Broadleaves and mixed forest management

Broadleaves and mixedwoods are a significant part of B.C.'s forested ecosystems, offering shelter and forage for many wildlife species and contributing to the overall biodiversity of this unique province. In addition, they are a renewable resource that provides employment opportunities now and in the future.

Our research concentrates on interactions between various broadleaf tree species and the surrounding vegetation. 

Silviculture of Temperate and Boreal Broadleaf-conifer Mixtures - LMH36

Broad-leaved species are a common component of British Columbia forests. They occur as pure stands as well as in mixture with conifer species. Retaining and managing broadleaves in our forests is desirable for many reasons, including: biodiversity, wildlife habitat, aesthetics, providing nurse crops for conifers, improving nutrient supplies, ameliorating or reducing risk of forest health problems, diversifying forest end products, and potentially increasing yield. However, problems can be encountered when the broadleaf species has a more rapid initial growth rate than the conifers. Critical questions exist about the feasibility of growing species mixtures and their consequences, and the management of mixtures (including appropriate initial densities, espacement, and arrangements as intimate or patchy mixes) and their use.

Effects of Red Alder on Stand Dynamics and Nitrogen Availability FRBC Project HQ96400-RE - EN09

This extension note provides a summary of results obtained to date from studies initiated in 1992 to document and demonstrate the effects of different amounts and spatial arrangements of red alder on forest productivity, stand dynamics, and nitrogen availability in broadleaf-conifer mixedwood stands in coastal British Columbia. Replacement series experiments have been planted at two locations in B.C. to evaluate the effects of various proportions of red alder when grown in mixture with Douglas-fir. Mixedwood plantations have also been established at three locations following an additive design. In the additive design, Douglas-fir and western redcedar were planted at a density of 1100 sph (with the two species planted in equal proportions at alternating planting spots), and one of eight "broadleaf" density treatments was subsequently applied to randomly selected plots. These treatments included: 0, 50, 100, 200 and 400 red alder per hectare, 50 bigleaf maple per hectare, 200 Sitka alder per hectare, and a delayed planting of 100 red alder per hectare in year 5.

Ectomycorrhizal Diversity of Paper Birch and Douglasfir Seedlings Grown in Single-species and Mixed Plots in the ICH Zone of Southern British Columbia - EN19

There are a number of incentives to retain broadleaf tree species, such as paper birch (Betula papyrifera Marsh.), following logging in the Interior Cedar-Hemlock biogeoclimatic zone. For example, the roots of paper birch are intimately associated with numerous species of ectomycorrhizal fungi. The retention in plantations of paper birch may, therefore, contribute to below-ground biodiversity by hosting a variety of mycorrhizal fungi. Furthermore, the retention of paper birch in young mixed plantations appears to reduce the incidence of Armillaria ostoyae among Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) (Morrison et al. 1988; Simard 1997) and improve both the nitrogen and pH status of soils. Finally, the presence of paper birch increases the diversity of tree species and contributes to the structural diversity of a stand (Simard and Vyse 1994).

Ectomycorrhizae are the nutrient-and water-absorbing organs of most woody plants and, as such, mycorrhization of planted seedlings is thought to be critical for adequate growth and survival. However, ectomycorrhizal fungi do not persist in the absence of a plant host and therefore the quantity and diversity of fungal inoculum often decreases after logging. Ectomycorrhizal species, such as paper birch, may act as reservoirs (refuge plants) for ectomycorrhizal fungi on a site, thereby maintaining a diversity of fungi that may eventually associate with planted conifers.

Effects of Bigleaf Maple (Acer macrophyllum Pursh) on Growth of Understorey Conifers and the Effects of Coppice Spacing on the Growth of Maple - EN24

Bigleaf maple is a desirable ecosystem component that adds to the structural and species diversity of British Columbia's coastal forests. The presence of bigleaf maple may accelerate nutrient cycling, improve site productivity, and contribute to long-term sustainability. Bigleaf maple can be planted on sites infected with laminated root rot for site rehabilitation and amelioration. Maple is also potentially valuable as a commercial tree species; the wood is used for high-value furniture, flooring, and face veneers.

LITE: A Model for Estimating Light under Broadleaf and Conifer Tree Canopies - EN23

This extension note briefly describes LITE, a model developed for estimating light penetration in the broadleaf-and conifer-dominated forests of British Columbia. A complete description of the model and instructions for use are provided by Comeau et al. (1998).

Evaluation of the Effectiveness of Chondrostereum purpureum for the Control of Mechanically Brushed Trembling Aspen (Populus tremuloides Michx.) Suckers in a 2-year-old Conifer Plantation: Third-year Results - EN49

Several vegetation control options are currently available to British Columbia foresters. Some of the more common options, such as herbicide application or manual brushing operations, may be limited in their effectiveness for a number of reasons. For example, public opposition may curtail the operational application of herbicides, while site conditions may preclude the use of manual brushing of competing vegetation (Boateng and Comeau 1997). Other less common methods may be restricted in their use to specific ecosystems. The Research Branch of the B.C. Ministry of Forests, in partnership with the Canadian Forest Service, the Biology Department of the University of Victoria, and Mycologic Inc., are currently involved in testing the use of a fungus, Condrostereum purpureum, as a method of controlling vegetation that competes with planted conifer seedlings. The purpose of this research was to evaluate promising methods for managing vegetation in conifer plantations.

An Evaluation of Two Chondrostereum purpureum Carrier Formulations Used for the Control of Sitka Alder in a 41-year-old Not Satisfactorily Restocked Stand - EN61

This note describes the response of brushed Sitka alder stumps to the application of paste and spray formulations of the C. purpureum mycoherbicide. Information about site and plot locations and baseline seedling parameters are also included for the purpose of comparing treatment applications in the future.

Competitive Effects of Trembling Aspen on Lodgepole Pine Performance in the SBS and IDF Zones of the Cariboo–Chilcotin Region of South-central British Columbia - TR05

A retrospective study was carried out between 1992 and 1999 in the Cariboo-Chilcotin area of the Southern Interior Forest Region to quantify the effects of trembling aspen competition on lodgepole pine performance and to identify competition indices or other measures of competition that could be used by field staff. In six stands in the Sub-Boreal Spruce (SBS) dw1 and Interior Douglas-fir (IDF) dk3/dk4 biogeoclimatic variants, target pine were selected across neighbourhoods with varying densities of tall aspen (i.e., aspen as tall or taller than the target pine). Data pertaining to pine size and condition, and to the size and location of aspen within a 1.78-m radius of the target pine, were collected three times. Measurements commenced when stands were 7-12 years old. Various approaches were used to identify levels of aspen abundance where pine performance declined below acceptable levels. These included analyses of regression and correlation, tests of existing competition indices, and visual and statistical characterization of trends.

Growing-space Management in Boreal Mixedwood Forests—The Establishment of EP 1192.01, Fort Nelson River Site - EN64

In northern British Columbia, boreal and sub-boreal forests dominate the landscape. Significant portions of these forests comprise mixed stands of conifer and deciduous species, or "mixedwoods." Historically, management prescriptions for boreal mixedwoods emphasized the creation of conifer or deciduous monocultures and pure stands. However, this practice of "unmixing" boreal mixedwoods is neither ecologically desirable nor biologically successful (Grover and Greenway 1999). This study explores not only the spatial and temporal interaction of aspen and spruce, but also the impact of a variety of operational brushing tools designed to manipulate and promote the early establishment of mixedwood growing space. With its large plot size and replicated design this research trial will help provide both short- and long-term information needs supporting the continuing evolution of boreal mixedwood management.

Lodgepole Pine Response to Aspen Removal in Variable Radii in the SBSdw2 Variant near Williams Lake, B.C. - TR14

A study was established in 1994 in the SBSdw2 variant of the Cariboo-Chilcotin region of the Southern Interior Forest Region to investigate the effects of removing aspen in 50 or 100 cm radii around crop lodgepole pine versus broadcast removal or no treatment. The primary objective of the study was to assess whether the free-growing criterion (current in 1994), which specified that no overtopping vegetation could be present within a 1 m radius around crop trees, was appropriate in pine-aspen stands, or whether a 50 cm radius zone would be adequate.

After 9 years, during which treatments were maintained annually, there were no differences in pine survival or growth between the 50 and 100 cm radius treatments. Even in the untreated control, there was no mortality as a result of vegetation competition, and neither were there vigour losses. There also were no significant differences in pine stem diameter or height as a result of any of the treatments, but height:diameter ratio (HDR) was significantly lower in the broadcast treatment than in the control and 50 cm treatment.

During the 9 years of the study, total aspen density decreased from approximately 50000 to 22000 stems ha-1. Tall aspen density (i.e., the density of aspen as tall or taller than the target lodgepole pine) was approximately 5000 stems ha-1 at age 9 years. At that time, tall aspen density was more strongly correlated than was aspen basal area with pine stem diameter growth. Related work (Newsome et al. 2003) showing that competition effects are only weakly expressed in 9-year-old pine-aspen stands suggests the need for longer-term measurements at the Tyee Lake site.

Early Effects of Manipulating Aspen Density on Lodgepole Pine Performance, Aspen Sucker Production, and Stand Development in the IDFxm Subzone near Williams Lake, B.C. - TR15

An experiment was established at Meldrum Creek in the IDFxm subzone of the Cariboo-Chilcotin region in 1998 to study the effects of reducing aspen density to 0, 1000, 2500, or 4000 stems ha-1 on lodgepole pine performance. After 4 years, when the stand was 10 years old, the treatments had resulted in no significant differences in mean lodgepole pine stem diameter, diameter increment, height, leader length, crown width, or height:diameter ratio (HDR). Survival was at least 92% in all treatments, including the untreated control. One of the objectives of the study was to test and refine competition thresholds for aspen retention on dry-belt IDF sites that had been defined in an earlier study in the Cariboo-Chilcotin (Newsome et al. 2003).

Regression analysis showed that aspen within a 1 m radius of target pine were more important competitors with the pine than aspen farther away. However, aspen competition was relatively unimportant when the stand was 10 years old. The density of aspen that was as tall as, or taller than, target pine predicted, at best, 14.6% of the variation in pine stem diameter increment. At the stand level, reducing aspen density immediately changed the diameter distribution of aspen and reduced its basal area (BA); and, after 4 years, aspen continued to have less basal area than pine in the 0 and 1000 stems ha-1 treatments. Two years after cutting, aspen sucker density ranged from 16 623 stems ha-1 in the 4000 stems ha-1 treatment to 33 599 stems ha-1 in the 0 stems ha-1 treatment. Because of substantial variability in the numbers of suckers counted, however, these differences between treatments were not statistically significant. Sucker densities naturally declined by one-third to one-half between years 2 and 4 after cutting, but still exceeded 8500 stems ha-1.

Suitability of Native Broadleaf Species for Reforestation in the Cariboo Area of the Southern Interior Forest Region - EN73

A study to gather information about the establishment and growth of broadleaf trees, and to compare their performance with that of common conifer species in the eastern half of the former Cariboo Forest Region (now part of the Southern Interior Forest Region), was established in 1993. Black cottonwood, aspen, birch, interior spruce, and lodgepole pine were planted on sites in the ICHwk2, SBSwk1, SBSdw1, SBSdw2, and IDFdk3 biogeoclimatic variants. Conifers were performing well after 10 years, but survival of broadleaves was generally poor and their growth was moderate at best. Broadleaves readily naturally regenerate in the Cariboo following disturbance, however, and generally have better initial growth than conifers. Therefore, these results should not be considered representative of the overall potential of broadleaf trees to contribute to the maintenance of forest health and timber supply in the Cariboo. This paper provides 10 years of results from this study and includes conclusions and recommendations regarding the potential use of planted broadleaf seedlings in the Cariboo.

Effects of Variable Aspen Retention on Stand Development, Aspen Sucker Production, and Growth of Lodgepole Pine in the SBSdw1 Variant of South-central British Columbia - TR32

In 1999, an experiment was established to examine the effects of reducing aspen density on stand-level lodgepole pine and aspen growth in the SBSdw1 biogeoclimatic variant of the Cariboo-Chilcotin. Aspen retention treatments of 0, 500-800, 1000-1500, and 2000-2800 stems ha-1 were applied in an 11-year-old mixed-species stand of aspen and lodgepole pine. One year after cutting, aspen basal area in these retention treatments was 0, 1.25, 3.05, and 2.89 m2 ha-1, respectively, compared with 5.36 m2 ha-1 in the control. Four years after treatment, based on stand-level measurements taken in permanent measurement plots, pine vigour tended to be better in treatments where <1000 aspen stems ha-1 had been retained but there were no significant differences in mean stand-level lodgepole pine height, stem diameter, quadratic mean diameter, or basal area as a result of the aspen retention treatments.

Aspen suckering was assessed 2 and 4 years after cutting. Sucker densities differed significantly between aspen retention treatments after 2 years, ranging from 28 187 stems ha-1 in the complete aspen removal treatment to 344 stems ha-1 in the 2000-2800 stems ha-1 treatment. Sucker densities appear to have declined naturally by approximately 35% between years 2 and 4 after cutting; however, this apparent decline may be partly due to a change in the sampling method. There were no significant differences between treatments in sucker height in either year 2 or 4 after cutting.

In addition to stand-level measurements, the ongoing performance of target lodgepole pine that had, or had not, met existing British Columbia Ministry of Forests free-growing requirements at a stand age of 12 years was assessed. By 2003, pine in the free-growing group were larger than those in the not free-growing group according to all measurement criteria. Regression analysis showed that tall aspen (i.e., aspen at least as tall as the target pine) within a 1.78-m radius were more important competitors with the target pine than aspen that were further away. When the stand was 13 years old, tall broadleaf basal area explained 25.7% of the variation in 2000-2003 lodgepole pine stem diameter increment.

Early Effects of Manipulating Aspen Density and Spatial Arrangement on Lodgepole Pine Performance, Aspen Sucker Production, and Stand Development in an 11-Year-Old Stand in the SBPSxc Subzone of South-central British Columbia - TR29

The Clusko aspen removal study, established in 2001 in an 11-year-old lodgepole pine-trembling aspen stand in the SBPSxc subzone, investigates the effects of five levels of aspen removal on target pine, neighbourhood competitive interactions, and stand development. Treatments include: (1) an untreated control; (2) complete aspen removal; broadcast retention of (3) 1000 and (4) 2500 aspen stems ha-1; and (5) a spatial treatment that removed aspen within a 1-m radius around target pine.

Two years after treatments were applied, 2001-2003 target pine stem diameter increment was significantly larger in the 0, 1000, and 2500 stems ha-1 removal treatments than in the uncut control. In 2003, target pine stem diameter was significantly larger in the complete aspen removal treatment than in the control, and height:diameter ratio was smaller. Aspen removal treatments had no significant effect on lodgepole pine height, leader length, or crown width within 2 years of treatment.

Regression analysis showed that when the stand was 13 years old, lodgepole pine stem diameter growth decreased with increasing density of aspen that were at least as tall as the target pine. The relationship was strongest where aspen were included within a 2.56-m radius plot, which was the largest neighbourhood examined in this study, and was not statistically significant in neighbourhoods with smaller radii. At age 13, tall aspen density accounted for a maximum of 21.2% of the variation in pine growth, with the strongest relationship occurring between 2-year pine stem diameter increment (2001-2003) and 2003 tall aspen density. At the stand level, reducing aspen density immediately changed the diameter distribution of aspen and reduced its basal area, although after 2 years aspen continued to have greater basal area than pine in all but the complete aspen removal treatment. Two years after cutting, aspen sucker density had decreased significantly with the level of aspen retention. Complete aspen removal resulted in an average density of approximately 93 000 suckers ha-1 after 2 years, compared with approximately 44 000 and 22 000 suckers ha-1 in the 1000 and 2500 stems ha-1 retention treatments, respectively.

Effects of Red Alder on Stand Dynamics and Nitrogen Availability - EN76

This extension note provides an update on the ongoing additive and replacement series experiments of Experimental Project (EP) 1121.01; no conclusions are drawn. This project was established to assess the competitive effects of a range of red alder densities on understorey conifer growth.

Assessing the Effects of Sitka Alder on the Growth and Foliar Nutrition of Young Lodgepole Pine in Central British Columbia (SBSdw3): 9-year Results - EN79

The 9-year post-treatment effects of different levels of Sitka alder (Alnus viridis ssp. sinuata [Regel] Á. Löve & D. Löve) retention (0, 500, 100, 20 clumps per hectare) on the development of retained alder and on the growth and foliar nutrition of young, naturally regenerated lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were evaluated in the Sub-Boreal Spruce biogeoclimatic zone in central British Columbia. Alder development was inversely related to alder retention density, with the largest height and crown width increments occurring at the lowest alder densities. Low to moderate levels of alder cover (<35%) did not significantly inhibit the diameter at breast height (dbh) or height growth of lodgepole pine. Over the 9-year response period, pine dbh and height increments in the high alder retention treatment were both reduced by 11% (9 mm and 42 cm, respectively) relative to the no alder retention treatment. However, the average height of lodgepole pine, and the average height difference between the pine and alder, exceeded freegrowing guidelines for the SBSdw3 in all of the alder retention densities 6 years following treatment. Our results indicate that brushing on submesic to mesic sites in the SBSdw3 is likely unnecessary unless Sitka alder is taller than regenerating lodgepole pine and alder percent cover is uniformly very high (>40-50%) at early stages of pine development. The presence of Sitka alder improved the foliar nitrogen (N) concentration of young lodgepole pine growing on this site. However, the facilitative effects of alder retention on pine foliar N status were partially offset by an imbalance of foliar N relative to other nutrients (especially sulphur, S). Deficiencies of S (and possibly phosphorus, P, and potassium, K) induced by high foliar N levels may partially explain the smaller dbh and height growth of lodgepole pine in the alder retention treatments at this site.

Relative Impact of Aspen Competition and Soil Factors on the Performance of Lodgepole Pine and Hybrid White Spruce in North-central British Columbia - TR39

Releasing conifers from the competition effects of aspen (Populus tremuloides Michx.) is a key focus of plantation management in sub-boreal and boreal forests, often at considerable cost. However, other factors affect early plantation performance. This study investigates the relative influence of aspen competition and soil factors on the performance of planted lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca [Moench] Voss × engelmannii Parry ex Engelm.) in north-central British Columbia. Plots were established across a gradient of natural aspen competition levels that resulted from a test of aspen control treatments at one site. Within these plots, 240 of each of the target conifer species were measured and their immediate soil and vegetative environment quantified. Regression trees and regression analysis were used to examine the importance of aspen competition relative to other factors in determining target conifer size. Soil factors generally provided the best partitioning of height growth differences for lodgepole pine and hybrid white spruce, whereas a mix of vegetation competition and soil factors provided the best partitioning of diameter growth differences. Regression models accounted for 19-28% of spruce size and 24-33% of lodgepole pine size. The single variable explaining the most variability in lodgepole pine size was aspen competition, whereas it was humus depth for hybrid white spruce. Practices should be altered to alleviate soil-induced growth reductions, particularly for hybrid white spruce.

Will Minor Spruce Components of Boreal Broadleaf Stands Replace Themselves after Clearcut Harvesting? - TR63

We examined natural regeneration of white spruce (Picea glauca) in 13 broadleaf stands in two areas of northeastern British Columbia, 14-25 years after harvest. Spruce natural regeneration was present in 11 of the 13 stands. Fort Nelson stands had more uniform spruce distribution and higher stocking than Dawson Creek stands. Regression analyses indicated that mineral soil seedbeds and seed source location relative to the harvested stand were able to predict Dawson Creek spruce regeneration, with a large component of unexplained variation. Distribution of spruce regeneration was more variable in harvest-origin stands than spruce found in mature aspen-dominated stands of wildfire origin. Model simulations indicated that rotation lengths of at least 80-100 years would be required for post-harvest spruce natural regeneration to contribute 10-20% of stand merchantable volume at the next rotation.

This technical report addresses the following questions:
1. What is the occurrence and distribution of white spruce natural regeneration in broadleaf-dominated stands that are being managed for broadleaf production in northern British Columbia?
2. How does this distribution compare with the distribution of a minor white spruce component in wildfire-origin broadleaf-dominated stands?
3. Can a combination of inventory and site information provide reliable prediction of white spruce natural regeneration?
4. Will the post-harvest broadleaf-dominated stands develop into stands similar to those that occurred previously on site?

The Growth of Bigleaf Maple and Planted Conifers 14 Years after Maple Clump Thinning - TR75

Bigleaf maple (Acer macrophyllum Pursh) is a native broadleaf commonly found in the coastal forests of the Pacific Northwest. Following harvesting, vigorous sprouting from cut stumps can create large, rapidly growing clumps of maple sprouts, which can severely reduce the survival and growth of neighbouring conifers. During 1996, ten 0.09-ha plots containing up to 490 bigleaf maple clumps per hectare (cph) were established. A series of maple clump thinning treatments ranging from 0 to 400 cph was assigned to the plots to study the effects of varying maple clump density on understorey light and conifer growth. Select maple clumps were removed by manually cutting all clump sprouts. Post-treatment results over 14 years indicated that the maple clump thinning treatments did not result in any long-lasting differences in conifer survival and growth. In contrast, the clump thinning treatments resulted in a significant decline in cut maple and an increase in uncut maple clump sprout density and volume increment with increased uncut maple cph. Conifer volume increment and total stand volume increment showed no response across the maple cph treatments. Stand periodic annual volume increment of the maple-conifer mixedwood plots ranged from 7.6 to 13.1 m3/ha/yr over 14 years post-thinning.

The Role of Broadleaf Trees: Impacts of Managing Boreal and Sub-boreal Mixedwood Forests in British Columbia - EN110

Within the boreal and sub-boreal forests of northern British Columbia large areas of broadleaves occur naturally in mixture with conifers or as pure stands. Many conifer plantations contain significant numbers of naturally regenerating trembling aspen, birch, and cottonwood. Broadleaves have historically been undervalued and considered an impediment to conifer establishment and growth, as reflected in the freegrowing guidebooks that suggest limits to the presence of broadleaf trees in regenerating stands. Legislation and policy have evolved to promote practices that minimize broadleaf impact and optimize conifer stand growth and yield with the goal of supporting a sustainable timber supply.

Although broadleaves certainly can have antagonistic effects on conifer growth and survival and currently have lower value, they also contribute positive influences and attributes. They provide various ecological, social, and non-timber values; have significant value in shaping forest ecology, stand structure, and function; and exert a strong influence on forest diversity and resilience.

Adjusting Free-growing Guidance Regarding Aspen Retention in the Cariboo-Chilcotin - TR102

Over a 6-year period, from 2008-2014, recommendations for change to broadleaf-tree-related free-growing guidelines were made for seven Cariboo Region biogeoclimatic subzones/variants. In large part, the project involved examining available research, primarily from Cariboo Region Experimental Project 1152, and verifying the extent to which it could be applied across the landscape. As a result of this work, in 2013, Chilcotin and Central Cariboo Forest District policy declared aspen a non-deleterious brush species in the SBPSxc and IDFdk4. In 2015, recommended adjustments to free-growing guidance for the IDFdk3, SBSdw1, SBSdw2, SBPSmk, and SBPSdc were incorporated into the Silviculture Survey Procedures Manual as an accepted alternative within South Area guidelines for the Williams Lake, Quesnel, and 100 Mile Timber Supply Areas. For the biogeoclimatic subzones/variants examined in this project, universal adjustments were made to the definition of a competitive broadleaf tree, and the term "conifer-brush ratio" was replaced with "brush-conifer ratio". Broadleaf trees can now be up to 125% taller than crop lodgepole pine (brush-conifer ratio of 1.25) and up to 150% taller than other acceptable conifer species (brush-conifer ratio of 1.5) before they have to be considered in free-growing surveys. The new brush-conifer ratios are used to define both countable broadleaves (i.e., those considered when assessing broadleaf density within free-growing plots) and broadleaf presence within a 1-m cylinder around crop conifers. The allowable number of occupied quadrants within the 1-m cylinder was also universally increased; whereas only one quadrant was previously allowed to be occupied, either one or two adjacent quadrants can now be occupied with countable broadleaf vegetation.

Assessment of a 14-year-old Mixed Western Redcedar:Red Alder Plantation in Southwestern British Columbia - EN121

During March of 2002, a replacement series research trial was established on Vancouver Island combining western red cedar with red alder. Mixing these tree species makes ecological sense since shade intolerant alder normally has rapid height growth whereas cedar is much slower growing and shade tolerant. Alder also fixes nitrogen and may improve the growth of species in mixture. These two species were planted in four mixtures or proportions at a total density of 1600 stems per hectare varying the proportions from 100:0, 75:25, 50:50 and 0:100 cedar:alder. After 14 years, a comparison of the various mixed stands indicated that the largest stand volume was found in the pure alder mixture. Also, the largest cedar stand volume was achieved with a pure cedar mixture however, relative yield analysis showed a significant cedar growth increase under the 50:50 mixture. This result is not considered conclusive given the early age of this trial. Continued assessment of this mixedwood study will increase our understanding of the stand dynamics of cedar:alder mixtures.

Influence of Red Alder Density on Growth of Douglas-fir and Western Redcedar – 20-year Results - EN122

Red alder (Alnus rubra [Bong.]) (hereafter referred to as alder) is the most common broadleaf tree species in the coastal Pacific Northwest, and occurs in pure stands and in mixed stands with coniferous species (Deal and Harrington 2006). Alder in conifer dominated stands can be beneficial because it improves soil nitrogen through fixation of atmospheric nitrogen, and it adds biodiversity. In young conifer stands, alder is considered a strong competitor due to its rapid juvenile growth, which can greatly reduce light availability and lead to competition for canopy growing space. In 1992, a long-term experimental project (EP 1121.01) was initiated to improve our understanding of both beneficial and competitive effects of alder in mixture with Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn.) (hereafter referred to as cedar). The objectives of this research are to (1) examine the effects of alder density on soil nitrogen and foliar nitrogen in Douglas-fir, (2) study the effects of alder density on total stand volume, (3) investigate the effects of alder density on conifer growth, and (4) provide an assessment of the effects of plot radius on the estimation of competition effects. Study results found significant variation in Douglas-fir and cedar response across sites. Soil mineralizable nitrogen was found to increase with increased alder density and, Douglas-fir stand volume was found to have benefited from 200 alder per hectare at age 15. For cedar 100 alder per hectare was found the most beneficial. This Extension Note provides a summary of recently published research (Fang 2018; Fang et al. 2019).

Evidence of Phosphorus Deficiencies and Mycorrhizal Adaptations in Coastal Temperate Rainforests of British Columbia: Implications for Stand Management - EN124

Historically, nitrogen (N) has been hailed as the primary or sole nutrient limiting growth in forest ecosystems, and management plans have generally focussed on retaining and supplementing supplies of N alone (Brockley 1996). However, in certain forest ecosystems, a second macronutrient, phosphorus (P), can also play a significant limiting role in primary productivity. In this Extension Note we provide evidence of pervasive P deficiencies across temperate rainforests along the west coast of Vancouver Island, and outline how this nutritional constraint may inform stand management plans.