Dale Worledge

Coarse root biomass for eucalypt plantations in Tasmania, Australia: sources of variation and methods for assessment

This study develops a feasible method for evaluating coarse root biomass (roots >2xa0mm diameter) of well established plantations of eucalypts and then examines coarse root biomass variability across tree age and size, fertilization treatment, species and site for Eucalyptus globulus and E. nitens in Tasmania, Australia. The most efficient sampling protocol consisted of rootball excavation and soil coring for bulk coarse roots, which when compared with total tree excavation estimated total coarse root biomass contained inside the sampled area to within 10%. Across all treatments, an average of 76% of the coarse root biomass was located within the rootball. The majority (>65%) of the coarse roots outside the rootball were located in the surface 20xa0cm of soil. When size class distribution was examined, 75% of coarse root biomass was found to occur in the larger (20+ mm) diameter size class, a size class that displayed considerable spatial heterogeneity. At the stand level, coarse root biomass ranged from 2.18 to 7.38xa0kg m−2 depending primarily on tree size but also on fertilization treatment, species and site. It is estimated that allocation to coarse root biomass production was around 0.2xa0kg m−2 year−1 (around 6% of estimated NPP) for the E. nitens stands examined in this study and around 1xa0kg m−2 year−1 (around 20% of estimated NPP) for the E. globulus stand examined. Robust relationships using above-ground parameters could be used to predict coarse root biomass regardless of fertilization or site, but species changed the relationship.

Growth and water use of Eucalyptus globulus and E. nitens in irrigated and rainfed plantations

Summary Early patterns of growth and water use of Eucalyptus globulus subsp globulus Labili, and Eucalyptus nitens (Deane and Maiden) Maiden were measured for the first four years in a plantation established on a low rainfall site in south-east Tasmania. Half the plantation was irrigated to maintain soil water deficits at levels where available water did not limit growth: the other half was subjected to a series of water stress cycles which were interrupted by rainfall or terminated by supplementary irrigation to end severe drought stress. Height of E. globulus was greater than that of E. nitens irrespective of water status. For both height and diameter, differences due to levels of available water remained insignificant until the third year of growth. Increments in volume were significantly higher in E. globulus than E. nitens in the third and fourth year of growth and these differences were more apparent in the rainfed than the irrigated treatment. However there were no differences in water use between ...

Soil water under forests (SWUF): a model of water flow and soil water content under a range of forest types

A new model (soil water under forest, SWUF) is suitable for predicting the daily water content within both surface soil layers and the sub-soil under a range of forest types, and is suitable for use in models of mineralisation of soil organic matter as well as models of forest production. This empirical cascading bucket-type model was largely derived by combining algorithms from well-tested models for prediction of soil water under agriculture. However, it extends these to predict the water content of the litter layer, and the influence of the litter layer, weeds and understorey, and site mounding, on SWUFs. Measurements of soil water content under native forest, and pine and eucalypt plantations, were available for 59 sites across southern Australia. The model was parameterised to about half (27) of these datasets, while the remainder (32) were used for validation, for which the model explained 86% of the variation in observed water content. Sensitivity analysis indicated that important input data required were the observed upper limit of water content, bulk density, and climatic data, particularly solar radiation. The estimated area of ground that was covered by litter and canopy were also important inputs.

Wood production per evapotranspiration was increased by irrigation in plantations of Eucalyptus globulus and E. nitens

Wood volume growth per unit evapotranspiration was calculated from water balance and growth measurements in irrigated and water-limited Eucalyptus globulus and E. nitens plantations in the 3rd, 4th and 5th year of growth. Wood volume growth per unit evapotranspiration (plantation water productivity) was increased by irrigation for both species in the 3rd and 4th growing year but only in E. nitens in the 5th year. Irrigated trees required significantly less water than water-limited trees to produce 1xa0m3 of wood. At the same site, stomatal conductance was significantly greater in irrigated compared to water stressed trees through spring, summer and early autumn of each year. These data provide indirect evidence that leaf-scale measures of water-use efficiency are not well correlated with stand-scale measures of plantation water productivity. This was probably due to increased proportional allocation of assimilated carbon to stem wood in the irrigated compared to the water-limited stands. These results are consistent with recent studies in Brazil and Australia and suggest that plantation management systems, inclusive of tree breeding, that maximise growth rather than leaf-scale water-use efficiency, will also maximise the amount of wood produced from each unit of water used by the stand.