To investigate the effects of Light on Species diversity in an Old and a New Coppice - Assignment Example

We will be conducting an experiment on the species diversity under an old and a new coppice in a place called Nower Wood. Coppicing is a very natural and environmentally friendly way of obtaining wood so it does not harm the tree much, which has been performed for many years. A coppiced tree is cut down near the base at an early stage in its growth. Because it has not fully developed, several new stems will grow out at the cut off point. This can be repeated with the new stems to make the plant have many more branches, which are very useful for making wooden implements, such as for furniture or firewood.

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The new coppice is only several months to a year old, so the coppicing trees will not be fully developed, and the trees will be only a few feet tall, without much foliage. The old coppice trees on the other hand, are several years old, and are well established, tall, and have many leaves. There will not be much light under the old coppice due to the developed trees’ foliage.

Hypothesis

I think that the types of plant and the percentage of species diversity will vary as to how dark the area under the coppice chosen is – under an older coppice, there would be less light due to the size and amount of leaves, so there would be a greater variety of plants in the new coppice.

Trees shadow other plants around them as they also need to photosynthesise to produce energy for themselves. The chloroplasts in the leaves try to capture as much light as possible for the plant, so this does not allow much light to reach the ground. The younger coppices would contain undeveloped trees which would be smaller with less foliage, and so would not shadow the ground as much.

I might also expect the plants in the old coppice to transpire less. Transpiration is the loss of water from plants through the stoma in its leaves. A plant transpires more as: the temperature increases, the wind blows more and the drier the climate. If the plants did transpire less, I would expect there to be more moisture in the soil humus as the type of dead plants in the old coppice would retain more moisture.

Basis for Hypothesis

Plants need light to photosynthesise and to grow. They trap sunlight in their leaves for use in converting Carbon Dioxide and water into glucose and oxygen through the following equation:

Carbon Dioxide + Water + Energy (Sunlight) Glucose + Oxygen

6CO2 + 6H2O + Energy C6H12O6 + 6O2

If all plants photosynthesised in the same way, then in shadier areas there would be fewer plants, or less well nourished plants.

Some plants have adapted to shadier conditions by having a higher rate of photosynthesis e.g. Dog’s Mercury and bluebells. Plants have evolved in this way as trapping sunlight requires a green substance called chlorophyll, and in shadier conditions where less sunlight gets through the trees’ leaves, the plants need to make the best use possible of that light. To do this they have evolved so that they have a higher rate of photosynthesis. This means they can use what little light they have as best they can and so would prosper in dark areas of woodland, however, in lighter places other plants would grow better as they would be able to use all of the light whereas bluebells can only photosynthesise up to a certain point. I might therefore expect the plants in the old coppice to have a higher rate of photosynthesis, and to be different from the types of plants in more open areas.

Aspect (where the light is coming from) would also affect the plant distribution, so that we might expect there to be more plants on the south side of the hill, as this is the direction from which most of the light is getting to the coppices.

Light is not the only factor affecting the plant growth though. There are many other factors affecting plant growth, such as the soil pH. Different plants prefer a slightly different pH to others, so the types of plants growing in an area with acid soils, would be different to those in normal soils.

Depending on how much water which the plant receives, will also affect the variety of plants, as some plants might require much more water than others, so there might be less of those plants at times of year when there is less rainfall.

The climate and temperature will affect the plants’ growth and also the variety of plants, as different plants are better adapted to different conditions.

A major unnatural factor is human management, as some of the forest we will be studying will be managed i.e. coppices would be planted and looked after by humans. Humans would make sure that the coppice trees were not affected by other woodland plants, e.g. if other plants were to crowd the coppice trees, or steal its light or its water, then the tree might end up dying. Therefore, because of human management, there would not be as much variety of plant life in the coppices as we might expect. Squirrels (an introduced species) also affect the plants, as they eat many of the seeds dropped.

Method

To help with estimating the percentage of species diversity, we have a square (10�10 5cm squares) which is divided into quadrats by string tied at the centre points of each side to make this sort of shape . This makes it easier to estimate the percentage of species diversity in the area of woodland being investigated, as each quarter is 25% of the whole area.

We used this method of estimating the percentage of species diversity in different places on our school field. Making sure that no one was behind us; we threw the square behind us to a random place. The place was random so that our results were not influenced by anything.

Once we had thrown the square, we went over to where it had landed and roughly estimated the percentage of species diversity for the area. We then recorded the types of plant and what percentage area they covered. We repeated this method for different areas, and encountered different results. Nearer to the hedge there were less plants, and the ones which were there were different from the usual grass.

However, this is not a very suitable method for collecting random data, as the thrower of the square is able to see what he/she is throwing it at which might affect his/her results – he might deliberately throw the square at a more interesting place, so we should use a different, more random and safer method to collect our data. In our visit to Nower wood, we chose to use a different method to the previous experiment, in which we were not getting random results as we could see where we were throwing the measuring square (which was split up into quadrats or smaller percentages of the total area).

The new method involves using two axes of thirty metres of tape each. We took two random numbers given to us from our teacher (one for the X axis and one for the Y axis) and using those numbers we came to certain coordinates within the axis-grid (see diagram 1). At the coordinates we set down our square and roughly estimated the percentage of species diversity using an information sheet which told us with pictures the most common woodland plants e.g. x% of bare ground, or y% of russet grass. We used the same person to estimate the ground cover so it would be a fair test (different people’s opinions might differ).

This method was repeated 5 times for both the old and the new coppice. At any one of the random coordinates for the old and new coppice, we used an auger (basically a giant screw) to get a soil sample, which we took from the bottom of the screw, as that is where one would find the main soil composition (see diagram 3). From this soil sample, we were able to obtain the moisture level, pH, and the amount of humus (dead or organic matter) there was in the soil. To find its pH, we put the soil in a test tube, mixed it with a solution and added some indicator. Depending on what colour it was, it was decided what pH the soil had. Once again, the same person had to estimate the pH in the old and new coppice in order to make it a fair test. We also took a light reading using a light box, by pointing it horizontally in the coppice.

We took in to account the soil composition, as otherwise it would not be a fair test. The other factors such as climate, temperature and rainfall, would all be the same, as the old and new coppice are in the same wood.