Answers to some frequently asked questions we get about prairies and savannas
Below are eleven frequently asked questions (FAQs) that TPE has answered in a concise manner. The intent is to provide a starting point for learning more on each of these topics. Look for more answers to FAQs in the future on more specific themes like land management.
What is a prairie or savanna remnant, and why is the TPE mission of saving remnants so important?
How can I assess the quality of a remnant?
Should I be adding new plant species to my remnant?
What is “fire-refugia” and why is it important?
What is the conservation value of large prairie restoration complexes?
What is the difference between reconstruction and restoration?
How do prairie plantings (i.e., reconstructions) contribute to prairie conservation?
Is the origin of seeds important?
Are herbicides needed to control invasive plant species?
What does “fire-dependent” mean?
What are the different fire-dependent ecosystem types found in the upper Midwest?
Remnants are the last remaining pieces of the once vast prairie and savanna ecosystems that dominated our region for thousands of years up until the early to mid-1800s. Remnants are sites that have not been plowed, developed, overgrazed, or otherwise disturbed and have some part of the original prairie or savanna still intact. There is a range in quality of remnants associated with how intact they are.
Because the original ecosystems are now so rare, remnants are often the last refuge of many rare and endangered species of plants, invertebrates, and soil organisms that depended upon the original ecosystems. Not even the largest of remnants today house all the species of the original ecosystems, as many small remnant sites combined often have species that are missing from the top largest sites combined. In addition, remnants are blueprints of how the original prairie and savannas were composed and structured. This is knowledge critical to informing any attempts to bring back those ecosystems on a larger scale. Lastly, the genetic diversity of many rare species is not fully captured by just a few sites, a pool of many sites across the range are needed to do that. Therefore, the conservation goal should be to find and protect as many remnants as we can, especially those of highest quality. They are simply that rare.
A simple initial approach is to conduct informal surveys to compile a plant species list. More complete lists from formal surveys are even better. A list can be used to look at how many native prairie species are present and evaluate the density of non-native invasive species and aggressive native species. Comparing these characteristics to those of high-quality prairie or savanna remnants with similar abiotic conditions and topography can provide a rough measure of the quality of a remnant. An important consideration during an assessment is the presence of plant species that are only found in high-quality remnants. For example, Hoary puccoon is found only on high-quality remnants, whereas Common milkweed, while it can be present in high-quality remnants, can easily reestablish in old farm fields. Ecologists use a ranking system (0-10) to assign Coefficients of Conservatism values (C values) to each plant species based on this idea, with Hoary puccoon being a 10 and Common milkweed a 1 in the example given. There are formal methods of using C values for making an assessment, but such assessments should be left to professionals. If identification is difficult for someone, one can hire professional contractors to do an assessment, or perhaps local TPE volunteers can help.
Most remnants are degraded to some extent, including having lost species. In some cases, adding some species back to remnants might be desirable. If species are added, the origin of the seeds should be nearby and of similar ecotype. Be certain that the species are suitable for the type of remnant where introductions are done (see Henderson 1998) and that they are within the historical range of those species. Any introduced species, along with the genetic origin of them, should be documented. Collecting seed from species already on-site and spreading those to degraded areas within a site is a good practice.
Refugia are areas in a prairie or savanna that aren't treated with a management action such as burning, grazing, or mowing, while the rest is treated. Fire-refugia are areas left unburned during a prescribed fire, thus offering refuge for invertebrates and other organisms that will be negatively impacted by fire. In the original historic prairies and savannas, fires in our region that were started by Native Americans and lightning moved across large swaths of the landscape. However, due to variables of the weather, topography, and other hindrances to the movement of fire on that day, patches often did not burn or burned with very low intensity, thus creating natural fire-refugia. Given the diminished size and fragmentation of today’s existing prairie and savanna remnants, it is recommended that fire-refugia be included when burning remnant prairies unless it is known to be unnecessary or not feasible.
Large prairie complexes are functioning ecosystems with a mosaic of fire-dependent communities which link isolated remnants across a landscape. They increase chances for long-term survival and provide critical habitat for grassland, prairie and savanna dependent invertebrates, reptiles, amphibians, birds and mammals that need large areas of habitat for feeding and reproduction. For example, the Wisconsin state endangered regal fritillary butterfly needs its host plant, any violet species such as the prairie violet, bird’s-foot violet or arrow leaf violet, but it also prefers large tracts of grassland with enough nectar plants from late June through September. Small, isolated remnants are the last bastions of prairie species and genetic diversity on the landscape, but they alone cannot support animal species that depend on a larger grassland ecosystem and species on these small remnants are also suspectable to extirpation.
The terms restoration and reconstructions often have different meanings, depending on who is using them. One way to define them is that a reconstruction is adding prairie plants to a place where few prairie plants are present, such as an agricultural field. These are often called prairie plantings. Restoration could be defined as working on degraded remnant prairies that retain relict native plants and still have a lot of the components of the original ecosystem still intact. Nearly all remnants are degraded and need to be restored to some extent because of a lack of fire, invasive species, or other stressors.
Planting prairie plants can contribute to the total acres that have prairie plants on the landscape. These additional areas provide some of the habitat features provided by remnants and may reduce the fragmentation of prairies. The greatest conservation value of reconstructions is when they are placed adjacent to or provide connecting bridges or close “island hops” between remnants. However, a prairie planting cannot duplicate all of the characteristics of old-growth remnant prairies on human timescales and seldom has the plant diversity or other component diversity (e.g., invertebrates, microbes) of remnant prairies. See the planting page for more information.
The degree of importance is generally unknown, but theoretically, seed from distant and different abiotic conditions may not fit well in a new environment. Plant populations have adapted over time to specific soil types, topography, and climate. The plants from introduced seed could fail, be aggressive, or may not be as hardy over time as native local plant seed collected or acquired from nearby locations that have similar abiotic conditions. Genetic diversity is healthy for prairie ecosystems, but the introduction of non-local genetic material could compromise the genetics in locally-adapted plants growing in nearby remnants.
In many cases, herbicides are the only effective means of invasive plant control. However, there are some non-herbicide methods for controlling native and non-native invaders. Many of those methods are labor intensive but are doable for smaller infestations to reduce density or eradicate invasive species. Common methods are pulling or digging, smothering, girdling, mowing, double cutting and root-severing. See more on some of these methods in these blog posts (link). Bio-control options are limited and most often only reduce invasive species density, and sometimes not to the desired goal. Herbicide use can also be minimized by using methods with more targeted application, such as using cut-stump treatments rather than basal spraying or foliar spraying. Having a mature, diverse set of expected plant species and healthy sod of the native system is critical to hindering establishment and in accelerating suppression of troublesome invasive plants. Fire is a critical ecologic process in achieving such sod.
Fire-dependent refers to an ecosystem which evolved and is maintained by the repeated presence of fire. Fire is a natural process that shapes habitat structure and species composition. Without fire, the health of fire-dependent ecosystems declines as sun-loving, fire-adapted/resilient, low available nitrogen adapted species like prairie and savanna grasses and wildflowers are replaced by shade-tolerant, fire-sensitive, nitrogen-needy species. In fact, without fire, grasslands and savannas in much of North America, including the Midwest, would have been restricted to serpentine soils, alvars, river scours, and dune environments.
Many different ecosystems are fire-dependent, including: prairies, savannas, barrens, pine and oak forests, and some types of wetlands (e.g., fens and sedge meadows). Each of these broad types of ecosystems can be broken down in more specific plant communities, depending on the classification system used. For instance, the Wisconsin DNR lists six types of prairies: sand, dry, dry-mesic, mesic, wet mesic and wet. A few species such as jack pine and black spruce require fire for seed germination, but will be driven out if fire is too frequent. Fire intervals may vary across types, and less so within types. Even plant communities that are not strictly fire-dependent are adapted to withstand low frequency fire.