Establishment, suppression and growth of Eucalyptus delegatensis R.T. Baker in multiaged forests .III. Intraspecific allelopathy, competition between adult and juvenile for moisture and nutrients, and frost damage to seedlings

Field and pot experiments were designed to test the relative roles of allelopathy, competition for moisture and competition for nutrients in the suppression and growth of Eucalyptus delegatensis. In pot experiments litter cover was associated with slightly slower growth rates than in other treatments. A fertilization treatment was associated with increased growth rates in both trenched and untrenched situations in a field experiment, but the effect of fertilization was subdued in comparison with the effects of trenching or of total tree removal in the clear-felling treatment. Saplings and seedlings in the forest were under significantly greater moisture stress, as indicated by xylem pressure potential and stomata1 resistance, than those growing in the adjacent clear-felled areas. Surface soils in clear-felled areas had moisture contents above the level which caused seedling stress while surface soils within the forest were often below this level. These findings suggest that adult trees suppress seedling and sapling regrowth largely through their effect on soil moisture. However, another form of seedling growth suppression also occurs in the open as a result of frost damage.