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The following glossary will help you navigate the world of tree seedlings and other PRT products.

The crop production cycle used to produce tree seedlings, expressed in growing seasons in the same location and growing medium. The first number represents the growing seasons in the first location and the second number the growing season in a second location; e.g. 1+0, one season in one location and growing medium; 2+0, two seasons in one location and growing medium; 0.5+1.5 = a half or partial growing season in one location and growing medium, and then a half or partial season plus another full growing season in a second location.
Short form: BR Seedling crops grown in field beds and harvested without soil or “bareroot”.
Renewable energy obtained from materials derived from biological sources. PRT’s purpose-grown woody biomass is through the growing and management of willow.
Biogeoclimatic zone
Short form: BGC Zone Forest zones (defined on the basis of dominant tree species, other plant systems, geographic and climatic criteria) used in nurseries as part of the seedlot description.
Short form: B/O The practice of shortening day-length using dark-out systems so that the “critical photoperiod” for shoot growth is not met. This promotes changes to the morphology of seedling growth, from shoot elongation to bud set. Blackout promotes uniform bud set in the crop as compared with crops grown without blackout. Blackout is one of several tools used by nurseries to morphologically ready seedlings for shipping on specified dates.
Cavities per Block
Short form: Cav per Blk Number of cavities in a standard Styroblock area (14" by 24").
Cavity Volume
Short form: ml per Cav Volume of container cavity, expressed as milliliters, cubic centimeters or cubic inches.
Cold Storage
Storage of trees for winter and spring planting at temperatures above freezing, typically at 2°C (36°F).
Common Name
The common or popular name rather than the Latin or scientific name.
Coniferous Trees
Cone-bearing seed plants with vascular tissue; all conifers are woody plants, the great majority being trees with just a few being shrubs. Typical examples of conifers include cedars, Douglas firs, cypresses, firs, junipers, kauris, larches, pines, hemlocks, redwoods, spruces and yews. These trees, also referred to as evergreens, usually retain their needles throughout the year.
Container Seedlings
Container seedlings are grown as “plugs” in containers. The important aspect is that their roots are not damaged during the harvesting process and, as a result, they generally perform better than bareroot products. See Plug Seedlings.
Contract Specifications
Describes the contract specifications of the seedling product. Defines the acceptable specifications for a product, usually expressed by height and root collar diameter (RCD) ranges.
Deciduous Seedlings
Trees that drop their leaves each autumn are called ‘deciduous’, from the Latin term “to fall”. Alternative names for deciduous trees are broadleaves or hardwoods. Some of the more common species are oak, poplar, beech, apple and chestnut. There are also deciduous conifers, which are coniferous trees that drop their needles each autumn. Examples include Larch, Metasequoia and Bald Cypress, among others.
Delivery Date
The date specified for delivery of seedlings in a contract.
Short form: Elev Seed collection elevation.
External Order Number
Short form: EON Order number provided to PRT by customers. The “Request Key” is an example for use in British Columbia.
Extractable Plug
Orders that are packaged to extractable plug standards will contain all seedlings in the crop that have a cohesive plug when lifted.
Fall Planting
Short form: FA Seedlings that are lifted and shipped directly from the nursery to the field for planting between September 16 and December 31. Cold storage is not required.
Field Germination
Short form: Field Germ Percentage of seeds that germinate to the point of being visible above the seed covering in field or container conditions.
Field Performance
Ability of trees to perform their intended function on a reforestation site.
Freight on Board
Short form: FOB FOB Nursery Gate indicates that the buyer pays shipping costs and takes responsibility for the goods when they leave PRT’s premises.
Frozen Storage
Storage of trees for winter and spring planting at temperatures below freezing (–2°C/28°F).
Short form: GH Polyethylene film or glass-covered structure, complete with heat and ventilation.
Specially graded sand for seed covering, usually graded between 4½ and 10 mesh, also called forestry sand. It is used to prevent the growth of algae, moss and liverwort on top of the seedling plug.
Growth Monitoring
Scheduled measurements of seedling morphology which are compared to crop plan targets.
Internal Order Number
Short form: ION Internal control number given to every PRT contract order.
Short form: Inven A projection of the number of seedlings that will meet contract seedling specifications.
To bend the root system laterally, forming a “J”—hence the name.
Lab Germination
Short form: Lab Germ Seed germination results from tests performed in a controlled laboratory setting.
Latin Name
The scientific naming system of designating plants and animals by two Latinized words signifying the genus and species.
Short form: Lat Seed collection latitude.
Geographic area where seed was collected, often referring to the name of an area or creek drainage.
Short form: Long Seed collection longitude.
Microsite Selection
Process of selecting the best planting spot for a seedling within a limited area.
Short form: MP Miniature plugs used for the first phase (source container) and then transplanted to larger destination containers for growth completion. Very small cavity volume at high seedling density.
Mini-plug Transplant
Short form: MPT Second phase for miniature plug transplanted to a larger container for growth completion.
Natural Seed
Seed collected from natural forest settings. No improved genetics.
Nutri-plug® Plus
Value added product. PRT seedling plugs injected with controlled release fertilizer prior to planting. Effectively replaces fertilizer tea bags and other on-site fertilizing methods, at time of planting. It also delivers the fertilizer to the tree rather than to surrounding vegetation.
Open Compound
Short form: OC Outdoor growing area.
Seedlings in excess of a customer’s order.
Planting Density
Number of seedlings planted per hectare or acre.
Planting Season
Short form: SoP Season of planting, where SP = Spring; SU = Summer; FA = Fall; WI = Winter.
Planting Year
Short form: YoP Year of planting.
Plug Copper Treated
Short form: PCT Container seedling grown in a styroblock which is coated with a copper-containing compound that affects the way the roots develop. Chemical root pruning.
Plug Seedlings
Many foresters and nurseries refer to container-grown seedlings as “plug” seedlings. These seedlings are grown in cells in blocks or trays made from expanded polystyrene or polythene. PRT seedlings are grown in expanded polystyrene (dense white Styrofoam). The growing medium contains a high component of peat moss in most cases. By the time of harvesting, the roots bind the medium into a cohesive “plug” that keeps the shape of the cell.
Potting Test/RGC Test
Simple test involving potting of seedlings to demonstrate the viability of roots and buds, done for 28 days under greenhouse conditions with day temperatures of 18°C/64°F to 28°C/82°F and night temperatures of 12°C/54°F to 24°C/75°F.
Products are defined by the combination of Species, Type, Size, Age, and SoP.
PRT Stock
Overrun or spec-grown seedlings in excess of customers’ needs, made available for sale to others.
Root collar diameter.
Temperature-controlled trailer (“refrigerator car”) used to transport seedlings over long distances and also for storing seedlings in the field.
Regeneration Systems
Type of system used by foresters to regenerate a site and decided by the type of harvesting used, such as clear-cut, partial cut, single-tree selection and shelter wood.
Scatter Diagram
Short form: Scatter Graphical representation of seedling population, used for growth monitoring, inventory projections, pre-lift assessments and audits.
Seed Orchard Seed
Seed sources based upon known individuals derived from tree breeding. Intensively-managed plantation of specifically arranged trees for the mass production of genetically improved seeds to create plants or seeds for the establishment of new forests.
Seed Origin
Seed orchard or natural collection seed source.
Seed Source
This covers all material from a single tree to any collection of trees within a region of provenance or seed zone.
Seed Zone
A geographic area, defined on the basis of ecological characteristics and genetic information, within which seeds may be collected and freely deployed without any significant loss of adaptation and growth potential.
Numeric or alphanumeric code applied to a batch of tree seeds, used to identify the source and ownership of the seed.
Seeds per gram
Short form: SPG Number of seeds per gram after drying to specific moisture content for long-term storage.
Site Preparation
Any of a number of methods used to modify planting sites to improve the ability of seedlings to establish and grow. Common methods include burning, mounding, disc trenching and piling. In the US, herbicides are commonly used for site preparation.
Somatic Seedling
Short form: SSB Tree started from a somatic embryo.
Spec Stock
Seedlings grown on speculation that are for sale to any buyer and not grown for a specific customer.
The basic unit of biological classification. ‘Fir’ and ‘pine’ are two examples of species classifications.
Species Code
Abbreviation for each seedling species. PRT uses a two-letter code in upper case; e.g. PL = Lodgepole Pine.
Spring Planting
Short form: SP Spring delivery products are lifted in the late fall, packaged and stored at –2°C/18°F over the winter. This allows for a wide delivery window in the spring, enabling the seedlings to be planted when field conditions are optimal, typically from mid-April to mid-June.
Starter Plants
Plants grown from seed or cuttings in smaller containers to be transplanted to the field or into larger containers for further growing. PRT’s Starter Plant program primarily includes cranberry plants with plans underway for raspberry and strawberry plants.
Stock Size (Metric)
Part of the product definition referring to the cell size. It can be represented as cells per block and volume per cavity (in metric measurement), e.g. 412B = 112/95 ml; or by diameter and length of plug, e.g. 412B = 4 cm diameter by 12 cm in length. Figures are rounded to the nearest whole number.
Stock Type
Short form: StkTyp Growing systems are called types. Stock Type refers to the kind of styroblock, or other container system, used to produce a seedling. Examples include PCT (Plug Copper Treated), PSB (Plug Styrofoam Block) and CRC (Container Rooted Cutting), among others.
Storability Test
The practice of freezing seedlings to specific temperatures and then evaluating them, post-freezing, to determine if the seedlings have been damaged or not. The two most common methods use are:
• Foliar analysis—plants are potted and put in controlled conditions for a specific period of time post-freezing and assessed to determine if leaves are damaged or not.
• Chlorophyll fluorescence—measures the photosynthetic capacity of seedlings pre- and post-freezing and provides fast and reliable results for storability testing.

Summer Planting
Short form: SU Summer delivery products are lifted in the summer, packaged and shipped immediately to the customer for out planting. Seedlings are morphologically active and it is recommended they be planted within three days of being delivered from the nursery. Typical summer planting dates are from June 20 to late July.
Surplus Seedlings
Seedlings that were grown under contract for customers but that are in excess of the amount ordered, and thus not required by the customer and made available for sale to others.
Process of thawing frozen stored trees for a customer prior to shipping.
Trees Lifted
Short form: Lift Total number of seedlings lifted for an order.
Trees per Box
Number of trees packaged per box.
Trees Requested
Short form: Req Number of trees requested for an order.
Trees Shipped
Short form: Ship Number of trees shipped from nursery or cold storage.
Value Added Product
Refers to “extra” feature(s) of a seedling product that go beyond standard expectations and provide something “more” to the end product. An example would be browse-protection devices.
Year of Sowing
Short form: YoS Year that a crop is sown.