Michigan Forest Vulnerability Assessment

This chapter describes the major forest communities across Albert’s Ecological Sections VII and VIII and summarizes current threats and management trends. This information lays the foundation for understanding how shifts in climate may contribute to changes in forests, and how climate may interact with other stressors on the landscape.

• More than 70 percent of the forest land in Michigan occurs within the assessment area, most of which is owned by private landowners.

• Major stressors and threats to forest ecosystems in the region are:
• Fragmentation and land-use change
• Fire regime shifts
• Nonnative species invasion
• Forest pests and disease
• Overbrowsing by deer
• Management practices over the past century have tended to favor early successional stages of many forest types across the landscape and reduce species diversity and structural complexity.
• A major ecological transition zone for both terrestrial and aquatic systems occurs between the northern and southern halves of Michigan’s Lower Peninsula.
• The forest products industry is a major contributor to the region’s economy.

This chapter summarizes our understanding of observed changes and climate trends in the assessment area and across the Midwest region, with a focus on the last century.

• Mean, maximum, and minimum temperatures have been increasing across all seasons, with winter temperatures warming the most rapidly.
• Mean, maximum, and minimum temperatures have been increasing across all seasons, with winter and spring temperatures showing the most rapid warming.
• The assessment area has received more precipitation, particularly in the summer and fall.
• More precipitation has been delivered in heavy events of 3 inches or greater.
• Annual snowfall has been increasing slightly across northern Michigan, and the number of large winter storms has increased.
• Climate change has also been indicated by trends in lake ice, growing season length, and wildlife range shifts.

This chapter examines how climate may change in the assessment area over the next century, according to a range of model projections. Published scientific literature provides the basis for describing possible trends in a range of climate-driven processes, such as extreme weather events and snowfall.

• Temperature is projected to increase across all seasons during the next century, with dramatic warming projected in winter.
• Precipitation is projected to increase in winter and spring across a range of climate scenarios, but summer precipitation may decrease.
• Intense precipitation events may continue to become more frequent than in the past.
• Snowfall is projected to decline across the assessment area by the end of the 21st century, with more winter precipitation falling as rain.
• Soils are projected to be frozen for shorter periods during winter.

This chapter summarizes the potential impacts of climate change on forests in northern Michigan, drawing on information from a coordinated series of model simulations and published research.

• Boreal species such as quaking aspen, paper birch, tamarack, jack pine, and black spruce are projected to experience reduced suitable habitat and biomass across the assessment area.
• Species with ranges that extend to the south such as American basswood, black cherry, and white oak may experience increased suitable habitat and biomass across the assessment area.
• Many common species in northern Michigan may decline under the hotter, drier future climate scenario.
• Forest productivity will be influenced by a combination of factors such as carbon dioxide fertilization, water and nutrient availability, local disturbances, and species migration.
• Model projections do not account for many other factors that may be modified by a changing climate, including:
• Drought stress
• Changes in hydrology and flood regime
• Wildfire frequency and severity
• Altered nutrient cycling
• Changes in invasive species, pests, and pathogens

This chapter focuses on the vulnerability of major forest systems in the assessment area to climate change, with an emphasis on shifts in dominant species, system drivers, and stressors.

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

We consider a system to be 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.
• 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.
• 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.
• 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.
• Droughts will increase in duration and area (limited evidence, low agreement). A study using multiple climate models indicates that drought may increase in length and extent, and an episodic precipitation regime could mean longer dry periods between events.
• 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.
• 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 invasive species, insect pests, and pathogens will increase or become more damaging (limited evidence, high agreement). Evidence indicates that an increase in temperature and greater moisture 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). Impact 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 communities.
• Southern species will be favored by climate change (medium evidence, high agreement). Impact models agree that many temperate species will experience increasing 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 communities will change across the landscape (limited evidence, high agreement). Although few models have specifically examined how communities may change, model results from individual species and ecological principles suggest that recognized forest communities may change in composition as well as occupied range.
• Forest productivity will increase across the assessment area (medium evidence, medium agreement). Model projections and other evidence support modest productivity increases for forests across the assessment area, although there is uncertainty about the effects of increased CO2. It is expected 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 diverse systems are more resilient to disturbance, and low-diversity systems have fewer options to respond 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 especially 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 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 across forest types, ownerships, management objectives, and site-specific conditions.

• 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.
• Information on anticipated climate change impacts may allow the forest products industry, recreation, and other sectors to adapt and capitalize on potential new opportunities.