Gl Unwin

Response of blackwood (Acacia melanoxylon) regeneration to silvicultural removal of competition in regrowth eucalypt forests of north-west Tasmania, Australia

Saplings of blackwood (Acacia melanoxylon) responded positively to release from competing young Eucalyptus obliqua in native forests of north-west Tasmania. In the treated area, 6 years after establishment of the regrowth forest on a cleared and burned seedbed, the young emergent eucalypts were culled by stem injection of herbicide. The dense sub-canopy (principally Pomaderris apetala) was also removed in two gap treatments (3.6 and 7.2 m diameter); each treatment applied to 27 single tree plots. During the 6 years following silvicultural treatment, periodic annual increment (PAI) of blackwood stem diameter increased from 0.8 cm per year in the untreated area to 1.4 cm per year where eucalypts (only) had been removed. The additional removal of the sub-canopy increased blackwood PAl (diameter) to 1.6 cm per year in the small gaps and 2.1 cm per year in the larger gaps. These are statistically significant increases of 75, 100 and 160%, respectively. However, the larger sub-canopy gaps produced heavier, broader blackwood crowns, increased branch size and retention and reduced the length of branch-free bole. Maximum blackwood diameter and volume gains were therefore achieved at the expense of tree form and future log quality. In contrast, the removal of competing eucalypts (only) produced a smaller stem diameter response, but the remaining dense sub-canopy maintained excellent stem form and clear bole.

Throughfall and its spatial variability in a temperate rainforest of simple structure

Abstract There are few throughfall data from southern hemisphere closed-forest, and none from Tasmanian callidendrous cool-temperate rainforest, which has a simpler structure than most primary rainforests. We determined throughfall, measured its local spatial variation, and tested its relationships with rainfall, rainfall intensity, wind speed, canopy dryness, canopy cover, and other structural variables in a cool-temperate callidendrous rainforest in Tasmania. Eighty-two percent of the precipitation was measured as throughfall, which occurred after 2.3 mm of rain fell on dry canopies. The cumulative rainfall in 25 randomly located funnel rain gauges on the forest floor varied from 160 to 567 mm. Canopy cover and other structural variables did not predict the spatial pattern of throughfall. While throughfall in rainfall events was related to rainfall amount and intensity, wind speed did not affect throughfall as a percentage of rainfall. Percentages of throughfall to rainfall over 100 for many low rainfall events may indicate a contribution of fog drip to precipitation on the forest floor. The high local spatial variability in throughfall indicates the mean moisture conditions on the forest floor may not be a good indicator of the potential for localised fire damage.