Vascular plants of a successional alvar burn 100 days after a severe fire and their mechanisms of re-establishment

Abstract

In order to describe the vascular plant community 100 days after a severe fire in alvar woodland near Ottawa, Ontario, we set out fifty one m square quadrats at 5 m intervals along transects at each of five sites and recorded presence and cover of vascular plant species in each quadrat. The woodlands that burned were dominated by Thuja occidentalis, Populus tremuloides, Abies balsamea, Picea glauca, and Pinus strobus in approximate order of importance. The post-fire flora was diverse and mostly native. Although substantial variation occurred in presence, frequency and cover of species between the sites, there was remarkable similarity in a distinctive group of dominants including Populus tremuloides, Geranium bicknellii, and Corydalis aurea. Rare species present in the burned woodland included Astragalus neglectus, Calystegia spithamaea, Carex richardsonii, Corydalis aurea, Muhlenbergia glomerata, Panicum flexile, Panicum philadelphicum, Petasites frigidus, Scutellaria parvula, and Viola nephrophylla. Of these, Corydalis aurea and Calystegia spithamaea were frequent. The development of vascular flora following the fire was a consequence of growth from roots, rhizomes, and root crowns that survived the fire, and seeds buried in the soil. Although abundant in the burned woodland, Corydalis aurea and Dracocephalum parviflorum had not been previously recorded at the site, suggesting that these species are adapted to early post-fire succession, surviving periods of up to 130 years between fires as seeds in a very large and widespread subterranean seed bank. Not only is post-fire succession well underway within a hundred days of a fire, but even in its earliest stages, it appears to serve as a specific niche for a distinctive group of species including some that are rare and restricted. A diverse native flora is involved indicating the importance of management involving removal of woody biomass.