Density and diversity of soil arthropods as 'biological probes' of complex soil phenomena

Soil is both a resource and a habitat for the plants and animalsof the forest. When we use the word forest, we usually think onlyof trees and wood resources. However, we must also think of thethousands of species of animals that live in, on, and under the trees,and of their functions in the forest ecosystem. No part of the forestecosystem is more diverse than the arthropods that inhabit the soil(Anderson. 1975. Proc. V Int. Coll. Soil Zool.). The most abundantOregon soil arthropods are oribatid mites (250,000/m2; 75-100 spe-cies/m2) and springtails (50,000/m2; 20-30 species/m2). These abun-dances and species counts approximate or exceed diversities re-ported from any terrestrial ecosystem in the world (Petersen andLuxton. 1982. Oikos 39:287-388), probably, in large part, because ofthe depth and complexity of litter in the Northwest. A single core(7.5-cm diameter) is likely to contain over 50 species and a one-ft2sample, 200-250 species, especially if taken from old-growth forests.