WJAF 15(4) 2000 177 Regeneration of White Spruce Under Aspen Canopies: Seeding, Planting, and Site Preparation James D. Stewart, Canadian Forest Service, Northern Forestry Centre, 5320-122 Street, Edmonton, Alberta, Canada, T6H 3S5, and Simon M. Landhäusser, Kenneth J. Stadt and Victor J. Lieffers, Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3. ABSTRACT: This study investigated the establishment and survival of naturally and artificially seeded white spruce (Picea glauca), as well as three sizes of planted white spruce stock, on different types of scarification beneath mature aspen (Populus tremuloides) in northern Alberta. White spruce seed rain, natural and hand- seeded regeneration establishment and survival, and understory vegetation response were monitored for 4 yr on scarified strips (light blading, heavy blading, and ridged) and on undisturbed controls. Despite a heavy seed rain in 1993, seedling establishment on control plots was almost nil. On scarified plots, the number of seeds required to produce a live seedling after 3 growing seasons ranged from 15 to 37 and up to 68 in one site. Most mortality occurred during the summer. Germination rate on the hand-seeded plots ranged from 19 to 28% on the scarified strips. There was no significant difference in survival from seed (15%) after three growing seasons among the three scarification treatments. Survival of planted stock was 98% on scarified strips and 96% on control strips. Diameter growth was least on control plots but was not significantly different among the scarified treatments. In contrast, height increment was greatest on the light blading treatment and differed little among the other two treatments and control. These results suggest that spruce regeneration in aspen forests can be promoted by scarification or underplanting. West. J. Appl. For. 15(4):177–182. White spruce (Picea glauca) can be difficult and expensive to regenerate on clearcuts, yet it regenerates naturally in the understory of aspen (Populus tremuloides) dominated stands (Lieffers and Stadt 1994). This suggests that white spruce reforestation might be more successful, and possibly less expensive, if natural regeneration under aspen was encour- aged or supplemented by site preparation and seeding or planting. The use of aspen as a nurse crop for spruce was suggested in Europe over three decades ago (Börset 1962) and, along with alder and birch, has been used in several countries (e.g., Martynov and Krasnovidov 1982, Leikola and Rikala 1983, Horndasch 1984). In Canada, there was recognition of the potential of underplanting in the 1960s (e.g., Lees 1963, 1970), but the idea was abandoned with the development of mechanized clearcut harvesting. Establishment of under- NOTE: James D. Stewart is the corresponding author and can be reached at (780) 435-7224, Fax: (780) 435-7359, E-mail: jstewart@NRCan.gc.ca. The authors thank Barb Hamel, Susan Hayduk, Dave Kelsberg, Kim Krause, Richard Ouellet, Robert Proudfoot, Rod Sanderson, Pete Tollestrup, and Darcy Tostyniuk for technical help, Dan MacPherson for his support and assistance in setting up and carrying out this research, and Ken Greenway for review of an earlier draft of this paper. We are grateful to Alberta-Pacific Forest Industries, the Canadian Forest Service, and the Natural Sciences and Engineering Research Council for funding. Copyright © 2000 by the Society of American Foresters. story spruce was not followed up until the recent resurgence of interest in managing boreal forests as mixedwoods (Lieffers et al. 1996). In addition to the advantages for spruce regenera- tion, total stand volumes may be greater in mixed stands than in pure stands (Börset 1962, Kelty 1989). Mineral soil and decayed wood provide the best seedbeds because they are relatively free from competing vegetation, and white spruce is tolerant of their low nutrient availability (Rowe 1955, DeLong et al. 1997). Site preparation can also be used to enhance natural and artificial regeneration of white spruce and temporarily remove shrub and herbaceous com- petitors. Prepared mineral soil seedbeds are receptive to white spruce establishment for 3 to 5 yr in clearings, and up to 7 yr in partial-cut stands (Eis 1967, Lees 1963, 1970). Creating receptive seedbeds could be enough to ensure the establishment of a white spruce understory provided there is an adequate source of seed. The occurrence of good to exceptional seed production years ranges from every 2–4 yr at the southern extreme of the boreal mixedwood in Saskatchewan and Manitoba (Rowe 1955, Waldron 1965), to every 10–12 yr at the northern extreme in Alaska (Zasada 1972). For a white spruce understory to become established, seedbed receptivity and seed source availability must coin- cide; therefore, it may not always be possible to depend on natural regeneration. Direct seeding or planting may be Downloaded from https://academic.oup.com/wjaf/article-abstract/15/4/177/4741255 by guest on 09 June 2020