Category The World Around us

WHERE DO FORESTS GROW?

Forest will grow in areas where the temperature rises above 10°C (50°F) in the summer and the annual rainfall is more than 200mm (8in). The type of forest depends upon the local climate, the soil and the altitude. Forests that grow in the extreme north of the Northern Hemisphere are called boreal forests; temperate forests grow in areas of moderate climate in both the Northern and Southern Hemispheres. Tropical regions are best known for their vast, dense areas of rainforest.

Tropical rain forests grow around the equator in South America, Africa, and Southeast Asia. They have the highest species diversity per area in the world, containing millions of different species. Even though they cover only a small part of the earth, they house at least one half of all species. The temperature is stable year-round, around 27°C (60° Fahrenheit). As you can tell from the name, it rains a lot in these forests. Most tropical forests receive at least 200 cm (80 inches) of rain in a year. Tropical forests generally have a rainy and dry season.

The high temperatures, abundant rainfall, together with twelve hours of light a day promotes the growth of many different plants. One square kilometer (0.6 miles) can have up to 100 different tree species. Broadleaf trees, mosses, ferns, palms, and orchids all thrive in rain forests. The trees grow very densely together and the branches and leaves block most of the light from penetrating to the understory. Many animals adapted to life in trees — such as monkeys, snakes, frogs, lizards, and small mammals — are found in these forests.

The soil can be several meters deep, but due to nutrient leaching, it lacks most of the essential nutrients for plant growth. The thin topsoil layer contains all the nutrients from decaying plants and animals, and this thin layer sustains the many plant species in the forest. One might think that the soil would be very rich because it supports so much life, but when tropical forests are clear-cut, the soil is useless for agriculture after only a few years — when the topsoil becomes depleted.

Temperate forests occur in the next latitude ring, in North America, northeastern Asia, and Europe. There are four well-defined seasons in this zone including winter. In general, the temperature ranges from -30 to 30°C (-22 to 86 F) and the forests receive 75-150 cm (30-60 in) of precipitation per year. Deciduous — or leaf-shedding — trees make up a large proportion of the tree composition in addition to some coniferous trees such as pines and firs. The decaying fallen leaves and moderate temperatures combine to create fertile soil. On average, there are 3-4 tree species per square km. Common tree species are oak, beech, maple, elm, birch, willow, and hickory trees. Common animals that live in the forest are squirrels, rabbits, birds, deer, wolves, foxes, and bears. They are adapted to both cold winters and warm summer weather.

Temperate evergreen coniferous forests are found in the northwestern Americas, South Japan, New Zealand, and Northwestern Europe. These forests are also called temperate rain forests because of the large amount of rainfall they see. The temperature stays pretty constant throughout the year, with a lot of precipitation, 130-500 cm (50-200 in). All this rain creates a moist climate and a long growing season, which results in very large trees. Evergreen conifers dominate these forests. Common species are cedar, cypress, pine, spruce, redwood, and fir. There are still some deciduous trees such as maples and many mosses and ferns — resulting in a Jurassic-looking forest. Common animals roaming the woods are deer, elk, bears, owls, and marmots.

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WHAT IS SPECIAL ABOUT CORAL REEFS?

Coral reefs are special areas of coastline made from living things. They grow in areas where the water is particularly warm, clear and shallow. Tiny sea animals cling to the coastline. When they die, they create limestone skeletons to which more creatures attach themselves. As these die, more creatures cling on, and the process continues. Coral reefs are among the strongest structures on Earth, as well as making up some of the world’s most beautiful coastlines.

Coral reefs are communities of hundreds of thousands of tiny animals called coral polyps. They grow in sunlit shallows of warm clear water. The reefs are built up as new corals attach atop the skeletons of dead animals. These coral reefs play a fundamental role in protecting coastlines from erosion and contribute to the formation of white sandy beaches.   Found around coastlines in the tropics, coral reefs provide homes for about a third of all fish species on Earth.

The coral species that are the reef’s foundation have very specific needs for light, temperature, salinity and oxygen.   They are easily damaged or killed.  Reefs are sensitive to unusually warm waters caused by global warming.  They are smothered by erosion from deforestation and dredging of rivers and bays.   They are blown up by fishers using dynamite, poisoned by collectors working for the aquarium trade and inadvertently damaged by boaters and scuba divers who stand on reefs or inadvertently hit them with fins or dangling equipment, breaking off pieces of the fragile coral. Damage from anchors and accidental boat groundings is a severe problem.

Cyanide and other toxins are used to stun reef fish so they can be captured alive to be sent to fish markets as aquarium specimens. The accumulation of poisons is killing the reefs. Improvements in the ability to keep corals alive has spurred a worldwide demand for live corals for aquariums.

Recently, scientists have become alarmed by increased occurrences of “coral bleaching”.

In many parts of the world the reefs are turning white and dying.
Coral gets its beautiful colors from the algae that live within.  This algae produce oxygen and sugars for the coral polyps to eat. The coral, in turn produces carbon dioxide and nitrogen which enhances algae growth.

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DO BEACHES ALWAYS REMAIN THE SAME?

Beaches are changing all the time. Shingle and sand on beaches is constantly shifted around by the action of the wind and waves —a process known as longshore drift. The same beach may be made of pebbles at one time of the year, yet be sandy a few months later.

Beaches are constantly changing. Tides and weather can alter beaches every day, bringing new materials and taking away others. Beaches also change seasonally. During the winter, storm winds toss sand into the air. This can sometimes erode beaches and create sandbars. Sandbars are narrow, exposed areas of sand and sediment just off the beach. During the summer, waves retrieve sand from sandbars and build the beach back up again. These seasonal changes cause beaches to be wider and have a gentle slope in the summer, and be narrower and steeper in the winter.

Most beach materials are the products of weathering and erosion. Over many years, water and wind wear away at the land. The continual action of waves beating against a rocky cliff, for example, may cause some rocks to come loose. Huge boulders can be worn town to tiny grains of sand.

Beach materials may travel long distances, carried by wind and waves. As the tide comes in, for example, it deposits ocean sediment. This sediment may contain sand, shells, seaweed, even marine organisms like crabs or sea anemones. When the tide goes out, it takes some sediment with it.

Every beach has a beach profile. A beach profile describes the landscape of the beach, both above the water and below it. Beaches can be warm, and rich in vegetation such as palm or mangrove trees. Beaches can also be barren desert coastlines. Other beaches are cold and rocky, while beaches in the Arctic and Antarctic are frozen almost all year.

The area above the water, including the intertidal zone, is known as the beach berm. Beach berm can include vegetation, such as trees, shrubs, or grasses. The most familiar characteristic of a beach berm is its type of sand or rock.

Sandy

Most beach sand comes from several different sources. Some sand may be eroded bits of a rocky reef just offshore. Others may be eroded rock from nearby cliffs. Pensacola Beach, in the U.S. state of Florida, for instance, has white, sandy beaches. Some sand is eroded from rocks and minerals in the Gulf of Mexico. Most sand, however, is made of tiny particles of weathered quartz from the Appalachian Mountains, hundreds of kilometers away.

Rocky

Some beach berms are not sandy at all. They are covered with flat pebbles called shingles or rounded rocks known as cobbles. Such beaches are common along the coasts of the British Isles. Hastings Beach, a shingle beach on the southern coast of England, has been a dock for fishing boats for more than a thousand years.

A storm beach is a type of shingle beach that is often hit by heavy storms. Strong waves and winds batter storm beaches into narrow, steep landforms. The shingles on storm beaches are usually small near the water and large at the highest elevation.

Other types of beaches

Some beaches, called barrier beaches, protect the mainland from the battering of ocean waves. These beaches may lie at the heads of islands called barrier islands. Many barrier beaches and barrier islands stretch along the Atlantic and Gulf coasts of the United States. These narrow beaches form barriers between the open ocean and protected harbors, lagoons, and sounds.

Beaches near rivers are often muddy or soft. Soil and sediment from the river is carried to the river’s mouth, sometimes creating a fertile beach. Hoi An, Vietnam, is an ancient town that sits on the estuary of the Thu Bon River and the South China Sea. Hoi An’s soft beaches serve as resort and tourist center.

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CAN COASTLINES BE PROTECTED FROM THE SEA?

It is possible to prevent or, at least, slow down the erosion of some coastlines. Groynes help to prevent longshore drift; while trees and grasses can be specially planted to stop sand dunes being blown away. Sea walls help to prevent coastal erosion and protect low-lying areas from flooding.

As sea levels rise and coastal communities face the threat of erosion and flooding, coastal defence structures, often built with concrete, have become the norm in many parts of the world.

But these hard engineered structures, like seawalls, breakwaters and groynes, are both expensive and bad for the environment. Our team of University of Melbourne scientists is joining a growing number of international researchers looking at whether natural coastal defence structures could be a better option. We are trialling mussel reefs and mngrove forests in Melbourne’s Port Phillip Bay to see how well they protect our shorelines.

Natural coastlines have in-built coastal defence in the form of sand dunes and beaches, saltmarsh, mangroves, seagrass and kelp beds, and coral and shellfish reefs. These natural structures can reduce the height of waves as they approach the shore and trap sediment, increasing the height of the land relative to sea level. This reduces flooding and erosion. Mussel reefs and mangrove forests are particularly important in Port Phillip because they are native habitats that have suffered significant declines historically. We are creating the mussel reef from recycled shell and natural basalt rock, and we expect it to reduce wave height and promote accretion of the eroding foreshore.

For the mangrove forests we will use a ‘hybrid’ approach, which involves planting the mangroves within concrete cultivars that attenuate waves, accrete sediment and provide the right conditions for the forests to grow. Elsewhere, other natural habitats are being used to protect shorelines. For instance, in the United States, oyster reefs have been widely restored on the east coast to provide erosion control. Oysters need something hard to attach to, and lots of creative reef designs have been engineered to replace lost habitats and enhance oyster populations.

In contrast, artificial structures are expensive to build and maintain and cause significant ecological damage. In particular, they lead to a loss of biodiversity through the replacement of natural habitats and are often hotspots for invasive species.

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HOW ARE BEACHES FORMED?

Beaches are made as rocks, worn away from headlands, are ground down into shingle and sand. The sea then deposits these particles in a sheltered place, forming a beach.

Rocks or coral reefs located off the shore are worn down by moving waves. As these materials are worn down, they become small particles of sediment that are carried by the waves in a state of suspension. In the case of sediment from further inland, the particles are washed to the larger body of water, where they are swept up by the waves and into the same state of suspension. These suspended particles cause the moving water to have increased erosive ability, resulting in greater amounts of eroded particles in the water.

In some cases, fish and other marine animals contribute to the speed of erosion. This is particularly true in beaches that are located near coral reefs. Many of these animals rely on algae growing on the coral as a major dietary supplement. As they eat away the algae, they inadvertently cause the coral to break off into small pieces. Some pieces may even work their way through the digestive tracts of these animals, resulting in even smaller particles that are washed up into the waves.

Erosion is typically thought to decrease the size of certain landforms, however, this is not always the case. In fact, erosion actually works to increase the size and width of some beaches. This growth occurs as the waves deposit the aforementioned sediment onto the land. Additionally, beaches may experience growth in size near river deltas, where rivers carry eroded sediment to the ocean. This sediment is deposited along the beach before being carried off into the ocean.

The type of wave that reaches the coastline also plays a part in the formation of beaches. Constructive waves, which are those that allow the water to recede and the beach particles to stop moving between waves, result in compacted sediment. This firm beach surface prevents future erosion. Destructive waves, which are fast forming and do not allow the water to recede between waves, result in a near-constant state of sediment suspension in the water. Because the particles remain in the waves, rather than being deposited on the shoreline, the beach in these areas is more likely to suffer from future erosion. With destructive waves, the sediment is not given a chance to settle and become compacted.

Picture Credit : Google

 

WHAT ARE ARCHES AND STACKS?

Perhaps the most dramatic coastlines are seen where rocky headlands have been eroded into arches and stacks. As the sea erodes the rocky coastline, only the toughest rocks remain, sometimes forming arch-shaped head-lands. Eventually, the roofs of these arches may fall, leaving tall, rocky columns known as sea stacks.

A stack or sea stack is a gelogical landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erision. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.

Isolated steep-sided, rocky oceanic islets, typically of volcanic origin, are also loosely called “stacks” or “volcanic stacks”.

Stacks typically form in horizontally-bedded sedimentary, or volcanic rocks, particularly on limestone cliffs. The medium hardness of these rocks means medium resistance to abrasive and attritive erosion. A more resistant layer may form a capstone. (Cliffs with weaker rock, such as claystone or highly jointed rock, tend to slump and erode too quickly to form stacks, while harder rocks such as grnite erode in different ways.)

The formation process usually begins when the sea attacks lines of weakness, such as steep joints or small fault zone in a cliff face. These cracks then gradually get larger and turn into caves. If a cave wears through a headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast, the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. This stump usually forms a small rock island, low enough for a high tide to submerge.

Picture Credit : Google