Hemlock landscape and design



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Hemlock landscape and design

Hemlock landscape and design refers to the use of trees, landscape and other plantings in landscape architecture, landscape gardening and landscape architecture in combination with other techniques, including planning, design, planting and development of land. While hemlocks are generally not preferred as large trees, they are useful in woodland areas where they provide shade and as a screen for vistas.

History

The history of landscape architecture, landscape gardening and landscape architecture in relation to hemlocks is relatively short. However, certain aspects of landscape design that used hemlocks prior to the late 20th century can be traced to ancient societies including the indigenous peoples of North America, and the hemlocks themselves have been used for hundreds of years. Hemlocks have been included in plantings that represent the early roots of landscape architecture in the Middle East. The use of the hemlock was mentioned by authors as early as Ancient Greece and Rome, notably by Vitruvius and Pliny the Elder. The trees were used to fashion the columns of temples and cathedrals, and, as was the case in Egypt and elsewhere in the region, for the palaces of royalty. One of the greatest centers of planting, including hemlocks, was China in its Song, Yuan and Ming Dynasties, a long time when hemlock trees, were valued and planted for their decorative, architectural and structural beauty. For example, the Qianlong Emperor's Summer Palace had about 5,000 to 6,000 hemlocks, and the Yuan tree is considered the most beautiful in the world.

Hemlocks are native to North America and other continents.The most important hemlock plantings in the United States are located in various parts of the Northeast, including upstate New York, the Adirondack Mountains, and parts of the Canadian provinces of Ontario, New Brunswick and Newfoundland. For example, hemlocks are found in over a million acres (40,000 ha) of U.S. National Park Service land. Hemlocks thrive in colder climates and in acidic soil, so they are a popular tree in eastern North America.

Ecology

Hemlock trees are a popular food source for many species of wildlife. The bark is of value as food for many species, including squirrels, owls, and woodpeckers. Various insects are found in association with the plant, especially the eastern caddis fly (Eudistylia vancouverensis). Bats often use hemlock hollows to roost. Hemlocks attract a wide variety of nesting birds, including songbirds, white-throated sparrows, and American redstarts. Hemlocks are the primary nesting trees for the rare golden-winged warbler.

Fungi use hemlock branches and trunks to create their mycelium. The hemlock bark beetle is associated with hemlock trees.

Hemlocks serve as larval host for the hemlock looper, and the hemlock tiger moth.

Cultivation

The hemlock was introduced to Europe and became widely naturalized, growing throughout Europe and temperate Asia, including most of Russia. It was often planted as a hedgerow tree, both in England and Scotland. In Scotland, hemlocks are common throughout much of the central belt, particularly in the area around the Grampian Mountains. Since the 1990s, hemlock has spread in parts of North America, and in Europe as an ornamental tree. Hemlocks grow relatively well in the cold climates of northeastern North America. Their long, straight trunks, stiff evergreen leaves and slow growth rate make them popular as specimen trees. The bark is a brownish, crumbly texture.In the right conditions, hemlock can grow taller than any other tree, with a mature height of up to , some specimens may grow as tall as tall.

In the southern hemisphere, hemlock is naturalised in parts of southeastern Australia and the island of Tasmania.

Some varieties of hemlock were widely used in traditional horticulture in North America.

Seed is still collected in order to produce new hybrids.

Invasive species

Hemlocks have been known to escape and become invasive outside their native ranges. In the eastern United States, hemlock grows in many of the same habitats as English and eastern redcedar, and has competed for the same space. In the UK, it has replaced mature elms in many areas. In Australia, its invasive range has grown from in 2000 to . In New Zealand, hemlocks have encroached onto a wide range of native ecosystems, including high-altitude ecosystems (Mount Cook), lowland areas, lakes and rivers. It has been suggested that it will take until the end of the century for hemlock to overtake many species in these ranges.

The genus Hemignea is the native name for the New Zealand weevil, Hemialictus nigrofemoratus, which feeds upon hemlock.

Ecology

Hemlock trees have a symbiotic relationship with the hemlock woolly adelgid, a hemipteran insect, the adult of which lives as a parasite on the inner bark. The hemlock woolly adelgid, a conifer pest, has a direct life cycle. If a female adult has been feeding on a hemlock tree, she deposits eggs on the adelgid cambium, if that cambium is damaged or torn during the feeding, the eggs will drop off and die. The eggs hatch and the larvae feed on the cambium layer. The larvae also feed on the phloem tissue and eventually emerge as the adults. Adult females are long and mature females lay more than 1000 eggs per week.

The hemlock woolly adelgid is native to China, Korea, Japan, and Siberia.A natural enemy of the hemlock woolly adelgid is the bark beetle, Phyllophaga cuspidata, which was accidentally introduced to North America and was quickly colonized by another bark beetle, Hylurgus lignarius, which also feeds upon the hemlock woolly adelgid.

The hemlock woolly adelgid is sensitive to the fungal disease known as hemlock woolly adelgid, Hemlock woolly phytoplasma, phytoplasma hemlock and hemlock wood woolly disease and to cold and wet conditions. It attacks hemlock trees in the northern part of its range, but can live in temperate areas when conditions are suitable.

Treatment

Adults and larvae of the hemlock woolly adelgid can be removed from infested trees by hand with soft brushes. Trees should be removed if the infestation has extended to more than 10% of the canopy. Insecticides that are systemic can be sprayed on the tree or infested limbs. Fumigation with insecticides should be avoided because it harms wildlife and can make trees susceptible to diseases. Resistant hemlock trees can be planted in an infested area.

References

External links

Category:Nematocera of Asia

Category:Insects described in 1906

Category:Insects of China

Category:Insects of Korea



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