Additionality – Greenhouse gas removals or reductions that are additional to what would otherwise occur in a business-as-usual scenario. Additionally has the potential to become a marketable forest carbon credit.


Baseline – Generally, the reference against which program or project are measured.

Baseline Scenario – Representative of the most likely alternative land use scenario in the absence of the project.

Benchmark – Reference point against which comparisons can be made. (ISO 21678:2020)

Biogenic – Produced in natural processes by living organisms, but not fossilized or derived from fossil resources. (ISO 21930:2017)

Buffer Pools – A function of the risk rating of a project, the buffer pool is a certain amount of credits set aside to protect the project in case of losses.


Carbon Density – The amount of carbon stock expressed per unit area, mass or volume. For studies of forest carbon density is always reported per unit of land area. Typical units: Mg ha-1; kg m-2; g m-2.

Carbon Dioxide (CO2) – A naturally occurring molecular structure that holds most of the carbon in the atmosphere in its gas form. CO2 is also a by-product of burning fossil fuels from fossil carbon deposits, such as oil, gas and coal, of burning biomass and of land use changes and of industrial processes (e.g., cement production). CO2 is the principal anthropogenic GHG that affects the Earth’s radiative balance. It is the reference gas against which other greenhouse gases are measured and therefore has a GWP of 1. (IPCC)

Carbon Dioxide Removal (CDR) – An amount of CO₂ removed from the atmosphere (i.e., negative emissions), generally measured over a specified period of time. Additional carbon sequestered and stored by a forest carbon project (relative a baseline, or BAU, scenario) is equal to that project’s removals.

Carbon Flux – The amount of carbon (C) moving from one stock to another over a specified period of time. Typical units: Pg yr-1; Mg ha-1 yr-1; g m-2 sec-1.

Carbon Pools (or Stocks) – A system that has the capacity to store or release carbon. In forests, five main carbon pools or stocks are commonly recognized: above-ground biomass, below-ground biomass, dead wood, litter and soil organic matter.

Carbon Sequestration – Any process by which CO2e is removed from the atmosphere and stored in solid or liquid form.

Carbon Sink – A negative source of CO2 in the atmosphere (NEP>0) via absorption and storing of carbon in vegetation, the atmosphere, and the ocean.

Carbon Source – A positive source of CO2 to the atmosphere (NEP < 0).

Chlorofluorocarbons (CFCs) – Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example is CFC-12 (CCl2F2), used as a refrigerant in refrigerators and air conditioners and as a foam blowing agent. Gaseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere, are broken down by strong ultraviolet radiation, release chlorine atoms, and then react with ozone molecules. (UNFCCC)

CO2 Equivalent (CO2e) – Describes different greenhouse gases in a common unit. For any quantity and type of greenhouse gas, CO2e signifies the amount of CO2 which would have the equivalent global warming impact.


Disturbance – Forest disturbances are events that cause change in the structure and composition of a forest ecosystem, beyond the growth and death of individual organisms. The sets and patterns of natural disturbances that characterize a particular area or ecosystem are referred to as the ecosystem’s disturbance regime. Disturbances, both human-induced and natural, shape forest systems by influencing their composition, structure, and functional processes. Climate change is impacting forests by altering the existing disturbance regimes.

Double-counting – The scenario under which a singular GHG emission reduction or removal is monetized separately by two different entities or where a GHG emission reduction or removal is sold to multiple buyers (Verra).


Embedded Carbon – The carbon stored in a product or building.

Embodied Carbon – The life cycle (either cradle to gate or cradle to grave) emissions associated with producing a product or service. Embodied carbon does NOT include the carbon contained (e.g. embedded, stored) in the product itself.

Environmental Product Declaration (EPD) – Environmental declaration providing quantified environmental data using predetermined parameters and, where relevant, additional environmental information. (ISO 21930:2017)


Forest Carbon Stock – It is the amount of carbon sequestered from the atmosphere and stored in a forest ecosystem, mainly within living biomass and soil and, to a lesser extent, in deadwood and litter.

Forest Carbon Flux – It is the transfer of carbon (mass) to and from the per-unit forest area per unit time. Carbon efflux is the transfer of carbon out of the forest to another pool, and the influx is the transfer of carbon from other pools to the forest.

Forest Carbon Cycle – It is the constant movement of carbon between the atmosphere and forests. The biological part of this cycle involves carbon sequestration by plants from the atmosphere via photosynthesis and loss of carbon through respiration and decay.

Forest Composition – The makeup of the forest in terms of the living organisms or groups of organisms and non-living components present in the forest; all of the tree species that are found in the forest. (Wisconsin DNR, 2000) Most commonly refers to the types of tree species most abundant in the overstory. This may also be referred to as “cover type” by land managers.

Forest Ecosystems – A unit of biological organization made up of all of the organisms in a given forest area interacting with the physical environment so that a flow of energy leads to characteristic trophic structure and material cycles within the system. (Odum 1967) Forest ecosystems are defined vertically from the top of the tree canopy to the “bottom” of the soil. While sediments and roots can extend for many meters, sampling is rarely done below 1m in depth.

Forest Function or Process – Ecosystems processes defined by the flow of matter and energy.

Forest Pathogens – Forest pathogens are living species responsible for forest diseases that are not classified as animals, such as bacteria, fungi, and algae. Forest pathogens are usually, but not always, microscopic organisms that attack trees in ways that can be detrimental to tree, and ultimately forest, health. For example, pathogens can destroy roots and reduce water and nutrient uptake, cause cankers or wilt diseases that reduce the flow of water to the leaves or needles, or cause leafspots and defoliation that reduce the tree’s carbohydrate reserves and its likelihood of surviving a hard winter. (USFS)

Forest Pests – Living organisms – plants, animals and pathogenic agents – detrimental to the forest health. This term usually refers to insect pests.

Forest Stand – An aggregation of trees or other growth occupying a specific area and sufficiently uniform in species composition, size, age, arrangement, and condition as to be distinguished from the forest or other growth on adjoining areas.

Forest Structure – Generally, the vertical and horizontal spatial arrangement of the component parts of a forest ecosystem.


Global Warming Potential (GWP) – The index used to translate the level of emissions of various gases into a common measure to compare the relative RF of different gases without directly calculating the changes in atmospheric concentrations. GWP is calculated as the ratio of RF that would result from emitting 1kg of a GHG to that from the emission of 1 kg of CO2 over a period of time (usually 100 years). (UNFCCC)

Greenhouse Effect – Warming that results when the atmosphere traps heat radiating from Earth towards space. (NASA)

Greenhouse Gas (GHG) – Atmospheric gases, both natural and anthropogenic, that allow solar radiation to reach the Earth’s surface and re-absorb IR emitted by the Earth. This property causes warming, or the greenhouse effect. H2O, CO2, N2O, CH4, and O3 are the primary GHGs in Earth’s atmosphere. Additional gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). (IPCC, UNFCCC, WMO)

Gross Primary Productivity (GPP) – The rate at which primary producers undertake photosynthesis or chemosynthesis occurs to produce biomass.

Growth and Yield Models – Forest growth and yield models attempt to quantify the growth of a forest and are commonly used for two principal purposes: 1) to predict the future status of a forest and the nature of any harvests from that forest, and 2) to help consider alternative cultivation practices.


Heterotrophic Respiration – Carbon lost by organisms other than the living plants that use photosynthesis to produce energy. It includes respirations from the litter layer and carbon release from decomposition of standing dead trees and coarse woody debris.


Infrared Radiation (IR) – Heat energy emitted from all solids, liquids, and gases. In the context of GHGs, IR refers to the heat energy emitted by the Earth’s surface and the atmosphere. GHGs strongly absorb IR and radiate some of it back towards the surface, creating the greenhouse effect. (UNFCCC)


Leakage – Net changes of anthropogenic emissions by GHG sources that occur outside the project or program boundary but are attributable to the project or program (Verra).

Life Cycle Assessment (LCA) – Compilation and evaluation of the inputs, outputs and potential environmental impacts of a product system throughout its life cycle. (ISO 21930:2017)


Methane (CH4) – A GHG with a GWP of 28-36 over 100 years. CH4 is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. (UNFCCC)


Net Ecosystem Productivity (NEP) – The difference between gross primary production (GPP) and total ecosystem respiration. NEP represents the total amount of organic carbon available in an ecosystem.

Net Primary Productivity (NPP) – The difference between productivity (a result of photosynthesis) and respiration. Because NPP is measured as a change and can be calculated at intervals, we can consider it a flux. NPP is directly correlated to carbon (C) and is typically measured in units of metric tons of biomass C per hectare per year.

Nitrous Oxide (N20) – A powerful GHG with a GWP of 265-298 over 100 years. Major sources of N2O include soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning. (UNFCCC)


Opportunity CostForgone profits from harvest (through higher retention, longer rotations, lost development options, etc.) or alternative land uses like agriculture or development.


Permanence – A guarantee that carbon sequestered or stored through project activities will not be re-released back into the atmosphere for an agreed upon timeframe (i.e., 100 years).

Photosynthesis – The primary function of photosynthesis is to convert solar energy into chemical energy and then store that chemical energy for future use. For the most part, the planet’s living systems are powered by this process. (MSU Extension)

Prescribed Fire – Any fire ignited by management actions under certain, predetermined conditions to meet specific objectives related to hazardous fuels or habitat improvement. (USFS)


Radiative Forcing (RF) – A change in the balance between incoming solar radiation and outgoing infrared radiation. Without RF, solar radiation would enter Earth in amounts approximately equal to the IR emitted from Earth. The addition of GHGs to the atmosphere traps an increased fraction of the IR, reradiating it back toward the Earth’s surface. The result is a warming influence. (UNFCCC)

Reduction – A verified decrease in GHG emissions caused by a project, as measured against an appropriate forward-looking estimate of baseline emissions for the project.

Registered – A project is considered “registered” when the project has been verified by an approved third-party verifier, submitted by the project developer to the registry operator for final approval, and approved by the registry operator.

Residence Time – The length of time that a gas remains in the atmosphere.

Respiration – The release of waste products (e.g. H20 and CO2) as a tree processes photosynthetically stored sugars for energy required in growth, transport and maintenance.

Retired – When credits are transferred to a retirement account in the Reserve System, they are considered retired. Retirement accounts are permanent and locked to prevent ‘retired’ credits from being transferred again. Credits are retired when they have been used to offset an equivalent metric ton of emissions or have been removed from further transactions on behalf of the environment.

Reversal – Release of a project’s stored carbon back into the atmosphere (reversal is a threat to permanence)– e.g., wildfire, disease, or voluntary termination of the project.


Stand-replacing Fire – Fires that replace more than 75% of the upper canopy layer (also called high-severity fires). (USFS)


Technosphere – Sphere or realm of human technological activity which results in a technologically modified environment. (ISO 201930:2017) Note: Primary resources are acquired or extracted from the environment/nature (the geosphere or biosphere) into the technosphere and emissions to air, water or land are released from the technosphere into the environment.


Uncertainty – A parameter associated with the result of measurement that characterizes the dispersion of the values that could be reasonably attributed to the measured amount (Verra).


Verified – A project is considered “verified” when it has completed a vigorous verification process by an independent accredited third-party verifier.

Verifier – An individual that is employed by or subcontracted to an approved third-party verification body and is qualified to provide verification services for specific standards and methodologies.


Whole-building LCA – Life cycle assessment applied to a building-related functional equivalent (a whole building, or part of a building).


Zero – Net zero is similar in principle to carbon neutrality, but is expanded in scale. To achieve net zero means to go beyond the removal of just carbon emissions. Net zero refers to all greenhouse gases being emitted into the atmosphere, such as methane (CH4), nitrous oxide (N2O) and other hydrofluorocarbons.

Developed by Michigan State University, Forest Carbon and Climate Program.