Transcript Impacts of Climate Change on Western Forests

Impacts of Climate Change
on Western Forests
Dr. Mark Johnston
Saskatchewan Research Council and
Prairie Adaptation Research Collaborative
Projections (broad generalizations) for the future
climate of the Prairie Provinces
Temperature: increasing, greater in winter than summer,
greater at night than during day
Precipitation: great uncertainty, annually small increase
to significant decrease
Evaporation: increased
Soil moisture: decreased
Growing season: increased
Atmospheric CO2: increased
Extreme events: increased frequency and magnitude
Hydrology: increased variability, earlier peak flows
Major environmental drivers of
change in forests

Temperature


Moisture availability


Soil is key
Nutrient Availability


Both air and soil temperatures are important
Especially nitrogen
Atmospheric CO2 concentration

Interactions with other factors
Types of Impacts to Forests

Changes to productivity (growth rates)

Changes to disturbance regimes

Forest fires, insect pests

Changes in species composition

Shifts in forest boundaries
35
250 mm
Montreal Lake, SK
Wet soils
200 mm
30
Medium soils
Biomass Index
25
150 mm
100 mm
20
15
10
50 mm
Dry soils
 Dry soils – productivity declines in the future
 Medium soils – productivity increases, then declines
5
 Wet soils – productivity increases in the future
Note: Analysis assumes soils fully recharged following snowmelt
0
61-90
2020
2050
Scenario
2080
Source: Johnston 2001
Soil warming impacts

Warming will release additional
nutrients, especially nitrogen

N is generally limiting in boreal forests
so should increase growth

But dependant on water availability
Increased CO2

Often assumed to increase growth

But increases constrained by N availability,
water availability

Effect offset by other pollutants, e.g. ozone

Studies have shown transient response – may
not be long-lasting
30-50% increase in fire
season severity under
2 X CO2
(Flannigan et al. 2001)
Insects

Drought increases vulnerability to insect
feeding – higher carbohydrate levels in foliage

Jack pine budworm increases under drought
conditions

Forest tent caterpillar associated with drought in
forest fringe area

Forest fragmentation shown to increase FTC
populations
Species composition

Changes in environment often lead to new
species

But constrained by need to migrate – seed
dispersal

Land use activities (roads, agriculture,
urbanization) may prevent migration

Rate of climate change greater than species
ability to move
Future climate?
(Hogg and Hurdle 1995)