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White D.A.,CSIRO | White D.A.,Cooperative Research Center for Forestry Ltd. | Battaglia M.,CSIRO | Battaglia M.,Cooperative Research Center for Forestry Ltd. | And 7 more authors.
Tree Physiology | Year: 2010

This paper reports on variation in leaf area index (L) in five Eucalyptus globulus Labill. plantations in response to application of nitrogen, thinning at age 2 years and variation in climate wetness index (the ratio of rainfall to potential evaporation). Observed L is compared with: (i) L predicted to optimize net primary productivity for a given average annual temperature, annual water use and potential evaporation (Lopt) and (ii) L calculated as a linear function of climate wetness index (Leq). L peaked in fertilized plots at between 4 and 5 years of age or immediately after canopy closure. The value of L from canopy closure to age 8 years was not strongly related to annual rainfall or climate wetness index. At two sites with total soil nitrogen <1.2 mg g -1, L in fertilized plots was about two units greater than in unfertilized plots. This difference persisted until measurements ended in 2004 when the trees were 8 years old. The L of plots thinned to 300 and 600 stems ha-1 at age 2 years recovered quickly and was not significantly different from L in unthinned plots when the trees were 8 years old. Lopt was a good predictor of the leaf area index of 8-year-old plots of E. globulus when nitrogen and phosphorus were non-limiting (model efficiency (EF) was 0.5). For the same plots, Leq underestimated observed L by an average of two units, and the model efficiency was low (-3.25). Data from two nitrogen-limited sites demonstrated that for fertilized plots Lopt (EF = 0.6) was a much better predictor of L than Leq (EF = -3.36). At the same sites, Leq (EF = 0.42) was a better model for predicting L of unfertilized plots than Lopt (-3.59). These results provide evidence that comparing observed L with Lopt can identify stands limited by factors other than growing climate. © The Author 2010. Published by Oxford University Press. All rights reserved.

Drake P.L.,Murdoch University | Drake P.L.,Cooperative Research Center for Forestry Ltd. | Drake P.L.,Bentley Delivery Center | Mendham D.S.,Cooperative Research Center for Forestry Ltd. | And 7 more authors.
Plant and Soil | Year: 2012

Aims: Growers of Eucalyptus globulus Labill. plantations can establish second and later rotations from coppice or by replanting with seedlings. At most locations where E. globulus is grown commercially, water availability is a major driver for productivity. Thus growers must consider which reestablishment technique will maximize productivity whilst sustaining site resources for subsequent rotations. In this study we aimed to compare the stand-scale water balance components of young coppice and seedling E. globulus. Methods: A second rotation E. globulus coppice and seedling trial was monitored for two successive seasonal cycles. Coppice and seedling plots were instrumented with sap flow- and meteorological-sensors so that stand-scale water balance components could be estimated on a daily time step. Results: Stand-scale transpiration rate (E) and rate of interception (E I) were larger in coppice compared to seedlings, but the rate of soil evaporation (E S) was lower. At approximately 2 years of age each coppice stump was reduced to a single dominant stem, a standard management practice for E. globulus growers, which reduced stem biomass by approximately 70% and caused E to fall to a value approximating that in seedlings. The cumulative transpiration of coppice was 425 mm greater than seedlings up to 34 months of age. Without the coppice reduction (down to one stem/stump), we estimate that the difference would have been much greater. The water-use efficiency of stem production (WUE stem) was greater in young coppice compared to seedlings but this benefit is likely to be offset by the loss of biomass (and thus transpired water) during coppice stem reduction. Conclusion: Under the conditions of this study, which included reducing coppice to a single stem, reestablishment with seedling E. globulus resulted in a higher water-use efficiency of stem biomass production compared to coppice of a similar age. © 2011 Springer Science+Business Media B.V.

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