Sapwood

Understanding Sapwood

Sapwood is the tree's circulatory system—the living, active wood that keeps the tree alive by moving water and dissolved minerals from the soil up to the leaves where photosynthesis occurs.

Structure and Function

Location

• Forms the outer rings of wood beneath the bark
• Typically lighter in color than heartwood
• Thickness varies by species (from 2-3 cm to 10+ cm)
• Represents the most recent years of growth

Function

• Water transport: Moves hundreds of liters per day in large trees
• Nutrient distribution: Delivers dissolved minerals throughout the tree
• Storage: Stores some carbohydrates and other compounds
• Living tissue: Contains living parenchyma cells (unlike heartwood)

Sapwood vs Heartwood

Sapwood (Outer Rings)

• Light-colored (white, pale yellow, cream)
• Physiologically active
• Contains living cells
• Permeable to water
• Less durable (subject to decay and insect attack)
• 10-30% of trunk diameter typically

Heartwood (Inner Core)

• Dark-colored (brown, red, black)
• Physiologically inactive (dead cells)
• Filled with tannins, resins, oils
• Impermeable
• Highly durable and rot-resistant
• Provides structural strength

Why It Matters

For the Living Tree

Without functional sapwood, a tree cannot:

• Transport water from roots to canopy
• Survive drought periods
• Support photosynthesis
• Maintain turgor pressure in leaves

For Timber Use

Sapwood characteristics affect wood quality:

• Less desirable: More prone to decay, insect damage, and fungal attack
• Poor durability: Not suitable for outdoor use without treatment
• Different properties: Lower density, different color than heartwood
• Processing: Often removed or chemically treated in commercial lumber

For Tree Health

Damage to sapwood is serious:

• Girdling: Complete removal kills the tree
• Partial damage: Reduces water transport capacity
• Insect/disease entry: Sapwood is vulnerable to borers and fungi
• Decay progression: Typically starts in sapwood, then moves to heartwood

Visual Identification

When you see a fresh-cut log:

• The lighter outer rings are sapwood
• The darker inner core is heartwood
• The transition line may be sharp or gradual
• Some species have distinct color differences; others don't

Interesting Facts

• In young trees, almost all wood is sapwood
• As trees age, inner sapwood converts to heartwood
• Some species (like cedar, teak) have thick heartwood and thin sapwood
• Other species (like maple, ash) have mostly sapwood even when mature
• Ring-porous trees (like oak) have distinct annual sapwood rings
• Diffuse-porous trees have more uniform sapwood structure

Costa Rican Examples

Cedro Amargo (Cedrela odorata)

• Distinctive pink-brown heartwood
• Narrow pale sapwood band
• Clear visual difference

Caoba (Mahogany) (Swietenia macrophylla)

• Rich reddish-brown heartwood
• Yellowish-white sapwood
• Prized for heartwood color and durability

Cristóbal (Platymiscium pinnatum)

• Orange-brown heartwood
• Cream to light yellow sapwood
• Rosewood family with aromatic wood