How Trees Grow

The buds, root tips, and cambium layer are the three growing parts of the tree. Buds elongate the branches and widen the crown (branches and leaves), the cambium layer adds diameter to the tree, and the root tips grow in length to support the growth of the tree.

Additionally, the roots absorb water and nutrients from the soil, which are then carried up through the sapwood or xylem to the leaves. Water and nutrients are then combined with carbon dioxide from the air and sunlight to make food through a process known as photosynthesis. This food is carried by the inner bark or phloem to all growing parts of the tree, even back down to the root tips

Click here to go to the Life Cycle of a Tree.

Buds

Buds are tiny leaves, stems and flowers located in a small case at the base of each leaf. Buds are formed during the summer months for the following year. Each spring as the tree comes out of dormancy, the scales fall off and the tree’s leaves, stems and flowers open up and grow.

The tree increases each year in height and crown spread of branches when the buds produce a new growth of twigs. Air supplies carbon which is absorbed through stomata or small holes or pores on the leaf surfaces. Leaves process the food obtained from carbon, sunlight, water and nutrients from the soil, and release moisture by transpiration. Trees produce oxygen as a byproduct through the photosynthesis process.

Roots

Root tips produce new growth and absorb water and nutrients from the soil. The taproot grows straight down while the lateral roots branch out. Additionally, the roots provide anchorage support for the tree. Roots use oxygen from the soil to carry out the growth process. Compaction of soil or an abundance of water is usually harmful to tree growth. However, some trees, such as baldcypress, have adapted to grow in wet conditions with a limited supply of oxygen.

Soils

Soil is one of the determining factors in what vegetation is present in an area. Some of the influences on vegetation species present include: soil acidity, alkalinity and salinity; saturation; topsoil and subsoil characteristics; soil texture (sand, silt, clay); soil structure and compaction. There are thousands of soil series. New series and phases (subdivisions) are classified everyday. Each series has different characteristics although there may be some similarities seen in other series.

Trunk

The outer bark protects the inner wood layers from injuries, pests and disease. Hidden beneath the bark of the tree are the wood layers. The inner bark or phloem carries synthesized food from the leaves to the cambium layer and other growing portions of the tree. The cambium layer is microscopic and actively builds the cells which make more wood and bark. Sapwood or xylem transports sap or water and nutrients from the roots to the leaves. The center of the tree, which provides strength and support, is the heartwood (dead wood or inactive wood).

Seasonal Changes

The majority of tree growth occurs in late spring and early summer. During most of the growing season, trees (plants) produce a material called chlorophyll. Chlorophyll enables plants to convert water and carbon dioxide in the presence of sunlight into carbohydrates, which plants use for food. This process is known as photosynthesis. Chlorophyll is what gives plants their green color. Tree leaves have other colors present most of the time, but the green chlorophyll is so dominant that it masks the other colors until fall.

Late spring and early summer is the time, typically, when flowers become fruit and the crown develops a full canopy of leaves. In addition, a new layer of wood is added around the trunk, branches, and roots. These layers are called growth rings. A light ring (or early wood) grows during this season when there is typically more rain. The shape and width of growth rings reflect what type of year the tree is experiencing. A wide growth ring may indicate that the tree had a year with optimum conditions. A narrow growth ring may be the result of a drought, competition with other trees for nutrients and sunlight, or other factors.

In the fall, production of the woody layers slows down and a dark growth ring or late wood forms. Most trees disseminate or disperse their fruit around this time thereby planting seeds nearby for reproduction. Or some of the fruit may have been eaten by birds or animals, passed through the digestive system and/or carried to new locations for dispersal. The seeds from the fruit will lie dormant until germination begins in early spring.

Also during this season, chlorophyll production slows, the chlorophyll in the leaves breaks down, and the green color fades. When this happens, yellow and orange pigments, called carotenes and xanthophylls, become visible. Red, pink, and purple pigments or anthocyanin may also develop. The most important environmental factors controlling autumn leaf coloration are temperature, light, and water availability. Cool temperatures (above freezing), drought, and bright sunny days favor the production of anthocyanin.

Maples, sassafras, sweetgum, and sumac produce large amounts of anthocyanin, which accounts for their deep red colors. Some trees do not form anthocyanin pigments. Hickory and elm leaves are an example of this since they often display bright yellow autumn colors. Oak leaves often turn brown with very little yellow or orange coloration. This is because they contain large amounts of tannin or brown color and relatively few carotenes.

For more information on the changing of leaf color, click here (link to article http://txforestservice.tamu.edu/main/popup.aspx?id=209)

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Educator Extensions

Project Learning Tree (PLT) is an award-winning environmental education program designed for teachers and educators of students in pre-kindergarten through grade 12. The PLT Activity Guides are available from participating in a one day workshop. Find more information about Texas PLT and workshops near you at http://plttexas.org/. If you can’t find a workshop in your area, contact us to schedule one at your facility.

The following activities relate to How Trees Grow from the PLT PreK-8 Activity Guide:

Grades PreK - 2

  • Every Tree for Itself (#27)
  • How Plants Grow (#41)
  • Have Seeds, Will Travel (#43)
  • The Closer you Look (#61)
  • To Be a Tree (#62)
  • Tree Factory (#63)
  • Bursting Buds (#65)
  • Tree Cookies (#76)
  • Signs of Fall (#78)
  • Tree Lifecycle (#79)

Grades 3 – 6

  • Every Tree for Itself (#27)
  • Have Seeds, Will Travel (#43)
  • The Closer you Look (#61)
  • Tree Factory (#63)
  • Bursting Buds (#65)
  • Tree Cookies (#76)
  • Trees in Trouble (#77)
  • Signs of Fall (#78)
  • Tree Lifecycle (#79)

Grades 6 – 8

  • Every Tree for Itself (#27)
  • Have Seeds, Will Travel (#43)
  • Trees in Trouble (#77

For more information about Texas PLT, TEKS correlations and how you can get these resources:

Visit - www.plttexas.org or www.plt.org

Texas Project Learning Tree is sponsored by:
  • Texas Forestry Association
  • Texas A&M Forest Service

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Life Cycle of a Tree

As with all living things, trees have a life cycle – from conception (seed), to birth (sprout), to infancy (seedling), to juvenile (sapling), to adult (mature), to elderly (decline), and finally to death (snag/rotting log). Because trees are renewable, the cycle begins again either artificially through planting or naturally with regeneration of new seeds.

For the life cycle to run full circle, external and internal conditions must be favorable for the tree. This includes adequate space, water, nutrients, and sunlight for the individual species. The tree’s chances of growth and survival through a complete cycle greatly improve with these conditions. However, even with optimum conditions, various stresses such as insects, diseases, injuries, competition from other trees, weather, and time itself weaken the tree and can cause it to die. Although a cycle may be stopped at any time for many different reasons, a new cycle can begin again through varying regeneration methods (seed bank, new seed, root or stump sprout, transplanting, etc.). It may be the same tree, a new tree, or another tree of a different species but all trees originate from seeds.

Seed

Think about which came first - the tree, or the seed? Regardless of what you believe, the more you learn about them, trees are simply amazing. Seeds come in a wide variety of shapes, weights, colors, and sizes, depending on the species. All seeds develop from male and female parts of the trees producing fruits but not all of them are easily recognizable or edible. Some seeds are contained in a protective nut like an acorn, pecan, or hickory. Other seeds are found in fleshy fruits, like the black cherry, mulberry, or persimmon. The fruit of a pine is a cone and the seed is winged and resembles a miniature helicopter when falling in the wind from an open pinecone.

Wind, water, animals, and people disperse seeds to a wide range of landscapes including the forest floor, open fields, yards, rocky slopes, and roadsides. Anywhere the conditions are favorable for germination, seeds will sprout and grow.

Sprout

An embryo is within each seed, but not all seeds will germinate. Favorable environmental conditions enable the embryo to grow, expand, and break through the seed coat using the stored food supply of the seed for the necessary energy to grow. The root grows downward to the soil to anchor the sprout and search for water and nutrients, while the sprout emerges from the ground seeking sunlight. Ideally, the sprout will find light and then the leaves, needles, or scales will develop further to allow the tree to make its own food through photosynthesis.

Seedling

The sprout persistently grows and begins to develop woody characteristics. The soft green stem begins to harden, change color, and develop a thin protective bark. Leaves or needles develop and continue to search out light. The root grows and branches down and out resembling an upside down underground tree with a flattened top. The majority of the tree’s roots are in the upper portions of soil to absorb available water and nutrients but also to breathe. Like us, tree roots need oxygen or they will die. The seedling must compete with other trees and plants for its share of nutrients, water, sunlight, and space. Other threats include fire, flood, drought, ice and snow, disease, insect attacks, and the threat of being consumed by animals. At this stage, the tree is most susceptible to being killed. If it can survive these early years without harm, the seedling is well on its way to the next phase in the cycle.

Sapling

A sapling is a small tree usually between 1 and 4 inches in diameter at 4.5 feet. This is the standard height where a tree’s diameter is measured – diameter at breast height (DBH). Typically, a sapling is the size of a tree that is growing in a commercial nursery for transplanting to your yard. In this juvenile state, the tree is not mature enough to reproduce. However, it is growing rapidly. The sapling encounters similar types of competition and threats to that of a seedling.

Mature

With favorable conditions, a sapling will continue to develop into a mature tree. During this stage in the cycle, each tree will grow as much as its species and site conditions will permit. In addition, flowers develop, reproduction ensues, fruits form, and seed dispersal can now occur.

The optimum time to harvest trees for forest products beneficial to people is during this stage in the lifecycle. In Texas, the majority of products are made from southern yellow pine (loblolly, longleaf, shortleaf, and slash). Hardwoods such as ash, hickory, mesquite, pecan, and oak are also used but southern yellow pine is the main commercially grown species to meet public demand for wood products such as those listed below. A few of the products made from Texas trees include: paper, dimensional lumber, cabinets, molding, doors, pallets, boxes, crates, trusses, fireplace mantels, furniture, oriented strand board (OSB), flooring, crossties, joists, decking, log homes, posts, poles, cooking wood, fencing, fuel, interior finishing, pilings, bridges, animal bedding, mulch, heavy construction timbers, charcoal, shingles, and many more. If a tree is never harvested, over the course of time it continues to provide many other benefits, but eventually will begin to decline.

Decline

At this point, the tree’s survival is determined more by external stresses rather than the tree’s vigor. These stresses take a toll on the tree making it more susceptible to insects and diseases, and it eventually succumbs to a causal agent or the pressures of competition from other more vigorously growing plants adjacent to the tree. The end result is no surprise.

Snag

The life span of a tree is as wide-ranging as the number of tree varieties, yet death is inevitable. Usually it is a combination of factors that finally overcome a tree and cause it to die. Injury, drought stress, followed by disease, rot, root dieback, coupled with a lightning strike and insect infestation is just one of many scenarios. However, sometimes it can be just one factor serious enough to cause mortality. Yet, the cycle does not end here. A standing dead tree, also called a snag, still plays a vital role in the life cycle.

Decomposition takes time. A snag slowly breaks down and returns nutrients to the soil as small limbs, bark, and branches fall to the ground. The snag also provides habitat, cover, and food for wildlife and insects. In turn, animals, insects, and fungi help break down the tree. Eventually, the snag will fall to the ground and gradually return nutrients to the soil where they are taken up again by other trees by providing for their growth.

And, the cycle begins anew.

Educator Extensions

Project Learning Tree (PLT) is an award-winning environmental education program designed for teachers and educators of students in pre-kindergarten through grade 12. The PLT Activity Guides are available from participating in a one day workshop. Find more information about Texas PLT and workshops near you at http://plttexas.org/. If you can’t find a workshop in your area, contact us to schedule one at your facility.

The following activities relate to How Trees Grow from the PLT PreK-8 Activity Guide:

Grades pre K - 2

  • We All Need Trees (#13)
  • Trees as Habitats (#22)
  • Nature’s Recyclers (#24)
  • Every Tree for Itself (#27)
  • Have Seeds Will Travel (#43)
  • Tree Lifecycle (#79)

Grades 3 - 6

  • We All Need Trees (#13)
  • Trees as Habitats (#22)
  • The Fallen Log (#23)
  • Nature’s Recyclers (#24)

Grades 6 - 8

  • Trees as Habitats (#22)
  • The Fallen Log (#23)

Children’s books that help depict a tree’s lifecycle include:

  • The Grandpa Tree by Mike Donahue;
  • The Lifecycle of an Oak Tree by Angela Royston;
  • The Lifecycle of An Oak Tree by Linda Tagliaferro;
  • From Acorn to Oak Tree by Jan Koffke;
  • The Pecan Tree by Barbara Langham

For more information about Texas PLT, TEKS correlations and how you can get these resources:

Visit - www.plttexas.org or www.plt.org

Texas Project Learning Tree is sponsored by:
  • Texas Forestry Association
  • Texas A&M Forest Service

 

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