Saproxylic Diptera assemblages in a temperate deciduous forest: implications for community assembly

Saproxylic insects, those that feed on wood or bark, compose a large proportion of forest organisms. Flies (Diptera) are often the most abundant and species-rich groups in forest microhabitats, yet most work to date on saproxylic insect diversity and ecology has focused on beetles (Coleoptera). We compared saproxylic Diptera assemblages reared from two tree species (sugar maple and American beech) at two stages of decay (ca. two years, and ca. six years after death) for a total of 20 logs in an eastern Canadian Nearctic old-growth forest. We found that communities are distinct within both species type and decay stage of wood. Early decay stage wood is more variable in community composition than later decay stage; however, as the age of the decaying wood increases, the abundance of Diptera increases significantly. Most indicator species are discernible in later decay stage and wood type. Both stochastic and deterministic processes seem to play a role in community of temperate deciduous forests. To retain the highest saproxylic Diptera diversity in a forest, a variety of decaying wood types at different stages of decomposition is necessary.