species of hemlock
native to the west coast of North America
, with its northwestern limit on the Kenai Peninsula
, Alaska
, and its southeastern limit in northern Tulare County
, California
.
coniferous
tree
growing to 20–40 m—60–120 feet tall, with exceptional specimens at 59 m-180 feet tall. They have a trunk diameter of up to 2 m-6 feet. The bark
is thin and square-cracked or furrowed, and gray in color. The crown is a neat slender conic shape in young trees with a tilted or drooping lead shoot, becoming cylindric in older trees. At all ages, it is distinguished by the slightly pendulous branchlet tips. The shoots are orange-brown, with dense pubescence about 1 mm long. The leaves
are needle-like, 7–25 mm long and 1–1.5 mm broad, soft, blunt-tipped, only slightly flattened in cross-section, pale glaucous blue-green above, and with two broad bands of bluish-white stoma
ta below with only a narrow green midrib between the bands; they differ from those of any other species of hemlock in also having stomata on the upper surface, and are arranged spirally all round the shoot.
The cones
are small, but much longer than those of any other species of hemlock, pendulous, cylindrical, 30–80 mm long and 8–10 mm broad when closed, opening to 12–35 mm broad, superficially somewhat like a small spruce
cone. They have thin, flexible scales 8–18 mm long. The immature cones are dark purple (rarely green), maturing red-brown 5–7 months after pollination. The seed
s are red-brown, 2–3 mm long, with a slender, 7–12 mm long pale pink-brown wing.
The Tsuga mertensiana range matches that of Tsuga heterophylla—Western Hemlock fairly closely, likewise mostly less than 100 km from the Pacific Ocean
apart from a similar inland population in the Rocky Mountains
in southeast British Columbia
, northern Idaho
and western Montana
. Their ranges however differ in California, where Western Hemlock is restricted to the Coast Ranges, while Mountain Hemlock is found in the Klamath Mountains
and Sierra Nevada. Unlike Western Hemlock, it mostly grows at high altitudes except in the far north, from sea level to 1000 m in Alaska, 1600–2300 m in the Cascades in Oregon
, and 2500–3050 m in the Sierra Nevada.
, two subspecies
and a minor variety:
sites where it grows slowly, sometimes attaining more than 800 years in age. Arborescent
individuals that have narrowly conical crowns until old age (300 to 400 years) and shrubby krummholz
on cold, windy sites near timberline add beauty to mountain landscapes. Areas occupied by mountain hemlock generally have a cool to cold maritime climate that includes mild to cold winters, a short, warm to cool growing season and moderate to high precipitation.
Best development of mountain hemlock is on loose, coarse-textured, well-drained soils with adequate moisture, and in British Columbia
, on thick and very acidic organic matter and decayed wood. Adequate soil moisture appears to be especially important in California
and Montana
, where summer drought is most pronounced.
Mountain hemlock will grow on most landform
s, but individuals typically develop best in mixed stands of forest on sheltered slopes or in draws. From southern British Columbia south, the tree grows better on northerly exposures. The preference for relatively moist, cool sites evidently becomes a necessity as the climate becomes more continental
in western Montana and more mediterranean
in the central Sierra Nevada at these extremes of its range. In these locations, mountain hemlock typically grows in isolated populations in north-facing glens and cirque
basins where snow collects and may remain well into summer.
Mountain hemlock is adapted to sites with long-lasting snowpack
s. In the spring, mountain hemlocks emerging through 2 to 4 m (6.6 to 13.1 ft) of snow were transpiring
, whereas nearby whitebark pine
s did not transpire until the soil beneath them was free of snow. Mountain hemlock is very well adapted to cope with heavy snow and ice loads, with tough branches, and the drooping branchlets shedding snow readily.
Mountain hemlock is tolerant of shade and other forms of competition. It is more tolerant than all its associates except Pacific silver fir
, western hemlock
, and Alaska cedar. Mountain hemlock is considered a minor climax species on most of its habitats; however, it pioneers on glacial moraines in British Columbia and Alaska. Pacific silver fir is a major climax species in many communities of the mountain hemlock forest in British Columbia and Washington and northern Oregon. Alaska cedar, western redcedar, and western hemlock are climax associates on some sites. Mountain hemlock is more commonly the major climax species in the mountain hemlock zone south of central Oregon where Pacific silver fir does not occur.
Mountain hemlock often succeeds lodgepole pine
or subalpine fir
when these species pioneer on drier sites. It also tends to replace Engelmann spruce
when the two species occur together, possibly because hemlock is better able to withstand the allelopathic effects of spruce than are other associated species.
landscape
s in California
, and particularly in garden
s in northern Great Britain
and Scandinavia
, where it is appreciated for its blue-green color and tolerance of severe weather. Cultivation is limited by the very slow growth of young plants and its susceptibility to urban air pollution
.
Several cultivar
s have been selected, mainly for intensely glaucous
foliage color including:
.
Tsuga
Tsuga is a genus of conifers in the family Pinaceae. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock....
native to the west coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, with its northwestern limit on the Kenai Peninsula
Kenai Peninsula
The Kenai Peninsula is a large peninsula jutting from the southern coast of Alaska in the United States. The name Kenai is probably derived from Kenayskaya, the Russian name for Cook Inlet, which borders the peninsula to the west.-Geography:...
, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, and its southeastern limit in northern Tulare County
Tulare County, California
Tulare County is a county located in the Central Valley of the U.S. state of California, south of Fresno. Sequoia National Park is located in the county, as are part of Kings Canyon National Park, in its northeast corner , and part of Mount Whitney, on its eastern border...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Description
Tsuga mertensiana is a large evergreenEvergreen
In botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...
coniferous
Pinophyta
The conifers, division Pinophyta, also known as division Coniferophyta or Coniferae, are one of 13 or 14 division level taxa within the Kingdom Plantae. Pinophytes are gymnosperms. They are cone-bearing seed plants with vascular tissue; all extant conifers are woody plants, the great majority being...
tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
growing to 20–40 m—60–120 feet tall, with exceptional specimens at 59 m-180 feet tall. They have a trunk diameter of up to 2 m-6 feet. The bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
is thin and square-cracked or furrowed, and gray in color. The crown is a neat slender conic shape in young trees with a tilted or drooping lead shoot, becoming cylindric in older trees. At all ages, it is distinguished by the slightly pendulous branchlet tips. The shoots are orange-brown, with dense pubescence about 1 mm long. The leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
are needle-like, 7–25 mm long and 1–1.5 mm broad, soft, blunt-tipped, only slightly flattened in cross-section, pale glaucous blue-green above, and with two broad bands of bluish-white stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
ta below with only a narrow green midrib between the bands; they differ from those of any other species of hemlock in also having stomata on the upper surface, and are arranged spirally all round the shoot.
The cones
Conifer cone
A cone is an organ on plants in the division Pinophyta that contains the reproductive structures. The familiar woody cone is the female cone, which produces seeds. The male cones, which produce pollen, are usually herbaceous and much less conspicuous even at full maturity...
are small, but much longer than those of any other species of hemlock, pendulous, cylindrical, 30–80 mm long and 8–10 mm broad when closed, opening to 12–35 mm broad, superficially somewhat like a small spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
cone. They have thin, flexible scales 8–18 mm long. The immature cones are dark purple (rarely green), maturing red-brown 5–7 months after pollination. The seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s are red-brown, 2–3 mm long, with a slender, 7–12 mm long pale pink-brown wing.
Distribution
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
apart from a similar inland population in the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
in southeast British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, northern Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
and western Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
. Their ranges however differ in California, where Western Hemlock is restricted to the Coast Ranges, while Mountain Hemlock is found in the Klamath Mountains
Klamath Mountains
The Klamath Mountains, which include the Siskiyou, Marble, Scott, Trinity, Trinity Alps, Salmon, and northern Yolla-Bolly Mountains, are a rugged lightly populated mountain range in northwest California and southwest Oregon in the United States...
and Sierra Nevada. Unlike Western Hemlock, it mostly grows at high altitudes except in the far north, from sea level to 1000 m in Alaska, 1600–2300 m in the Cascades in Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, and 2500–3050 m in the Sierra Nevada.
Taxonomy
There are three taxaTaxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, two subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
and a minor variety:
- Tsuga mertensiana subsp. mertensiana. Northern Mountain Hemlock. Central Oregon northwards. Cones smaller, 30–60 mm long, 12–25 mm broad when open, with 50–80 scales.
- Tsuga mertensiana subsp. mertensiana var. mertensiana. Northern Mountain Hemlock. Leaves gray-green on both sides.
- Tsuga mertensiana subsp. mertensiana var. jeffreyi (Henry) Schneider. Jeffrey's Mountain Hemlock. Mixed with var. mertensiana; rare. Leaves greener, less glaucous above, paler below; cones indistinguishable from the type. At one time it was thought to be a hybrid with Western HemlockWestern HemlockTsuga heterophylla. the Western Hemlock, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California.-Habitat:...
, but there is no verified evidence for this.
- Tsuga mertensiana subsp. grandicona Farjon. California Mountain Hemlock; syn. T. hookeriana (A.Murray) Carrière, T. crassifolia Flous. Central Oregon southwards. Leaves very strongly glaucous. Cones larger, 45–80 mm long, 20–35 mm broad when open, with 40–60 scales.
Ecology
Mountain hemlock is usually found on cold, snowy subalpineSubalpine
The subalpine zone is the biotic zone immediately below tree line around the world. Species that occur in this zone depend on the location of the zone on the Earth, for example, Snow Gum in Australia, or Subalpine Larch, Mountain Hemlock and Subalpine Fir in western North America.Trees in the...
sites where it grows slowly, sometimes attaining more than 800 years in age. Arborescent
Arborescent
Arborescent is a term used by the French thinkers Deleuze and Guattari to characterize thinking marked by insistence on totalizing principles, binarism and dualism...
individuals that have narrowly conical crowns until old age (300 to 400 years) and shrubby krummholz
Krummholz
Krummholz or Krumholtz formation — also called Knieholz — is a particular feature of subarctic and subalpine tree line landscapes. Continual exposure to fierce, freezing winds causes vegetation to become stunted and deformed...
on cold, windy sites near timberline add beauty to mountain landscapes. Areas occupied by mountain hemlock generally have a cool to cold maritime climate that includes mild to cold winters, a short, warm to cool growing season and moderate to high precipitation.
Best development of mountain hemlock is on loose, coarse-textured, well-drained soils with adequate moisture, and in British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, on thick and very acidic organic matter and decayed wood. Adequate soil moisture appears to be especially important in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, where summer drought is most pronounced.
Mountain hemlock will grow on most landform
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
s, but individuals typically develop best in mixed stands of forest on sheltered slopes or in draws. From southern British Columbia south, the tree grows better on northerly exposures. The preference for relatively moist, cool sites evidently becomes a necessity as the climate becomes more continental
Continental climate
Continental climate is a climate characterized by important annual variation in temperature due to the lack of significant bodies of water nearby...
in western Montana and more mediterranean
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...
in the central Sierra Nevada at these extremes of its range. In these locations, mountain hemlock typically grows in isolated populations in north-facing glens and cirque
Cirque
Cirque may refer to:* Cirque, a geological formation* Makhtesh, an erosional landform found in the Negev desert of Israel and Sinai of Egypt*Cirque , an album by Biosphere* Cirque Corporation, a company that makes touchpads...
basins where snow collects and may remain well into summer.
Mountain hemlock is adapted to sites with long-lasting snowpack
Snowpack
Snowpack forms from layers of snow that accumulate in geographic regions and high altitudes where the climate includes cold weather for extended periods during the year. Snowpacks are an important water resource that feed streams and rivers as they melt. Snowpacks are the drinking water source for...
s. In the spring, mountain hemlocks emerging through 2 to 4 m (6.6 to 13.1 ft) of snow were transpiring
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
, whereas nearby whitebark pine
Whitebark Pine
Pinus albicaulis, known commonly as Whitebark Pine, Pitch Pine, Scrub Pine, and Creeping Pine occurs in the mountains of the Western United States and Canada, specifically the subalpine areas of the Sierra Nevada, the Cascade Range, the Pacific Coast Ranges, and the northern Rocky Mountains –...
s did not transpire until the soil beneath them was free of snow. Mountain hemlock is very well adapted to cope with heavy snow and ice loads, with tough branches, and the drooping branchlets shedding snow readily.
Mountain hemlock is tolerant of shade and other forms of competition. It is more tolerant than all its associates except Pacific silver fir
Pacific Silver Fir
Abies amabilis, commonly known as the Pacific silver fir, is a fir native to the Pacific Northwest of North America, occurring in the Pacific Coast Ranges and the Cascade Range from the extreme southeast of Alaska, through western British Columbia, Washington and Oregon, to the extreme northwest of...
, western hemlock
Western Hemlock
Tsuga heterophylla. the Western Hemlock, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California.-Habitat:...
, and Alaska cedar. Mountain hemlock is considered a minor climax species on most of its habitats; however, it pioneers on glacial moraines in British Columbia and Alaska. Pacific silver fir is a major climax species in many communities of the mountain hemlock forest in British Columbia and Washington and northern Oregon. Alaska cedar, western redcedar, and western hemlock are climax associates on some sites. Mountain hemlock is more commonly the major climax species in the mountain hemlock zone south of central Oregon where Pacific silver fir does not occur.
Mountain hemlock often succeeds lodgepole pine
Lodgepole Pine
Lodgepole Pine, Pinus contorta, also known as Shore Pine, is a common tree in western North America. Like all pines, it is evergreen.-Subspecies:...
or subalpine fir
Subalpine Fir
The Subalpine Fir or Rocky Mountain Fir is a western North American fir, native to the mountains of Yukon, British Columbia and western Alberta in Canada; southeastern Alaska, Washington, Oregon, Idaho, western Montana, Wyoming, Utah, Colorado, New Mexico, Arizona, northeastern Nevada, and the...
when these species pioneer on drier sites. It also tends to replace Engelmann spruce
Engelmann Spruce
Picea engelmannii is a species of spruce native to western North America, from central British Columbia and southwest Alberta, southwest to northern California and southeast to Arizona and New Mexico; there are also two isolated populations in northern Mexico...
when the two species occur together, possibly because hemlock is better able to withstand the allelopathic effects of spruce than are other associated species.
Cultivation
Outside of its native range, Mountain Hemlock is grown as an ornamental tree. It is planted as a specimen tree in native plantNative plant
Native plant is a term to describe plants endemic or naturalized to a given area in geologic time.This includes plants that have developed, occur naturally, or existed for many years in an area...
landscape
Landscape
Landscape comprises the visible features of an area of land, including the physical elements of landforms such as mountains, hills, water bodies such as rivers, lakes, ponds and the sea, living elements of land cover including indigenous vegetation, human elements including different forms of...
s in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, and particularly in garden
Garden
A garden is a planned space, usually outdoors, set aside for the display, cultivation, and enjoyment of plants and other forms of nature. The garden can incorporate both natural and man-made materials. The most common form today is known as a residential garden, but the term garden has...
s in northern Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
and Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, where it is appreciated for its blue-green color and tolerance of severe weather. Cultivation is limited by the very slow growth of young plants and its susceptibility to urban air pollution
Air pollution
Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....
.
Several cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s have been selected, mainly for intensely glaucous
Glaucous
Glaucous is used to describe the pale grey or bluish-green appearance of the surfaces of some plants, as well as in the names of birds, such as the Glaucous Gull , Glaucous-winged Gull , Glaucous Macaw , and Glaucous...
foliage color including:
- 'Blue Star'
- 'Glauca'.
External links
Short radio episode Mountain Hemlock from "An Appreciation," by Harriet Monroe, Sierra Club Bulletin, 1916, dedicated to John Muir. California Legacy ProjectCalifornia Legacy Project
The California Legacy Project began in 2000 as a project at Santa Clara University in Santa Clara, CA and later partnered with Heyday Books in Berkeley, CA. The project uses a research team of SCU interns to create radio scripts for the radio anthology "Your California Legacy" on KAZU 90.3 FM,...
.