UPTAKE OF MOISTURE AND NUTRIENTS BY HIERACIUM-PILOSELLA AND EFFECTS ON SOIL IN A DRY SUBHUMID GRASSLAND

In dry sub-humid environments (<550 mm annual rainfall) in New Zealand , Hieracium pilosella (hawkweed) grows in approximately circular or ir regular shaped patches surrounded by areas of bare soil. The study dir ectly assessed the extent of root distribution, soil moisture, and nut rient uptake in the areas of bare soil zone (''haloes'') surrounding p atches, and how hawkweed affected the soil. The results indicate that H. pilosella exploits the halo areas surrounding the plant patches for a major part of moisture and nutrients uptake. As a result, the soil in the halo zone is drier than that under the plant patch and is relat ively depleted in such nutrients as available phosphorus and basic cat ions. The plant increases soil acidity and soluble aluminium content i n the soil immediately beneath the living patch. The combined effects of reduced moisture, reduced base cation availability, and the high so luble aluminium status and increased acidity of the soil, make the imm ediate hawkweed environment unfavourable for the development of compet ing plant species.