Download Silvicultural Systems for Mixedwood Management

Silvicultural Systems
for Mixedwood
Management
Phil Comeau
Dept. of Renewable Resources
University of Alberta
Outline
 Ecology
 Aspen and spruce silvics
 Successional considerations (TIME)
 Spatial considerations
 Examples of silvicultural systems
 Clearcutting
 Advance regeneration or planting
 “Continuous cover”
 Shelterwood – uniform and group
 Retention
 Selection
Tolerance and Limiting
factors to regeneration and
growth of aspen
Aspen


Regeneration requirements






an intolerant species
Removal of apical dominance
Light, soil temperature, nutrients
Aspen basal area >5 m2/ha can inhibit
aspen regeneration; little aspen
regeneration observed when basal
area above 15 m2/ha in healthy
stands
Good aspen regeneration has been
reported in openings 40 m diameter in
30 m tall stands (Kabzems 2001).
Openings less than 0.5 tree height in
diameter may be a problem.
Poor aspen regeneration observed in
narrow strips through dense patches
of spruce
Growth

Rapid initial growth reaching near full
height by age 70.
Tolerance and Major Limiting
factors to regeneration and
growth of white spruce
White Spruce
 Intermediate shade tolerance
(survives fine in shade, but grows
“best” in nearly open conditions)
 Regeneration
 Seedbed (mineral soil, dw, or
humus)
 Seed supply (variable production
and heavy predation)
 Competition – shrubs, grass,
aspen, …
 Hare
 Chinook and frost injury

Growth
 Slower early growth than aspen,
catching up at age 60 or greater
Regenerating spruce in
the understory
2000 Growing Season Frost Events
25
Sum of Frost Events
 Reduced frost and
winter injury
 Reduced vigour of
Calamagrostis
canadensis
Deciduous-dominated
20
Conifer-dominated
15
10
5
0
0
50
75
Harvest Residual (%)
EMEND – Stewart et al.
100
Successional
Considerations
 In the absence of tending codominant mixtures of
spruce and aspen occur in a
mid-successional window
 Age 60-140+
 <60 – Aspen dominated
 >140 – increasing conifer
dominance or reversion to
“young” aspen
 Fire likely to be less common
as the major stand initiating
disturbance (replaced by
harvesting??)
Space
 Within mixedwood
stands – spatial
heterogeneity –
intimate and patchy
 Forest/Landscape –
desired forest
composition (Aspen,
mixed and conifer)
needs to be defined
and considered
Silvicultural Systems
 Clearcutting
 Avoidance/protection of
advance regeneration
 Shelterwood or “Retention”
system to reduce windthrow
of tall spruce
 Underplant to provide
advance regeneration
 Plant
 Tend (herbicide, brush, pct) –
to accelerate spruce growth,
alter composition, alter within
stand spatial patterns (Doug
Pitt)
Understory Protection
Harvest
(aka Natural Shelterwood;
commercial thin)
 Remove overstory aspen at
ages 60 to 80 while leaving
advance regeneration of white
spruce (commercial thinning)
MGM2005a simulation: Underplant at 40, harvest aspen at 60, clearcut at 120
300
Volume (m 3/ha)
250
200
150
100
Underplant stands at age 40 to provide
advance regeneration where desired
50
0
0
20
40
60
80
Age
Spruce
Aspen
100
120
Shelterwood Systems
 Planted spruce seedlings grow well under
shelterwoods with removal of 25% or more
of the basal area (e.g. Man and Lieffers
1999, EMEND (Stewart et al. unpubl)
 Uniform shelterwood can create a problem
for aspen regeneration if much canopy is
retained – but lead to Conifer or CD stands
 Group or strip shelterwoods
 openings wider than 50% of the tree height
can abundant aspen regeneration
 Studies so far indicate that spruce natural
regeneration is unreliable in Alberta
(Kabzems 2001)
Retention Systems
 Widely practiced
 Uniform and group
retention
 Biodiversity and
structural objectives
 15% of aspen volume left
to provide wind
protection (Understory
protection harvesting)
 Issues
 impacts on aspen and
spruce regeneration and
growth ?? (EMEND and
Adaptive Mixedwoods
studies)
Tending/Silviculture -- Age
shifts
 Establishment and tending practices will
change:
 stand composition at different stages
 rate at which component species reach
merchantable sizes or volumes
 rate of volume development of component
species
 age at which stands reach different “stages”
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.
For. Chron. 72: 286-292
Conclusions


Selection of an appropriate system – based on starting stand characteristics,
stand and forest level objectives
Need to keep TIME and SUCCESSION in mind
 Mixedwood stands are mid-successional (take time to develop and have a natural
tendancy to move on to spruce in time) (it may take 2 or 3 cyles of aspen regeneration
before spruce eventually dominates)
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Aspen regeneration requires reasonable size gaps or very open canopies
Sw natural regeneration unreliable - Requirements to achieve successful natural
Sw regeneration not well understood (C. canadensis likely one of the key
factors).
Can create a range of mixedwood compositions – in time and space – with some
planning – (expect some surprises!)
Range of options available
 Use of advance regeneration can save cost and accelerate development of spruce
component of the stand
 Clearcutting and group/strip shelterwood, and group/strip selection systems have
potential application
 Traditional shelterwood systems a problem economically (returning for small aspen volumes)
 Windthrow is an issue with any types of canopy retention,


risks are lower if retained trees are in groups
Harvest planning can help reduce windthrow problems
 Tending will cause age/time shifts in stand development