Soil quality assessment under shifting cultivation and forests in Northeastern Himalaya of India

The study aimed to evaluate the impact of shifting cultivation on soil quality, in Wokha district of Nagaland, using weighted soil quality index (SQIw). Four forest sites and three sites under shifting cultivation were selected and physical (texture and bulk density) and chemical (pH, electrical conductivity, cation exchange capacity, organic carbon, available N, P, K, exchangeable cations) parameters were analyzed. The SQIw was calculated on a minimum data set selected by principal component analysis, followed by varimax rotation algorithm and through subsequent normalization of the parameters using the linear scoring function. Significant (P < 0.05) variations in SQIw were found across the depth of the soil and land use according to severity of factors associated with land use. Three different classes of soil quality were also identified: high quality (SQIw > 0.70) for two forest soils (FS1 and FS2) and land under shifting cultivation (JH1), low quality (SQIw < 0.50), only to FS3, and intermediate quality (0.50 < SQI < 0.70) in all other soils. The approach used in this study proved to be sensitive to evaluate the soil quality, however further research is required to better understand the sustainability of shifting cultivation by including more physical, biological and chemical indicators.     

Impact of Acacia auriculiformis on the chemical fertility of sandy soils on the Batéké plateau,D.R. Congo

A 17‐year chronosequence of Acacia auriculiformis fallows on Arenosols of the Batéké Plateau (D.R. Congo) was surveyed and compared with virgin savannah soils to assess chemical soil fertility changes induced by these N‐fixing trees. Significant increases in organic carbon content, total nitrogen content, cation exchange capacity and sum of base cations were found after relatively short fallow periods of only 4 years and did not only affect the forest floor, but extended to at least 50 cm depth. The Acacia act as a major source of organic matter (OM), hence increasing organic carbon and nitrogen content and decreasing the C/N ratio. The increased OM content suggests that humification processes are the main cause of the significant decrease in pH. Total exchangeable cations initially increased slowly but doubled (topsoil 0–25 cm) and tripled (subsoil 25–50 cm) after 10 years. The point of zero net proton charge was systematically lower than soil pH and decreased with increasing OM content, thereby increasing the cation exchange capacity, although concurrent acidification retarded a significant beneficial impact at field pH on Acacia fallows of 10 years and older. Although the chemical soil fertility improves steadily with time, after 8 years of Acacia fallow the absolute amounts of available nutrients are still small and slash and burn practices are required to liberate the nutrients stored in the remaining biomass and litter before each new cropping period.     

Microbial biomass and enzyme activities in coniferous forest soils as affected by lignite-derived deposition

A forest ecosystem study was conducted along a deposition gradient of air pollutants in old Scots pine stands located near the industrial belt around the city of Bitterfeld in northeast Germany from 1999 to 2000. In order to estimate the impact of different atmospheric deposition loads on microbial biomass and enzyme activities, samples were taken from the forest floor (L, F, and H horizon) and the mineral topsoil (0–10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH ₄NO ₃ extractable) Cr and Ni, effective cation exchange capacity, and base saturation in the humus layer along the 25-km long transect reflected that great portions of the past depositions were characterized by alkaline fly ash. Alkaline depositions significantly ( P <0.05) decreased the microbial biomass C and N contents, microbial biomass C-to-organic C ratios, and microbial respiration rates, but increased the metabolic quotient (qCO ₂) of the mineral topsoil and forest floor. Variations in microbial biomass and activity can mainly be predicted ( r ² =0.60) by the concentrations of Ca, Zn and Cd in these forest soils. The specific activities (activity kg ^-1 organic C) of l-asparaginase, l-glutaminase, arylsulfatase, and in part, acid phosphatase were significantly ( P <0.05) higher at forest sites receiving higher fly ash loads than those of the other sites, and thus followed the trend of the qCO ₂. In contrast, the specific activity of ß-glucosidase was significantly ( P <0.05) decreased at heavily affected sites compared to moderate and less affected sites, suggesting an inhibition of C mineralization in the forest floor of pine stands affected by predominantly alkaline emissions. A great portion ( r ²=0.91) of the variation in the specific enzyme activity data in forest soils in emission areas can be predicted from a linear combination of the variables total organic C and NH ₄Cl-extractable Ca, pH and effective cation exchange capacity.     

Prediction of Soil Acidification Using a Dymanic Model at a Bamboo Forest in Osaka Prefecture

This study is based on research of throughfall formation and soil chemistry processes. Through the experimental verification of the cation exchange part of the simulation model; making use of results of the flux of acid deposition on the forest and the chemical weathering of soil mineral, we predicted the future soil acidification. The result indicated that chemical weathering occupies the important portion of acid neutralization capacity of the soil and that significant soil acidification will not occur in this field within 40 years, even if the present acid load continues in the future.     

The Effect of Lake-Water Infiltration on the Acidity and Base Cation Status of Forest Soil

In this article, the effects of the artificialrecharging of groundwater by infiltrating surface water throughforest soil, i.e. sprinkling infiltration, on the acidity andbase cation status of the soil are described. The study wascarried out in the Ahvenisto esker area, Hämeenlinna,southern Finland, during 1996–1998. The sample plots werelocated in a 110- to 160-yr-old Scots pine (Pinussylvestris L.) stand. The site was classified as the Oxalis-Maianthemum type. The soil consisted of a mixture oftill and glaciofluvial sediments. The pH of the organic layerincreased from 4.7 to >6.5 soon after the start of irrigationon the infiltration plot. The pH of the 0–10 cm mineral soillayer also increased from 4.9 to 6.4 as a result ofinfiltration. Sprinkling infiltration increased theexchangeable Ca and Mg concentrations in the organic anduppermost mineral soil layers. The output of Ca and Mg inpercolation water from the 0–100 cm thick layer was lower thanthe input to the soil surface via irrigation in 1996. Theretention of Ca and Mg on cation exchange sites took placewithin a relatively short period of time, since retention wasobserved only in 1996 but no longer in 1997 or 1998 indicatingsaturation of the cation exchange sites by base cations. Lakewater infiltration leads to the neutralisation of forest soilacidity, and increases the capacity of the soil to withstandacidic inputs by increasing the concentrations of exchangeablebase cations on cation exchange sites in the soil.     

Carbon storage and other properties of soils under agriculture and natural vegetation in São Paulo State, Brazil

Abstract. Topsoil (0–20 cm) and subsoil (60–100 cm) properties are compared at agricultural and nearby natural vegetation sites in São Paulo State. Differences are related to land use and climate, in order to estimate soil carbon storage under various ecosystems and also to study the effects of high-input agriculture on the chemical composition of soils with low activity clays. Within each land use, organic carbon in the topsoil is most strongly related to clay + silt content. This relationship is stronger for cropped, short savannah (cerrado) and tall savannah (cerradão) sites than for semi-deciduous and evergreen forest sites. Losses of topsoil carbon with cropping can be predicted if the initial carbon and the clay+silt contents are known. The greatest carbon losses after long term cultivation occurred in forest mineral topsoils, ranging from 6% for perudic clayey soils to 37% for ustic sandy soils. No significant difference in carbon content was found between the paired savannah-cultivated sites. In most of the originally less fertile soils cation exchange capacity was greater in the cultivated topsoil (Ap) than in the topsoil under savannah or forest (A1), probably because of liming and phosphate fertilization. Most subsoils at agricultural sites show increases in exchangeable bases (mainly Ca) and base saturation, but no significant change in pH.     

Effects of Soil-Use Intensity on Selected Properties of Mollisols in Entre Ríos,Argentina

In the province of Entre Ríos (Argentina), land-use changes have been noticeable in recent years, because the portion of land devoted to pasture decreased whereas the proportion and length of crops in the rotation increased. We evaluated soil-use intensity effects on selected physical and chemical properties of a Mollisol in a crop–pasture rotation experiment located in Entre Rios. Treatments included (1) continuous cropping, (2) crop–pasture rotation, (3) pasture, and (4) natural (never-cultivated) land as a reference. Soil samples were analyzed for chemical (pH, carbon and nitrogen contents, extractable phosphorus, cation exchange capacity) and physical (aggregate stability, percolation index, bulk density, pore-size distribution, and specific surface area) properties. Clearing of the native vegetation resulted in a significant reduction of soil organic carbon content and losses of structure stability and soil porosity. No differences were seen in cation exchange capacity between native forest and cultivated land, whereas specific surface area increased with decreased levels of organic carbon content following agricultural use. Although the studied soil properties showed no significant differences when crop–pasture rotation and continuous cropping were compared, the former soil management system is recommended to maintain or promote sustainability.     

Impacts of land use/cover change on soil properties in the Mediterranean region of northwestern Jordan

This study was carried out to evaluate the effects of deforestation on physical and chemical properties of soils under native forest in the Mediterranean region of northwestern Jordan. Land use/cover maps of 1953, 1978 and 2002 were interpreted and analysed within GIS to quantify the shift from forest to rainfed cultivation. Six sites were sampled in a non‐changed forest and in cultivated fields, three for each. Different soil properties of texture, bulk density, organic matter, total nitrogen, pH, cation exchange capacity (CEC), phosphorous and potassium were analysed. Results showed that many forests were changed into cultivated lands at a rate more than the reforestation. Subsequently, adverse effects on the studied physical and chemical properties were observed. The most affected properties were particle size distribution, bulk density of surface soil and subsoil. Organic matter and CEC decreased in cultivated soil as compared to the forest soil. Cultivated soils were found to exhibit a significantly lower status in physical and chemical soil properties as compared to forest soils. This general decline in the soil physical and chemical properties, in turn, contributed to soil erosion, reduction of soil fertility and land degradation. There is an urgent need to improve soil quality by developing sustainable land use practices to reduce the rate of soil degradation and to ensure long‐term sustainability of the farming system in the study area and in similar biophysical settings. Copyright © 2008 John Wiley & Sons, Ltd.     

南亚热带森林演替过程土壤水分、有机质和交换性阳离子的变化格局

Information on the distribution patterns of soil water content （SWC）, soil organic matter （SOM）, and soil exchangeable cations （SEC） is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax （monsoon evergreen broad-leaved forest, or MEBF）, a transitional forest （coniferous and broad-leaved mixed forest, or MF）, and a pioneer forest （coniferous Masson pine （Pinus rnassoniana） forest, or MPF） of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca^2＋ were found to increase in the soil during forest succession, being highest in the top soil layer （0 to 15 cm depth） except for Na^＋. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences （P = 0.05） among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity （CEC） was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K^＋ to Na^＋ in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca^2＋ concentration among the three forests and Ca^2＋：K^＋ in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.     

Changes of lignin phenols and neutral sugars in different soil types of a high-elevation forest ecosystem 25 years after forest dieback

Long-term effects of forest disturbance 25 yr ago on lignin and non-cellulosic polysaccharide pools in an unmanaged high-elevation Norway spruce (Picea abies L. [Karst.]) forest were investigated by comparing three dieback sites with three adjacent control sites with non-infested spruce on identical soils. Samples were taken from the forest floor and the mineral soil; one Ah horizon sample per site was physically fractionated into density and particle size fractions. Additionally, changes in the above- and belowground input of lignin and non-cellulosic polysaccharides after forest dieback were quantified. Lignin and its degree of structural alteration in plant and soil samples were assessed by CuO oxidation and subsequent analysis of the lignin phenols. Non-cellulosic polysaccharides were determined after hydrolysis with trifluoroacetic acid (TFA), derivatisation of their neutral sugar monomers by reduction to alditols, and subsequent acetylation. The total plant-derived input of lignin and non-cellulosic polysaccharides to the soil was similar for the dieback and the control sites. The chemical composition of the input has changed considerably after forest dieback, as shown by significantly higher syringyl/vanillyl (S/V) ratios and significantly lower (galactose+mannose)/(arabinose+xylose) (GM/AX) ratios. This indicates a changed plant input and a higher contribution of microbial sugars. Contents of lignin phenols in the forest floor and coarse particle size fractions of the A horizons were significantly smaller at the dieback sites (p<0.01). Moreover, larger acid-to-aldehyde ratios of vanillyl units (Ac/Al)_v indicated an increased degree of lignin phenol alteration. Also contents of neutral sugars were significantly (p<0.01) smaller in the forest floor, but not in the A horizons of the dieback sites. The GM/AX mass ratios as well as the (rhamnose+fucose)/(arabinose+xylose) (RF/AX) ratios in the forest floor and coarse particle size fractions of the mineral topsoil were significantly (p<0.01) larger after forest dieback, indicating a larger relative contribution of microbial sugars. In general, the lignin phenol and neutral sugar pools of all three soil types exhibited similar response patterns to the changed site conditions. Our results demonstrate that the lignin and neutral sugar pools of humic topsoil horizons are highly sensitive to forest disturbances. However, the two compounds show different patterns in the mineral soil, with the major neutral sugar pool being stabilized against changes whereas the lignin phenol pool decreases significantly.     

Evaluation of soil fertility under different Cupressus chengiana forests using multivariate approach

The distribution and growing conditions of Cupressus chengiana forests along with the physical and chemical properties of soils in Northwest Sichuan were studied in 2002 to investigate the conditions and characteristics of soil fertility of C. chengiana and to compare and investigate differences of soil fertility for six C. chengiana populations and their relationships with vegetation, climate and disturbance. The results of the study at 0-20 cm soil depth showed that 1） significant differences （P〈0.05） existed among populations for soil bulk density, soil total porosity, capillary porosity, maximum water-holding capacity, capillary water-holding capacity and topsoil natural water content; 2） chemical characteristics of soil organic matter, total N, total P, alkali-hydrolyzable N, available P, available K and cation exchange capacity were significantly different among the populations; and 3） based on the significant effect of soil fertility factors on forest growth, soil physical and chemical characteristics could be selected as an integrated fertility index （IFI） for evaluation of different C. chengiana populations. Principal component and cluster analyses showed significant differences probably due to the difference of vegetation conditions, management measurements, human-induced disturbances and environmental factors. In order to protect the soil ecological functions in fragile ecological regions, C. chengiana could be used in programs enclosing the hill for natural afforestation, natural forest protection programs, and programs replacing agriculture with afforestation measures.     

Characterization of Degraded Soils in the Humid Ethiopian Highlands

Hardpan is a major cause of land degradation that affects agricultural productivity in developing countries. However, relatively, little is known about the interaction of land degradation and hardpans. The objective of this study was, therefore, to investigate soil degradation and the formation of hardpans in crop/livestock‐mixed rainfed agriculture systems and to assess how changes in soil properties are related to the conversion of land from forest to agriculture. Two watersheds (Anjeni and Debre Mewi) were selected in the humid Ethiopian highlands. For both watersheds, 0–45 cm soil penetration resistance (SPR, n  = 180) and soil physical properties (particle size, soil organic matter, pH, base ions, cation exchange capacity, silica content, bulk density and moisture content) were determined at 15 cm depth increments for three land uses: cultivated, pasture and forest. SPR of agricultural fields was significantly greater than that of forest lands. Dense layers with a critical SPR threshold of ≥2000 kPa were observed in the cultivated and pasture lands starting at a depth of 15–30 cm but did not occur in the undisturbed forest land. Compared with the original forest soils, agricultural fields were lower in organic matter, cation exchange capacity, and exchangeable base cations; more acidic; had a higher bulk density and more fine particles (clay and silt); and contained less soluble silica. Overall, our findings suggest that soil physical and chemical properties in agricultural lands are deteriorated, causing disintegration of soil aggregates, resulting in greater sediment concentration in infiltration water that clogged up macro‐pores, thereby disconnecting deep flow paths found in original forest soils. Copyright © 2016 John Wiley & Sons, Ltd.     

CHANGES IN THE PHYSICAL AND CHEMICAL PROPERTIES OF A MINERAL TOPSOIL UNDER THE INFLUENCE OF PEAT DEBRIS

Changes are reported of particle size distribution, organic carbon and nitrogen values, cation exchange capacity and exchangeable cation populations, and in iron and aluminium patterns as a result of adding varying rates of acid peat debris to a mineral topsoil. Up to 3 cm of peat had beneficial effects on soil chemical and physical properties but 5 to 8 cm was sufficient to cause considerable acidification, release of Fe and other ions from primary minerals and the development of an iron seam (or pan) which contains up to 7 per cent free iron. Greater thickness of peat (up to 30 cm) caused soil reaction to drop to pH 4 or less and produced so much humic acids as to inhibit iron precipitation and to facilitate its removal from the profiles. The effects of soil moisture on the pattern of peat humification in the deeper additions (20–30 cm) are also outlined.     

Changes in forest floor and mineral soil carbon and nitrogen stocks in a boreal forest after clear‐cutting and mechanical site preparation

Significant amounts of organic carbon (C) and nitrogen (N) are accumulated in soil in boreal forests. However, increased concern has been shown regarding the negative impacts of forestry operations on both the C sequestration and N stocks in soil. Changes in the C and N stocks in woody debris, forest floor and mineral soil (0–20 cm) were studied in Eastern Finland for 10 years after stem‐only clear‐cutting followed by soil harrowing. Samples were taken from the uncut forest and from the different microsites formed by the harrowing (ridges, furrows and undisturbed areas). Carbon and N from logging residues were not incorporated into the forest floor or mineral soil stocks to any great extent. After 5 years the C stock above the mineral soil was smaller (< 20%) in the treated area than in the uncut forest and after 10 years it was < 50% smaller. The corresponding N stock was marginally larger (< 5%) after 5 years, but smaller (< 20%) after 10 years. In the mineral soil there were no changes; only the furrows lost C and N when compared with the other microsites, but not when compared with the forest. Harrowing increased the spatial variation in the forest floor C and N stocks. The comparison of the N losses from the soil and logging residues and woody debris with the leaching losses, the amounts utilized by the regenerating vegetation or estimated to be immobilized by the stumps at the same site indicated that N which remained after the clear‐cutting was retained at the site. For a full understanding of the impact of such a disturbance on stocks at a site all significant fluxes and stocks would need to be monitored.     

Effects of prescribed fire on rates of decomposition and nitrogen mineralization in a ponderosa pine ecosystem

Summary The effects of a prescribed fire in a ponderosa pine ecosystem on the rates of decomposition and nitrogen mineralization (including ammonification and nitrification) in the forest floor and mineral soil horizons were evaluated. The prescribed fire immediately increased the rates of nitrogen mineralization and nitrification in the forest floor of all burned plots and in the mineral soil of one plot. The rates of decomposition, as measured by CO2 evolution, in both the forest floor and mineral soil were not significantly different immediately after the burn when expressed on an organic matter basis. The rates of nitrogen mineralization in the forest floor and mineral soil were higher 6 and 10 months after the burn. The rate of decomposition (as measured by respiration) was lower in the forest floor but not in the mineral soil 6 and 10 months after the burn. Volatile organics that may inhibit rates of nitrogen mineralization may have been consumed by prescribed fire.     

Effects of tree harvesting, forest floor removal, and compaction on soil microbial biomass, microbial respiration, and N availability in a boreal aspen forest in British Columbia

The effects of timber harvesting and the resultant soil disturbances (compaction and forest floor removal) on relative soil water content, microbial biomass C and N contents (C_mic and N_mic), microbial biomass C:N ratio (C_mic-to-N_mic), microbial respiration, metabolic quotient (qCO₂), and available N content in the forest floor and the uppermost mineral soil (0-3 cm) were assessed in a long-term soil productivity (LTSP) site and adjacent mature forest stands in northeastern British Columbia (Canada). A combination of principal component analysis and redundancy analysis was used to test the effects of stem-only harvest, whole tree harvest plus forest floor removal, and soil compaction on the studied variables. Those properties in the forest floor were not affected by timber harvesting or soil compaction. In the mineral soil, compaction increased soil total C and N contents, relative water content, and N_mic by 45%, 40%, 34% and 72%, respectively, and decreased C_mic-to-N_mic ratio by 29%. However, these parameters were not affected by stem only harvesting or whole tree harvesting plus forest floor removal, contrasting the reduction of white spruce and aspen growth following forest floor removal and soil compaction reported in an earlier study. Those results suggest that at the study site the short-term effects of timber harvesting, forest floor removal, and soil compaction are rather complex and that microbial populations might not be affected by the perturbations in the same way as trees, at least not in the short term.     

Soil fertility differences across a land-use intensification gradient in the highlands of Chiapas,Mexico

In the highlands of Chiapas, southern Mexico, soil texture and soil chemical properties were measured in 70 agricultural fields covering a range of slope positions and managements. Fields represented four corn cropping systems: long fallow, short fallow, pasture–cultivation rotation, and annual continuous cultivation, in addition to fallow at rest (forest, shrubland, and pastures). Fields were located in four slope positions (upper, middle, and lower slopes, and doline floor) in a karst landscape developed on limestone with additions of acid volcanic ashes. Distribution of clays and sands were related to the toposequence and the percentage of clay fraction increased from upper slope to doline floor. Sand presented a reverse pattern. Some soil chemical properties also vary in a characteristic way along the toposequence. Exchangeable Ca²⁺ and Mg²⁺ effective cation exchange capacity (ECEC) and pH were higher in the doline floor than in the other slope positions. Soil organic matter and total N contents were 30.4 and 35.2% higher under long fallow than under annual continuous cultivation. Soil Olsen P was greater under cultivation than under fallow (irrespective of the cropping system), with the highest values under annual continuous cultivation (16.2±8.3 mg kg⁻¹) and the lowest in the forest (5.3±2.5 mg kg⁻¹). Exchangeable K⁺ was 74 and 51% higher in cultivated plots of the long and the short fallow than under forest and shrubland, respectively. Exchangeable Ca²⁺ and Mg²⁺ and ECEC did not vary significantly among the cropping systems. Inputs of basic cations through burning of tree and shrub vegetation increased the soil pH. These results indicate that land use intensification is leading to a decline in soil organic matter and total N, whereas Olsen P increased with intensification due to the continuous application of P fertilizers and sheep manure as soil conditioners in intensively cultivated fields.     

Microbial activities in forest soils exposed to chronic depositions from a lignite power plant

Atmospheric emissions of fly ash and SO₂ from lignite-fired power plants strongly affect large forest areas in Germany. The impact of different deposition loads on the microbial biomass and enzyme activities was studied at three forest sites (Picea abies (L.) Karst.) along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant (sites Ia, II, and III, respectively), representing high, moderate and low emission rates. An additional site (site Ib) at a distance of 3 km from the power plant was chosen to study the influence of forest type on microbial parameters in coniferous forest soils under fly ash and SO₂ emissions. Soil microbial biomass C and N, CO₂ evolved and activities of l-asparaginase, l-glutaminase, β -glucosidase, acid phosphatase and arylsulfatase (expressed on dry soil and organic C basis) were determined in the forest floor (L, Of and Oh horizon) and mineral top soil (0-10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH₄NO₃ extractable) Cd, Cr, and Ni, effective cation exchange capacity and base saturation in the humus layer along the 15 km long transect significantly (P<0.05) reflected the effect of past depositions of alkaline fly ash. Soil microbial and biochemical parameters were significantly (P<0.05) affected by chronic fly ash depositions. The effect of forest type (i.e. comparison of sites Ia and Ib) on the studied parameters was generally dominated by the deposition effect. Alkaline depositions significantly (P<0.05) decreased the microbial biomass C and N, microbial biomass C-to-N ratios and microbial biomass C-to-organic C ratios. Microbial respiration, metabolic quotient (qCO₂) and the activities of l-asparaginase, l-glutaminase, β-glucosidase, acid phosphatase and arylsulfatase were increased by long-term depositions from the power plants. Acid phosphatase had the highest specific (enzyme activities expressed per unit organic C) activity values among the enzymes studied and arylsulfatase the lowest. The responses of the microbial biomass and soil respiration data to different atmospheric deposition loads were mainly controlled by the content of organic C and cation exchange capacity, while those of enzyme activities were governed by the soil pH and concentrations of mobile heavy metals. We concluded that chronic fly ash depositions decrease litter decomposition by influencing specific microbial and enzymatic processes in forest soils.     

Humusveränderungen nach Einbringung von Buche und Eiche in Kiefernreinbestände

Humus changes after introduction of beech and oak into Scots‐pine monocultures Medium‐ and long‐term (16 to 83 years) effects of an introduction of broadleaf‐tree species (Common beech [Fagus sylvatica] and European‐Sessile Oak [Quercus robur/petraea]) into mature Scots‐pine (Pinus sylvestris) stands on humus type and chemical properties of the Oh layer (pH value, base saturation, C : N ratio) were studied on 16 sites in Bavaria/Germany. The sites investigated covered a large range with respect to elevation, climate, parent material, and soil type. At most sites, the introduction of beech resulted in a significant change of the soil humus type from biologically inactive humus types to more active ones. The strongest changes occurred on the poorest sites, where forest floors under pure pine were particularly biologically inactive. In most cases, the changes in humus type were accompanied by significant increases in the pH value and the base saturation and significant decreases in the C : N ratio of the Oh layer. However, the latter effect was not noticed at most sites with initial C : N ratios higher than 30. In contrast to beech, the introduction of oak did not result in a systematic change of the humus type, the pH value, or the base saturation of the Oh layer. In spite of the considerable change of humus type under beech to biologically more active types, the introduction of broadleaf trees did not result in a systematic change of the thickness or the mass of the forest floor. A decrease in the mass of the Of layer was compensated by an increase of the Oh‐layer mass. All studied sites considered, the introduction of broadleaf trees into Scots‐pine monocultures resulted on average in an 8% decrease of the total amount of organic carbon (C_org) in the forest floor; the C_org amount in the uppermost 10 cm mineral soil increased by 9%. At 35% of all investigated sites, broadleaf tree introduction resulted in increased (+5% to +18%) topsoil (forest floor and uppermost 10 cm mineral soil) C_org stocks. At 30% of the sites, the stock changes were less than ±5%, and on 35% of all sites, soil C_org stocks decreased by –5% to –36%. The average change in the topsoil C_org stock for all studied sites was –5%. The introduction of beech into Scots‐pine monocultures resulted in an ecologically desired translocation of soil organic matter from the forest floor into the mineral topsoil. It is an effective and sustainable silvicultural measure to restore and revitalize acidified, nutrient‐depleted topsoils with biologically inactive humus types.     

Patterns of trace metal concentration and acidity in montane forest soils of the northeastern United States

Forest floor and mineral soil samples were collected from subalpine spruce-fir forests at 1000 m above mean sea level on 19 mountains in the northeastern United States to assess patterns in trace metal concentrations, acidity, and organic matter content. The regional average concentrations of Pb, Cu, and Zn in the forest floor were 72.3 (2.9 s.e.) μg g^?1, 8.5 (0.7) μg g^?1, and 46.9 (2.0) μg g^?1, respectively. The regional average concentrations of Pb, Cu, and Zn in the mineral soil were 13.4 (0.8) μg g^?1, and 18.2 (1.2) μg g^?1, respectively. The regional average pH values of the forest floor and mineral soil were 3.99 (0.03), and 4.35 (0.03), respectively. The Green Mountains had the highest concentrations of Pb (105.7 μg g^?1), and Cu (22.7 μg g^?1), in the forest floor. They also had the highest concentrations of Cu (18.0 μg g^?1), in the mineral soil. Site aspect did not significantly influence any of the values. Concentrations of Pb were lower than concentrations reported earlier in this decade at similar sites while concentrations of Cu and Zn remained the same. We believe that these lower Pb concentrations reflect real changes in forest Pb levels that have occurred in recent years.