Presence or absence of dead trees is not a criterion for ecological similarity. Light conditions for tree regeneration is neither the sole nor necessarily the most important effect of any disturbance nor is fire the only natural disturbance that affects forests. The keystone element in a forest is not regeneration conditions but structure, the spatial arrangement of trees, living and dead, vertically and horizontally, across the landscape. Natural forests display a broad spatial diversity in both the horizontal and vertical dimensions, in large part from the influence of disturbances. This complexity is in turn crucial for biodiversity, the living things in the forest.
Disturbances are thus more than just events that kill trees.
They are central processes that make regeneration possible and create structures and conditions in the forest that other species need. Wind can blow down a couple of trees, creating a gap in the canopy where light can reach the forest floor. Shrubs and herbs can thrive in the opening and in turn create hiding cover and food for birds. Several tens of metres away, the direct opposite may occur, a dense patches of trees that grew up in a gap formed some time ago and now shade out the understorey. A fire can burn an extensive area, leaving canopy trees unaffected but remove all the understorey.