How a Tree Grows

J.G. Mexal

H/R 302

Spring 2005

Forestry & Society

How a Tree Grows-

• Trees are the 2nd largest organism- Eucalyptus

Sequoia

• Trees are the oldest organism-bristlecone pine (5,000 yrs)

Norway spruce (9,550 yrs)

• They can grow: as much as 25 ft/yras little as 25 mm/yr (1”)

• They can survive: 10 ft of precipitation10 in of precipitation

• They can survive: >100oF temperatures<-50oF temperatures

Trees live a long time!

• Alder• White birch• Sugar maple• Oak• Douglas-fir• Bristlecone pine• Norway spruce

• 25 yrs• 50 yrs• 300 yrs• >500 yrs• >700 yrs• >2,000 yrs• >9,000 yrs

Forestry & Society

How a Tree Grows-

• What does your tree look like?– A 100 ft tree weighs about 4,000 lbs– Has > 200,000 leaves (~120 lbs)

• Will shed 3,600 lbs of leaves in a lifetime

– Produce >5,000 seeds/yr– Have 1,300 lbs of roots– Require

• 8,000 lbs of CO2

• 2,900 lbs of H2O for Ps, and 5,000,000 lbs for Ts

– Generate over 8,000 lbs O2

Source: Ed Gilman, IFAS

Trees in the forest grow with one trunk, and codominant stems toward the top of the tree

Source: Ed Gilman, IFAS

Forestry & Society

Comparison between forest tree and landscape tree

Source: Ed Gilman, IFAS

Factors affecting tree growthGenetic

InformationEnvironmental

Conditions

Physiological Processes

Tree Growth

Bark Cambium

Heartwood

Sapwood

Latewood

Earlywood

Forestry & Society

How a Tree Grows-Functions

• Seed- reproduction• Leaves- photosynthesis (carbon

capture)• Roots- water & nutrient uptake• Bark- protection• Cambium/buds-growth• Xylem- water transport (up) [dead]• Phloem- carbohydrate transport

(down)

How a Tree Grows

Our secondary growth model:

A typical hardwood tree in cross section (transverse surface).

What can you identify?

Source: Ed Gilman, IFAS

The Bark:

The bark is everything outside the vascular cambium.

As you can see, there is a lot going on in the bark.

Source: Ed Gilman, IFAS

The Bark: periderm:

Periderms form the outer bark.

They are subdivided further.

Source: Ed Gilman, IFAS

The Bark: periderm: phellogen (cork cambium):

The phellogen is the region of cell division that forms the periderm tissues.

Phellogen development influences bark appearance.

Source: Ed Gilman, IFAS

The Bark: periderm: phellem (cork):

Phellem replaces the epidermis as the tree increases in girth.

Photosynthesis can take place in some trees both through the phellem and in fissures.

Source: Ed Gilman, IFAS

The Bark: periderm: phelloderm:

Phelloderm is active parenchyma tissue.

Parenchyma cells can be used for storage, photosynthesis, defense, and even cell division!

Source: Ed Gilman, IFAS

The Bark: phloem:

Phloem tissue makes up the inner bark.

However, it is vascular tissue formed from the vascular cambium.

Source: Ed Gilman, IFAS

The Bark: phloem: sieve tube elements:

Sieve tube elements actively transport photosynthates down the stem.

Conifers have sieve cells instead.

Source: Ed Gilman, IFAS

The Bark: phloem: companion cells:

Companion cells provide sieve tube elements with needed metabolites.

Conifers have albuminous cells instead.

Source: Ed Gilman, IFAS

The cambium:

The cambium is the primary meristem producing radial growth.

It forms the phloem & xylem.

Source: Ed Gilman, IFAS

The Xylem (wood):

The xylem includes everything inside the vascular cambium.

Source: Ed Gilman, IFAS

The Xylem: a growth increment (ring):

The rings seen in many trees represent one growth increment.

Growth rings provide the texture seen in wood.

Source: Ed Gilman, IFAS

The Xylem: vessel elements:

Hardwood species have vessel elements in addition to trachieds.

Notice their location in the growth rings of this tree

Source: Ed Gilman, IFAS

The Xylem: fibers:

Fibers are cells with heavily lignified walls making them stiff.

Many fibers in sapwood are alive at maturity and can be used for storage.

Source: Ed Gilman, IFAS

The Xylem: axial parenchyma:

Axial parenchyma is living tissue!

Remember that parenchyma cells can be used for storage and cell division.

Source: Ed Gilman, IFAS

The Xylem: rays (multiserrate & uniserrate):

Rays are radial parenchyma cells.

Parenchyma cells give rise to adventitious tissues.

Source: Ed Gilman, IFAS

Forestry & Society

How a Tree Grows/Diffuse vs Ring Porous

Silver Maple White Oak

50X

Diffuse Porous

Ring Porous

Forestry & Society

How a Tree Grows-Idealized

Annual rings

leaves

fruit

Taproot

Lateral root

Leaves

Fruit

A tree can produce 200,000 leaves/yr

Woody Stem Structure

Shoot Growth

3o lateral = 6 cm2 o lateral = 10 cm

Lateral branch = 14 cm

2o lateral = 10 cm

2 o lateral = 12 cm

Forestry & Society Shoot Growth in Eastern White Pine

Terminal growth = 44 cm

Lateral branch = 26 cm

Lateral branch = 19 cm

Biomass Partitioning/ Nelda Methany 2005

Time (yrs)3 557 20

Percent100

Leaves/Roots

Wood

Fine Roots

30%

35%

35%

5%5%

90%

Forestry & Society

How a Tree Grows

• Growing regions or meristems– Buds- height, flowers, leaves, (roots)– Cambium- diameter– Cork cambium - bark

• Factors– Temperature– Light– Water

Tropics vsBoreal

Where a tree grows!!

Tropical forest

Desert Dry tropical forest

32

59

oF86

20” 80” 140”

Forestry & Society

Urban Forestry CO2 capture

Basic Photosynthetic Reaction

• CO2 + H2O CH2O + O2

• 1.47 lb 0.60 lb 1.00 lb 1.07 lb

λ

Forestry & Society

How a Tree Grows/Kozlowski & Pallardy 1999

clear day overcast day

Forestry & Society

How a Tree Grows

• Most forests are regenerated sexually – seeds are required– exceptions: aspen, oak, eucalyptus

• Environmental factors:– light (forest gap)– moisture (mineral soil)– temperature (dormancy & germination)

Forestry & Society

How a Tree Grows - Piñon

• Flower primordia (buds) form in fall (yr-1)

• Flowers develop in spring (yr-2)

• Pollination occurs

• Overwinter

• Fertilization occurs in spring (yr-3)

• Growth of cone

• Maturation of cone with seeds in fall

• Total time elapsed >24 mo.

Drought

Pine life cycle

Forestry & Society

How a Tree Grows/Reproductive Cycle of Pinus contorta (Owens & Molder 1984)

Forestry & Society

How a Tree Grows-female cones

Pinus elliotii (slash pine)

1 mo.12 mo.24 mo.

pollination

maturation

fertilization

Rachis

Viable seed

Empty seed

Bract

Forestry and Society

Pinus eldarica cone

Forestry and Society Pine seed size variation

Pinus pinea (Italian stone pine) Pinus nigra (Japanese black pine)

wing

Forestry & Society

How a Tree Grows-Germination

• Seed is dispersed• Overwinters (dormant)• Germinates• Growth commences

• 10,000,000/ac• 4,000,000/ac• 4,000/ac @ 25 yrs• 100/ac @ 100 yrs

Nothofagus in Chile

0.001%

Ponderosa pine seed rain following harvest-CO / WJAF 21(1):19:06

0

10

20

30

40

50

60

70

80

90

100

Shelterwood

Seedtree

Year

Seeds/m2

Logged ’80-’81 winter

0

2

4

6

8

10

12

14

16

18

20

Germination

Survival

Seedlings/m2

~48% of seed consumed by animals regardless of year

Dendrochronology

Forestry & Society

Xylem production- earlywood vs latewood

Phloem

5 = Earlywood cells

3,4 = Latewood cells

L = Preceeding year

1,2 = Developing xylem cells

Forestry & Society

Silviculture/Response to Thinning

Juniper/NM

10 mm

False rings

Wider rings

Competition

Forestry & Society

Dendrochronology/Skaptar Jokull Volcano eruption in Iceland causes ‘the summer that wasn’t’ in western Alaska. (http://abcnews.go.com/sections/science/DyeHard/dyehard.html)

Earlywood

LatewoodEruption occurs June 8, 1783

No Latewood, indicating very early onset of winter

Review Questions

• Define: xylem, conifer, phloem, hardwood, cambium, softwood, cord, evergreen, board foot, deciduous, basal area, MAI, CAI, PAI, closed forest, earlywood (spring wood), latewood (summer wood), dendrochronology, false ring

• What environmental factors affect seed production germination? Why does piñon have good seed crops every 4-5 years?

• Describe the basic process of photosynthesis.• Why do trees produce so many seed, yet so few

germinate?