Resource competition is an important structuring mechanism in communities of insects living as larvae in ephemeral resource patches. Old-growth forest and recently burnt forest, two important boreal forest habitats, differ in several ways that could affect the intensity of resource competition in saproxylic (living in dead trees) Coleoptera. I studied the level of density-dependent effects in an experiment in two burnt-forest sites and two old-growth forest sites. A total of 140 bolts (0.5 m lengths of Norway spruce, Picea abies, bole) were exposed to colonization by saproxylic Coleoptera for increasingly longer times: 0.5, 1, 2, 4, and 8 weeks. Density (number of emerged Coleoptera per bolt) increased with increasing exposure time in a forest-type-specific manner. The increase showed concave-down linearity (the increase leveled off) in the old-growth sites, but a concave-up continuous increase in the burnt-forest sites. This showed that density-dependent effects, and possibly the intensity of resource competition, were more important for saproxylic Coleoptera in the old-growth-forest bolts than in the burnt-forest bolts.