Can spacing overstory aspen improve growing conditions for underplanted white spruce

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Can spacing overstory aspen improve growing
conditions for underplanted white spruce?

• Phil Comeau, Cosmin Filipescu, Richard Kabzems
  and Craig DeLong

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Sierra Road experiment

• Randomized block design was used, with three
  separate blocks each containing sixteen 40 m by
  40 m plots.
• Established in the fall of 1991 in a 41 year-old
  aspen stand located 85 km east of Fort Nelson,
  B.C. (58o 45N, 121 o 37 W).
• At this site, a factorial experiment was
  established with the original intent of examining
  the effects of spacing and fertilization on aspen
  growth.

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• 4 levels of spacing 1) untreated (between 6000
  and 8000 stemsha-1) 2) 3000 stemsha-1 (1.83 m
  square spacing) 3) 2000 stemsha-1 (2.24 m
  square spacing) and 4) 1000 stemsha-1 (3.16 m
  square spacing).
• Spacing treatments were completed during fall of
  1991 using chainsaws, with slash left untreated
  on the ground.
• 4 levels of fertilization 1) untreated 2) 100
  kgha-1 of N applied as ammonium nitrate 3) 200
  kgha-1 of N applied as ammonium nitrate and, 4)
  a complete fertilizer mix comprising 200 kgha-1
  of N (ammonium nitrate) plus 100 kgha-1
  phosphorus, 100 kgha-1 potassium, 25 kgha-1
  magnesium, 50 kgha-1 sulphur, and 1.5 kgha-1
  boron.
• Fertilizer was applied in the selected plots by
  hand during June of 1994.
• White spruce (20 415B Styroblock) planted in
  early July 1996 at a density of 1300 stemsha-1
  (2.8 m square spacing).

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• Height, root collar diameter, and damage were
  measured in 1999 and 2002.
• Transmittance (difn) at 10 spruce, aspen leaf
  area index (LAI) and understory LAI were measured
  in 2002 using LAI-2000 plant canopy analyzers.
• These measurements were conducted for plots
  representing all four levels of thinning and for
  two levels of fertilization (1) unfertilized, and
  (4) the complete mix.

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• Hare damage was observed in 1999 and 2000, but
  was concentrated in one block.
• Damage averaged 55 in the unthinned x 100
  kgha-1 fertilization treatment in 2000.
• Very little hare damage was observed in
  unfertilized plots or in fertilized plots thinned
  to densities of 1000 or 2000 stems per hectare.
• Overall survival of tagged seedlings gt99 over 5
  years.

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Figure 1. Relationships between aspen basal area
and overstory leaf area index (LAI-o), understory
LAI (LAI-u), and light levels above the
understory (difn) at the Sierra Road site.
Lines shown are described by the equations
solid black line LAI-o0.661x ln(BA)-0.586
(n24 R20.734 RMSE0.181) solid green
LAI-u2.232-0.382xln(BA) (n17 R20.281
RMSE0.275) dashed blue line
difn0.904-0.169xln(BA) (n24 R20.811
RMSE0.037). (All equations are significant
(plt0.03).
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Conclusions

• Underplanted spruce did fine without thinning,
  even under stands with very high aspen basal area
  (up to 52 m2/ha).
• Thinning to 2000 sph resulted in small increases
  in diameter and height growth to age 5.
• Thinning to 2000 aspen/ha reduced basal area to
  33 m2/ha and thinning to 1000 aspen/ha reduced
  basal area to less than 20 m2/ha
• Results suggest that aspen basal area should be
  maintained above 20 m2/ha (to keep light levels
  below 40) to avoid stimulating growth of shrub
  and herb layers.
• Spruce might do better if planted immediately
  after thinning, or if thinning were done after
  spruce exceeded 1.5 m in height.

We gratefully acknowledge funding provided by the
B.C. Ministry of Forests and the B.C. Forest
Investment Initiative to support completion of
this work. This project was initiated by Dave
Coopersmith in 1991 with FRDA funding, other
funding for this project provided by Forest
Renewal British Columbia and the B.C. MOF.