Optimum time for sampling floristic diversity in tropical eucalypt woodlands of northern Queensland

Abstract

The timing of vegetation sampling in highly seasonal environments is one of the critical factors in determining the proportion of the flora captured in a single sampling. Four sites were located within a 20 km radius of Mareeba, north Queensland and sampled every three months for three years. The sites were located in a variety of eucalypt communities and across an altitudinal range from 380 to 840 m above sea level. In these eucalypt communities experiencing highly seasonal rainfall typical of the tropical savannas, vegetation sampling in the early dry season (May) maximises the diversity of flora recorded. The ANOVA analysis showed a significant effect of month of sampling for the number of ground taxa recorded (P < 0.005). There was significant variation (P < 0.005) in species diversity between the sites but in all four study sites the May sampling recorded greater than 84% of the total recorded flora, whereas the November samplings accounted for between 21% and 56% of the flora. This supports the experience of other researchers that a May sampling is near optimum for sampling the ground layer floristic diversity in tropical eucalypt woodlands.

Most vegetation survey and mapping data are of necessity collected at less than ideal times of the year due to access and resource issues. Care must be exercised in using data collected in the dry season, as only a limited proportion of the total ground flora is likely to be recorded. Studies designed to capture the full florisitic inventory of species present in these highly seasonal environments need to budget resources and plan to access these environments in the late wet season.