Soil-Ph Declines and Organic-Carbon Increases under Hawkweed (Hieracium pilosella)

Changes in soil chemistry in relation to hawkweed (Hieracium pilosella) presence were determined at a site receiving less than 600 mm rainfall where hawkweed was colonising Pallic Soils (yellow-grey earths). pH was significantly lower (by 0.5 units) and organic carbon values were significantly higher (0.7% absolute, 40% relative) within hawkweed patches than in adjacent soil, but there was no significant difference in total nitrogen. These differences are attributed to the change from sparse vegetation dominated by ephemeral annual plant species to continuous vegetation dominated by a perennial.