Tree biology
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  • Organs- roots, stem, leaves, flowers, fruit.Meristems- undifferentiated cells
  • Ground tissue- when a stem is green, it is where photosynthesis occurs. This is storage and support. Becomes less prominent as a stem gets larger. Most of the tissue in a tree trunk is xylem.Pith never enlarges with diameter growth- in a mature tree, it’s still very tiny in the center of the wood (xylem)
  • Remember, Meristems are regions of cellular growth. Cambiums are Secondary Meristems, meaning they are responsible for lateral growth
  • 1- conduction of water and dissolved minerals2- support3- carbohydrate storage4- defense against disease and decay
  • Usually only a few rings in the outer portion of the wood conducts water- sapwood. Heartwood is nonconducting tissue that contains no living cells.
  • Non living
  • Trees with wide vessel elements early in the year are called ring porous. diffuse porous.
  • Nonliving in the rest of the wood
  • Adventitious tissues contain dormant buds that produce epicormic sprouting when the tree is under stress or loses its normal buds.Axial or radial transport
  • So remember we have the cork cambium that produces the outer bark. The vascular cambium produces both the xylem and the phloem.Phloem moves the sugars produced in leaves during photosynthesis to other parts of the tree for storage and consumption. Unlike xylem, which creates diameter growth each year, old phloem gets crushed and resorbed or becomes part of the bark.
  • Very slow process, requires energy to move sugars.
  • Think of these as the “engine room”Phloem moves sugars both up and down the stem. Xylem only moves water up. Stump treatment.Source and sink- sugar transport
  • Leaves are where all the action takes place… we’ll get to those in a moment.Vascular tissues, we covered that. Cuticle. Photosynthesis- Palisade parenchyma and spongymesophyll. Chloroplasts, chlorophyll. Transpiration- loss of water which moves water up the xylem. Stoma. Spongy mesophyll- flexibility, water vapor among.
  • The leaves of broadleaved plants are thin and are not protected by any thick coverings. The cell fluids are usually watery and freeze readily. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. The separation layer also protects the stem from moisture loss and disease.
  • 2-3x diameter of crownMost are within the top 18” soil
  • Large roots-Anchorage, storage, conductionAbsorbing roots- have cells modified into root hairs for taking up water and mineralsTap root- usually get choked out or restricted in downward growth in mature trees.Apical meristemGeotropismOsmosis
  • Ground tissue- bulk of the roots- for storage, support, and uptake.
  • Chloroplasts, chlorophyll, why leaves are greenBreaking the carbohydrate bonds releases energy, used for all its biological functions
  • Transpiration is the loss of water from the leaves through evaporation.It moves water and mineralsup the tree, like sucking water up a straw. It also cools off leaves.Rate of water movement depends on T, humidity, and soil moisture.Guard cells around stoma open and close to prevent evaporation, but also allow CO2 in for photosynthesis. Usually open during the day.Cuticle, leaf hairs, sunken stomata- adaptations for dry/hot conditions.
  • Excurrent- apical dominance (apical bud). Effects of removal.Pine tree rarely looks decurrent, due to it’s genetics.However, will a tree planted on an urban street attain the size that the same tree in the woods will?
  • 1- upper and lower vascular elements plug- limit vertical spread of decay.2- wall formed by the last cells of the growth ring (axial parenchyma)- limits internal spread3- wall formed by ray cells- limiting lateral spread4- strongest, new growth ring that forms after injury
  • A top down view.None of these walls are infallible.
  • Monocot- like grassesIrregularly scattered vascular bundles. Since there’s no rings and annual production of xylem, palms never increase in diameter.Vascular tissue embedded in very strong fibrous tissue. Parenchyma cells for storage.No CODITOnly ONE apical meristem, if lost, it will die.
  • Seedling will grow a single root, then all others are adventitious coming from the base- root initiation zone.Most roots are close to the stem, forming a root mat.No secondary growth, never increase in diameter.Also form mycorrhizal associations


  • 1. Tree Biology ISA Arborist Certification Study SessionAngela Belden, Resource Forester Assistant, Missouri Department of Conservation
  • 2. Tree Anatomy Basic structure- cells, tissues, organs, organism. Growth- ◦ Meristems  Apical meristems  Lateral meristems
  • 3. Stem Anatomy
  • 4. Stem Anatomy- early
  • 5. Stem AnatomyThe cambiums- secondary meristems Cork cambium Vascular cambium
  • 6. Stem Anatomy- cambiumsCork cambium(phellogen)--the region ofcell divisionthat forms theouter barktissues.
  • 7. Stem Anatomy- cambiumsThe vascularcambium-- theregion of celldivision thatproduces radialgrowth.It forms the phloem& xylem.
  • 8. Stem Anatomy- xylemThe xylemincludeseverything insidethe vascularcambium. Wood!
  • 9. Stem Anatomy- xylemThe rings seen inmany treesrepresent onegrowth increment.Growth ringsprovide the graintexture seen inwood.
  • 10. Stem Anatomy- xylemTracheids– cellsused forconducting water& minerals.Conifers onlyhave tracheidsand are thusconsideredsoftwoodedspecies.Hardwood specieshave vesselelements in
  • 11. Stem Anatomy
  • 12. Stem Anatomy- xylemFibers are cellswith heavilylignified wallsmaking them stiff.Many fibers insapwood are aliveat maturity andcan be used forstorage.
  • 13. Stem Anatomy- xylemParenchyma–living cells usedfor storage, celldivision, anddecay defense.Axial parenchymaruns parallel withthe growth rings.
  • 14. Stem Anatomy- xylemParenchyma–living cells usedfor storage, celldivision, anddecay defense.Rays are radialparenchymacells. Parenchyma cells give rise to adventitious tissues.
  • 15. Stem Anatomy- barkThe bark iseverything outsidethe vascularcambium.
  • 16. Stem Anatomy- bark: phloemPhloem tissuemakes up theinner bark.However, phloem is livingvascular tissueformed from thevascularcambium.
  • 17. Stem Anatomy- phloemSieve tubeelements– cellsthat activelytransportcarbohydratesfrom the leavesdown the stem.Conifers havesieve cellsinstead.
  • 18. Stem Anatomy- phloemCompanioncells–providesieve tubeelements withneededmetabolites.Conifers havealbuminous cellsinstead.
  • 19. Leaf Anatomy
  • 20. Autumn Leaf FallTrees thatkeep theirleaves areevergreens,trees thatlose theirleaves aredeciduous. Abscission zone– area at the base of the petiole that breaks down and causes leaf (or fruit) drop
  • 21. Autumn Leaf FallDeclining intensity of sunlight triggers theprocesses leading up to leaf fall in autumn. Chlorophyll reduces, unmasking carotenoids. Clogged phloem veins trap sugars in the leaf and promote production of anthocyanins.
  • 22. Root Anatomy
  • 23. Root Anatomy
  • 24. Root Anatomy
  • 25. Root Anatomy
  • 26. Root Anatomy
  • 27. Mycorrhizae Is a symbiotic relationship- mutually beneficial- with a tree and a fungus Fungus increases surface area of roots Facilitates uptake of minerals that are otherwise unavailable Fungus gets to share the tree’s carbohydrates.
  • 28. Photosynthesis & Respiration
  • 29. Transpiration
  • 30. Tree Growth & DevelopmentTree shape, height, etc, are determined by genetics, but its environment plays a part as well.
  • 31. Tree Growth & Development Plant growth regulators are hormones that work in concert. ◦ auxin, cytokinins, gibberelins, ethylene, abscisic acid…etc. Environmental triggers ◦ Budbreak ◦ Leaf fall ◦ Seed germination ◦ Geotropism ◦ Phototropism
  • 32. Tree DefensesChemical – to dissuade animal/insect feeding, stop pathogen infection, or help prevent rotMechanical – Thick bark, thorns, leaf hairs, thick cuticles – Shiny wax, leaf hairs – CODIT (Compartmentalization of Decay In Trees)
  • 33. CODITCompartmentalizatio nOfDecayInTrees
  • 34. CODIT
  • 35. Palms- StemPalm stem-monocot Tree stem- diocot
  • 36. Palms- Roots Root initiation zone Root mat
  • 37. Image credits: Dr. Ed Gilman and Scott Jones, University of Florida Sharon Lilly, ISA Arborists’ Certification Study Guide Natural Resources Canada website Kathy Ripke, University of Minnesota Department of Horticultural Science Taiz and Zeiger, 1998. Plant Physiology, 2nd ed.