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 CO 2 : increased Extreme events: increased frequency and magnitude Hydrology: increased variability, earlier peak flows

Major environmental drivers of change in forests  Temperature Both air and soil temperatures are important  Moisture availability Soil is key  Nutrient Availability Especially nitrogen  Atmospheric CO 2 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

Dry soils – productivity declines in the future Medium soils – productivity increases, then declines Wet soils – productivity increases in the future Note: Analysis assumes soils fully recharged following snowmelt Dry soils Medium soils Wet soils 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 CO 2  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)