1

Tree growth and juvenile wood formation*

Mature wood development

Timejuvenile woodmature wood

3

Juvenile wood

Wood formed by the vascular cambium under the prolonged influence of the apical meristem in the live crown. Also know as core wood and crown wood.

Juvenile wood is formed throughout the life of the tree not just in young trees.

Mature wood is formed by the vascular cambium lower down the stem where the influence of the live crown is much less.

Juvenile-mature wood distinction is completely different from heartwood-sapwood distinction

(Josza)

*

4

Juvenile wood-mature wood vs. heartwood-sapwood

sapwood

heartwood

juvenile wood

mature wood

sapwood/juvenile wood

sapwood/mature wood

heartwood/juvenile wood

heartwood/mature wood

5

Physiology of juvenile wood formation

(Josza)

6

Juvenile wood – characteristics and properties

Anatomy• Wider growth rings• Thinner cell walls• Less latewood• Shorter longitudinal tracheids• More spiral grain

Ultrastructure• Larger S2Ө

Chemistry• More lignin• Less cellulose• Hemicelluloses differ

Properties• Lower wood density• Lower strengths• Greater longitudinal shrinkage• Paper strengths

– burst, tensile ↑– tear ↓

*

7

Juvenile/mature wood ring profiles

(Josza)

8

mw

jw

Microfibril angle

(Josza)

*

9

(Mansfield)

10

Longitudinal tracheid length in second growth Douglas-fir(at breast height)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 5 10 15 20 25 30 35 40 45 50

Rings from pith

Cel

l le

ng

th (

mm

)

(Forintek)

Juvenile wood vs. Mature wood

Wood Property Juvenile wood

Mature wood

Density (kg/m3) 427 489

Fiber length (mm) 2.98 4.28

Cell wall thickness (µm) 3.88 8.04

S2Ɵ (°) 55 20

Longitudinal shrinkage (%) 0.90 <0.10

Modulus of Rupture (psi) 7,700 10,660

Modulus of Elasticity (106 psi) 1.12 1.75

12

The transition from juvenile wood to mature wood is not sudden as might be interpreted from some graphical representations. The transition is gradual as the right stem profile illustrates.

(Josza) (Haygreen & Bowyer)

13

Juvenile wood (first 20 years of growth) marked on 50 year-old Douglas-fir log ends and visible on lumber ends.(Forintek)