Category The World Around us

Deserts are hot, dry areas formed by the constant weathering and erosion of the land by fierce winds, extreme temperatures and occasional flows of water. They can contain barren mountain ranges, vast canyons cut into the Earth and huge plains covered with rocks or sand dunes. Many deserts have unusual rock formations, produced by certain kinds of erosion caused by wind and sand.

Sand covers only about 20 percent of the Earth’s deserts. Most of the sand is in sand sheets and sand seas–vast regions of undulating dunes resembling ocean waves “frozen” in an instant of time.

Nearly 50 percent of desert surfaces are plains where eolian deflation–removal of fine-grained material by the wind–has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles.

The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. Bedrock outcrops commonly occur as small mountains surrounded by extensive erosional plains.

Oases are vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. Oases are often the only places in deserts that support crops and permanent habitation.

Underground channels carry water from nearby mountains into the Turpan Depression of China. If the channels were not covered, the water would evaporate quickly when it reached the hot, dry desert land.

Soils that form in arid climates are predominantly mineral soils with low organic content. The repeated accumulation of water in some soils causes distinct salt layers to form. Calcium carbonate precipitated from solution may cement sand and gravel into hard layers called “calcrete” that form layers up to 50 meters thick.

Caliche is a reddish-brown to white layer found in many desert soils. Caliche commonly occurs as nodules or as coatings on mineral grains formed by the complicated interaction between water and carbon dioxide released by plant roots or by decaying organic material.

Most desert plants are drought- or salt-tolerant. Some store water in their leaves, roots, and stems. Other desert plants have long tap roots that penetrate the water table, anchor the soil, and control erosion. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion.

Deserts typically have a plant cover that is sparse but enormously diverse. The Sonoran Desert of the American Southwest has the most complex desert vegetation on Earth. The giant saguaro cacti provide nests for desert birds and serve as “trees” of the desert. Saguaro grow slowly but may live 200 years. When 9 years old, they are about 15 centimeters high. After about 75 years, the cacti are tall and develop their first branches. When fully grown, saguaro are 15 meters tall and weigh as much as 10 tons. They dot the Sonoran and reinforce the general impression of deserts as cacti-rich land.

Although cacti are often thought of as characteristic desert plants, other types of plants have adapted well to the arid environment. They include the pea family and sunflower family. Cold deserts have grasses and shrubs as dominant vegetation.

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The floor of a forest is teeming with wildlife. Decaying vegetation provides food for insects and allows many kinds of fungi to grow. The warm, humid atmosphere of a tropical rainforest is the perfect environment for plants and mosses that thrive in shady areas. Palm trees will grow here amongst other young trees growing towards the forest canopy. Climbing plants such as liana twist and curl around the trunks of the trees.

The forest floor, also called detritus, duff and the O horizon, is one of the most distinctive features of a forest ecosystem. It mainly consists of shed vegetative parts, such as leaves, branches, bark, and stems, existing in various stages of decomposition above the soil surface. Although principally composed of non-living organic material, the forest floor also teems with a wide variety of fauna and flora. It is one of the richest components of the ecosystem from the standpoint of biodiversity because of the large number of decomposers and predators present, mostly belonging to invertebrates, fungi, algae, bacteria, and archaea. Certain (adapted) plants may be more apparent in tropical forests, where rates of metabolism and species diversity are much higher than in colder climates.

The major compartments for the storage of organic matter and nutrients within systems are the living vegetation, forest floor, and soil. The forest floor serves as a bridge between the above ground living vegetation and the soil, and it is a crucial component in nutrient transfer through the biogeochemical cycle. Much of the energy and carbon fixed by forests is periodically added to the forest floor through litterfall, and a substantial portion of the nutrient requirements of forest ecosystems is supplied by decomposition of organic matter in the forest floor and soil surface. The sustained productivity of forests is closely linked with the decomposition of shed plant parts, particularly the nutrient-rich foliage. The forest floor is also an important fuel source in forest fires.

The amount of material in the forest floor depends on the balance between inputs from litter production and outputs from decomposition, and amounts also reflect the site’s disturbance history. Both litter production and decomposition are functions of the site (e.g., wet versus dry; cold versus warm; nutrient rich versus nutrient poor) and the vegetation that occupies the site (e.g., conifer versus broadleaf). A site’s forest floor is determined by its areal weight, depth, and nutrient content. Typically, forest floors are heaviest and deepest in boreal forests and mountain forests where decomposition rates are slow. In contrast, the lightest and thinnest forest floors usually occur in tropical forests where decomposition rates are rapid, except on white sands where nutrients could not be supplied from mineral weathering.

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The world’s forests provide many resources for human beings. Trees are cut down for timber, which is used for many different purposes, from building materials and fuel to making paper and chemicals. Forest areas are also cleared to create land for farming and other uses. There is a great deal of concern about the rate at which rainforests in particular are being destroyed. It is thought that an area of rainforest the size of a soccer pitch disappears every second. Such devastation has a dramatic effect on plant and animal species, as well as on the land itself.

As much as 80% of the world’s forests have been destroyed or irreparably degraded. Our ancient forests are looted every day to supply cheap timber and wood products to the world. The price for this destruction is escalating climate change, biodiversity loss and community displacement. And it’s happening in our region. Indonesia has lost 72% of its ancient forest, Papua New Guinea 60% and the Solomon Islands are predicted to lose all of them by 2014. Back in Australia, we are part of the problem.

The illegal and destructive logging operations are pushing species such as the orang-utan towards the brink of extinction and devastating local communities. What’s more, forest destruction accounts for around 20% of global carbon emissions. That’s more than the world’s entire transport sector.

Agri-business is responsible for massive rainforest destruction as forests are cleared or burned to make way for cattle ranches, palm oil or soya plantations. Irreplaceable rainforests are converted into products that are used to make toothpaste, chocolate and animal feed. Indonesia’s peatlands only cover 0.1% of the land on Earth, but thanks in part to the activities of the palm oil industry they contribute to 4% of global emissions. If expansion of the palm oil industry continues unabated, that figure can only rise.

Today, forests face another threat – climate change. When we destroy forests, we add to climate change because forests trap carbon and help stabilise the world’s climate. When forests are trashed, the carbon trapped in trees, their roots and the soil is released into the atmosphere. Deforestation accounts for up to 20% of all carbon emissions. This is why Indonesia is the world’s third largest greenhouse gas emitter after the US and China. At the same time, climate change itself threatens forests on a terrifying scale.

As their forest is cut down, millions of indigenous people suffer human rights abuse, and increased poverty and disease. Their food and medicine sources are destroyed. Their drinking water is polluted by soil erosion. With less than 5% of the logs’ value given back to the communities, the business of logging is moving landholders from subsistence affluence to a desperate type of poverty.

Some of the world’s most rare animals and plants call the last remaining rainforests in our region home. As their habitats are destroyed, many face extinction.

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Forests can be classified according to a wide number of characteristics, with distinct forest type’s occurring within each broad category. However, by latitude, the three main types of forests are tropical, temperate, and boreal.

Tropical

Most tropical forests receive large amounts of rain annually (up to 100 inches), which is spread evenly throughout the year. However, there are some tropical forests that receive seasonal rainfall and experience both a wet and dry season. While tropical forests have many layers, most of the nutrients are held in the vegetation within the canopy; therefore, the soils are typically low in both mineral and nutrient content. Shallow roots allow for ‘catching’ any nutrients released by decaying leaves and ground litter.

Tropical forests are particularly important since they are unusually rich in bio­logical diversity, especially insects and flowering plants. This incredible amount of biodiversity—accounting for 50 to 80 percent of the world’s plant and animal species, with a potential for millions still undiscovered—is what defines these forests and makes them most unique. In just a few square kilometers, hundreds—even thousands—of tree and plant species can be found.

Deforestation is one of the greatest concerns in tropical areas, especially within rainforests which cover only a small area (approximately 7 percent) of the Earth’s surface. Aside from their vast biodiversity, tropical forests provide homes to a large number of indigenous people. And, in looking beyond the typical forest offerings, tropical forests supply both local and global markets with a variety of ingredients for medicines; nearly half of all medicines used today are linked to discoveries within these forests.

Temperate

Temperate forests—common throughout North America, Eurasia, and Japan—are primarily deciduous, characterized by tall, broad-leafed, hardwood trees that shed brilliantly colored leaves each fall. These forests experience varied temperatures and 4 seasons, with winter often bringing below freezing temperatures and summer bringing higher heat and humidity. Rainfall also varies, averaging 30 to 60 inches annually, allowing for soils that are well developed and rich in organic matter. They also provide habitat for a wide variety of smaller mammal species, including squirrels, raccoons, deer, coyotes and black bear and many bird species, including warblers, woodpeckers, owls, and hawks.

Temperate forests are often most affected by human activity since they are located in or near the most inhabitable areas. The land in these areas has long been used for agriculture and grazing, although great expanses of forest regeneration and small areas of pristine forest exist. The hardwoods are valuable for making furniture and other commodities, and many remaining forests have been modified to accommodate recreation and tourism.

Boreal

Boreal forests (also known as taiga) are located just south of the tundra and stretch across large areas of North America and Eurasia. They are one of the world’s largest biomes, encompassing about 11 percent of Earth’s land area, but have very short growing seasons with little precipitation and represent relatively few tree species. The forest is dominated by coniferous trees, which have needle-shaped leaves with minimal surface area to prevent excessive water loss. These forests provide habitat for a few large mammal species, such as moose, wolves, caribou, and bears, and numerous smaller species, including rodents, rabbits, lynx, and mink.

Despite the remote locations and often inhospitable environment, boreal forests have long been a source of valuable resources. Fur trading began in the 1600s and continued well into this century. Boreal forests are also rich in metal ores—including iron—and coal, oil, and natural gas. Most importantly, the forest serves as a major source of industrial wood and wood fiber, including softwood timber and pulpwood. However, the low productivity rate in these forests leads to a slow rate of forest regeneration.

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