Characterization of soil mesofauna in a xero-mediterranean ecosystem after a 3-year grazzing management

Abstract

A plot of 47.6 ha at the Omayed Biosphere Reserve , 83 km W of Alexandria and 10 km S of the seashore , was sub jested to varying intensities of grazing pressure (sheep and goats) since 1977, as follows : FI, 50 % grazing pressure (GP) preceded by complete protection from 1974 to 1977 ; F2, completely protected since 1974 ; F3, 50 % GP ; F4, 25 % GP ; while FO is the outside free-grazing areas with 100 7o GP. Soil mesofauna were sampled from July 1979 to July 1980 under Anabasis articulcuta and Thymelaea hirsuta, from windward and leeward sides, making a total of 30 samples for each habitat type. The compositional relation of taxa was investigated by the Ascending Hierarchic Classification (ARC) and Correspondence Analysis (CA) methods. Results indicate the effect of proximity , but the main controlling factor in ordination is the intensity of GP, so that the faunal assemblages of all F2 habitats are on one side of the factorial axis and the assemblages of the FO habitats on the other side, with the FI and F3 (including F4) occupying intermediate positions. Some detritivores are disfavoured by complete protection, while some herbivores (or phytophages , or pests), like the seed harvester ants (Messor spp.), are clearly favoured. Accumulation of undecomposed organic matter may eventually lead to deterioration in soil fertility as detritivores (e.g., the sand roach Heterogamia syriaca) are gradually being eliminated. Prescribed burning may be advisable to overcome some shortcomings of complete and prolonged protection.