Role of earthworms in moorland soil amelioration with specific reference to the effect of Lumbricus rubellus in soils colonized by birch
Both broad-leaved trees and earthworms are often described as having an ameliorating effect on acidic podzolized soils. The role of earthworms, in particular Lumbricus rubellus, in soil changes occurring after birch colonization of heather moorland was investigated. A highly acid podzol under heather appears to have been converted to a mull or moder brown earth within one generation of birch growth. The crucial change in soil characteristics occurs after about thirty years of birch growth with a dramatic decrease in raw surface humus and consequential changes in other soil factors, such as pH, moisture and porosity. L. rubellus populations increase by about three times from birch stands of twenty-four to thirty-two years. Other earthworm species, noticeably L. terrestris increase steadily in number with increasing age of birch. Investigations into earthworm respiration revealed that the earthworms are not making a large contribution to organic matter catabolism directly by their population metabolism. However, L. rubellus seems capable of consuming much of the annual leaf litter, up to 100% in older birch areas, but it is reckoned to consume only about 1% of the annual reduction of raw mor humus occurring after about thirty years of birch growth. Even considering the stimulating effect that earthworm activities can have on microbial decomposition, it is concluded that the earthworm populations are not high enough to be decisive in mor humus reductions. Earthworms may, however, be important if conditions are intermediate between mor and mull, and also in maintaining an established mull humus system.