1. The ecology of common understorey species associated with ridges was compared with species found on lower-slopes and those species occurring ubiquitously in two 4-ha plots in lowland rain forest at Danum, Sabah, East Malaysia (4″ 58â€™ N, 117â€™ 46â€™ E) over 3 years.
2. During the study period one dry period occurred (psychrometer-measured ridge soil water potential, 20 cm depth -0.67 MPa), but other, more severe, dry periods have occurred since records began in 1985 (estimated ridge water potential -1.21 MPa, March 1992). Lower soil water potentials occurred on ridges which had up to 0.22 MPa lower water potentials than lower-slopes (estimated difference March 1992, 0.40 MPa).
3. At dry times, Dimorphocatyx muricatus (ridge species) had higher pre-dawn (-0.21 v. -0.57 MPa; all quoted differences are significant at p