(CNA Corporation, 2007), meaning that it can exacerbate existing threats that natural communities face, increasing their vulnerability to these threats (see Figure 2.1, right). The field of conservation ecology is in the initial phases of developing general “rules of thumb” of how species and communities are likely to respond to the most direct aspects of climate change (e.g., changes in air or water temperature) by integrating the observed changes in our ecosystems with ecological theory (Hall and Root, 2012). As pointed out in the Climate Action Plan for Nature (2010), everything about climate change is fluid and evolving fast, including downscaled models, development of practical tools, policy responses, and funding for mitigation and adaptation programs. With this in mind, this Review is a living document intended to be modified and expanded as new science, tools, policies, and funding become available. In this section we review the biological significance and conservation status of terrestrial communities in the Chicago Wilderness region and discuss what is presently known about how climate change may affect specific communities. We also examine the ways in which climate change may be expected to exacerbate existing threats that communities currently face.
The information presented in this section primarily reflects the opinions of local researchers, scientists and land managers who participated in expert workshops on climate change held in 2009 (see Introduction). A main outcome of this collaborative work was the creation of a list of climate change impacts that are thought to be of greatest concern for our region’s terrestrial and aquatic systems. We present the information for terrestrial communities in Table 4, which lists the climate change impacts, the communities they are likely to affect, and the existing threats they are expected to amplify. Additionally, participants were asked to prioritize the top three threats from the list they felt were likely to have the greatest impact on the Chicago Wilderness region. The top climate change related threats for terrestrial systems are (not in a ranked order):
- Increased temperatures and changing patterns of precipitation will stress some native species and promote some invasives, suggesting that the threat of invasives will increase. Further, new natives from the south may be able to colonize, and potentially become invasive.
- Increased temperatures will promote range shifts in sensitive species. Some species will be constrained in their response by lack of connected habitats through which to move, and others will be constrained by habitat loss, lack of mobility, or lack of genetic variation.
- Species will respond in complex ways, and many key interactions may be disrupted (e.g. through mismatches in phenological shifts, or rate of range shifts).
Terrestrial communities can be described in terms of a shade and a moisture gradient, both of which extend across prairies, woodlands and wetlands. Each of the Chicago Wilderness terrestrial community types, and what is known about how they may be impacted by climate change, are reviewed here. Table 2 summarizes these climate change impacts; presenting first the impacts expected to affect all Chicago Wilderness terrestrial communities, followed by additional impacts that may affect specific community types. At the end of this section we outline some initial no-regret strategies and actions that land managers can implement to promote biodiversity adaptation for species and communities. Lastly, we present research questions and initiatives that have been identified by local researchers and land managers as critical to helping us move forward in our knowledge and understanding of the ways in which climate change will affect biodiversity and ecosystem functioning in our region.
Given the loss of prairie habitat (i.e., less than one-hundredth of one percent of original prairie remains in Illinois), and the generally poor condition of what remains, the Biodiversity Recovery Plan regards all prairie types with a high level of concern and places sand prairies in dune and swale topography, dolomite, and fine textured-soil prairies at the highest priority level. The 2006 State of Our Chicago Wilderness Report Card gave prairies a grade of “D”. The report cited conversion to agricultural fields, habitat degradation by past cattle grazing, overgrowth by brush and other invasive species, heavy browsing by excessive populations of white-tailed deer and changes in hydrology as the causes.
Warmer air temperature and changes in precipitation patterns are likely to affect prairies in a multitude of ways. The expected changes in climate may cause a general shift in overall species diversity and structural composition in prairie habitats, favoring warmer and drier-biome plant species and stress colder and wetter-biome species. Possible impacts to prescribed fire management could also lead to changes in community assemblages (see Plants page, section 3.1). Moreover, it is likely that species will exhibit differential shifts in their ranges due to differences in dispersal abilities/rates, leading to the disruption of key species interactions. This unsynchronized pattern of migration can easily lead to mismatched shifts in the timing of various ecological events and disrupt species interactions, potentially causing communities- and their system functionality- to be torn apart.
A hotly debated topic in the literature has been the use of a conservation strategy termed assisted migration. This strategy has been proposed for species, like many of those found in our prairie grasslands, with poor dispersal abilities that occur in highly modified landscapes subject to the effects of climate change. The concept is to facilitate or mimic natural range expansion as a direct management response to climate and the lack of landscape connectivity that prevents species from migrating appropriately (Shirey and Lamberti, 2010; Vitt et al., 2010). One of the arguments against translocating plants is the associated risk of a species becoming invasive in its introduced range. While it is true that intercontinental movement of a non-native species has resulted in problems with invasive species, the vast majority of introduced species do not become invasive. For example, less than 1 percent of species become invasive when imported to a new range (Williamson and Fitter, 1996), and only a small percent of those (7.5 percent of invasives in the US) are a result of intra-continental species introductions (Mueller and Hellmann, 2008; Vitt et al., 2010). Nonetheless, the decision to undertake assisted migration for a particular native species should be extensively researched and weighed. Vitt el al. (2010) proposed a framework for determining, prioritizing, and developing collection strategies for potential target species for assisted migration. These types of tools can greatly help in the decision making process of whether assisted migration is a viable option for a particular species.
Another climate change issue that is likely to affect prairie grasslands is higher CO2 levels. Increasing levels of CO2 in the atmosphere may cause a shift in species composition, but the precise way in which this will occur is uncertain. For example, many tall grass prairie species have a C4 photosynthesis physiology that allows them to be more efficient at photosynthesizing compared to trees, shrubs and cool-season grasses with a C3 physiology (Lattanzi, 2010). From this perspective, it’s possible that C3 plants may benefit more from an increase in atmospheric CO2 than C4 plants, potentially giving them a competitive advantage. On the other hand, C4 plants have historically fared better in more arid environments than C3 plants, which may give them an edge as prairies become drier (Lattanzi, 2010). Ultimately, increased growth and reproduction will depend on a variety of factors such as soil nutrient availability, overall precipitation and temperature. These differences in competitive abilities and potential for changes in relative advantage over time, implies that managers will need to be more agile in their management strategies.
Prairies contribute significant ecological benefits to humans by retaining considerable moisture on site. The deep roots of prairie plants help maintain the porosity of the soil and thus maintain recharge areas. Further illustrating the importance of prairie protection is the role they play in carbon mitigation. Grasslands store more carbon per acre than most other ecosystems because 90% of their biomass is underground, thus locking the carbon underground. As precipitation patterns shift to more extreme storm events, it will be imperative that we find ways to adapt both our built infrastructure to cope with the excess run-off, and our natural communities like prairies that provide this ecological service. It will be equally important to do this in such a way as to not turn our forest preserves into stormwater management facilities, but rather as a component of an overall regional adaptation plan.
Possible Adaptation Strategies and Actions for Prairie Grasslands
- Focus on managing for wetter habitats;
- Increase the genetic diversity of species by widening the seed source collection range, specifically to more southern populations and meta-populations. Both a defined range expansion (e.g. initially increasing a seed sourcing range from 50 to 150 miles) and a rate at which seeds from more southern populations are staggered into local Chicago Wilderness populations needs to be determined;
- Structures and other large, long-term projects should be designed with climate change forecast in mind;
- Consider assisted migration and the use of tools to guide strategic framework for maintaining climate sensitive species in highly fragmented or isolated areas, or for which suitable habitat may no longer occur (migration (e.g., Vitt et al., 2010);
- Design and implement a monitoring protocol to evaluate climate change effects on local plants and animals and
- Maintain large patches (e.g., similar to Gooselake Prairie) to provide moisture and temperature gradients to allow species to find appropriate microclimates for survival in the face of changing climates.
Tree dominated communities have been referred to by a variety of names, such as forested, woodland, or wooded. Forested communities broadly refer to habitats dominated by trees, with an average canopy cover greater than 50%. However, most tree-dominated communities within the Chicago Wilderess region do not fall strictly within this category, so instead we refer to them collectively as “wooded” communities. This section describes five main community types: savannas, woodlands, upland forest, floodplain forest and flatwoods.
Savannas are wooded communities that represent a shade gradient between prairies and more forested woodlands, and often have soils that are transitional between prairie and forest and support a distinctive plant and animal assemblage. There are two savanna types in our region, sand and fine-textured soil, and subtypes that are characterized by soil moisture from dry-wet. Savannas typically have a graminoid groundcover and an average tree canopy cover of less than 50% but greater than 10%. We will first describe climate impacts on savanna communities, and move on to the more heavily forested communities.
Most of the major climate change impacts anticipated to affect prairie grasslands are also applicable to savannas and more forested communities. There is, however, the additional threat of increasing temperatures promoting increases in tree pests, and positively influencing invasives and disease vectors (see Plants page, section 2.3). This is likely to occur through greater reproduction of tree pests due to warmer temperatures and longer growing seasons that allow for greater range expansion. Warmer temperatures and changes in precipitation patterns that would lead to an overall drier environment may shift wooded communities toward more open conditions (i.e., savanna). However changes in moisture alone are not likely to return wooded ecosystems to more open conditions; fire management and canopy manipulation would need to play a primary role in this. Burn windows may also be changing as a result of climate change (see Plants page, section 3.1). A warmer and drier climate will likely affect savanna communities across the board, with additional drought stress in the late summer expected to favor warmer-biome plant species over colder-biome forest species. In particular, the wet-mesic fine-textured-soil savannas are at greatest risk because once the hydrology is lost in this community it is extremely difficult to restore.
Open woodlands, with shade levels intermediate between savannas and forests, have been especially negatively impacted by changes to the landscape brought about by settlement and urban development. These systems have seen increased canopy closure due to invasion by fire-sensitive mesic species (such as sugar maple, A. saccharum) and exotic shrubs (e.g., buckthorn, Rhamnus cathartica), which has altered understory plant community composition and prevented oaks from reproducing (Packard and Mutel, 1997). Additional stress from rapid climate change may decrease the overall health of woodlands. As the health of a community declines, it could become more vulnerable to exotic species and outbreaks of pests and pathogens, further shifting species composition and structure. Controlling weedy species currently costs the United States more than $11 billion a year. The most widely used herbicide in the United States, glyphosate (RoundUp®), loses its efficacy on weeds grown at carbon dioxide levels that are projected to occur in the coming decades (Wolfe et al. 2007). Higher concentrations of the chemical and more frequent spraying thus will be needed, and both herbicide use and costs are likely to increase as temperatures and carbon dioxide levels rise (Kiely et al. 2004). Warmer winter temperatures may also limit the time period when snow cover allows for canopy manipulation treatments, which are often necessary to increase canopy openness, to be implemented without causing soil disturbance.
(see Plants page, section 4.4). At the other end of the spectrum, dry habitats may get drier, leading to more stress on trees and lowering their resistance to disease as well as reducing the ability for communities to resist non-native invasions. Floodplains, a good example of wetter forest habitat, occur along rivers and streams where the frequency and duration of flooding have greatly shaped their communities. As such, floodplains are likely to be at a higher risk for increased stress on native species due to the more extreme flooding predicted for the region. Likewise, flatwoods may be at higher risk from more extreme floods, but also face challenges from increased drought stress. The reason for this is the soils of flatwoods have an impermeable, or slowly permeable layer, that causes a shallow water table and restricts the movement of water down into the ground, instead moving it laterally over the surface. This not only makes flatwoods more likely to be flooded, but also puts them at greater risk to dry up completely in the summer months. Depending on the timing of this latter scenario (little or no water availability for an extended period), it could prove problematic for amphibians like the blue-spotted salamander (Ambystoma laterale) that use ephemeral ponds and wetlands in flatwoods as key breeding and reproduction grounds (see Wildlife page, Table 1: Amphibians). [Ephemeral wetlands, however, can occur in just about any terrestrial habitat type. These wetlands are crucial habitat for local amphibians, and will be one of the most vulnerable habitats to climate change.] Neither floodplains nor flatwoods were regarded as conservation priorities in the Biodiversity Recovery Plan, and we recommend that they be considered as such in light of the changes in climate predicted for our region.
Across the taxonomic spectrum, fauna associated with forested communities will be affected by the changes to their habitats. Amphibians like the Western chorus frog (Pseudacris triseriata) or spring peepers (Pseudacris crucifer) will face challenges due to an overall drier environment, while savanna species like the eastern bluebird (Sialia sialis) may be affected by shifts in plant community structure, to which they strongly respond (see Wildlife page, Table 1: Birds). One group of animals that may fare quite well with climate change, however, is lumbricid earthworms (see Wildlife page, Table 1: Invertebrates). These earthworms are not native to North America, and have spread to areas where earthworms did not formerly exist in Illinois. Because lumbricid earthworms make their living decomposing forest leaf litter, they can cause a significant shift in forest soils that rely on a large amount of undecayed leaf matter for development (Seidl and Klepeis, 2011). This shift in soil ecology can result in habitats that are unsuitable for certain species of trees, ferns and wildflowers, further stressing native species.
The Chicago Wilderness Report Card on the Health of the Region’s Ecosystem’s gave wooded communities of all types, including savannas, a D+ indicating that most are changing for the worse. These changes include invasive species crowding out native tree species, shrubs, grasses and wildflowers- a stress to the community that will increase with climate change.
Possible Adaptation Strategies and Actions for Wooded Communities
- Utilize river corridors to provide large-scale connectivity among these communities;
- Prioritize high quality wooded communities and maintain appropriate density of woody species present in them through active, restoration-focused management;
- Engage urban forests as genetic paths (pollen dispersal) and sources of propagules by planting native species in streets and parks; and
- Promote regional tree diversity through management in natural areas and planting in urban systems to increase resiliency of regional forest.
Generally speaking, increased storm intensity and flooding may increase non-point source pollution from agricultural and urban areas, threatening the water quality for all wetlands. Additionally, wetland plants depend on seasonal hydrological patterns of wetlands and, in light of the expected changes in precipitation patterns and increases in evaporation rates in our region, it is very likely that hydrological cycling may change and negatively affect wetland communities. There is a possibility that some wetlands may begin to dry out as temperatures rise, evaporation rates increase and there is more pressure on groundwater resources; this could create a feedback loop that further fragments and stresses the remaining wetland habitats (see Plants page, sections 4.6; 4.7).
Fens, which are groundwater-fed peatlands that are highly sensitive to hydrologic changes, may also face greater challenges because they are created and maintained by a continual internal flow of groundwater that will likely be reduced due to a variety of climate-related factors. Recharge rates and patterns will be affected by storm events and drought periods. While storm events may produce a great amount of precipitation, infiltration will not be at an equivalent rate. Furthermore, encroachment of invasive woody species (e.g., buckthorn and honeysuckle) that do not maintain infiltration as well as deep-rooted native plants will impact infiltration rates and wetland communities too. In addition, higher temperatures, earlier snowmelt and less snowpack, more severe and frequent floods that result in increased stormwater runoff and thus less groundwater recharge, and a greater demand on groundwater resources all threaten the continued existence of fens in this region. Marshes are especially important habitats for breeding and migrating wetland birds alike. The ability of marshes to achieve their maximum structural diversity, or the “hemi-marsh stage” where the surface is approximately 50% open water and 50% emergent vegetation, is critical to wetland birds. It is likely that higher evaporation rates, greater pressure on groundwater, and changes in precipitation patterns may compromise the ability for marshes to maintain, or even reach, the hemi-marsh stage for a duration that can benefit wetland birds.
In 2006, Chicago Wilderness experts convened to determine how we are doing as individuals and as a region in assuring the health of our unique natural areas. This collaborative work, called The State of Our Chicago Wilderness: A Report Card on the Health of the Region’s Ecosystem, graded wetlands as a “D+”. The report cited that remaining wetlands suffer from a number of threats, primarily altered hydrology due to intense development and the introduction of invasive species such as purple loosestrife (Lythrum salicaria), reed canary grass (Phalaris arundinacea) and common reed (Phragmites australis). However, in spite of the loss of more than 90 percent of our native wetlands, the Chicago Wilderness region retains one of the most diverse assemblages of wetlands in North America. It is of great value to ensure the continued survival of wetlands in the region because they not only support a great deal of biodiversity, but they also provide essential ecological services to human communities such as water purification and flood abatement. There is evidence that some wetland animal species have already responded to climate change. For example, climate change is associated with earlier breeding in amphibians (Beebee, 1995), earlier emergence of dragonflies (Odonata) (Hassall et al., 2007), and compositional shifts of entire insect communities (Burgmer et al., 2007, Rahel and Olden, 2008). It is also very clearly documented that sex determination in turtle eggs is closely linked to temperature, and this taxonomic group has already began to feel the affect of a warming environment (Tucker et al., 2008).
Possible Adaptation Strategies and Actions for Wetlands
Adapted from Recommendations for a National Wetlands and Climate Change Initiative drafted by the Association of State Wetland Managers January 2009.
- More stringently control drainage through regulation, focusing on total volume and runoff quality with consideration for how peak flow, attenuation, and timing may change due to changes in precipitation patterns;
- Prevent fragmentation of wetland ecosystems; more fully protect migration corridors;
- Prioritize wetlands with regard to management and adaptation. Establish “on the ground” priorities for the most cost effective application of protection and adaptation strategies. For example wetlands with deep carbon storage could be identified and targeted for acquisition or more stringent regulations;
- Identify at risk ephemeral wetlands of high value, and investigate ways to either eliminate factors already limiting their hydroperiod, or to keep their hydroperiod long enough for priority species they support (e.g., in most years hydroperiod until July 1 is sufficient for blue-spotted salamanders, or August 1 for tiger salamanders);
- Adopt buffers to reduce potential for erosion and pollution, to maintain lower water temperatures, and to facilitate migration of plants and animals;
- Install water control structures at the outlets of freshwater wetlands. Such structures can, in some instances, help maintain water levels during dry periods. However, structures may be quite expensive, require maintenance, and interrupt natural succession. It also must be determined who controls the adjustments of water levels and the criteria for adjustments;
- Prioritize drainage tile removal as an effort to restore hydrology to sites;
- Identify (map through GIS) wetlands and wetland species most at risk from climate change within Chicago Wilderness. This will require identification of plant and animal species with greatest vulnerability such as species with poor distribution and limited range. This work can build upon previous Chicago Wilderness efforts that developed a Conservation Design for woodland communities, marsh birds has and wetland herpetofauna;
- Formulate protection plans and strategies for these wetlands or classes of wetlands that are identified; and
- Consider assisting turtles with temperature sex determination to help adapt to climate change.
Overall, climate change impacts expected to exacerbate the greatest number of existing threats are 1) Increased temperatures promoting increases in tree pests in forested communities and 2) Increased temperatures promoting species that are invasive or act as disease vectors (Table 4). Both of these impacts are expected to amplify the threat of altered fire regimes, erosion and sedimentation, invasive species, and changes in structural diversity. Additionally, change to structural diversity has the potential to become the fastest growing threat to our region because it is affected by the greatest number of climate change impacts (five out of nine; Table 4), followed by invasive species (four out of nine; Table 4). How these structural changes manifest themselves, and the extent to which they occur, could greatly reshape the floral and faunal assemblages that are capable of continued survival in our region.
The range extensions of species not currently found in the Chicago Wilderness region will likely become increasingly more pervasive due to climate change. We should expect to see spatial shifts both in range boundaries (e.g., moving north in the Northern Hemisphere) and in the density of individual animals or plants within various subsections of a species’ range (see Plants page, section 2.1). Further, it’s important to recognize that shifts in density and abundance include extirpation (loss of a species from a local area) and extinction (Hall and Root, 2012). A critical issue to bring up within this context is that arguably, from a functional point of view, not all species matter per se for the integrity or the functioning of an ecosystem, but rather it is the loss of individual traits that are essential for the production of organic matter and the functioning of biochemical cycles that is of greatest importance (Inchausti and Loreau, 2002). Coming from this perspective, we may need to adapt some of our longstanding species-specific management strategies and policies to focus more broadly on the functional categories that different species—whether they are native or migrating in from other regions—provide to an ecosystem. It is also crucial to begin managing for biodiversity by managing ecosystems from a landscape perspective to address fragmentation. This does not mean that species no longer matter, or that we completely stop species-specific management (because every natural community is of course composed of the individual species represented within them), but it does imply a broader, more flexible perspective for achieving management goals.
Given that the region is going to change and some species currently represented as part of the regional floral or faunal community may not be able to adapt to these changes, we will likely face hard decisions as to when to continue conservation efforts for a given species and when to shift focus and resources to something different. Factors that could influence continued conservation support for a species might be if the Chicago Wilderness region represented the only remaining habitat, important migration routes, or the heart of the range for a species. On the other hand, if the Chicago Wilderness region represented the southern range of a species distribution, or it was known that assisted migration could be implemented successfully for that species, then resources might be allocated to focus on different species. These decisions, however, will not be based on biological considerations alone, but also the societal value judgments that frame restoration and conservation priorities in this region.
Lastly, we need to begin managing ecosystems with a focus on landscapes to address fragmentation. This kind of research informed management could be challenging because the complexities of species interactions, and how these interactions influence ecosystem services, are still being discovered. As has been the case with restoration ecology, we will only arrive at these answers through adaptive management, which is the integrated process of testing, learning, and adjusting.
Below we present research questions and initiatives for terrestrial communities at large that will help us move forward and contribute to climate change adaptation management. Not surprisingly, there are more questions than there are answers at this point. Although information for best management practices in light of climate change is beginning to emerge, there will be a lag time before the data from on-going projects makes its way down the pipeline in the form of useable management strategies. In the meantime, we recommend: 1) discussing and sharing ideas on what is, and what is not, working for land managers, 2) incorporating conservative adaptation strategies into management planning, and 3) becoming involved with the much needed research initiatives.
Research Questions/Initiatives for Terrestrial Communities
- Which plant species are most sensitive to climate change and why? (see Plants page).
- Are plants and animals responding to changes in temperature and precipitation with the same or different strategies? For example, while many plant species respond to changes in temperature as a cue for when to emerge, the specific trigger (e.g., the total number of days above a certain temperature- or accumulated warmth- versus crossing a particular temperature threshold) may differ. Alternatively, daylight length may be the driving force behind emergence for some animal pollinators, which could lead to a timing mismatch if their host plants are instead more closely cued into temperature change. As temperatures rise and rainfall patterns change, it is likely that some plant species may increase seed production while others decrease. Understanding how species’ life history traits can influence their response to climate change is key to developing refined adaptation strategies (see Plants page, section 1.1).
- How will competitive interactions change with a changing climate (e.g., C4 versus C3 plants)?
- Gain a better understanding of community assembly information with regard to assisted migration, such as what the impact of the order of introduction will be and does this matter? What happens when we move a suite of species together?
- Most often research focuses on investigating one species at a time, holding all other factors constant. We need to focus now on interactions among species with changing climate, and especially across trophic levels.
- Design projects aimed at gaining a better understanding of seed transfer zones and addressing questions like how do we make successfully bridge the gap between the collection of bulk seeds to actual site dispersal? And what are best practices for seed collection, staggering rates, and dynamic seed transfer zones?
- Once a more complete understanding of the above questions has been gained, there should be a focus on adapting our recommendation for seed sourcing from one that suggests an “on-site policy of local is best” to one that includes the concepts of dynamic seed transfer zones, reciprocal transplants and knowledge of plant genomes of the area.
- Develop longitudinal monitoring to capture baseline information on the change in local flora/fauna in terms of distribution, abundance and phenology, and help to identify changes in species assemblages. Data can be used, for example, to match flowering phenology with bird migration data or to examine whether plant species are declining due to a loss or change in pollinator species. Currently, there are only a handful of programs that monitor plant phenology, and they do not have extensively long histories (examples of existing databases: Cook County forest Preserve database, ~ 40 yrs; Chicago Botanic Garden on-site prairie phenology, ~20 yrs; Plants of Chicago database, ~16 years; Plants of Concern database, ~9 years; Project Budburst, ~3 years).
- Coordinate and work with a resource-monitoring program in the form of an early invasive species watch program in NE Illinois/S Wisconsin to help support the Plants of Concern and similar programs. Aim to identify a list of potential species coming into the area from the southern regions.
- Design more advanced modeling systems that take into account monitoring for a future dynamic system (as opposed to modeling for current system).
- Develop metrics for our adaptation strategies and research programs to evaluate terrestrial systems.