Alaska Extension Review

Transcription

1 Alaska Extension Review 1997 Trial Season Alaska Cooperative Extension University of Alaska Fairbanks Fairbanks, Alaska April 1998 Dr. Robert Wheeler, Editor Extension Forestry Specialist 308 Tanana Loop, P.O. Box University of Alaska Fairbanks Fairbanks, AK (907) /6363

2 by Robert A. Wheeler, Forestry, Specialist, Alaska Cooperative Extension, and John N. Alden, Affiliate Research Professor, University of Alaska Fairbanks INTRODUCTION: SEED TREES AND SEED COLLECTION: Internationally, it is not uncommon to find successful rural seedling production operations that have developed quality seedlings using locally supplied materials and equipment. Careful attention to details outlined in this discussion should help ensure success with local spruce seedling production.gardening professionals and the Alaska Cooperative Extension can further assure desired results with your tree seedling production project. Success with seedling production requires consistent care in the production, handling, and planting of the seedlings. Planting site preparation and follow-up seedling care can further assure longterm success with your seedlings. This discussion is intended to cover the production of spruce seedlings from seed tree and seed collection to nursery production and distribution for tree planting. The Alaska Cooperative Extension has an excellent booklet on tree planting and tree care after planting. White and black spruce cones mature in the fall in late August and September, Squirrel collection activity within a stand of trees can be a good indicator of seed ripeness. Ripeness of collected cones can be estimated based on cutting several cones in half and examining seeds cut in half. Seeds with embryos extending at least 80-90% of the length of the embryo cavity are considered to be sufficiently ripe to assure good viability. Care should be taken that the cones are not collected to early as this can significantly reduce seed viability. If the cones are collected to late many of the good seeds may have already escaped as the cone scales open during ripening. Cones should be collected in loose weave gunny sacks and stored in cool, dry conditions that allows them to air dry. Excessive heat or moisture should be avoided as it can reduce viability and increase the development of mold on the cones and bags. Careful documentation should be placed within each bag and also tagged on the outside to indicate species, date of collection, location of collection and owner. The form and vigor of your seed trees are typically traits that are inherited. In order to assure quality seedling production it is best to be selective for tree rate of growth, stem form, branchiness and branch angle for the trees that you collect seed from. The presence of insects and disease should also be considered. hi addition to selecting trees for quality traits it is also necessary to consider how adaptable your seeds are to the sites where you intend to be planting the seed. Attempts to transfer seeds from beyond their normally adapted range can result in problems. The United States Forest Service has established tree seed zones and guidelines for seed transfer within Alaska in their publication PNW-GTR-270 (Provisional tree seed zones and transfer guidelines for Alaska, 1991). Transferring seed from below the Alaska Range to regions above the range can result in susceptibility of the seedling to fungus such as needle cast and rust and are more susceptible to cold temperature damage. Seed transfer rules vary by species and conditions but general rules of thumb suggest that the more the environmental conditions vary when comparing the collection site to the planting site for: distance, aspect, elevation, temperature extremes, and latitude the more restrictive the ability to successfully transfer seeds are. 36 Alaska Cooperative Extension

3 TIMING SEEDLING PRODUCTION: In order to produce seedlings for planting in June or early July, the best time to sow in a greenhouse is in late January or early February. Success with these planting times are believed to be due to 1) the seedlings set dormancy and harden for the winter under natural field conditions, and 2) the nursery manager avoids over-wintering costs and potential losses at the nursery. Although there is considerable interest in late fall planting in August and September, these seedlings are more susceptible to frost heave (lifting of the seedlings out of the ground by frost), and early frost injury or kill if the seedling has not be sufficiently hardened off at the nursery. Seedlings overwintered in the nursery and outplanted the 2nd growing season are subject to root binding if planted in small containers which can reduce seedling survival and growth once outplanted. SEEDLING CONTAINERS: ' A comparison of bare root seedlings versus container grown seedlings would indicate some advantages and disadvantages of either approach. However, for tree planting here in Alaska, where growing seasons are short and cold soils can be difficult to mend and lift seedlings from at needed times, there is perhaps more emphasis on container grown stock. The use of containers has several advantages including ease of processing for mass production, development of uniform seedlings, easier for planting on harsh sites, and also provide for convenient controlled application of mycorrhizal inoculation of root systems. Container grown stock are more easily grown inside greenhouses in which it is easier to control day and night temperature regimes, day length and light intensity, watering and fertilizing, and carbon dioxide concentration. There are a number of forest tree seedling containers on the market, several of which have been used here in Alaska and generally occur in the form of either 1) plastic tubes, 2) styrofoam blocks, and 3) pre-formed plugs. Nurseries and greenhouses can be contacted to purchase supplies of these containers. Some are more durable than others and vary in size and color. Containers that are light in color will tend to have less heat buildup if exposed to direct light and have less tendency to degrade by sun exposure. Depending on the size of seedling you wish to grow and the amount of root mass needed will determine to some extent the size of the containers. Containers come as generally tubes, blocks, or plug molds; however, a number of new products are available with variations on shape, size and materials. Commonly used containers include the Ray Leach Single Cell (tubes), plastic dibble tubes, styrofoam blocks, and Spencer-lemaire Root Trainers. Dr. Alden prefers using the Ray Leach "Stubby 7" size container for cold soils using one-year-old seedlings. He has found that the least expensive and most durable are the hard plastic Swedish Multipot or PGI Permapot containers with about 50 cells per square foot. When transferring the container grown seedling to the field for planting it is common to remove the tree seedlings from their containers and wrap them in plastic wrap and transport them in a damp and shaded enclosure or bag to the field for planting. GROWING MEDIUM: As with the size and type of containers, there are many alternatives available for growing medium to plant seed or seedlings in containers. Commercially prepared medium are available in convenient bulk wrapped cubes but are more expensive than self-prepared mediums which can be easily made from ingredients 1997 Alaska Extension Review 37

4 available at most commercial nursery/greenhouse retailers. Commonly used mixtures include 1 to 3 parts of medium textured acid peat moss to 1 part coarse to medium horticulture grade vermiculite mix. Vsto Vz part Perlite can be added to the mixture as well as fertilizer and micronutrients. Dr. Alden had the following recommendations for conifer seedling mixtures: I add a full compliment of nutrients to the growing medium in the form of slow release fertilizers, for example, Osmocote ( ) and MagAmp for the major micronutrients, and Micromax for the minor micronutrients which are added at or below the manufacturer's recommendations. I also added Magnesium sulfate, Dolomite, and lime. The acid peat is a strong buffer and holds the ph at about 5.5 even after ample lime is added. Conifers prefer acid soils which also helps to limit losses from "damping~off" for several years after transplanting, and reduce "transplanting check." The practice of applying large quantities of fertilizers after seedlings enter dormancy and before outplanting or "nutrient loading" is also becoming a common practice in order to reduce "transplanting check." Tips for Filling Containers (cells) with Growing Medium 1. Add moisture to the growing medium but only to a point of dampness to touch. Do not saturate as this makes it much more difficult to load tubes. If the mixture is to dry it will have a tendency to fall out the bottoms of open tubes leaving a smaller amount of medium for root development. 2. Apply gentle pressure, but do not compress the growing medium into the cells. Low bulk density and air space is essential for optimum root growth. 3. Do not allow the growing medium to dry after the containers are filled. Greenhouse and Growing Conditions for Seedling Production COLD STRATIFICATION: TEMPERATURE: Cold stratification of seeds, a common procedure for improving germination of fir and pine seeds, has been found to have been unnecessary for white and black spruce and lodgepole pine. Placing seeds on a moistened medium in near-freezing conditions in order to stimulate more rapid seed germination and remove seed dormancy. Conifer seeds will germinate well in 60 to 70 F conditions. Germination of seed will be inhibited if temperature exceeds 75 F and the best green house temperature for preemergence of conifer seeds is from 65 to 70 F, After the seedlings emerge, the recommended temperatures for seedling growth are 75 to 80 F during the light period (day), and 65 to 70 F during the dark period (night). Temperatures above 85 to 90 F will inhibit seedling survival and growth and care must be taken to be sure that sufficient circulation is provided for greenhouse environments. Once the seedlings have growth 8 inches tall, gradually reduce the growing temperatures 5 to 10 F per week (especially if possible during the dark period). Reduced temperatures, photoperiods, and perhaps light intensity are necessary to induce dormancy and the hardening of seedlings for eventual transplantation. Cool temperatures and even mild frost during the night periods can be beneficial to completion of the hardening process for over-wintering container grown seedlings. 38 Alaska Cooperative Extension

5 LIGHT: Conifer seeds germinate well at low light intensities and can even occxir in full darkness. Minimum photoperiod and light intensity recommended for the seedling emergence phase at latitudes north of 60 are 20 hours and 350 micromoles/mvsec. or Vn full sun light. Optimum average light intensities are likely in the micromoles/mvsec.range during the period of rapid seedling growth. Maximum outdoor light intensity on a clear day in mid June at Fairbanks is about 1800 micromoles/mvsec. Once the seeds have germinated and the seedlings begin the period of rapid elongation (usually lasting about 60 days) it will be necessary to maintain a hour light period. As the time approaches for outplanting or hardening it will be necessary to reduce the photoperiod back to at least 12 hours. Most nurseries harden seedlings under natural conditions of light and temperatures. Artificial darkness is often required to reduce photoperiods and harden low latitude seedlings (seeds derived from southern latitudes) during late summer at high latitudes (60 to 68 N) nurseries. The problem of growth cessation, dormancy, and winter hardening of stock in the nursery is avoided if the seedlings can be transplanted to the field by June or early July. IRRIGATION: Maximum seedling growth can only be achieved at low to moderate levels of plant moisture stress. In order to maximize seedling growth, photosynthesis, and seedling vigor it is necessary to limit the amount of plant moisture stress caused by limited water, higher temperatures, and seedling transpiration. For seed germination and seedling emergence, you will want to bring the soil medium in all containers to field capacity (the point after which adding more water will simply run out of the soil as drainage) and maintain the surface moisture. Covering the trays with plastic can help prevent evaporation of surface moisture. However, after seedling emergence, allow the growing medium surface to dry. Excessive moisture at this stage can cause mortality by disease and mold. Maintain humidities at about 30% or less if "damping-off" disease problems develop. It may be helpful to weight the trays to determine moisture loss. At about 70% of field capacity weight, irrigate the containers to field capacity again (at about 7 to 10 day intervals) during the first days after seedling emergence. During the late stages of rapid seedling growth, irrigate to field capacity weight. Transpiration losses increase rapidly as the seedlings grow larger, increasing the potential for moderate to heavy plant moisture stress. It may become necessary to irrigate on a frequent, several times per day basis. As you begin to get closer to the time of outplanting, you will want to develop some hardiness in the seedlings to limit transplanting shock. Hardiness can be developed by reducing the growth of the trees which may require reducing temperatures, light, and water. Full dormancy and hardiness is not required for seedlings out-planted in late June or July, but to avoid breakage during handling of the seedlings it would be helpful to partially harden them so they are not succulent. REFERENCES: Cleary, B. D., and Greaves, R. D Regenerating Oregon's Forests: A Guide for the Reforestation Forester. Oregon State University, OSU Extension Service. 286 pp. Seeds of Wood Plants in the United States, USDA Forest Service Agricultural Handbook No pp Alaska Extension Review 39