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Trees are dependent upon certain soil and atmospheric conditions which influence their growth and development.

1. INFLUENCE OF MOISTURE

The form of the tree and its growth and structure depend greatly upon the supply of moisture.
Bald Cypress (Hydrophyte)
Botanists have taken the moisture factor as the basis of classification and have subdivided trees into those that grow in moist places (hydrophytes), those that grow in medium soils (mesophytes), and those that grow in dry places (xerophytes).
Joshua Tree (Xerophyte)
Water is taken up by the roots of the tree from the soil. The liquid absorbed by the roots carries in solution the mineral salts—the food of the tree—and no food can be taken up unless it is in solution.
Joshua Tree (Xerophyte)
Much of the water is used by the tree and an enormous amount is given off in the process of evaporation.

These facts will explain some of the fundamental principles in the care of trees.

To a tree growing on a city street or on a lawn where nature fails to supply the requisite amount of water, the latter must be supplied artificially, especially during the hot summer months, or else dead branches may result.
Sprinklers
Too much thinning out of the crown causes excessive evaporation, and too much cutting out in woodlands causes the soil to dry and the trees to suffer for the want of moisture.
Tree Without Water
This also explains why it is essential, in wooded areas, to retain on the ground the fallen leaves. In decomposing and mixing with the soil, the fallen leaves not only supply the trees with food material, but also tend to conserve moisture in the ground and to prevent the drying out of the soil. Raking off the leaves from wooded areas, a practice common in parks and on private estates—hurts the trees seriously.
Tree Without Water
Some soils may have plenty of moisture, but may also be so heavily saturated with acids or salts that the tree cannot utilize the moisture, and it suffers from drought just the same as if there had been no moisture at all in the soil. Such soils are said to be "physiologically dry" and need treatment.
Salty Soil
In the development of disease, moisture is a contributing factor and, therefore, in cavities or underneath bandages where there is likely to be an accumulation of moisture, decay will do more damage than in places that are dry and exposed to the sun.
Mossy Bark

Directions

Study the lesson for one week.

Over the week:

  • Read the lesson.
  • Review the synopsis.
  • Recite aloud the vocabulary words and their definitions.
  • Learn the concepts.
  • Complete the enrichment activities.
  • Study the review questions.

Synopsis

This lesson overviews moisture from the soil and in the atmosphere as a requirement of trees. Trees that grow in moist places are called hydrophytes, trees that grow in medium soils are called mesophytes, and trees that grow in dry places are called xerophytes. Either too little water or too much water can harm trees. For example, too much moisture is a contributing factor to the development of disease in trees.

Vocabulary

Moisture: A moderate degree of wetness.
Atmosphere: The gases surrounding the Earth.
Botanist: A person engaged in botany, the scientific study of plants.
Hydrophyte: A plant that lives in or requires an abundance of water, usually excluding seaweed.
Mesophyte: Any normal terrestrial plant that grows in environments that have an average supply of water.
Xerophyte: Any plant suited for life in a habitat where water is scarce, such as in a desert.
Transpiration: The loss of water by evaporation in terrestrial plants, especially through the stomata; accompanied by a corresponding uptake from the roots.
Stomata: The tiny pores in the epidermis of a leaf or stem through which gases and water vapor pass.
Evaporation: The process of a liquid converting to the gaseous state.

Concepts

PROPERTIES OF WATER AND TRANSPIRATION

  1. All matter is made up of tiny particles called atoms. There are different types of atoms, such as hydrogen, oxygen, sulfur, gold, and neon.
  2. Water is made of tiny molecules consisting of two hydrogen atoms (H) and one oxygen (O) atom bonded together.
  3. Find the molecules of water in the diagram below.
  4. The oxygen atom is slightly negative and the hydrogens atoms are slightly positive.
  5. This means that the water molecules are weakly attracted to one another and tend to stick together (see Activity 4).
  6. Leaves have tiny pores called stomata (see green pores) through which they lose water via evaporation.

As water evaporates through the stomata, the attractive forces between water molecules pulls more water up through the roots. This process is called transpiration.

Enrichment

Activity 1: Narrate the Lesson

  • After reading or listening to the lesson, narrate the lesson aloud using your own words.

Activity 2: Study the Lesson Pictures

  • Study the lesson pictures and describe how they relate to the lesson.

Activity 3: Conduct an Experiment: The Fullest Glass

Note: This phenomenon occurs because water molecules are attracted to each other (see Concepts Section).

Materials

  • One glass per child
  • Pennies
  • Water

Directions

  • Fill the cups of water up to the brim.
  • Add one penny at a time and watch the water bulge form at the top of the glass.
  • Who can add the most pennies without spilling?

Activity 4: Take a Nature Walk

  • Bring a small sketchbook and embark on a nature walk.
  • Seek out trees growing in different conditions with regard to moisture - along a river, from a dry rocky outcrop, in a swamp, in a field, etc.
  • Observe and sketch the trees, including their structures and habitats.
  • Use the gathered information to create the field book entry.

Activity 5: Complete a Field Book Entry   

After your nature walk, complete page 31 in 'Science Field Book for Fourth Grade.'

Review

Question 1

Compare and contrast hydrophytes, mesophytes, and xerophytes.
1 / 3

Answer 1

All are trees that require water, however hydrophytes grow in moist soils, mesophytes in moderate soils, and xerophytes in dry soils.
1 / 3

Question 2

How does transpiration help draw moisture up from the roots to the leaves of a tree?
2 / 3

Answer 2

As water evaporates through the stomata, the attractive forces between water molecules pulls more water up through the roots. This process is called transpiration.
2 / 3

Question 3

Can too much moisture harm trees?
3 / 3

Answer 3

Too much moisture is a contributing factor to the development of disease in trees.
3 / 3

  1. Compare and contrast hydrophytes, mesophytes, and xerophytes. All are trees that require water, however hydrophytes grow in moist soils, mesophytes in moderate soils, and xerophytes in dry soils.
  2. How does transpiration help draw moisture up from the roots to the leaves of a tree? As water evaporates through the stomata, the attractive forces between water molecules pulls more water up through the roots. This process is called transpiration.
  3. Can too much moisture harm trees? Too much moisture is a contributing factor to the development of disease in trees.

References

  1. 'Studies of Trees' by Jacob Joshua Levison. gutenberg.org/ebooks/16116. n.p.

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