Editor’s Note: Mima Mounds near Littlerock, Washington, is one of several prairie landscapes in the Salish Sea region. As described in a previous article, Bringing Back the Riches of the Prairies, a unique community of plant species inhabits the gravelly soils deposited by glaciers during the last ice age. During early spring, prairies are carpeted in wildflowers. What happens on the prairie later in the year, when the spring beauties have gone to seed?

A spring prairie bouquet of desert parsley (yellow flowers at left), common camas, and balsamroot (large yellow flowers at right). photo by Thomas Noland

The Mima Mounds Natural Area Preserve looks very different in August than in May. In May, a carpet of blue camas and yellow desert parsley shimmers in the sun. The grass is green and lush; small trees here and there show off their new leaves.

Mima Mounds in late summer. photo by Thomas Noland

Reindeer lichen. photo by Thomas Noland

Harvest brodiaea. photo by Walter Siegmund, Creative Commons. License at Creative Commons Legal Code

Bracken sporting fall colors. photo by John F. Williams

If you walk through the Preserve with Wilderman in August, he’ll show you where native species are thriving. Here, there’s a thick carpet of reindeer lichen. There, clusters of harvest brodiaea. The cooler and wetter north sides of the mounds are dense with western bracken ferns. Tiny red berries are just starting to appear in patches of kinnikinnick. Native Roemer’s fescue and invasive grasses grow side by side.

where is the summer nectar?

What you won’t see in late summer, though, are large numbers of nectar-bearing flowers. In spring, mild weather and reliable moisture encourage both nectar-bearing plants and the insects that depend on them. Later in the summer, warmer and drier weather leaves emerging insects with fewer choices. Native plants like spreading dogbane and pearly everlasting are rare or entirely absent. Non-native plants like tansy ragwort, a European weed that’s toxic to livestock, can be important food sources for pollinating insects.

It’s not clear whether the limited availability of summer nectar sources is natural or a symptom of the degraded state of most Puget Sound prairies. Has this ecosystem niche always been relatively empty? The question requires further investigation. For rare summer butterflies like the valley silverspot and the Puget Sound fritillary, it’s a matter of survival.

Herbarium collections suggest that the prairies were once more diverse. Susan Waters, founder and senior research ecologist at Quamash EcoResearch, cautioned that those collections aren’t necessarily representative, though. Collectors often focus on plants that are showy or unusual in some way. Common plants, because they are common, are less noteworthy and less likely to appear in collections.

Moreover, herbarium collections cover a limited time period, only back to the late 1800s in Washington state. The Puget Sound prairies first appeared around 16,500 years ago. As glaciers receded, they left well-drained, gravelly, nutrient-poor soil. Very different from the rich mix of clay and organic material found in wet lowland meadows, these “prairie” soils support their own unique and diverse ecosystem.

Camas flower. photo by Thomas Noland

how does restoration help the prairie?

We don’t know what species were present in pre-settlement prairies, but we do have reference sites that have been either preserved intact or have been under restoration for fifteen years or more. Waters compared these sites to more recent prairie restorations and found an explosion of previously unrecognized diversity in both plant and pollinator species.

Pollinators like bumblebees visit flowers where they can find them among the grasses on summer prairies. photo by Thomas Noland

what about climate change?

Neither Waters nor Wilderman was willing to predict the impact of climate change on Puget Sound prairies. Warmer and drier summers are likely to challenge native plants accustomed to milder conditions. Different plants have different requirements, though, so not all will respond to climate change in the same way. Some plants may bloom later or earlier, some for longer or shorter periods. The overlap between flower emergence and the emergence of pollinator species may change. Will insect populations be decimated if their preferred food is unavailable? Or will non-native invaders help fill gaps in the insect food supply? Waters’s research suggests that both outcomes are possible.

Back at Mima Mounds, Wilderman says that the tansy ragwort is allowed to stay, for now, carefully segregated from the Preserve’s neighbors. With its help, he hopes valley silverspots and Puget Sound fritillaries will be waiting as the prairie’s native plants recover.

The Mima Mounds Natural Area Preserve is located in Thurston County, south of Olympia, Washington. It includes a ½-mile ADA-accessible paved loop, with additional gravel trails to the north and south. Parking requires a Washington state Discover Pass.

The nearby Glacial Heritage Preserve is open to the public only on Prairie Appreciation Day, the second Saturday in May.

Most intact Puget Sound prairies are in the South Sound, but the Pacific Rim Institute is in the process of restoring their 175-acre preserve on central Whidbey Island.

Katherine Derbyshire is a Seattle area freelance writer focused on science and technology. Follow her climate coverage on Twitter @carbon_to.

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