Populus

Canadian poplar (Populus x canadensis)

The poplars (Populus ) are a genus of flowering plants in the family of the willow family ( Salicaceae ). These mostly tree-like plant native to North America and Eurasia. They grow on river banks and in woods and are often grown as wood, paper and energy.

• 6.1 Outer systematics
• 6.2 Internal systematics
• 6.3 hybridization

• 8.1 plantations
• 8.2 Protection plantations
• 8.3 Landscape Maintenance
• 8.4 Using the wood
• 8.5 Research and Breeding

Features

Habitus and gender distribution

Poplars are deciduous trees or shrubs that reach heights of growth of 30 to 45 meters. The trunk is usually erect, the bark is rough or smooth, and often gray. Like all representatives of the willow family ( Salicaceae ) are dioecious poplars, so there are male and female plants. In all the sections of the genus but also individuals were observed, exceptionally, whose inflorescences contained both female flowers and stamen flowers.

The leaves are triangular, heart - or egg-shaped and either entire or lobed. The petiole is long, flattened the round cross section or side. The leaves on long and short shoots, ie the preformed in winter buds and the leaves formed in the summer are often designed differently. The winter buds have several unequal scales.

Wood and bark

The wood of all the species of poplar is quite similar, the differences due to environmental conditions are greater than the differences between species. Poplar wood has a very high cellulose content, which makes it flexible. The density at a moisture content of 15 percent is on average 0.45 g cm -3, where the values ​​are 0.41 to 0.60. The aspen is about 0.49. The values ​​of poplar wood are in areas similar to the wood of coniferous trees common spruce and White Pine.

The wood of poplar is diffuse-porous; the vessels of the early wood not larger than that of the latewood. The Rays are essentially made up of equal sized cells. In the wood parenchyma starch, protein and oil is stored. The heartwood, which occurs no living parenchyma more is formed in Populus tremuloides from the fifth year, and is color not clearly demarcated in all poplars.

The bark has a relatively thin-walled cork cells. Young trees have smooth bark with continuous periderm. Later, the bark is often rough and furrowed.

Root

Poplars forming heart root systems to horizontal root systems. Taproots are not occupied, but pronounced horizontal roots from which branch off on the one hand sinker down, on the other hand shoots sprout up, serve the vegetative propagation. The fine roots of poplar trees are compared to other trees quite long, sparsely branched and thin. The roots form both ectomycorrhizas as well as vesicular - arbuscular mycorrhiza.

Flowers and Fruit

The inflorescences are pedicled, hanging catkins. Male and female kittens are very similar. The flowers are in the axils of lanceolate or serrated blade carrier and are stalked. The bracts falling early as during anthesis. A perianth is absent in both male and female flowers, but the male and female organs are surrounded by a more or less pronounced discus. The male flowers have four to 60 stamens, whose filaments are not attached. In the female flowers the ovary is unilocular and sitting. The ovary consists of two to four carpels and is surrounded at the base or up to three quarters of its height from the discus. The ovules are too many to two to four parietal placentae. The style is short and carries two to four scars. Nectaries absent.

The poplars are wind pollinated ( anemophily ), the flowers appear before the leaves.

The fruit is a two-to vierklappige capsule that contains numerous winged seeds. The seeds are surrounded by a long, thick fleece of hair, endosperm is hardly trained or missing entirely. The weight of a seed is usually only a few tenths of a milligram, but a tree may annually produce 25 million seeds. The spread of seeds carried by the wind ( Anemochorie ).

Ingredients

Poplars form as secondary ingredients phenols, but no nitrogen-containing phytochemicals. The quantitatively most important are phenol glycosides, flavonoids and tannins. Among the phenolic glycosides include salicin, salicortin, Tremuloiden and tremulacin. They are particularly found in leaves, twigs and bark. In feeding experiments, they reduce the growth of many insects.

In the fall of the sugar sucrose, raffinose and stachyose are formed in the root of the stored starch. While strength in the winter occurs only in small amounts, raffinose and stachyose can account for 6-7 percent of both root dry mass. Fats are also stored in the root and in the bark. In contrast to previous opinions, as the poplars were considered to be pure fat-storing species, are the fats in addition to carbohydrates only part of the reserve materials dar.

The chromosome number is 2n = 38 in all species The nuclear genome is with 2C = 1.2 picograms comparatively small.

Growth

The flowering occurs depends on the latitude February to April. Even within a population, the heyday of individual trees can differ by two months. The fertilization of the eggs occurs within 24 hours after pollination. The seeds are spread by wind and water, wherein the distance may be several kilometers; usually there are but a few hundred meters. The seeds are often only a few weeks germinate, they germinate under favorable conditions, ie on moist mineral soil, once made ​​. In the first year the seedlings root depths of 75 to reach up to 150 cm, while the height growth much more modest. The first flowering occurs around the age of five to ten years. Poplars are usually 100 to 200 years old.

The poplars may very well vegetatively, that is propagated by root rashes. Even broken branches and fallen trees - eg by flooding - can take root again. Especially poplars of the section Populus often grow in large " clone colonies " that have arisen from a single seed. The saplings can occur up to 40 m from the mother tree removed. Even if some of the total aboveground tree population is destroyed by a fire, survived the root network. Thus, the colony survive thousands of years. In the American state of Utah, a group of poplars is known, which may not exist at this location since 80,000 years.

In the section Tacamahaca Cladoptose occurs: Branches are dropped by the formation of a abscision, similar to the autumnal leaf fall.

Poplars are the fastest growing woody plants in the temperate latitudes. This property favors their ecological role as a pioneer woody plants. The growth is not like most trees such areas restricted to the preformed in the winter bud leaves. The poplars grow later in the year with new leaves on. Growth is - ended only by the shortened photoperiod in the fall - at least in some species.

Dissemination

Poplars are in the temperate regions of the northern hemisphere ( Holarctic distribution ). Its distribution ranges from the subtropical regions of China, where they have a diversity center, to the boreal zone. In America, their occurrence ranges in the south to Mexico. Populus ilicifolia occurs in East Africa.

In Central Europe, the black poplar (Populus nigra), the white poplar (Populus alba), and aspen (Populus tremula ) at home; next to the natural hybrid gray poplar (Populus canescens ).

Locations

Poplars are commonly found along rivers, where they are part of the floodplain forests. Many species such as the black poplar are tolerant, while drought is often poorly tolerated against flooding and also Überschlickung. With willow and alder they belong to softwood, the lowest level floodplain.

They also grow in temperate, boreal and montane forests. Many species are due to their rapid growth at the juvenile stage and vegetative propagation aggressive settlers on previously disturbed sites.

Worldwide there are about 80 million hectares of natural poplar stock, of which 28.3 million hectares in Canada ( 2001), 21.9 million in Russia and 17.7 million in the U.S. ( 2003). The main use is the production of wood here. As the fourth largest poplar China follows with 2.1 million hectares. Here, the main use is in the natural through the woods.

Diseases and predators

At poplars over 650 species of fungi were detected. At Populus tremuloides over 300 species of insects and 250 species of fungi have been found. Worldwide economically important diseases are leaf rust ( Melampsora spp.), Leaf and shoot bleach ( Venturia spp.), Leaf spot disease Sonia Mars, the tribe cancer Hypoxylon mammatum, the blight pathogen Phellinus tremulae and Septoria

In Central Europe, major diseases are of bacterial poplar cancer ( Xanthomonas populi ), the cortical firing ( Dothichiza populae ), brown spot Grind the leaf rust ( Melampsora spp.), The shoot tip disease ( Pollaccia radiosa ) and leaf blight (Mars Sonia spp.). An insect the Great Pappelbock ( Saperda carcharias ), the Small Pappelbock ( Saperda populnea ) and the Moschusbock ( Aromia moschata) are worth mentioning. Browsing and Fegeschäden are possible by mice, rabbits, rabbit, red, fallow and roe deer.

Nearly a hundred moth caterpillar species settle on poplars.

System

Outer systematics

The genus Populus has been counted to the family of pasture plants since time immemorial. She is a monophyletic group and the sister group of the genus Salix.

Inside systematics

Within the genus, it often occurs hybridizations. There are several divisions in the sections, the number of species varies according to the Arranger between 22 and 89 Above all agents of the Russian and Chinese poplars tend to have a larger number of species. The following outline is from Eckenwalder 1996:

• Section Abaso Populus mexicana, North America

• Euphrates poplar (Populus euphratica )
• Populus ilicifolia in East Africa
• Populus pruinosa

• Big-leaf cottonwood (Populus lasiocarpa )
• Populus glauca, including Populus wilsonii
• Populus heterophylla

• Black poplar (Populus nigra)
• Canadian black poplar (Populus deltoides), including Populus and Populus sargentii wislizensii
• Fremont cottonwood (Populus fremontii )

• Populus angustifolia
• Balsam poplar (Populus balsamifera )
• Populus suaveolens, including Populus cathayana, Populus koreana and Populus maximowiczii
• Populus ciliata
• Lorbeerblättrige poplar (Populus laurifolia )
• Birch poplar or Simon poplar (Populus simonii )
• Populus suaveolens
• Chinese balsam poplar (Populus szechuanica )
• Western balsam poplar (Populus trichocarpa )
• Populus yunnanensis

• Populus adenopoda
• White poplar (Populus alba)
• Grey poplar (Populus x canescens )
• Populus gamblei
• Großzähnige poplar (Populus grandidentata )
• Populus guzmanantlensis
• Populus monticola
• Populus sieboldii
• Populus simaroa
• Aspen (Populus tremula ), including Populus davidiana
• American aspen (Populus tremuloides )

Gene sequences based on phylogenetic studies this structure based on morphological characteristics have confirmed in the sections substantially.

Hybridization

The poplars are very common natural hybrid. The individual species of the relevant section hybridize with each other. Types of the two sections Tacamahaca and Aigeiros hybridize reciprocally, while species of section Populus not hybridize with species of other sections. Unlike many other plant taxa polyploidy comes after hybridization not occur in the poplars.

A result of natural crossing, and very widely used by growing the two hybrids:

• Grey poplar (Populus × canescens ( Aiton ) Sm ): hybrids of P. alba × P. tremula.
• Canadian poplar (Populus × canadensis Moench ) hybrids of P. deltoides × P. nigra. It arose spontaneously after the American Populus deltoides was introduced to Europe in the 17th century.

Rarely occur in triploid hybrids, which are then sterile, but can be propagated clonally. An example is the Convarietät Astria, a hybrid of Populus tremula × Populus tremuloides.

Evolution

Within the genus, the section Abaso is regarded as the most primitive, have evolved over Leucoides from the others. The section Populus is considered the most developed.

Fossil genus is very often represented by their leaves. The oldest finds date from the late Paleocene of North America and are around 58 million years old. You can section Abaso be assigned. In the late Eocene fossils first appeared on the section Leucoides, as well as the first fossils in Eurasia. In the Oligocene occurred in North America and Eurasia representatives, which are viewed as a common precursor of the sections Tacamahaca and Aigeiros, clearly the two sections identifiable fossils, as well as those of section Populus only appeared in the Miocene.

Use

Poplars grow quickly, are easy to grow and many forms form upright, strong main stems. These properties make it a popular poplar timber.

The use of poplars for timber, fuel and bedding for animals is occupied for the Mediterranean to Central Asia since ancient times. First, especially Populus nigra and Populus alba were used. After the introduction of the American Populus deltoides to Europe this type as well as the hybrid Populus was xcanadensis increasingly used. Since the early 20th century, the poplar breeding was carried on in a scientific way. 1947, the International Poplar Commission (International Poplar Commission) under the aegis of the Food and Agriculture Organization of the UN ( FAO) was founded.

The wood of poplar is whitish to pale yellow in general. It is soft, yet resilient. For this purpose, it is less flammable than other native woods. Therefore, it is processed into matchsticks, which should not burn too quickly after lighting. Heat-treated poplar wood is used for interior finishing of saunas.

Comminuted poplar wood is used as wood wool for packing purposes. This is also good for keeping small animals, because the wood contains no essential oils (such as pines and other conifers ). Poplar wood is finely cleaved to it (eg Camembert ) and chopsticks to make food packaging. Resolved to cellulosic pulp is made ​​into paper. Made of poplar wood pallets and plywood are produced in simple qualities. The core of snowboards often consists of a very flexible wood of poplars. Similarly, the body of stringed instruments, guitars and drums, as it is said to have good response characteristics.

In Italy, specially painted in Renaissance paintings and panel paintings on poplar panels, including the portrait of the Mona Lisa.

Although the stem wood of the tree is not very resistant to decay in case of injury, the processed wood is somewhat form- and weather- resistant, as long as it can dry quickly after penetration. It bleaches outdoors to a silver - gray color. In the north- west of Russia poplar wood is traditionally used for the production of roofing shingles.

As oak wood contains tree bark tannins, which have been used for tanning leather. Because of the phenols present in the leaves, buds, branches and bark extracts for the treatment of burns, itching, and swelling of the joints as well as tea were used for use in mild urinary infections traditionally.

Worldwide, there are about 6.7 million hectares planted poplars, of which 3.8 million to 2.9 million timber production and environmental protection. 30 percent of the area are agroforestry systems. Of the total area accounts for 4.9 million (73 percent) to China, 1 million to India. It is followed by France with 236,000, Turkey with 130,000, Italy 118,800, Argentina and Chile with 63,500 to 15,000 hectares. The timber harvesting from natural stands in 2003 amounted to 100 million m³ in Russia and 16 million in Canada. In five countries, more than one million cubic meters were harvested from planted stands: Turkey ( 3.8 million), China ( 1.85 million ), France ( 1.8 million), Italy ( 1.4 million) and India ( 1.2 million).

There are essentially three forms of poplar plantations: production plantations, protective planting and landscape conservation plantings.

Plantations

In plantations monoclonal stocks are used as a fast growing wood in short rotation crops. They are in Northern and Western Europe and in North America in 20 - to 30 -year-old culture used with rotation periods 3-5 years. In Italy, the poplar plantations are harvested after 10 to 15 years. The wood is used in the form of wood chips and wood pellets to produce energy, but can also be used as an industrial wood for the wood products industry for the production of particle board and other materials.

Balsam poplars of the section Tacamahaca other hand, are rather grown in forests, often along with other types. This form is prevalent in North America. In pure stands, the rotation period is 40 to 50 years. In Asia, the Middle East and North Africa column forms are commonly grown in narrow intervals of one meter at 10- 20-year rotation. Short-rotation plantations for biomass recovery ( for paper or energy ) is grown in dense monoclonal stocks and harvested every one to five years.

In agroforestry ( Agroforestry ) poplars are grown along with sugar cane, corn, wheat, soybeans and other crops. Widespread is this method of cultivation in North India and China.

Protective planting

Plantations to protect river banks and as a windbreak are common for centuries. As a windbreak poplars are well suited because of their rapid growth. By choosing the poplar species can also the width and height of the crown are quite well determined in advance. Frequently columnar forms are planted as the pyramid poplars. Are widely used as a windbreak poplars in Russia, Ukraine and Canada.

Along river banks reduce poplar not only erosion, but also improve the water quality. Because of their Raschwüchsigkeit and unpretentiousness they see as a pioneer tree species in the forest recultivation of opencast mines dumps or use.

Landscape maintenance

For landscape maintenance individual trees or small groups are planted, often poplars. Examples of commonly used cultivars are Populus nigra cv. italica in temperate areas and Populus nigra var thevestina in Asia and the Mediterranean. In Western and Central Europe, there are the cultivars Robusta, serotina, Regenerata and marilandica of Populus canadensis. Frequently poplars are found in row plantings along ditches, roads and property boundaries.

Use of wood

→ Main article: poplar

The wood is in sufficient size to timber and peeled veneers processed ( for match manufacture ). It is also used in pallets and packaging industries. Further processing areas are particleboard, fibreboard and chipboard moldings. For indoor use poplar wood is good usable under direct weather exposure, it is only a limited shelf life.

A major part of the poplar wood but it is used in the pulp, paper and board industry. The use as firewood and as biomass for energy production is not very significant.

Research and breeding

The genome of Populus trichocarpa was the first genome of a tree, which has been completely sequenced. Poplars were between 1994 and 2004 by the pine trees most commonly used in the biotechnology sector, with 47 percent of all studies, the tree species most commonly used for genetic modifications. In China 2002 the first genetically modified poplars have been approved for commercial cultivation until the end of 2002 1.4 million of these poplars were planted. Transgenic poplars are next examined in the United States, Canada, the European Union and China in release experiments. Altered wood quality, pest resistance and improved heavy metal uptake and its accumulation to soil remediation are at the center of research activities.

For the breeding favorable properties of the poplars are the easy formation of species hybrids, which have often better properties by the heterosis effect and the possibility to keep the properties of such hybrids constant by clonal propagation. In 1992, the Catalogue of Poplar Cultivars to 280 cultivars, which consist mainly of clones. Since 2006 there is an official database in which 332 cultivars were registered in March 2008.

Etymology

The name Populus was used before Linnaeus. In Latin, the word populus ( feminine as opposed to masculine populus, which means " people" ) since Cato the Elder is always in the meaning poplar. The etymology of the Latin word is not known. Pliny the Elder already distinguished the three species occurring in southern Europe. The German name is derived from the Old High German poplar popel, Middle High German papele, papel same meaning.

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