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Vertical variation
Density decreases with increasing height
More pronounced in SW
Reasons: greater stress at base because of weight above & higher proportion of heartwood (extractives) at base
Juvenile wood around pith has different density
Proportionally more juvenile wood in upper part
Horizontal variation
Influence of age is clearer than on vertical axis
SW juvenile & very old wood has low density
HW density is greatest around pith (extractives)

Environmental effects
Soil quality, climate, tree spacing, nutrients effect density which is expressed through ring width & latewood proportion
Determination of density
Measure overdry mass & volume via measuring apparatus or water displacement
Diana Smith method
Samples submerged in water
Application of cyclical pressure (air in) & vacuum (air out)
Takes volume out of equation
ρ [g/cm3] = 1 / (MC [decimal] + 1/1.53)
X-ray absorption
Transverse x-rays are absorbed depending on the density, the denser the wood, the more energy is lost in the material
Importance of density
Affects: hygroscopicity, s&s, mechanical, thermal, acoustical, electrical, transportational