Forest Ecosystem Vulnerability Assessment and Synthesis for Northern Wisconsin and Upper Michigan

This chapter describes the forests and related ecosystems across the Laurentian Mixed Forest Province in northern Wisconsin and western Upper Michigan and summarizes current threats and management trends. The information lays the foundation for understanding how shifts in climate may contribute to changes in forest ecosystems, and how climate may interact with other stressors on the landscape.

• The assessment area of northern Wisconsin and western Upper Michigan contains approximately 16 million acres of forest land. Private individuals and organizations own more than 60 percent of forest land.

• Current major stressors and threats to forest ecosystems in the region include:
• Fragmentation and land-use change
• Fire regime shifts
• Nonnative species invasion
• Forest diseases and insect pests
• Overbrowsing by deer
• Extreme weather events
• Historical land use and past management practices tended to favor younger forests across the landscape and often reduced species diversity and structural complexity.
• The forest products industry is a major contributor to the region’s economy, and much of the forest land in the assessment area is managed according to at least one sustainability certification standard.

Many of the climatic changes that have been observed across the world over the past century are also evident in the assessment area. This chapter summarizes our current understanding of observed changes and current climate trends in the assessment area and across the Midwest region, with a focus on the last 50 to 100 years.

• Mean, maximum, and minimum temperatures have been increasing across all seasons, with winter temperatures warming the most rapidly.
• Precipitation patterns have changed across the region. The number of intense precipitation events has increased.
• Snowfall has generally decreased across the assessment area, although the severity of large winter storms may have increased.
• Climate change has also been indicated by trends in lake ice, growing season length, and wildlife range shifts.

This chapter describes climate projections for the assessment area over the 21st century, including projections related to patterns of extreme weather events and other climate-related processes. Temperature and precipitation projections are derived from downscaled simulations of climate models. Published scientific literature provides the basis for describing possible trends in a range of climate-driven processes, such as extreme weather events and snowfall.

• Temperatures are expected to continue to increase over the next century. A range of climate scenarios project warming in all seasons.
• Precipitation is projected to increase in winter and spring across a range of climate scenarios. Projections of summer and fall precipitation are more variable, and summer precipitation may decrease.
• Intense precipitation events are expected to continue to become more frequent.
• Snowfall is projected to continue to decline across the assessment area, with more winter precipitation falling as rain.
• Soils are projected to be frozen for shorter periods during winter.
• Soils are projected to be frozen for shorter periods during winter.

This chapter summarizes the potential impacts of climate change on forests in the Laurentian Mixed Forest Province in northern Wisconsin and western Upper Michigan, drawing on information from a coordinated series of model simulations and published research.

• Boreal species such as black spruce, balsam fir, quaking aspen, paper birch, and white spruce are projected to have reductions in suitable habitat and biomass over the next century.
• Species with ranges that extend to the south such as American basswood, black cherry, northern red oak, and red maple may have increases in suitable habitat and biomass.
• Many species currently common in northern Wisconsin and western Upper Michigan are projected to decline under a hotter, drier future climate scenario.
• Forest productivity will be influenced by a combination of factors such as carbon dioxide (CO2) fertilization, water and nutrient availability, and species migration.
• The model projections used in this assessment do not account for many other factors that may change under a changing climate. Scientific literature was used to provide additional information on these factors including:
• Altered precipitation and hydrology
• Drought stress
• Wildfire frequency and severity
• Altered nutrient cycling
• Changes in invasive species, insect pests, and forest diseases
• Interactions among these factors

Forest ecosystems across the Northwoods will experience direct and indirect impacts from a changing climate over the 21st century. We assessed the vulnerability of major forest systems in the assessment area to climate change over the next 100 years, focusing on shifts in dominant species, system drivers, and stressors.

The adaptive capacity of forest systems was also examined as a key component to overall vulnerability. Synthesis statements are provided to capture general trends. Detailed vulnerability determinations are also provided for nine major forest systems.

A system is considered vulnerable if it is at risk of a composition change leading to a new identity, or if the system is anticipated to suffer substantial declines in health or productivity.

Potential impacts of climate change on ecosystem drivers and stressors

• Temperatures will increase (robust evidence, high agreement). All global climate models project that temperatures will increase with continued increases in atmospheric greenhouse gas concentrations.
• Growing seasons will get longer (robust evidence, high agreement). There is high agreement among information sources that projected temperature increases will lead to longer growing seasons in the assessment area.
• Winter processes will change (robust evidence, high agreement). All evidence agrees that temperatures will increase more in winter than in other seasons across the assessment area, leading to changes in snowfall, soil frost, and other winter processes.
• The amount and timing of precipitation will change (medium evidence, high agreement). All global climate models agree that there will be changes in precipitation patterns across the assessment area.
• Intense precipitation events will continue to become more frequent (medium evidence, medium agreement). There is some agreement that the number of heavy precipitation events will continue to increase in the assessment area. If they do increase, impacts from flooding and soil erosion may also become more damaging.
• Soil moisture patterns will change (medium evidence, high agreement), with drier soil conditions later in the growing season (medium evidence, medium agreement). Studies show that climate change will affect soil moisture, but there is disagreement among climate and impact models on how soil moisture will change during the growing season.
• Droughts will increase in duration and area (limited evidence, low agreement). A study using multiple climate models indicates that drought may increase in extent and area, and an episodic precipitation regime could mean longer dry periods between events.
• Climate conditions will increase fire risks by the end of the century (medium evidence, medium agreement). Some national and global studies suggest that wildfire risk will increase in the region, but few studies have specifically looked at wildfire potential in the assessment area.
• Many nonnative species, insect pests, and pathogens will increase or become more damaging (limited evidence, high agreement). Evidence indicates that an increase in temperature and greater ecosystem stress will lead to increases in these threats, but research to date has examined few species.

Potential impacts of climate change on forest communities

• Boreal species will face increasing stress from climate change (medium evidence, high agreement). Ecosystem models agree that boreal or northern species will experience reduced suitable habitat and biomass across the assessment area and that they may be less able to take advantage of longer growing seasons and warmer temperatures than temperate forest species.
• Southern species will be favored by climate change (medium evidence, medium agreement). Ecosystem models agree that many temperate species will gain suitable habitat and biomass across the assessment area and that longer growing seasons and warmer temperatures will lead to productivity increases for temperate forest types.
• Forest ecosystems will change across the landscape (medium evidence, high agreement). Although few models have specifically examined how communities may change, model results from individual species and ecological principles suggest that species composition and recognized forest communities will change.
• Forest productivity will increase across the assessment area (medium evidence, low agreement). Some model projections and other evidence suggest forest productivity may increase in the assessment area, although there is uncertainty about the effects of and limitations of increased CO2. It is also anticipated that productivity will be reduced in localized areas.

Adaptive capacity factors

• Low-diversity systems are at greater risk (medium evidence, high agreement). Studies have consistently shown that more-diverse systems are more resilient to disturbance, and low-diversity systems are more vulnerable to change.
• Species in fragmented landscapes will have less opportunity to migrate in response to climate change (limited evidence, high agreement). The dispersal ability of individual species is reduced in fragmented landscapes, but the future degree of landscape fragmentation and the potential for human-assisted migration are two areas of uncertainty.
• Systems that are limited to particular environments will have less opportunity to migrate in response to climate change (limited evidence, high agreement). Despite a lack of published research demonstrating this concept in the assessment area, our current ecological understanding indicates that migration to new areas will be particularly difficult for species and systems with narrow habitat requirements.
• Systems that are more tolerant of disturbance have less risk of declining on the landscape (medium evidence, high agreement). Basic ecological theory and other evidence support the idea that systems that are adapted to more frequent disturbance will be at lower risk.

This chapter summarizes the implications of potential climate change to forest management and planning in northern Wisconsin and western Upper Michigan. This chapter does not make recommendations as to how management should be adjusted to cope with these impacts, because impacts and responses will vary by ecosystem, ownership, and management objective.

• Plants, animals, and people that depend on forests may face additional challenges as the climate shifts.
• Greater financial investments may be required to manage forests and infrastructure and to prepare for severe weather events.
• Management activities such as wildfire suppression or recreation activities such as snowmobiling may need to be altered as temperatures and precipitation patterns change.
• Climate change may present opportunities for the forest products industry, recreation, and other sectors if changing conditions are anticipated.