Nutrition of Eucalypts

Nutrition of Eucalypts

Most eucalypts grow naturally on soils low in fertility. Commercial plantations of eucalypts have been established around the world over a range of climates and soils. These two themes are central to this book.

Nutrition of Eucalypts provides a comprehensive survey of nutritional ecology of eucalypts in their natural environment and in plantations.

The authors, who are all at the forefront of research and development in their fields, are from the various eucalypt growing regions including Brazil, India, China, Spain and Australia. Their text aims at a state-of-the-art presentation.

The book includes a key and descriptions for recognising nutrient deficiencies in eucalypts.

  1. Page vii
  2. Page 1
    Abstract

    Phosphorus is most often the nutrient limiting nitrogen-fixation during the early stages of soil development and plant succession, controlling biomass increment and hence soil accumulation of organic matter in the soil in most ecosystems. The importance of phosphorus in Australian soils has been recognized in determining viability of agricultural production systems and in determining the composition and productivity of natural ecosystems. While Australian forest soils undoubtedly have low total and ‘available’ phosphorus concentrations compared with agricultural soils, it is likely that other continents with similar geological histories have similar phosphorus-depleted soils under forest cover. In Australia, forests are generally restricted to the higher rainfall areas where soils are predominantly acidic, deficient in phosphorus and other nutrients, and are often coarsely textured in the surface horizons. Horizontal and vertical variation in phosphorus concentrations are a feature of all forest soils. Concentrations of organic phosphorus in surface strata of many forest soils exceed those of inorganic phosphorus. In unfertilized soils such as forest soils, much of the inorganic phosphorus is dispersed throughout the soil matrix and cannot be identified using X-ray diffraction or thermodynamic techniques. Selective dissolution techniques are useful for identifying broad classes of phosphorus compounds, but less useful in determining actual composition of inorganic or organic phosphorus compounds present. Organic phosphorus in forest soils is difficult to extract even using strong alkalis and acids. Almost half of the organic phosphorus in soil remains unidentified, present in, or bound to, compounds of high molecular weight. From the limited evidence gained to date by nuclear magnetic resonance (NMR) techniques, it appears that organic phosphorus extracted from Australian forest soils comprises predominantly phosphorus monoesters (inositol phosphorus and some sugar phosphorus compounds). Many of the organic (and inorganic) phosphorus compounds identified in soils are indicative of microbial-phosphorus metabolism. Compared with agricultural soils, the assessment of ‘plant-available’ phosphorus in forest soils has been less successful due to the poorer nutrient-status of forest soils (particularly ‘available’ inorganic phosphorus), lower rates of phosphorus-uptake (per unit time) by trees, the greater volume of soil explored by tree roots, greater mycorrhizal infection of tree roots and greater phosphorus recycling through litter. It has been suggested that more appropriate measures of ‘available’ phosphorus in forest soils may be measurements using biological indices such as enzyme activity or rates of mineralization, measures of easily extractable organic phosphorus or estimates of microbially-bound phosphorus. Other indices based on the kinetics of phosphorus-uptake by plant roots have also been suggested.

  3. Page 31
    Abstract
    Address for correspondence: 107 Central Avenue, St Lucia, Queensland 4067, Australia.

    The geological history of Australia is traced from the Late Cretaceous to the present-day. The broad genus termed Eucalyptus appeared in the Oligocene and became widespread across southern Australia amongst the extensive rainforest vegetation of the early Tertian1. It is apparent from the disjunctions in present-day eucalypt distributions that the subgenera had evolved before the Miocene. Since the Miocene, frequent periods of aridity have reduced the rainforests to refugia, while the eucalypts have ‘exploded’ across the length and breadth of the continent. In gaps in the rainforests, ‘giant’ species of Eucalyptus (in the subgenera Monocalyptus. Renantherac, in the Symphyomyrtus-. Transvcrsaria, and possible in the Corymbia) evolved. The changes in structure and biodiversity of the present-day plant communities, their community-physiological and eco-morphological attributes along ecological gradients of temperature (from the temperate to the tropical climatic region), evaporation (from the arid to the perhumid climatic zone) and nutrient availability (including soils with problems of imbalance and toxicity) have imposed the constraints in which eucalypts have speciated. Many of the species of Eucalyptus are ecological generalists and show considerable plasticity in growth form (from a tree 30 m tall to a low shrub of 2–3 m in height). Ecotypes of species within the subgenera Corymbia, Eudcsmin, Monocalyptus and some Symphyomyrtus, flourish on soils which have been shown to provide inadequate nutrition to agricultural species. Nutrient-conservation strategies (e.g. internal nutrient recycling, the ‘trapping’ of nutrients from decomposing litter by rootlets, especially mycorrhizae, staggered seasonality’ of rootlets and foliar shoots, etc.) have been identified in a number of species. The high magnesium: low calcium ratio of serpentinitic soils is associated with stunted eucalypts and some speciation of ironbarks (Symphyomyrtus. Adnataria) and bloodwoods (Corymbia: Gummiferae). The calcareous, solonized soils which developed after the retreat of the seas in the early Tertiary, have been invaded by mallee species of the Bisectaria and Dumaria sections of Symphyomyrtus. Several mallee or tree species of the section Adnataria (Sympbyomyrtus), related to the savanna woodland eucalypts on medium-nutrient soils, have survived at the edges of the Murray Basin. The nutrient-rich, basaltic and alluvial clay soils impose severe moisture stresses during the first dry season which the young seedlings of only a few species of the Adnataria section of Symphyomyrtus are able to survive. Two species of the Exsertaria section have become prominent along the drainage systems of Australia. Eucalypts in coastal areas may be salt-planed by sea-spray but no eucalypts survive the large amounts of sodium chloride on salt pans inland.

  4. Page 61
    Abstract

    The distribution across Australia of the genus Eucalyptus is determined by a variety of environmental factors but particularly by the availability of water which is strongly influenced by landforms. Landforms play a role in determining the frequency and severity of disturbances, such as fire, that interact with other landform related factors in limiting the distribution of species and communities. Although the growth and distribution of some species of native trees are noticeably affected by the chemical content of soils and their parent materials, it is argued that the chemical content of soils and their related geochemical processes have a smaller role in the nutrition of name forests and woodlands, than the biological processes of nutrient cycling. It is argued that nutrient cycling supplies most of the phosphorus, nitrogen and other nutrients required for tree growth in native ecosystems. There are a number of corollaries to this argument: of the importance of surface soils tor nutrition may be particularly pronounced in plant communities growing on inhospitable landforms and soils; (2) soils with a low concentration of total phosphorus or other nutrient do not necessarily have low availability of that nutrient; and (3) total concentrations of nutrients in parent material or in soils play little, if am, role in determining the distribution and growth of eucalypts and other tree species, furthermore, the concept that soils have an inherent ‘fertility’ or ‘infertility’ is not particularly useful when applied to Australian native plants since it largely fails to recognize the roles of plant anatomy, morphology and physiology, and nutrient-cycling in determining the availability of nutrients. Over biological time scales, rates of carbon and nutrient cycling are related to rates of plant growth. Over geological time scales, carbon and nutrient cycling are key processes in soil development and must be invoked to explain the changes in the proportions of different forms of phosphorus, as well as carbon, nitrogen and sulfur.

  5. Page 77
    Abstract

    Euicalypts have evolved predominantly on the Australian continent where nutrient availability in most soils is low and limits tree growth. Their survival and growth on nutrient poor soils depends on mechanisms which enhance nutrient uptake and contribute to efficient use and retention of nutrients within the tree. An important mechanism contributing to efficient nutrient uptake by eucalypts is the symbiosis between fine roots and ectomycorrhizal fungi. A broad range of fungal taxa form ectomycorrhizal with the eucalypts, and these fungi can occupy different niches in the soil litter layers and utilize a number of mechanisms in enhancing uptake of nitrogen and phosphorus the uptake of nutrients, particularly phosphorus, which are immobile in soils is increases! primarily through greater exploration of the soil volume by the fungal hyphae. Ectomycorrhizae compensate for the lower rooting densities, and lower specific absorption capacities of the fine roots of eucalypts compared with those of agricultural crops. Low absorption capacities of some eucalypts can be attributed to slow growth rates and to the allocation of assimilates to tap roots as a strategy for survival. Eucalypts arc particularly low in the amount of phosphorus contained in above ground components, and generally have lower amounts of nitrogen than northern hemisphere species. Proportionally more of the dry matter and nutrients is contained within roots of eucalypts growing in low nutrient or dry environments than on moister, higher nutrient sites. Foliage contains a major proportion of above ground nitrogen and phosphorus in young trees. Stems and branches of older eucalypts contain most of the trees’ nutrients and they appear to the major sinks for additional nutrients taken up when the supply in the soil is increased. The nutrient requirement of voting eucalypts is met largely by uptake from soils, whereas the biochemical and biogeochemical cycles of nutrients account for much of the nutrient demand of older eucalypts. Strategies which contribute to efficient use of nutrients by eucalypts and to their ability to survive and grow in low-nutrient environments include the genetic regulation of maximum growth rates, the capacity to store and to reuse nutrients in excess of current requirements for growth, and strong development of biochemical cycling. Nutrient retranslocation from senescent leaves and from wood in the transition from sapwood to heartwood are the major components of the biochemical cycling of nitrogen, phosphorus and other mobile nutrients. Retranslocation of phloem-immobile nutrients such as calcium is generally a minor component of nutrient transfers within a tree, although it may be significant in some eucalypt species where there are strong gradients in nutrient concentrations across the wood and bark. Gaps in our knowledge of the nutritional physiology of eucalypts include: a lack of quantitative information on the internal cycling of nutrients; a need for more studies to distinguish between potentially mobile and structurally bound forms of nutrients; and a requirement for better understanding of how changes in the supply of nutrients in the soil, either from nutrient application or other forest disturbance, affect uptake, storage and internal cycling of nutrients by the tree. A better knowledge of eucalypt nutrition will help formulate management options aimed at sustaining native forest ecosystems and increasing the productivity of plantations.

  6. Page 109
    Abstract

    This review focuses on growth and photosynthetic response to nitrogen and phosphorus in trees commonly grown for wood production. For an E. grandis W. Hill ex Maiden trial plantation at Gympie, stem growth in well-nourished plantations was 50 m3 ha−1 year−1 (current annual increment) at canopy closure and canopy development was strong. Leaf area index (LAI) was 5 in fertilized plots compared with about 1 in control plots. LAI for individual fertilized trees peaked at 6.3 compared with 2 for control trees. Substantial differences in canopy assimilation between nutrient treatments were largely due to extent of foliage, although photosynthetic efficiency of energy conversion by canopies increased from 0.44 g MJ−1 for control trees to 0.76 g ML−1 for high-nutrient trees. Biomass partitioning and photosynthetic response to nitrogen and phosphorus nutrition were examined on small seedlings growing exponentially. Relative growth rate (RGR) for whole plants was linearly related to nutrient concentration in the tissues, but the relationship between stem mass and leaf mass was constant during early growth, and was largely unaffected by variation in tissue nutrient concentration. However, the relationship between leaf mass and root mass was dependent on nutrient concentration in the tissues. Nitrogen-dependent changes in RGR were attributed more to extent, than to unit performance of foliage, whereas phosphorus-dependent changes in RGR were related to effects of the treatment on net carbon gain per unit dry·weight. Specific leaf area was increased by the higher relative addition rate of either nutrient, so that photosynthetic comparisons are best made on a mass basis. Kxpressed in those terms, CO2 assimilation was nutrient-saturated at 4.2% nitrogen and 0.35% phosphorus.

  7. Page 123
    Abstract

    We have assembled a database of nutrient concentrations in components of 110 species of Eucalyptus growing in native forests and in plantations and glasshouse trials around the world. In this paper, we use this database to analyse for differences between taxa, sites and plant components. The database permits a number of both general and specific comparisons of concentrations in foliage, litter, twigs and bark. In all such comparisons, concentrations of calcium and manganese were significantly greater in Symphyomyrtus than in Monocalyptus. At a lower level of certainty, concentrations of potassium are greater and magnesium less in Symphyomyrtus than in Monocalyptus, while the concentrations of nitrogen and phosphorus are similar in both. Data for other elements are limited but do not vary consistently between the two sub-genera. Thus, since fertility is most often defined by nitrogen and phosphorus, our analyses do not support the widely-held hypothesis that Symphyomyrtus species have intrinsically greater nutrient requirements and a stronger preference for more fertile soils than Monocalyptus species. Concentrations of almost all elements are greater in foliage from eucalypt plantations than from native forests, reflecting the increased availability of nutrients in plantation soils due to intensive silviculture. While there is no definitive evidence for nutrient limitation of native forests, the data indicate that the availability of boron may be sub-optimal in many plantation soils. Foliage contains the highest concentrations of all elements with the exception of calcium, which is greatest in bark. Concentrations are lowest in stemwood, but its nutrient component is large relative to all other components and it constitutes a major sink for all nutrients. Nutrient concentrations in foliage are important in the identification of nutritional deficiencies and imbalances since they are responsive to changes in site fertility. Nitrogen to phosphorus ratios are particularly sensitive to the addition of fertilizers and our analysis suggests that a ratio of close to 15 may be optimal for a range of eucalypt species.

  8. Page 155
    Abstract

    Jarrah (Eucalyptus marginata Donn ex Sm.) and karri (E. diversicolor F. Muell.) forests occur only in south-western Australia. They develop as open and tall open forests, often on infertile soils and within a region that is subject to summer drought and recurrent fires. Compared with the vegetation which develops in similar climatic regions in other parts of the world, the stature of these forests is unusual and is explained by plant adaptations which allow the vegetation to cope with the harsh environment. Jarrah is the more extensive of the two forest types, covering about 1.6 Mha. Karri occurs towards the south on more fertile soils within an area of higher rainfall, covering approximately 174 000 ha. Both forests grow either as pure stands or in mixtures with other tree species, the most common associate being Eucalyptus calophylla (marri). Understorey vegetation differs markedly between the two types of forest. In jarrah forest the shrub stratum is often sparse but is rich in species and is usually limited to a height of less than about 1 m. In karri forest, the understorey develops as a tall, dense, shrub layer up to 5 m high often dominated by one or two native legumes and the non-legume Trymalium spathulatum. Both types of forest are utilized for commercial timber production and both are burned regularly to reduce fuel loads on the forest floor and thus minimize the risk of uncontrolled wildfires. Soils of the jarrah forest are nutrient-poor and contain especially small amounts of total nitrogen and extractable phosphorus compared with other eucalypt ecosystems. Karri forest soil also contains only small amounts of labile forms of phosphorus but is relatively well supplied with other nutrients. Slow growth rates of the trees, especially in jarrah forest, and the development of efficient, conservative biochemical and biogeochemical nutrient cycles appear to be characteristics which allow these forests to cope with the low nutrient status of the soils. Biochemical cycling of phosphorus is more important in jarrah and karri forest than in other dry and wet sclerophyll eucalypt forests and this may be an adaptation to the low concentrations of labile soil phosphorus. The understorey plays a key role in biomass production, nutrient uptake and nutrient cycling in karri forest, and legumes in this stratum are critical for replacing nitrogen volatilized during prescribed burns. The vegetation in the understorey is also significant in biogeochemical nutrient cycling in karri forest. Litterfall from the understorey contributes substantially to annual accession of nutrients to the forest floor. Furthermore, this litter decomposes and releases nutrients more rapidly than plant residues from the eucalypt overstorey. In contrast, the understorey plays only a minor role in biomass production, nutrient uptake and nutrient cycling in jarrah forest, but nitrogen-fixing plants (native legumes, as well as Macrozamia and Allocasuarina) are important for input of nitrogen to the ecosystem. The extreme seasonal climate of the region exerts a strong influence on biological processes in jarrah and karri forests. Climatic control of moisture in the litter layer and upper soil horizons determines the seasonal variation in rates of many of the processes critical to the functioning of the ecosystems. The mild climate of the southern region, coupled with the generally more fertile nature of karri forest soils compared with those in jarrah forest, partly explains many of the differences between the two ecosystems. These differences are reflected in the rate of key processes such as Litterfall, nutrient transfers in litter and rain, nitrogen-fixation, forest floor microbial activity, nutrient uptake and tree growth, which are up to five times greater in karri forest than in jarrah. Both forest types appear to be nutritionally resilient in the short term following regular disturbances such as prescribed burning and wood harvesting. However, the forests could be vulnerable in the long term to losses of nitrogen. The situation regarding phosphorus, which is in low supply in both ecosystems, is uncertain due to insufficient information. More research is required to quantify the chemical transformations and fluxes of nitrogen and phosphorus following disturbance, and to establish the effects of disturbance on the long-term nutritional stability of jarrah and karri forest.

  9. Page 191
    Abstract

    This chapter summarizes the research on nutrient-cycling in south-eastern Australia, in the wetter forests of the Great Dividing Range, Victoria, and of north-eastern and southern Tasmania, concentrating on tall open-forest (e.g. Eucalyptus rçgnans), open-forest (e.g. E. obliqua) and to a lesser extent on closed-forest. Annual litterfall ranges up to 9.4 t ha−1 and contains up to 87.7 kg ha ‘ nitrogen, 4.6 kg ha ‘ phosphorus, 14.0 kg ha−1 potassium, 11.3 kg ha−1 magnesium and 48.8 kg ha-1 calcium. Dead leaves account for about 50% of total litterfall when total litterfall is less than 4 t ha-1, and for about 30% with total litterfall greater than 8 t ha−1. Mean foliar mass in open forests is 7.1 ± 0.4 t ha-1 and mean retention time for leaves is 3.0 ± 0.6 years. The mean concentration of nitrogen in litter is 0.50% with total annual litterfall less than 4 t ha ‘, increasing to 0.75% with total annual litterfall greater than 8 t ha−1. A similar pattern holds for phosphorus so that the most productive forests have the most nutrient-rich litter. The mean decomposition constant (k) is 0.26 year ‘ so that mean residence time (r) of organic matter in the litter layer is 3.8 years, similar to other temperate forests of the world. In situ rates of net annual mineralization are highly correlated with, but much less than, rates of mineralization measured in the laboratory. However, the in situ rates are correlated with, and quantitatively similar to, the annual return of nitrogen in litterfall. The carbon : nitrogen ratio in soil provides an estimate of quality of the substrate for mineralization of nitrogen, while the index (N2/C) includes both quality (N/C) and quantity (N) and is highly correlated with the rate of mineralization. The carbon : nitrogen ratio of surface soil is 13–17 in tall open-forest, and 20–30 in open-forest. 1 he rate at which the carbon : nitrogen ratio can be reduced determines the rate of NH4+-nitrogcn availability and hence the rate of nitrification. No matter how small the proportion of resistant soil organic matter (carbon : nitrogen = 10, approaching that of humic acid) in E. obliqua forest, carbon : nitrogen of decomposable soil organic matter is too high to allow nitrification, and ammonium-nitrogen dominates. In E. regnans forest, the rate of nitrification increases with age up to 80 years then decreases with age. Increases in the concentration of H2PO4 due to mineralization measured in situ are small and frequently negative due to adsorption of H2PO4 by reactive, colloidal surfaces. Following disturbance, NO3− nitrogen is produced in soils which were nitrifying before disturbance, and concentrations of NO3− nitrogen and other ions in soil solution are directly related to severity of disturbance. Disturbance by fire results in an immediate increase in the concentration of NH4+-nitrogen in topsoil, followed by immobilization so that net mineralization following disturbance is less than that in undisturbed forest. Concentrations of NO3− -nitrogen in soil solution in small sub-plots treated with herbicide were up to ten times those in the control catchment over the 3 years of measurement, demonstrating the importance of uptake by regeneration in controlling solution chemistry. Eucalyptus obliqua forests are resistant to disturbance, whereas E. regnans forests are resilient. The stock of nitrogen in soil of a typical E. regnans forest has accumulated during the millennia over which fire has been an evolutionary and ecological force. Experiments show that a rate of nitrogen-fixation of 20 kg ha-1 year-1 maintained for 20 years is sufficient to replenish the nitrogen lost in a typical timber-harvesting operation in E. regnans forest. Rates of nitrogen-fixation in the drier forests are much lower and regular burning to reduce fuel loads may lead to a long-term net loss of nitrogen.

  10. Page 229
    Abstract

    The distribution of native forests on the south coast of Australia is related to climate and soils. A review of studies in these forests indicates that soil nutrients arc an important factor at the finer scale and can either change gradually, as on a slope, or abruptly, as is the case when the parent materials of the soil change. Differences in accumulation and turnover in sclerophyllous forests can be related to soil nutrients; however, rainforests (broad leaved non-eucalypt forests) accumulate higher quantities of nutrients in part as a result of lower efficiency of nutrient redistribution. Perturbation within forests will have varying effects on nutrient availability depending on the spatial extent, type and intensity. Harvesting removes nutrients but effects on native forests will be in the long term; however, intensive harvesting of plantations could have shorter term effects due to relatively high levels of nutrients being removed. Nutrients at highest risk are calcium and boron rather than phosphorus as might be expected, but the effect of removing these nutrients is less well understood. Growth of forest stands can be modified by nutrient application. The interaction between insects and animals on forest nutrient regimes is less well known, although the episodic infestations of insects appear to be significant.

  11. Page 249
    Abstract

    Nutrient losses due to timber harvesting in eucalypt forests and plantations may reduce long-term productivity through a reduction in nutrient availability. Losses of nitrogen, phosphorus, potassium, calcium and magnesium are simulated under various harvesting regimes using a nutrient budget model based on published data. The model predicts net losses of up to 395 kg ha−1 of nitrogen, 35 kg ha−1 of phosphorus and 969 kg ha−1 of calcium over an 80-ycar forest rotation and up to 376 kg ha−1 of nitrogen, 24 kg ha−1 of phosphorus, 209 kg ha−1 of potassium, 550 kg ha~’ of calcium and 54 kg ha−1 of magnesium over a 20-year plantation rotation. Losses of all nutrients are greatest when logging is followed by regeneration-burning and when stems are debarked off-site, which particularly affects calcium. Because of short rotation times, harvesting of timber is more-likely to lead to a decline in productivity in plantations than in native forests despite applications of fertilizer. Calcium, potassium and nitrogen are most likely to be depleted under current practices in plantations, and phosphorus and calcium in forests. Effective nutrient conservation demands that harvest residue be burned only as a prerequisite of regeneration, and that stems should always be de-barked on-site.

  12. Page 259
    Abstract

    At the end of 1993, Australia had a eucalypt plantation estate of about 125 000 ha. New plantations were being established at an annual rate of about 15 000 ha and this appears to be increasing. Even without a further increase in the rate of planting, this would result in a plantation estate of around 240 000 ha by the turn of the century. The major use intended for these plantations is as a source of fibre for the manufacture of pulp and paper, but there is also some interest in producing solid wood products. The largest planting targets are in Tasmania, Western Australia and Victoria, with private industry generally planting larger areas than state government departments. In temperate climatic zones in Southern Australia, the major species that have been used for planting are: (1) E.globulus m Western Australia and low elevations in Tasmania and Victoria, (2) E. nitens at high elevations (above 300 m) in Tasmania and Victoria, and (3) E. regnans’m selected sheltered sites in Tasmania and Victoria. In subtropical climatic zones on the east coast, the main species that have been used are: (1) E. grandis and the closely related E. saligna on moist coastal sites, and (2) E. pilularis on dry, ridge-top sites. Nursery techniques vary considerably, but as eucalypts have no dormant period, most use some sort of container to protect the roots during transport and planting. Some growers raise the seedlings in pots initially, before transplanting them into open beds to produce large, hardy, open-rooted seedlings that can be planted in very cold conditions. Most growers apply ‘starter doses’ of nitrogen and phosphorus fertilizer soon after planting to assist early growth, but few apply fertilizer in later years. This may change in the future as research has shown that substantial additional growth can be obtained from adding extra fertilizer on some sites. Some mineral deficiencies have been reported but trace elements appear to be adequate in most soils. Despite considerable research, chemical analysis of foliage has not proved to be as successful a tool for diagnosing nutrient deficiencies in eucalypts as in conifers. Various refinements to chemical methods have shown promise, including a bioassay technique applied to the roots. Classification and mapping of land and soil for intended plantations has provided considerable benefits for management, including greater definition of fertilizer schedules for particular soil types. The outlook for eucalypt plantations in Australia is positive, but continued planting is dependent on the economic success of plantation projects. A prerequisite for a good return on investment in plantations is conversion to high-value products such as pulp and paper. In some areas, particularly in Western Australia and parts of Victoria, an important objective of planting programs is to provide land-care benefits and to improve the sustainability of agriculture.

  13. Page 275
    Abstract

    Eucalypts grown for specialty timbers and pulpwood in New Zealand include Eucalyptus rcgnans F. Muell., E. delcjjatensis R.T. Baker, E. fastigata Deane & Maiden, E. nitens (Deane & Maiden) Maiden, E. saligna Sm. and E. botryoides Sm. A national resource of approximately 15 000 ha has been established. The criteria used in species selection are suitability for the desired product, growth rate, and site factors such as winter frost patterns and tolerance to exposure. Nursery practice is to produce bare-rooted seedlings for large-scale winter planting, and container-grown seedlings mainly to extend the planting season for small-scale planting. Eucalypt seedlings require fertile soils, and regimes for applying fertilizers have been developed to maintain balanced nutrition with high levels of nitrogen and phosphorus in seedlings. Before plantations are established on new sites, the particular site requirements for cultivation, weed control and fertilizer should be tested. In trials throughout New Zealand, responses to additions of nitrogen and phosphorus fertilizers differ with location and cannot always be predicted from the results of soil tests for total-nitrogen and Bray and Kurtz No. 2 available phosphorus, although such tests are useful in identifying acute deficiencies. The relative importance of cultivation, fertilizer and weed control, and the degree of interaction between them also differ from site to site. Repeated fertilizer applications generally elicit an improvement in growth but in some trials there is little long-term benefit and thus the extra expense may not be warranted. In trials combining different fertilizer and thinning treatments on sites with soil derived from pumice, fertilizer produced a strong response in tree diameter. Nutrient concentrations in leaves do not always closely reflect growth rates. Studies of seasonal variation in foliar nutrient concentrations reveal distinct trends, but these are not always repeated in subsequent years. Further research is needed to refine foliage sampling for diagnostic purposes. A national collection of foliage from E. saligna, E. delegatensis and E. regnans has provided data for the development of provisional DRIS (Diagnosis and Recommendation Integrated System) standards for each species. These standards require further refinement and validation to improve their diagnostic accuracy. Nutrient contents of the above-ground portions of stands have been investigated but long-term effects of eucalypts on soil nutrients and properties have not been studied in New Zealand. In schemes for the land-treatment of effluent, the use of eucalypts rather than pasture is being investigated as a more sustainable option and the resulting trees can be used as a source of energy. With improved silvicultural knowledge in plantation management from regime trials and growth models, the emphasis for research is now on a better understanding of the siting of eucalypts and their growth interactions to help managers improve the uniformity of eucalypt productivity from their plantations.

  14. Page 303
    Abstract

    There are approximately 550 000 ha of commercial eucalypt plantations in South Africa, producing 5.7 × 106 m3 of round-wood per annum. The MAP is in excess of 850 mm and soils are typically acidic and highly leached. Careful matching of species to site is necessary as soils are highly variable and MAT ranges from 13.5°C to over 22.0°C. Intensive silviculture is practised on rotations of 6 years (for pulpwood) to 25 years (for sawn and veneer timbers). As acute symptoms of nutrient deficiency are rare, fertilizers are used only at the time of establishment. Fertilizer trials began in 1952, and their main findings arc-discussed, particularly with reference to the status of the organic matter in the topsoil. Research on the methods of applying fertilizers and the maintenance and magnitude of responses arc also presented. Foliar analysis is examined as a diagnostic tool for soil and site conditions and tree growth, together with its suitability for explaining responses to fertilizing. Foliar norms are given and the importance of their ratios highlighted. Data on the nutrient content of the above-ground components of eucalypt biomass are discussed in relation to nutrient budgets and the effects of afforestation on site fertility. It is concluded that research needs to focus on the maintenance of site productivity, with particular regard to the active management of organic matter and the relationships between the status of soil-water and fertility.

  15. Page 327
    Abstract

    Eucalypt plantations make up more than 30% of the total area of exotic forests in Argentina, and eucalypti will be the most-planted exotics over the immediate future because of market demands and their excellent growth. Growth rates of Eucalyptus grandis W. Hill ex Maiden have shown dramatic responses to site selection, with mean annual increments ranging from 22 to 50 m3 ha−1 year−1.

    Prescriptions for fertilizers are presently lacking in extension programs throughout the country. However, fertilizer experiments established at the time of planting have demonstrated significant responses to nitrogen and phosphorus by the time the trees are harvested. Maximum responses were obtained at amounts of approximately 50 kg ha−1 of nitrogen and 58 kg ha−1 of phosphorus. A network of fertilizer trials has been recently established in order to develop nutritional strategics for the different forest soils in Argentina.

  16. Page 335
    Abstract

    The main trees used in plantations in Brazil are cucalypts. Most of the area planted with eucalypts is in the savanna region, where soils are generally infertile. This has led to the development of large research programs, on eucalypt nutrition and fertilizer application to plantations, which are designed to assist the forest companies in their afforestation programs. Some eucalypt species are tolerant of exchangeable aluminium and have relatively low calcium and magnesium requirements. Ammonium is the form of nitrogen preferred by most eucalypt species cultivated in the savanna areas. Young eucalypts have a high phosphorus requirement which decreases with age. Broadcast application of phosphate rock associated with localized addition of soluble phosphorus sources in soils with high phosphorus-fixing capacity is important to improve and maintain eucalypt productivity. The amount of potassium fertilizer required for adequate growth depends on the concentration of potassium in the soil, and the quality of the site, and may reach 200 kg ha−1 of potassium on good sites. Eucalypts have shown good responses to applications of sulfur in areas far from the coast. In these areas, the dry season may last more than 3 months and boron may be necessary to reduce dieback and to improve stem form.

  17. Page 357
    Abstract

    Since the beginning of the 19th century, more than 150 species of Eucalyptus have been introduced into Chile. The first commercial plantations were established in 1987, by a coal-mining company. Eucalyptus globulus subsp. globulus became a very popular species for small plantations, farm avenues and windbreaks. It is used for many purposes including firewood, sawlogs, veneer, and during the last few years, for the production of pulp, both by domestic and foreign industry. The importance of cucalypts as commercial species has increased considerably over the last 5 years. The rate of planting has increased from an average of 2000 ha per year to more than 30 000 ha per year during the 1990s. New species have been used to plant areas unsuitable for E. globulus; among them, E. nitens, E. dclegatensis, E. viminalis and E. carnal’dulensis are the most important. The increasing importance of Eucalyptus as commercial species, has produced fundamental changes in the technologies for nurseries and establishment of plantations. Important programs for genetic improvement are carried out by both independent companies and state institutions in collaboration. Modern nurseries have replaced the traditional low-technology nurseries, and an intensive approach, including soil-treatment, weed control and addition of fertilizers has been adopted at establishment. This chapter presents the advances made in the last few years in terms of genetic improvement, nursery techniques and the establishment of eucalypt plantations in Chile.

  18. Page 371
    Abstract

    Kucalypts (mainly Eucalyptus globulus Labill.) were introduced to the Iberian Peninsula about 150 years ago for ornamental purposes, but today, bleached pulp from eucalypt is a major asset to the economy of Portugal and Spain. The two countries together have an area of eucalypt plantations that may reach approximately 1 million ha. Estimates of mean annual increments in stem volume at 10 years of age range from 20 to 40 m3 ha−1 year−1 on the Atlantic seaboard, to 3–4 m3 ha−1 year−1 in the interior. In fertilizer trials in the field, the major role in increasing productivity seems to be played by the addition of nitrogen, in most soils. However, water is generally a major limiting factor and changes in its availability change nutrient use efficiency, total production and the proportion of total biomass allocated to stemwood. The modification of physical and chemical properties of soils in F. globulus plantations, compared with soils under native trees is related to increase in compaction and decrease in aggregate stability (largely resulting from soil mobilization) and with the increase in calcium in the forest floor as a result of litter turnover.

  19. Page 389
    Abstract

    Eucalypts of many species are important in plantation forestry and are significant in timber supply in southern China. This chapter reviews management of nutrition and the diagnosis of nutrient deficiencies in eucalypt plantations in China. Appropriate fertilizers, the use of mycorrhizae and the establishment of mixed stands of eucalypts are all crucial to the management of eucalypt plantations. In the national afforestation program based on extensive eucalypt plantations, particular efforts are being taken to prevent the risk of decreased fertility and subsequent site degradation.

  20. Page 399
    Abstract

    Eucalypts have been extensively planted in India, often on marginal land. There has been concern that eucalypts may impoverish the soil and lower the water-table, and so research has concentrated on these aspects, together with detailed studies of the cycling of nutrients. The concentration of nutrients in foliage is greater, and the degree of selerophylly less, in eucalypts planted in India than in native eucalypts in Australia. Nutrient cycling studies have largely concentrated on a local provenance of Eucalyptus tereticornis called E. hybrid (Mysore gum). Nitrogen and phosphorus use efficiencies of E. hybrid are much greater than for plantations of other broad-leaved species and tropical pines planted on soils with small nutrient reserves. On richer soils, luxury consumption by eucalypts results in a decrease in nutrient use efficiencies and thus the relatively small return of nutrients from plant to soil may lead to impoverishment of the soil where the timber is harvested. The substantial research base already established must be increased so that the nutrition of eucalypt plantations can be properly managed, and site deterioration prevented by, for example, increasing the rotation and ensuring that bark and other non-marketable components remain on site. Sound land-use planning must ensure that the potential of eucalypts is harvested, commensurate with the rehabilitation of degraded lands.

  21. Page 417
    Abstract

    Mineral deficiencies in eucalypts are common in nursery-grown seedlings and during the early establishment phase in plantations. Five categories of deficiency symptoms have been observed: leaf chlorosis, leaf necrosis, leaf reddening due to accumulation of anthocyanins, leaf deformation and dieback of shoot tips. A key to deficiency symptoms based on symptoms which have been verified in pot or field trials is presented. Symptoms of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, copper, zinc, manganese, boron and molybdenum deficiencies are described and illustrated in colour. Factors such as nutrient toxicity, air pollutants and fungicides which can result in damage to eucalypt foliage are discussed, and selected examples illustrated in colour. Understanding the behaviour and function of nutrients in the tree should facilitate diagnosis of nutrient deficiencies from the development of symptoms. Alternative procedures should be used in parallel with the documentation of symptoms to ensure a correct diagnosis. Diagnosis by biochemical and anatomical tests, by plant analysis and by tissue testing are briefly reviewed.