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What determines growth of trees?

  • Genetics
  • Space
    • Sunlight, CO2 to production of Carbohydrates
    • Constrained by:
      • The enironment
        • Sunlight, water, nutrients, physical space (i.e., growing space)
      • Genetics:
        • Adaptations (natural selection)
        • Random (e.g., bottleneck effects)
  • Interaction of genetics (g) and environment (e) determines growth
    • Growth = GXE

How do trees allocate carbohydrates?

Primarily survival:​

  1. Respiration maintenance
  2. Foliage renewal
  3. Fine root renewal
  4. Reproduction

Secondary allocation: Primary growth​

  • Terminal and lateral branch expansion
  • Root expansion
  • Phloem renewal

Tertiary allocation: Secondary Growth​

  1. Xylem renewal, basal increments
  2. Production of resin/gum/chemicals for protection

How are carbohydrates used?

ProcessDominantCo-DominantSuppressed
Respiration26%29%50%
Secondary Growth42%41%8%

Tree Crown

Production Centre:​

Through photosyntehsis, sunlight and carbon dioxide is transformed into carbohydrates

  • Most productive area is above canopy horizon

Indicators for productive crowns

  • Crown ratio (% of tree height)
  • Crown diameter

Crown and stem form

Crown and stem form is determined by two types of growth "behaviors":

  • Decurrent: Grows towards the light
  • Excurrent: Growth is geocentric - towards the center of the earth

Strong differences between species, but also within species

Apical dominance: Important for wood quality

Tree Roots

  1. Plate root systems
  2. Sinker root systems
  3. Heart Root System
  4. Tap Root System

Stem Function

  • Heartwood vs. sapwood

Sapwood:

  • Phloem: Downward transportation of carbohydrates from the leaves
  • Xylem: Transportation of water through xylem conduits
  • Storage of carbohydrates in the parenchyma

Heartwood:

  • Completely dead center area; stability

Defense:

  • Bark, resin, gum

Physical support of the crown

Stem growth​

  • Ring width decreases towards the bark
  • High quality wood with narrow rings grows on old trees
  • Ring width by stem height:
    • Thicker rings at the top

Wood Density​

  • Indicator for strength, stiffness, pulp yield, etc.
  • Strong effect of ring age:
    • Juvenile vs. mature wood

Branch Thickness: Thick branches develop when physical space is abundant

  • Branch thickness is top indicator of wood quality

Takeaways​

  • Primary and secondary growth are low priority for trees
  • Allocation to secondary growth is reduced for trees with smaller crowns
  • Crown characteristics are key variables to predict future productivity
  • Stem form is influenced by genetics and the environment
  • Important to manage for stem form and select for apical dominance
  • Wood quality is higher on trees with smaller rings and low proportion of juvenille wood (older trees)