Explore Braunton - The Most Biodiverse Parish in England

An Introduction to Grasses


Grasses are flowering plants.  They vary enormously in size, growth habit and appearance, and many are of great economic importance to us.  Grasses are probably the most diverse group of plants and are found in virtually all habitats, from reed sweetgrass in freshwater to marram grass in sand dunes.  They feed populations right across the world from rice in Asia to oats, rye and maize and wheat in much of the Northern Hemisphere.  There are about 160 species of grasses in the UK.  Many of them have been introduced at one time or another, either for fodder or cereal crops or as ornamental plants.  The climate in the UK is particularly good for grass growth, which is luxurious and green for much of the year.  The wind has carried the light seeds to grow on rocky cliffs, marshes and just about every other habitat.

Grasses are very successful as plants, largely because they grow continuously from the base.  This means that they are not destroyed by grazing and mowing – which is why our lawns are made of grass.  Most of our Grasslandsgrasslands do in fact have to be artificially managed to maintain them – without mowing or grazing most grasslands would return to scrub and eventually to woodland.  This is particularly noticeable on some downlands where grazing has been discontinued.  Many of our ‘wild’ grasslands are much less diverse than they used to be because the mixture of grasses and other flowering plants has been replaced by monocultures of high-yielding grasses like ryegrass for grazing animals and silage making.

What is grass?

A grass has long, narrow leaves with parallel veins.  Its stem is hollow and round, and its flowers, whilst green and inconspicuous, are definitely flowers like any others, producing pollen and seeds.  Each separate floret is very small and enclosed by a pair of scales, the lemmae.  The florets are grouped together in spikelets, each spikelet being enclosed by scales called glumes.  Most grasses flower in June and July, although it is possible to find some in flower all year round.  (See below).

Grass Parts

Sexual Reproduction of Grasses

Amongst the flowering plants – grasses and others – there is a wealth of variation in the appearance and form of the flowers.  However, although their flowers may appear to be very different, they all have the same basic structure which allows sexual reproduction to take place.

The diagram below shows the structure of a flower, with the sepals and petals removed to expose the reproductive parts.

Grass Reproduction

The stamen is the male part of the flower and consists of a pollen-producing anther at the end of a fine filament.  In wind pollinated plants (this includes most grasses) these are held well clear of the flower to allow the pollen to be blown away.  The female part of the flower is called the carpel.  This consists of a stigma, which attaches the pollen, connected by the style to the ovary, which contain the eggs.  Pollen is deposited on the stigma from another plant, either by wind or insects visiting the flower.  The pollen grain grows a tube down through the style and into the ovary where it enters an egg.  The genetic material from the pollen passes down the tube and fuses with that of the egg to create a new individual.  The fertilised egg develops into a seed which can be dispersed by the plant.

Sexual reproduction is very important if a plant (or animal) population is to remain healthy and varied.  The exchange of genes between plants of the same species means that genetically new individuals will constantly be created.  This is the key process behind evolution.  Occasionally an individual will arise which is much better suited to its environment than its relatives.  This individual will therefore be more successful, produce more offspring and so spread the advantageous genes through the population.  Without this ability to change and adapt, plants (and animals) would soon become extinct whenever there was a change in the environment e.g. a rise in temperature, increase in rainfall etc.

A genetically uniform population is more susceptible to disease.  Large groups of genetically identical individuals are liable to be decimated by a disease or pest, which spreads through them unchecked.  In the past this has been a problem with agricultural crops, where vast quantities of plants are grown from the seed of just a few individuals.  A group of genetically varied plants is likely to contain a number of resistant individuals, which helps to slow down the course of disease or pests.

Parts of a Grass


Grass


What is Grassland?

Grasslands can be found all over the world, on every continent except Antarctica and in climates ranging from the tropics to the tundra.  They occupy about 25% of the land surface of the world.

Grasslands are characterised as lands dominated by grasses rather than large shrubs of trees.  Often a grassland will be composed of many different species of grass, along with some broad-leaved grassland herbs as daisies and buttercups.  Grasses have thin stems and straight narrow leaves, and height varies between species.  All grasses grow from the base not the tip, and can withstand losing the top shoots.  This is different from other plants and partly explains their adaptability and success both in natural habitats and cultivation.  Growth rate varies throughout the year, but most grasses are evergreen.

Grass plants can be annual or perennial, and are well adapted to living in difficult conditions.  Some can survive droughts, others thrive in wetlands and some withstand extremes of temperature.  Annual varieties are very good at colonising land which suddenly becomes available.  They grow very rapidly, and within one year will produce masses of seed which is spread by the wind, and then die.  Perennial grasses continue growing from year to year.  They too produce seed but they also spread by means of underground stems.  In this way the plant can spread across an area, forming a dense mat of aerial leaves and underground roots.  This is very important as it helps to bind soil together and prevent erosion.

Grasslands and Wildflowers

Grasses and flowering plants and belong to the group of plants known as the monocotyledons.  These plants only produce one seed leaf on germination and include the grasses, sedges and rushes.  The plants which we usually think of as flowers, with their brightly coloured blooms, belong largely to the group called the dicotyledons (some flowers are monocotyledons).  Their seeds produce two leaves on germination, and they are generally thought to be more primitive than the monocotyledons.

Grasses are wind-pollinated plants so they do not have brightly coloured or scented flowers to attract insects.  Indeed, the flowers are often insignificant to look at.  Their pollen is carried by the wind to other plants of the same species, allowing fertilisation to occur.  Much of the pollen will be lost, so to increase the chances of success, vast quantities must be produced.  (Grass pollen is the cause of hayfever ).All grasses have long leaves which have parallel veins and no stalks.

It is easy to confuse grasses with rushes and sedges.  Rushes however, have small, brown flowers which usually occur in clusters.  The woodrushes also have long white hairs growing along the edges of their leaves.  Sedges are more confusing, as the flowers are similar to grass flowers.  However, the stem of a sedge is always triangular and solid, whereas a grass is hollow and round.  The leaves of a sedge are always arranged in threes, and when looked at in cross-sections may be triangular or ‘W’ shaped.  Grass leaves are never triangular and are arranged in twos.
 

Grassland Habitats in the British Isles

Mixed deciduous woodland is the natural vegetation community over much of the UK, and almost all land (unless it is too high or dry) will revert to woodland unless something happens to prevent it.  Most grassland in the UK owes its existence to the grazing of animals, which prevents the development of scrub or trees, or to the artificial management of areas by cutting or re-seeding.

Pollen records show us that during the end of the last Ice Age much of the UK was covered with semi-arctic grassland.  After the Ice Age the climate warmed and trees colonised, covering the country in a dense wild wood, and making grassland habitat a rarity.  The only patches to be found were at high altitudes where peat bogs had failed to develop, very windswept cliff tops, and areas where wild animals gathered and grazed.

The appearance of Neolithic people (4,000 BC) saw the sudden resurgence of grasses and grassland herbs.  Some of these, such as white clover, may well have been introduced by people, but others such as meadowsweet, are able to grow in woodland as well as grassland, and may well have persisted here during the domination of the wildwood.  The majority, however, spread back from the remaining fragments of late Ice Age grassland.  Meadow and pasture communities today are composed mainly of plants which at one time grew too far north or too high to be reached by the wildwood.

Types of Grassland

Agricultural grasslands in the UK historically fall into two categories.  Those which were used for grazing farm animals were termed pastures, and those cut for hay were known as meadows.  Meadows are much more species-rich than pasture, and were often sited on land liable to be flooded by a river in spate.  In the 17th century, sheep farming was very important to the British economy.  The number of sheep a farmer could keep depended on how much food could be stored for the winter months.  Many farmers increased their stocks by building sluices and flooding the valley bottoms early in the year.  River water which comes from underground springs is often warmer than the frozen ground in winter.  By flooding the meadows the farmers warmed up the ground, producing an early “bite” of grass for the sheep to eat in the spring.  Once the weather warmed up and drier pastures began to grow, the sheep could be moved off the water meadow.  This was then flooded again to produce another crop of grass which was cut in June, and stored as hay for winter.  Meadow land was therefore more productive than ordinary pasture and consequently more valuable.  In 1801 a farm at Itchen Abbas in Hampshire paid 55 shillings per acre in rent for flood meadow compared with 12 shillings per acre for dry pasture.  Flood meadows have all but disappeared from our countryside today (Thomas, 1998).

More Grass = More Food

Since World War II an increasing population, and a greater demand for food has led to the ploughing up of permanent pasture and meadows, mainly in lowland areas, to make room for arable crops.  Farmers have also been given more productive grasses to grow with chemical fertilisers, producing improved grassland with a high food value for dairy stock.  Sheep can be grazed on poorer land and are often kept on thin unimproved grasslands in upland areas.  Traditional pastures and meadows now only survive in remote and unprofitable locations.

Seeds

Seeds are the result of sexual reproduction, and are the means by which plants maintain genetic variation in a population (see page 8).  Seeds are also the way in which plants spread across a landscape.  In most cases they will fall within a relatively short distance of the parent plant.  This means they are guaranteed to fall in a habitat which is suitable for growth, but they will have to compete with their parents and siblings for space, light, etc.  Many plants have developed clever dispersal mechanisms for spreading their seed over some distance.  Some are light and blow in the wind, others have wings and parachutes, and some are sticky or have hooks which allows them to attach to animals.

Dispersal Experiment

Children will be surprised at how many seeds they gather on their feet on a walk through a field.  Many seeds which don’t seem to have any dispersal mechanism become sticky when wet and attach to the feet of birds and other animals.

You will need: a metal tray, a seed tray, a trowel, accesses to an oven, some muddy shoes from a walk in a field.

  1. Sterilise the soil by placing it in the metal tray and heating it in the oven (or use a peat-free potting compost).  Once the soil has cooled, place it in the seed tray.
  2. Scrape the mud from the shoes on to the sterilised soil or potting compost.  Water thoroughly.
  3. Place a piece of glass over the tray and leave it in a warm place until germination takes place.  How many different varieties of plants do you have?

Parachutes

This is best done inside, or outside on a still day.

You will need: some chalk, a hairdryer and a tape measure.

  1. Collect some dandelion seeds with their parachutes still attached.
  2. Drop a parachute directly above a cross-chalked on the floor.  Measure how far it travels horizontally from the cross.  Repeat this 10 times and find the average distance.
  3. Repeat the experiment but this time use a hairdryer blowing the air from one metre away, and see how far the parachute is carried.
  4. Repeat with a gentler wind (hairdryer two metres away).
Does the wind strength affect the distance travelled by the seed?  Do the seeds always land in the same place?  Try this experiment with other parachute seeds.  Which travels the furthest?

This, and any other grassland activity, has been produced with the kind permission of Gig Hardy of Staffordshire Wildlife Trust. It has been taken from their Grasslands Pack Key Stage 1 & 2.

There is also a Key Stage 3 & 4 Pack and both packs can be obtained from Staffordshire Wildlife Trust at The Wolseley Centre, Wolseley Bridge, Staffordshire, ST17 0WT    Tel: 01889 880100

 
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