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Counting Eucalyptus obliqua tree rings at Warra. |
Image: Leigh Edwards |
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Project summary:
Age and stand structure were investigated in five multi-aged wet Eucalyptus obliqua forest stands within the 200 ha Warra silvicultural systems trial site. Ring counts determined tree age and size relationships. The forest structures included several regrowth (up to 110 years old) and several possible oldgrowth (>110 years old) cohorts. All five stands had cohorts arising from fires in 1934 and 1898, as well as older trees pre-dating the 1898 fire. A 1914 cohort was also present in four of the stands. There was a large diameter range within any single regrowth cohort and a large overlap in diameter range between regrowth cohorts across all five stands. This indicated that age inferences based on tree size alone are unreliable.
Tighter diameter ranges for cohorts were observed on a plot basis, indicating that diameter and age are more closely related on a stand scale. The relationship between age and diameter was much stronger for dominant and codominant trees than for subdominant and suppressed trees. The measured age range of individual regrowth cohorts varied from seven to ten years. This variation was attributed to a combination of ring-counting error, variable growth rates to achieve the sampled stump height and to protracted germination periods following non-stand-replacing fires. The ring counts for oldgrowth trees were of low reliability due to the presence of hollows, rot and narrow annual growth rings. The counts indicated that eucalypts originated, presumably after wildfires, in each century from the 1500s to the present. There has been a modest increase in fire frequency at the site in the 200 years since European settlement.
Methodology: Ring counts were conducted on stumps from 14 to 279cm in five stands at the Warra SST. Fifty-six E.obliqua stumps were sampled from five 0.1 ha plots on which the diameter and crown class of trees greater than 10 cm dbh had been assessed prior to felling.
Datasets: None available.
Publications: Alcorn, P.J., Dingle, J.K. & Hickey, J.E. (2001). Age and stand structure in a multi-aged wet eucalypt forest at the Warra silvicultural systems trial.Tasforests 13: 245-260.
Harris, S., Allen, K., Baker, P., Bird, T., Bowman, D., Connolly, A., d’Arville, L., Harwood, C., Rozefelds, A. & Wardlaw, T. (2009). Guidelines for collecting and conserving dendrochronology samples from Tasmanian public reserves. Tasforests 18: 145-157.
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