Stand structure, canopy architecture and thinning response in mature Queensland maple (Flindersia brayleyana F. Muell.) plantations

Brown, Peter Leonard. (2002). Stand structure, canopy architecture and thinning response in mature Queensland maple (Flindersia brayleyana F. Muell.) plantations PhD Thesis, School of Integrative Biology, The University of Queensland.

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Author Brown, Peter Leonard.
Thesis Title Stand structure, canopy architecture and thinning response in mature Queensland maple (Flindersia brayleyana F. Muell.) plantations
School, Centre or Institute School of Integrative Biology
Institution The University of Queensland
Publication date 2002
Thesis type PhD Thesis
Supervisor Doley, David
Keenen, Rod
Total pages 217
Collection year 2002
Language eng
Subjects L
270499 Botany not elsewhere classified
620399 Forestry not elsewhere classified
Formatted abstract
Understorey retention has been proposed as an effective strategy to enhance the biodiversity protection services of managed forests. The effect of the understorey on established trees in rainforest plantations is not well understood, but is often assumed to be limited. This assumption was tested in a 67-year-old plantation of Flindersia brayleyana F Muell. at Gadgarra, North Queensland.

Prior to this study the plantation had received no thinning and only minimal and early weed control. Before treatment, mean stem diameter at breast height (DBH) was 36 cm, stand basal area 78 m2 ha-1 and canopy stem density 770 stems ha-1. Understorey species were removed from two areas (brushed treatment) and in two adjoining areas thinning for crown release around selected F brayleyana crop trees reduced total stand basal area by 47 % to 36.5 m2 ha-1 and residual density to 330 stems ha-1 Mean annual DBH increment of released stems during 2.5 years after thinning was 5.1 ± 0.33 mm y-1, as compared with stems in the unthinned stand 0.5 ±0.14 mm y-1 For released stems, 6-monthly wet season and dry season stem diameter increments were linearly related to seasonal rainfall up to 2800 mm per 6 months.

The presence of the understorey had a significant negative impact on DBH increment in crop trees. In the understorey-removed-only (brushed) treatment, mean DBH increment in maple stems was 1.3 mm y-1 or two times that in control trees. The basal area increment for this treatment was 0.42 m2 ha-1 y-1 on a standing crop tree basal area of 54.3 m2/ha. The positive growth impacts of understorey removal on crop tree growth were small in comparison to those achieved through thinning together with understorey clearance which resulted in a 10-fold increase over control trees. The post-thinning basal area increment for maple stems was 0.81 m2 ha-1 y-1 The sample size used in this study was too small to determine whether the effects of the understorey on canopy trees differed between the wet and dry season, or between crown dominance classes, or on two different soil types, basaltic or metamorphic. Therefore, the mechanisms whereby the understorey exerts competitive effects on the canopy remain unknown.

Released trees with a crown ratio (crown diameter: DBH) below 13 did not achieve a mean DBH significantly different from untreated (control) stems. Crown ratios <13 occurred in 23 % of retained stems in the thinned stand and in 63 % of stems in the unthinned stand. Trees with a crown ratio greater than 13 had a mean DBH increment of 5.4 mm/y-1 after thinning. The extent of response in DBH increment, after such a long and severe period of competitive suppression, suggests that F brayleyana has a relatively high level of flexibility to respond to changing competitive conditions. Thinning could result in a stand with a mean DBH of 60 cm in 100 years.

Of 23 crown architectural parameters and competition indices for thinned and brushed F brayleyana, initial crown diameter was the best predictor of DBH increment (R2 = 0.51) with all other significant predictors having R2 values <0.1. DBH was a strong predictor of DBH increment in control or undisturbed stems (R2 = 0.63) and a weak predictor in stems from thinned and brushed plots (R2 <0.1). The implications of these results for managing older tropical plantations or forest regrowth are discussed.
Keyword Queensland maple
Plantations -- Australia

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 17:50:30 EST