their relative contribution to the development of water-stable soil aggregates. Arrows indicate path coefficients, where * is significant at P<0.05, **P<0.01, and ***P<.001. Source: After Miller and Jastrow (1990).

In addition to the presence of mycorrhizal fungi, roots release their own carbohydrates that act as foci for bacterial and fungal activity in soil. The development of links among bacteria, fungi, and soil organic matter to form soil aggregates is greatly enhanced by the presence of readily utilizable carbon. The addition of starch to soils provided an easily obtained source of energy for the growth of bacteria and provided “hot spots” for fungal growth and an increase in the density and mean size of aggregates (Guggenberger et al., 1999). The importance of residual islands of plants and their mycorrhizae or the ability of animals to move mycorrhizal fungal propagules between established and developing plants is thus important during the initial stages of plant recolonization of a highly disturbed system to effect rapid soil accretion and stabilization. These factors were found to be important contributions to the reestablishment of vegetation on Mount Saint Helens after pyroclastic disturbance (Allen et al., 1984; Allen, 1987; 1988).