Drought stress is one of the most important factors limiting the survival and growth of plants in the harsh karst habitats of southwestern China. Detailed knowledge about the ecophysiological responses of native plants with different growth forms to drought stress could contribute to the success of re-vegetation programs. Two shrubs, Pyracantha fortuneana and Rosa cymosa, and four trees. Broussonetia papyrifera, Cinnamomum bodinieri, Platycarya longipes and Pteroceltis tatarinowii, were randomly assigned to four drought treatments, i.e. well-watered, mild drought stress, moderate drought stress, and severe drought stress. Midday water potential, the maximum quantum efficiency of PSII photochemistry (F-v/F-m), pigments, osmotic solutes (soluble sugars and proline), cellular damages, and antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were investigated. Drought stress significantly decreased pigments content, but increased the ratio of carotenoids to total chlorophylls in the studied species. After prolonged severe drought stress, the two shrubs exhibited higher F-v/F-m less reductions of midday water potential, and lower increases of malondialdehyde content and ion leakage than the four trees. Prolonged severe drought stress largely decreased accumulations of osmotic solutes and activities of antioxidant enzymes in the four trees, but significantly increased proline content and superoxide dismutase activity in the two shrubs and peroxidase activity in P. fortuneana. The positive relationships were observed among activities of antioxidant enzymes, and between contents of osmotic solutes and activities of antioxidant enzymes. These findings suggested that the two shrubs had higher tolerance to severe drought stress than the four trees due to higher capacities of osmotic adjustment and antioxidant protection. (C) 2010 Elsevier B.V. All rights reserved.