Effects of Red Alder on Stand Dynamics and Nitrogen
Availability
B.C. Ministry of Forests Experimental Project (EP) 1121
Why is Red Alder Important?
Red alder is found throughout the Coastal Western
Hemlock Biogeoclimatic Zone and is the most abundant broad-leaved
species in coastal British Columbia. Red alder is harvested to
produce saw lumber for remanufacture into moldings, furniture, and
pallets, to produce chips for pulping and for firewood.
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. Red alder is
resistant to laminated root rot and its presence may also reduce or
ameliorate the effects of Phellinus weirii root disease
on Douglas-fir. Red alder and other hardwoods contribute to
biodiversity at both the stand and landscape levels.
How Does Red Alder Influence
Conifer Growth?
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 depends largely on the density
and size of the red alder component of the stand.
A series of long-term studies have been initiated to improve
understanding of both the competitive and beneficial effects of red
alder when grown with conifers. Studies have been established to
document and demonstrate the effects of different amounts and spatial
arrangements of red alder on growth and survival of conifers and
hardwoods, stand dynamics, crown characteristics, nitrogen
availability, nutrient cycling, and long-term productivity. This
study has five major components: 1) replacement series
field experiments; 2) additive field
experiments; 3) "cluster" experiment; 4)
modeling light penetration through alder
canopies; and 5) ecosystem modeling.
Replacement Series Field Experiments
Replacement series experiments are useful for
identifying the nature of interactions between two species and how
they change as the proportion of each species changes. A replacement
series experiment involves planting two species together in a
succession of different proportions, while keeping the total number
of trees per hectare (tph) constant.
In this study, red alder and Douglas-fir have been planted in a
series of 5 proportions (alder: Douglas-fir - 1:0, 0.5:0.5,
0.25:0.75, 0.11:0.89, 0:1.0) at a total density of 742 trees/ha (3.67
m spacing), following an experimental design protocol prepared by the
Oregon State University Hardwood Silviculture Cooperative. One
installation was planted at East Wilson Creek in 1992 and another at
Holt Creek in 1994
(Table 1).Each installation consists of one
replicate of each of the five treatments. Treatment plots are 70 m x
70 m (0.49 ha) at East Wilson Creek and 60 m x 60 m (0.36 ha) at Holt
Creek. Additional installations are being established in Oregon and
Washington by other members of the Hardwood Silviculture Cooperative.
In each treatment plot at both locations, data on stem diameter,
height (Figure 1) and crown dimensions are being
collected for all trees within a 0.10 ha permanent measurement plot.
The amount of light reaching each tree is also being measured, and
soil samples are being collected to document changes in soil nitrogen
capital, pH, and organic matter content. A climate station has been
installed at each installation to provide data on solar radiation,
soil and air temperature, soil moisture, and rainfall.
FIGURE 1. (8k gif)
East Wilson Creek replacement series: tree heights for 1992, 1993 and
1994 (Fd = Douglas-fir; Dr = red alder).
Additive Field Experiments
Additive experiments have been established at three
locations (Table 1). In the additive design,
Douglas-fir and western red cedar were planted in all plots at total
densities of 1100 tph (with the two species planted in equal
proportions at alternating planting spots), and one of eight
"broadleaf" density treatments (Table 2) was applied to 0.36 ha or
0.49 ha treatment plots. Due to space limitations treatments were not
replicated on individual sites and not all treatments could be
applied at all sites. Problems with survival of planted trees due to
site conditions, vegetation competition, and browsing have been
encountered at two locations (Shawnigan Lake and Surrey Nursery) that
have now been dropped from the study.
Data collection regimes for the Gough Creek, Waterloo Creek, and
Holt Creek additive installations (Figures 2 and 3) are the same as
for East Wilson Creek and Holt Creek replacement series
installations.
TABLE 1.
Field installations established for replacement series,
additive and cluster experiments.
Replacement Series
- East Wilson Creek - Sunshine Coast Forest District; CWHdm
biogeoclimatic subzone, soil moisture regime=3, soil nutrient
regime=c, year established:1992.
- Holt Creek - Duncan Forest District, CWHxm biogeoclimatic
subzone, soil moisture regime=5, soil nutrient regime=d,
established 1994.
Additive Experiment
- Gough Creek - Sunshine Coast Forest District, CWHdm
biogeoclimatic subzone, soil moisture regime =3, soil nutrient
regime=c, established 1992.
- Waterloo Creek - Port Alberni Forest District, CWHdm
biogeoclimatic subzone, soil moisture regime=4, soil nutrient
regime=c, established 1992.
- Holt Creek - Duncan Forest District, CWHxm biogeoclimatic
subzone, soil moisture regime=5, soil nutrient regime=d,
established 1994.
Cluster Study
- Holt Creek - Duncan Forest District, CWHxm biogeoclimatic
subzone, soil moisture regime=4, soil nutrient regime=d,
established 1994.
TABLE 2.
Description of additive experiment - eight treatments
Treatment:
- 1 - 0 red alder (control) _
- 2 -50 red alder/ha (14.2 x 14.1 square spacing)
- 3- 100 red alder (10.0 x 10.0 square spacing)
- 4- 200 red alder/ha (7.1 x 7.1 square spacing)
- 5 - 400 red alder/ha (5.0 x 5.0 square spacing)
- 6 - 100 red alder/ha planted in year 5 (10.0 x 10.0 square
spacing)
- 7 - 50 bigleaf maple/ha (14.2 x 14.1 square spacing)
- 8 - 200 Sitka Alder/ha (7.1 x 7.1 square spacing)
FIGURE 2. (8k
gif)
Gough Creek additive installation: tree heights for 1992, 1993 and
1994 (Cw= western red cedar; Fd = Douglas-fir; Dr = red alder).
FIGURE 3. (14k
gif)
Waterloo Creek additive installation: tree heights for 1992, 1993 and
1994 (Cw= western red cedar; Fd = Douglas- fir; Dr = red alder).
Cluster Experiment
In some cases, growing species mixtures as patches may
be more desirable than growing red alder and conifers in intimate
mixtures. However, there is little information on the influence of
patches of red alder on light, soil properties, or performance of
conifers either within the patch or outside the patch. To provide
some information on the influence of red alder patches a "cluster"
experiment was initiated in 1994 at Holt Creek.
For this experiment, eight patches of red alder were planted at
Holt Creek in May 1994, in a 6 ha area that had previously been
planted with Douglas-fir in March 1994. Patches of alder, 8 m x 8 m,
were located at least 50 m apart within the opening, and at least 40
m from the edge of the adjoining stand. Two alder densities were each
randomly assigned to four patches_25 trees/patch (2500 tph or 2 m
spacing) or 81 trees/patch (10 000 tph or 1 m spacing).
The cluster experiment will examine the effects of distance and
direction from the red alder patch and the effect of patch density on
growth of Douglas-fir, on light, and on soil nitrogen, soil pH, and
soil organic matter content.
Modeling Light Penetration through red alder
canopies
The amount of light that penetrates through red alder
canopies varies as a function of 1) stand characteristics (number,
size, spatial arrangement, and crown architecture of red alder), 2)
season (the locations of the sun and leaf development of the canopy),
3) time of day, and 4) weather conditions.
Light is one of the major factors involved in interactions between
red alder and conifers. A model is currently being developed for
estimating the amount of light penetrating red alder canopies. The
model will estimate light penetration through alder stands of various
sizes and configurations and demonstrate light penetration varies
diurnally and seasonally. Model output will include estimates of
hourly averages and of hourly, daily, weekly, and seasonal totals.
Ecosystem Modeling
Ecosystem models are useful tools for exploring the
tradeoffs between beneficial and detrimental effects of red alder on
stand growth, and on long-term site productivity. The FORCYTE_11
Ecosystem model has been calibrated for red alder, Douglas-fir,
western red cedar, and western hemlock. Simulations using FORCYTE_11
indicate that between 100 and 200 well-spaced stems of red alder per
hectare will increase Douglas-fir yields by up to 13%
(Figure 4). However, this study and others
indicate that intermixing alder with Douglas-fir will lead to
substantial losses in the conifer component unless alder densities
are less than 200 trees per hectare. Simulations with mixtures of red
alder and western red cedar, or with red alder and western hemlock
provide similar results. However, performance of western red cedar or
western hemlock declines when red alder densities exceed 500 trees
per hectare.
FIGURE 4.(8k
gif)
Effects of initial red alder density on cumulative stemwood biomass
yield of Douglas-fir and red alder for a site index (SI) of 30 m at
50 years and red alder SI of 17 m at 50 years. Results are based on
simulations using FORCYTE_11.
In simulated replacement series experiments, maximum whole-stand
yield was achieved with a stand composed of 60% Douglas-fir and 40%
red alder(figure 5). Douglas-fir yield was
highest in the stand with only 20% red alder component.
FIGURE 5. (5k
gif)
Results from a simulated replacement series experiment showing total
stemwood biomass yield over 80 years. FORCYTE_11 simulation was done
for a medium-quality Douglas-fir site, with 1000 total trees per
hectare (planted); red alder were harvested at age 40, and
Douglas-fir at age 80.
Simulations suggest that site productivity may decline with
successive eighty-year rotations of pure Douglas-fir (where alder is
precluded from the stand). However, establishment and retention of
200 red alder per hectare appear to be more than enough to maintain
soil nitrogen and site productivity.
Further refinements in the capabilities of this model are
underway, including simulation of the effects of different spatial
arrangements of red alder. Data from field experiments will be used
for calibration and validation of model predictions.
This research was supported by FRDA I, FRDA II,
Forest Renewal B.C., and the B.C. Ministry of Forests. Support from
the Hardwood and Vegetation Management Technical Advisory Committee,
and assistance from Deborough Dowsling, is gratefully acknowledged.
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