Text 1

⁶ The uniformitarian principle means that the basic processes and limiting factors of climate remain the same over time. It is borrowed from the same principle in geology which was popularised in the book Principles of Geology (1830). This idea can be summarized by the phrase “the present is the key to the past.” This of course does not mean that today’s climate is the same as in the past.

⁷ The limiting factors principle suggests that a tree’s rate of growth is constrained by the resource which is most limited. So plants in a particular area adapt to the climatic conditions in which they grow. Two factors of climate are important for plants to grow, namely sunlight and moisture. The amount of sunlight as well as its duration and quality are essential. At high altitudes, greater ultraviolet light can slow down the growth of plants. The period of time that the sun shines in a day can affect the reproduction of plants by affecting their flowering.

⁸ The cross-dating principle applies to matching ring patterns between trees. The climate of a certain region will affect the trees in that region in a similar manner. Therefore, similar patterns of ring widths will develop in the trees.

Tree Growth and Effect on Rings

⁹ In trees that grow in a tropical climate, the cambium cells grow at a steady unchanging rate. So the rings that show the age of the trees cannot be clearly distinguished. Therefore, for trees to give us information about past climate through their rings, they need to grow in difficult conditions which include significant variations in temperature and drought.

¹⁰ Trees that grow in temperate climates show a difference in growth between the seasons. In spring and summer, cambium cells become progressively larger whereas in autumn and winter they progressively become smaller. This change in cell size can be seen as distinguishable rings.

¹¹ With advances in technology, the width of the rings can be measured using computer software and a scanner. (SeeFig. 2). Wide rings show healthy growth while narrow ones show weak growth. The variations in the width of the rings indicate the climate in which the tree has grown.

Divergence Problem

¹² One of the problems that dendroclimatologists are trying to solve is known as the “divergence problem”. As mentioned above, the width of tree rings represents the growth of trees. However, since the 1950s, it has been found in the forests in the far northern latitudes, e.g. in Canada, Northern Scandinavia and Russia, that the width of tree rings in these areas do not match the increasing temperature. This could be due to the fact that while the temperatures in these regions have risen significantly, the amount of water has not proportionately increased. So the trees grow more slowly. Some scientists think that the existence of the divergence problem means the tree ring data in this area are not suitable for reconstructing past climate trends. However, trees in other regions, where there is sufficient water for growth, are not affected by this divergence and thus may be used in reconstructing climate patterns.

Note:The words in bold are assessed. See Unit 7 Vocabulary The words in italics are in the glossary below.

Glossary

Biophysics (n) -The physics of biological processes and the application of methods used in physics to biology.

Reconstruct (v) -To form a picture of (a crime, past event, etc) by piecing together evidence or acting out a version of what might have taken place.

Core (n) - The core of a fruit is the central part of it. It contains seeds or pips.

Astronomer (n) - An astronomer is a scientist who studies the stars, planets, and other natural objects in space.

Lignin (n) - A complex polymer occurring in certain plant cell walls making the plant rigid.

Principle (n) - A principle is a general belief that you have about the way you should behave, which influences your behaviour.

Altitude (n) - The vertical height of an object above some chosen level, esp above sea level; elevation.

Steady (adj) - A steady situation continues or develops gradually without any interruptions and is not likely to change quickly.

Dendroclimatology (n) - A branch of dendrochronology concerned with constructing records of past climates and climatic events by analysis of tree growth characteristics and especially annual rings.

Baobab (n) - A thick-trunked tree (Adansonia digitata) of the bombax family, native to Africa: fiber from its bark is used for making rope, paper, etc., and the gourdlike fruit has an edible pulp.

Understanding the text: Skimming & Scanning

1. What is A.E. Douglass known for?

2. How are tree rings formed? Describe the process.

3. How many main principles of dendrochronology are there?

4. What is the reason given in the text for the “divergence problem”?

5. Tree rings are formed from the _______________ of dead cells which contain ___________. (ONE word in each gap)

6. The uniformitarian principle maintains that climate factors which limit tree growth stay the same and it isn’t possible for climate today to differ from the past. True or False?

7. The text states that the divergence problem is due to the fact that temperatures and the quantity of water have both increased. True or False?

Analysing The text: main ideas

Give the main ideas of paragraphs 1-8 in Text 1: Part One.

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Analysing The text: Critical Thinking Skills

1. What are the limiting factors of climate?

2. If the cross-section of a tree shows rings of small, tightly packed cells, alternating with rings of larger cells, what can you say about the climate in which the tree is growing?

3. If you take a core sample from a date palm, could you easily find the tree’s age? Give a reason for your answer.

4. Which type of trees will have more distinct rings in Oman – those watered regularly as on a farm or trees growing in the wild? Give reasons for your answer.