to understand growth responses to competition control treatments

USING ECOPHYSIOLOGY RESEARCH

Bill Parker – Ontario Forest Research Institute

and

Doug Pitt – Canadian Forest Service

Key ecological features of white pine and white spruce regeneration

• Intermediate in shade tolerance, slow initial growth

• Favoured by sheltered, moderate microenvironment

• Maximum height growth at 50% sunlight

• Maximum diameter and volume at 100% sunlight

• Weevil and blister rust damage to open grown white

pine seedlings

• Susceptibility of white spruce to spring frost damage

Seedling microclimate Seedling physiology

• May – October

• Light (PFD), Ta, RH

• Soil moisture (SMC), Ts

• Periodic assessment

• Net photosynthesis (Pn), etc.

• Relative growth rates

White pine restoration and shelterwood sites (ON)

1. Treatments: none (C), herbaceous only (H), woody only (W), and both (B)

2. Microclimate – growing seasons 1- 4

3. Seedling physiology – growing seasons 2- 4

Soil moisture availability differs with treatment over time

Day of year

140 160 180 200 220 240 260 280

SMC

(%)

6

8

10

12

14

16

18

20

22

24

26

CHWB

Day of year

140 160 180 200 220 240 260 280

SMC

(%

)

6

8

10

12

14

16

18

20

22

24

26

May June July August September May June July August September

Growing season 1 Growing season 4

Restoration site

Light availability differs with treatment over time

Years of treatment

1 2 3 4

Lig

ht

(%)

0

20

40

60

80

100

CHWB

Restoration site

Maximumheight

Treatments affect photosynthesis through light and SMC

Light (PFD: umol m-2 s-1)

0 400 800 1200 1600 2000

Pn (u

mol

CO

2 m

-2 s

-1)

0

2

4

6

8

10

12

CHWB

SMC (%)

10 12 14 16 18

Pn (u

mol

CO

2 m

-2 s

-1)

0

2

4

6

8

10

12

r = 0.77, p < 0.0001 r = 0.50, p < 0.002

Restoration site

Light (%)

0 20 40 60 80 100

RVR

0

30

60

90

120

150

180

CHWB

Soil heat sum

1000 1050 1100 1150 1200 1250

RH

R

1

2

3

4

5

6Restoration site

r = 0.88, p < 0.001 r = 0.67, p < 0.002

Growth driven by treatment effects on light and soil warming

In shelterwoods, less treatment influence on soil moisture…

Day of year

120 140 160 180 200 220 240 260 280

SMC

(%)

6

8

10

12

14

16

18

20

22

24

26

Day of year

140 160 180 200 220 240 260 280

SMC

(%)

8

10

12

14

16

18

20

22

24

26

28

CHWB

May June July August September May June July August September

Growing season 1 Growing season 4

Shelterwood

…and light due to the dominant effect of overstory on microclimate / resources

Years of treatment

1 2 3 4

Lig

ht

(%)

0

20

40

60

80CHWB

ShelterwoodMaximumheight

Treatments affect photosynthesis through light and SMC

Light (PFD: umol m-2 s-1)

0 200 400 600 800

Pn (u

mol

CO

2 m

-2 s

-1)

1

2

3

4

5

6

7

8

CHWB

SMC (%)

10 12 14 16 18 20

Pn (u

mol

CO

2 m

-2 s

-1)

1

2

3

4

5

6

7

8r = 0.63, p < 0.001 r = 0.59, p < 0.001

Shelterwood

Light (%)

25 30 35 40 45 50

RHR

1

2

3

4

5

6

Light (%)

25 30 35 40 45 50

RVR

0

20

40

60

80

100

120

140

CHWB

Shelterwood

r = 0.91, p < 0.0001 r = 0.85, p < 0.001

Growth driven by treatment effects on light

Boreal mixedwood site (ON)

1. Treatments: none (C), herbaceous only (H), woody and herbaceous (B), radial woody only (RW), radial both (RB)

2. Microclimate – growing seasons 1- 4

3. Seedling physiology – growing seasons 3 - 4

Treatments have little effect on soil moisture availability

Day of year

140 160 180 200 220 240 260 280 300

SM

C (

%)

25

30

35

40

45

50

55

60

CHBRBRW

Growing season 4

May June July August September

Boreal mixedwood

Radial and broadcast woody control increase light levels

Year of treatment

1 2 3 4

Lig

ht

(%)

0

20

40

60

80

100

CHBRBRW

Maximumheight

Boreal mixedwood

Treatments have little effect on photosynthesis

Years of treatment

3 4

Pn

(u

mo

l C

O 2 m

-2 s

-1)

0

1

2

3

4

5

6

7C H B RB RW

A

B

ABABAB

NS

Boreal mixedwood

Light and humidity interact to regulate photosynthesis

Light (PFD: umol m-2 s-1)

0 500 1000 1500 2000

Pn (u

mol

CO

2 m

-2 s

-1)

0

2

4

6

8

10CHBRBRW

VPD (kPa)

0 1 2 3 4 5 6

Pn (u

mol

CO

2 m

-2 s

-1)

0

2

4

6

8

10Boreal mixedwood

r = -0.31, p < 0.00250% light

Leaf gas exchange of white spruce is sensitive to humidity

VPD (kPa)

0 1 2 3 4 5 6

Gw

v (

mm

ol H 2O

m-2

s-1

)

0

20

40

60

80

100

120

140

160

CHBRBRW

r = -0.54, p < 0.001

Boreal mixedwood

This response improves WUE in open environments

Light (PFD: umol m-2 s-1)

0 500 1000 1500 2000

WU

E (

um

ol C

O 2 m

ol H 2

O-1

)

0

10

20

30

40

50

60

70

80CHBRBRW

r = 0.40, p < 0.001

Boreal mixedwood

Do competition control treatments influence spring frost damage?

Damage is dependent on:

1. Minimum air temperature

2. Light levels after frost event

Lower temperature and higher light increase frost damage

Time

0 100 200 300 400 500 600 700

Ta (

oC)

-8

-6

-4

-2

0

2 C

H B RB RW

Time

900 1100 1300 1500 1700

Ligh

t (um

ol m

-2 s

-1)

0

400

800

1200

1600

2000June 6, 2007

Herbaceous layer presentWoody layer present

Boreal mixedwood

White pine in clearcuts:

• Competition for light and H2O

with herbaceous and woody

vegetation

White pine in shelterwoods:

• Competition for light is most

important

Boreal mixedwood:

• Sheltered environment assists

white spruce regeneration

Thanks to all for their support!!

Conclusions