When we speak of native grasslands we are really referring to a broad group of ecosystems that include tallgrass prairie, oak savanna, cultural meadows and alvars. All of these ecosystems share some the same plants and animals, but each one has its own unique features and species. Wildlife, both game and non-game species thrive in these grasslands and many that we are familiar with use grasslands almost exclusively or at least for part of their life cycle. Surprisingly, even species we think of as woodland species, such as the American Woodcock (Scolopax minor) use grasslands during several periods in their lifecycle.
Native grasslands are a unique habitat that can be comprised of roughly a dozen species of native grasses and up to 200 forbs (flowers). But only the right mix of the grasses and flowers will provide the optimum habitat for wildlife. Its a fine balancing act between too thick and too thin, too much grass and not enough.
The optimum mix for a grassland is about half the plants being grasses and the other half being forbs. This is also variable depending if its a prairie or savanna, with savanna's having slightly more grasses interspersed with occasional black oak trees (about 20% canopy). If a grassland becomes too thick with grasses birds and animals have a difficult time roaming through the site, having to fly rather than walk among the protection provided by the tall grasses. Its the spaces in between the plants that provide corridors and spaces to move, feed and escape from predators that make native grasslands such a quality spot for birds and small mammals. These spaces also provide ample room for young birds to forage for insects which is a necessity for the protein they provide for growing birds.
If a native grassland becomes too thin (not enough grass) the area becomes an easy target for avian predators and can become a wildlife sink (high predation rates). The tall grasses provide the overhead protection only as long as they are present in the right quantities.
All grasslands need a good component of forbs (flowers). Native grasslands contain flowers with a wide blooming period. Some plants begin to bloom as early as April with others flowering as late as October. This long bloom period provides an extended timeframe for pollinators and other insects to use the area as a nectar source. Attracting insects to these areas is not only key to helping with Ontario's disappearing pollinator species, but it is these insects that provide the food source for a great number of the birds and animals we are creating these habitats for.
In order to gauge the appropriate density of a grassland we can simply apply the "football" analogy. Take a regular sized football and toss it into a grassland about 10 meters from you. If the ball gets hung up in the grass and does not touch the ground then the area can be considered too thick. If the ball lands on the ground and you can still easily see the football, the grassland is too thin. If the ball lands on the ground, but is difficult to see from where you threw it, the grassland is about right. The birds and animals can walk around the grassland, but avian and other predators will have difficulty seeing them.
There are lots of areas in Ontario that can be considered as "old fields". These are typically fields that were once pasture or cultivated fields but have been left unused and have reverted over time into dense stands of goldenrods and asters. While these "old fields" do provide some habitat that mimics grasslands, their densities are usually too thick to provide quality habitat. The monoculture nature of these old fields do not provide the spaces for foraging or roaming that native grasslands do. In the winter, these old fields are usually flattened by the snow providing little overwintering habitat. Native grasslands usually stand tall in the winter, providing lots of nooks and crannies for wildlife to hide and forage for seed. Old fields bloom late in the year, September and October, and do provide good quality areas for pollinators, but their bloom cycle is short lived compared to that of native grasslands.