Plant, any multicellular eukaryotic life-form characterized by
- photosynthetic nutrition (a characteristic possessed by all plants except some parasitic plants and underground orchids), in which chemical energy is produced from water, minerals, and carbon dioxide with the aid of pigments and the radiant energy of the Sun,
- essentially unlimited growth at localized regions,
- cells that contain cellulose in their walls and are therefore to some extent rigid,
- the absence of organs of locomotion, resulting in a more or less stationary existence,
- the absence of nervous systems, and
- life histories that show an alteration of haploid and diploid generations, with the dominance of one over the other being taxonomically significant.
Plants range in size from diminutive duckweeds only a few millimetres in length to the giant sequoias of California that reach 90 metres (300 feet) or more in height. There are an estimated 390,900 different species of plants known to science, and new species are continually being described, particularly from previously unexplored tropical areas of the world. Plants evolved from aquatic ancestors and have subsequently migrated over the entire surface of Earth, inhabiting tropical, Arctic, desert, and Alpine regions. Some plants have returned to an aquatic habitat in either fresh or salt water.
Crop, In agriculture, a plant or plant product that can be grown and harvested extensively for profit or subsistence. By use, crops fall into six categories: food crops, for human consumption (e.g., wheat, potatoes); feed crops, for livestock consumption (e.g., oats, alfalfa); fibre crops, for cordage and textiles (e.g., cotton, hemp); oil crops, for consumption or industrial uses (e.g., cottonseed, corn); ornamental crops, for landscape gardening (e.g., dogwood, azalea); and industrial and secondary crops, for various personal and industrial uses (e.g., rubber, tobacco).
Forest species plants
Trees grow and die with or without or management but the number of trees on every acre and the ratio of live versus dead trees can be influenced by our actions. Keeping a healthy forest in line with an owner’s goals requires active management of vegetation. Although in the short run, letting nature take its course may seem to have few adverse consequences, in the long term it can have profound effects on the forest.This is because the natural processes themselves have already been altered at scales well beyond the boundaries of a single forest property. Years of fire suppression have radically affected millions of acres of forestland in California. This has resulted in stressed trees, disease outbreaks, and dominance of tree species that reproduce in crowded shady conditions. In the absence of fire, it is possible to thin trees to reduce competition and create openings so shade-intolerant trees can grow. Another threat that can overwhelm the landscape without active management is the spread of aggressive exotic plants.
Forests are areas with trees grouped in a way so their leaves, or foliage, shade the ground. Forests can be found just about anywhere trees can grow, from below sea level to high in the mountains. From tropical rain forests near the Equator to boreal forests in cold climates close to the Arctic Circle, different types of forests can be found all over the world.
One way to classify different types of forests is by the type of trees a forest has. Deciduous forests have trees with green leaves that change color in the fall and drop altogether in the winter. Trees that are common in deciduous forests are oak and maple. The northeastern United States is covered in deciduous forest, and tourists flock to the area every autumn to experience the orange, yellow, and red leaves blanketing the region.
Evergreen forests have trees with leaves that stay green all year long. One of the places evergreen forests can be found is on the opposite side of the North American continent—in the Pacific Northwest, which includes the Canadian province of British Columbia and the U.S. states of Washington and Oregon. The Pacific Northwest is full of evergreen trees like fir
Sometimes forests are classified by the type of leaves on their trees. Trees in broad-leaved forests have wide, flat leaves. Tropical rain forests are a type of broad-leaved forest. Tropical rain forests, such as Brazil’s Amazon Basin rain forest, are found near the Equator. They contain more than half of the world’s biodiversity, or variety of plant and animal species.
Coniferous forests have trees with cones and needles instead of leaves. Coniferous forests have the tallest (coast redwood), largest (giant sequoia), and oldest (bristlecone pine) trees in the world.
Many forests are mixed, meaning they have both broadleaf and coniferous trees. The eucalyptus forests of Australia are mixed forests, for instance. The evergreen eucalyptus trees are mixed with deciduous trees like beech.
Tundra is an area where tree growth is difficult because of cold temperatures and short seasons. Vegetation in tundra is limited to a few shrubs, grasses, and mosses. Scientists estimate roughly 1,700 different species live in the tundra, which isn’t much compared to forests and grasslands. The ground is often too cold for plants to set down roots, and without plants, few animal species can survive.
Deserts have almost no precipitation, or rainfall. In fact, deserts are specifically defined as areas with an average annual precipitation of less than 10 inches per year. Deserts usually have really high daytime temperatures, low nighttime temperatures, and very low humidity.
Desert soil is often sandy, rocky, or gravely. Plant life is highly specialized to adapt to these coarse, dry conditions, with long roots, small leaves, stems that store water, and prickly spines that discourage animals from touching or eating them. Cactuses, which are native to deserts in North and South America, are an example of this kind of plant. Despite the barren look of hot deserts, they are full of animal life. Most desert animals, such as lizards or snakes, are nocturnal, meaning they are active at night. Nocturnal animals take advantage of the cooler nighttime temperatures of the hot desert.
The interesting thing about the ice sheet “vegetation region” is that there really isn’t any vegetation there at all! An ice sheet is a large stretch of glacier ice that covers the land all around it for more than 50,000 square kilometers (20,000 square miles). Currently, the only ice sheets are in Antarctica and Greenland. Don’t confuse the ice sheets, called polar ice caps, with other ice shelves or glaciers; an ice sheet is much, much bigger.
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