Alvar is the name used for a distinctive habitat formed by a thin covering of soil or no soil at all, over a base of limestone or dolostone bedrock. These alvars support specialized species communities and are found only in the North America Great Lakes Basin, Estonia, Sweden, Ireland and UK. Ontario contains 75% of the alvars in North America.
I find the extreme conditions in which plants can grow in the alvars, especially the open pavement and shoreline alvars, quite fascinating. Pools of water collect in slight depressions in the surface of the rock ‘pavement’ after rain and spring snow melt, and then small amounts of silt and sand accumulate and provide a habitat for plants to take root in the shallow holes, grikes and joint fractures shaped by water erosion. The reason I found the alvars and the plants growing there so fascinating is that they remind me of a rock garden situation, a really though one, with little soil and rooting space for the plants, high temperatures in the summer and more than this with high variation on the moisture levels throughout the seasons.
Many of the alvar plant species are perennials, of which some are more or less confined to this particular environment. For example species like Cirsium hillii, Solidago ptarmicoides and Astragalus neglectus have a high alvar confinement (above 70%), while others like Zigadenus elegans have a low<50 % alvar confinement. Besides knowing and protecting them, the ability to grow in such conditions it is a proof of their adaptability and more of them should be tested into cultivation.
The following images have been taken in the Bruce Peninsula area, in Ontario – it is a gallery that gradually it will be updated with more species.