Proposal for a aspen and white spruce mixedwood management silvicultural study
(Second draft for reviewing)
TITLE:
Planting white spruce under aspen stands and cluster planting
-new approaches for managing spruce and aspen mixedwood
stands
PROJECT LEADER:
Jian Wang
Red Rock Research Station
Ministry of Forests
AGENCY CONTACT:
Dennis B. Sabourin
Silent Running Forestry Consultants Ltd. Chetwynd
Richard Kabzems, Prince George Region, Ministry of
Forests
Daniel Lousier, UNBC
PRINCIPAL CLIENTS:
Canfor, Chetwynd Division
LOCATION:
Rice Property, Dawson Creek Forest District
RATIONALE AND LITERATURE REVIEW:
Canfor-Chetwynd operation has purchased the Rice Property with an area of about 6,000
ha. Within the area there are several types of aspen stands: young (about 20 years) and
old (about 80-100 years) pure aspen stands. There is some ingress of white spruce in the
old aspen stands. Some portions of the land were used as agriculture practices in the past.
Canfor’s main management objective is to regenerate the land to conifer (mainly white
spruce) forest. Two important considerations influence achievement of this objective.
Young aspen stands (age class 2) are of limited extent relative to older age classes within
the Dawson Creek District. Secondly it is difficult to regenerate white spruce on
clearcuts because of vegetation competition (mainly blue-joint grass). In order to
accommodate higher level plans (TSA and LRMP) and achieve the most efficient spruce
regeneration, we propose this silviculture study funded by FRBC through Canfor to
explore a new way of managing aspen-white spruce mixedwood forests in the BWBS
zone. We propose to plant white spruce under aspen overstory to create an aspen and
spruce mixedwood stand. This relatively extensive, low impact strategy will be
compared to more intensive management approaches such as mechanical site preparation
and herbicide methods as well as using sheep to control vegetation.
Regeneration conditions for spruce can be improved by manipulating the forest canopy
and ground surface. In boreal mixedwood forests, mechanical site preparation treatments
such as trenching, blading, ploughing, mixing or mounding, are commonly used to reduce
competition, raise soil temperature and perhaps stimulate mineralization of nutrients
(Lieffers and Beck 1994.). There have been several attempts to apply shelterwood
systems and mechanical site preparation to regenerate white spruce in boreal mixedwood
sites (Youngblood and Zasada 1991). The sheltwood cuts, however, relied on natural
regeneration and lacked thorough investigations of the environmental conditions. It is
not clear from these trials how residual density of aspen in combination with site
preparation affects the regeneration conditions and establishment of white spruce.
Lieffers and Stadt (1994) report that height growth of white spruce seedlings growing
under an aspen dominated canopy at 40% full sunlight was approximately equal to that of
seedlings growing in full sunlight. However, they also indicate that total growth is best at
full sunlight. They suggest that using a shelterwood system which permits 30 to 40% of
full sunlight to penetrate the aspen canopy may provide favourable conditions for the
establishment and growth of white spruce while avoiding rapid increases in the cover of
understory vegetation that can occur following complete removal of the aspen canopy. In
12 year old aspen stands, light levels exceeding 40% of full sunlight are encountered at
aspen densities below 10000 stems ha-1 (Iron Creek). In 30 and 40 year old stands (both
spaced and unspaced), light levels exceeding 40% are encountered at densities below
3000 aspen/ha. However, it is important to note that these densities will have resulted
from self-thinning of stands which initially established at much higher densities. If an
aspen stand were maintained at 3000 or fewer stems per hectare from age 5, it is likely
that individual trees would be substantially larger than those encountered in natural
stands, and that light levels associated with these densities would be lower.
Grass cover will increase from dense to less dense aspen stands. The dominant perennial
grass in this area is blue-joint grass (Calamagrostis canadensis (Michx.) Beauv.), a
rhizomatous grass that can severely impact reforestation success (Eis 1981, Lieffers et al.
1993). Soil temperatures may also be lower in areas with heavy covers of blue-joint
grass (Hogg and Lieffers 1991), limiting the potential for regeneration and growth of
spruce.
One negative effect of vegetation control seems to be an increased probability of damage
from frost. Sutton (1984) and LePage and Coates (1994) found that frost damage
increased in areas where vegetation control was effective. In a study conducted near
Fairbanks, Alaska, Cole et al. 1999 found greater susceptibility to early winter frost
damage on plots with the greatest vegetation control. When considering a weed control
application, it is important to consider the degree to which frost damage might occur on
the site. At some point damage to seedlings from frost may outweigh any gain through
vegetation control.
Man and Lieffers (1997) observed a significant decrease of net photosynthesis in white
spruce seedlings planted on open sites compared to seedlings under canopy during frost
periods in spring and fall. Seedlings under shelterwood canopies showed early bud
break, reduced terminal bud and seedling mortality, increased capacity for
photosynthesis, and improved growth. All of these suggest that the shelterwood system
can be used as an alternative to improve the extreme conditions created by clearcutting
and promote white spruce regeneration.
The short-term and long-term effects of different densities of aspen on the development
of mixed species stands is a fundamental information need which has dramatic
implications for management of boreal forests. Aspen and white spruce in a mixture may
avoid competition through differential shade tolerance, physical separation of canopies,
phenological differences, successional separation, and differences in soil resource
utilisation. Aspen may also be able to positively affect the growth of white spruce by
improving litter decomposition and nutrient cycling rates, controlling grass and shrub
competition, ameliorating environmental extremes (Man and Lieffers 1999b). These
positive relationships likely make mixed-species stands more productive than pure stands
of the same species (Man and Lieffers 1999a).
Although there are some aspen and white spruce mixture studies such as planting white
spruce under aspen canopy Delong (1997) and thinning young aspen stands and plant
white spruce (Coopersmith and Hall 1999) in BC, additional empirical trials are needed
to quantify spruce and aspen growth at aspen densities between 400 and 2000 stems ha-1
well spaced.
This study would build on the initial underplanting studies of DeLong (1997) and
mixedwood studies described by Coopersmith and Hall (1999). In particular, it would
quantify the light environments and spruce growth at aspen densities between 400 and
2,000 stems/ha, which have not been addressed by existing studies. Information is still
needed to make informed decisions regarding appropriate amounts of aspen and white
spruce that should be maintained at various stages of stand development in order to
achieve different management objectives.
OBJECTIVES:
(1) To establish white spruce regeneration under an aspen overstory.
(2) To determine the relative efficacy of several mechanical and chemical site
preparation methods for establishing spruce under aspen stands.
(3) To determine the impacts of aspen densities on survival rate and growth
performance of under-planted spruce.
(4) To determine the impacts of aspen densities on herbaceous and shrub
communities, and on aspen suckering success.
(5) To determine the optimum aspen densities required to maximise underplanted
spruce survival rate and growth and yield.
(6) To select a suitable site preparation method for under-planting spruce in old
(mature) aspen stands
7) To compare several operational vegetation control methods in white spruce
plantations
8) To analyze the cost-benefits of various site preparation techniques on seedling
survival and growth rates.
PROPOSED APPROACH:
1. For the young aspen stands
For the young aspen stands, because of high density of aspen there is not enough light in
the understory for white spruce seedlings to grow. We are planning to manipulate aspen
density through thinning in order to increase the understory light level. Thinning the 20year-old aspen stand will reduce overstory density and site preparation will reduce the
vegetation cover on forest floor, both of which can result in an increase of light received
on the ground surface and raise soil temperature. However, we have to be careful about
the mechanical site preparation because it may stimulate the ingress of grass like bluejoint grass. The following aspen densities: (1) 0 aspen (clearcut) just use what Canfor has
already planted or are going to plant this coming summer, (2) 600 stems ha-1 aspen, (3)
1200 stem ha-1, (4) 2500 stems ha-1, (5) 5000 stems ha-1 and (6) a unthinned aspen stand
(density should be higher than 5000 stems ha-1) will be created through thinning. White
spruce seedlings will be planted (2500 seedlings ha-1) in all the treatments. In the high
aspen density treatments (5000 stems ha-1 and unthinned) there may be not enough room
for a small excavator to do the mechanical site preparation. In that case we can just raw
plant these two treatments. The data will be analysed separately to compare spruce
growth and survival under different aspen densities when they are raw planted.
The split-plot design will be used for this trial. The treatment plots will be 8080 m with
a 4040 m permanent measuring plot in the centre leaving a 20m wide buffer zone
around the measurement plot. The plot will be divided into 2 subplots for the site
preparation treatments: raw planting and mechanical mounding. All the treatments will
be replicated three times. A total of 18 plots will be established and 11.52 ha of land base
needed.
2. For the old aspen stands
Based on our field observations, understory light level may be adequate for spruce
seedlings to grow under old (80-100 years) aspen canopy. However this remains to be
decided after we have a field trip. Therefore in the old aspen stands we will plant spruce
seedlings (2500 seedlings ha-1) under aspen overstory with different site preparation
methods; raw plant, chemical site preparation, and mechanical site preparation. As in the
young aspen stands, treatment plots will be 8080 m with a 4040 m permanent
measuring plot in the centre leaving a 20m wide buffer zone around the measurement
plot. The plots will be divided into two subplots to apply different site preparation
methods: (1) raw planting and mechanical site preparation. The treatment will be
replicated three times. Area of about 6 ha land base needed for this treatment.
In both young and old aspen stands white spruce will be planted to a density of 2500
seedlings ha-1. All seedlings will be measured for initial height and root collar diameter
immediately after planting. At the end of each growing season, survival rate, total height
and root collar diameter will be measured. Any damage or animal browsing will be
recorded.
3. Cluster planting (As Richard suggested, I added this part but it is very primitive.)
Cluster planting or strip treatments provide a potentially useful option for managing
mixtures of white spruce and aspen where white spruce is a minor stand component
(<50% Sw volume at rotation age). Short-term benefits of cluster planting include
reduced planting and vegetation management costs, increased survival and faster greenup. Long-term benefits include increased biodiversity of juvenile and mature stands,
aesthetically varied landscapes, and increased harvest yields. Cluster planting should be
considered under old aspen stands because there may be some gaps larger enough to plant
a cluster of 10 white spruce seedlings with a inter-tree distance of 1.0m. Cluster planting
arrangements will be designed to produce 15%, 30%, and 45% spruce volumes at
rotation. Three hectares of each cluster planting will be established. In total 9 ha of
cluster planting will be established. Only one cluster planting (30%) will be monitored
as part of the research study design. The other two cluster planting designs will be less
intensively monitored, but analyzed and described for extension and demonstration
purposes.
4. Measurement of seedling environments
Photosynthetically active radiation (PAR) will be measured above selected seedlings
between 10:00 and 14:00 solar time in the middle of growing season with a ceptometer
AccuPAR (We have the equipment).
Daily mean, maximum and minimum air temperature at 0.5 m above the forest floor and
15 cm in the soil will be measured. All the temperature sensors will be suspended in the
centre of a horizontal white PVC pipe to shield them from direct radiation. Sensors will
be connected to a data logger (CR21, Campbell Scientific Inc. We have extra dataloggers
and no need to purchase).
5. Economic analysis of site preparation (I do not have more expertise in this
respect)
This will be done as a directed study by a senior university student (may be not suitable
for a graduate student) to collect local information from several site preparation studies in
northern B.C., and identifying limiting factors (e.g. excess soil moisture) plant
community (herbaceous vs. shrub, vs. hardwood trees), growth responses of white spruce
seedlings after 10 or more years.
6. Vegetation management (I think we may proposing too much)
The study on vegetation management will be conducted on clearcut sites in which Canfor
has already planted white spruce using sheep grazing along, herbicide and manual
vegetation control. The herbicide treatment will be monitored within the research study
comparing underplanting and cluster planting. A replicated but less intensive monitoring
design will be used for the sheep grazing and manual vegetation control treatments. This
will provide quantitative comparisons between vegetation management treatments.
END PRODUCTS

Demonstration area for the promotion of the concepts and practices of mixedwood
management in the BWBS zone.

The establishment can be used as a long-term growth and yield monitoring
installation for mixedwood stands.

A better understanding of stand level dynamics of aspen and spruce mixedwood
forests.

A better understanding of the effects of pre-commercial thinning of young aspen
stands.

Demonstration of operational methods of aspen stand density manipulation.
PROPOSED TECHNOLOGY TRANSFER:




Contribution to ‘free-growing’ guidelines
Contribution to mixedwood stocking standard guidelines
Field trips
Professional reports and possibly scientific publications
DURATION: 3 years (2000- 2003)
APPROXIMATE BUDGET
Graduate student stipends
Technical assistance
Travel, accommodations
Consumable materials and supplies
$20,000
$20,000
$5,000
$5,000
Total for 2000/01
$50,000
The same total for 2001/02 and 2002/03 years
The operational costs such as site preparation, thinning, seedlings and planting etc. will
be paid through Canfor’s operational budgets.
Approximate budget for the operational costs: (Dennis, please add more details here)
Thinning (14 ha) young aspen stand
$14,000
Mechanical site preparation (7 ha)
$3,500
Planting (14 ha)
$7,000
Total
$24,000
REFERENCES
Coopersmith, D. and Hall E. 1999. Experimental Project 1077- the Siphon Creek
mixedwood trial: The use of a simple height-diameter ratio to predict the growth success
of planted white spruce seedlings beneath aspen canopies. Research Note #PG17, Prince
George Forest Region, BC.
DeLong, C., R.M. Annas, and A.C. Stewart. 1991. Boreal White and Black Spruce
Zone. IN: D. Meidinger and J. Pojar, Eds. Ecosystems of British Columbia. Special
Report Series, No. 6. B.C. Ministry of Forests, Victoria.
DeLong, C. 1997. Operational considerations for underplanting hardwood stands with
white spruce. Research Note #PG11. Prince George Forest Region, BC.
Eis, S. 1981. Effect of vegetative competition on regeneration of white spruce. Can. J.
For. Res. 11:1-8.
Hogg, E.H., and Lieffers, V. J. 1991. The impact of Calamagrostis canadensis on soil
thermal regimes after logging in northern Alberta. Can. J. For. Res. 21:387-394.
LePage, P. Coates, K. D. 1994. Growth of planted lodgepole pine and hybrid spruce
following chemical and manual vegetation control on a frost prone site. Can J. For. Res.
24:208-216.
Lieffers, V. J., MacDonald, S. E., and Hogg, E. H. 1993. Ecology of and control
strategies for Calamagrostis canadensis in boreal forest sites. Can. J. For. Res. 23:20702077.
Lieffers, V.J. and K.J. Stadt. 1994. Growth of understory Picea glauca, Calamagrostis
canadensis, and Epilobium angustifolium in relation to overstory light transmission. Can.
J. For. Res. 24: 1193-1198.
Lieffers, V.J., R.B. Macmillan, D. MacPherson, , K. Branter and J.D. Stewart. 1996.
Semi-natural and intensive silvicultural systems for the boreal mixedwood forest.
Forestry Chronicle 72: 286-292
Man R and Liffers, V. J. 1999a. Are mixtures of aspen and white spruce more productive
than single species stands? Forestry Chronicle 75:505-513.
Man R and Liffers, V. J. 1999b. Effects of shelterwood and site preparation on
microclimate and establishment of white spruce seedlings in a boreal mixedwood forest.
Forestry Chronicle 75:837-844.
Man R and Liffers, V. J. 1997. Seasonal photosynthetic responses to light and
temperature on white spruce (Picea glauca) seedlings planted under an aspen (Populus
tremuloides) canopy and in the open. Tree Physiol. 17:437-444.
Sutton, R. F. 1984. Plantation establishment in the boreal forest: glyphosate, hexazinone,
and mannual weed control. For. Chron. 60:283-287.