Climate-induced Shifts in Fire Frequency, and Resulting Effects on Stand Composition

Carissa D. BrownNorthern Biogeography Lab

Department of Geography, Memorial University

Black spruce (Picea mariana)

Fire drives secondary succession and species distribution in boreal forests

Fire drives secondary succession and species distribution in boreal forests

Short window of opportunity

Temperature trends (1960-2009)

Burrows et al. 2011 Science; Chapin et al. 2005 Science

Climate-fire regimes

Flannigan et al. 2005

Ratio of 3xCO2 / 1xCO2 area burned:

Climate-fire-succession

Balshi et al. 2009

Kasischke and Turetsky 2006

Fire drives secondary succession and species distribution in boreal forests

What happens if fire regimes change?

How will changes in fire-climate interactions effect black spruce

distribution?

1990

1991

1990

1991

2005

mature forest

long-interval

fire

short-interval

fire

mature forest

long-interval fire

short-interval fire

mature forest long-interval burn short-interval burn

Post-fire colonisation: is seed available?

Seed availability

mature forest

LI SI

short interval

Num

ber o

f via

ble

seed

s/m

2 /ye

ar

0

2

4

6

8

Brown and Johnstone, 2012, For. Ecol. Man.

long interval

Fire history

Will seed germinate and survive?

Nu

mb

er

of e

me

rge

d s

eed

ling

s

Fire historyBrown and Johnstone, 2012, For. Ecol. Man.

Black spruce emergence

fire

return

interval

seed

availability

establishmentgrowth

and

survival

long

short

seed

Closely timed fires short-circuit regeneration cycles

A failure in two parts

1. Lack of seed2. Unsuitable substrate

A failure in two parts

Long-term disruption

Indirect climate effects caused by a change to the disturbance regime may

initiate vegetation shifts of a larger magnitude or opposite direction than

would happen due to climate alone

mammal

Carbon storage

wood

organic horizon

1990/91

2005

mature forest long-interval burn short-interval burn

Fire history

How will shifting fire regimes influence tree distributions in the

boreal forest?

If serotiny loses its advantage (ecosystems become less resilient), what will succeed?

The prediction

Regions that have experienced a novel disturbance regime will become more suitable

for alternative tree species dominance

Dalton Complex, Alaska Boundary Fire, Alaska

Taylor Complex, AlaskaEagle Plains, Yukon

Black spruce ecosystems

Future scenarios for successional shifts

black spruce self-replacement

historic regime

severityfrequency

BS seed

severityfrequency

BS seedmoisture

In the absence of seed limitation

Current distributions

Black spruce

Current distributions

Black spruce

White spruce

Current distributions

Black spruce

White spruce

Paper birch

50 km

Black spruce

White spruce

Paper birch

Shifting regimes in Labrador

…and many, many field assistants, labmates, and colleagues.

ACKNOWLEDGEMENTS

Dr. Jill Johnstone, University of Saskatchewan

0 50 100 150 200 250

0

1

2

3

4

5

Mean stand age

See

dlin

g de

nsity

. m2

Stand recovery to 4000 trees/ha

Viglas, Brown, et al. in review, Can. J. Forest Research

High severity fire (good post-fire seedbed)

Low severity fire (poor post-fire seedbed)

Thresholds for stand recovery

Range of seed requirements

Threshold for recovery: 50 – 150 years

Patterns between species: AlaskaN

umbe

r of

seed

lings

Soil moisture (%)

Black spruce Alaskan birch

Species-specific optimal seed bed conditions