Ant and Earthworm Bioturbation in Cold-Temperate Ecosystems.

In temperate ecosystems, earthworms and ants are the most important organisms for bioturbation. Little is known about how these groups contribute to bioturbation in different environments and to what extent overall bioturbation depends on their diversity. We developed a formula that allows quantification of annual earthworm bioturbation, thereby taking differences between earthworm ecotypes into account. With this formula, we calculated earthworm bioturbation at three sites, each with vegetation types typically found in Northern Europe. Earthworm bioturbation was low (1 Mg dry soil ha−1 y−1) in Scots pine and Norway spruce forests with acidic soil (pH 3.9–4.4) and high (between 15 and 34 Mg dry soil ha−1 y−1) in broadleaf forests, grasslands, alder carr and spruce forests on calcareous soil. Burrowing (endogeic and anecic) earthworms accounted for most of the earthworm bioturbation, and these worms had the highest population densities at moderate-to-high soil pH (pH 5–7.2). Estimates of ant bioturbation at the same sites were based on nest abundance, size and residence time. Mean ant bioturbation varied between 0.2 and 1 Mg dry soil ha−1 y−1, but individual plots had up to 2.4 Mg dry soil ha−1 y−1. In soils with pH higher than 5, the relative contribution of ants to total bioturbation was only 1–5%. Ant bioturbation was higher than earthworm bioturbation only in some forest soils with pH 3.9–4.4. Thus, earthworms appear to be the dominant cause of bioturbation in most types of terrestrial ecosystems in the cold-temperate areas of Europe and when information on local earthworm communities and monthly soil temperatures is available, bioturbation can be quantified using the presented 'earthworm bioturbation formula'. [ABSTRACT FROM AUTHOR]