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Keywords:

  • compensatory mechanisms;
  • diversity;
  • drought;
  • rain forest;
  • Intermediate Disturbance hypothesis

Abstract

1 In 1998, the forests of Lambir Hills National Park experienced a severe drought. Between late January and mid-April, less than one-fifth of the normal expected rainfall was received. To investigate the effects of the drought, survival among 6993 trees (≥ 1 cm d.b.h.) in the drought period (1997–98) was compared with survival among 7270 trees in the same area before the drought (1993–97).

2 Mortality rates for the pre-drought and drought periods were calculated using maximum likelihood techniques. Forest wide mortality rates during the drought were 7.63% year−1 as compared to 2.40% year−1 during the pre-drought period. Logistic regression was used to investigate habitat effects. During the pre-drought period, soil type was the most important predictor of tree survival, while during the drought period, slope was the most important.

3 The mortality rate of large (≥ 10 cm d.b.h.) rare trees (< 2 individuals ≥ 1 cm d.b.h. ha−1) did not differ between pre-drought and drought periods, while that of large common trees (> 35 individuals ≥ 1 cm d.b.h. ha−1) increased 6.5 fold in response to the drought suggesting a possible compensatory mechanism maintaining the persistence of rare species. Mortality of large common and rare species however, did not differ significantly during the drought due to small sample sizes.

4 The results of a comparative analysis of the impacts of droughts in four tropical forest sites provide evidence in support of the Intermediate Disturbance hypothesis.