Forested watershed

Models projections are mixed for many common species that make up northern hardwood forests in Michigan. American basswood, American beech, black cherry, eastern white pine, green ash, northern red oak, red maple, and sugar maple are generally projected to increase under mild climate scenarios, but these species are more likely to decrease under hotter, drier conditions. Deciduous forest systems may be more able to increase productivity across a range of climate scenarios than coniferous forest systems.

Climate projections and forest ecosystem models suggest that forest ecosystems may become more water-limited under climate change, due to longer and warmer growing seasons, precipitation changes, earlier snowmelt. Hardwoods on moist, rich soils may be buffered from short-term droughts or seasonal moisture stress, but these forests may suffer on marginal soils. Increased CO2 concentrations may also increase the water-use efficiency of some species, reducing the risk of moisture stress.

Low species diversity gives these forests few alternatives if conditions shift beyond tolerable limits.

Under a high emissions scenario, researchers forecast more insect pest damage in northern forests due to increased metabolic activity in active periods and increased winter survival. Drought-stressed trees are also typically more vulnerable to insect pests and diseases. The possibility exists for interactions among multiple stressors to lead to more severe climate change impacts.

Quaking aspen and bigtooth aspen can tolerate a wide range of soil types and moisture conditions and aspen is a management priority for many landowners. These species may do well with a moderate amount of future warming, and the Tree Atlas and LANDIS models project either no change or slight increases for quaking aspen and bigtooth aspen by the end of the century under the mildest future climate scenario. Both models indicate that these species will fare much worse under hotter, drier climate scenarios.

Quaking aspen, balsam poplar, and paper birch are boreal species near their southern range limits in Michigan. Multiple forest impact models tend to agree that these species are more likely to decline in suitable habitat and biomass across a range of climate scenarios by the end of the century. These species exist on a wide range of soils and landforms, and this forest type is a management priority for many landowners.

Aspen and paper birch are pioneer species evolved to thrive with regular disturbance. Wildfire and blowdown events could become more common under climate change, and continued management could benefit this forest type, but it is unknown whether aspen-birch forests would continue to persist if stand-replacing disturbances become much more frequent.

If climate change results in increased moisture stress during the growing season, drier sites will be exposed to greater drought stress and mortality. Warmer growing-season temperatures might encourage more suckering after disturbance, but projected temperatures in the assessment area may be beyond the physiological limits of aspen and birch species.

Lowland conifer forests are not expected to expand to new territory or outcompete other forest types, but acid or alkaline soil conditions may make them less suitable for invasive species or competing forest types.

These are boreal species near their southern range limits in Michigan. Multiple forest impact models tend to agree that these species are more likely to decline in suitable habitat and biomass across a range of climate scenarios by the end of the century. These forests may not maintain their identity if dominant species decline and water tables change.