Tree Biology

Mike SillsRegional Urban Forester, Texas A&M Forest Service Dallas Region

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Tree Biology

• “If you can work on CARS, you can work on ANYTHING.”

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Tree Biology

• “If you can work on CARS, you can work on ANYTHING.”–“If you can work on ANYTHING, then you can figure out how TREES WORK.”

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Tree Biology

Tree Biology

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vacuole Nucleus

mitochondria

roughendoplasmicreticulum

chloroplast

Cell => Tissue => Organ => OrganismCell Wall, Cellulose, Lignin 

Tree Biology

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Tree Biology

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Occurs in cells that contain chloroplasts

Occurs in mitochondria

Tree Biology

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Tree Biology

Tree Biology

• What makes stomata open and close?–Responses to signals from the environment

•Light: stomata are open•Dark: stomata are closed•High CO2 inside leaf: stomata are closed•Low CO2 inside leaf: stomata are open•Drought stress: stomata are closed

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Tree Biology

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ApicalMeristems

Shoot tip

Root cap

Tree Biology

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Terminal bud

Lenticels

Leaf budFlower bud

Terminal budScale scars

Leaf scars

This year’s growthNode

Internode

This year’s growth

Lateral bud

Last year’s growth

Tree Biology

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Lumenlearning.com

Tree Biology

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Tree Biology

Tree Biology

• Symplasm (sapwood) vs. Apoplasm(heartwood)

• Xylem of Gymnosperms (pines, spruces)–Tracheids (dead)–Fibers (sclerenchyma)–Parenchyma cells (live)

• Vessels (xylem of hardwoods)–Stacks of dead, hollow cells

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Tree Biology

• Phloem (conifers)–Sieve cells

• Phloem (hardwoods)–Sieve tube elements–Companion cells

• Movement of carbohydrates (sugars) is slow and requires energy

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Tree Biology

• Phloem–Rays

• Transport and store carbohydrates• Restrict decay  (CODIT)

• Bark–Old phloem

• Crushed & living cells reabsorbed into tree• Cell walls incorporated into bark

– Impregnated with wax and oil–Lenticles

• Gas exchange

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Tree Biology

Tree Biology

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The cohesion-tension theory of sap ascent is shown. Evaporation from the mesophyll cells produces a negative water potential gradient that causes water to move upwards from the roots through the xylem. Image credit: OpenStax Biology

Tree Biology

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Tree Biology

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Tree Biology

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Mycorrhizae

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Tree Biology

Tree Biology

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