Adaptation
The process of adjusting to an actual or expected environmental change and its effects in a way that seeks to moderate harm or exploit beneficial opportunities.
Adaptive capacity
The general ability of institutions, systems, and individuals to moderate the risks of climate change, or to realize benefits, through changes in their characteristics or behavior. Adaptive capacity can be an inherent property or it could have been developed as a result of previous policy, planning, or design decisions.
Agreement
The extent to which evidence is consistent in support of a vulnerability statement or rating. See also confidence, evidence.
Basal area
The amount of area occupied by the cross-sections of live tree stems within a given forest stand. It provides a measure of forest stocking and tree density.
Biodiversity
The variety of life, including the number of plant and animal species, other life forms, genetic types, habitats, and biomes in an ecosystem.
Biomass
The mass of living organic matter (plant and animal) in an ecosystem; also organic matter (living and dead) available on a renewable basis for use as a fuel. Biomass includes trees and plants (both terrestrial and aquatic), agricultural crops and wastes, wood and wood wastes, forest and mill residues, animal wastes, livestock operation residues, and some municipal and industrial wastes.
Carbon dioxide (CO2) fertilization
Increased plant uptake of CO2 through photosynthesis in response to higher concentrations of atmospheric CO2.
Climate
Climate, in a narrow sense, is usually defined as the average weather or, more rigorously, as the statistical description in terms of the average and variability of defining factors over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation, and wind. Climate, in a wider sense, is the state, including a statistical description, of the climate system.
Climate change
A change in the state of the climate that can be identified (for example, by using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external factors, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.
Climate change scenario
See representative concentration pathway (RCP).
Climate model
See general circulation model.
Climate normal
The arithmetic mean of a climatological element computed over three consecutive decades. Also referred to as a climate norm or a 30-year norm.
Climatic water deficit
The difference between potential and actual evapotranspiration. Higher climatic water deficit generally reflects greater atmospheric moisture demand relative to the water available from soils, indicating greater potential water stress for forests.
Community
An assemblage of plants and animals living together and occupying a given area.
Confidence
A qualitative assessment of uncertainty as determined through evaluation of evidence and agreement. See also evidence, agreement.
Consecutive dry days
The number of consecutive days without meaningful precipitation.
Convective storm
Convection is a process whereby heat is transported vertically within the atmosphere. Convective storms result from a combination of convection, moisture, and instability. Convective storms can produce thunderstorms, tornadoes, hail, heavy rains, and straight-line winds.
Coupled Model Intercomparison Project (CMIP)
A climate modeling activity from the World Climate Research Programme, which coordinates and archives climate model simulations based on shared model inputs by modeling groups from around the world. The CMIP Phase 3 (CMIP3) multimodel dataset includes projections using Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (SRES). The CMIP Phase 5 (CMIP5) dataset includes projections using the Representative Concentration Pathways (RCPs). The CMIP Phase 6 (CMIP6) involves a suite of common model experiments as well as an ensemble of CMIP-endorsed Model Intercomparison Projects (MIPs). See also representative concentration pathway (RCP), shared socioeconomic pathway (SSP).
Disturbance
Stresses and destructive agents such as invasive species, diseases, and fire; changes in climate and severe weather events such as hurricanes and ice storms; pollution of the air, water, and soil; real estate development of forest lands; and timber harvest. Some of these are caused by humans, in part or entirely; others are not.
Disturbance regime
The temporal and spatial characteristics of a disturbance agent and the impact of that agent on the landscape. More specifically, the cumulative effects of multiple disturbance events over space and time.
Downscaling
Methods for obtaining high-resolution climate or climate change information from coarse-resolution general circulation models; involves examining the statistical relationship between past climate data and on-the-ground measurements.
Driver
Any natural or human-induced factor that directly or indirectly causes a change in an ecosystem.
Dynamical downscaling
A method for obtaining high-resolution climate or climate change information from relatively coarse-resolution general circulation models (GCMs) using a limited-area, high-resolution model (a regional climate model, or RCM) driven by boundary conditions from a GCM to derive smaller-scale information.
Ecological province
Climatic subzones, controlled primarily by continental weather patterns such as length of dry season and duration of cold temperatures. Provinces are also characterized by similar soil orders and are evident as extensive areas of similar potential natural vegetation. Also referred to as ecoprovince.
Ecological section
A subdivision of an ecological province having broad areas of similar geomorphic process, stratigraphy, geologic origin, drainage networks, topography, and regional climate. Also referred to as ecosection.
Ecoprovince
See ecological province.
Ecoregion
A region characterized by a repetitive pattern of ecosystems associated with commonalities in climate and landform that characterize that larger region.
Ecosection
See ecological section.
Ecosystem
A volumetric unit of the Earth's surface that includes air (climate), land (landform, soil, water), and biota. Ecosystems are defined by land area, and contain all the interactions between living organisms and their physical environment.
Emissions scenario
A plausible representation of the future development of emissions of greenhouse gases and aerosols that are potentially radiatively active, based on demographic, technological, or environmental developments.
Evaporative demand
Evaporative demand quantifies the potential loss of water from the surface as driven by atmospheric factors including temperature, wind speed, humidity, and cloud cover. Periods of high evaporative demand are connected to droughts and increased fire danger.
Evapotranspiration
The sum of evaporation from the soil and transpiration from plants.
Evidence
Mechanistic understanding, theory, data, models, or expert judgment used to determine the level of confidence in a vulnerability statement or rating. See also agreement, confidence.
Exposure
The nature and degree to which a system is exposed to significant climate variations.
Fire-return interval
The number of years between two successive fire events at a specific location.
Fire-return interval departure
A measure of how much current wildfire frequency (fire-return interval) differs from historical fire frequency.
Forest land
Land that is at least 10 percent stocked by forest trees of any size, or land formerly having such tree cover, and not currently developed for a nonforest use.
Forest type
A classification of forest vegetation based on the dominant species present, as well as associate species commonly occurring with the dominant species.
Forest type group
Based on definitions from the US Forest Service Forest Inventory and Analysis (FIA) program, a combination of forest types that share closely associated species or site requirements and are generally combined for brevity of reporting.
Fragmentation
A disruption of ecosystem or habitat connectivity, caused by human or natural disturbance, creating a mosaic of successional and developmental stages within or between forested tracts of varying patch size, isolation (distance between patches), and edge length.
Fundamental niche
The total habitat available to a species based on climate, soils, and land cover type in the absence of competitors, diseases, or predators.
General circulation model (GCM)
Numerical representation of the climate system based on the physical, chemical, and biological properties of its components, their interactions, and their feedback processes, and accounting for all or some of its known properties. Also referred to as a climate model.
Greenhouse effect
The rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) absorb and emit energy from the sun.
Growing season
The period in each year when the temperature is favorable for plant growth.
Habitat suitability
How suitable environmental conditions are for individual species. Comparing current and projected future habitat suitability can help identify areas where species may become more or less well suited to the landscape over time.
Hardwood
A dicotyledonous tree, usually broad-leaved and deciduous. Hardwoods can be split into soft hardwoods (for example, red maple, paper birch, quaking aspen, and American elm) and hard hardwoods (for example, sugar maple, yellow birch, black walnut, and oaks).
Hydric
Pertaining to sites or habitats with abundant moisture throughout the year, frequently including saturation, ponding, or flooding.
Impact
The direct and indirect consequences of climate change on systems, particularly those that would occur without adaptation.
Impact model
Simulations of impacts on trees, animals, and ecosystems; It uses projections from general circulation models as inputs, and include additional inputs such as tree species, soil types, and life history traits of individual species.
Imperiled species
Certain plant and animal species are considered imperiled when they face a high risk of extinction because they have small and/or declining populations, need specific, rare habitats, or face severe anthropogenic threats. These plant and animal species may be at greater risk from environmental changes because of their imperiled status.
Integrated assessment model (IAM)
Models that integrate knowledge from two or more domains into a single framework. They are one of the main tools for undertaking integrated assessments. One class of IAM used in respect to climate change mitigation may include representations of multiple sectors of the economy, such as energy, land use, and land-use change; interactions between sectors; the economy as a whole; associated greenhouse gas emissions and sinks; and reduced representations of the climate system. This class of model is used to assess linkages between economic, social and technological development, and the evolution of the climate system. Another class of IAM additionally includes representations of the costs associated with climate change impacts but includes less detailed representations of economic systems. These can be used to assess impacts and mitigation in a cost–benefit framework and have been used to estimate the social cost of carbon.
Invasive species
Any species that is nonnative (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause damage, injury, or disruption to ecosystem processes or other species within that ecosystem.
Land cover
The physical characteristics of the land surface such as crops, trees, or concrete. See also land use.
Land use
Describes the human use of land. It represents the economic and cultural activities (e.g., agricultural, residential, industrial, mining, and recreational uses) that are practiced at a given place. Land use differs from land cover in that some uses are not always physically obvious. See also land cover.
Merchantable timber volume
The amount of live tree wood that meets size and quality standards for potential timber use within a given area. It provides a measure of available commercial wood volume across the landscape.
Mesic
Referring to sites or habitats where soil moisture is available to plants throughout the growing season.
Mitigation
Measures to reduce the amount and rate of future climate change by reducing emissions of heat-trapping gases (primarily carbon dioxide) or removing greenhouse gases from the atmosphere.
Parcelization
The subdivision of a single forest ownership into two or more ownerships. Parcelization may result in fragmentation if habitat is altered under new ownership.
Peak flow
The maximum instantaneous discharge of a stream or river at a given location.
Phenology
The timing of natural events such as the date that migrating birds return, the first flower dates for plants, and the date on which a lake freezes in the autumn or opens in the spring; also refers to the study of this subject.
Precipitation
The process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc.
Process model
A model that relies on computer simulations based on mathematical representations of physical and biological processes that interact over space and time.
Productivity
The rate at which biomass is produced per unit area by any class of organisms, or the rate of energy utilization by organisms.
Projection
A potential future evolution of a quantity or set of quantities, often computed with the aid of a model. Projections are distinguished from predictions in order to emphasize that projections involve assumptions concerning, for example, future socioeconomic and technological developments that may or may not be realized, and are therefore subject to substantial uncertainty.
Pulpwood
Roundwood, whole-tree chips, or wood residues used for the production of wood pulp for making paper and paperboard products.
Radiative forcing
The change in the net (downward minus upward) radiative flux (expressed in watts per square meter) at the tropopause or at the top of atmosphere due to a change in an external driver of climate change, such as a change in the concentration of carbon dioxide or in the output of the sun. Sometimes, internal drivers are still treated as forcings even though they result from the alteration in climate, for example, aerosol or greenhouse gas changes in paleoclimates. The traditional radiative forcing is computed with all tropospheric properties held fixed at their unperturbed values and after allowing for stratospheric temperatures, if perturbed, to readjust to radiative-dynamical equilibrium. Radiative forcing is instantaneous if no change in stratospheric temperature is accounted for. The radiative forcing once rapid adjustments are accounted for is the effective radiative forcing.
Realized niche
The portion of potential habitat a species occupies; usually it is less than what is available because of predation, disease, and competition with other species.
Refugia
Locations and habitats that support populations of organisms that are limited to small fragments of their previous geographic range.
Relative stand density index
An index that describes how densely trees occupy a forest relative to the maximum density the site can support. Higher values indicate greater competition for light, water, and nutrients.
Representative concentration pathway (RCP)
Scenarios that include time series of emissions and concentrations of the full suite of greenhouse gases and aerosols and chemically active gases, as well as land use and land cover. The word “representative” signifies that each RCP provides only one of many possible scenarios that would lead to the specific radiative forcing characteristics. The term “pathway” emphasizes that not only the long-term concentration levels are of interest but also the trajectory taken over time to reach that outcome. RCPs usually refer to the portion of the concentration pathway extending up to 2100, for which integrated assessment models produced corresponding emissions scenarios. See also radiative forcing, scenario.
Resilience
The ability to prepare for threats and hazards, adapt to changing conditions, and withstand and recover rapidly from adverse conditions and disruptions.
Risk
Threats to life, health, and safety, the environment, economic well-being, and other things of value. Risks are evaluated in terms of how likely they are to occur (probability) and the damages that would result if they did happen (consequences).
Runoff
That part of the precipitation that appears in surface streams. It is the same as streamflow unaffected by artificial diversions or storage.
Saw log
A log meeting minimum standards of diameter, length, and defect, including logs at least 8 feet long, sound and straight, and with a minimum diameter inside bark of 6 inches for softwoods and 8 inches for hardwoods, or meeting other combinations of size and defect specified by regional standards.
Scenario
A plausible and often simplified description of how the future may develop, based on a coherent and internally consistent set of assumptions about driving forces and key relationships. Scenarios may be derived from projections, but are often based on additional information from other sources, sometimes combined with a narrative storyline. See also climate change scenario, emissions scenario.
Sensitivity
The degree to which a system is affected, either adversely or beneficially, by climate-related stimuli.
Severity
The proportion of aboveground vegetation killed and the degree of forest floor and soil disruption.
Shared socioeconomic pathway (SSP)
A basis for emissions and socioeconomic scenarios, an SSP is one of a collection of pathways that describe alternative futures of socioeconomic development in the absence of climate policy intervention. The combination of SSP-based socioeconomic scenarios and Representative Concentration Pathway–based climate projections can provide a useful integrative frame for climate impact and policy analysis. See also representative concentration pathway (RCP), scenario.
Snowpack
Layers of accumulated snow that usually melts during warmer months.
Snow water equivalent
The amount of water contained in snowpack. It is a way of measuring the amount of snow while accounting for differences in density.
Socioeconomic
Referring to a combination of social and economic factors, such as the education, income, and work status of individuals or communities.
Softwood
A coniferous tree, usually evergreen, having needles or scale-like leaves.
Species distribution model
A model that uses statistical relationships to project future change in where species might occur.
Statistical downscaling
A method for obtaining high-resolution climate or climate change information from relatively coarse-resolution general circulation models (GCMs) by deriving statistical relationships between observed small-scale (often station level) variables and larger (GCM) scale variables. Future values of the large-scale variables obtained from GCM projections of future climate are then used to drive the statistical relationships and so estimate the smaller-scale details of future climate.
Stochastic
Involving or containing a random variable or process.
Streamflow
Discharge that occurs in a natural surface stream course whether or not it is diverted or regulated.
Stressor
An agent, condition, change in condition, or other stimulus that causes stress to an organism.
Tension zone
A transitional band that corresponds to a number of climatic factors. Vegetation north and south of the tension zone reflects varied habitat conditions as a result of climatic differences.
Timberland
Forest land that is producing or capable of producing more than 20 cubic feet per acre per year of wood.
Topkill
Death of aboveground tree stem and branches.
Transpiration
Liquid water phase change occurring inside plants with the vapor diffusing to the atmosphere.
Troposphere
The lowest part of the atmosphere from the surface to about 6 miles in altitude in mid-latitudes (ranging from 5.6 miles in high latitudes to 9.9 miles in the tropics on average) where clouds and weather phenomena occur.
Uncertainty
An expression of the degree to which a value (such as the future state of the climate system) is unknown. Uncertainty can result from lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from quantifiable errors in the data to ambiguously defined concepts or terminology, or uncertain projections of human behavior. Uncertainty can be described using quantitative measures or by qualitative statements.
Vapor pressure deficit
The difference between how much moisture is in the air and the amount of moisture in the air at saturation (i.e., at 100% relative humidity). Vapor pressure deficit measures atmospheric dryness, and higher values demonstrate where trees may experience greater atmospheric water stress over time.
Veneer
A roundwood product from which veneer is sliced or sawn and that usually meets certain standards of minimum diameter and length, and maximum defect.
Vulnerability
The degree to which a system is susceptible to, and unable to cope with, adverse effects of climate change, including climate variability and extremes. Vulnerability is a function of the impacts and adaptive capacity of a system. For this assessment, a system may be considered to be vulnerable if it is at risk of a composition change leading to a new identity, or if the system is anticipated to suffer substantial declines in health or productivity.
Water stress
Water stress occurs when demand for water by people and ecosystems exceeds available supply.
Weather
The state of the atmosphere at a given time and place, with respect to variables such as temperature, moisture, wind velocity, and barometric pressure.
Windthrow
Trees uprooted or broken by wind.
Xeric
Pertaining to sites or habitats characterized by decidedly dry conditions.