Adaptive Management Projects
Project Summary: Salal Cedar Hemlock Integrated Research (SCHIRP) Program: A Synthesis
Contacts:
Mike Wyeth - Silviculture Branch (Mike suggested this program as an AM candidate)
Gordon Wheetman (UBC Professor - Forestry Faculty)
Louise de Montigny (MoF Research Branch)
Shannon Berch (MoF Research Branch)
Background:
The project was developed in response to concerns raised by staff of Western Forest Products about the poor conifer regeneration on Tree Farm License #25 on northern V.I. Research was conducted to determine silvicultural practices to alleviate the growth problem, and to understand the fundamental cause of the poor nutrition of trees.
The problem occurred on sites formerly occupied by old-growth cedar-hemlock (CH) forests, 5-8 years after clearcutting and slashburning. Symptoms included chlorotic foliage and a near cessation of growth of Sitka spruce, western hemlock, western red cedar and amabilis fir, coincident with the expansion of the ericaceous shrub, salal, on the cutovers.
SCHIRP serves as an example of cooperation between industry, government, and universities in conducting research that addresses both fundamental questions and applied problems. The research focused on site productivity after harvesting.
A large experimental effort has been directed towards testing whether conversion of CH sites to more productive hemlock amabilis-fir (HA) conditions can be achieved. Fundamental to this experimental effort has been the need to understand the origin of the differences between the two forest types.
Objective:
The objective of this decade-long research effort was to determine the underlying causes of poor growth of regenerating cedar, hemlock, amabilis fir and Sitka spruce on cutovers of old-growth cedar-hemlock forests invaded by salal on northern Vancouver Island, British Columbia, and to recommend the most effective methods of improving tree growth.
Experimental Design:
Over the 1983 to 1993 period a series of studies were conducted to:
- Establish if the low nutrient supply in CH forests existed prior to harvesting.
- Determine the origin of the low nutrient supply in CH forests by comparing stand structure, humus forms, soils, cycling of N and P, organic matter decomposition, and soil fauna in CH and HA forests.
- Document the post-harvest decline in nutrient availability in CH cutovers.
- Determine the extent to which salal contributes to growth check conifers through competition and mycorrhizal interactions.
- Establish field trials to test the effectiveness of silvicultural treatments for promoting conifer growth on CH sites, including:
- fertilization: single-tree screening, conventional plot, and operational trials;
- organic fertilizers, including sewage sludge, fish silage and pulp sludge;
- fertilization, scarification and variations in planting density;
- mechanical site preparation and burning;
- salal eradication (manual and herbicides);
- starch or lime amendments.
Results:
A series of fertilization trials identified deficiencies of nitrogen and phosphorus as the cause of the growth check of conifers, and determined that additions of 200-300kg N ha-1 and 50-100 kg P ha-1 would provide an effective means of improving tree growth rates. Equivalent tree growth responses were achieved through additions of organic wastes such as sewage sludge and fish silage. Other silvicultural practices such as burning, cultivating, liming, higher planting densities or herbicide application, were less effective in promoting conifer growth.
The nutrient deficiencies in conifers on CH cutovers were the result of two main factors: low nutrient availability in soil and humus, and competition and interference from salal. Salal immobilized substantial amounts of N in biomass and an in vitro study suggested it was able to use organic forms of N through its mycorrhizal fungi, which would reduce the amount of N available to trees. The mycorrhizae of salal also interfered with those of hemlock, which further reduced their ability to take up nutrients. High concentrations of phenolic acids were associated with salal, which interfere with mineralization of N.
The low availability of N and P in CH cutovers originated in forest floors of the old- growth forests prior to clearcutting. Nutrient availability was low in all layers of the forest floor in CH forests; and this appeared to result from three main factors. First, cedar litter contains little N and more material resistant to decomposition than other species, and produces forest floors with low rates of N mineralization. Second, the forest floors in CH forests are wetter and have less soil fauna, leading to incomplete decomposition and mineralization of N. Third, the salal understorey in CH forest interferes with mineralization of N through the production of tannins and the activities of its mycorrhizal fungi.
The most effective procedure for regenerating CH cutovers is planting hemlock and cedar, and fertilizing at five years with at least 200 kg N ha-1 and 50 kg P ha-1, or organic wastes. a second fertilization may be necessary to achieve crown closure and thus shade out the salal. Continued monitoring of established long-term trials of these procedures is needed to test these predictions.
Monitoring:
The study area is located on northern Vancouver Island, between the towns of Port Hardy and Port McNeil, B.C. The area is within the very wet maritime subzone of the Coastal Western Hemlock (CWH) biogeoclimatic zone, and has a maritime climate with mild winters and cool moist summers.
Initial field trials demonstrated deficiencies of N and P as the cause of poor growth. Subsequent studies examined the decline in N and P availability following clearcutting and burning, and the role of salal in contributing to poor conifer growth. The origin of poor N and P supply were investigated in studies comparing nutrient cycling in old- growth CH forests with second-growth forests of hemlock-amabilis which do not have low nutrient supply.
The studies conducted included investigations of soil fauna, microbial biomass, mycorrhizae, structure and dynamics, nutrient cycling, allelopathy, competition, nutrition, plantation yield forecasting, humus chemistry, and economics. Studies were conducted within a framework of field experiments that examined the effects of fertilization, organic fertilizers, mechanical site preparation, plantation densities, vegetation control and different plantation species.
Recommendations:
The growth check of the conifers can best be relieved by fertilization with additions of 300 kg N ha-1 and 100 kg P ha-1, or fish silage or sewage sludge. With this treatment crown closure will be reached after a few years, shading the salal and leading to sustained improvement in the growth rates of conifers.
Attempts to alleviate the growth check by mechanical site preparation or vegetation control have not been effective. Although cedar grows best on CH sites, it may perpetuate the N supply problem through its litter. Hemlock might provide a long-term improvement in N availability and should be encouraged on fertilized CH sites. Although slashburning helps to prepare planting spots and increases the assart flush of nutrients, it may reduce the available N capital of the site in the long term.
Time Frame:
Monitoring and research are still continuing. Many long-term studies will be underway for a number of years to come.
Costs:
No formalized funding. An initial substantial grant was obtained by NSERC but subsequently many people have brought money into the project - funded their own research.
Current Status:
First 10 years completed. Utilizing obtained results to make changes and implement operationally. The extensive research has now shifted over into operational use. Management experiments are taking place in the Port McNeil District.
References:
C.E. Prescott and G.F. Weetman. 1994. Salal Cedar Hemlock Integrated Research Program: A Synthesis - SCHIRP. Faculty of Forestry, UBC and FRDA II, Vancouver, B.C.
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