A broad-scale and high resolution spatial simulation of forest composition and biomass changes under climate change: Northern Wisconsin and Upper Michigan

Background/Question/Methods

Forests in the northern Great Lakes region have been experiencing the effects of a warming climate and will be further affected by the continuous warming (and likely wetter) climate. The collective effects of changing climate are complex due to strong interactions with forest growth and succession, increasing timber harvesting, and frequent natural disturbance. We present the first regional, spatial simulations of the Northern Lake States forests incorporating high resolution (250 m) spatial dynamics. We conducted simulations with LANDIS-II under two General Circulation Models for climate change (PCM, GFDL) and two different carbon emission scenarios (B1, A1fi), incorporating wind disturbance, forest management, and mitigation alternatives to evaluate those complex interactions on forest composition and biomass over the next 150 years. Our study area includes northern Wisconsin and western portion of Upper Peninsula of Michigan, an area of 8.2 million ha including the Chequamegon-Nicolet and Ottawa National Forests and other diverse ownership. We considered the influences of different management due to land ownership (national, state and county forests, private corporate and private industrial forests) on rates of timber harvesting. Downscaled climate data were used to reflect sub-regional spatial variations of changing climate. We included wind disturbance within the simulations. 

Results/Conclusions

Our general results suggest that five northern tree species (Abies balsamea, Betula papyrifera, Picea glauca, Pinus banksiana, P. resinosa) decrease their biomass over time, with strong interaction among diverse ecoregions and climate changes. Acer saccharum will continue to increase its abundance. A broad re-invasion of previously available habitat for Tsuga canadensis, is possible under climate change scenarios. Regionally, we found a net positive change trend in aboveground live biomass in comparison to the current biomass throughout simulation scenarios of B1 and A1fi with wind disturbance and without harvesting, indicating that succession remains the dominant driver rather than natural disturbance. However, timber harvesting at current rates lowers aboveground forest biomass compared to the control over time and changes in aboveground biomass over time were non-linear across a range of ecoregions and forest types. Harvesting by climate change interactions show strong interactions with regional biomass and tree species decline, and slower invasion of new species. Our study demonstrates the importance of spatially interactive processes in affecting the forest biomass and suggests that active mitigation strategies to maximum carbon sequestration via increasing harvesting rotation period and tree planting practices may have positive effects on aboveground biomass and carbon storage in the region.