Volunteer vascular plant establishment on roofs at the University of Saskatchewan

A survey of volunteer vascular plants growing on the roofs of seven buildings at the University of Saskatchewan campus was completed between 24 June and 15 August 2004. The data collected included floristic composition, plant density, plant height, air and subsurface temperatures. Three broad groups of plants were identified: trees and shrubs, common ruderals, and species often associated with marshland. Vegetation composition was similar on all roofs, although unique characteristics were noted depending on the method of construction and time since routine maintenance was conducted. The plants grew well in what appeared to be a very harsh environment. The diversity of marsh plants is directly related to problems in roof drainage. Water drains into the cracks between the styrofoam panels, and because the insulation is impermeable, moisture can remain beneath them with very little loss through evaporation. Despite air temperatures as high as 61 °C, the plants are able to take advantage of this semi-permanent water supply. The importance of gaps between adjacent roofing panels is emphasized by the linear distribution pattern of the plant cover.