DCIA - directly connected impervious area
See full definition: directly connected impervious area (DCIA).
NIPF - non-industrial private forestland
See full definition: non-industrial private forestland (NIPF).
PM10 - particulate matter less than 10 microns in diameter
i-Tree Eco  - uses sample or inventory data to assess forest structure, ecosystem services and values for any tree population (including number of trees, diameter distribution, species diversity, potential pest risk, invasive species, air pollution removal and health effects, carbon storage and sequestration, runoff reduction, VOC emissions, building energy effects). It runs on local field data and hourly meteorological and pollution data. The program includes plot selection programs, data entry programs or mobile application data entry, table and graphic reporting and exporting, and automatic report generation. The program includes the ability to forecast simulate future tree population totals, canopy cover, tree diversity, dbh distribution and ecosystem services and values by species based on user-defined planting rates and default or user-defined mortality rates (e.g., user can simulate effect of emerald ash borer by specifically killing off ash trees). This program also includes a Pest Detection Protocol for long-term pest detection and monitoring. This protocol allows users to input health signs and symptoms of their trees to produce indications of potential pests, diseases and threats to their forest.
i-Tree Hydro  - simulates the effects of changes in tree and impervious cover within a watershed on hourly stream flow and water quality. It contains auto-calibration routines to help match model estimates with measured hourly stream flow and produces tables and graphs of changes in flow and water quality due to changes in tree and impervious cover within the watershed.
i-Tree Streets  - is similar to Eco, but focuses on street tree populations using reference city street tree data. This program has been incorporated with in i-Tree Eco. Street tree analyses within Eco do not use reference city data, but rather use local pollution and weather data to estimate ecosystem services.
i-Tree Vue  - is the precursor program to i-Tree Landscape and has now been superseded by the newer Landscape program that has many new data and capabilities.
i-Tree Storm  - helps assess widespread street tree damage in a simple and efficient manner immediately after a severe storm. It is adaptable to various community types and sizes and provides information on the time and funds needed to mitigate storm damage.
i-Tree Canopy   - allows users to easily photo-interpret Google aerial images of their area to produce statistical estimates of tree and other cover types along with calculations of the uncertainty of their estimates. This tool provides a simple, quick and inexpensive means for cities and forest managers to accurately estimate their tree and other cover types. i-Tree Canopy can be used anywhere in the world where high-resolution, cloud-free Google images exist (most areas). Use of historical imagery can also be used to aid in change analyses.
i-Tree Database  - allows international users to submit local city, pollution and precipitation data to be imported into i-Tree. Once data are processed, users can run i-Tree Eco for that international city. User can also view and submit new tree species information to help build a global tree database.
i-Tree Design  - links to Google maps and allow users to sketch their home and see how the trees around their home affect energy use and savings, and other environmental services. Users can use this tool to assess which locations and tree species will provide the highest level of benefits. This is a simple tool geared toward homeowners, school children or anyone interested in tree benefits. This program allows users to add multiple trees, illustrate future and past benefits, and the display of priority planting zones.
i-Tree Landscape  - ) integrates national landscape and environmental data to aid in forest management and planning. This tool contains national maps and data related to landscape structure (e.g., tree canopy, land cover, and basic demographic information), ecosystem services and values from trees (e.g., carbon storage, air pollution removal, reduced runoff) and risks to forest and human health (insects and diseases, wildfire potential, ultraviolet radiation exposure, air pollution exposure, surface temperatures, projected future climates). Users can select their area of interest to easily explore these multiple data sets and weight the data to prioritize areas for management actions (e.g., most important areas to plant or protect trees). This tool is an easy-to-use web-based tool that can improve forest management and planning, and easily engage stakeholders in management prioritizations and decisions to improve forest and human health and sustainability.
i-Tree MyTree   - is a phone app that allows users to easily quantify the benefits and values of individual trees. The benefits considered include CO2 sequestration, storm water interception, reduced energy usage, and air pollution removal.
The terms below describe basic tree morphology and biology, as well as standard metrics and practices widely used across all applications of forestry.
absorbing roots  - Non-woody roots formed at the ends of woody lateral roots; responsible for water and nutrient absorption.
afforestation  - The establishment of forest trees by planting or seeding an area not previously forested.
backfill  - Soil used to fill in the excavated area around the roots of a newly planted tree or shrub. May be native soil, or a mixture or native soil and amendments such as compost.
basal area  - For an individual tree, a measurement of the cross-sectional area of the trunk at breast height. For a forest stand, the sum of the basal areas of the individual trees in the stand.
biological maturity  - The point in a life cycle of a tree at which there is no net biomass accumulation (i.e., when annual growth is offset by breakage and decay).
biomass  - The total (above and below ground) weight of wood and bark in trees. Typically expressed as green or oven-dry weight, in units of tons.
biome  - The largest ecological unit, distinguished by an extensive complex of terrestrial communities, corresponding to a particular climatic zone or region, and associated with an environmental region.
botanical variety  - A group of individual plants that have noticeable differences from their species and retain those differences when reproducing in nature from seed.
bulk density  - The mass of soil per unit volume. A measure of the ratio of pore space to solid materials in a given soil. Expressed in units of g/cm3 of oven dry soil.
canopy  - The upper level of a tree and/or forest, consisting of branches and leaves of taller trees.
carrying capacity  - The maximum amount of animal or plant life a particular forest environment can support indefinitely without ecosystem degradation, given limitations of food, shelter, competition, predation, and other available resources. Usually expressed in terms of an individual species.
clinometer  - An instrument used to estimate the height of a tree, using a vertical angle measured from a known distance from a tree.
compacted live crown ratio  - The percent of the total length of the tree which supports a full, live crown. For trees that have uneven length crowns, ocularly transfer lower branches to fill holes in the upper portions of the crown, until a full, even crown is created.
condition  - General term for describing tree crown health. Assessed in the field by identifying a tree’s crown condition or dieback.
coniferous  - Describes woody plants that produce seeds in cones. Most coniferous trees are also termed “evergreen” since they keep their needles for years at a time.
corridor  - A strip of wildlife habitat unique from the surrounding landscape, that links one isolated ecosystem (e.g. forest fragment) to another. Allows certain species access to isolated habitat areas, and contributes to the genetic health of the populations involved.
crown  - commonly refers to the leaves and branches in the uppermost part of a tree. Also, the point where the tree trunk meets the roots of a tree.
crown class  - An evaluation of an individual tree's crown in relation to its position in the canopy and the amount of full sunlight it receives. The four recognized categories are: dominant (D), codominant (C), intermediate (I), and overtopped or suppressed (S).
crown height  - The vertical height measured from the ground to the first (lowest) branch of a tree.
crown width  - The horizontal distance from a point on the edge of a tree canopy to the furthest point on the opposite edge of the canopy.
decurrent growth  - A tree growth pattern that generates a rounded morphology, due to lateral buds forming branches that grow outward. Helpful in tree identification.
diameter at breast height (DBH)  - The diameter of the tree stem measured at 4.5 ft (1.37 m) above the ground (i.e. breast height).
See also: DBH.
dieback  - The recent mortality of branches with fine twigs, beginning at the terminal portion of a branch and proceeding toward the trunk. Considered only when it occurs in the upper and outer portions of the tree.
See also: dieback.
disturbance  - A natural or human-induced environmental change (e.g. timber harvesting, windstorms, fire) that alters one or more of the communities within an ecosystem.
dormant  - A state of inactivity. Deciduous trees are dormant from the time leaves fall until new ones appear.
economic maturity  - The point in a life cycle of a tree or stand when harvesting is most profitable (i.e., when the rate of value increase of an individual tree or stand falls below a desired alternative rate of return).
ecotype  - A genetic subdivision of a species resulting from the selective action of a particular environment and showing adaptation to that environment. May be geographic, climatic, elevational, or soil related.
evapotranspiration  - The combined processes of evaporation and transpiration, which transport water into the atmosphere from sources such as soil, vegetation, tree canopies, and surface water.
excurrent growth  - A tree growth pattern that generates a triangular shape and strong central leader branch, due to the dominance of a growing tip or apical bud over other lateral buds. Helpful in tree identification.
foliage  - Leaves and other above-ground plant organs specialized for photosynthesis, respiration, and transpiration.
forest type  - An association of tree species that commonly occur together because of similar ecological requirements.
fragmentation  - Breaking up of a contiguous tract of forest into smaller patches, often isolated from each other by non-forest habitat.
guild  - A collection of species with similar habitat needs, as well as similar responses to habitat changes. One guild species is often used to represent the others when developing a management plan.
hardiness  - The ability of a plant to withstand cold temperatures without death of woody tissues and/or flower buds.
hardiness zones  - Geographically defined areas divided by the temperature extremes experienced during a typical year, which determine what species will grow well.
hybrid  - A cross between two parent plants that are unlike, often involving two species of the same genus.
indicator species  - A species with such specialized ecological needs that it can be used to assess the quality, condition, or extent of an ecosystem. Assessments are typically based on species presence and density, or the accumulation and effect of materials in their tissues.
invasive  - A non-native species that grows and spreads rapidly, establishing itself over large areas and displacing native species.
inventory  - The process of gathering information on the health and diversity of trees in a forest or plot. Normally involves detailed descriptions and measurements of trees and planting sites.
lateral root  - Woody roots that grow horizontally outwards. Can extend 2-3 times beyond the dripline; responsible for conducting water and nutrients.
leaf area index (LAI)  - The total one-sided leaf surface area per unit of canopy ground surface area. Estimated by dividing leaf area by the ground area directly under the tree canopy.
See also: LAI.
loam  - Classification of soil texture with roughly equal proportions of sand, silt, and clay. Often considered ideal for plant growth.
multiple use and value  - A conceptual basis for managing a forest area to yield more than one use or value simultaneously. Common uses and values include aesthetics, water, wildlife, recreation, and timber.
net annual growth  - The average annual net increase in the volume of trees during the period between inventories.
non-industrial private forestland (NIPF)  - Forestland owned by a private individual, group or corporation not involved in wood processing.
See also: NIPF.
noxious weed  - Legal designation used for plant species determined to be major pests of agricultural systems, and are subject by law to certain restrictions.
nutrient  - Any element taken in by a plant that is essential to its growth. Obtained from the soil, air, and/or water.
nutrient cycling  - Movement of mineral elements (also called nutrients) within an ecosystem as organic matter decomposes, releasing bound nutrients back to plants.
old-growth  - A term for forests in the US that approximate the structure, composition, and functions of native forest prior to European settlement.
organic matter  - Plant and animal residue in soil in various stages of decomposition. Provides nutrients to trees.
origin  - A term relating to the continent or region that a particular tree species is native to (i.e., where the species developed or occurs naturally).
patch  - A small area of a particular ecological community surrounded by distinct ecological communities.
photoperiodism  - The physiological reaction of trees and other plants to changes in light availability or the length of day.
poletimber tree   - A tree with DBH ranging from 13 to 23 cm (5 to 9 in). Generally considered too small to produce timber.
productivity class  - A classification of forest land in terms of potential annual cubic-foot volume growth per acre at culmination of mean annual increment in fully stocked natural stands.
rare species  - A species that exists only in a few restricted areas or habitats, or that occurs in low numbers over a relatively broad area.
rarefaction  - Technique used for assessing species richness of a sample of trees. Species richness is estimated by plotting the number of species against the number of samples to create rarefaction curves. For i-Tree, the value produced using the rarefaction technique is the number of species one would expect to find if 4 trees were sampled in each 85 stratum. For the entire study area, this value is the number of species one would expect to find if 250 trees were sampled within the study area.
reforestation  - Re-establishment of forest cover on areas that previously supported forest cover.
regeneration  - Replacement of one forest stand by another as a result of natural seeding, sprouting, planting, or other methods.
root ball  - Soil containing all or a portion of the roots that are moved with a tree or other plant when it is transplanted.
root system  - The subsurface organ system responsible for anchoring a tree, as well as absorbing water and minerals.
saturated zone  - A layer in an aquifer below the water table, where all pores are saturated with water.
sawtimber tree   - A tree with DBH ranging 23 cm (9 in) or greater. Generally considered large enough to produce timber. THIS IS THE SAME A POLETIMBER TREE
seedling  - A young tree originating from seed, less than 1.2 m (4 ft) tall and smaller than 5 cm (2 in) in diameter at ground level.
shoot system  - The aboveground organ system in trees responsible for food production and respiration. Includes the stem, branches, and leaves.
shrub  - A woody plant smaller than a tree, usually divided into separate stems near the ground.
silviculture  - The practice of controlling the establishment, composition, growth, and quality of forest stands.
site quality  - The productive capacity of a specific forest site affected by growth factors such as light, heat, water, nutrients, and anchorage. Often expressed as tree height at a given age.
species diversity  - The number of species and abundance of each species that live in a particular location, taking into account both species richness and species evenness.
See also: species richness.
species dominance  - A measure of the degree to which a species is more numerous than others or contributes more of the total biomass.
species evenness  - A measure of how closely matched the numbers of each species are to each other.
species richness  - The number of different species represented in the study area.
See also: species diversity.
stand  - A group of vegetation identified and managed as a single unit because of their similarity in species, age, and condition.
stumpage  - The price of standing trees, measured as unit value per stump. Also used to refer to the right to harvest a particular stand.
succession  - The natural replacement(s) of one plant community by another over time and in the absence of disturbance.
tap root  - A large central root growing down into the soil, used for storage and anchorage in young plants.
timber cruising  - The process of estimating quality, quantity, and characteristics of trees in a forest.
See also: inventory.
timberland  - Forestland capable of producing crops of industrial wood at rates of more than 20 cubic feet per acre per year.
tolerance  - A characteristic of trees that describes the relative ability to thrive with respect to growth factors such as light, heat, water, nutrients, and anchorage.
tree  - A large woody perennial plant with a single well-defined stem carrying a definite crown. Sometimes defined as attaining a minimum DBH of 3 in (7.6 cm) and a minimum height of 15 ft (4.6 m) at maturity.
tree size class  - A classification of trees based on diameter at breast height. Includes sawtimber trees, poletimber trees, saplings, and seedlings.
tropism  - The process by which plants grow in different directions as a response to environmental stimuli (e.g. light, gravity, water).
understory  - The smaller vegetation (shrubs, seedlings, saplings, small trees) within a forest stand, occupying the vertical zone between the canopy and the herbaceous plants of the forest floor.
vertical structure  - The arrangement of plants in a given community, from the ground into the main forest canopy.
This glossary section focuses on terms that have very specific meanings and uses for one or more i-Tree applications, as well as some words used commonly in modeling software similar to i-Tree. Some of these terms have more general definitions in the field.
alternative case  - In i-Tree Hydro, the hypothetical scenario that is modeled and contrasted with the existing “base case” scenario. Often the alternative case models changes in existing land cover due such factors as additional green infrastructure, and changes in the amount of tree or impervious surfaces.
avoided runoff  - A measure of the stormwater runoff that is avoided because of rainfall interception, evaporation and transpiration by trees. It is estimated by comparing the differences in hourly and annual surface runoff values between modeled areas with trees and without trees..
bark area index  - The area of tree bark (m2) relative the projected tree crown area (m2). This index represent the area of bark which can intercept water and is also is used to represent the surface area of a leafless deciduous tree in winter.
base case  - In i-Tree Hydro, the current or initial situation that is modeled. This case typically represents the current watershed or project area conditions that are used for model calibration and contrasting with alternative model cases..
base flow  - The portion of stream flow that is supplied via subsurface flow. Primary source of stream water during periods of low flow.
benefit  - an improvement or gain in environmental, social, health or economic conditions due to the natural biological functions of trees .
carbon sequestration  - the amount of atmospheric carbon removed by trees annually.
carbon storage  - The amount of carbon currently contained within a plant’s woody tissue (above and below ground), including the amount of carbon within leaves for evergreen species.
cold check  - A quality assurance (QA) procedure for field surveys and inventories, where a measured plot is randomly revisited and inspected for the accuracy of critical measurements without the original field data collection crew present.
compensatory value  - A structural value of the tree itself, based on an estimated cost of having to replace a tree with a similar tree.
crown light exposure  - the number of sides of a tree receiving sunlight from above. There is a maximum of five sides considered, including the top of the tree.
depression storage  - The capacity of a particular area of land to hold surface runoff and prevent it from flowing elsewhere.
depth of root zone  - The average distance that plant roots penetrate into the soil for normal development of its root system.
dieback  - entirely dead braches and recent mortality of branches with fine twigs, which begins at the terminal portion of a branch and proceeds to the trunk.
See also: dieback.
digital elevation model (DEM)  - A computer model or 3D representation of surface terrain, showing elevation.
See also: DEM.
directly connected impervious area (DCIA)  - The portion of impervious cover that drains directly (i.e., conveys water overland or through a storm sewer network) to a stream.
See also: DCIA.
ecosystem service - processes or benefits produced by the environment that are utilized by people (e.g., clean air, water, food, materials).
energy effects  - estimated impact of trees on residential building heating (Btus) and cooling (kWh) use. Estimated based on tree distance and direction to residential structures, tree height, and tree condition.
energy effects value  - The value assigned to the energy effects of a tree based on state average utility costs or the social cost and externality values for avoided pollutant emissions from power plants.
event mean concentration (EMC)  - The flow-proportional average concentration of a given pollutant during a storm event. Measured in units of mass per volume (usually mg pollutant / liter of runoff).
See also: EMC.
externality values - The value or cost associated with an action from one party that either positively or negatively affect another party, but the first party neither bears the costs nor receives the benefits. Externalities are not reflected in the market price of goods and services. A classic example of a negative externality is air pollution, where the associated health costs are paid by society and not the producer of the pollutant. Trees often produce positive externalities (e.g., cleaner air).
gross sequestration  - A measure of the carbon sequestered by trees, calculated as the difference in estimates of carbon storage between Year X and Year X+1.
See also: carbon sequestration.
ground cover  - a non-tree or non-shrub material that lies upon or occupies space on the earth. Eco provides 11 default ground cover classes (e.g., grass, building, water)
See also: ground cover.
groundwater recharge  - The process of water moving from the surface to the water table. Maintains the supply of fresh water that flows through the groundwater system to wells, streams, springs, and wetlands.
herbaceous cover  - a category of ground cover that includes any woody plants less than 30.5 cm (12 in) in height or non-woody plants, regardless of height.
hot check  - A quality assurance (QA) procedure for field surveys and inventories, where a trainer observes and check measurements of a survey crew during data collection to ensure they are correctly performing measurements on a plot.
impervious cover  - a category of ground cover that includes paved roads, buildings, paved parking lots and other hard surfaces that prevent rainfall from naturally infiltrating into the soil.
impervious depression storage  - The segment of depression storage in a watershed found in impervious areas, such as water stored on road depressions that do not drain away or infiltrate into the soil system.
See also: depression storage.
infiltration excess overland flow  - Also known as Hortonian Flow; occurs when precipitation exceeds the infiltration capacity of the soil.
initial soil saturation  - The amount of water storage in the soil at the start of a simulation. A value of 0% represents soil that is absolutely dry; value of 100% represents completely saturated soils.
inventory  - The collection of data on every tree within a particular area (in contrast to a sample that only collects data on a subset of trees in an area).
See also: inventory.
land use  - a description of the primary purpose of an area i-Tree Eco has 13 default land use classifications (e.g., residential, park, golf course).
See also: land use.
leaf storage  - The typical water depth that a single leaf can hold. Intercepted precipitation that exceeds leaf storage is shed as throughfall.
leaf-off day  - The day of the year representing the mid-point of a four week transition period for deciduous trees from full canopy to no leaves. In i-Tree Eco, this date is based frost-free periods for a region.
leaf-on day  - The day of the year representing the mid-point of a four week transition period for deciduous trees from no leaves to full canopy. In i-Tree Eco, this date is based frost-free periods for a region.
metadata  - Data that describes and gives information about other data, such as how it was collected and derived, by whom, as well as scale, resolution and accuracy.
net sequestration  - A measure of the carbon sequestered by trees calculated as the gross carbon sequestered minus the carbon emissions due to decomposition from trees.
See also: carbon sequestration.
pervious depression storage  - The segment of depression storage in a watershed found in pervious areas, such as depressions caused by landscaping, areas of compacted soil found in parks, fields, etc.
See also: depression storage.
plantable space  - the amount of an area that is readily suitable for establishing new trees (i.e., plantable soil with no restrictions from overhead obstructions or surrounding land uses).
plot   - a defined area within which all trees are measured. In i-Tree Eco, the standard plot is a 0.1-acre circular plot (radius of 37.2 ft). Often 200 plots are inventoried in a plot-based sample of cities, which yields a standard error of about 12-15% for the total number of trees..
plot-based sample inventory  - the measurement of trees in a group of randomly distributed sample plots within a defined area. This plot information is used to generate estimates of tree population totals for the forest population within the defined area.
pollution removal value  - The monetary value associated with tree effects on atmospheric pollution. This value is estimated based on the economic damages associated with increases in pollution emissions and/or the impact of air pollution on human health.
quality assurance (QA)  - A procedure to ensure field data are collected accurately. QA involves a series of “hot” and “cold” checks of field plots.
See also: QA.
rarefaction  - Rarefaction is a mathematical technique to standardize species richness from several different samples with unequal size. This process is performed using rarefaction curves, plots of the number of species as a function of the sample size. In i-Tree, strata represent the different samples, where each contains a different number of trees sampled. Rarefaction is stated as the number of tree species found within a standardized sample size over all strata (x species found from a sample of y individual trees). Typically, the standardized sample size is identical for each individual stratum, but larger for the entire study area.
reference object  - A permanent landmark used find the location of a plot center. The description of a reference object includes direction and distance from the plot center to the object.
saturation excess overland flow  - Occurs when soils or depression storage are saturated with water, in which case any additional precipitation or irrigation creates runoff.
shrub  - any woody material that is at least 30.5 cm (12 in) in height with a DBH less than 2.54 cm (1 in).
stratification  - A method of subdividing a study area into similar groups for analysis (e.g., subdividing a city into land use classes). Stratification allows from comparisons among strata.
structure  - Descriptions of various elements related to the physical arrangement and composition of the landscape.
topographic index (TI)  - A grid of indices derived from a DEM that assumes topography drives flow. It is calculated using the upslope contributing area (α) and the slope of the grid cell (β). TI influences a multitude of variables such as flow accumulation, soil moisture, evapotranspiration, etc.
See also: TI.
tree ID  - a unique number assigned to a tree. Every tree in an inventory or sample should have a unique tree ID.
tree cover  - The amount or percent of an area covered by tree canopies when looking directly down from above the area.
unsaturated zone time delay  - A value that controls the travel time for water moving from the unsaturated zone to the saturated zone. It is estimated from hydraulic conductivity data and soil layer depths, then calibrated as part of the modeling process.
utility conflict   - Descriptors or potential or existing conflicts between tree branches and overhead utility lines.
See also: line clearance.
evaporation  - The vaporization of a liquid into a gas. In the hydrologic cycle, this includes the vaporization of water from lakes, rivers, etc. into the atmosphere.
geographic information system (GIS)  - A computer system used to store, display, and analyze data related to positions on Earth’s surface.
See also: GIS.
green infrastructure  - An interconnected network of designed landscapes that supports native species, maintains natural ecological processes, and helps manage air and water resources. Includes parks, parkways, riparian buffers, residential landscaping, street trees, rain gardens, green roofs, and window boxes.
groundwater  - Water stored underground in natural pore spaces between soil particles or rock fractures.
hydrology  - The study of the waters of the earth, including their distribution, movement, and composition.
landscape architecture  - A profession involving the research, planning, design, and management of natural and built environments.
low impact development (LID)  - An approach to stormwater management using design techniques that detain and filter runoff close to its source.
See also: LID.
management plan  - A document prepared by natural resource managers to guide the management of a forest property. Consists of inventory data and prescribed activities designed to meet ownership objectives.
National Land Cover Database (NLCD)  - A Landsat-based, 30-meter resolution land cover database for the United States. Provides descriptive data such as thematic class (e.g. urban, agricultural, forested), percent impervious surface, and percent tree canopy cover.
See also: NLCD.
nonpoint source pollution  - Water pollution caused by rainfall or snowmelt moving both over and through the ground, carrying with it a variety of pollutants associated with human land uses.
pH  - A numeric designation of acidity and alkalinity in soil or water. Classified as acidic (pH < 7), neutral (pH = 7), or alkaline (pH > 7).
particulate matter  - Tiny particles of solid or liquid suspended in a gas. Sources can be anthropogenic or natural.
preservation  - A management philosophy or goal that seeks to protect indigenous ecosystem structure, function, and integrity from human impacts. Generally excludes management practices.
topography  - The shape or configuration of an area of land, represented on a map by contour lines and relief shading.
The terms below focus on management practices and tree functions used in the care and surveying of trees in urban settings.
air quality index  - Rating system developed by the U.S. Environmental Protection Agency to report daily air quality based on levels of five major air pollutants. The higher the AQI value, the greater the level of air pollution and the greater the health concern. An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy. The six levels of health concern are: Good - AQI of 0 to 50; Moderate - AQI of 51 to 100; Unhealthy for Sensitive Groups - AQI of 101 to 150; Unhealthy - AQI of 151 to 200; Very Unhealthy - AQI of 201 to 300; and Hazardous - AQI greater than 300.
bioindicator species  - A tree, woody shrub, or herbaceous cover that responds to ambient levels of atmospheric pollution with easily diagnosed symptoms.
biological control  - The use of living organisms (e.g. parasites, pathogens, predators) to control invasive species or pest species.
bioretention  - The retention of stormwater through the use of vegetated depressions engineered to collect, store, and filter runoff.
buffer  - A vegetated zone adjacent to a stream, wetland, or shoreline where development is restricted or controlled to minimize the effects of development.
community forest  - A forest where the local community members are one of the major stakeholders in forest management and land use decisions.
detention  - The intentional temporary storage of stormwater. Used to control discharge rates, allow for infiltration, and improve water quality.
dripline  - A ring around the outer edge of the tree canopy projected down to the ground level, which receives most of the rainwater shed from the canopy.
filter strip  - A band of close-growing vegetation, usually grass, planted between pollution sources and downstream of receiving water bodies.
greenspace  - Any vegetated area that serves as recreation or open space. Can include neighborhood and regional parks, gardens, cemeteries, playing fields, bike and walking paths, and urban landscaping.
greenway  - A strip of land composed of natural vegetation, used to create connected networks of open space that include traditional parks and natural areas.
ground cover  - The type(s) and density of vegetation and other surfaces that occupy space near or upon the ground.
See also: ground cover.
hardscape  - Artificial landscape elements like patios, walls, fountains, walkways that are impervious to water penetration.
importance value (IV)  - Index value that describes the dominance of a tree species in the urban forest. Importance value is calculated as the sum of the percent of total population (number of trees) and percent of total leaf area.
See also: IV.
infiltration capacity  - The maximum rate at which water can be absorbed by a soil per unit area, under set conditions.
infiltration rate  - A measure of the rate at which soil is able to absorb rainfall or irrigation. Typically measured in units of mm/day.
land use  - The major human activities and management practices in an area of interest.
See also: land use.
line clearance  - Pruning and removing trees from an area with the intent of reducing the risk of damaging power lines.
See also: utility conflict.
natural area  - An area of land or water with predominantly native vegetation or natural ecological features, allowed to respond to the forces of nature with minimal human influence.
ornamental tree  - A tree that is used for its ornamental qualities, such as its flowers, leaves, scent, etc.
rain garden  - A form of bioretention for use in smaller areas. Strategic placement next to hard, impervious surfaces helps a rain garden effectively collect runoff from these areas.
recharge area  - A land area in which surface water can infiltrate the soil and reach the zone of saturation or groundwater table.
riparian area  - A vegetated ecosystem bordering a waterbody. Characteristically has a high water table and may be subject to periodic flooding.
root protection zone  - The surface area of tree roots to be protected from construction damage, usually soil compaction damage. Best accomplished by fencing off the entire zone.
shade tree  - Any tree grown specifically for its shade. Usually applies to large trees with spreading canopies.
shelterbelt  - One or more rows of trees planted upwind of an area protect it from winter winds and blowing snow. Also commonly known as windbreaks or hedgerows.
site analysis  - An evaluation of the conditions, restrictions, and environment of a planting site.
site considerations  - The factors taken into account when assessing a site for planting, tree conservation, or preservation.
soil amendment/soil conditioner  - Material mixed into the soil to add organic matter, improve drainage and/or improve aeration.
soil texture  - The relative proportions of sand, silt and clay particles in a mass of soil. Important in choosing an appropriate tree species.
stream management zones  - Areas adjacent to waterbodies where management strategies are applied to protect water quality and maintain stream temperature through shading.
structural soil  - A mix of rock, soil and binding agent that can be used under sidewalks, roads, and parking areas. Can be compacted while still maintaining pore space for the air and water that tree roots need to sustain healthy trees.
tree box  - Regularly-spaced rectangular openings in the sidewalk that provide growing space for street trees.
urban ecology  - The study of natural systems and human-constructed environments in urban areas.
urban ecosystem  - The community of living organisms and nonliving elements that make up the whole landscape of an urban environment.
urban forestry  - The management of an urban forest in a way that sustains healthy forests and maximizes benefits to society.
urban heat island - an urban area with higher temperatures relative to surrounding rural areas.
urban heat island effect  - A phenomenon where air temperatures in urban areas are 2-10°F warmer than surrounding rural areas, often dues to high concentrations of impervious surfaces and limited evapotranspiration.
urban planning  - The development or redevelopment of communities by planning for land use, housing, transportation, and economic development.