Effect of radiata pine on soil chemical characteristics

Soil nutrient contents and distributions beneath planted mature pine (P. radiata) have been compared with those beneath adjacent native eucalypt at two sites (Wee Jasper and Billapaloola) in the Tumut District, N.S.W. The soil nutrients studied included total nitrogen, phosphorus, potassium, calcium, magnesium and sodium, together with exchangeable aluminium, calcium, magenesium, potassium and sodium. Planting of pine resulted in a redistribution of nutrients within the ecosystem. At Wee Jasper, nutrients accumulated in the pine stand and it appeared that this had occurred from deeper rooting in the soil profile, while at Billapaloola, nutrients were removed to a greater degree from the soil surface. Changes in total quantities of nutrients were small and there was no evidence of a potential productivity decline in the subsequent rotation from these changes.     

Nutrient export and harvest residue decomposition patterns of a Eucalyptus dunnii Maiden plantation in temperate climate of Uruguay

The potential export of nutrients from Eucalyptus plantations harvested for pulp production may be high. However, depending on the harvest method, the nutrients from the residue can be recycled. The aims of this study were (i) to quantify the content and distribution of nutrients in different residue components at harvest for a Eucalyptus dunnii Maiden plantation; and (ii) to quantify the decomposition rates of the harvest residues, and the return of nutrients to the soil in the temperate climate conditions of Uruguay. Six trees of a 9-year-old E. dunnii plantation with average diameter at breast-height (DBH) were harvested, and the biomass produced and the N, P, K, Ca and Mg contents in commercial and non-commercial logs, leaves, branches, bark and litter were estimated. Decomposition of the remains of leaves, branches, non-commercial logs, bark and litter was studied in the field for 2 years. Although commercial logs accounted for 61% of the biomass produced, only 27% of the N, 35% of the P, 18% of the K, 16% of the Ca and 41% of the Mg present in the forest were exported with the product. When logs are exported without de-barking in the site, the nutrient export would increase to 41%, 55%, 46%, 68% and 66% of the total extraction of N, P, K, Ca and Mg, respectively. Residue decomposition showed that the leaves lost the highest proportion of biomass (half life 0.86 years), and bark was most resistant to decomposition in the field (half life 5.36 years). As regards the nutrients, K was lost most rapidly and Ca showed the slowest loss, while N, P and Mg losses were generally more gradual, and proportional to the decomposition rate.     

Productivity,nutrient cycling,and succession in single- and mixed-species plantations of Casuarina equisetifolia,Eucalyptus robusta,and Leucaena leucocephala in Puerto Rico

Tree growth, biomass productivity, litterfall mass and nutrient content, changes in soil chemical properties and understory forest succession were evaluated over a 8.5-year period in single- and mixed-species (50 : 50) plantations of two N₂-fixing species, Casuarina equisetifolia and Leucaena leucocephala, and a non-fixing species, Eucalyptus robusta. At the optimal harvest age for maximum biomass production (4 years), total aboveground biomass ranged from 63 Mg ha⁻¹ in the Eucalyptus monoculture to 124 Mg ha⁻¹ in the Casuarina/Leucaena mixture, and was generally greater in the mixed-species than in single-species treatments due to increased productivity of the N-fixing species in the mixed stands. Total litterfall varied from 5.3 to 10.0 Mg ha⁻¹ year⁻¹ among treatments, or between 5.9% and 13.2% of net primary production. Litterfall production and rates of nutrient return for N, P, K, Ca and Mg were generally highest for Leucaena, intermediate for Casuarina and lowest for Eucalyptus. These rates were usually higher in the mixed-species than in monospecific stands due to differences in biomass productivity, but varied considerably depending on their species composition. Total system carbon and nutrient pools (in biomass plus soils to 40-cm depth) for N, P, K, Ca, Mg, Mn at four years were consistently greater in the plantation treatments than in the unplanted control plots. Relative to the single-species plantations, these system pools were generally larger in the mixed-species plantations for C (−10% to +10%), N (+17% to +50%), P (−1% to +63%), K (−19% to +46%), Ca (−10% to +48%), Mg (+5% to +57%) and Mn (+19% to +86%). Whole-tree harvests at four years would result in substantial system carbon and nutrient losses, although these estimated losses would not exceed the estimated gains realized during the four-year period of tree growth at this site. At 7.5 years, soil organic matter and effective cation exchange capacity were reduced in all plantation treatments relative to the control. Changes in soil nutrient content from 0 to 7.5 years were highly variable and not significantly different among treatments, although stands containing Leucaena generally showed higher rates of nitrogen and phosphorus accretion in soils than those with Eucalyptus and/or Casuarina. Natural regeneration of secondary forest tree and shrub species increased over time in all plantation treatments. A total of 24 native or naturalized forest species were recorded in the plantations at 8.5 years. Woody species abundance at this age was significantly greater beneath Casuarina than either Eucalyptus or the Eucalyptus/Leucaena mixed stands. Species richness and diversity, however, were greatest beneath stands containing Eucalyptus and/or Leucaena than in stands with Casuarina.     

Nutrient exports under different harvesting regimes in fast-growing forest plantations in southern Europe

In the humid and temperate areas of southern Europe, forest plantations are dominated by fast-growing species (Eucalyptus globulus, Pinus radiata and Pinus pinaster), which are grown on acidic soils with low reserves of available nutrients. In this study the amounts of nutrients exported from the plantations under different regimes and intensities of harvesting were evaluated and, on the basis of the results obtained, silvicultural management methods aimed at improving the nutritional status of the plantations were proposed. We found high ratios between nutrients exported by harvesting and those available in soil stores, indicating limitation for P, Ca and Mg over the long term, which is consistent with frequently found deficiencies of these nutrients. Current harvesting practices (removal of stem wood and bark) result in high rates of export of P, K, Ca and Mg, especially in eucalypt plantations, because of the high productivity and low nutrient efficiency of this species. Comparison of the amounts of nutrients exported by harvesting, with natural inputs (rainfall and weathering) and outputs (stream water), suggests that intensive exploitation of these plantations may result in negative budgets, especially if whole tree harvesting is carried out. The application of fertilizers containing P, Ca and Mg should be encouraged in all cases to favour the return of nutrients, especially where logging residues are extracted. The cost of harvesting in terms of nutrients can also be reduced by careful selection of the tree species planted and of the tree fractions harvested and by reducing the intensity of harvesting.     

Results of long-term K and Mg fertilizer experiments in afforestation

Results from long-term fertilizer experiments on Scots pine (Pinus sylvestris) planted on old arable land in the north-eastern German lowlands demonstrate the necessity for fertilization with KMg on poorly buffered sandy soils.Applying KMg to young Scots pine increased pole production over a 60 year period by a total of 129 m³ ha⁻¹ (26%). In other experiments the improvement was as much as 93%.KMg manuring on light soils ensures optimal K and Mg nutrition and creates the conditions for uninterrupted growth and healthy development of the plantation. On degraded soils, KMg treatment leads to improved utilisation of the low soil nitrogen supply.With increasing eutrophication due to atmospheric nitrogen, KMg fertilization overcomes the depletion of soil cations and resulting imbalance in tree metabolism.Adequate application of KMg is a prerequisite for success in underplanting with beech (Fagus silvatica) on soils with a land use classification below 30, increasing the growth in height of beech by about 30%.KMg fertilizer favours biomass production and thus the fixation of N deposited through the atmosphere by the vegetation. Thereby, KMg fertilizer use and other silvicultural measures reduce the negative effects of atmospheric N-input in forest ecosystems to a certain extent, especially the N-pollution of groundwater. However, they cannot replace the technologies to reduce the N emissions.     

Nutrient content of standing crop and biological cycling in Pinus patula ecosystem

Nutrient contents were estimated in different components of Pinus patula trees growing in six stands ranging from 8 to 34 years of age in the Darjeeling hills, India. The highest concentrations of most nutrients were found in the leaves but the maximum nutrient pool was contained in the bole which accounted for about 58 to 85% of the total aerial contents of different elements. Among the nutrients, N concentration (2.2%) was the highest, followed by Ca Mg K P Na. Nutrient contents in the standing crop increased with stand age and were nearly 2102 kg Ca, 1911 kg N, 875 kg Mg, 478 kg K, 285 kg P and 82 kg Na per ha in above-ground biomass of the 34-year-old stand. The annual uptake of N is highest but its accumulation in the standing stock is lower than that of Ca in the 34-year-old stand. The uptake and storage of Mg closely resembled those of K. Nutrient return and release were also determined to establish biological cycling in the 34-year-old P. patula ecosystem. Litter is resistent to decay and the forest floor retained a very rich nutrient store over the mineral soil. Turnover rates and times for nutrient fluxes showed the higher efficiency of the return pathway and the greater stability of the soil pool.     

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.     

Export of Nutrients in Plant Biomass Following Harvest of Eucalypt Plantations in Kerala,India

Abstract

Pools of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were examined in the soil and above-ground plant biomass at the end of a 7 year rotation at two E. tereticornis lowland sites and two E. grandis highland sites in Kerala, India. Potential export rates of these nutrients were also examined for different biomass removal scenarios from the plantations. Pools of nutrients were measured in the above-ground components of the tree crop, forest floor and understorey, and in soil down to 1 m depth. At harvest, large quantities of biomass and nutrients are removed from eucalypt plantation sites, with the quantities of nutrients exported unlikely to be replaced through natural atmospheric and weathering inputs. Between 24 Mg ha^-1 and 115 Mg ha^-1 of biomass was exported in stem wood across the sites, and this increased to 40-145 Mg ha^-1 in scenarios where all of the branches, bark and understorey were also exported. Stem wood had the lowest concentration of nutrients and had a relatively low export of nutrient per kg of biomass. On average, 54 kg, 12 kg and 65 kg of N, P and K were removed per hectare in stem wood only, equivalent to 0.46%, 0.17%, and 6.7%, respectively, of above- and below-ground (to 1 m depth) site pools. Export increased to 194 kg, 30 kg, and 220 kg of N, P and K per hectare if the branches, bark and understorey were also removed (equivalent to 1.6%, 0.5% and 24.7% of above- and below-ground site pools down to 1 m depth). Export of Ca and Mg was also high, with an average of 88 kg and 11 kg of Ca and Mg removed per hectare if only the stem wood was taken (3.12% and 1.34% of total above-ground and exchangeable below-ground to 1 m depth), increasing to 501 kg ha^-1 and 66 kg ha^-1 if the branches, bark and understorey were also removed (21.7% and 11.3% of total above-ground and available below-ground to 1 m depth). Removals of this magnitude represent a significant proportion of site nutrient pools and have the potential to reduce future plantation productivity unless steps are taken to promote retention of biomass and nutrients on site and/or replacement of nutrients through fertilizer application.     

Split fertilizer application affects growth, biomass allocation, and fertilizer uptake efficiency of hybrid Eucalyptus

Fertilization is indispensable to the establishment success of many eucalypt plantations. Split application of fertilizer has proven effective in agronomic systems; however, its potential impact on eucalypt tree growth and fertilizer uptake efficiency (FUE) is not well understood. This study investigated the effects of split fertilizer applications on seedling growth and biomass production, nutrient uptake, and FUE for the Guanglin No. 9 clone [hybrid of Eucalyptus grandis (Hill ex Maiden) × Eucalyptus urophylla S.T. Blake]. Three application timings and a control were established at rates of 125 and 250 g inorganic fertilizer (16N–7P–7K) per seedling. Split application played a more pronounced role than fertilization rate in eucalypt seedling growth and biomass accumulation. Compared to a single-time application, split applications increased eucalypt seedling height and root collar diameter growth, biomass, and nutrient uptake. The ratio of root to seedling dry mass showed a decreasing trend with split applications, whereas ratios of stem and branch to seedling dry mass tended to increase with split applications. Split applications also significantly improved FUE compared to the single-time application treatment. Findings of this study suggest that split applications of inorganic fertilizer with two application times could be an appropriate fertilization method to improve seedling growth and FUE of this eucalypt clone.     

The effect of stand age on the accumulation of nutrients in the aboveground components of an Aleppo pine ecosystem

Nutrient dynamics of an Aleppo pine (Pinus halepensis, Mill.) ecosystem located in the Kassandra peninsula, Central Macedonia, Northern Greece, were studied using a chronosequence approach. The nutrient composition of the Aleppo pine trees, the understory evergreen broadleaves and forest floor in adjacent stands of 23, 48, 70 and over 100 years old was determined to estimate postfire nutrient losses. The concentration of nutrients in the Aleppo pine trees, except of Ca, was reduced with increasing stand age. Ca was the most abundant nutrient in the aboveground vegetation and in forest litter, followed by N, K, Mg and P. The accumulation of nutrients in the aboveground biomass was positively related to stand age. For younger stands nutrient accumulation was considerably larger in the understory vegetation as compared to the pines, due to substantial enhancement of the understory biomass and the number of understory species present. In middle-aged stands, however, nutrient accumulation in the understory and overstory vegetation reached a balance. In addition, considerable quantities of nutrients have been accumulated in the forest floor particularly in stands of 48 years old. Therefore, any destruction during the period of maximum nutrient accumulation in the forest floor will cause degradation of the ecosystem. It is postulated that the competition for nutrients between overstory and understory vegetation may be as important as competition in soil. Forest management practices leading to the direct conversion of the understory biomass into littermass would be of great significance for the sustainability of the Aleppo pine ecosystem.     

Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China

The distribution in tree biomass and understorey vegetation and annual biological and geochemical cycling of total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured in young, middle-aged and mature plantations (8-, 14- and 24-years old) of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in southern China. Although >98% of nutrients occurred in the soil, soil nutrient content decreased with plantation age. Nutrient outputs from the soil exceeded inputs in stands of all ages but the net soil nutrient loss increased significantly for N, P and Ca with plantation age. Comparison of nutrient fluxes showed that the smallest (and hence limiting for nutrient cycling) fluxes were litter decomposition in the young plantation in contrast to canopy fluxes (apart from for Mg) in the middle-aged and mature plantations. Nutrient use efficiency, release of nutrients from litter decomposition and nutrient return, particularly in litterfall, increased significantly with plantation age. These results suggest that, as stand age increases, nutrient cycling in Chinese fir plantations is increasingly dominated by biological processes and becomes less dependent on external nutrient sources in rainfall and the soil. It therefore appears that prolonging the rotation length of Chinese fir plantations by approximately 5 years could be beneficial for maintaining the soil nutrient status for successive plantings.     

Conversion of native forest to exotic Pinus radiata plantation: Response of understorey plant composition using a plant functional trait approach

This study aimed to determine the response of native plant species to changed growing conditions, especially increased shade, following establishment of exotic Pinus radiata plantation on cleared native eucalypt forest. In the Northern Hemisphere, species tolerant to shading are typically herbaceous perennials, with large seeds, no obvious mechanism of seed dispersal, and spread by clonal means. We investigated whether life form, mode of seed dispersal, leaf area, specific leaf area (SLA), nutrient uptake strategy, seed mass, fire response, plant height, and clonal spread differed between understorey species of pine plantation and native forest. Further, we asked whether plant functional traits that confer tolerance to stress through shading differ from those in other floras. The study was conducted on the Delatite Peninsula in north-eastern Victoria, Australia. Vegetation of adjacent native forest and pine plantation were surveyed using eight 7 m × 7 m plots per site, randomly located within five paired sites. Differences in plant traits between land-use types were tested by Non-metric Multi-dimensional Scaling (NMDS), analysis of similarity (ANOSIM) and paired t-tests. Cluster analysis of the nine plant traits was used to define emergent groups, with differences between land-use types examined by ANOSIM and indicator species analysis. There was a significant change in the composition of understorey vegetation following conversion to pine plantation that included a decline in the richness of native species. NMDS of plant attributes showed a clear separation of native forest from pine plantation with land use strongly correlated in ordination space (r² = 0.611). Cluster analysis produced seven emergent groups of plant functional traits for 78 identified plant species. Phanerophytes split into two groups (myrmecochorous trees and shrubs; myrmecochorous shrubs), perennial herbs into four groups (upright herbs, myrmecochorous herbs, barochorous herbs, flat rosette herbs) with one group representing therophytes and anemochorous perennials. Perennial herbs with intermediate SLA and clonal spread were tolerant of the shaded conditions in pine plantation while the two groups of phanerophytes and the myrmecochorous herbs were largely excluded. Shared traits of excluded emergent groups included those that provided an over-riding adaptation to mineral nutrient stress, including myrmecochory, low SLA, ectomycorrhizal and ericoid mycorrhizal associations and N₂-fixation. These plant traits could not provide tolerance to stress through shading, which is better explained by the open canopied nature of the native forest.     

Atmospheric nutrient inputs to three forest types in East Texas

The effect of forest type on atmospheric nutrient inputs to the forest ecosystem was measured for individual storm events for 1 year in three East Texas forest types: beechmagnolia, pine-mixed hardwoods and loblolly pine plantation. Total annual bulk precipitation inputs (kg/ha) for Ca, Mg, N, K and Na were, respectively: 5.0, 1.1, 4.1, 3.3 and 9.9. Total througfall inputs were increased by forest type, but the magnitude differed with each nutrient. Over $\text{3}\text{4}$ of the total K and $\text{1}\text{2}$ the total Mg throughfall input were due to the forest canopy. However $\text{2}\text{3}$ of the Ca and most of the Na throughfall input resulted from bulk precipitation. Although stemflow nutrient concentrations (ppm) were higher than throughfall and bulk precipitation, total annual stemflow nutrient inputs were only a minor component of the loblolly pine plantation ecosystem.     

Allometry, biomass, and chemical content of Novel African Tulip Tree (Spathodea campanulata) Forests in Puerto Rico

The African tulip tree, Spathodea campanulata, the most common tree in Puerto Rico, forms novel forest types with mixtures of native and other introduced tree species. Novel forests increase in area in response to human activity and there is no information about their biomass accumulation and nutrient cycling. We established allometric relationships and chemically analyzed plant parts of African tulip trees to determine the concentration and standing stock of chemical elements (C, N, P, K, Ca, Mg, S, Mn, Al, Fe, Na), and ash. Trees ranged in diameter at breast height from 8 to 85 cm and in height from 8.8 to 28 m. The concentrations of N, P, K, and Ca in leaves of the African tulip tree were similar to those of the native pioneer Cecropia schreberiana and higher than those of mature forest tree species in Puerto Rico. The over bark wood volume of African tulip trees in nine forest stands where it was dominant ranged from 163 to 849 m³/ha. Aboveground biomass ranged from 60 to 296 Mg/ha, and N and P stocks ranged from 190 to 988 and 32 to 137 kg/ha, respectively. Novel forests on abandoned agricultural lands can store more biomass and elements than native and plantation forest stands of similar age.     

Biomass and nutrient accumulation in pure and mixed plantations of indigenous tree species grown on poor soils in the humid tropics of Costa Rica

Aboveground biomass and nutrients and soil chemical characteristics were examined in young plantations of four indigenous tree species: Hieronyma alchorneoides, Vochysia ferruginea, Pithecellobium elegans, and Genipa americana, growing in mixed and pure stands at La Selva Biological Station, Costa Rica. Total tree biomass production rates ranged from about 5.2 Mg ha⁻¹ year⁻¹ for G. americana to 10.3 Mg ha⁻¹ year⁻¹ for H. alchorneoides pure stands, and for the species mixture it was about 8.9 Mg ha⁻¹ year⁻¹. Branches and foliage formed 25–35% of total tree biomass but they represented about 50% of total tree nutrients. H. alchorneoides, the four species mixture, and P. elegans had the greatest accumulations of total aboveground nutrients per hectare. The importance of the plantation floor as a nutrient compartment varied temporally. When forest floor litter biomass was at its peak, plantation floor litter N, Ca, and Mg were roughly equal to, or greater than stem nutrients for all species except for P. elegans. For P. elegans, the plantation floor consistently represented a very low proportion of total aboveground nutrients. G. americana and V. ferruginea trees showed 55–60% less biomass accumulation in mixed than in pure stands while H. alchorneoides and P. elegans trees grew 40–50% more rapidly in mixture. P. elegans foliage had 60% lower Ca but higher P concentrations in mixed than in pure stands, and G. americana had higher foliar Mg in mixed than in pure stands. V. ferruginea stands had the highest concentrations of soil Ca, Mg, and organic matter, particularly in the top layers. Relative to pure plantations, soil nutrient concentrations in mixed plantations were intermediate for N, P, and K, but lower for Ca and Mg. The results of this study can be used in the selection of tree species and harvest designs to favor productivity and nutrient conservation.     

Simulated biomass and soil carbon of loblolly pine and cottonwood plantations across a thermal gradient in southeastern United States

Changes in biomass and soil carbon with nitrogen fertilization were simulated for a 25-year loblolly pine (Pinus taeda) plantation and for three consecutive 7-year short-rotation cottonwood (Populus deltoides) stands. Simulations were conducted for 17 locations in the southeastern United States with mean annual temperatures ranging from 13.1 to 19.4 °C. The LINKAGES stand growth model, modified to include the “RothC” soil C and soil N model, simulated tree growth and soil C status. Nitrogen fertilization significantly increased cumulative cottonwood aboveground biomass in the three rotations from a site average of 106 to 272 Mg/ha in 21 years. The equivalent site averages for loblolly pine showed a significant increase from 176 and 184 Mg/ha in 25 years with fertilization. Location results, compared on the annual sum of daily mean air temperatures above 5.5 °C (growing-degree-days), showed contrasts. Loblolly pine biomass increased whereas cottonwood decreased with increasing growing-degree-days, particularly in cottonwood stands receiving N fertilization. The increment of biomass due to N addition per unit of control biomass (relative response) declined in both plantations with increase in growing-degree-days. Average soil C in loblolly pine stands increased from 24.3 to 40.4 Mg/ha in 25 years and in cottonwood soil C decreased from 14.7 to 13.7 Mg/ha after three 7-year rotations. Soil C did not decrease with increasing growing-degree-days in either plantation type suggesting that global warming may not initially affect soil C. Nitrogen fertilizer increased soil C slightly in cottonwood plantations and had no significant effect on the soil C of loblolly stands.     

Impact of plantation forestry with teak (Tectona grandis) on the nutrient status of young alluvial soils in West Venezuela

On alluvial sandy loams in the western Llanos of Venezuela, biomass and inventories of macronutrients were determined for ten teak plantations (0.5–9 years old) and a mature forest stand which preceded them. Mean tree and stratified random sampling methods of estimating biomass are compared with regression estimates.Aboveground biomass of the mature forest averages 398 t ha^?1. The average yearly productivity of biomass per ha of the teak plantations is greater on sites with soils having higher clay contents; It was measured as 23 t (9-year-old plantation), 16 t (7 years), 10–14 t (6 years) and 7–14 t (4 years).The original ecosystem stores per ha for these sites range between 8380 and 8840 kg N (total), 4550 and 4890 kg P, 2290 and 2540 kg K, 6720 and 6850 kg Ca and 960 and 1760 kg Mg.In the mature forest most N, P and Mg is stored in the soil, whereas 70% of the K and 40–50% of the Ca is stored in the vegetation. The ecosystem K stores of the teak plantations are an average of 40% lower than in the original forest. This difference is interpreted as being due to leaching loss caused by replacement of the original forest.Using data from the literature and from this study, a nutrient budget has been calculated for the first rotation period of teak. It is predicted that substantial amounts of Ca will be removed from the site by the teak harvest. These exports may not be replenished by atmospheric inputs and soil mineral weathering, especially on the highly productive sites.     

Biomass and nutrients in Nova Scotian forests,and implications of intensive harvesting for future site productivity

Among four conifer and four hardwood stands in central Nova Scotia, Canada, average potential whole-tree (above-ground) harvest removals of biomass, N, P, K, Ca, and Mg were 136 000, 310, 38, 144, 360, and 39 kg/ha, respectively. These represented average increases over bole-only harvesting of 50% for biomass, 170% for N, 200% for P, 160% for K, 100% for Ca, and 120% for Mg. Thus, a moderate increase in potential biomass yield via the whole-tree harvest, was obtained at the expense of much larger increases in removals of major nutrients. On average, the whole-tree contents of biomass and nutrients were smaller than quantities present in the forest floor plus mineral soil. For biomass, the whole-tree averaged 35% the organic matter (d.w.) of the forest floor plus mineral soil, 6% of total nitrogen, 4% of total phosphorus, 1% of total potassium, 29% of total calcium, and 0.5% of total magnesium. Within this data set, only the calcium comparisons indicated a short-term cause for concern with respect to impoverishment of site nutrient capital by whole-tree harvesting.Bivariate statistical analyses of data for 12 stands and 20 variables revealed that: (i) soil organic matter and nutrient quantities were only occasionally significantly intercorrelated; (ii) quantities of biomass and nutrients in the whole-tree compartment were strongly inter-correlated with each other, but were independent of site class; and (iii) only soil K and Mg were significantly (P<0.05) but weakly (r²=−0.35) correlated with site class. Factor analysis of the same data set revealed that four multivariate factors accounted for 93% of total variance: (i) factor 1 (45% of total variance) loaded heavily on tree variables; (ii) factor 2 (an additional 18% of total variance) loaded heavily on bole and soil variables; (iii) factor 3 (an additional 16%) loaded heavily on soil variables; and (iv) factor 4 (an additional 14%) loaded heavily on soil variables, especially Ca, Mg, and K, and site class.It seems unlikely that one or several whole-tree harvests of these natural stands, if done on rotations of >ca. 50 years, would result in important depletions of site nutrient capital. However, calcium removals as a percentage of total site capital were large. This may be a cause for concern, and warrants further investigation.     

马尾松、桉树及其混交林土壤养分变化特征及评价

研究马尾松纯林、桉树纯林和3种不同模式混交林土壤养分含量的变化规律,并对其土壤养分状况进行主成分综合排序。结果表明：土壤有机质、全 N、全 P、水解 N、速效 P 和速效 K 皆表现为随土壤深度增加而减少,全 K 则表现相反;在各林分中,桉树纯林的土壤有机质、速效 P 含量最高,混交林次之。混交林则土壤全 N、全P 和速效 N 含量总体上大于纯林。马尾松纯林除在浅层土中速效 P 含量最高外,其他养分指标都低于桉树纯林和混交林。土壤养分综合评价为桉树纯林＞混交林 A＞混交林 C＞混交林 B＞马尾松纯林,表现为桉树纯林养分状况最好,马尾松纯林最差,与针阔树种的生长特性和凋落物养分归还能力有关。混交林中种植密度较大的混交林A 养分状况相对较好,表明其养分储存能力较好,消耗较少。而相同种植密度下,混交林 C 的林分土壤养分状况优于混交林 B。     

火炬松人工林养分体内转移与内循环研究

对江苏省下蜀林场火炬松人工林 (15年生 )地上部分养分体内转移和内循环特点进行了初步研究 ,结果表明 :(1)在体内养分转移中 ,叶的贡献最大 ,N、P、K和Mg元素的平均转移量均大于枝和干 ;地上部分养分N、P、K和Mg元素的转移率分别为 44 9% ,34 5 % ,2 0 8%和 30 7%。 (2 )地上部分养分归还量N、P、K、Ca和Mg元素分别 5 5 787,6 13,2 6 70 ,70 79和 2 0 30kg·hm- 2 ·a- 1 分别占需要量的 36 6 7% ,44 6 5 % 5 5 3% ,78 0 2 %和 42 84% ;地上实际消耗土壤中的养分量N、P、K、Ca和Mg分别为 2 2 48,2 13,4 6 4,2 6 98和 7 41kg·hm- 2 ·a- 1 ,分别占吸收量的 2 3 99% ,2 2 76 % ,11 84% ,2 4 32 %和 2 1 0 9%。 (3)与当地的杉木林和次生栎林相比 ,该火炬松人工林养分利用率高 ,并处于养分消耗阶段。