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.



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.


Description of additive experiment - eight treatments


  • 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.

Last Modified: 2000 MAY 23.
Questions? Contact Research Branch.
Webmaster: For.Prodres@gov.bc.ca