Land and Ecosystem Management
Regenerating White Spruce in Boreal Forests of Alaska
Over the past several decades, three major forms of disturbance have occurred at unparalleled levels in the boreal forests in Alaska. First, fire regimes have shifted, with an increase in the total area burned, a doubling of decadal frequency of large fires, and a greater proportion of early-and mid-growing season fires compared to the 1960s and 1970s.
At the same time, major insect infestations grew to unprecedented levels. Spruce bark beetle infested nearly 3 million acres of white spruce and P. × lutzii forests, killing more than 90 percent of the trees greater than 4 inches in diameter. In addition recent spruce budworm outbreaks resulted in spruce top kill and dieback, little cone production, and mortality of seedlings and saplings.
Finally, as production of softwood timber from the Pacific Northwest diminished in the early 1990s over concerns for wildlife habitat, product demand of Pacific Rim markets shifted to accept more white spruce round logs and chips from interior Alaska and the Kenai Peninsula, leading to increased harvesting.
Increasing levels of wildfire, insect-caused mortality, and timber activity have brought into question the adequacy of natural and artificial white spruce regeneration. With passage of the 1990 Alaska Forest Resources and Practices Act, resource managers faced legal challenges to their continued failure to secure adequate regeneration after timber harvesting and they lacked the means to restore forest ecosystems after major disturbances. There remained a critical need to enhance management options for regenerating, restoring, and managing boreal stands and landscapes. To address this need, a suite of collaborative, interdisciplinary, long-term studies were established to identify options for meeting various silvicultural objectives.
Sites that lack active management, such as this old clearcut in the
Matanuska-Susitna Valley, present challenges for white spruce establishment
because of competing vegetation.
Herbicides are an effective tool in vegetation management on some sites, yet the primary use in northern latitudes has been for release of already established plantations once competing vegetation affects seedling growth rather than as a site preparation treatment to improve conditions for seedling establishment. We asked whether the choice of chemical or mechanical site preparation offers important advantages over planting with no site preparation.
Second, since white spruce seedlings with larger shoot and root sizes and greater root collar diameters may grow faster and tolerate competing vegetation better than small seedlings, we asked whether, across a range of sites, large planting stock have significant and persistent advantages over small stock in ability to grow quickly and occupy sites before naturally occurring competitors become dominant.
Finally, secondary successional processes after disturbances allow broadleaf trees, shrubs, and herbaceous species to rapidly reoccupy boreal forest sites, and these dynamics can influence stand development for decades. We asked whether reforestation success immediately after disturbances differs from reforestation success after a delay of several years during which competing vegetation may become fully established, and whether this difference imparts advantages for seedling survival and growth that are influenced by choices of seedling stock sizes.
Dr. Michael Newton and Elizabeth Cole, Oregon State University
Alaska Department of Natural Resources and Alaska Division of Forest Service
US Department of Interior
US Department of the Army, Fort Richardson Army Base
Tanana Chiefs Conference
Ninilchik Native Association
Cook Inlet Region, Inc.
LocationMap of five Alaska study sites, with distribution of white spruce shaded.
Field installations for this study were established in five regions of Alaska. The Tanana site is about 35 miles west of Fairbanks in the Tanana River uplands. The Fort Richardson site is northeast of Anchorage in the Matanuska-Susitna Valley on the Fort Richardson Army Base. The Chitina site is in the Copper River Basin about 60 miles southeast of Glennallen. The CIRI site is about 25 miles south of Soldotna. The Ninilchik site is about 17 miles north of Homer. At each site, we installed two complete experimental installations (units) that differ in time since disturbance. The “New” unit was an operational clearcut unit with overstory trees harvested immediately before site preparation. The “Old” unit was operationally harvested at least three years before planting. The study was established at four sites in 1995 with planting in spring 1997; the Chitina site was established and planted 1 year later.
Experimental design and treatments
The experimental design for each unit was a completely randomized design with a split plot arrangement of treatments with repeated measurements of survival and growth through time. We compared planting immediately after harvesting to planting after a delay of ≥ 3 years, three site preparation treatments, and five seedling stock types. Three replications of site preparation were assigned: (1) mechanical scarification with a bulldozer with brush blade or straight blade to remove plant cover and expose about 85 percent bare mineral soil before planting (Blade); (2) control of vegetation by a single broadcast herbicide application of 1.65 kg ha-1 of hexazinone (Velpar L®) plus 1.1 kg ha-1 of glyphosate (Roundup®) using a waving wand attached to a backpack sprayer, applied in the fall before planting (Spray); and (3) no site preparation (Control). Five seedling stock types with 30 seedlings of each were hand planted at 3 by 3-m spacing in each plot in randomly assigned rows of 15 seedlings. Stock types included 1-year-old container-grown seedlings from a commercial nursery in Washington State (S10), 1-year-old container-grown seedlings from a commercial nursery in southern British Columbia (P10), 2-year-old bare-root transplants grown at the Alaska State Nursery at Palmer as container stock for 1 year and then transplanted for 1 year in a nursery field (AP1), 2-year-old bare-root transplants grown as container stock for 1 year at a commercial nursery in Washington State and then transplanted to a nursery field for 1 year (SP1), and 3-year-old bare-root transplants grown at the Alaska State Nursery as container stock for 1 year and then transplanted for 2 years in a nursery field (AP2).
One-year-old container-grown seedling, 3 years after planting
on a sprayed plot (ruler is one meter).
- More planted white spruce seedlings survived in experimental units where a bulldozer blade (mechanical scarification) was used to remove vegetation before planting compared to units where herbicides were applied before planting, or to sites with no site preparation.
- The bare soil exposed by mechanical scarification provided opportunities for wind-disseminated seeds to colonize. At some sites, this led to more forbs and woody shrubs, which compete with white spruce seedlings for light and soil nutrients.
- White spruce seedlings were taller and larger at sites where herbicides were applied in the fall before planting compared to mechanically scarified sites or sites with no site preparation. Spraying reduced abundance of competing vegetation without providing the microsites for seed germination found after the blade scarification treatment.
- When comparing “old” sites cleared 3 years prior to planting, where a full component of competing species had become established, to “new” sites cleared immediately prior to planting, no difference was found in white spruce seedling survival or height growth that could be attributed to site preparation techniques.
- Initially, blade scarification appeared to increase growing season soil temperatures, but differences lasted only 3 to 4 years as vegetation developed on site. Frost-heaving during the first or second year after outplanting was especially prevalent with small planting stock in blade-scarified plots on the old units in two regions.
- Seedling age was not a strong predictor of seedling performance. Nursery practices that resulted in large stock types provided the greatest future gains in growth and productivity. Seedlings grown to larger sizes before outplanting are less likely to be over topped by competing vegetation and may be more likely to withstand herbivory by small mammals, compared to smaller seedlings.
- Seedlings produced in nurseries outside Alaska, requiring direct manipulation of day length, had greater survival, height, and volume after 11 years than did seedlings produced by a nursery in Alaska without light environment modification. Rearing, lifting and handling, storage, and distribution processes used elsewhere can accommodate seedlings intended for Alaska.
White spruce, 11 years after planting at Ninilchik on a plot
that was mechanically scarified.
- No disadvantage was found, in terms of seedling survival and subsequent growth, in waiting to reforest an area due to financial constraints or lack of nursery stock, for example. Productive white spruce forests may be successfully restored through vegetation control and use of quality planting stock.
Cole, E.; Newton, M.; Youngblood, A. 1999. Regenerating white spruce, paper birch, and willow in south central Alaska. Canadian Journal of Forest Research. 29: 993-1001.
Cole, E.; Youngblood, A.; Newton, M. 2003. Effects of competing vegetation on juvenile white spruce (Picea glauca (Moench) Voss) growth in Alaska. Annals of Forest Science. 60: 573-583.
Youngblood, 2005.Crafting a competitive edge: white spruce regeneration in Alaska. Science Findings 69
Youngblood, A.; Cole, E.; Newton, M.2011. Survival and growth response of white spruce stock types to site preparation in Alaska. Canadian Journal of Forest Research. 41(4): 793-809.
Youngblood, A. 2012. Make Way for Seedlings: Regenerating White Spruce in Alaska. Science Findings 143
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