Summary Rates of N mineralization and of N uptake were measured in situ in three eucalypt forests and a cool-temperate rainforest, and were correlated with productivity. All of the soils had a high capacity for immobilization, and nitrification was insignificant. Changes in both organic and inorganic P fractions during in situ containment of soils were small. While the concentration of inorganic available P was not related to forest productivity, a measure of labile organic P was closely related both to productivity and to P in the microbial biomass. Estimates of inorganic- and organic-N availability were highly correlated with independent estimates of organic-P availability, and the results are discussed in relation to biological control of nutrient availability in the surface horizons of forest soils. 相似文献
This study examined the effect of wildfire and salvage harvesting on runoff generation and sediment exports from three small forest catchments in south-eastern Australia. In 2006, wildfire burnt a radiata pine catchment and two adjacent natural eucalypt forest catchments which formed part of a long-term hydrological research project. Subsequently, only the pine plantation catchment was salvage harvested. The combined effect of fire and salvage harvesting in the pine catchment caused a substantial increase in runoff compared to the burnt eucalypt forest catchments and pre-fire conditions, particularly in response to high intensity, short duration summer storms. Post-fire maximum suspended sediment concentrations from fixed-interval sampling greatly exceeded pre-fire values for both eucalypt and pine catchments, while sediment (suspended and bedload) exported from the pine catchment exceeded each of the eucalypt catchments by a minimum of 180 and 33 times. However, the export increase was probably closer to 320 and 71 times based on a survey of eroded channels in the pine catchment combined with measured post-survey exports. Notably, seven summer storm events accounted for approximately 80% of the pine catchment sediment yield. Hillslope process measurements indicated that the highest runoff velocities occurred in log drag-lines formed by cable harvesting, while soil water repellency was more extensive in the harvested pine catchment than in the adjacent eucalypt catchment. The latter effect probably resulted from higher burn severity in the pines combined with reduced soil moisture due to less shading after harvesting. Runoff modelling indicated that the log drag-lines acted as an extension to the drainage network and increased peak flows at the harvested catchment outlet by 48% for a high intensity summer storm event, while substantial reductions in modelled runoff were achieved through increasing the hillslope surface roughness coefficient. It is recommended that post-fire salvage operations should avoid the formation of log drag-lines when using cable harvest techniques and maximise surface cover to limit increases to runoff, erosion and catchment sediment exports. 相似文献
Techniques for rapid visual assessment of fuel characteristics have a broad range of applications in wildland fire management and research. We developed and tested a technique for assessing forest fuels which provides hazard ratings for distinct layers within the overall fuel complex, including bark, elevated shrubs, near-surface and surface (forest litter) fuels. These layers are comprised predominantly of fine fuel particles <6 mm diameter. The technique was used to model fuel accumulation in dry eucalypt forest of Eucalyptus marginata at two locations with contrasting understorey structures. We found that visual fuel hazard ratings described patterns of fuel dynamics over time in a similar fashion to models for fuel load accumulation. Visual hazard ratings can be related qualitatively to factors that reflect the difficulty of fire suppression by experienced fire fighters including visibility through the forest, access, difficulty of working machinery, flame height and spotting potential. The ability to relate hazard ratings to fire spread prediction needs to be tested. 相似文献
This study was carried out to explore the possibility of making cement-bonded wood-wool composite building products using eucalypt (Eucalyptus camaldulensis) and poplar (Populus deltoides). The experimental design consisted of three treatments - ratio of wood-wool mixture, percentage concentration of cement, and calcium chloride (CaCl2). The mechanical properties in terms of modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond (IB) strength were investigated. The ratios of wood-wool to cement were 40:60 and 60:40 by weight. The addition of the woody material to cement clearly reduced the maximum hydration temperature and increased the time to maximum temperature. Eucalypt was generally less compatible with cement than poplar wood. Test results showed that boards made with poplar wood-wools had superior properties compared to the eucalypt and mixed wood-wools. The presence of eucalypt in mixture of woody materials typically resulted in decrease in mechanical properties. It has been noted that a dose of 5% of CaCl2 by weight of cement can enhance the effect of cement. Application of Duncan's Multiple Range Test for the mean values of the results showed that the effects of all variables and their interactions on the mechanical properties in terms of MOR, MOE and IB were highly significant (p ≤ 0.01%). The mechanical properties of most produced boards were found to satisfy the minimum requirements of ISO standard. 相似文献
Optimum ages for early combined-trait selection were derived for a breeding objective of reducing the total cost of unbleached eucalypt kraft pulp, assuming typical heritabilities and age-age genetic correlations for basic density and growth. The optimum biological selection age, the selection age where average annual gain is maximised, was four years for an assumed rotation age of 15 years. The optimum economic selection age, the selection age where the present value of all future gains is maximised, was three years. These conclusions were relatively robust to changes in assumptions used in analysis. 相似文献
Lack of information concerning root growth of trees limits our knowledge of plant development and fertilizer response. The objective of this work was to study root growth dynamics of an E. urophylla forest after harvesting and the supply of nutrients from the roots and the soil to the new sprouts originating from the stumps. About 7-year-old eucalypt trees were felled and the sprouts and roots were sampled at 0, 60, 120, 180, 240, 330 days after harvesting. The roots were separated into fine roots (<1 mm), medium roots (1–3 mm), coarse roots (>3 mm), and taproot. Nutrient supply to sprouts from the old roots and the soil was calculated based on the change in nutrient content of the roots with time and accumulation of nutrients in the sprouts. Fine, medium and coarse root biomass increased with time after harvesting. However, the increase was more pronounced with fine roots. Between harvesting and day 60 of the new growth, all nutrients allocated to the sprouts, excluding potassium, were supplied by the soil. K was the nutrient most dependent on root reserves for the initial growth of sprouts. The contribution of the old roots to N, P, Ca, and Mg accumulation in the sprouts increased between day 60 and 120. At 330 days after harvesting, about 9.2, 23.9, and 12.6% of the N, K, and Mg, respectively, that had accumulated in the sprouts were supplied by the roots, while all P and Ca were supplied by the soil. 相似文献
From a sample of 665 hollows found in 154 jarrah (Eucalyptus marginata) and 85 marri (Corymbiacalophylla), we identified 204 hollows in 84 trees that were potentially suited to one or more of 10 species of hollow using birds and mammals. Occurrence of these hollows increased with tree age, tree size, and species (marri bore more usable hollows than jarrah) and increased amounts of dead wood in tree crowns. Hollow occurrence was most likely in trees with moderately senescent crowns with damage to intermediate sized branches, and the largest hollows were more likely to occur in more highly senescent crowns. Evidence of termite invasion at the tree butt was not related to occurrence of hollows. For all but one of the birds and mammals we considered, dead trees were no more likely than live trees to contain hollows.
Our study indicates that for the purpose of forest management planning, 130 years can be taken as the typical minimum age for the formation of usable hollows in jarrah and marri. The current minimum prescribed diameter for “habitat trees” (trees retained in logged areas to supplement existing hollows), which corresponds to a mean age of 171 years, is thus a realistic minimum size for these retained trees. We recommend raising the prescribed range of crown senescence for retained habitat trees to increase the probability of providing large hollows suited to large species such as red-tailed black cockatoo, and common brushtail possum, and maternal hollows used by smaller species. Retaining the largest trees with appropriate crown attributes will substantially increase the probability that these trees will bear usable hollows. 相似文献