The total amount of living tissue on Earth, known as biomass, quantifies the collective mass of all organisms within a specific area or the entire planet. This measurement offers insights into the presence and energy stored within life, forming a basis for understanding how ecosystems function.
Understanding Biomass
Biomass is the total mass of organic matter in a given area or ecosystem at a specific time. It encompasses all living organisms, from microscopic bacteria to immense trees. This organic matter is typically expressed as total mass or average mass per unit area, often measured by carbon content due to its prevalence in living things.
Categories of biomass contribute in varying proportions to the global total. Plant biomass, primarily terrestrial, constitutes the vast majority, around 80% (approximately 450 gigatons of carbon, Gt C). Bacteria, including those in deep subsurface environments, form the second largest component, estimated at about 70 Gt C (roughly 15% of global biomass). Fungi, archaea, protists, animals, and viruses account for the remaining smaller percentages.
The Ecological Role of Biomass
Biomass plays a central role in the flow of energy through ecosystems. Producers, mainly green plants and algae, form the base of food webs by converting solar energy into chemical energy through photosynthesis, generating their own biomass. This stored energy then transfers to higher trophic levels as consumers feed on producers or other consumers. Each transfer, however, results in a significant energy loss, typically around 90%, meaning only about 10% is used to build new biomass at the next level.
Biomass is also fundamental to nutrient cycling within ecosystems. Plant biomass, for instance, absorbs carbon dioxide during photosynthesis, a key process for the ecosystem’s carbon balance. Decomposers, such as fungi and bacteria, break down dead organic matter, releasing stored energy and converting complex organic compounds into simpler inorganic forms. This recycling of nutrients maintains soil fertility and supports new plant growth, ensuring continuous availability of essential elements.
Measuring Life: Quantifying Biomass
Quantifying biomass involves various methods, depending on the scale and type of organisms studied. One common technique measures the dry weight of organisms to avoid water content variability. For smaller organisms or specific samples, direct destructive sampling methods are used, where organisms are collected, dried, and weighed. This provides accurate measurements for sampled individuals or areas.
For larger scales, such as forests, non-destructive techniques are often employed. Sampling methods like quadrats or transects estimate biomass over broader areas. Allometric equations, mathematical relationships between measurable plant characteristics (like tree height or trunk diameter) and biomass, are widely used to estimate the biomass of individual trees or stands without harvesting them. Remote sensing technologies, including satellite imagery and LiDAR (Light Detection and Ranging), estimate biomass over vast regions by analyzing vegetation indices or structural properties of plant canopies.
Global Distribution and Dynamics of Biomass
Most of Earth’s biomass is on land, with terrestrial environments containing approximately 470 Gt C, significantly higher than the roughly 6 Gt C in marine biomass. Forests, particularly tropical rainforests, account for the largest share of terrestrial plant biomass. Marine environments, despite covering 71% of Earth’s surface, hold a smaller total biomass, predominantly composed of microbes like bacteria and protists (around 70% of marine life).
Biomass is not static; it constantly changes due to natural processes and human activities. Natural dynamics include plant growth, seasonal cycles, and disturbances like wildfires or insect outbreaks. Global warming, for example, influences plant distribution, causing some species to shift to higher elevations or latitudes.
Human activities, however, substantially impact biomass distribution and quantity. Deforestation leads to significant losses of plant biomass and releases stored carbon, while agriculture can increase plant biomass in cultivated regions. The cumulative effect of human actions, including land-use change and increased human-made materials, has even led to anthropogenic mass surpassing global living biomass in recent years, highlighting humanity’s profound influence on the planet’s living tissue.