S u z a n n e B r a i sP a s c a l D r o u i n

U Q AT

This work was supported by Natural Sciences and Engineering Research Council of Canada and Fonds québécois de recherche sur la nature et les technologies

• Leaching of nutrients or soluble components (Spears et al.

2003);

• Production of weathering agents such as oxalic acids by wood decomposing fungi (Fransonn et al. 2004);

• Active transfer of nutrients from mycelium (Frey et al. 2003,

Wells et Boddy 2002);

• Modifications of soil physical environment (Spears et al.

2003);

• Interactions between organic substrates, microbial decomposers and detritivores (Busse 1994, Moore et al. 2004).

First mentioned by McKee & Stone (1966);

Comparisons between alignic and lignic forest floor (Kayahara et al. 1996);

Rate of incorporation in forest floor (Harvey et al. 1981);

Site of nitrogen fixation (Larsen et al. 1982, Jurgensen et al. 1992);

Up to 92 % of total CWD in jack pine stands (Brais et al.2005);

Large carbon pool in black spruce stands (Manies et al. 2005;

Hagemann et al. 2010);

Brais et al. 2006

0,000,100,200,300,400,500,60

0 10 20 30 40 50 60 70 80

Woo

d de

nsit

y(g

cm

-3)

Time

k = 0.060 year-1; t0.50 = 12 years; t0.95 = 50 years

0,000,100,200,300,400,500,60

0 10 20 30 40 50 60 70 80Woo

d de

nsit

y (g

cm

-3)

Time

k = 0.020 year-1 ; t0.50 = 35 years ; t0.95 = 150 years

Trembling aspenPopulus tremuloides

Jack pinePinus banksiana

Hypotheses

Dead wood lying on or buried within the forest floor contributes to the biochemical and structural heterogeneity of the forest floor and mineral soil. The nature and magnitude of this contribution is linked to tree species and wood decay stage.

We also expected deadwood to represent a larger proportion of organic nutrient pools under jack pine than under aspen.

Objective

Compare lignic and alignic forest floor characteristics and functions with that of logs for two species of contrasting organic matter quality.

• Continental climate• Mean annual temperature : 

1.2°C• Precipitation :  918 mm,  50% 

between May and September

• Post-fire 85-year old aspen –jack pine forest

• Fresh clayey soils• Forest floor : Mor (8 cm)

1

9

11

05

101520253035

aspe

n

pine

aspe

n

pine

aspe

n

pine

sector 1 sector 9 sector 11

Basa

l are

a (m

2ha

-1)

aspen pine other snags100 m

Tree, snag, log, forest floor (lignic + alignic) inventories and sampling

Published equations for tree and snag biomass and concentrations

Nutrient availability in mineral soil under logs and forest floor using Plant Root Simulators (Western Ag Innovations inc. Saskatoon, Canada)

Effects of tree cover (aspen vs pine) on stand characteristics: Mixed linear model with sampling plots (n = 2 or 3) nested within

sectors (n = 3). Compound symmetry accounts for correlations between nested observations.

Type 1 test of hypothesis

Effects of species and OM origin (alignic FF, lignitic FF, fresh and decomposed logs) on OM and soil properties: Mixed linear models with origin (n = 2 or 4) nested within sampling

plot (n = 2 or 3) nested within sectors (n = 3). Interaction between tree cover and origin .

0

10000

20000

30000

40000

50000

60000

fresh logs decomposedlogs

lignic forestfloor

alignic forestfloor

Aspen Pine

Aspen deadwood = 15 % aboveground C; Jack pine deadwood = 27 % aboveground C

Pr > F = 0.013

• Species effect (Pr>F <0.012)

• Logs vs FF (Pr>F <0.001)

• ff_alignic vs ff_lignic (Pr>F <0.001).

• Some effects more pronounced for aspen (N, Ca)

0

5000

10000

15000

20000N

0

4000

8000

12000

16000Ca

0

1000

2000

3000

logs

fres

h

logs

dec

ligni

c ff

alig

nic

ff

logs

fres

h

logs

dec

ligni

c ff

alig

nic

ff

Aspen Pine

K

Aspen Pine SE Pr > F

C 15.4 27.3 4.1 0.102

N 8.9 17 4.8 0.157

P 7.5 16.5 5 0.214

K 8.3 14.2 2.5 0.140

Ca 10.8 17 4.3 0.289

Mg 10.2 17 3.9 0.228

0

2

4

6

lignic ff alignic ff lignic ff alignic ff

Aspen Pine

Acidity exc.

0

1

2

3

4K exc.

0

20

40

60

lignic ff alignic ff lignic ff alignic ff

Aspen Pine

Ca exc.

0

20

40

60

80CEC

Highest concentration of N03 found under ff_alignicHighest concentration of Ca under decomposed logsHighest concentration of K under fresh logsSpecies effect for Ca onlyNo interaction between cover and necromass origin

0

100

200

300

400NO3

0

500

1000

1500

2000

2500Ca

0

50

100

150

logs

fres

h

logs

dec

ligni

c ff

alig

nic

ff

logs

fres

h

logs

dec

ligni

c ff

alig

nic

ff

Aspen Pine

K

Discussion

CWD including lignic forest floor constitutes a major pool of organic C but a lesser pool of nutrient in natural stands;

Well decomposed deadwood is more persistent and abundant under jack pine than under aspen cover;

Lignic forest floor is distinct from alignic and well decomposed logs. In jack pine stands, alignic forest floor is a source of acidity influencing numerous soil processes;

Discussion

Lower nitrogen availability under CWD than under alignicforest floor is consistent with other studies and might result from greater N being transferred from the mineral soil to the forest floor;

Nutrient fluxes from necromass to mineral soil are not related to pool size or concentration. Active and selective processes operate at small scales and increase the complexity of the root environment;

Nature or rates of processes controlling nutrient release differ among nutrients.

Conclusion

Much has been written about the effects of fine litter on soil, decomposed wood may be responsible for some of these effects;

Measuring and comparing nutrient pools do not tell the whole story. Timing, localisation and mechanisms of nutrient release from decomposing wood need to be better understood;

Deadwood, including buried wood, contributes to the structural and functional complexity of the forest floor.

Many thanks to Mario Major, Émilie Robert and Jeanne Therrien.