Snail populations, beech litter production, and the role of snails in litter decomposition.

Abstract

The population densities of snails living in beech litter were studied form March 1968 to April 1969. Litter production over one year was measured and the role of snails in litter disappearance assessed.Snails were extracted from litter using a modified Vágvölgyi (1952) flotation method, extraction efficiencies being 84%. The mean annual population density of the twenty-one species of snail recorded on the main sampling site was estimated at 489/m2. Carychium tridentatum was the most numerous species, with a mean density of 200/m2. Acanthinula aculeata, Punctum pygmaeum and Vitrea contracta also had fairly high mean densities. The mean annual biomass was 699 mg dry wt./m2 or 278 mg ash-free dry wt./m2. Hygromia striolata and Oxychilus cellarius/alliarius were the most important species in terms of biomass on the main site. Within the limits of accuracy imposed by the sampling regime the population densities of four out of five of the species (C. tridentatum, A. aculeata, V. contracta, Retinella pura) studied remained unchanged throughout the year, whereas P. pygmaeum had a significantly higher autumn population. C. tridentatum populations were highly aggregated at all times of the year, most markedly so in June. Other species were aggregated at certain times of the year only. Samples taken from other sites showed total population densities of snails ranging from 185-1082 snails/m2.A total tree litter production of 652 g/m2/annum was recorded of which 584g/m2/annum was of beech material. 72% fell in the October-December period. 58% of the beech litter-fall was leaves, 5.2% bud-scales, 27% fruits and 10% twigs and bark. Summation of appropriate field layer peak standing crops amounted to 23.3 g/m2. This was considered as potential litter and was equivalent to 3.4% of the total litter input. The litter standing on the woodland floor in Septermber 1968 was 2,700 g/m2, hence, assuming a steady state, litter turnover time was estimated as 4.5 years.It was calculated that the total snail population ingested 0.35-0.43% of the annual litter input, of which 49% was assimilated. The role of the individual species is examined in relation to concepts of "key species" in ecosystem functioning. The possible role of slugs in decomposition processes is also discussed.