Glossary

Glossary

A

Glossary Term	Glossary Definition
abiotic	Literally, “without life.” Inanimate or nonliving.
abiotic pollination	Does not require other organisms, but relies on environmental components such as water or wind.
abscise	To fall off, as with leaves.
abscission layer	Layer of cells between a leaf and the stem that is killed by hormones to make the leaf fall off the plant.
adventitious buds	Buds that form in an unexpected place on a plant, such as an internode. May be stimulated by extreme pruning or other wounding.
aeration	The exchange of air between the soil pores and the atmosphere that supplies the root zone with oxygen and removes carbon dioxide.
aerobic	Requiring or using oxygen to live or proceed.
aesthetic threshold	In pest management, the point at which visible or aesthetic damage becomes intolerable, requiring action to control the pest causing the damage.
aggregation	The process by which individual particles of sand, silt, clay, and organic matter cluster and bind together to form peds.
alternate host	A secondary host required by an insect or disease-causing organism to complete its life cycle.
ametabolous	Little or no bodily form change during growth development in arthropods. See also metamorphosis.
anaerobic	Literally, “without oxygen”; living or active in the absence of oxygen.
angiosperms	Flowering plants; plants which produce seeds in a closed or covered ovary (fruit). Contrast gymnosperms.
anion	A negatively charged ion. Plant nutrient examples include nitrate (NO3–,), phosphate (H2PO4–), and sulfate (SO42–).
annuals	Plants that die after a single growing season and reproduction cycle.
anther	Plant reproductive structure that holds pollen.
apical bud (also called the terminal bud)	The growing point at the tip of a shoot.
apical dominance	Growth at the terminal, or apical, bud at the expense of lateral bud growth.
apical meristems	Area at the tips of twigs and roots from which new plant growth arises; the highest growing meristem on a plant.
arachnid	A grouping of arthropods including spiders, scorpions, mites, and ticks.
arborist	An individual whose expertise pertains to the management and removal of individual trees, often in a horticultural or landscape setting.
arthropod	Invertebrate members of the phylum Arthropoda that have a segmented body, jointed limbs, and exoskeleton.
aspect	The orientation of the slope of a landscape, which affects amount of exposure to sunlight, and thus soil temperature and moisture.
attractant	Bait or other material that lures insects or animals.
axillary	Bud located in the axil of a leaf. See also lateral bud.

B

Glossary Term	Glossary Definition
backflow	In a plumbing or irrigation system, backward movement of water caused by suction instead of outflow of water. Can lead to contamination of water supplies.
backyard forest	Small, privately owned forest parcels, typically less than five acres.
bacterial ooze	Sticky liquid containing pathogenic bacteria, which seeps from cankers or lesions.
bait	A food or other substance that attracts insects or animals to a trap.
banding	Fertilizer application method in which the fertilizer is placed in a concentrated row or strip adjacent to plants.
bark	Outermost layer of stems and roots of woody plants.
Batesian mimicry	With insects, physical resemblance to another species to stymie enemies. Contrast cryptic coloration and Muellarian mimicry.
bee families	Within the order Hymenoptera there are seven recognized families of bees, including Apidae, Megachilidae, Halictidae, Andrenidae, Colletidae, Melittidae, and Stenotritidae.
beneficial organisms	Organisms that benefit plants by preying on, parasitizing, or otherwise destroying pest insects or other arthropods. Often referred to as biological control agents or natural enemies.
biennial plants	Plants that take two growing seasons to complete their life cycle.
bilateral symmetry	In biology, a body that is symmetrical across a plane—that is, one side is a mirror image of the other. Humans have bilateral symmetry around a vertical plane, bisecting the body into left and right sides.
biodiversity	The variety of species inhabiting a particular ecosystem.
biological control (or biocontrol)	The use of living organisms to suppress pest organisms.
biological control agent	A predator, parasite, or disease agent that feeds on, or in some other way destroys, a pest species. Biological control organisms may be native to an area or introduced.
biosolids	Products of municipal wastewater treatment that contain nutrients, organic matter, and inorganic constituents. Class A biosolids have been treated to remove pathogens and are suitable for use in gardens and landscapes. Biosolid composts and blends are soil amendments, while dried biosolids products are used as fertilizers.
biotic	Literally, “of life.” Related to or caused or produced by living organisms.
biotic pollination	Relies on living pollinators to move pollen from one flower to another.
blight	Pathological condition of plants in which portions of a plant become necrotic and die. May be caused by a variety of agents and conditions.
bolt	Sudden growth of some herbs or vegetables, in which the plants quickly send up flower stalks, bloom, and set seed. May be brought on by heat stress.
botanical name	Scientific name, plus any race, subspecies, or variety specifier. See scientific name.
bracts	A modified leaf structure, usually associated with a flower or cone scale.
branch bark ridge	Raised area of tissue where two branches or branch and trunk are attached. Often, but not always, externally visible as a raised and coarser line of bark than surrounding area.
branch collar	Swollen area at base of branch where the branch attaches to the parent branch or trunk. Natural target cuts are made just outside the branch collar to maximize the ability of the plant to compartmentalize the resulting wound.
bud dormancy	Waiting period for buds in which they do not mature or progress; may be indefinitely long.
bud	Undeveloped plant shoot that will produce a leaf, a flower, or both, but has not unfolded yet. Buds are classified by location, status, morphology, or function. See also axillary bud, mixed bud, lateral bud, simple bud, terminal bud. Note: “fruit bud” is poor usage—all plants must flower before setting fruit; therefore, there is no such thing as a “fruit bud.”
bud scales	Modified leaf structures that protect buds.
bud scale scar	Place on a twig where there used to be a bud scale.
bulb	Modified stem tissue, forming an underground storage organ of perennials such as tulips and daffodils.

C

Glossary Term	Glossary Definition
C:N ratio	The ratio of carbon to nitrogen in organic materials. Materials with a high C:N ratio are good bulking agents in compost piles, while those with a low C:N ratio are good energy sources.
caliche	A layer of soil where particles have been cemented together by calcium carbonate. Caliche is found in some soils in arid regions where minerals accumulate in soil. Caliche can act as a “hardpan,” restricting root growth and water movement and limiting soil depth.
cambium	The living layer of cells of a woody plant, producing phloem and xylem cells for those layers.
canopy	The aboveground parts of a plant or multiple plants, including the trunk(s), stem(s), branches, and leaves. The term may refer to a single plant or to the collective upper layer of vegetation—such as in a garden, orchard, or forest—formed by the leaves and branches of the tallest plants. In forestry, “canopy” often describes the aboveground portion of an entire stand of trees or an entire forest.
canopy closure	The period in a forest’s development where tree crowns develop a closed overstory and branches of trees are touching.
canopy gap	An area in a forest without significant overstory.
carbon dioxide fertilization	The process of increasing the atmospheric CO2 level in a greenhouse in order to increase the photosynthetic rate of plants growing there.
carpel	The carpel and pistil are reproductive parts of a flower in a plant, and they have a very slight difference between them. A carpel is composed of the stigma, style, and ovary. A pistil is the union of the carpels, or it can be the single carpel—we can say that the pistil is a fusion of carpels.
carrying capacity	In a habitat, the number of members of a species that can be supported by the available resources.
cation	A positively charged ion. Plant nutrient examples include calcium (Ca²+) and potassium (K+).
cation exchange capacity (CEC)	A soil’s capacity to hold cations as a storehouse of reserve nutrients. Clay and organic matter contribute to soil CEC.
cephalothorax	The foremost part of a spider that consists of a fused head and thorax.
cerci (singular: cercus)	Paired appendages on the abdomen of some insects. May be sensory organs, weapons, copulatory tools, or merely vestigial.
certified pesticide applicator	A person trained and certified, per standards of the EPA, in the handling and application of restricted pesticides. Certification is required for commercial pesticide use.
chlorophyll	Pigment that gives green plants their color and absorbs sunlight, allowing photosynthesis to occur.
chloroplast	Plant cell organelle containing chlorophyll and in which photosynthesis takes place.
chlorosis	Distinctive yellowing of green plant tissues, often indicating iron deficiency.
chlorotic	Distinctive yellowing of green plant tissues, often indicating iron deficiency.
clay	The smallest type of primary soil particle (less than 0.002 mm in diameter).
cline	A gradual change in the characteristics of a species over a continuous distance. For example, plants of a given species at higher elevation are typically not exactly the same as plants in the same species growing at lower elevations. There is a gradual morphological change in the plant with the increase in elevation.
clone	An individual plant or plants which have been asexually (vegetatively) propagated from a single individual source or “parent” plant.
cohort	A group of trees established during the same stage of forest development.
cold composting	A slow composting process that involves simply building a pile and leaving it alone until it decomposes. This process may take months or longer. Cold composting does not kill weed seeds or pathogens.
commensal rodents	Rodents that live in close proximity to humans; typically, rats and mice.
common name	(1) A familiar or colloquial name for a plant, insect, disease, or pest organism. Any organism may have several common names. (2) The standard, accepted name of a pesticide’s active ingredient, which is established by the appropriate professional societies.
compaction	The process by which pressure—often from heavy equipment or frequent traffic—compresses soil into dense layers that degrade its structure, eliminate pore space, and resist root penetration and water movement. Shallow compaction commonly occurs during activities such as site development.
competitive exclusion	In a community or habitat, the use or defense of a nutrient or other resource by one group or individual so that no other group or individual can access that commodity or resource.
complete fertilizers	A fertilizer containing all three macronutrients: nitrogen, phosphorus, and potassium (N, P, K).
complex metamorphosis	A series of changes and stages of maturity in certain insects involving easily visible changes in shape, form, and size. Normally includes stages as egg, larva, pupa, and adults. Contrast simple metamorphosis.
compost	Stabilized organic matter created by the natural decay and breakdown of organic waste material under conditions managed by people. Compost is used as a soil amendment to increase soil organic matter and slowly release nutrients.
conduction	Transfer of heat energy through material, from areas of higher energy (warmer) to areas of lower energy (cooler).
constitutive secondary compounds	Chemicals regularly produced at low concentrations by a plant’s roots for environmental competition and self-defense. (In contrast, see definition for “induced secondary compounds.”)
consulting forester	An individual with forestry training who assists landowners in forest management activities like planning, planting, and harvesting.
consumer horticulture (CH)	Cultivation, use, and enjoyment of plants, gardens, landscapes, and related horticultural items to the benefit of individuals, communities, and the environment. These activities rely on the understanding and application of the art, science, and business of horticulture.
contact herbicides	Chemical product applied directly to foliage, damaging or killing that foliage.
contact pesticide	Chemical product applied directly to pest (to plant foliage), damaging, or killing that pest.
convection	Movement of fluid material (gaseous, liquid, or semi-liquid) driven by the natural phenomenon of warmer materials being less dense and therefore rising above cooler, denser material. Rising warmer material creates a void underneath where cooler material is then drawn in.
corms	Short, enlarged underground stem tissues that provide food storage for a plant.
corolla	The collection of petals in a flower.
cotyledons	Embryonic or seed leaf; the first proto-leaf or leaves sprouting out of a seed. Contains the food for the sprouting plant.
cover crop	Plants grown to protect soil from water runoff and soil erosion and to add organic matter to soil.
cross-pollination	Transfer of pollen from one flowering plant to another flowering plant. Contrast self-pollination.
crown	The aboveground portion of a woody plant that is measured from the lowest live branch to the top of the plant. Also described as the canopy minus the distance from the base of the plant (root crown) to the lowest live branch. Usually refers to an individual tree, shrub, or vine.
crowns	Stems compressed to a very short form, as in strawberry plants or African violets.
cryptic coloration	With insects, physical appearance mimicking surrounding environmental elements such as twigs, leaves, rocks, etc., as camouflage for defense. Contrast Batesian mimicry and Muellarian mimicry.
cultivated variety or cultivar (cv.)	A variation of a species which originated in cultivation and persists under cultivation. A wild variation may also be found that only persists under cultivation. Perennial plant cultivars are normally perpetuated by asexual propagation; that is, cuttings, grafting, layering, or tissue culture, among other methods. Cultivars may arise via: • A chance seedling that is very different. • Selection of a plant with good traits from a seedling or mature plant group. These traits may not only include the usual aesthetic qualities (flower, fruit, color, etc.) but also factors such as disease or insect resistance, drought tolerance, cold hardiness, plant form, and other attributes. • A mutation (bud sport). • Selective breeding and hybridizing.
cultural conditions	Site conditions that influence plant growth and longevity.
curing	The final stage of the composting process, occurring after the most easily degradable organic matter has broken down. Curing involves the slow microbial decomposition of the more resistant components of organic matter and the decomposition of any phytoxins that formed during the composting process. Occurs at relatively low temperatures.
cytoplasm	Everything inside a cell, except for the nucleus.
cytoplasmic streaming	Method of movement or flow of the cytoplasm within a plant or animal cell.

D

Glossary Term	Glossary Definition
day-neutral	Plants whose reproductive cycle is not affected by length of day and night.
deadheading	Pruning term used to describe removal of spent flowers and the flowering stem. More often used on herbaceous annual and perennial plants. Described as a way to keep them blooming by preventing them from setting seed. Performed on woody plants such as hybrid roses and lilacs when gardeners find the look of spent flowers objectionable.
decomposition	The breakdown of plant and animal residues by decomposer microorganisms, releasing nutrients, carbon dioxide or methane, and water.
denitrification	Biological conversion of nitrate to nitrogen gas (N2) and nitrous oxide (N2O). Denitrification occurs in soil pores that are saturated with water and depleted of oxygen.
diagnose	The positive determination of the nature and cause of plant damage. The positive identification of an insect or other pest.
dichotomous key	A tool that assists in identifying natural organisms through a series of couplets or choices that lead the user to a correct identity.
dicotyledons	Member of the Dicotyledones class; flowering plants with two embryonic leaves per seed. Also known as “dicots.”
dolomitic limestone	A type of limestone that contains magnesium as well as calcium.
dormant bud	A bud that does not develop in the season it was formed. Plant stress, including pruning, can cause dormant buds to break and develop into a leaf or stem.

E

Glossary Term	Glossary Definition
economic threshold	In pest management, the point at which the cost of crop losses equals the cost of controlling the pest that is causing the loss.
El Niño Southern Oscillation (ENSO)­­	Recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean (National Weather Service).
ecotype	Differences in the characteristics of a species at discrete locations in its geographical distribution. Examples are dry site vs. wet site plants, lowland plants vs. plants from higher altitudes, plants native to seashore locations vs. the same species found farther inland. The divergent species may be called subspecies, depending on the degree of divergence.
electrical conductivity	A measure of soil salinity (salt accumulation).
elytra	With coleopteran insects, the outer pair of wings.
epidermis	Outermost layer of plant tissue, somewhat analogous to skin. May be covered with a waxy substance to reduce water loss.
epigeous germination	Style of germination in which the seed leaves push out of the ground, as with tomatoes, for example. Contrast hypogenous germination.
eradication	The complete elimination of a pest from a site, an area, or a geographic region.
establishment	Period after planting when woody plants are primarily growing roots to replace those lost in the transplanting process. Shoot and trunk growth is usually slower than normal during this period as energy goes to the roots. The length of the establishment period depends on the conditions at the site and size of the plant as well as its health and vigor. Not all plants successfully establish in the landscape.
eutrophication	A process by which bodies of water receive excess nutrients (typically phosphorus in fresh water) resulting in excess algae growth and subsequent loss of oxygen when the algae die and decay.
evapotranspiration	Evaporation + transpiration. The biological process of plants taking in CO2 and releasing water vapor into the atmosphere as they live and grow.
exclusion	Preventing the establishment of a pest in a previously uninvaded area.
exfoliation	Automatic shedding or self-stripping of bark or outer layers of material. Diagnostic for some species.
exoskeleton	Literally an exterior skeleton. Tough outer shell, typically made of chitin, for protection and support on many creatures including insects and crabs.

F

Glossary Term	Glossary Definition
fasciation	Distorted plant tissue growth resulting in flattened, rather than round, twigs and stems.
fertilizer	Any material used as a source of plant nutrients. Commonly used to correct deficiencies in nitrogen, phosphorus, and potassium.
fibrous roots	A many-branching root system with no central axis or tap root.
filament	Portion of the stamen that supports the anther.
fire frequency	The length of time it takes (on average) for fire to return to the same area twice.
fission	In biology, a style of reproduction for one-celled organisms by simple cell division.
floricane	A flexible stem that lives for two years, producing flowers and fruit the second year. Typical of Rubrus genus members.
flower bracts	Modified leaf structure that protects the flower bud; may be quite showy and overshadow the flower itself, as with poinsettia, for example.
fluid flow	A part of fluid mechanics and deals with fluid dynamics. It involves the motion of a fluid subjected to unbalanced forces. This motion continues as long as unbalanced forces are applied.
foliage	Plant leaves.
foliar necrosis	Death of leaves or parts of leaves.
foliar-applied herbicides	Chemicals in solution that are applied to, and absorbed through, plant leaves.
force	Bringing a cultivated plant into active growth or flowering outside of its natural growing season.
forest development	The process of structural changes that occur over the course of a forest’s life span.
Frankia	Bacteria that live in association with roots of alders and some other plants and convert atmospheric nitrogen to plant-available forms, a process known as nitrogen fixation.
frass	Excrement left by insects.
free-to-grow	The point at which the leader of a young tree is above the height of surrounding pressures (e.g., wildlife browse).
fresh organic matter	Leaves, roots, manure, and other plant and animal residues that will decompose in the soil.
fronds	Leaf-like structures of ferns.
frost pocket	Microclimate area, typically a low spot, where cold air tends to pool producing frost when the higher surrounding area has no frost.
fruiting body	Reproductive structure (spore-producing part) of a fungus.
fuel load	A measure of the amount of woody fuels available to burn in the event of a forest fire.

G

Glossary Term	Glossary Definition
generalists	Bees that can be found foraging on a number of different types of flowers.
genus	A taxonomic grouping of organisms that ranks above species and below family.
girdling	Damage to trunk, stem, or branch caused when roots, stake ties, or another type of wrap are left in place around them. The living tissue below the bark of the trunk or branch is killed as it grows against the girdling object.
green infrastructure	Defined by the US Water Infrastructure Improvement Act of 2019, “The term ‘green infrastructure’ means the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.’’
green manure	Cover crops that are grown to incorporate into the soil for nutrient and organic matter benefits. They can also be left on the soil surface as mulch.
green roof	A building roof that is partially or completely covered with vegetation, a growing medium, and a waterproof barrier.
growing degree days (GDD)	A 24-hour period during which temperatures reach at least one degree above the lower limit of an organism’s developmental threshold. That is, the combination of time and temperature required for an organism to develop. Also, heat unit.
growth habit	Refers to the genetic tendency of a plant to grow in a certain manner. Ground cover, cane-growing, weeping, and mounding are terms used to describe growth habit.
grub	Worm-like larvae, especially of beetles and bees.
gummosis	Gummy sap exuded from trees, especially fruit trees; usually associated with pathological conditions such as mechanical wounds, insect infestations, and bacterial infection.
gymnosperms	Plants that produce unenclosed, or naked, seed. Contrast angiosperms.

H

Glossary Term	Glossary Definition
habitat feature	A structure or element of a forest that provides benefits to wildlife.
halteres	Small, knobbed structures on either side of the thorax of a fly that are modified hind wings.
hardwoods	General term for broadleaf, or deciduous, trees.
heading (also called topping)	Cutting back of limbs, branches, or buds to reduce the size of a woody plant. This term originally described cutting a stem back to a bud to stimulate lateral growth or cutting to a very small lateral branch. Over time it has also come to be used interchangeably with topping, meaning to shorten a stem or branch without consideration for buds or side branches. When heading is used as a synonym for topping, it refers to a poor pruning practice that can substantially shorten the useful life of the pruned branches or entire plant.
heartwood	Nonliving older wood in the center of a tree trunk or limb. It is usually denser and harder than the living sapwood.
hemolymph	Internal bodily fluid of insect groups that have an “open” circulatory system; somewhat analogous to blood in mammals.
herbaceous perennials	Lacking permanent woody stems; plants that do not add to the diameter of their stems each year, and typically die back to the ground during cold temperatures but survive the winter because of their underground plant parts. May be ephemeral, annual, biennial, or perennial.
herbivores	Insects and other animals that eat primarily living plant material.
hidden hunger	A plant nutrient deficiency with no visual symptom.
high-grading	a form of harvesting where high-quality trees are removed and poor-quality trees are left behind, resulting in a degraded forest.
higher insects	Insects that undergo complex metamorphosis. Contrast primitive insects.
higher plants	Complex plants that have internal vascular systems; also called Tracheophyta or “tracheophytes.”
honeydew	A sweet, sticky substance excreted by aphids and related bugs that is deposited on plant leaves and stems.
host plant	A plant on which a particular disease can develop or a species of insect lays its eggs, or that is the source of nutrients for insects or a parasitic plant. Contrast nonhost.
host range	All plants or cultivars of a plant on which a disease can develop or an insect or animal can feed on to complete its development.
hot composting	A fast composting process that produces finished compost in about three months. High temperatures are maintained by mixing balanced volumes of energy materials (“greens”) and bulking agents (“browns”), keeping the pile moist, and turning it frequently.
hybrid	Cross between two inbred lines of a species, or the cross between two species within a genus (interspecific hybrid), or sometimes two genera within a family (intergeneric hybrid). Hybrid vegetable and corn seed are derived from crossing different lines of each particular species.
hydrozone	An area of landscape that contains plants with similar water needs.
hypha (plural: hyphae)	With fungi, the thread-like growth of elongated cells. See also mycelia.
hypogeous germination	Style of germination in which seed leaves remain underground, as with oaks, for example.

I

Glossary Term	Glossary Definition
imbricate	Bulbs that do not have a papery covering, such as lilies.
immobilization	The process by which soil microorganisms use available nitrogen as they break down materials with a high C:N ratio, thus reducing the amount of nitrogen available to plants.
induced secondary compounds	Defensive chemicals produced in high concentrations by a plant’s roots when triggered by environmental stress or pest invasion. (In contrast, see definition for “constitutive secondary compounds.”)
infectious disease	Contagious disease; disease caused by microscopic pathogens that can spread rapidly. Contrast non‑infectious disease.
infiltration	The movement of water into soil.
inflorescence	A group of individual flowers arranged in a cluster. Examples: lilac, daisy, sunflower.
infrastructure	Term used to describe the structures and systems, such as roads, sidewalks, traffic signs, above- and belowground utilities, that are required for a community.
insect	A small invertebrate animal having an exoskeleton, three body regions, six jointed legs, and one pair of antennae.
instar	A developmental stage of insect larvae between molts. A species may have several instars. Newly hatched larvae before their first molt are first instars or first instar larvae.
integrated pest management (IPM)	A multi-pronged and unified pest control system that uses all available, necessary techniques and tools to manage pest populations and resulting problems, while striving to minimize adverse effects on other species and the environment.
internode	The regions on a stem between nodes. See also node.
intersectional peony	A cross between tree peonies and herbaceous peonies often referred to as Itoh peonies in honor of the plant breeder.
invasive species	A non-native species that outcompetes native species for their ecological niche.
ion	An atom or molecule with either a positive or negative electrical charge.
ISA certified arborist	ISA stands for International Society of Arboriculture, a nongovernmental professional organization which promotes the professional practice of arboriculture. ISA certified arborists must have worked in the industry a minimum of three years, pass a test to show a level of knowledge about trees, and stay up-to-date on best practices through continuing education.

K

Glossary Term	Glossary Definition
key pests	Common and chronic troublemakers for plants in a landscape or garden.
key plants	Plants in a landscape or garden that are problem-prone and likely to require the most attention.
key problems	The abiotic or biotic problems in a landscape or garden that are most likely to impact plant health and require attention and intervention.

L

Glossary Term	Glossary Definition
larva (pl. larvae)	An immature stage of an insect that undergoes complete metamorphosis, like caterpillars, maggots, or grubs.
lateral	A branch that is attached to, and smaller than, a larger branch or trunk. Term often used when pruning and making a reduction cut back to a side branch or lateral.
lateral bud	A bud on the side of a woody stem, in contrast to an apical bud found at the tip of a stem or root.
lateral buds	Embryonic plant shoot arising along the sides of stems. Brussels sprouts are edible lateral buds. See also axillary.
leaching	Movement of water and soluble nutrients down through the soil profile.
leader	Sometimes called the central leader or terminal shoot. Refers to the primary, upright stem of a woody plant, most often the top of a main trunk.
leaf scars	Place on a stem where there used to be a leaf attached.
lenticels	Small openings along a stem that allow gas exchange. Often seen as small bumps. Distinctive size, color, or shape may be diagnostic for species identification.
light compensation point	The level of light intensity at which the rate of photosynthesis (and a plant’s CO2 requirement) equals the rate of respiration (the plant’s CO2 output). A balanced light level for plants.
light duration	Indicates the photoperiod or length of time that the light source is emitting light.
light quality	Refers to the color of the light emitted by a source. A light’s color is determined by the light’s wavelength (measured in nanometers, nm).
light quantity	Relates to the intensity or the energy output of a light source.
light saturation point	The amount or intensity of light above which a plant’s photosynthetic rate will not change.
lime	Ground limestone rock (calcium carbonate, CaCO3) applied to soil to raise pH.
line	An inbred group of plants with homogeneous genetic material whose seed give very uniform progeny. Lines are usually associated with annual crops, vegetables, and flowers.
live crown ratio	The proportion of the total height of a tree that contains living foliage, most often applied to conifers.
loam	A soil with roughly equal influence from sand, silt, and clay particles.
local food	Food grown within a defined radius (generally 50 to 100 miles) of where it is sold or consumed.
long-day plant	Plants that require longer days and shorter nights in order to produce flowers. For example: peas, bellflower. Contrast short-day plant. See also photoperiodism.

M

Glossary Term	Glossary Definition
macropore	A large soil pore. Macropores include earthworm and root channels, and they control a soil’s permeability and aeration.
male confusion	In pest management, an effect of pheromone-impregnated lures to obscure the scent of live females so that mating does not occur.
meristems	Collection or area of undifferentiated plant cells from which new growth arises.
mesophyll	Spongy layer of cells in dicot leaves where photosynthesis and gas exchange occurs.
metabolism	The sum total of the biochemical activity within a plant.
metamorphosis	A change in the size, shape, or appearance of an insect as it matures. See also complex metamorphosis and simple metamorphosis.
microclimate	Small-scale areas where local conditions may differ from those of the surrounding climate zone.
micronutrient	A nutrient used by plants in small amounts (iron, zinc, molybdenum, manganese, boron, copper, and chlorine). Also called a trace element.
micropore	A small soil pore, typically a fraction of a millimeter in diameter. Micropores are responsible for a soil’s ability to hold water.
mineral nutrients	Plant nutrients absorbed from soil in the form of inorganic ions.
mitochondria	Cellular structure responsible for power generation in plant cells.
mitosis	Cell division producing daughter cells that are identical to the parent cell.
mixed buds	Embryonic plant shoot containing both vegetative tissue (leaves) and reproductive tissue (flowers).
mobile	A plant nutrient that can relocate within a plant. Contrast non-mobile.
monostand	A field or space with a single species of plant growing.
mosaic	Random pattern of colors, primarily shades of green, produced in leaf tissue; may be symptomatic of viral infections.
Muellarian mimicry	With insects, physical appearance evolved to appear like more dangerous species, as a form of defense. Contrast cryptic mimicry and Batesian mimicry.
mycelia (singular: mycelium)	Bunches of thread-like fungal hyphae.
mycelial fans	Masses of fungal mycelia; named for the shape produced by certain species of fungus.
mycorrhiza	Beneficial fungi that infect plant roots and increase their ability to take up nutrients from the soil.
mycorrhizal fungi	Beneficial fungi that inoculate plant roots and increase their ability to take up nutrients from the soil.

N

Glossary Term	Glossary Definition
naiad	Immature stages of aquatic insects that undergo incomplete metamorphosis, analogous to nymphs, but occurs in an aquatic environment.
native soil	soil that is relatively undisturbed by human development and has its original horizons intact.
natural enemies	Predators and parasites that attack pest species.
necrosis	Death of living tissue, usually resulting in discoloration of the affected area.
neonicotinoids	A group of insecticides used widely on brans and in urban landscapes.
niche	The combination of a role an individual species plays in an ecosystem and the environmental conditions it requires.
nitrifier	A microbe that converts ammonium to nitrate.
nitrogen cycle	The sequence of biochemical changes undergone by nitrogen as it moves from living organisms to decomposing organic matter to inorganic forms and back to living organisms.
nitrogen fixation	Conversion of atmospheric nitrogen into plant-available forms by Rhizobia or Frankia bacteria.
node	The area on a stem from which a leaf or twig sprouts.
non-infectious diseases	Physiological disease caused by adverse chemical, environmental, or soil conditions. Contrast infectious disease.
nonhost	A plant that is not susceptible to a pathogen or is inhospitable to an organism.
nonselective pesticide	A pesticide that damages or kills all types of pests.
noxious weed	Non-native plant species that are destructive to ecosystems, highly competitive, and are difficult to control.
nutrient cycles	Pathways of nutrient inputs and outputs, transformations, and flows through soil-plant systems.
nymph	An immature stage of insects that undergo simple metamorphosis in which the insect body resembles the adult.

O

Glossary Term	Glossary Definition
organic amendment	A material of biological origin that is added to soil to build soil organic matter and improve soil health. Examples include compost, manure, and cover crop residues.
organic fertilizer	A natural fertilizer material that has undergone little or no processing. It can include plant, animal, and mineral materials. Organic fertilizers are generally richer in nutrients than organic amendments.
organic mulch	An organic material (often woody) that is placed on the surface of the soil to reduce evaporation loss, protect the soil surface from erosion, smother weeds, and buffer soil temperature changes. Examples include ground bark, arborist chips, and straw.
overstocked forest	A forest that has more trees than the site can sustain without incurring significant competition.

P

Glossary Term	Glossary Definition
Pacific Decadal Oscillation (PDO)­­	The Pacific Decadal Oscillation is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years (NASA).
palisade cells	In dicot leaves, chlorophyll-rich, elongated cells arranged perpendicular to the plane of the leaf.
parasite (adj.: parasitic)	An organism that attaches to or feeds within a host organism without killing it. Fleas are considered parasitic.
parasitoid	An organism that invades or attaches to a host organism’s body, feeding on it until the host dies.
parent material	Geologic material from which soil has formed. Examples include glacial deposits, alluvial (flood) deposits, loess (wind-blown) deposits, volcanic deposits, and weathered bedrock.
parthenocarpic	The development of fruit without prior fertilization.
parthenogenesis	Asexual reproduction without fertilization or mating.
pathogen	A disease-causing organism. Pathogenic organisms include bacteria, viruses, fungi, parasitic plants, and nematodes.
peat moss	The product of peat bogs used as an acidifying soil amendment. Also known as sphagnum peat moss or peat humus. Peat bogs are ancient carbon sinks; therefore, use of peat moss as a commercial soil amendment is not considered a sustainable practice.
ped	An aggregate of soil particles formed by natural processes.
perennial plants	Plants that grow and continue to reproduce over multiple years. May be long-lived or short-lived, hardy or tender, flowering or non-flowering.
permeability	The rate at which water moves through a soil.
pest resurgence	In pest management, the rebound of a pest population after a broad-spectrum pesticide has been applied that killed not only some of the target pest but also other beneficial organisms that had kept the pest in check. The beneficial agent is no longer there to help keep the target pest in check, so that pest can recover and expand.
petiole	The stalk of a leaf, attaching the leaf to a stem.
pH	A measure of soil acidity or alkalinity. Values less than 7 indicate acidity, a value of 7 is neutral, and values greater than 7 indicate alkalinity. Most soils have a pH between 4.5 and 9.
phenological­­	Timing of natural, cyclical events such as bloom or leafing out.
phenology	The study of life cycle events (for either plants or animals) as related to seasonal and climatic changes.
pheromone	A volatile chemical substance secreted by animals to stimulate a response in or convey information to others of its species.
phloem	Type of living plant tissue responsible for movement of nutrients throughout the plant. In trees, located within the cambium layer.
phloem-immobile	Nutrients that cannot relocate within a plant via the phloem.
phloem-mobile	Nutrients that can relocate within a plant via the phloem.
photoinhibition­­	When a plant receives too much light, resulting in reduced photosynthesis and plant growth.
photoperiodism	Changes in a plant’s growth and development induced by the relative length of light and dark periods (length of day and night).
photosynthesis	Chemical reaction involving chlorophyll within plant cells that converts sunlight plus carbon dioxide into sugar (energy) the plant can use.
photosynthetically active radiation	Wavelengths of visible light that are most effective in stimulating photosynthesis in plants.
phytotoxicity	Harm to seed germination or plants caused by substances present in the growth medium, such as natural acids found in uncured compost.
pinching back	Removing the growing tips of twigs to encourage bushier growth.
pistil	Female portion of a flower, made to catch pollen.
pith	Spongy, nonvascular tissue in herbaceous dicot stems.
plant growth regulator	Synthetically produced chemical that mimics a plant hormone to regulate a plant’s growth.
plant health care	A holistic approach to managing gardens and landscapes focused on improving overall plant health in order to prevent or avoid plant diseases and problems.
plant injury	Nearly instantaneous damage to a plant caused by mechanical impact or sudden, short-term environmental changes.
plantation forest	A forest that was started via artificial planting and managed to be even-aged.
pollination	Transfer of pollen from male parts of a flower (stamen) to the female parts of a flower (pistil); fertilization, required for most fruit and nut production.
population dynamics	The science or study of how a population’s size grows and shrinks over time as related to births, deaths, and migration, and the study of the factors affecting those changes.
predator	An animal that attacks, feeds on, and kills other animals.
preharvest interval	The minimum number of days permitted by law between the last pesticide application and the harvest date.
primitive insects	Insects that do not undergo complex metamorphism but merely get larger as they mature. Most primitive insects have external mouthparts. Contrast higher insects.
primocane	A new shoot that is vegetative, usually arising from the crown, base of old canes, or roots, depending on the caneberry species. Usually primocanes are vegetative, but some cultivars are considered primocane-fruiting, meaning they can produce fruit on current-season primocanes. Primocanes overwinter and become floricanes the following year.
proboscis	Elongated mouthparts found in moths and butterflies adapted for collecting liquids, like nectar, from plants.
product brand name	Commercial title of a product; the trade name.
prolegs	Unjointed legs of caterpillars and sawflies; distinguished from “true legs” which are jointed.
protoplasm	Archaic term for the entire contents of a living cell.
pruning	The removal or reduction of parts of a plant, tree, or vine that are not required for growth or production, are not visually pleasing, or are causing injury to the plant.
pupa (pl. pupae)	An intermediate stage of development for insects that undergo complex metamorphosis. Insects do not feed during the pupal stage. Usually involves a chrysalis or cocoon.

R

Glossary Term	Glossary Definition
ray cells	Specialized xylem cells that move water and nutrients laterally rather than vertically within a plant.
recyclers (also known as decomposers)	Organisms such as worms, insects, and fungi that ingest or otherwise break down organic matter, releasing the carbon, nitrogen, and other raw materials from the organic matter.
reduction cut	Reducing the length of a branch by cutting back to a side branch that is one-third to one-half the diameter of the cut branch or larger. Cutting back to a side branch of this size reduces the risk of disease or decay entering the wound.
Registered Consulting Arborist (RCA)	Registered Consulting Arborists have taken and passed higher level training through the American Society of Consulting Arborists (ASCA). Registered Consulting Arborists typically have more education than other arborists and may be highly specialized in their practice.
relative humidity (RH)	How saturated the air is, relative to how much water vapor it is capable of holding, given as a percentage.
removal cut	Pruning a branch all the way back to its point of origin.
resilience	The ability of a forest to recover from disturbance and maintain structure and function.
resistance	The ability of a plant to avoid or repel infection from a specific pathogen; the ability a pest develops to withstand pesticides.
respiration	Transport and exchange of oxygen from outside an organism into its cell, concurrent with production of energy and release of carbon dioxide.
restricted entry interval	The length of time following an application of a pesticide when a person is required to wear protective clothing and equipment in a treated field.
reticulate	Net-like, as in leaf veining.
Rhizobia	Bacteria that live in association with roots of legumes and convert atmospheric nitrogen to plant-available forms, a process known as nitrogen fixation.
rhizomes	Creeping horizontal stem, usually underground, with roots below and stems above; not a true root.
rhizomorphs	Dark clumps or strands of fungal mycelia that resemble roots, on or just below the soil surface.
rhizosphere	The thin layer of soil surrounding plant roots that is influenced by the presence of roots, making it an environment of high biological activity.
riparian	Wetlands around surface water, like the banks of a river or lake. Riparian areas are usually protected by laws or regulations.
roguing	Simple removal and destruction of problem plants.
root cap	A group of tough cells produced by the apical meristem at the tip of a root that serves as a battering ram to allow the root to force its way down into the soil.
root hairs	Small extensions of epidermal cells in a plant root that take up water and nutrients for a plant.
rootstock	On a grafted tree, the root and collar system to which the scion is grafted. Rootstock controls tree size, fruiting precocity, and soil moisture tolerance and may provide some resistance to soil insect pests and diseases.
rosette	Plant growth form in which many leaves emerge radially on very short stems.

S

Glossary Term	Glossary Definition
salts	Compounds consisting of positive and negative ions. Examples include table salt (NaCl) and fertilizers such as potassium chloride (KCl) and ammonium sulfate ((NH4)2SO4).
sand	The coarsest type of primary soil particle (0.05 to 2 mm in diameter).
saprophytes	Organism that obtains nutrition from dead and decomposing organic material, often aiding in their decomposition.
sapwood	Portion of a woody stem containing live xylem; the portion of a woody stem where active movement of water and nutrients takes place.
scientific name	Latin name consisting of genus and a specific epithet for the species. May also include the name of a recognizable race, subspecies, or varietal.
scion	Grafted material on a tree; a cutting destined to be grafted onto another rootstock.
secondary pest	Pests that infrequently or occasionally cause damage but rarely stress or kill their host plants; secondary pests are often less important than key pest species.
secondary pest explosion	In pest management, a consequence of applying a broad-spectrum insecticide that kills not only the primary target but also beneficial agents that had been keeping another (secondary) pest in check.
seedling rootstock	The original rootstock of a tree grown from seed.
selective pesticide	See narrow spectrum pesticide.
self-compatible	Fruit varieties that can set fruit when pollinated with their own pollen.
self-fruitful	Fruit varieties that can set fruit when pollinated with their own pollen.
self-incompatible	Fruit trees that cannot be fertilized by their own pollen to produce fruit. These trees require pollen from another variety for fruit production.
self-pollination	Transfer of pollen from the anther to the stigma of the same plant. Contrast cross-pollination.
sepals	Modified leaf structure that encloses and protects a flower bud.
sequester, or carbon sequestration	The process of capturing carbon and putting it into a form that is not immediately released. While there are multiple types of carbon sequestration, this chapter refers to the capture of carbon dioxide (CO2) by plants through the process of photosynthesis. Photosynthesis converts CO2 into sugars used by plants for growth.
shoot	This usually refers to a newly developing stem and its leaves, but it sometimes is used to refer to stem tissue.
shoot system	The stem and leaves of a plant (all the parts of a plant except for its roots).
short-day plants	Plants that require longer nights and shorter days in order to produce flowers. For example, strawberries, poinsettia.
shuck	A papery sheath surrounding newly developing fruit in some plant species such as stone fruits and tomatillos.
signs	The vegetative or reproductive structures of a pathogen or pest that are either individually or collectively large enough to be visible without a microscope. Contrast symptom.
silt	A primary soil particle of intermediate size (between the size of sand and clay) at 0.002 to 0.05 mm in diameter.
silviculture	The art and science of managing forest to meet the needs and desires of landowners and society.
simple buds	Embryonic plant shoot containing either vegetative tissue or reproductive tissue, but not both. Also, a flower bud containing reproductive tissue for a single flower.
simple metamorphosis	A set of changes or stages of maturity during the life cycle of certain insects that involve little more than changes in size; typically includes egg, nymph, and adult stages. Contrast complex metamorphosis.
simple plants	Single-celled or few-celled plants that do not have an internal vascular system.
site productivity	A measure of the ability of a site to grow trees.
slash	Woody debris removed from trees during logging or pruning.
snag	A standing dead tree, typically taller than six feet and greater than eight inches in diameter.
soil	A natural, biologically active mixture of weathered rock fragments and organic matter at the earth’s surface.
soil frost line	Average depth to which soil freezes each winter.
soil health	The continued capacity of a soil to function as a vital living ecosystem that sustains plants, animals, and humans.
soil horizon	Horizontal layers formed in the soil that differ from each other in color, texture, structure, or other characteristics.
soil profile	A vertical section of the soil from the surface through all its horizons.
soil salinity	The saltiness of a soil. Saline soils contain enough soluble salts to harm seed germination and crop growth.
soil solution	The solution of water and dissolved minerals found in soil pores.
soil structure	The arrangement of primary particles (sand, silt, and clay) into aggregates (peds) in a soil.
soil texture	How coarse or fine a soil is. Texture is determined by the proportions of sand, silt, and clay in the soil.
soil-applied products	Control for weeds, nematodes, and insects. Applied primarily to the soil surface for root absorption rather than to vegetation.
species	The basic unit of taxonomy designating a group of individuals that are capable of interbreeding. A uniform population of individuals, distinct from other individuals in terms of predetermined or marked characteristics. There are many definitions of this term. Each species has a unique Latin binomial name consisting of the genus name followed by the specific epithet; for example, the scientific name for red maples is the Latin binomial Acer (genus) rubrum (specific epithet).
spiracle	Opening in an exoskeleton to facilitate gas exchange; opening to a respiratory tube.
spur-type	In apples, least vigorous growing varieties.
spurs	On woody flowering plants, a specialized branch with very short, compressed internodes that give rise to flower buds. Typical of apple, chokeberries. Also known as fruiting spurs.
stabilized organic matter	Soil organic matter that remains after the decomposition of plant and animal residues. It is dark in color and tends to resist further decomposition. It is sometimes called humus.
stamen	Male part of a flower.
stand	A subsection of a forest with similar characteristics, like age, composition, and structure.
stand density	A measure of the number of trees in a given area, often measured as trees per acre.
stolon	Modified stem that spreads laterally across the ground surface, rooting at their joints to form new plants.
stomata	Pores on leaves and stems that control gas exchange in plants. From the Greek word for “mouth.”
storage, or carbon storage	The long-term holding of carbon, usually in the form of plant tissue. Woody plants store carbon for longer periods as it is held in stems and roots for many years until the tissue breaks down through decomposition. Through decomposition, some of the carbon returns to the atmosphere, but much of it remains in storage as soil organic matter.
structural diversity	The variability in height, density, and arrangement within a forest.
stub cut	A pruning cut made too far away from the branch collar or natural target that leaves a stub of tissue. Stub cuts are undesirable because they delay compartmentalization of the pruning wound and are visually unappealing.
stylet	Small, hard, piercing mouth-part of an insect, used to extract fluids.
sub-shrub	A perennial that is largely herbaceous but slightly woody at the base.
sucker, also called root sprout	Shoot or stem originating from the root system of a plant. Plants, such as poplar, lilac, and privet, produce root sprouts as part of their normal growth process. Root sprouts may appear some distance from the parent plant but remain connected through the common root system. Systemic herbicides applied to root sprouts frequently damage the parent plant.
survival watering	Applying enough water to enable a plant to survive through a dry period.
susceptibility	The degree to which a plant is vulnerable to infection by a specific pathogen.
symptoms	Any detectible change in an organism resulting from the activities of a pathogen, other pest, or environmental conditions. Contrast sign.
systematists	Taxonomists; scientists who specialize in the classification of organisms.
systemic pesticide	A pesticide that is absorbed by a plant or animal and translocated within that plant or animal.

T

Glossary Term	Glossary Definition
taproots	One main fleshy root that grows straight down into the ground.
terminal bud	Embryonic plant shoot located at the tip of a stem.
thermophilic	Heat loving. Type of bacteria that require high temperatures to thrive.
thinning	The process of removing trees from a forest to reallocate resources to remaining trees.
thorax	The middle body segment of an insect between the head and the abdomen that bears the legs and wings (if present).
tolerance	The ability of a tree or plant to survive and grow under a given site condition, chemical injury, or infection by a disease without serious damage or loss in yield. (e.g., ability to tolerate dry soils).
topping	Pruning cuts that are not at the natural target but leave stubs. Often refers to an improper style of pruning where an entire plant is pruned to a certain height or shape where most or all cuts are improperly made. Impacts of topping include water sprout growth and possibly poor wound compartmentalization, which can lead to wood decay.
trade name	Commercial title of a product; a product’s brand name.
translocating herbicide	A chemical that moves through the vascular system of a plant, such as herbicides that enter the roots or foliage and are moved to the growing points and roots to control the (susceptible) pest plant species from the inside.
transpiration	The giving off of water vapor through a plant’s leaves or stomata. This causes water to be drawn up through a plant’s roots, thereby moving water and nutrients through a plant.
trapline approach	Foraging on a repeated sequence of floral resources in a series of feeding locations.
Tree Risk Assessment Qualification (TRAQ)	Arborists with a Tree Risk Assessment Qualification have taken advanced training and passed a rigorous exam on how to assess risk. Becoming an ISA certified arborist is a prerequisite to taking this training.
tree vigor	The potential for a tree to become a large tree. The greater the vigor, the larger the tree at maturity.
trunk taper	The difference in diameter between the top and bottom of a stem. Under normal conditions, tree trunks are widest at the base and narrow higher in the crown. This gives them more structural strength to withstand physical forces like gravity and wind. Lack of trunk taper suggests that the plant is not developing normally or has been planted too deep in the soil so that the root flare at the base has been buried.
tubers	Enlarged underground stems that provide nutrient storage for the plant.
tunicate	Bulbs that have a paper-like covering that protects the bulb scales from drying and mechanical injury.

U

Glossary Term	Glossary Definition
urban heat island	term used to describe how urban areas have an average temperature that is two to seven degrees Fahrenheit higher than adjacent rural areas.

V

Glossary Term	Glossary Definition
variety (botanical)	A fairly consistent natural variation of the species, which will more or less breed true.
vector	An agent that carries disease inoculum from one host to another.
vermicomposting	Composting done by red worms; typically done in a controlled environment such as a worm bin for the most efficient job.
vernal pool	Seasonal pool of water that provides habitat for distinctive plants and animals.
vernalization	The process or stimulus which causes a plant to produce a flower bud, such as the chill of winter (verb: vernalize).
visible spectrum	Wavelengths of electromagnetic radiation that are visible to the human eye: violet to red light.

W

Glossary Term	Glossary Definition
water sprout (also called epicormic shoot)	Vigorous shoots that arise from latent buds on branches or the trunk as a result of plant stress, including pruning. Some plant species are more prone to forming water sprouts.
water-holding capacity	The ability of a soil’s pores to hold water for plant use.
waterwise	The practice of planning and implementing a landscape design that focuses on the reduction of water use.
weed-and-feed products	Commercially available products that are a combination of herbicide (plant killer) and fertilizer.
well-being	Positive outcome that reflects life satisfaction, resilience, and realization of potential.
wetting front depth	Depth in the soil profile to which surface-applied water has soaked in.
wildland urban interface	An area where structures and human development are adjacent to or intermingle with wild vegetation.
woody perennials	Plants that retain woody stems and branches from year to year and add diameter growth each year. May be evergreen or deciduous. Contrast herbaceous perennials.
wound wood	New tissue formed to compartmentalize the outside of wounds. When pruning woody plants, wound wood originates from the branch collar. Making improper pruning cuts into the branch collar interferes with a plant’s ability to form wound wood.

X

Glossary Term	Glossary Definition
xylem	In vascular plants, the internal structure through which water and dissolved nutrients are moved. As a plant grows, old xylem is retained and becomes the woody part of a plant.

Z

Glossary Term	Glossary Definition
zone of differentiation	In plant shoots, twigs, and roots, the region below or behind the zone of elongation; cells here are maturing and differentiating for the different tissues they will be part of. Another name for the zone of maturation.
zone of elongation	Region near the tip of a twig or root just behind the meristem, where new cells are elongating to move the meristem farther out from previous growth.
zone of maturation	In plant shoots, twigs, and roots, the region below or behind the zone of elongation; where plant cells are maturing and differentiating for the different tissues they will be part of. Another name for the zone of differentiation.