Section 3
Seedling Production
Container seedling production in the U.S. has never really received anywhere near the amount of attention as in Canada. The Pacific Northwest is the only part of the U.S. where containerized seedlings in small amounts have been consistently grown. There are a few operations in the southeastern U.S. Part of the reason for the difference between the U.S. and Canada is the cold Canadian climate, the long day lengths, and the high restrictions put on pesticides like methyl bromide (a soil sterilant).
What has been the Canadian experience? Until the mid 1970's, British Columbia reforestation employed only bareroot seedlings. But from a small start, container seedling use grew until by 1980 more than half the seedlings planted in the province were grown in containers. In 1987, about 76% of the approximately 230 million seedlings grown were container grown. Interior spruce and lodgepole pine between them make up over three fourths of the container seedlings grown in British Columbia.
Virtually all the container grown seedlings in British Columbia are produced in styroblocks. This design involves a matrix of styrofoam which contains cavities of a specified size, the whole shaped in the form of a rectangular block. The blocks are designated by the dimensions of the cavity - 211's are styroblocks with cavities which measure about 2 centimeters in diameter at the top and are about 11 centimeters deep. Each block has about 245 such cavities. The most commonly employed block is one with cavities ca 3 cm in diameter and 13 cm deep - hence termed 313's. One configuration for 313's has 198 cavities per block; a second, rapidly gaining in favor, has 160. The largest cavities commonly used are 415's, although a few 615's have been employed to produce special seedlings. The great majority of seedlings are grown in 313's with the larger cavities being used to produce seedlings for extremely stressful or brushprone sites where it is believed the smaller seedlings do not have a high survival potential.
Most of the container grown seedlings are raised under one of two schedules, i.e., a) seeds are germinated in greenhouses in late March or early April and the seedlings are grown through the spring and early summer and then hardened off for cold storage until planting in the spring of the following year, and b) seeds are germinated in open compounds in mid-May/early June and the seedlings are grown until mid-summer when they are hardened off. They are then maintained either out-of-doors (lower mainland, Vancouver Island), or in unheated greenhouses (interior B.C.) over winter after which they are grown for a second period in spring before initiating dormancy in early June. These plants, now termed "plug 2-0's", are then "hot planted" throughout July and August. All of the seedlings raised under regime "b" are planted in the interior and are either interior spruce or lodgepole pine.
In the past, the Ministry of Forestry (MOF) has established morphological standards for each type of container seedling and contracted for the great majority of seedlings grown in British Columbia. Prices for seedlings have varied with the size of the cavity and with the production protocol with 1-0 313's costing about 17¢ per seedling and 415's between 25 and 30¢. In 1988, the MOF sold most of its nurseries and the Canadian Forest Act of 1987 mandates the responsibility for basic silviculture to licensees. Accordingly, it is very probable that the range of seedling types and costs will vary more widely across the province than they have in the past.
In Canada, 38% of the seedlings grown were container seedlings in 1981. But a greatly increased reforestation program in British Columbia since that date together with similar increases in seedling production in Quebec and Ontario have all been based almost exclusively on increases in production of container grown seedlings. Currently, well over half on the seedlings grown in Canada are produced in containers of some configuration, i.e., styroblocks in British Columbia, root trainers in Alberta, paperpots in Ontario and Quebec.
What about the U.S. experience? In contrast, the use of container seedlings in the United States is much less, probably because the vast majority of the seedlings used in the south are 1-0 bare root plants which can be produced for no more than 3-4¢ per seedling. About three fourths of the container seedlings planted in the U.S. are grown in the two northwest states. It is interesting that in the early 1970's development of container protocols was much more rapid in Oregon and Washington than in B.C. even though the initial impetus for this stock came from experiments with Professor J. Walters' bullets (Univ. of British Columbia). By 1976 about one fourth of the seedlings grown in these states (54 million) were container grown. Since that time, production has been relatively constant albeit a lot less since the reduction in the annual cut in the early 1980's.
The question might well be asked as to why there has been an increasing trend towards the use of container grown seedlings in British Columbia and not in the adjoining U.S. states. There appear to be several reasons:
a) Species. The species currently predominant in the reforestation program of British Columbia are interior white spruce and lodgepole pine. Both these species may be grown in containers with the expectation that the seedlings will have comparable survival and growth to that exhibited by bareroot seedlings. In Oregon and Washington, Douglas-fir seedlings make up more than 90% of the plantations. This species can be grown in containers, but most foresters believe that bareroot seedlings are superior, particularly for the brush prone sites which occur over much of western Oregon and Washington.
b) Planting season. In the great majority of British Columbia forest areas planting is possible only from mid-April until late summer. Accordingly, seedlings are generally lifted and stored (save for those used in "hot" planting prior to outplanting). The container configuration is much more flexible in that seedlings may be over-wintered and then removed from containers and stored prior to initiation of active growth in the spring. In contrast, seedlings grown in bareroot nurseries, even those in the coastal part of British Columbia, must be lifted prior to frost events in the fall and after the ground thaws in the spring. In the northwestern states, much of the forest lands planted are "open" all winter so that seedlings may be lifted from bareroot nurseries throughout the winter and transported for immediate planting in plantations.
c) Growing season at the nursery. Virtually without exception nurseries in Oregon and Washington can grow seedlings of a plantable size as bare root plants within two years. In British Columbia the same condition obtains for coastal species, but the great majority of the current reforestation employs interior species. While it is possible for greenhouse based nurseries in the interior of British Columbia to produce plantable seedlings within on year, bare root installations must grow their plants for three or four years in most locations to achieve plantable material.
Although the logistics of seedling production in British Columbia are not without problems, a fairly efficient technology for the production and outplanting of the needed seedlings has developed. However, serious questions about the current reforestation system remain, i.e., a) are the seedlings produced in nurseries in the lower mainland or in artificially heated greenhouses in the interior really well adapted to make vigorous growth after outplanting? and b) does the container configuration which produces "wads" of roots in lieu of the spreading root system of the natural seedling prejudice such plants for an increased susceptibility for root disease and for instability at the sapling stage? Certainly data describing the toppling incidence in plantations grown from container grown lodgepole pine seedlings suggest that this species, at least, may not be well adapted to container production.
Although the quality of seedlings grown in British Columbia and the PNW has definitely improved during the past few years, the container production system still has the following problems:
1. With continuing financial constraints on the B.C. silviculture program, 313's appear to be the largest container which can be used for the great majority of the seedlings. With some species, especially Douglas-fir, this cavity may be too small and too closely spaced to produce top quality stock.
2. The root form of lodgepole pine suffers when this species is grown in containers because it apparently can not initiate first order laterals after the seedlings are several weeks old. The result is that the first order laterals are directed downward by the container walls, and when the seedlings are outplanted the root system is primarily a vertically directed one rather than the horizontal laterals and vertical tap root of a natural root system. This different root form is alleged to result in unstable seedlings and a high incidence of toppling.
3. The container system is designed to guide the developing roots down the walls of the container to a hole in the bottom where the roots are air-pruned. This results in a large proportion of the active root tips at time of planting being concentrated in the lower end of the root system. Particularly in the northern interior region, which is characterized by cold soils, seedlings with this pattern of roots appear to have very slow root growth because the active root tips are placed by the planting procedure in the colder portion of the soil. The slow root growth is reflected by extreme planting check of the shoot until the seedling is able to generate in place a more superficial root system.
4. Extreme differences in climate between the interior of the province, where most of the seedlings are planted, and the coastal region, where many of the seedlings are grown make it difficult to produce properly acclimated seedlings at time of planting.
5. The large size of the province and the relatively short planting seasons result in extreme logistical difficulties in lifting, packing, storing, and shipping large numbers of seedlings. As a result, it is not uncommon for seedlings to receive less than favorable treatment sometime during the nursery-planting sequence.
6. Emphasis on morphological parameters, i.e., minimum calipers and heights, can result in the production of seedlings whose annual growth cycle is not synchronized with the natural environment. Further, the fertilization schedules employed result in luxury consumption of nutrients which may reduce the seedlings' resistance to stress.
How do countries outside North America grow containerized seedlings? The Europeans certainly use a containerized seedling technology not unlike that found in North America. In fact, much of the original work with containers was done in countries like Germany and Sweden.
In tropical countries the container system is vastely different.
The common system over most of Africa, Latin America, and Southeast
Asia is a container system that utilizes a black plastic bag called
the "polybag" . This is literally a plastic bag of 1 mil or greater thickness with one or two small holes punched in the bottom for drainage. The bag is filled with local soil or some mix of soil, organic matter, and ash. The seed is hand poked into the media and a seedling grown. This system works, but has many limitations. Name several limitations to this kind of system. It does have one major advantage - it is very cheap.
