Structure and Function of Forest Trees Kenneth Williams Fisheries Extension Specialist Langston University Aquaculture Extension Program Elements of Forestry

Trees Longest lived organisms on earth. Heights of 100 meters diameters of 10 meters. Due to longevity, trees must withstand extremes of climate. Trees allocate much of their energy to diameter growth. Not so in other plants. Physiology of trees a young science.

3 TISSUE SYSTEMS OCCUR IN PLANTS Dermal Tissue System – Function: Protection from the environment and water loss. Vascular Tissue System – Function: Conduction of water, nutrients, sugars and hormones throughout the plant. Ground or Fundamental Tissue System – Function: Storage, support, filler tissue and site of photosynthesis.

Dermal Tissue System Function: Protection from the environment and water loss. Tissues: a) epidermis - single layer of cells on primary (herbaceous ) plant parts. b) periderm or bark - a corky tissue that replaces epidermis on secondary (woody) plant parts.

Vascular Tissue System Vascular Tissue System Function: Conduction of water, nutrients, sugars and hormones throughout the plant. Tissues: a) xylem - conducts water and nutrients up roots, stems and leaves. b) phloem - conducts water, sugar, hormones, etc. primarily down roots, stems and leaves, but also can move up at times.

Ground or Fundamental Tissue System Function: Storage, support, filler tissue and site of photosynthesis. Tissues: a) cortex - outer region of stems and roots. b) pith - center of stems. c) mesophyll - middle of leaves and flower petals

PLANT ORGANS, TISSUE SYSTEMS, TISSUES AND CELL TYPES 3 TISSUE SYSTEMS OCCUR IN PLANTS Dermal Tissue System Function: Protection from the environment and water loss. Tissues: a) epidermis - single layer of cells on primary (herbaceous ) plant parts. b) periderm or bark - a corky tissue that replaces epidermis on secondary (woody) plant parts. 2) Vascular Tissue System Function: Conduction of water, nutrients, sugars and hormones throughout the plant. Tissues: a) xylem - conducts water and nutrients up roots, stems and leaves. b) phloem - conducts water, sugar, hormones, etc. primarily down roots, stems and leaves, but also can move up at times. 3) Ground or Fundamental Tissue System Function: Storage, support, filler tissue and site of photosynthesis. Tissues: a) cortex - outer region of stems and roots. b) pith - center of stems. c) mesophyll - middle of leaves and flower petals

MERISTEMS AND GROWTH Primary Growth - growth in length that gives rise to primary (herbaceous) tissues called the primary plant body. Apical meristem or apex - the growing points located at the tips of stems and roots Secondary Growth - growth in width or diameter that gives rise to secondary (woody or corky) tissues called the secondary plant body.

Apical meristem

Shoot diagram

Shoot growth Fixed shoot growth – 1 period of spring growth, often over quickly. Ex. Dogwood. Free shoot growth – continual growth throughout season (most in spring) ex. Cottonwood Recurrent flushing – several periods of growth throughout season. Ex. White oak

Shoot growth Free growth – fast growing hardwoods – poplar, willow, cottonwood and sweetgum. Fixed growth – slower growing hardwoods and conifers – northern oak, sugar maple, white pine. Free growth Ex. willow Fixed growth Ex. Red oak

Recurrent flushing – several periods of growth throughout season. Ex. White oak and fast growing conifers ex. Red pine. Each growth spurt ends in new bud formation. Then the new buds grow in the next cycle 3-7 times per year.

Root growth Similar to shoots Taproot is the 1 st root to grow. Branch roots form off of it. Taproot may not persist. Root growth depends on soil and moisture conditions/ Ex. Red maples on upland sites have large taproots but have a shallow rot system in poorly drained soils.

Root growth Most growth in length occurs in the long roots. Most surface area is in the short of fine roots. The fine roots are also called feeder roots. They take up nearly all the water and nutrients. Larger roots provide a conduction path and mechanical support.

Fine roots, the mycorhizae Most of the fine roots are actually a fungus called mycorhizae plus tissues from the tree root. Mycorhizae increase root surface area, increase water and nutrient uptake and increase resistance to pathogens and nematodes.

Fine roots, the mycorhizae The mycorhizae receive most of its food from the host tee. This is a very important fungal/tree partnership and crucial to tree survival. All trees are mycorhizal Without this fungus trees will stunt and may die.

Root growth Mychorrizal fungi

Flowering and reproduction Flowers develop as vegetative shoot apical meristem transforms into a reproductive meristem. Flower shoots have a determinate growth pattern, they grow, flower and meristem disappears.

Conifer reproduction Male and female cones are borne separately on the same tree. Male cones are usually lower than female cones to reduce self pollination. Male cones are small (1-2 cm) release pollen in spring 1 year after forming. Female cones large, seeds released 2 years after pollination. Conifers are wind pollinated

Angiosperm reproduction Pollination may be by wind, insects, birds or bats. Flower and seed development may be in a few weeks ex. Poplars or several years, ex. Some oaks. Male and female reproductive parts may be in the same flower or male and female flowers on separate trees.

Angiosperm reproduction Seeds dispersed in spring can usually germinate immediately. Ex.silver maple Many trees disperse seeds in fall and winter. These seeds remain dormant until spring. Ex. Some oaks Some seeds can remain in the soil for years until conditions are right for germination.

Secondary growth Diameter growth occurs In the vascular cambium, the large sheet of cells below the bark. It ensheaths the entire plant body in a single layer of cells.. During growth cambium divides to produce xylem to the inside and phloem to the outside of this tissue.

Secondary growth Cambium activity is greater in spring than summer making the cells at this time larger. This results in annual rings. Usually 1 ring per year. Rings may be missing or incomplete or sometimes more than 1 per year.

Cross section

Xylem 3 functions: Conduction of water by cells called vessels. These cells are dead. Support by thick walled vessel cells. Storage – parenchyma cells transport and store starches. These cells may be in rays. Hardwoods more efficient than conifers in moving water due to structural differences.

Heartwood Healthy heartwood (dead parenchyma cells) Fungus rotted heartwood Sapwood (living parenchyma cells) can be 300 yr. old

Phloem Cells form sieve tubes – vertically arranged files of living cells with end walls that are porous. Phloem transports sugars and organic substances formed in leaves to other parts of the tree and roots. Phloem is only functional a few years before the cells are crushed in tree growth

Xylem and phloem

Tracheids Similar function as xylem in hardwoods, support and conduction

Cork cambium and bark Periderm or outer bark formed from the cork cambium which originates in the epidermis. Cells to the outside of the cork cambium have a thick layer of a waxy substance called suberin. Suberin is water repellant and resistant to bacteria and fungus. New periderms are continuously formed. Cork cells are dead at maturity.

Cambium

Cork cambium of cork oak

Leaf structure

Gas movement through leaves

Respiration Respiration provides energy for growth, maintenance and the construction of new cells. Respiration is the opposite of photosynthesis. The oxidation of sugars o carbon dioxide and water, releasing usable chemical energy.

Respiration The chemical equation for respiration is: (CH 2 O) O 2 6 CO H 2 O Photosynthesis occurs mostly in leaves. Respiration occurs in all living cells. Carbohydrates not used in respiration are stored as starches. An important tree reserve. Many trees have enough stored starch to re- foliate the tree 3 times. This allows the tree to recover from insect, weather and disease damage.

Growth substances or plant hormones Effects very complex and not always understood.

Secondary compounds 1000’s of chemicals produced by trees, many with no known function. Some may be defensive. Many have commercial value, ex. The terpenoids.

Water Single most important factor in tree growth and survival. Water makes up 80% of living cells. Most water in trees lost through transpiration. There is a continuous column of water from soil to roots to leaves in trees. This is called the soil-plant-atmosphere continuum.

Transpiration

Macronutrients

Micronutrients

Light Shade tolerance – ability of a tree to grow in the shade of other trees. Photoperiod – duration of daylight. Provides signals for bud set and leaf fall and other physiological functions.

Temperature Trees grow between 0C – 40C They become dormant when temperatures begin to drop.

Tree forms Excurrent growth form – single main stem ex. Pine tree. Decurrent growth form – multiply stems, ex. Elm tree.

Tree forms Decurrent growth Excurrent growth

Tree longevity Oldest bristlecone pine – 4844 years old Found in Nevada 1965.

Tree longevity Growth rate slows as trees age. They become less resistant to pests and disease. May be killed from storms, fungal rot etc. Physiology of tree longevity poorly understood.

Giant sequoia over 300 ft. high Largest trees

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