Most red spruce seeds germinate the spring following dispersal; some, however, may germinate in the fall soon after dropping from the tree. Germination is epigeal. On favorable seedbeds the usual spring germination period is from late May to early July. On duff, which is more subject to surface drying than most other seedbed materials, some seeds may lose viability by midsummer, and some may show delayed germination well into August (22). Little if any viable seeds remain in the forest floor beyond 1 year (13).
Adequate moisture is the chief factor controlling germination of red spruce. Germination takes place on almost any medium (mineral soil, rotten wood, or shallow duff) except sod. Mineral soil is an excellent seedbed for germination. Generally ample moisture is available and soil temperatures are moderate. Litter and humus are poorer seedbeds because they are likely to be hotter and drier than mineral soil (11). On thicker duff, germination may be poor also because moisture conditions are less favorable. Temperatures of 20° to 30° C (68° to 86° F) are generally favorable for germination. Seeds will not germinate satisfactorily at temperatures below 20° C (68° F) and are permanently injured by long exposure to temperatures higher than 33° C (92° F) (22).
Germination and initial establishment proceed best under cover. Seedlings can become established under light intensities as low as 10 percent of full sunlight; however, as they develop, they require light intensities of 50 percent or more for optimum growth. Seedlings starting in the open undergo heavy mortality when soil surface temperatures reach 46° to 54° C (115° to 130° F) even for a short time (11). Drought and frost heaving are major causes of mortality the first year. Crushing by hardwood litter and snow are also causes of seedling mortality. Winter drying in some years and locations can cause severe leader damage and dieback.
Natural reproduction depends more on seedling survival than on requirements for germination. Spruce seedlings have an exceptionally slow-growing, fibrous, shallow root system. Consequently, a critical factor in their survival and establishment is the depth of the 01 organic layers of the soil profile. When the combined thickness of these layers exceeds 5 cm (2 in), spruce seedlings may not reach mineral soil and the moisture necessary to carry them through dry periods. Red spruce seedlings and the commonly associated balsam fir seedlings are similar in many ways and are controlled by the same factors, but as a rule spruce is the weaker, slower growing species during the establishment period (22).
Seedlings that have attained a height of about 15 cm (6 in) can be considered established. Once established, their early growth is determined largely by the amount and character of overhead competition. Dense growth of bracken (Pteridium aquilinum), raspberry, and hardwood sprouts are the chief competition for seedlings on heavily cutover lands; but red spruce survives as much as 145 years of suppression and still responds to release (11,39).
Compared to its associates, red spruce is one of the last species to start height growth in the spring, usually beginning the first week in June and ending 9 to 11 weeks later. Radial growth usually begins about the second week of June and continues through August (22).
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm