FOREST RENEWAL BC - SCIENCE COUNCIL OF BC - FINAL REPORT
Final Report to March 31, 2001
FRBC Ref. No.: HQ96400-RE
Project Title: Effects of coastal hardwoods on mixed stand development and nutrient availability (EP1121)
Project Leader: K.D. Thomas1 and Phil Comeau2
Organisation: 1 BC Forest Service, Research Branch
2 University of Alberta (formerly BC Forest Service)
Team Members:
Brian D'Anjou (BC Ministry of Forests, Vancouver Region)
Robert MacDonald
Peter Fielder (BC Ministry of Forests, Research Branch)
Bill Reid (BC Ministry of Forests, Research Branch)
Project Start Date: April 1, 1996 Project End Date: March 31, 2001
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Table of Contents
Table of Contents i
List of Figures and Tables ii
Abstract 3
Introduction 4
Objectives 7
Methods 7
Effects of red alder density on conifer growth and nitrogen availability (EP1121.01) 7
Replacement Series Experiments 7
Additive Field Experiments 8
Effects of patches of red alder on microenvironment and on performance of conifers (EP1121.03) 8
Effects of bigleaf maple in growth of Douglas-fir and effects of coppice spacing on growth of maple (EP1121.02) 15
Plot establishment (Experiment 1) 15
Plot establishment (Experiment 2) 15
Modelling light penetration through broadleaf canopies 17
Results and Discussion 18
Effects of red alder density on conifer growth and nitrogen availability (EP1121.01) 19
Replacement Series Experiments 19
Additive Field Experiments 19
Effects of patches of red alder on microenvironment and on performance of conifers (EP1121.03) 22
Effects of bigleaf maple in growth of Douglas-fir and effects of coppice spacing on growth of maple (EP1121.02) [Experiment 1 and 2] 23
Modelling light penetration through broadleaf canopies 25
Summary and Conclusions 30
References 31
Statement of Expenditures 34
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List of Figures and Tables
Figure 1. Map of additive experiment at Waterloo Creek (near Courtney BC) showing plot layout and the trees in measurement plot. The site was planted 1992. Plot 1 = 100 Dr, Plot 3 = 50 Dr, Plot 5 = 0 Dr (control), Plot 6 = 200 Dr, Plot 7 = 400. 10
Figure 2. Map of additive experiment at Gough Creek near (Sechelt BC showing plot layout and the trees in measurement plot. The site was planted 1992. Plot 1 = 100 Dr, Plot 2 = 50 Dr, Plot 4 = 200 Dr, Plot 5 = 400 Dr, Plot 6 = 100, Plot 8 = 0 Dr (control). 11
Figure 3. Map of additive (plots 1-6) and replacement (plots 8-12) experiments at Holt Creek (near Duncan BC) showing plot layout and the trees in measurement plot. Additive Experiment: Plot 1 = 400 Dr, Plot 2 = 200 Dr, Plot 4 = 100 Dr, Plot 5 = 0 Dr (control), Plot 6 = 50 Dr. Replacement Experiment (% Dr/Fd): Plot 8 = 11/89, Plot 9 = 25/75, Plot 10 = 100/0, Plot 11 = 50/50, Plot 12 = 0/100. The site was planted 1994. 12
Figure 4. Map of additive experiment at Malcolm Knapp Research Forest showing plot layout and the trees in measurement plot.. The site was planted 1999. 13
Figure 5. Map of patch experiment at Holt Creek (near Duncan BC) showing plot layout and the trees in measurement plot. The site was planted 1994. 14
Figure 6. A survey map of the relative position of Experiment 1 and Experiment 2 maple coppice studies at Halpenny Road study site near Port Alberni BC (+ = maple coppices). Study 1 Coppices/ha: Plot 1 = 67, Plot 2 = 244, Plot 3 = 33, Plot 4 = 100, Plot 5 = 200, Plot 6 = 400 (control), Plot 7 = 133, Plot 8 = 0, Plot 9 = 167, Plot 10 = 300. 16
Figure 7. Average height of understorey Douglas-fir across a range of well spaced red alder densities, 1, 4, and 7 years after planting. There were no significant differences among treatments. 19
Figure 8. Average height of understorey western redcedar across a range of well spaced red alder densities, 1, 4, and 7 years after planting. There were no significant differences among treatments. 20
Figure 9. Average diameter at breast height of understorey Douglas-fir across a range of well spaced red alder densities 7 years after planting. There were no significant differences among treatments. 20
Figure 10. Average diameter at breast height of understorey western redcedar across a range of well spaced red alder densities 7 years after planting. There were no significant differences among treatments. 21
Figure 11. Height:diameter ratios for Douglas-fir across a range of well spaced red alder densities 1, 4 and 7 years after planting. There were no significant differences among treatments. 21
Figure 12. Height:diameter ratios for western redcedar across a range of well spaced red alder densities 1, 4 and 7 years after planting. There were no significant differences among treatments in year 1 and 7. 22
Figure 13. Gap fraction and estimated light levels within and around a 10 m wide patch of red alder at Holt Creek in 1999. In patch edges (tree stems) are at -5 and 5 m, red alder were approximately 4 m tall. 23
Figure 14. Average height of understorey Douglas-fir after initial spacing of maple coppices and five years after treatment. 23
Figure 15. Average height of maple stems following thinning to different spacing between leave-stems. 24
Figure 16. Average diameter of maple stems following thinning to different spacing between leave-stems. 24
Figure 17. Isolines showing pattern of leaf area index (LAI, m2/m2) distribution over the plot area based on LITE model estimates. 26
Figure 18. Display of fisheye photograph showing original image on left, thresholded image in centre, and chart indicating below-canopy reading values (grey scale) as estimated by SLIM, on right. 26
Table 1. Extension Products 27
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Abstract
This project addresses issues relating to Forest Operations and Decision-Support (testing regeneration and stand tending practices for managing broadleaf and mixedwood ecosystems, and developing extension activities to support integrated resource management) and addresses opportunities to maximise yield and return on investment through mixedwood management. An understanding of both the competitive and beneficial effects of red alder and bigleaf maple is fundamental to making sound mixedwood management decisions and at present there is little BC information or operational experience relating red alder or bigleaf maple spacing to broadleaf and conifer response. This project documents and demonstrates the effects of different amounts and spatial arrangements of broadleaves on growth and survival of conifers and broadleaves, stand dynamics, understorey light regimes, nutrient cycling, and long-term sustainability. This research includes five major components: 1) replacement series field experiments; 2) additive field experiments; 3) "cluster" experiment; 4) modelling light penetration through red alder and bigleaf maple canopies; and 5) ecosystem modelling. Initial results suggest that 200-400 well-spaced red alder per ha have had no negative impact on understorey conifer height and diameter growth. Maple coppices thinned to coppice densities of 30-60 cm between leave stems have very few re-sprouts and may be a useful tool in controlling maple coppicing without the use of herbicide. While growth and yield information is long-term, forest managers can apply short-term results to managing coastal broadleaf–conifer mixtures, and information from these studies will aid in the development of mixedwood models that incorporate growth, light, competition, microclimate and nutrient data to improve forecasts of stand tending practices on mixedwood yield and long-term sustainability. To date, research findings have been disseminated through two journal articles, two working papers, four extension notes, two progress reports, three models, two conference papers/posters, six field tours for forestry practitioners and researchers, and one workshop. In addition, the project provided data and support for a PhD thesis (in progress), a MSc thesis and eight co-op student work-term reports. The end-users of these results are forest practitioners at both the District and Regional levels, policy makers at both the Branch and Regional levels, forest researchers, and stand modellers. Current benefits experienced include: increased awareness and tolerance of broadleaves in mixture with conifers in coastal forests (Vancouver/Prince Rupert Regions); improved knowledge of acceptable densities of red alder that have no significant impact on understorey conifer growth(Vancouver/Prince Rupert Regions); initial validation of forest model simulations of differing red alder densities(Vancouver Region); light models that can be incorporated or adapted to mixedwood models (Research Branch). The project was conducted in the South-Island, Sunshine Coast and Chilliwack Districts, and the benefits of the project are being experienced in those Districts as well as Port McNeill, and Campbell River Districts. With re-measurements these project sites will continue to generate research results important to mixedwood management, modelling and growth and yield over the long-term.
Introduction
Red alder and bigleaf maple are common components of low elevation CWH zone forests in South-western British Columbia. These broadleaf species are potentially valuable as a source of lumber and fibre. Red alder can contribute to site nitrogen capital and long-term productivity through the process of symbiotic nitrogen fixation (Binkley 1983). Fried et al. (1990) report that total soil nitrogen, organic carbon content and the rate of cycling of macro-nutrients were much greater beneath bigleaf maple trees than beneath neighbouring Douglas-fir. Red alder and bigleaf maple are resistant to laminated root rot and their presence may reduce or ameliorate the effects of Phellinus weirii root disease on Douglas-fir. Red alder, bigleaf maple and other broadleaved species contribute to biodiversity at both the stand and landscape levels.
Red alder regenerates from seed. Exposed mineral soil provides ideal conditions for germination and establishment of red alder. Juvenile growth of red alder is much more rapid than that of most conifers. Three-year-old red alder can grow 2-3 m/yr in height, and can rapidly overtop neighbouring conifers. Red alder can remain dominant in a stand for up to 40 years. When it overtops conifers, it can substantially reduce light availability, and can cause physical damage to crop trees. The degree of light reduction and the amount of damage to conifers depend largely on the density and size of the red alder component of the stand. Miller and Murray (1978) estimated that between 50 and 100 alder per hectare would be sufficient to improve soil nitrogen and organic matter status without seriously affecting growth of Douglas-fir, on a nitrogen deficient site in Washington state. Using the FORECAST model Comeau and Sachs (1992) report that between 100 and 200 red alder per hectare will provide maximum sustainable yields of Douglas-fir. Straightforward techniques are required to estimate the potential impacts of different densities and spatial arrangements of broadleaves on the growth of associated conifers.
The presence of alder in patches or as scattered individuals in a forest can contribute to biodiversity, to long-term site productivity through addition of nitrogen to the soil, and to rates of nutrient cycling through influence on characteristics of litter and soil flora and fauna.
Red alder litter influences nutrient cycling in the forest and can also contribute to site nitrogen capital and long-term productivity through the process of symbiotic nitrogen fixation (Comeau and Sachs 1992). In pure stands of red alder, nitrogen fixation rates are usually between 100 and 200 kg/ha/yr (Binkley, Cromack and Baker 1994). In mixed stands, fixation rates of 80 to 125 kg/ha/yr have been reported (Miller and Murray 1978; Binkley, Cromack and Baker 1994).
Various studies suggest that intermixing alder with Douglas-fir will lead to loss of the conifer component unless alder densities are less than 400 trees per hectare (Comeau and Sachs 1992; Miller and Murray 1978). Studies are underway in B.C. and elsewhere to document the long-term effects of different amounts of red alder in intimate mixture (i.e. with various densities of alder uniformly distributed through the plantation) with conifers (e.g. Comeau et al. 1995). At low densities, live branches may be retained on red alder longer than is desirable for quality sawlog production. Consequently, it may be desirable to grow alder and Douglas-fir in patches if production of quality red alder sawlogs is desired in a mixedwood system.
Miller et al (1993) reported that the beneficial influence of alder on growth of Douglas-fir extended up to 15 m away from rows of planted trees on a poor quality site at Wind River in Washington. Rhoades and Binkley (1992) found that increases in N availability extended about 8 to 12 m downslope of the alder, but had no apparent effect upslope on the same infertile site. However, on a fertile site at Cascade Head no trends in N availability were observed along transects running across boundaries between adjoining red alder and conifer stands . Soil pH in the conifer stand at Cascade Head was depressed for about 5 m from the edge of the alder/conifer stand. However, no effects of alder on soil pH were observed at Wind River.
There is no available information on the effects of patches of red alder (or other temperate or boreal broadleaves) on the light regime in and around the patches. However, effects of a patch of red alder on light conditions would be expected to vary depending on both distance and direction from the alder and the size of the alder in a manner similar to the effects of location in canopy gaps (Messier 1996). Since direct light comes from the location of the sun, direct beam radiation comes predominantly from the southern hemisphere of the sky. On the south side of a patch of alder there would be little effect on direct sunlight, however direct light would be expected to be reduced substantially inside the patch and on the north side of the patch. Reductions in direct light would also be expected on the eastern and western sides of alder patches, with the magnitude of the reduction depending on the portion of the suns path that is obstructed by the red alder. Diffuse light comes from all directions in the sky, and is commonly assumed to be distributed fairly uniformly across the entire sky (Spitters et al. 1986; Canham 1988). Consequently, the effect of patches of red alder on diffuse light will vary primarily as a function of the amount of sky that is obstructed by the red alder, with direction having little influence on total diffuse light over the growing season.
There is little information on the influence of patches of alder on understorey light, soil properties and performance of conifers within the patch and outside of the patch. Better information is required regarding the distance over which red alder patches have an influence on soil nitrogen, on light, and on conifer performance. Such information is needed as a basis for making decisions about the number and distribution of alder patches in a mixedwood stand. To be useful, there is a need for such information from a range of sites and for a range of conifer species that may be found growing in mixture with red alder.