Biomass Estimator

Estimate biomass from measurements using allometric relationships

Organism Type

Total Length (cm)

Coefficient (a)

Species-specific constant (typically 0.005-0.02)

Exponent (b)

b = 3 for isometric, <3 for slender, >3 for robust fish

Understanding Biomass Estimation

Biomass is the total mass of living organisms in a given area or ecosystem, typically expressed per unit area (g/m² or kg/ha). Accurate biomass estimation is essential for understanding ecosystem productivity, energy flow, carbon storage, and wildlife management.

Allometric Equations

Fish Length-Weight Relationship

Formula: W = a × L^b

Where:

W = Weight (g)
L = Total length (cm)
a = Species-specific coefficient (0.005-0.02)
b = Allometric exponent (2.5-3.5)

Growth Types: b = 3 (isometric), b < 3 (negative allometry - slender), b > 3 (positive allometry - robust)

Mammal Body Length to Mass

General Formula: W = k × L^3

Coefficients vary by body form:

Small rodents: k ≈ 0.0001-0.0002
Carnivores: k ≈ 0.0003-0.0005
Ungulates: k ≈ 0.0004-0.0006
Large mammals: k ≈ 0.0005-0.0008

Bird Wing Length to Mass

Formula: W = c × WL^d

Wing length relationships vary by order. Passerines: d ≈ 2.7-2.9; Raptors: d ≈ 2.5-2.8. Coefficients reflect wing loading and body composition.

Population Biomass

Formula: Total Biomass = Population Size × Average Individual Mass

Biomass Density: Biomass / Area (kg/ha or g/m²)

Used for standing crop estimates and comparing productivity across ecosystems.

Typical Biomass Values

Ecosystem/Group	Biomass (kg/ha)	Notes
Tropical rainforest (total)	400,000 - 600,000	Highest terrestrial biomass
Temperate forest	200,000 - 400,000	Dominated by tree biomass
Grassland/Savanna	5,000 - 50,000	Highly variable by rainfall
Large herbivores (Serengeti)	100 - 500	Animal biomass peak
Small mammals (forest)	5 - 50	Mice, voles, shrews
Carnivores (apex predators)	0.1 - 5	Lowest vertebrate biomass
Fish (productive lake)	50 - 200	All species combined
Soil invertebrates	100 - 1,000	Often exceeds vertebrates

Biomass Pyramids and Trophic Levels

Energy transfer between trophic levels is typically 10% efficient (10% rule). This creates characteristic biomass pyramids:

Producers:

10,000 kg/ha (100%)

Herbivores:

1,000 kg/ha (10%)

1° Carnivores:

100 kg/ha (1%)

2° Carnivores:

10 kg/ha (0.1%)

Applications in Ecology and Conservation

Fisheries Management: Estimate harvestable biomass and set catch quotas
Carbon Sequestration: Calculate carbon storage in forests and marine ecosystems
Productivity Assessment: Measure ecosystem health and energy flow
Wildlife Management: Estimate food requirements and carrying capacity
Conservation Planning: Identify high-value habitats and prioritize protection
Climate Change Studies: Monitor changes in biomass distribution over time
Habitat Restoration: Track recovery of ecosystem biomass post-disturbance
Food Web Analysis: Understand energy transfer and trophic efficiency

Energy Content of Biomass

Approximate energy content by tissue type:

Fish/aquatic animals: ~5-6 kJ/g wet weight (20-24 kJ/g dry)
Mammals: ~6-8 kJ/g wet weight (varies with fat content)
Insects: ~20-25 kJ/g dry weight
Plant material: ~17-18 kJ/g dry weight
Wood: ~18-20 kJ/g dry weight

Measurement Techniques

Direct Methods

• Harvesting and weighing (destructive)
• Clip plots for vegetation
• Trawl surveys for fish
• Trapping and weighing animals

Indirect Methods

• Allometric equations from measurements
• Remote sensing (LiDAR, satellite)
• Acoustic surveys (fish biomass)
• Population density × average mass

Important Considerations

Species-Specific Equations: Use published equations for your species when available; general equations less accurate
Seasonal Variation: Biomass fluctuates with reproductive cycles, migration, and food availability
Age/Sex Structure: Different demographic classes have different mass; population estimates should account for this
Measurement Error: Length measurements easier than mass; allometric equations propagate measurement error
Wet vs. Dry Weight: Dry weight removes water content variability; conversion typically 20-30% dry weight for animals
Spatial Heterogeneity: Biomass varies greatly across landscape; stratified sampling improves estimates
Trophic Cascades: Changes in one trophic level affect biomass at other levels

Related Calculators

Species Density Calculator Leaf Area Index Calculator Carrying Capacity Calculator Population Growth Rate Calculator Plant Growth Rate Calculator

References

Froese, R., & Pauly, D. (Eds.). (2023). "FishBase." www.fishbase.org - Comprehensive length-weight relationships for fish species.
Whittaker, R. H., & Likens, G. E. (1975). "The biosphere and man." Primary Productivity of the Biosphere, 14, 305-328.
Peters, R. H. (1983). "The Ecological Implications of Body Size." Cambridge University Press - Allometric relationships across taxa.
Odum, E. P., & Barrett, G. W. (2005). "Fundamentals of Ecology." 5th Edition, Thomson Brooks/Cole.
Hairston, N. G., & Hairston, N. G. Sr. (1993). "Cause-effect relationships in energy flow, trophic structure, and interspecific interactions." The American Naturalist, 142(3), 379-411.