Wednesday, May 11, 2016

Tallgrass Prairie for Biodiversity

MacForest Tallgrass Prairie Restoration
Carolinian Canada describes “Tallgrass communities” – also known as tallgrass prairies and savannas – as natural grasslands with a great diversity of grasses, wildflowers and animal life.

The site defines prairie as a natural community that is dominated by grasses rather than by trees, as in a forest. Tallgrass prairies are dominated by fire adapted clumping grasses and depend on regular fires to maintain their unique floral composition. Growing with the grasses are many other kinds of non-grassy herbaceous plants known by the collective name of "forbs."

Tallgrass prairie species such as Big blue stem (Andropogon gerardi), Indian grass (Sorghastrum nutans), Switchgrass (Panicum virgatum), Black-eyed Susan (Rudbeckia hirta), Common evening primrose (Oenothera biennis), and Showy tick trefoil (Desmodium canadense) are some of the common species of tallgrass prairie habitat in our area which provide habitat for pollinators and other wildlife—key to maintaining the biodiversity of our native fauna.

Many prairie grasses and forbs are used by a variety of pollinators as egg laying and overwintering sites, and provide abundant seeds eaten by birds and other animals through the fall and winter. But tallgrass prairies are some of the most endangered ecological communities in Canada, with approximately 1 percent of their original extent remaining. Tallgrass Ontario reports that tallgrass communities once covered a significant part of southern Ontario's landscape. Owing to degradation and destruction through agriculture, urban development, invasion by non-native species, and mismanagement, less than 3 percent of the original extent remains in our region, with most remnants existing in small, isolated patches.

Sebastian Irazuzta is a 3rd year PhD student at McMaster University. His research focuses on the interaction between bees as pollinators and native plant species. He is particularly interested in how bees recolonize restored native tallgrass prairie habitat.

Sebastian explains that one reason we see so many bee species in tallgrass prairies is that the clumping grasses create a heterogeneous mix of exposed soil and dense vegetation, which are ideal for many ground nesting bee species. “The need for such habitat is a big concern since urban lawns and gardens may provide flowers but not bare ground nesting areas. Good bee habitat has to have both food sources and nesting sites” Sebastian explains.

At the McMaster forest where Sebastian carries out his research, they are working to restore natural habitat. McMaster University has owned a property on Lower Lions Club road for 50 years—a chunk of land originally a farm sold to developers, who sold it to Mac.  In the process developers had scraped a lot of topsoil off: “Now we have a very flat field of mostly clay, which hold water in the spring and then bakes hard in the summer sun. This is not conducive to growing much,” Sebastian says.

To help ameliorate the soil, they have been experimenting with bio-char because as Sebastian points out, “charcoal mixed into the soil increases the surface area for microbes to live on, retains moisture, and is beneficial for native plants species because carbon holds on to a lot of nutrients.” Tallgrass prairie plants transform the soil; over time the plants themselves will change the acidity and composition of the soil. These grasses are deep-rooted (up to 5 meters) and able to access a lot of water from deep down. As these deep roots die they add organic matter and break up the soil, thus reducing its density and making it easier for new roots and other organisms to penetrate. The situation with tallgrass prairie ecosystems is a “blessing and curse,” Sebastian says. “One of the reasons we have very little tallgrass in Ontario is that settlers quickly realized these areas were very rich and easy to plow under to produce food!” As a consequence, most tallgrass prairies were quickly transformed into farmland.

At the 115 acre property known as McMaster forest, Drs. Dudley and Harvey and their graduate students are re-establishing a complex tallgrass prairie on 10 acres along the southern end of the property.  A mix of 42 species of grasses and forbs, selected for their resistance to deer and tolerance to clay were seeded in 2014.  “At the start you couldn’t see across the property for the dense stand of Buckthorn, which is invasive and prevents other things from growing,” Sebastian says. “Invasive are takers—they don’t provide an optimal food source, nor do they provide habitat for local species.” This non-native invasive species along with a few non-native grasses took over open fields at Mac forest and created an ecologically poor environment.

Back in 2013 lots of volunteers helped with the buckthorn removal – a task that took all year.  With the guidance of the Conservation Authority, they did a controlled burn of many large Buckthorn piles. Tallgrass prairie plants are adapted to fire. Fire gives them a fighting chance because the non-native and often more aggressive, invasive species can not tolerate fire and will be killed off, leaving the fire adapted species to flourish. “We found that our seed mix did much better than the non-native plants that germinated within the burn areas,” Sebastian says.

Along with the Mac Forest, other efforts to restore more of this ecosystem in the Hamilton area are underway. The Hamilton Conservation Authority this year did a second controlled burn of the old gravel pit off Paddy Green Rd. This area has previously been planted with tallgrass prairie grasses and will regenerate with more vigor this summer. Organizations such as The Ontario Tallgrass Prairie and Savanna Association coordinate and support all groups interested in restoring grasslands. Many private land owners are also beginning to see the benefits of gardening with native tallgrass prairie species, and nurseries such as the St. William’s Nursery specialize in locally sourced native species and can provide a wide range of native seeds and potted plants for urban gardening. Currently they have contracts to plant tallgrass prairie habitat along highway lands.

Local threats to biodiversity?

Within urban areas, many native pollinator species depend on our gardens. Often people have a tendency to make things clean and neat in their garden before winter and early in the spring.  Often this involves removing dried stems and adding mulch to bare earth, which are used by some bees to lay eggs or overwinter. “There is now a push to encourage gardeners to hold off on the clean up—a few weeks into May, when bees have emerged,” Sebastian says.

As well, with city planners, the tendency is to be human-centric but it’s worth understanding that these native plants pay off economically as well. Because of their deep roots, many species are hardy when it comes to salt tolerance and drought stress. Native perennials are low maintenance, well adapted to cold winter conditions and require less inputs than ornamentals. Furthermore, city planners can find native perennials suited to a wide range of urban sites. In wetter conditions for example, plants like Blue Vervain (Verbena hastata) are pretty resilient and provide attractive purplish-blue flowers in late summer.

About Bees.

Sebastian’s yearly bee survey documents and compares how bee populations look and change over time in remnant tallgrass prairies and newly restored sites. He is interested in species abundance and richness (the number of different species). These two measures create species Diversity.  As well, Sebastian looks at the link between bee diversity and plant diversity. He collects bees on flowers - using this data to create “plant-pollinator webs of interaction” for different locations.  These webs can provide insight into the health and function of the local ecology and help us understand how newly emerging communities are structured.

The work also involves assessing the types of interactions in the bee community based on functional guilds.  These are groupings of interactions based on bee traits such as size, nesting behaviour, food preference, sociality and parasitism. Sebastian is monitoring parasitic bees, known as kleptoparasites (called Cuckoo bees) as they do not create their own nest and instead lay their eggs in the nests of other bee species. “Because cuckoo bees depend on a range of other bee species to survive they can be seen as the top of the food chain among bees. Finding many cuckoo bees in an area suggests a species-rich environment. Thus these species can be used as a quick way to asses ecological health” says Sebastian.

In comparing populations in remnant sites to the restored site, Sebastian notes a higher plant and bee diversity at established remnant prairie sites. However with the high diversity seed mix used to restore the Mac forest prairie site, he is hopeful for the appearance of a lot of these rare and specialized bees showing up in the next few years.

NOTE: The diversity of floral shapes and flowering times of Tallgrass prairie species provides the basis for the diversity of pollinators, the best known of which are Bees and Butterflies.  However these native plant species also attract a wide variety of other beneficial insects we often overlook such as Beatles, Moths, and Hover-flies.  Showy native plant species such as Wild bergamot (Monarda fistulosa), Butterfly milkweed (Asclepias tuberosa), New England aster (Symphyotrichum novae-angliae), and Culver's Root (Veronicastrum virginicum) provide colourful flower displays, are deer resistant and attract a wide diversity pollinators.