The Size and Shape of Things to Come

Prairie ecosystems are collections of living and non-living things, all interacting to form a community with distinct characteristics. And while we cherish big bluestem, prairie coneflowers, regal fritillaries, and bobolinks, it’s the non-living part - the landscape carved by glacial advances and retreats, the proximity to Lake Michigan, the rivers and streams, and the climate - that brought all these plants and animals together. And it is the ongoing interactions between the living and non-living and any changes to them that determine the long-term viability of the ecosystem. It can be overwhelming to try and consider what climate impacts are relevant, how the system is changing, and which actions to take in order to preserve the system. Let’s just tackle one aspect of the non-living piece – the size and shape of prairie patches and habitats.

Small and fragmented are the characteristics most associated with prairies in the Chicago region. How does that affect their potential viability, especially in the face of current and future climate impacts? Prairies owe their ecological history to wide open spaces throughout the US Great Plains, so size matters. But it matters in the context of several other elements of the habitat structure related to the size and shape - the level of fragmentation, the landscape matrix, and any connectivity between habitats. The site’s age and restoration history are important as well, but the overall geography strongly influences the functions that support a healthy ecosystem, providing prairies some protection from catastrophic events, which makes them more resilient. Therefore, exploring the impact that habitat size and shape (and related traits) have on healthy ecosystem functions is an excellent place to begin assessing management options.

The size that’s worthwhile for conserving and managing a prairie habitat will depend on the conservation goals. Small patches will have trade-offs - they are restricted in their potential to provide a complete set of ecosystem processes, but this is dependent on the management strategy and resources. While small patches may have some limitations, they are, nonetheless, potentially good places for climate refugia, migration pathways, green infrastructure, and other ecosystem services for a range of species. While some prairie species require large patches of habitat, like many grassland birds, others are quite content in a postage-sized inner-city patch - beetles, spiders, and some insects come to mind. And while not all species may call it home, a prairie habitat can be utilized occasionally by migrating animals. Bobolink, for example, require large patches (over 100 acres) for breeding, though they may briefly visit small patches when migrating. Pollinators, especially those with far reaching migratory pathways, like monarchs, have been known to breed in small backyard gardens. The location of the small patch site is also important. Proximity to the lake, for example, is a good location for migratory birds even if the site isn’t the “best choice”.

The diversity of responses needed to survive climate shocks are present in large, highly biodiverse ecosystems. But when patch size is limited by urban development or other landscape matrix issues, improving connectivity to other prairie patches is a next best approach. Connectivity allows individual species to move between populations, and this is particularly crucial for small urban plots or native landscaping within metropolitan areas. Although invasive species may also use connectivity as a route to invade a system, railways and other built environment activities have already provided plenty of access points. Thinking about small habitat patches at the landscape scale is important to create opportunities to build a network of habitats that add up to something bigger. This could be accomplished in phases, building from collections of small habitats. Many prairie restorations in this region are more limited in scope due to logistical issues - it takes a lot of resources (where to get all the native seed, for example) and a considerable amount of time to do all the preparation and seeding. Therefore, habitats are usually accomplished in phases, restoring smaller patches that are connected later.

Another strategy for making the most of small prairie patches is to consider the habitat shape. Creating, adding to, or expanding on prairie habitat in a way that creates a broader, rounder habitat shape can be a good way to minimize small patch limitations. This is because a rounder habitat reduces vulnerabilities by decreasing negative impacts on broad areas in the center, such as invasive encroachment, predation, and pesticide or herbicide overspray. A long skinny habitat is more prone to allowing these to penetrate across the entire patch. Even connecting two small patches together to create a more contiguous space will result in a more secure prairie.

The landscape surrounding the prairie habitat may frequently be fragmented by roads or other development – but this region also has some incredible urban forest and wetland habitats. Ecotones are the transition between two biomes, and these boundaries, boarders, gradients, and margins are where some of the most distinct ecosystem functions occur, such as predation, or where there is a scarcity of activity, such as nesting. Focus on these areas is vital to reducing invasive encroachment, improving patch sizes, creating connectivity, or fostering climate refugia. And the shape of a prairie patch is more important when it is on the smaller end, generally less than 1,000 acres, in large part because of the edge effects near ecotones.

Ultimately, bigger will always be better for most prairie goals since larger plant and animal populations need a larger habitat. Creating or conserving large patches is one of the best ways to support the wide array of ecological functions needed to be resilient to climate impacts. In the meantime, we can do a lot with a network of small and mighty habitats that share and enhance this fragmented landscape with millions of people.

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