My Science School

Mountain ranges differ in vegetation according to the region they are situated in. The Western Ghats are a chain of mountains which run parallel along the Western coast of India through Gujarat, Maharashtra, Karnataka, Kerala and Tamil Nadu.

These Ghats are considered to be a hotspot of biodiversity. Nearly 5,800 species of flowering plants occur here. A variety of vegetation types, from evergreen to semi-evergreen, moist deciduous to dry deciduous and high altitude grasslands are found here.

Dry scrub vegetation occurs at the foothills followed by moist deciduous forests at higher altitudes. Further up are the semi-evergreen and evergreen forests. The Silent Valley forest in the Western Ghats is the best example of a surviving tropical rain forest in India. These forests abound in orchids, timber trees, spices and medicinal plants.

Around the world, vegetation follows a similar pattern. The foothills may be covered in broad-leaved forests while the upper slopes have needle-leaved trees like spruce and pines.

The plants that grow on specific mountain ranges depend largely on the climate of the mountains. For instance the San Bernardino range in the USA has a Mediterranean climate with chaparral, scrub oak, elderberry and white alder among the flora present here.

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The mountain environment is challenging to say the least. Rain, snow, radiation and high winds make survival here difficult and sometimes impossible. Heavy rainfall is one of the biggest threats to vegetation. Flowing water can wash away the thin soil and even cause landslides, especially where trees have been cut down for mining and other commercial activities. In areas where the soil is not held together by the trees anymore, landslides can sweep away whole sections of forest.

To add to this, acid rain can makes the soil unsuitable for plants to grow. Furthermore, snow and ice freeze the ground and kill young shoots. The wind is another factor that prevents vegetation from thriving here. Mountain winds are much stronger than winds in the lowlands. They can batter and pound the slopes at extremely high speeds that flatten out any plants or trees growing here.

Another major cause of concern is global warming and increasing temperatures. Warmer and longer summers are leading mountain grasses and plants to dry out and catch fire more easily. In recent years mountain fires have been breaking out in record numbers around the world, causing severe destruction to vegetation and wildlife.

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Mountains have some of the most extreme weather on Earth, and some of the most challenging terrain, so it’s no surprise that not all plants can survive there. The rocky soil, thin air and harsh weather paint an unwelcome picture for most forms of life.

Mountain slopes are often rocky and steep. The soil is washed away in heavy rain and carried away by streams and rivers. In some places slopes are covered with scree. Scree is a mass of small, loose stones that cover a side or slope on a mountain. Some areas may have poor drainage and acidic soil which also prevents plants form growing. All in all, not a very promising environment for plants to grow.

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How do you protect yourself against the scorching sun? Maybe by wearing a cap, or carrying an umbrella. You might even apply a sunscreen. We have a variety of ways to choose from, but how would a plant protect itself? It turns out that they are way ahead of us!

As we know, plants use sunlight to make food through the process of photosynthesis. But sometimes that same sunlight can also be harmful for the plant. This happens at higher elevations as there is more radiation at higher altitudes. At lower altitudes the atmosphere absorbs most of the harmful ultraviolet or UV radiation, whereas at higher altitudes the atmosphere is unable to absorb this radiation.

UV radiation can damage the plant's DNA and prevent the plant from growing properly, but researchers have found that some plants produce a natural sunscreen that shields them from sun damage. This shield is made up from molecules called sinapate esters that plants produce and send out to the outer layers of their leaves. This creates an invisible barrier against UV radiation. What about photosynthesis? Would this also prevent the plants from using the sunlight to make their food? It was found that sinapate esters block UV but not the wavelengths needed for photosynthesis.

So not only does the plant protect itself, it selectively lets light in too. This is one of nature’s brilliant ways of ensuring that plants survive even under harmful conditions.

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You must have heard of bonsais, or miniature plants that are deliberately trained or pruned to remain small. Did you know that nature too has its version of bonsai?

These are not shaped by shears and scissors but by biting, cold winds, snow and ice at extreme altitudes. They are referred to as Krumholz - German for stunted tree. Just like some sportsmen like extreme sports, these trees are star players in extreme mountain weather!

They are found above the tree line on high mountains and are usually not more than eight feet tall. In some places they grow just knee high. They grow low to the ground to avoid being blown down by icy mountain winds. The same species of tree would grow to its regular size below the tree line much faster. But Krumholz take almost twice as long to grow and are severely stunted and deformed. These maverick trees grow very slowly and very little.

They may take double the years to grow the same diameter as their counterparts below the tree line, but they live almost twice as long. Researchers have also found that Alpine flowers above the tree line grew about one-third of an inch in 10 years! They grow so slowly that most cannot sprout, mature and produce seeds in a single season. Consequently they are perennials and live for many years.

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If you were to travel up a mountain and observe the plants on the way, you would see that there is a huge difference in vegetation at different levels. These levels contain distinct kinds of vegetation that are different from the next.

In high mountains like Mt Kilimanjaro in Africa, the experience can be likened to walking from the equator to Antarctica in a few days!

In fact Mt Kilimanjaro has five distinct ecological zones that show extremely diverse vegetation types. The first zone is the cultivated zone at the base of the mountain. Here you will find crops such as coffee and a variety of tropical fruit plants.

Further up is the forested zone where you will find orchids, ferns, and camphorwood trees. Then comes the moorland zone where heath-like vegetation and wildflowers grow. The next region is the Alpine desert zone where only mosses and tussock grasses grow. The last and most extreme zone is called the Arctic zone where no plant or animal lives exist.

A mountain range such as the Alps would also show a similar trend. The first zone would have agricultural land. The next would be a forested belt. This zone also marks the tree line, beyond which no trees can grow. The third would be an alpine meadow and finally at the top a region of permanent snow and ice with no plant life whatsoever.

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The Earth as you know is divided into three main climate zones according to latitude - tropical, temperate and polar zones. The type of vegetation found in mountainous ranges varies according to their location in these climate zones. However one must keep in mind that a huge mountain has the ability to change the weather and create its own climate and biome. (A biome is a naturally occurring community of flora and fauna.) However, a general outline is as follows - Temperate zone Mountains, such as the Rocky Mountains in Colorado, USA, have coniferous forests on the lower slopes and alpine vegetation above the tree line.

Tropical Zone Mountains such as the Nilgiris in South India have tropical rainforest as the dominant type of habitat. Over 2,700 species of flowering plants and 160 species of fern are found here. Tropical mountains have higher tree lines and may have grasses, heathers and shrubs at higher altitudes.

Desert Mountains have very few varieties of plants due to the harsh climate. Lack of rain, strong winds and the scanty soil makes it difficult for plants to grow. Cacti, grasses and shrubs are the dominant vegetation found here.

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The most significant adaptations of mountain plants are seen at higher elevations as these are the areas with extreme conditions. At these elevations trees begin to thin out as they cannot survive. Above the tree line, a few plants have developed some unique features to survive the extreme cold, strong sun and heavy winds.

Plants like sparse grasses and alpine perennials grow very close to the ground to avoid being uprooted by strong winds. Lichens and mosses cling to rocks and grow well in damp conditions. Most mountain plants have strong, clinging roots and short stems that can withstand strong winds. Their leaves are small, waxy or spiny to retain moisture and are not easily harmed by snow or wind. Their flowers are surrounded by leaves for protection and the grasses are often bunched together like a bush and sway in a rotating motion to withstand storms.

Some plants have stems which extend deep under the soil and allow storage of food through the harsh winter. These plants can immediately start growing in warmer weather, without waiting for the icy ground to thaw, deriving nutrients from their stems. Similarly the leaves of coniferous trees are thin, spiky and waxy to retain moisture even when the ground is frozen.

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If you have travelled up a mountain you might already know that the weather at its base is very different from its top. While the weather may be pleasant and mild at its base, it can turn fiercely windy and cold as you move towards the summit. For example Mt. Kilimanjaro in Africa, which is 5,895 m high, has five distinct climate zones, starting from warm at the base to freezing cold at the summit! To know the reason for this change, we need to understand the concept of atmospheric pressure.

Atmospheric pressure is defined as the force per unit area exerted on a surface by the weight of air above that surface. Since there is more air at sea level, there is more force exerted and therefore greater pressure, but the higher up we go, the air thins out and the atmospheric pressure becomes less. This scarcity of air leads to lesser absorption of heat and therefore it becomes colder as we go higher up.

Another factor that contributes to the harsh weather higher up on a mountain is the wind. Lesser air means lesser friction and therefore more wind. At higher altitudes it is very windy and an exposed person would not last long. It stands to reason that one would be well advised to cover up snugly if planning a trip up a mountain. If the cold doesn’t get you, the wind certainly will!

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Mountains are game changers when it comes to the weather of a place. The landscape and climate of an area near a mountain depend on whether it lies on the leeward or windward side of the mountain.

Windward, as the name suggests, is land facing the prevailing winds in that region. These winds hit the mountain and rise up. As the air moves up, it cools and forms clouds. These clouds then fall down as rain. So the windward side ends up with all the rainfall and also has the most fertile land and better weather conditions.

Once the winds have deposited their moisture on the windward side, they descend on the other side (leeward side) of the mountain as hot and dry winds. This side of the mountain is also called the rain shadow area since it gets very little rain. It is usually characterized by hot, dry weather. Many of the world’s biggest deserts are found in this area. Death Valley, USA, behind the Sierra Nevada range is in the rain shadow area of the mountains and is one of the driest places on the planet. Similarly the Gobi Desert is also located in the rain shadow of the Himalayas.

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Mountain soil, especially the soil that is found in regions of high rainfall, is generally found to be acidic. This is due to the prevailing weather conditions which are often wet and cold. The rainfall leaches or drains away basic minerals like calcium, magnesium, potassium and sodium from the soil leading to acidity in the soil.

Also carbon dioxide from decomposing organic matter forms a weak organic acid that is released directly into the soil. Another reason for acidity in the soil is the burning of fossil fuels. This releases Industrial gases like sulphur dioxide into the air which mix with rain and fall back down to earth as acid rain.

Acidic soil is not suitable for farming as essential nutrients for the growth of plants like phosphorous and nitrogen are washed out of it. In other words it decreases the availability of nutrients to plants and increases toxic elements in the soil. It is generally found that if a particular region has acidic soil, it is difficult to grow non-native plants there. In these cases improving the general properties of soil by adding nutrients to it may be carried out by hill farmers. This may be in the form of compost, wood ash, straw and manure.

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Some mountains, such as Mt. Everest, are growing taller due to the pressure generated by tectonic plates acting below them. But did you know that mountains can also get smaller? It may seem incredible, since mountains are perceived as eternal and immovable. In reality, however, mountains can be pictured as endless ‘construction sites’. Continental plates collide and force the Earth’s crust upwards, while at the same time, erosion acts on the exposed surfaces and break them down.

Erosion is the process by which things are broken down by the forces of nature, such as rivers, glaciers, wind and rain. One can add to this list, geological events such as earthquakes, landslides and volcanic eruptions, which are all constantly changing the shape of the Earth’s surface.

Let us consider two of these factors- water and wind more closely. Waterfalls as snow on high mountains and over a long period of time this snow turns into ice. This ice compacts and becomes a dense mass called a glacier, which then slowly moves down the mountain as a ‘river of ice’. The glacier collects soil, debris and rocks and becomes extremely corrosive to the surface that it travels over. A glacier can flatten out a valley and change the landscape considerably. Similarly strong winds can also be extremely corrosive over a period of time, wearing away at rocks and mountains making them smaller over many years.

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All mountains look old and majestic but you might be interested to learn that they are not the same ages. Mountains are classified as young and old according to when they were formed. There is a branch of study dedicated to this called Geochronology. Young mountains were formed several dozen million years ago, while old mountains were formed hundreds of millions of years ago.

The Himalayas are the youngest mountains on Earth. They are estimated to be around 40 million years old. The Rockies are another example of young mountains. They were formed between 80 and 55 million years ago. The oldest mountains on Earth form the Barberton Green-stone Belt in South Africa, estimated to be at least 3.2 billion years old!

One way to recognize young mountains from old is based on the level of erosion that has taken place on them. Young mountains tend to be taller and jagged with fewer signs of erosion, like the Himalayas, while older mountains have rounded tops and lower elevations, due to high levels of erosion. The Appalachian Mountains in North America is an older mountain range which formed around 480 million years ago. Its appearance is smooth and rounded because over many millions of years the action of water, wind and ice have worn it down into a landscape of rolling hills and broad valleys.

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We know by now that mountains are worn down by erosion and over millions of years can grow smaller in size. But have you ever wondered if a mountain range could disappear entirely off the face of the Earth? And if so, how would we know of its existence?

Due to science we can even find out the existence of mountains that have disappeared billions of years ago. How? By looking at its trace signature in the rocks. Even a long-gone mountain range would leave some ‘tracks’ behind. These tracks are folded rocks that were formed deep in the ground when the mountains were being formed. Even after the mountain eroded away completely, the presence of these rocks signifies that a mountain once stood there. Geologists have found a belt of rocks across the flat central part of Canada and USA, which marks the site of a mountain system that existed billions of years ago!

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You probably already know that Mt. Everest stands at 8,849 metres above sea level. Did you ever wonder how such a formidable mountain was measured? Moreover, before one starts measuring it, one must decide whether to measure from the base of the mountain to the peak or from sea level to the peak. Some measurements are also conducted from the centre of the Earth to the peak.

Once the baseline is decided one must decide on the method to be used. In the past, geometry was used to figure out the height, based on the angles between the top of the mountain and points on the ground whose positions were already known. A telescopic instrument known as the theodolite was used to measure this angle.

Another way to measure the height is by using a barometer. You may know that a barometer is used to measure atmospheric pressure. How then, can we measure a mountain with it? By using simple logic. We know that atmospheric pressure decreases as we go higher up. So the air pressure on the top of a mountain will be lower than the pressure at sea level. By comparing these two measurements we can calculate how tall a mountain is. Innovative science, wouldn’t you say?

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