Fast-growing Plantations Research Articles

The potential of willow and poplar plantations as carbon sinks in Sweden

Abstract A large share, estimated at 12–25%, of the annual anthropogenic greenhouse gas emissions is attributed to global deforestation. Increasing the forested areas therefore has a positive impact on carbon (C) sequestration and mitigation of high atmospheric CO 2 concentrations. Fast-growing species, such as willow and poplar, are of high interest as producers of biomass for fuel, but also as C sinks. The present study estimated the rate of C sequestration in biomass and soil in willow and poplar plantations. Calculations were based on above- and below-ground biomass production data from field experiments, including fine root turnover, litter decomposition rates, and production levels from commercial plantations. Accumulation of C in woody biomass, above and below ground, was estimated at 76.6–80.1 Mg C ha −1 and accumulation of C in the soil at 9.0–10.3 Mg C ha −1 over the first 20–22 years. The average rates of C sequestration were 3.5–4.0 Mg C ha −1 yr −1 in woody biomass, and 0.4–0.5 Mg C ha −1 yr −1 in the soil. If 400,000 ha of abandoned arable land in Sweden were planted with willow and poplar, about 1.5 Tg C would be sequestered annually in woody biomass and 0.2 Tg C in soils. This would be nearly one tenth of the annual anthropogenic emissions of C in Sweden today. These calculations show the potential of fast-growing plantations on arable land to mitigate the effect of high CO 2 concentrations over a short time span. Knowledge gaps were found during the calculation process and future research areas were suggested.

Nutrient fluxes in rainfall, throughfall and stemflow in Eucalyptus stands on the Zululand coastal plain, South Africa

Atmospheric deposition was assessed at two sites over a four-year period in post-canopy-closure (mature) Eucalyptus stands in the northern Dukuduku and southern KwaMbonambi commercial plantation forestry areas of Zululand, South Africa. The aim of this study was to determine the magnitude and relevance of nutrient addition with rainfall, throughfall and stemflow to commercial forestry in this region. Canopy cation exchange was used with rainfall and canopy drainage to derive wet, dry and total atmospheric deposition. Nutrient concentrations measured in the rainfall, throughfall and stemflow varied widely throughout the study period, and between sources and sites. Rainfall was slightly acidic at both sides, but became less acidic upon passing through the tree canopies. Canopy exchange and collection of dry deposition resulted in increased cation concentrations under the tree canopy, while the canopy generally absorbed nitrogen (N), from the rainfall, reducing the below canopy concentrations. Atmospheric deposition was shown to be responsible for large quantities of nutrients added to the eucalypt stands at each site. Annualised deposition averaged across all years at each site amounted to N, calcium, magnesium, and potassium (K) fluxes of 11.0, 6.0, 2.7 and 10.2 kg ha−1 y−1 at Dukuduku and 10, 10.6, 7.5 and 18.8 kg ha−1 y−1 at KwaMbonambi, respectively. Organic N fluxes contributed a further 8.1 kg ha−1 y−1 at Dukuduku and 7.1 kg ha−1 y−1 at KwaMbonambi to the total N deposition. Although K deposition values were high, additions of all other nutrients, although also high, were within the ranges reported in local and international research. Over the course of a full rotation, the atmospheric deposition levels recorded at these sites may have potential to supply a large proportion of the nutrients that are lost during stem-wood harvesting. This study adds value to understanding of nutritional sustainability of fast-growing plantation forests, demonstrating the importance of atmospheric deposition as a nutrient addition source to plantation-grown eucalypts along the Zululand coastal plain.

Effects of pure and mixed plantations of Populus deltoides with Alnus glotinosa on growth and soil properties: A case study of Foman Region, Iran

Plantation and application of fast-growing species, such as Populus deltoides increasingly, are common in the northern part of Iran. Concerns about decline in soil fertility and long-term productivity of fast-growing plantations have promoted interest in using nitrogen-fixing trees in mixed species plantations. P. deltoidesand Alnus glutinosa were planted in five proportions (100P, 70P:30A, 50P:50A, 30P:70A, 100A) in Foman, Iran. After 13 years, the effects of species interactions on tree growth and nutrient concentration in live and senescent leaves and soil properties were assessed. Diameter at breast height and total height of individualPopulus trees were positively affected by the presence of Alnus. Nitrogen concentrations in fully expanded and senescent leaves of Populus were higher in mixed plantations than monoculture plantations. The results of nutrition and nutrient return and growth indicated that mixed plantations of these two species were more productive and sustainable than their monoculture plantations. Within the framework of this experiment, it appeared that production was maximized when these two species were grown together in the relative proportions of 30% Populus and 70% Alnus. Key words: Mixed plantation, Alnus, Populus, growth, soil.

Biomass production and carbon storage of Populus ×canadensis Guinier I-214 plantations grown at Pogradeci region in Albania

Fast-growing plantations of Populus ×canadensis Moench (syn. P. ×euramericana (Dode) Guinier ex Piccarolo) clone I-214 have good potential for biomass production. The objective of the study was estimation of biomass using allometric equations and estimation of carbon allocation according to tree components. The study was carried out in five poplar stands (total area 16.9 ha) in the Pogradeci region, Albania. Poplar stands were 6, 8 and 11 years old, planted at a density of 2 500–4 444 trees ha−1. We used 0.2 ha sample plots per each poplar plantation, where diameter at breast height and tree heights were measured. Sample trees in each stand were selected for determination of fresh biomass with methods of moisture content (25 sample trees) and stem analysis (five sample trees). We noted a discrepancy in dry biomass estimation between the two methods, where the moisture content method underestimated the biomass compared with the stem analysis method. Allometric equations for dry biomass were determined based on field measurements. Trees had a diameter at breast height (DBH) ranging from 2.5–24 cm and 8–21 m for height. Diameter at breast height resulted as a better allometric predictor of dry biomass than tree height. Relationships between dry biomass and predictor variables (DBH or tree height) were non-linear (exponential), whereas the relationship between dry biomass and age was linear. The squared DBH was the best predictor variable and the relationship with dry weight was fitted with a linear regression. A total of 281 t C ha−1, 137 t C ha−1, and 54 t C ha−1 was stored in 11-, 8- and 6-year-old poplar stands, respectively. Of the total C stored in all stands, 81% of carbon was allocated in the aboveground components, whereas 19% carbon was allocated in the belowground components of the trees. One-way analysis of variance (LSD test) revealed a highly significant difference in dry biomass between 6- and 11-year-old poplar stands, while the difference between 6- and 8-year-old as well as 8- and 11-year-old poplar plantations was less significant.

Effects of nurse-tree crop species and density on nutrient and water availability to underplanted Toona ciliata in northeastern Argentina

Cultivation of high-value hardwoods is often more difficult than cultivation of many pioneer species commonly used in fast-growing plantations. On some sites, the facilitative effects of nurse trees can be necessary for initial crop species establishment, but their competitive effects can also reduce juvenile growth rates of the crop species. To improve establishment success in mixed-species plantations, we tested the effects of the nurse-tree species Grevillea robusta A.Cunn. ex R.Br., Pinus elliottii Engelm. × Pinus caribaea Morelet, and Pinus taeda L. and four densities (0%, 25%, 50%, and 75% of the initial density) on Toona ciliata M.Roem. light, soil water, and soil nutrient availability. Growth of T. ciliata tended to increase with decreasing nurse-tree density and increasing light availability. However, growth was greater under G. robusta than under the pines, even where light conditions were similar, corresponding to mostly higher nutrient availability and higher soil water contents underneath G. robusta. Wood δ13C of T. ciliata was positively correlated with growth, foliar nutrient contents (N, P, K, Mg, Ca), and soil water content at a depth of 20–40 cm. Our results suggest that G. robusta is less competitive for soil nutrients and water than the pine nurse-tree species.

Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths

1. Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil. 2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age – 25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected -15N, Rb+ (analogue of K+) and Sr2+ (analogue of Ca2+) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils. 3. Determination of foliar Rb and Sr concentrations and 15N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer. 4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for -15N than for Rb+ and Sr2+ in the upper 50 cm of soil, the highest SRUP values for Sr2+ and Rb+ were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth. 5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

Spatiotemporal Variations in Biomass Carbon Storage for Three Forest Management Regimes in Northeast China

Forests, which account for 76~98% of terrestrial plant carbon and 2/3 of terrestrial carbon sequestration in the world every year, can store or release large amounts of carbon as a result of natural environmental variability and human activities. Quantifying the spatiotemporal dynamics of forest biomass carbon storage is important not only for understanding the role of forests in global warming but also in supporting decision-making processes in forest management. We established biomass-volume models utilizing investigation data of sample plots in the Luishuihe forest area of Northeast China. Based on the models and a forest resource inventory database, forest biomass carbon storage at Lushuihe in 1987, 1995, and 2003 was estimated and mapped in a geographic information system (GIS). The forest biomass carbon storage in areas with 3 different management regimes during different time periods was also obtained based on area maps and maps of carbon storage in the GIS. The results showed that both carbon storage and density first decreased between 1987 and 1995, and then increased between 1995 and 2003. Such temporal dynamics of forest biomass carbon storage corresponded well to changes in Chinese forest policies. Forest biomass carbon storage and density of natural forests in key ecological welfare forest (EWF) areas, where harvesting is prohibited, steadily increased between 1987 and 2003 due to the prohibition of timber harvesting. Decreases in forest biomass carbon storage and density of natural forests in ordinary EWF areas, where harvesting is allowed under certain presumably beneficial conditions, were much less from 1995 to 2003 than from 1987 to 1995 due to decreased timber harvesting. In commodity forest (CoF) areas these decreases in natural forests were also less from 1995~2003 than 1987~1995 due to decreased timber harvesting. The area and biomass carbon storage of plantations in the 3 areas steadily increased between 1987 and 2003. The rate of decrease of carbon density in CoF areas was even less than that in local EWF areas because the area and carbon storage of fast-growing plantations in CoF areas were much greater than these in local EWF areas from 1995 to 2003.

How does drought tolerance compare between two improved hybrids of balsam poplar and an unimproved native species?

Poplars are one of the woody plants that are very sensitive to water stress, which may reduce the productivity of fast-growing plantations. Poplars can exhibit several drought tolerance strategies that may impact productivity differently. Trees from two improved hybrids, Populus balsamifera × Populus trichocarpa Torr. & Gray (clone B × T) and P. balsamifera × Populus maximowiczii A. Henry (clone B × M), having P. balsamifera L. as a parent and trees from native and unimproved P. balsamifera were subjected to a 1-month drying cycle in a growth chamber and then rewatered. The unimproved and native B clone maintained higher stomatal conductance (g(s)) than the hybrids, and high photosynthetic activity and transpiration, even when soil water content was nearly zero. As a result, both instantaneous water use efficiency (WUE(i)) and leaf carbon isotope composition (δ(13)C) indicated that this clone was less affected by drought than both hybrids at maximal drought stress. However, this clone shed its leaves when the drought threshold was exceeded, which implied a greater loss of productivity. The B × M hybrid showed a relatively conservative response to water stress, with the greatest decrease in transpiring versus absorbing surface (total leaf area to root biomass ratio). This clone was also the only one to develop new leaves after rewatering, and its total biomass production was not significantly decreased by drought. Among the two hybrids, clone B × T was the most vigorous, with the greatest transpiration (E(i)) and net CO(2) assimilation (A) rates, allowing for high biomass production. However, it had a more risky strategy under drought conditions by keeping its stomata open and high E(i) rates under moderate drought, resulting in a lower recovery rate after rewatering. The opposite drought response strategies of the two hybrids were reflected by clone B × T having lower WUE(i) values than clone B × M at maximal drought, with a very low Ψ(min) value of -3.2 MPa, despite closed stomata and stopped photosynthetic activity. Positive linear relationships between A and g(s) for the three hybrids indicated strong stomatal control of photosynthesis. Moreover, the three poplar clones showed anisohydric behaviour for stomatal control and their use under long-term drought should be of interest, especially the B × M clone.

Comparative study on physical and mechanical properties of laminated veneer lumber and plywood panels made of wood from fast-growing Gmelina arborea trees

Laminated products, such as laminated veneer lumber (LVL) or plywood (PW), have become important recently. The objective of this study was to determine and compare properties of panels fabricated with veneers of Gmelina arborea trees in a fast-growth plantation and glued with phenol formaldehyde resin. The results showed that LVL and PW physical and mechanical properties are comparable to those of solid wood with a specify gravity of 0.60. Moreover, these panels can be cataloged into group 2 of PS 1–95 of the Voluntary Products Standard of the United States. The difference in physical properties was not statistically significant between LVL and PW panels, except for water absorption. Some mechanical properties, such as hardness and glue-line shear, modulus of rupture in perpendicular flexure, nail and screw withdrawal parallel, and perpendicular strength, were statistically different between LVL and PW. However, no differences were established for the modulus of elasticity, tensile strength parallel to the surface, or tensile strength perpendicular to the surface. The differences were attributed to the venners’ orientation in the panels studied.

Thinning affects Pinus sylvestris needle decomposition rates and chemistry differently depending on site conditions

Changes in mass and chemical composition of Pinus sylvestris senescent needles were studied over a 5 year period in Mediterranean (MF) and Continental forests (CF) in the Pyrenees under varying levels of thinning (P0: reference, no thinning; P20: removal of 20% basal area, P30: removal of 30% basal area). Decomposition rates were higher in MF (k = 0.423 year−1) than in CF (k = 0.245 year−1). However, the maximum decomposition limit was higher in MF (87.9%) compared to CF (78.1%). The relative importance and timing of rainfall, and cellulose and lignin abundance on the decomposition process was similar among both sites. However, air temperature and degree-days only affected CF (the colder site) during the initial stages of decomposition, while litter moisture was significant only in MF (the drier site) in the latter stages of decomposition. Nutrient and carbon dynamics showed temporal patterns similar to those reported in higher latitudes (except for Ca), however, indicators of N mineralization such as C/N and lignin/N at the study sites were lower than values reported in the literature. Decreases in decomposition rates after thinning were higher in MF than in CF, indicating that this ecosystem could, in the short term, be more sensitive to human intervention. Thinning had similar temporary qualitative effects at both sites, slowing decomposition, increasing N and P immobilization and decreasing Ca immobilization. However, quantitative effects of thinning were site dependent in that the magnitude of nutrient immobilization was higher in CF. A conceptual model is presented to explain effects of thinning on litter N dynamics. These temporary changes are not trivial as nutrient immobilization and accumulated organic matter losses over a thinning cycle may affect tree growth particularly during short rotations and intensive fast-growing plantations. Under similar nutrient availability conditions, sites where nutrient release occurs faster may show higher post-thinning tree growth rates.

Organic residue mass at planting is an excellent predictor of tree growth in Eucalyptus plantations established on a sandy tropical soil

Tropical plantation forests are meeting an increasing proportion of global wood demand and comprehensive studies assessing the impact of silvicultural practices on tree and soil functioning are required to achieve sustainable yields. The objectives of our study were: (1) to quantify the effects of contrasting organic residue (OR) retention methods on tree growth and soil nutrient pools over a full Eucalyptus rotation and (2) to assess the potential of soil analyses to predict yields of fast-growing plantations established on tropical sandy soils. An experiment was set up in the Congo at the harvesting of the first rotation after afforestation of a native herbaceous savanna. Six treatments were set up in 0.26 ha plots and replicated in 4 blocks, with OR mass at planting ranging from 0 to 46.5 Mg ha −1. Tree growth over the whole rotation was highly dependent on OR management at planting. Over-bark trunk volume 7 years after planting ranged from 96 m 3 ha −1 in the treatment with forest floor and harvest residue removal at planting to 164 m 3 ha −1 in the treatment with the largest amount of OR. A comparison of nutrient stocks within the ecosystem at planting and at the end of the rotation suggested that nutrient contents in OR were largely involved in the different response observed between treatments. OR management treatments did not significantly modify most of the nutrient concentrations in the upper layers of the mineral soil. Conventional soil analyses performed before planting and at ages 1 and 3 years were unable to detect differences between treatments despite large differences in tree growth. In contrast, linear regressions between stand aboveground biomass at harvesting and OR mass at planting (independent variable) showed that OR mass was an excellent predictor of stand yield ( R 2 = 0.99). A large share of soil fertility comes from organic material above the mineral soil in highly weathered sandy soils and OR mass at planting might be used in conjunction with soil analyses to assess the potential of these soils to support forest plantations.

Comprehensive evaluation of kraft pulp properties from fast-growing woods

To develop new wood cellulose resources and fast-growing pulpwood plantation fiber sources, it is very important to evaluate their pulping properties. A comprehensive multi-index pulping-suitability evaluation model is investigated in this paper by considering four fast-growing wood species. First, a new evaluation-index system for kraft pulp was developed based on traditional evaluation-index systems. Then, the membership degree of every index was analyzed to obtain a fuzzy matrix. The proportional contribution of each parameter to the main pulping properties could then be determined. Finally, a comprehensive evaluation model of kraft pulp properties was developed. The model is reliable compared with traditional assessment methods. The results confirmed the feasibility and rationality of developing new wood cellulose resources and fast-growing pulpwood plantations using fuzzy comprehensive evaluations.

Diurnal and circadian patterns of gene expression in the developing xylem of Eucalyptus trees

The daily cycle of night and day affects the physiology and behaviour of almost all living things. At a molecular level, many genes show daily changes in expression level, often providing adaptive benefit to the organism. The roles that such daily patterns of gene expression play in coordinating carbon allocation processes during wood development in trees are not fully understood. To identify genes with diurnal expression patterns in wood-forming tissues of field-grown Eucalyptus trees, we used a cDNA microarray to measure transcript abundance levels at roughly four-hour intervals throughout a diurnal cycle in two clonal hybrid eucalypt genotypes. Eight percent of genes on the microarray (217 out of 2608) exhibited diurnally influenced expression profiles. Affected genes included those involved in carbon allocation, hormone signalling, stress response and wood formation. Eucalyptus homologues of the central clock genes Circadian Clock Associated 1 (CCA1) and GIGANTEA (GI) were expressed in developing xylem tissues and cycled with a circadian rhythm in constant light. The presence of a functional biological clock and diurnal transcript abundance patterns during xylogenesis suggests important roles for temporal control of xylem development and metabolism in fast-growing plantation trees.

The potential of plantations of Terminalia superba Engl. & Diels for wood and biomass production (Mayombe Forest, Democratic Republic of Congo)

• In the 1940s–1950s, large limba (Terminalia superba Engl. & Diels) plantations were established in the Democratic Republic of Congo to reduce the pressure on the natural forests. • The objective of this study was to evaluate the potential of these long-rotation plantations as production forests (timber) and carbon sinks. • Five different plantations, between 50 and 58 years old, were sampled. Over a sample surface of more than 73 ha, the diameter above buttresses of 2 680 trees, bole height of 265 trees and tree height of 128 trees was measured. • To estimate the commercial volume, a nonlinear power law regression was used (R 2 = 0.95). A power law variance function was applied to counter heteroscedasticity of the residual plot. Estimates of commercial tree and stand volume at 50 to 58 y were 5.6 ± 4.1 m3 and 183.9 ± 135.0 m3 ha−1. Stand volumes appear low but are explained by a large decrease in tree density. However, the mean volume increment of 3.2–3.7 m3 ha−1 y−1 corresponds well with teak plantations of a similar age. For limba, aboveground biomass and carbon estimates of this study (resp. 108.4 and 54.2 Mg ha−1) differ significantly from those of existing aboveground biomass models (resp. 135.7–143.9 Mg ha−1 biomass and 67.9–72.0 Mg ha−1 C). All aboveground biomass and carbon estimates for T. superba stands were lower than for the estimates of young fast-growing plantations like Tectona grandis L. f., Eucalyptus spp. and Acacia spp. (≤ 30 y).

Wood colour variation in sapwood and heartwood of young trees of Tectona grandis and its relationship with plantation characteristics, site, and decay resistance

• Wood colour of Tectona grandis produced from fast-growth plantations is highly variable and the causes of this variation are relatively unknown. • With the purpose of understanding the colour variation, different fast-growth plantations were sampled with different growth rates, tree ages, and sites. • Wood colour was measured with a CIELab system, where three variables are estimated: coordinate L* for lightness, coordinate a* defines redness and coordinate b* defines yellowness. • Results showed only a negative correlation between L* and a*. L* and a* were negatively and positively respectively correlated with pith distance in heartwood, but not for b*. No correlations were found between L* and b* in sapwood and plantation characteristics, while a* was positively correlated with age and height of tree and growth rate. In heartwood, tree age and diameter at breast height were correlated with all colour parameters, but tree height and plantation density were correlated with a* and b*. Cluster site had correlation with L*. Multiple correlation analysis showed that the heartwood is increasing darker (L*) and redder (a*) when the trees are older and bigger. Correlation coefficient shown that sapwood and heartwood with lighter colour (L*) is less resistance to fungal attack, but redness colour (a*) increasing decay resistance.

INFORMATION EXTRACTION OF THE FAST-GROWING PLANTATION AREA BASED ON CBERS SATELLITE IMAGES

In this paper,a method for detecting the fast-growing plantation based on remote sensing is proposed,and the measuring of the distribution of the fast-growing plantation in large areas has been realized.This method is based on the cure trajectory extracted from the multi-year CBERS images.According to the characteristics of the electromagnetic spectra obtained during the period when the fast-growing plantation was cut down and the soil was turned up,the land used for fast-growing plantation can be extracted.The test in Leizhou City of Guangdong Province shows that the overall accuracy of the extracting method is 88%,which indicates that CBERS CCD images can be used to extract fast-growing plantation in large areas.

Change from Agriculture to Forestry: Floristic Diversity in Young Fast-Growing Deciduous Plantations on Former Agricultural Land in Estonia

The understorey vascular plant cover and its relations with the overstorey tree species and site properties in young silver birch and hybrid aspen plantations were studied. Understorey vegetation was similar in both plantation types in terms of species richness, diversity, sensitivity to human impact, life-span and habitat preference. Nevertheless, in denser silver birch plantations some signs indicated a faster vegetation development overall, e.g., a higher share of shade tolerant plant species. The concentration of total N was higher in the humus layer of silver birch plantations consequently affecting the nutritional status of the understorey vegetation. The significant impact of the plantation type on the understorey vegetation was confirmed by the NMDS analysis. The hypothesis that semi-exotic hybrid aspen plantations may support the spread of alien species or may show a tendency towards smaller indigenous species richness was not confirmed. Irrespective of the overstorey tree species, a strong previ...

Influence of ligno-cellulosic particles on tribological properties of boards

There are two main possibilities to substitute conventional wood material in the panel production: the use of wood of fast-growing trees plantations and/or the use of alternative ligno-cellulosic raw materials. Especially particleboards produced from the ‘‘energetic’’ willow present the same or better mechanical parameters compared to particleboards conventionally produced mainly from soft woods. Increasing bio-fuel production, mostly from rape, will cause an escalation of the rape cultivation area and, as a result, will augment the amount of waste (rape straw) to be utilized. The aim of this study was to verify the friction coefficient of the new board types in tribological contact with tools surfaces. The investigations were performed in situ. The results of the friction coefficient related to the tools surfaces as well as lingo-cellulose materials are presented.

Dynamics of fine root distribution after establishment of monospecific and mixed-species plantations of Eucalyptus grandis and Acacia mangium

Introducing N-fixing species in the understorey of fast-growing plantations might be an attractive option to improve soil N status. Intensive fine root sampling was performed in a complete randomized block design to investigate the ability of Eucalyptus grandis and Acacia mangium seedlings in monospecific stands and mixed-species plantations to take up complementary resources from niche exploration of soil layers. The same soil layers were explored by the two species down to a depth of 2 m in monospecific stands. Whilst the development of E. grandis fine roots was not affected by A. mangium trees in mixed-species plantations, A. mangium fine roots were excluded from the upper soil layer from 18 months after planting onwards, despite the paramount importance of that horizon for tree nutrition in highly weathered soils, and were only found deeper and close to A. mangium trees 30 months after planting.

Changes in total carbon and nutrients in soil profiles and accumulation in biomass after a 30-year rotation of Pinus radiata on podzolized sands: Impacts of intensive harvesting on soil resources

A large proportion of plantations of radiata pine ( Pinus radiata D. Don) in southern Australia have been established on podzolized coastal sands with low nutrient reserves. Inter-rotational management of the forest floor and harvesting residues has been shown to be critical to maintain the productive capacity of these soils. In 1974 a study was initiated at the end of the first rotation to evaluate the long-term sustainability of fast-growing plantations on these podzolized sands. Growth was measured at 5, 10 and 20 years and prior to clear-felling at age 30. Soil sampling at the end of the first rotation in 1974 was repeated in 2004 prior to clear-felling to determine changes in carbon and nutrients in profiles after 30 years. Forest floor and tree biomass were measured to determine sequestration of carbon and nutrients in mature radiata pine. Productivity of radiata pine on infertile podzolized sands was either maintained at 26 m 3 ha −1 year −1 or improved from 21 to 27 m 3 ha −1 year −1 over two rotations from 1946 to 2005 and this was attributed to conservation of organic matter and nutrients through retention of litter and harvesting residues after the first rotation. Total carbon (23.4 Mg ha −1) and N (595 kg ha −1) remaining in residues and litter after harvesting compensated for losses of carbon (9.2 Mg ha −1) and N (582 kg ha −1) in soil (0–75 cm) over the rotation. Total S, P, K, Ca and Mg remaining on site after conventional harvesting (stem wood and bark) increased during the second rotation (1975–2005). Accumulation of nutrients in the above-ground biomass and soil over 30 years exceeded deposition in rainfall indicating a redistribution of S, P, K, Ca and Mg from the sub-soil to tree biomass. The net accumulation of N in biomass (201 kg ha −1) also exceeded atmospheric deposition indicating significant inputs from nitrogen fixation during the rotation. Intensive harvesting including removal of log residues and branches for biofuels but leaving foliage on site increased nutrient exports by approximately 30% but did not exceed accession of nutrients over 30 years except for N. In contrast, whole-tree harvesting including foliage increased nutrient exports by 70–150% and fertilizers are likely to be required to compensate for the additional removal of nutrients and to maintain site productivity in the next rotation.