Use of growth characteristics for predicting plant age of three obligate-seeder Proteaceae species

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Journal Article
Australian Journal of Botany, 2005, 53 (2), pp. 101 - 108
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We tested the ability to predict plant (and hence population) age for three fire-sensitive obligate-seeder Proteaceae species (Banksia ericifolia, Banksia marginata and Petrophile pulchella) in the heath and woodland vegetation of the Sydney region. To do this we sampled the number of growth whorls, as well as other growth characteristics (stem girth and height measurements, and canopy area and volume estimates), in areas of known time since last fire (TSLF). The average number of growth whorls was a very good predictor of plant age for both Banksia species (R2 = 98%, 99%), but this needed to be corrected for linear underestimation in P. pulchella (R2 = 92%). This technique could successfully be applied to these species in similar habitats across a large spatial scale, and so this information can be used to determine the age of a population in areas of unknown TSLF. A sample size of 15 plants was sufficient for accurate age estimates of all species; however, better estimates of TSLF for a particular plant community were obtained when estimates from two or more of the species were combined. We thus provide empirical evidence for the validity and accuracy of the growth-whorl technique for predicting plant age and hence TSLF This information will assist in informing the development of appropriate management strategies for plants in relation to fire. Of the other growth characteristics studied, stem girth was the most reliable predictor; however, in general these other characteristics had wide confidence intervals on the predictions for sites greater than 10 years TSLF, owing to a non-linear relationship with age. © CSIRO 2005.
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