Structure and Function of Forest Trees

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

2. 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. 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. 

4. 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. 

5. 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. 

6. 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

7. 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

8. 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.

9. Apical meristem

10. Shoot diagram

11. 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

12. 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

13. 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.

14. Root growth • Similar to shoots • Taproot is the 1st 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.

15. 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.

16. 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.

17. 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.

18. Root growth • Mychorrizal fungi

19. 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.

20. 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

21. 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.

22. 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.

23. 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.

24. 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.

25. Cross section

26. Cross section

27. Cross section

28. 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.

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

30. 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

31. Xylem and phloem

32. Tracheids Similar function as xylem in hardwoods, support and conduction

33. 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.

34. Cambium

35. Cork cambium of cork oak

36. Leaf structure

37. Gas movement through leaves

39. 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.

40. Respiration • The chemical equation for respiration is: • (CH2O)6 + 6 O2 6 CO2 + 6 H2O • 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.

42. Growth substances or plant hormonesEffects very complex and not always understood.

43. 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.

44. 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.

45. Transpiration

46. Macronutrients

47. Micronutrients

48. 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.

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

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