Emergence of morel (Morchella) and pixie cup (geopyxis carbonaria) ascocarps in response to the intensity of forest floor combustion during a wildfire.

We studied the density of ascocarps (mushrooms) of morels (Morchella) and pixie cups (Geo-pyxis carbonaria) as a function of postfire duff (forest floor organic layer) depth in the first 4 y after a wildfire. The great majority of ascocarps of both species appeared in the first summer (2004) after an Aug 2003 fire in predominantly pine-spruce montane stands in Kootenay National Park, British Columbia. The spatial distribution of the ascocarps of both species was strongly biased toward (i) microsites with thin postfire duff and (ii) proximity to standing burned tree trunks. The bases of ascocarps of both species invariably were found just below the surface of the mineral soil. A field experiment in nearby intact forest showed that complete or partial duff removal in the absence of damage to the roots or crown did not lead to ascocarps of either species. We conclude that for both fungal species an unusually large abundance of ascocarps simultaneously requires damage to the associated trees and major duff reduction.