STOCK HANDLING INNOVATIONS

Foresters have successfully planted billions of frozen winter stored trees over the years by thawing them at cold storage facilities and then planting them promptly during the spring season in efforts to minimize the loss of carbohydrate reserves prior to planting. The silviculture industry is continually looking at ways to improve and streamline the planting process, and during a recent roundtable discussion with key industry professionals, innovations to stock handling were discussed and the new development of planting frozen seedlings utilizing individually wrapped or unwrapped, frozen plugs was explored. The participants in the conversation included Dale Likes from Canfor, Dan Livingston and Dave Swain from PRT, Clare Kooistra from Conifera Consulting, and Dirk Brinkman from Brinkman and Associates. 

Operational Impacts
Planting seedlings with frozen plugs can potentially eliminate the difficulty of coordinating temperature management between the contractor’s field schedule, which can vary with unpredictable production factors, and the cold storage facility’s thaw schedule. Although cold storage facilities annually carry out this thawing activity, it is very challenging to deal with the logistics of thawing hundreds of thousands of seedlings in a short period of time. 

Cold storage operations would benefit from the elimination of the lead time required to thaw the seedlings and reduce the risk of exposing the seedlings to undue storage stress from premature thawing. Experience has shown that planting schedule notification can be reduced from 10 days to 3-5 days or possibly less. In theory, response time could be completely eliminated as trees could be moved out of freezer storage right into planting trucks, although seedling orders are not necessarily readily accessible in freezers, so some stock movement and lead time may still be needed. 

Planting frozen seedlings may permit planting contractors to experience less downtime from response lags in thawing seedlots as cold storage facilities or the coordinating forester adjusts to schedule changes. In planting operations, frozen seedlings may also lead to reduced j-roots from planting rigid, frozen plugs. 
Planters like using frozen plugs since it decreases the chance of planting faults and could result in productivity gains. Contactors may be able to use less experienced planters during this period of labour shortage, since less damage could occur to frozen plugs and roots. It’s also easier to place frozen plugs in the ground, so there may be less risk of planters unnecessarily compressing the soil around the seedling. How firmly the plug is planted may change as the seedling thaws after planting, but that shift in a quality indicator used by some auditors can be accommodated.

Managing foresters, cold storage personnel, and planting contractors would no longer have to manage the risks of thawed stock being held longer than scheduled before planting. There may also be some growth benefits due to the thawing process taking place in the ground, with the full cohort of plug moisture and carbohydrates being available to the planted seedling as it starts to grow.

The challenge to the nursery community in providing seedlings that can be planted while still frozen is to package the seedling in such a way to allow the root plugs to be separated while still frozen. To date frozen plugs have been wrapped individually in the fall at the nursery, however, the wrapping technology has not yet been perfected. An automated wrapping technology was developed because manual wrapping for this purpose is very labour intensive, in a time when labour is in short supply. PRT developed a prototype machine at PRT Pelton in Maple Ridge that processed 750,000 trees during last winter’s harvest. If that machine were to run two shifts per day, the nursery could process 1.5 million frozen plugs in a season. Other nurseries have wrapped similar amounts and have modified the lifting lines with more mechanical extractors, which improves efficiencies and reduces labour requirements.

Individual wrapping in the PRT experience generates more waste since it requires more than 2-3 times the amount of wrap and 10- 20% more bags and boxes for packaging the trees. This results in increased cold storage, trucking, and handling costs. Based on PRT’s current productivity information using the prototype machine, it is estimated that an upcharge on individually wrapped frozen plugs would be in the range of 5 cents per seedling, and production volume is limited. Since most customers are looking for ways to reduce waste and cost, this doesn’t present a good option. Others in the nursery community found that although they used more wrapping material, there was no need for more bags and boxes, so costs for this innovation may differ from PRT’s experience. However, all are agreed that if planting frozen seedlings became the norm, nurseries would need to invest significant capital for equipment, so a long-term commitment from customers would be essential. 

Seedling Impacts 
The combination of benefits from a simplification of spring reforestation logistics may offer one of the biggest eliminations of logistical inefficiencies but does planting seedlings while frozen have an impact on seedling performance? Research into this question was conducted and reported in 2002 and 2005 by Clare Kooistra and Jonathan Bakker. The findings of both trials were that, whether planted in warm or cold soils and warm or cool air temperatures, lodgepole pine, interior spruce and western larch seedlings performed equally as well when planted frozen as when planted thawed.

Although no physiological negative impacts of this practice were reported, the trails did show that western larch benefited when planted frozen. Larch is a deciduous species and flushes very rapidly once thawed, often while still in the boxes. Planting larch while still frozen allowed all the flush to develop after planting, thereby significantly reducing foliage loss. 

Using frozen plugs minimizes the problem of losing carbohydrate reserves, which has consequences to growth, if seedlings are thawed and kept in storage for long periods of time. Research work showed that stock that was left in a thawed condition for several weeks did not perform as well as seedlings planted with frozen plugs. However, in today’s world, stock handling has improved to the point where seedlings are generally planted in less than two weeks from the time thawing begins and thus carbohydrate losses are minimized. Planting frozen seedlings would help to reduce carbohydrate losses even further. Other trials such as those conducted by PRT used lodgepole pine, and showed no growth or survival difference whether the plug was frozen or not. However, eliminating the portion of the seedlings that do not get planted before being held longer than two weeks will likely have benefits for those seedlings, regardless of the species.

Other Innovations 
Is individual wrapping really required? What about packaging trees without any wrap? If this were done there is some concern that unwrapped seedlings would freeze together, so a short thaw period of a day or two would be needed, based on feedback from some initial trial work. In this operational trial, by the time the seedlings get to the field they were easily separated without affecting root integrity, and plug cohesiveness was maintained

Do seedlings need to be wrapped in bundles in the box? Historically, seedlings have been wrapped in bundles so that contractors, planters, and licensees would have an accurate seedling count. If unwrapped seedlings are used, ensuring an accurate seedling count is a potential challenge and concern. For instance, contractors would still require some form of reliable count per box to manage the piece rate system of paying planters, which provides key efficiencies in the field. Nurseries would need to adapt quality control or alternative counting measures to resolve this issue. 

The shift to planting frozen seedlings and/or unwrapped seedlings ties into the concept of lean manufacturing, pioneered by Toyota, whereby processes are simplified and waste is reduced. Some concern exists in the field that the current practice of wrapping plugs in bundles affects plug integrity by squishing them together, which can result in weakened plug integrity at planting and, ultimately, planting faults and this may be reduced in boxing unwrapped seedlings. From the nursery side, although it’s a challenge to keep track of amounts, the benefits to a packaging system without bundling are worth noting in that repetitive motion injures from bundling would be reduced and productivity opportunities may be enhanced.

Individually frozen seedlings in the box can be separated simply by alternating layer directions. Depending on clients’ wishes, PRT and others in the nursery community are packaging seedlings, whether thawed or frozen, lying lengthwise in boxes and have been using this practice for years. By laying the stock horizontally, approximately 10-20% more trees are packaged per box, thereby reducing waste, as fewer boxes and bags are needed. To be more efficient in packaging, the nursery, forest companies and planting contractors want to get as many trees as possible into each box, minimizing the number of boxes in cold storage and maximizing the number of trees on trucks. This has benefits all the way down the line since it reduces the total number of boxes to be handled. Currently the weight restriction of transport loads can be a limiting factor to maximizing seedlings per box, but this can be calibrated so that the number of trees per load has been maximized.

Planters want to carry as many seedlings as possible, so they prefer to load seedlings in their bags laterally, which nests and stabilizes them as they are planted out, right down to the bottom layer. 
Keeping plugs frozen until they are picked up from storage presents a simple solution to the carbohydrate reserve problem while benefiting both nurseries and planters by creating efficiencies. In order for individually wrapped, frozen seedlings for planting to be considered, the operational and capital issues must be tackled. Unwrapped trees may provide an alternative innovation but more trials with this packaging change will be required. 

All of these innovations are parts of the solution to stock handling issues that continue to be explored as the silviculture industry looks for ways to create efficiencies.