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The Dynamics of In-Stream Large Woody Debris

Mohammad Bataineh, Lori Daniels, Trevor Jones, Sonya Powell, Evan Henderson, and Dave Andison


Research Goals I) Understand LWD dynamics II) Links between riparian forests and LWD

Questions 1) Time since death of LWD ? 2) Rates of decay? 3) Processes determining recruitment ?


- small,

headwater streams

- width <3.5m, no transport - mature riparian forests - 5 pine-dominated sites - 5 spruce-dominated sites

Photo: Sonya Powell


LWD Time Since Death: • 2 to 143 years (n = 186 logs) • pine ≤ 86 years (n = 113) • spruce ≤ 143 years (n = 73)


Time since death (years)

80

P<0.001 c

60

c

40 20

b a

0 I

II

III

IV

Decay class

DC I - 1997

DC II - 1968

DC III - 1951

DC IV - 1943


Time since death (years)

80 c

60

P<0.001 c

b 40

a

20 0 Bridge

Partial

Loose

Buried

bridge Position class

bridge

partial bridge

buried


Time since death (years)

80

P<0.001 c

60 40 20

c

c

P<0.001 c

b a

b a

0 I

II

III

IV

Bridge

Partial

Loose

Buried

bridge Decay class

Position class

Young LWD

Old LWD

bridge decay I & II perpendicular

loose & buried decay III & IV angled & parallel


Mean frequency (per 50 m reach)

10

8

30 years Decay class I Decay class II Decay class III Decay class IV

P<0.001

6

4

2

0 BR

PB

L

Position class

B


10

1.0

5

0.5

0

0.0

Upper limit of age class (year) Black spruce White spruce Sit Y of death Sit 7 LWD7 Year

index

1.5

Tree-ring

15

2000

2.0

1975

20

1950

0.0

1925

0

1900

0.5

1875

5

1850

1.0

1825

10

1800

1.5

1775

15

1750

2.0

1725

Frequency of trees (n)

20

White & Black Spruce uneven-aged, variable rates of initial growth, tree death relatively continuous in 20th C


30

3

20

2

10

1

0

0

40

4

50 years

0

0

Upper limit of age class (year) Lodgepole pine White spruce LWD year of death

2000

1 1975

10 1950

2

1925

20

1900

3

1875

30

index

4

40 years

Tree-ring

40

1850

Frequency of trees (n)

Lodgepole Pine post-fire, even-aged, fast initial growth, tree deaths after crown closure, no LWD predated the fire

What happens during the first 50 years after fire?


2001 Dogrib Fire - 5 headwater streams - white-spruce dominated - not salvaged - regenerating to pine


Frequency distribution of LWD Mature spruce LWD vs Pre-fire spruce LWD

Similar frequency distributions


Frequency distribution of LWD Mature LWD vs Pre-fire LWD + Post-fire recruits

Large pulse in recruitment following fire


Proportion of LWD

Proportion of LWD

LWD Depletion Rates: Mature spruce LWD vs Pre-fire spruce LWD


Proportion of LWD

Proportion of LWD

LWD Depletion Rates: Mature spruce LWD vs Pre-fire LWD

If no additional LWD input: 50% reduction of LWD in 50 years

50% reduction of LWD in 39 years


Proportion of LWD

Proportion of LWD

LWD Depletion Rates: Mature spruce LWD vs Pre-fire LWD

If no additional LWD input: 80% reduction of LWD in 83 years

80% reduction of LWD in 79 years


Future LWD Dynamics • Mature forests have ~continual long term supply of LWD due to stand dynamics • Burned forests have pulse of LWD from fire – Size of and duration of pulse? – Lag before LWD affects stream function? – Lag before new forest contributes new LWD?


Snag fall rates?

5 years post fire


Lag between fall and function?

5 years post fire


Time since death (years)

80

P<0.001 c

60 40 20

c

c

P<0.001 c

b a

b a

0 I

II

III

IV

Bridge

Partial

Loose

Buried

bridge Decay class

Young LWD nominal function

30 years

Position class

LWD increasing function

Old LWD multifunctional


How long before new forest will contribute new LWD?


20

2

10

1

0

0 4

50 years

0

0

Upper limit of age class (year) Lodgepole pine White spruce LWD year of death

2000

1 1975

10 1950

2

1925

20

1900

3

1875

30

index

3

Tree-ring

30

40

Lodgepole Pine

4

40 years

1850

Frequency of trees (n)

40

post-fire, even-aged, fast initial growth, tree deaths after crown closure


Implications of the Dogrib Study • 70-80-yr lag: fire to new functional LWD • snags surrounding headwater streams provide a source for LWD recruitment • retain post-fire buffer zones of snags especially in riparian forests that – are susceptible to seasonal floods and erosion – provide habitat for threatened, rare or endangered species


Chronosequence Study • Comparison of LWD in riparian forests of different ages and composition – ~50 year-old pine (n = 4) – ~50 year-old mixed species (n = 3) – ~100 year-old pine (n = 3) – >150 year-old spruce (n = 3)


3000

2000

1500

1000

500 45.00

0

Old Spruce

Alnus

Old Pine

Abies

Young Pine

Pinus

Picea

Young Mixed

40.00

Populus

35.00

Basal area (m2 ha-1 )

Density (trees ha-1 )

2500

30.00 25.00 20.00 15.00 10.00 5.00 0.00

Old Spruce

Alnus

Old Pine

Abies

Pinus

Young Pine

Picea

Young Mixed

Populus


Chronosequence Study â&#x20AC;˘ LWD time since death and depletion rates â&#x20AC;˘ Does LWD in young forests decay at the same rate as LWD in mature forest?


Conclusions • LWD persists decades to centuries • LWD position relates to decay and determines in-stream function with time • LWD recruitment depends on disturbance and stand dynamics • Changes to LWD abundance have long-term implications for stream function


Acknowledgements: Research Partners and Funding Agencies:

Research Assistants: K. Terry, K. Werner, J. Trau, S. Wilson, C. Bambrick, L. Parsons, B. Sawiz, V. Yan, J. Smith, O. Freeman, E. Henderson, A. Nicoll, N. Barrett, S. desRoches, R. Chavardes, and J. Amerongen-Maddison



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