Tree Growth and Wood Formation

1. FW1035 Lecture 1 Bowyer et al, Chapter 1 Tree Growth and Wood Formation • Basic macroanatomy of a tree stem • How a tree grows

2. Coast Redwood Sequoia sempervirens Tallest Living Individual: 380 feet (~2000 yo) Weight: up to ~2.7 million lbs Saturn V Rocket Height: 383 feet Weight: 6.7 million lbs

3. Mountain Ash Eucalyptus regnans Tallest Living Individual: 330 feet (~400 yo) “World’s tallest flowering plant.”

4. Planes-of-View in Wood Samples Transverse Plane (Cross-Section) Radial Plane Tangential Plane

5. Stem Macroanatomyand Transverse Anatomical Directions Sapwood Heartwood Longitudinal Direction is perpendicular to the transverse directions. Radial Tangential Vascular Cambium

6. Stem Macroanatomyand Transverse Anatomical Directions Sapwood Heartwood Longitudinal Direction is perpendicular to the transverse directions. Radial Tangential Vascular Cambium

7. Basic Wood Anatomy Microanatomy Annual Ring Softwood Hardwood

8. Ray Pore Ray An Electron Photomicrograph of Sugar Maple

9. Pore Ray Annual Ring Light Photomicrograph of Sugar Maple

10. Function: Transport from thephloem towards the pith. Rays in Wood • Ray cells are elongated in the radial direction • Width, height, density, and appearance vary - useful for ID Annual Ring Latewood Earlywood

11. Major Tissues in the Tree Stem Outer Bark • Protection Phloem (Inner Bark) • Transport (down) Cambium • Radial growth Xylem (Wood) • Transport (up) and mechanical support

12. Transport in Trees Sap - a water solution of sugars, minerals, O2, and growth regulators • Roots – water, dissolved minerals, other nutrient uptake • Xylem - flow up toward leaves • Phloem - downward flow (sugars and regulators) • Rays - flow towards the center of the tree (pith)

13. Diameter Diameter growth occurs at the lateral meristem (vascular cambium) Tissues formed are “secondary tissues” secondary xylem secondary phloem Height Height growth and branch shoot elongation occurs only at their tips Apical meristem Apical meristems only produce “primary tissues” primary xylem primary phloem Growth Tissues - “Meristematic Tissues” Meristem= Plant tissue which contains cells that have the capacity to divide to make new cells.

14. The Apical Meristem

15. The Apical Meristem Epidermis • single layer of thick, waxy cells that prevents moisture loss Procambium • meristematic region that provides growth • cell division produces primary phloem and xylem • further differentiation gives rise to the vascular cambium • primary xylem and pith is different from secondary xylem (wood)

16. Vascular Cambium The Vascular Cambium Lateral meristematic region • Division of cells here produces secondary xylem and secondary phloem tissues • Diameter expansion forces tangential elongation of phloem cells • Epidermis and primary phloem layers eventually fall off • Dead phloem cells compose the outer bark

17. Vascular Cambium Two Cell Types • Fusiform Initials - divide to produce new xylem or phloem cells that have longitudinally elongated shapes • Ray initials - short, rounded cells that divide to produce new xylem or phloem ray cells.

18. Cell Division Direction Cells can divide 2 ways: • Periclinal division- cells divide along the longitudinal axis of the stem (responsible for diameter growth of cambium) • Anticlinal division- cells divide in radial direction (responsible for circumference growth of tree, in general)

19. Periclinal Division After Periclinal division, one cell remains a cambial initial, the other a xylem or phloem “mother” cell. Mother cells may divide several more times before differentiating into mature xylem or phloem cells, or immediately differentiate into a xylem or phloem cell without further division.

20. Section of a young basswood (Tilia spp.) stem

21. Monocot Trees (E.g. Palms) Grow Differently.