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Prior to the contract commencement, a number of operations are required to get the stock to the planting site or to the interim storage facilities. These operations are critical to the success of the project and must be carried out carefully not only to ensure that the planting stock arrives in excellent condition but also to ensure that the contract itself runs as smoothly as possible. The following sections outline the procedures for thawing, storage, handling, and transportation of stock.
The goal of handling, storage, and transportation is to ensure that the growth potential, present when a seedling is lifted at the nursery, is maintained until it is planted in the field.
Proper stock handling, storage, and transportation procedures play a vital role in achieving high survival and the full growth potential of planted seedlings. Damage to seedlings is cumulative, often occurring at all stages from nursery to final planting. Seedlings are subjected to fluctuating levels of temperature, light, and moisture on their journey from nursery bed to planting hole. These stresses, together with physical damage, force the seedlings to shift resources to temperature adjustment and repair, resulting in lower growth potential. This leaves the seedling with less vigour for establishment after planting. Severe damage or stress will inevitably lead to seedling mortality. Stock handling, storage, and transportation guidelines are designed to minimize events that put seedlings under stress. These events include:
Minimizing stress through careful handling, controlling temperatures, and keeping the seedlings moist is the key to maintenance of seedling vigour. Remember, everyone involved is responsible for the well-being of the seedling. All staff and contractors involved in the reforestation process should view the stock handling video Seedling Care - Everyone's Concern prepared by the Silviculture Branch, Victoria (1989). A stock handling brochure (Nursery to planting site: A team effort) is also available.
Seedlings have a limited supply of carbohydrates when they are placed into storage. This carbohydrate supply can only decrease until the seedlings are planted and start growing again. Nurseries build up the seedlings carbohydrates for use in the field - a reserve that should not be wasted in storage. The status of this reserve is translated into the vigour of the seedlings. Losses of carbohydrates result in a reduction of the vigour of the seedling and the ability of the seedling to withstand stress.
Respiration occurs even at the low temperatures experienced during frozen storage. One of the products of respiration is heat. The rate of respiration is controlled primarily by temperature; the higher the temperature, the higher the rate of respiration and the faster the carbohydrate reserves are used up by the seedlings. It is therefore very important to dissipate the heat that is being generated inside the carton. See "Monitoring Temperatures" below for more information.
Respiration of cold- or freeze-stored, dormant stock uses small amounts of the carbohydrate reserves of the seedlings. Frozen storage at -1 to -2oC minimizes carbohydrate depletion (see "Types of Seedling Storage" below for more information).
After 6 months, frozen-stored stock has used the same amount of carbohydrates as cold-stored stock (at 1oC) uses in 2 months.
Frozen storage minimizes foliage diseases. Frozen storage arrests, but does not eliminate the risk of storage moulds. The mould will flourish when temperatures rise during thawing, so close monitoring for the disease is imperative. Botrytis ssp. and other storage moulds can proliferate at temperatures of 1-4oC, under high humidity and in the absence of light. These same storage conditions are the ones created for the protection of the seedling (namely cool temperatures, high humidity, and closure in a carton). (See "6.9, Stock Problems" for more information.)
In British Columbia, seedlings are stored or handled in five acceptable ways:
Frozen storage - Stock scheduled for planting after March 15 is generally frozen stored. The storage period for this stock can extend up to 7 months. Frozen storage generally applies to interior species that have been lifted in fall or early winter and are scheduled for spring planting. Take care when thawing out frozen stock (see "6.4, Thawing Frozen Stock").
Cold storage (prior to shipping) - Stock scheduled for planting prior to March 15 (mostly coastal stock) is usually stored at temperatures above freezing. The storage period for this stock is generally less than two months. Arrange short term storage in permanent buildings or in mobile refrigerated trailer vans.
Cold storage (prior to planting) - Stock (unless hot lifted) may be cold stored at 2oC in portable refrigerated trailers (or other facilities such as ice-cooled insulated sheds) near the planting site.
Cool storage (Field Cache Storage) - Cool storage immediately prior to planting at or near the planting site is required to protect seedlings while ensuring a continuous supply to the planters.
Hot lifting - There is no cold storage with hot lifting. Hot lifting is used mostly in summer and fall planting (see "Summer Planting" under "2.3, Season of Planting" in the section "Project Planning and Prescription Development"). For summer planting, seedlings are irrigated immediately before lifting. Once lifted, seedlings may be cool stored (<10oC) overnight. The volumes of seedlings that can be produced for such lifting are limited by the nursery space available, and by the volume of seedlings that can be lifted during the short lifting season. The various lift capacities by nursery are available from regional reforestation staff.
To be successful, hot-lifted stock must be planted immediately. It is recommended that transportation of seedlings to the field occur overnight and delivery be as close to the planting site as possible.
Hot lifting is also used for spring planting, mostly on the coast. However, holding stock over winter in the nursery, fields, or the greenhouse and lifting in the spring generally puts the seedlings at risk to hazards such as frost, cold temperatures that may damage trees, and wet ground in nursery beds (bare root). The volumes of seedlings that can be lifted and shipped in a hot-lift situation are often limited by the lifting window at the nursery and the proximity of the planting site.
Constant and proper monitoring of seedling cartons is an essential part of seedling storage and handling. Carton temperature is usually monitored using the probe-type thermometer pushed into the centre of a carton. This may not be effective for cartons stacked on pallets. Thermocouples with long traces are available and can be placed into the centre of pallets or be used in other circumstances where probe-type thermometers are ineffective. Refrigeration units should all be equipped with thermometers to monitor air temperatures and to regulate cycling of refrigeration units.
Local Storage Facilities
Primary storage facilities that are centrally located are not always convenient for planting programs. A variety of other local and interim storage facilities may be required. When using alternate storage facilities, give care and attention to maintaining constant temperatures.
Interim storage facilities may include:
The on-site temporary field storage must be maintained as closely as possible at the proper temperature (<10oC) to ensure seedling survival and vigour. This can be accomplished, where appropriate, by using portable refrigerator vans or reefer units to serve as on-site cold storage. These units provide a controlled environment but require constant monitoring and maintenance. Satisfactory field storage can often be prepared by using the natural environment, reflective tarps, and a little ingenuity. Refer to the following list for the do's and don'ts to be considered when developing a temporary field storage.
Seedling caches are best set up on the edge of the planting block in the shade of standing timber, preferably on snow or near streams. Shaded areas under bridges may form perfect caches, but sudden runoff from rain or heat may cause a river to rise, with potentially disastrous results.
Clean, good quality reflective-type tarpaulins are the best covers for seedling caches (see FERIC Field Note No.: Silviculture-32 Reflective tarpaulins for silvicultural use: Comparing ability to resist heat transfer, 1991 and FERIC Report, Effectiveness of reflective tarpaulins in protecting tree seedlings against heat stress, 1993).
Keep field cache temperatures below 10oC. Follow procedures outlined in "Temporary Field Storage" above. For spring planting, stock should not be field cached for longer than a week, while summer planting stock should be used within 3 days.
When summer or hot lifted stock is delivered to the field cache, the cartons must be opened and bundles placed upright in locations where indirect light is available. Do not leave them in closed reefers. Shade seedlings from the sun.
Whether storing or transporting stock, it is critical that cartons be spaced so that air is allowed to circulate freely around them. Heat buildup is a critical concern and can cause stress and seedling damage quickly. The heat from respiration must be allowed to dissipate.
Use refrigeration facilities that have been designed to accommodate pallets of cartons. With reefers or other forms of temporary storage, use spacers (2.5 × 10 cm) between layers of cartons. Also provide space between cartons (3-5 cm). This allows air to circulate around the pallets and cartons.
If curling rinks or other similar storage facilities are used, large portable fans will have to be used to circulate air. Air circulation is critical to maintaining proper box temperatures.
Thawing guidelines are currently under revision. For more information, contact the Nursery Services Section, Victoria.
Handling Active Seedlings (Summer Stock)
Once seedlings have become physiologically active, their vigour is reduced if left in cold dark storage. Active seedlings must be shipped to the field and planted immediately. If this is not possible, the following must occur:
Seedlings are very susceptible to shock resulting from physical abuse and stress. Seedling cartons must be handled carefully, like boxes of eggs rather than bales of hay. Key actions that will minimize damage to the seedlings when handling cartons include transferring stock from damaged to undamaged boxes as damaged boxes or punctured liners can lead to moisture stress. Also, never stack boxes more than three high, unless they are separated by spacers. This will prevent the seedlings from being crushed and will allow air movement between boxes.
The transportation of seedlings from the nursery or storage facility to the planting site is a critical phase in the reforestation process. During this transportation phase, the responsibility for the seedlings passes from the nursery to ministry or licensee personnel and finally to the planting contractor. In order to minimize damage when transporting both spring and summer planting stock the following concerns must be taken into account.
heat increases respiration = reduced field performance
If the planting contractor is responsible for transporting seedlings, these conditions must be clarified at the pre-work conference and monitored by the planting project administrator.
Disposal of Cartons
Conditions for the disposal or return of reuseable tree cartons are covered under Clause 1.7 of the Planting Contract Schedule A (FS 767). An example is included in Appendix 1, Forms Management. Charges for not returning reuseable cartons are outlined in Clause 4.9 of the FS 767. A basic charge of $25 each will be levied.
To obtain the required inside-carton temperatures, the ambient temperature of a refrigerated facility must be lower. For example, an ambient temperature of 0oC to -1oC may be needed to maintain carton temperatures of 1oC to 2oC. A dial probe thermometer, pushed through the side of the carton and liner into the foliage, is a simple method of determining carton temperatures. Monitor cartons in a number of places in the cooler unit to determine if the unit is cooling evenly.
For spring stock, keep all cartons closed, except for regular inspections or when dealing with a storage or stock problem. Never leave the cartons open: keep the polymer lined bag tightly rolled and closed to reduce the risk of damaging desiccation and stress.
Open boxes of summer (hot-lifted) stock and stand bundles of seedlings vertically.
Reefer Operation and Maintenance
The use of refrigerated reefer trailers is a common practice for temporary storage of cartons of seedlings. When properly maintained and operated, they are an excellent storage option. To ensure that reefers function properly check them regularly. Contract only quality reefers that are known to be in good working order. Include a maintenance schedule in the contract as well as how to contact the owner/operator in an emergency. Ensure reefer operator understands fully the maintenance requirements of the reefer. Check to see if reefer temperatures are in Fahrenheit or Celcius (oF or oC). Confusing the scales can result in frozen stock and root damage to seedlings.
If the contractor fails to follow the maintenance schedule, or a preventable malfunction occurs and seedlings are damaged or die as a result, ensure the reefer contract states that the operator will be held responsible for the loss.
Planters - the last link in the reforestation chain. Everyone down the chain must do their job correctly to ensure healthy, vigorous seedlings. But it is the planters who have the largest role to play in the survival of the seedling and the success of future plantation performance.
The following specifications should be included in the contract and reviewed at the
The planting contract administrator should ensure that:
The following is a list of common stock problems and the action to be taken. When you are in doubt about the quality of the planting stock, contact the ministry officer in charge of the contract or regional silviculture staff before planting.
The process of heeling in of bareroot planting stock is not commonly practiced today in British Columbia. Heeling in, which involves temporarily planting bareroot seedlings that are still in bundles, into trenches, puts an additional stress onto the seedlings. It is strongly advised that this process only be used as an absolute last resort. If, in your opinion, it must be done, contact the planting project administrator or silviculture staff before proceeding.
All district offices have a collection of Material Safety Data Sheets (MSDS) for each pesticide used in conifer seedling nurseries.
The Silviculture Practices Regulation (Part 3, Division 2) requires that:
Information on the use of pesticides on seedlings is recorded in two ways:
Hand washing facilities must be provided by the contractor to the workers at the work site.
When any pesticide has been applied within one month (30 days) of stock being packaged for storage or shipment, the date of the application is handwritten on the box as (year, month, day) of last application.
A ministry publication entitled Putting people first; Minimizing tree planter's exposure to seedling pesticides (FS 449) is also available.
Planting under certain weather conditions is a waste of time, funds, and trees. In deciding whether to continue or to suspend planting, several factors must be considered.
If soil moisture at the seedling root level is 40% or less, planting should be suspended. As a rough guide, soil that has reached this critically low level has lost its dark colour, is powdery or crumbly, and will not hold together when squeezed in the hand. The decision to suspend planting should also be based on current weather patterns and forecasts for the area. Hot and dry conditions being forecast should be factored into a decision to suspend.
Proper handling of seedlings and special care of the roots is critical when the relative humidity drops to 50%. At a relative humidity of 30%, or at 25oC air temperature, planting should be suspended, especially when soils are dry. If soils are still moist, planting on early shift is a practical means of avoiding such adverse conditions. If the planting program has to be extended to the point where the weather is unfavorably hot and dry and soil moisture levels are low, late starting projects on severe sites should be cancelled. The excess of trees thus available may then be used, if of suitable provenance, to plant alternate areas.
Frost and Snow
Planting should be suspended if the ground cannot be scalped free of frost crystals or snow, if acceptable naturals cannot be seen, or if the selection of appropriate microsites is impeded. Planters must be instructed not to use snow or frozen soil to back fill planted trees. The adverse consequences of planting in frozen ground can be reduced by planting south facing slopes first until the ground has warmed up on other aspects.
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