Effect of clear-felling on runoff in two small watersheds in Central Sweden

Small watersheds were used in a study of the effect of clear-felling on runoff from coniferous forest areas in Central Sweden. After a 3-year calibration period, two watersheds were clear-felled (on one of them the slash was left and on the other slash was removed) and a third was left as a reference.Runoff under forested conditions was 271 and 246 mm year^?1, respectively for the treated watersheds, while the precipitation measured 732 mm year^?1 as a mean for the investigated period. Clear-felling resulted in an increase in runoff of 119 and 75% (371 and 215 mm per year), respectively. The increase occurred during the period of snowmelt (April–May) and the period without snow (June–October). During winter (November–March) a very small increase in runoff was noted. The effect of clear-felling on runoff appears to be greater than has been reported from most other Scandinavian investigations.The increase in runoff during snowmelt is probably due to an increased snow accumulation in the clear-felled area as compared to the forest. The increased runoff for the period without snow is explained by reduced transpiration from the vegetation and reduced evaporation caused by an increased aerodynamic resistance.No effects of slash removal could be detected, probably because of the natural variation between the two treated watersheds.     

Acidity in four coniferous forest soils after different harvesting regimes of logging slash

The soil acidity of four coniferous sites, two in S Sweden and two in N Sweden, were studied 7–9 years after clear‐felling. Each site had three different slash treatments; (a) all slash harvested, (b) only needles remaining, and (c) all slash remaining. Our results verify that harvesting of slash after clear‐cutting means an acidification of the organic horizon in acid forest soils. On plots subjected to full slash harvest the pH‐value of the forest floor was 0.2–0.4 units lower than that of slash‐covered ones, and at three of the four study sites the exchangeable acidity was significantly higher on the slash‐cleared plots. Plots with only needles remaining were generally intermediate in acidity. The change in exchangeable acidity corresponded to approximately 10% of the theoretically estimated proton load caused by slash harvesting. The rate of proton flux associated with whole‐tree harvesting varied between 7–65 meq m^‐3 yr^‐1, which roughly corresponds to the amounts deposited in precipitation. Harvesting of stems accounted for about one third and needles for one third of the proton load.     

Effects of Afforestation with Pinus contorta on Nutrient Content, Acidity and Exchangeable Cations in Peat

Nutrient contents, acidity and exchangeable cations in the upper300 mm of peat beneath lodgepole pine have been compared withthose in peat from contiguous unplanted areas at each of sixsites. Nitrogen, phosphorus and potassium contents, which aresignificantly higher in flushed blanket bog peat than in peatfrom either raised bog or unflushed blanket bog, are not significantlyaltered by the presence of trees. Calcium and magnesium contents,on the other hand, although similar in peat from different bogtypes, are lower in peat beneath the tree crop. ExchangeableCa²⁺ Mg²⁺ and K²⁺ are replaced by Na⁺ and H⁺ in planted peatbut the increase in H⁺ content exceeds the loss of base cations,reflecting a higher number of exchange sites. This increaseaccounts for lower values of both base saturation and pH inplanted peat and is attributed to enhanced decomposition promotedby aerobic conditions beneath the tree crop.     

Effects of liming on chemical properties of soil, needle nutrients and growth of Scots pine transplants

The effects of limestone (2.0 and 4.0 Mg ha⁻¹) on chemical properties of soil, nutrient concentrations of needles and growth of Scots pine (Pinus sylvestris L.) transplants were investigated on three reforestation areas on infertile acidic sites in southern Finland. The limestone was applied either on the soil surface (unploughed plots) or was mixed into the topsoil (ploughed plots). All the treatments were replicated four times. Surface broadcast of lime elevated the pH in the organic layer and in the 0-10 cm layer of mineral soil. The increase in the pH of the organic layer after 21 years was, on average, 0.7 and 1.1 pH units, with a dose of lime 2 and 4 Mg ha⁻¹, respectively. On the ploughed plots, the pH in the uppermost 0-10 cm soil layer was 0.4-0.5 units higher than on the corresponding unlimed plots. Both doses of lime significantly increased the amount of exchangeable Ca and the base saturation (BS) in the topsoil on the ploughed plots, and the amount of exchangeable Ca and Mg, as well as the base saturation (BS) in the organic layer + the 0-10 cm layer of mineral soil on the unploughed plots. Regardless of the techniques used for application of lime, after 21 growing seasons the Ca and Mg concentrations in needles were significantly higher on the limed plots than on the controls. In needles, the Ca/Mn ratio was the best indicator for measuring the response to liming. Only on the unploughed plots did liming increase stand volume and dominant diameter of pines. Intensive disc ploughing produced significantly more stems and increased both stand volume and the dominant height of pines compared to unploughed plots.     

Effect of six years of nitrogen additions on soil chemistry in a subtropical <Emphasis Type="Italic">Pleioblastus amarus</Emphasis> forest,Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen (N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels (0, 50, 150, and 300 kg N ha^?1 a^?1, applied monthly, expressed as CK, LN, MN, HN, respectively) in three replicates. After 6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity (EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK, LN, MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al³⁺, EA, and Al/Ca, and exchangeable Al³⁺ in HN increased by 70% compared to CK. Soil base cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) did not respond to N additions. Nitrogen treatments significantly increased soil NO₃^?–N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH₄⁺–N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon, incorporated organic carbon, or particulate organic carbon. This study suggests that increasing N deposition could increase soil NO₃^?–N, reduce soil pH, and increase mobilization of Al³⁺. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.     

Long term accumulation of nitrogen in soils of dry mixed eucalypt forest in the absence of fire

In the Eden area in NSW, Australia, low fertility granitic surface soils were sampled from 156 sites and analysed for pH, organic C, total N, total P, available P, exchangeable bases and exchangeable Al. Fifty eight of these sites were also sampled to a depth of 40 cm. Time since fire ranged from 1 to 39 years and was used in the analysis as a surrogate for fire frequency. No information was available on fire intensity. No significant relationships were found between time since fire and P or base cations. However, the quantities of organic matter and total N (kg ha⁻¹), and the C/N ratio were significantly related to both time since fire alone and to the combination of time since fire and soil total P. Based on these relationships, it was estimated that there were average net increases of between 11 and 21 kg N ha⁻¹ year⁻¹ in surface soil, the actual quantity depending on the level of soil total P. There was little change in N in the initial 10 years after fire and there was a peak in N accumulation about 24 years after fire. The C/N ratio and surface soil pH decreased with time since fire. Accumulation of N and reductions in pH and C/N ratio were studied further in a small scale paired plot analysis. The repeatedly burnt plots had lower levels of both litter and understorey and the overstorey trees generally had healthier crowns than in the unburnt plots. The differences between the repeatedly burnt and the unburnt plots matched the models developed from the general survey. There were no significant changes in the C/N ratio, but the unburnt sites had higher levels of extractable mineral N and the relationships between the mineral N and the C/N ratio for burnt and unburnt sites were statistically significant. The quantities of extractable mineral N in the unburnt soils (2.3 kg N ha⁻¹) were about twice the levels in the burnt soils (1.2 kg N ha⁻¹). The pH of the surface soil (4.4 in 1:1 water) in the regularly burnt area was higher than in the unburnt area (pH 4.1) and the exchangeable aluminium also differed (0.62 c mol⁻¹ in the burnt area and 1.3 c mol⁻¹ in the unburnt). The combined data indicate that changes occur in forest soils when there is a long period of exclusion of fire. It is suggested that these changes generally lead to secondary changes, such as in pH and availability of other elements such as aluminium. The study highlights a number of issues including the rates of inputs of N to the system and the question of N saturation and its long term interaction with plant species. It is hypothesised that reduced burning leads to increased N availability and other soil changes which negatively impact on tree health.     

Recovery of Soil pH,Cation-exchange Capacity and the Saturation of Exchange Sites from Stemflow-induced Soil Acidification in Three Swedish Beech (Fagus sylvatica L.) Forests

Stemflow water acidifies the soil in beech stands impacted by atmospheric deposition. To investigate whether the soil recovers from acidification, stemflow was experimentally removed. A horizon material was sampled at a distance of 10 - 250 cm from the stems. Before the onset of the experiment, there were stemflow - induced gradients in the saturation of exchange sites with K⁺, H⁺ and Na⁺ that were larger near the stems, while the pHKCl, the cation - exchange capacity, and the saturation with Ca2⁺, Mg2⁺ and Mn2⁺ were smaller. After 8 yrs of recovery, the pHKCl and the saturation with Ca2⁺ and Mg2⁺ had increased close to the stems, while the saturation with Na⁺, H⁺, Mn2⁺ and 2⁺ and the C/N ratio had decreased. With some exceptions, e.g. base saturation, the recovery was not complete after 8 yrs. Soil far from stems had also changed similarly, probably because of the ongoing decrease in overall deposition in southern Sweden.     

Soil changes induced by Acacia mangium plantation establishment: Comparison with secondary forest and Imperata cylindrica grassland soils in South Sumatra,Indonesia

Acacia plantation establishment might cause soil acidification in strongly weathered soils in the wet tropics because the base cations in the soil are translocated rapidly to plant biomass during Acacia growth. We examined whether soils under an Acacia plantation were acidified, as well as the factors causing soil acidification. We compared soils from 10 stands of 8-year-old Acacia mangium plantations with soils from 10 secondary forests and eight Imperata cylindrica grasslands, which were transformed into Acacia plantations. Soil samples were collected every 5–30 cm in depth, and pH and related soil properties were analyzed. Soil pH was significantly lower in Acacia plantations and secondary forests than in Imperata grasslands at every soil depth. The difference was about 1.0 pH unit at 0–5 cm and 0.5 pH unit at 25–30 cm. A significant positive correlation between pH and base saturation at 0–20 cm depth indicated that the low pH under forest vegetation was associated with exchangeable cation status. Using analysis of covariance (ANCOVA), with clay content as the covariate, exchangeable Ca (Ex-Ca) and Mg (Ex-Mg) stocks were significantly lower in forested areas than in Imperata grasslands at any clay content which was strongly related to exchangeable cation stock. The adjusted average Ex-Ca stock calculated by ANCOVA was 249 kg ha⁻¹ in Acacia plantations, 200 kg ha⁻¹ in secondary forests, and 756 kg ha⁻¹ in Imperata grasslands at 0–30 cm. Based on a comparison of estimated nutrient stocks in biomass and soil among the vegetation types, the translocation of base cations from soil to plant biomass might cause a decrease in exchangeable cations and soil acidification in Acacia plantations.     

Chemical properties of forest soils along a fly-ash deposition gradient in eastern Germany

Chemical characteristics of forest soils subjected to long-term deposition of alkaline and acid air pollutants were analysed in spruce (Picea abies (L.) Karst.) stands in eastern Germany. Three forest sites along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant were selected, representing high, intermediate, and low fly-ash input rates. Past emissions caused an accumulation of mineral fly-ash constituents in the organic layer, resulting in an atypically high mass of organic horizons of forest soils, especially in the F and H horizons. Total mass of organic layers at the site with heavy deposition loads was as high as 128 t ha^–1, compared to 58 t ha^–1 at the low input site. Fly-ash deposition significantly increased the pH values in the L, F and H horizons and mineral topsoil (0–10 cm). Significantly higher concentrations of NH₄Cl-extractable cations (i.e. effective cation exchange capacities) and base saturations of >66% were found in the humic horizons at sites where the pH was increased due to the direct and indirect (i.e. higher proportions of deciduous trees) effects of fly-ash emissions. Stocks of basic cations were dominated by Ca²⁺ and decreased significantly along the fly-ash deposition gradient from 33.6 to 5.3 kmol_c ha^–1. Proportions of water-soluble basic cations out of the total potentially exchangeable (i.e. NH₄Cl-extractable) basic cations generally increased in the forest soil with decreasing deposition loads following the cation exchange capacity and base saturation along the fly-ash gradient. Higher proportions of monovalent cations, such as K⁺ and Na⁺, were observed in the water extracts from fly-ash-affected forest soils, while the NH₄Cl-extracts were dominated by bivalent cations, such as Ca²⁺ and Mg²⁺. These results suggest a greater leaching tendency for monovalent cations in these soils. Stocks of organic C and total N in the humus layer decreased from sites with high fly-ash deposition levels to sites with low levels, from 57.4 to 46.4 t C ha^–1 and from 2.43 to 1.99 t N ha^–1. The C/N ratios of the organic horizons varied from 22 to 25, revealing no distinct pattern along the fly-ash gradient. Measurements of hot-water-extractable and water-soluble organic C suggested a reduced availability or a faster decomposition of soil organic matter in soils with historically high fly-ash loads.     

The impact of six European tree species on the chemistry of mineral topsoil in forest plantations on former agricultural land

Influences on mineral topsoils of common European tree species (oak-Quercus robur L., lime-Tilia cordata Mill., ash-Fraxinus excelsior L., birch-Betula pendula Roth., beech-Fagus sylvatica L. and spruce-Picea abies (L.) Karst.) were studied in 30 to 40-year-old stands planted in adjacent plots on former arable land. Mineral soil samples from two depth layers (0–10 and 20–30 cm) under the different species were compared in terms of pH, base saturation, pools and concentrations of exchangeable macro- and micronutrients, total nitrogen and carbon. With the exception of pH (H₂O) and extractable Al and Fe, no significant differences between species were detected in the lower layer. The upper (0–10 cm) layer was, however, affected differently depending on tree species: significant differences in pH, base saturation, exchangeable base cations and other nutrients were observed. The most prominent differences were between lime and spruce. Lime had considerably higher pH, base saturation, base cation and boron pools compared to spruce, which had the most acidifying effect on the mineral topsoils. Among the deciduous species, beech had the most similar effect to spruce on the upper layer of mineral topsoils. Soil C, N and C/N ratios did not differ significantly among species.     

Drainage,Liming and Fertilization of Organic Soils. I. Long-term Effects on Acid/Base Relations

Abstract

Long-term changes of the acid/base relations of organic soils after drainage, fertilization and/or liming at three experimental sites—two ombrogenous and one soligenous—in south central Norway are discussed. These sites were drained, fertilized and/or limed in 1953–1956 and sampled in 1991–1992. Drainage at the ombrogelious sites caused: insignificant shifts of pH, higher bulk densities to 40 cm depth, higher ash percentage, higher contents of N and P to 20 cm depth and reduced concentrations of total Ca, K, Mg, Na, A1 and Fe in soil layers deeper than 20 cm. The soligenous site was not effectively drained; despite this, pH dropped about 0.5 unit in the surface and subsurface soil layers of the control plots, while small changes were measured for most other soil variables. The suggested reason for the pH drop is limited sulphide oxidation in the upper 20 cm drained layer. Base saturation at actual soil pH, when all treatments were included, was estimated with good precision by four regressors: pH, extractable Al, extractable Fe and extractable Ca (R²=0.90–0.95). Similar models explained 97–99”” of the variation in base saturation at soil pH=7.0. The lime effects at the properly drained oligotrophic sites were proportional to applied doses; for pH to 40 cm, base saturation to 60 cm, and Ca concentration to 60 cm depth. At the less well-drained soligenous site, effects were limited to the upper 30 cm layer. Both drainage and liming caused higher cation exchange capacities and proper drainage seems to be a prerequisite for the liming effect. Estimated recovery of calcium to 60 cm depth was 64–79% at the ombrogenous sites and 42–46% at the soligenous site.     

Fine Root Production and Nitrogen Content in Roots of Pinus sylvestris L. after Clear-felling

Effects of clear-felling on fine root production and N content in roots were studied in a Scots pine (Pinus sylvestris L.) stand. A plot was clear-felled and root samples were compared with a control plot. Even if reduced by 50%, a significant fine root (diameter<2 mm) growth was noticed up to 1 yr after the clear-felling. For live roots (diameters 2-4 and 4-6 mm) nitrogen content in root-wood and root-bark samples from the clear-felling, compared with the reference plot, were 30-50% already higher 2 months after the clear-felling. The difference did not increase in later comparisons. Nitrogen content in buttresses did not differ during the period studied, except for a higher percentage in bark at the clear-felling after two summers. A second study confirmed the results. It is suggested that there exists a continued nitrogen uptake in live roots after a clear-felling.     

The effects of limestone and of limestone plus NPK fertilization on the soil and mass balance of a spruce stand (Picea abies (L.) Karst.) in the Vosges mountains

Calcareous amendment and/or fertilization trials were carried out in a declining 66-year-old Norway spruce (Picea abies (L.) Karst.) stand in the Vosges mountains (northeast France, altitude 1100 m) in 1985. The aim was to test tree response to nutritional deficiencies (Ca + Mg) and to alleviate soil acidity. In 1988, experimental equipment was set up to collect atmospheric input (bulk precipitation, throughfall) and soil seepage water. The soils are podzolic (‘ocre-podzolique’), derived from an acid-poor granitic bedrock (‘granite du Valtin’). The soils are coarsely textured, hence very porous. They are very acid (pH 3.4 in the A₁ horizon, and pH 4.1 in the Bs horizon). The cation exchange capacity (CEC) is highly saturated in exchangeable acidity: 86% in the A₁ horizon. Ca²⁺ + Mg²⁺ saturation is very low (<10% in A¹ and <1% in the subsoil). Liming and fertilization significantly increase soil pH, base cation saturation and decrease soil acidity, especially in the surface horizons.

Bulk precipitation is dilute and acidic (pH 4.5); ion concentration of the precipitation greatly increases after passing through the tree canopy. Dry deposition is moderate and has values in the lower range reported for Europe.

Nitrification produced large amounts of NO₃⁻-N and H⁺ ions in the O layer and organo-mineral horizons. Nitrate and aluminium dominate the chemical composition of the soil see-page water.

Liming induces a considerable rise in the soil solution pH and the base cations (Ca²⁺ + Mg²⁺) and decreases nitrate and aluminium substantially. Liming alone seems to lower the rate of nitrification. Addition of fertilizers increases the deep drainage of base cations which could reduce the long term efficiency of liming.

Improvement of tree health-status accords with the positive effects of liming and/or fertilization on the soil's solid phase and solution.     

Computer simulation of long-term carbon storage patterns in Florida slash pine plantations

We developed a computer model to simulate carbon storage in managed slash pine plantations in Florida. The model is based on ecosystem level carbon dynamics and land use data structured by age class of planted trees. Based on a scenario of constant planting at the average level (1952–1979), Florida slash pine forests would store carbon at the rate of 2.81 × 10⁶ t year^?1. However, simulated carbon storage is sensitive to the age class distribution of the forests. There will be a 10⁶ t year^?1 decrease in carbon storage between 1980 and 1987, due to reduced levels of planting during the past decade. This trend is relatively independent of current planting levels.     

Effect of slash removal on Gremmeniella abietina incidence on Pinus sylvestris after clear-cutting in northern Sweden

The Gremmeniella abietina outbreak in Sweden in 2001-2003 forced forest owners to sanitary clear-cut large areas of middle-aged Pinus sylvestris stands. There is, however, little knowledge of effective reforestation of P. sylvestris on G. abietina-infected sites. Gremmeniella abietina disease incidence on P. sylvestris seedlings planted in 2003 was studied with and without (control) removal of infected P. sylvestris slash. Removed slash was piled in stacks around the regeneration plots. The seedlings were planted within 1 year after sanitation felling on three sites in northern Sweden. One year after planting, G. abietina pycnidia were found on 32% of the control seedlings and total infection, including stem cankers, reached 44%. Total and G. abietina-induced mortality was 15 and 10%, respectively. The method of removing and piling the infected slash reduced the number of infected seedlings by 50% and seedling mortality by 27% 1 year after planting, compared with control. Consequently, even if there is a clear sanitation effect of removing infected slash to the sides of the regeneration area, it does not eradicate the infection source from the stands. Postponed planting, slash burning or complete removal of the infected slash is needed to minimize the infection risk. The positive correlation found between slash coverage and infection rate indicates that clear-cuts with large amounts of infected slash should be given priority for slash treatment.     

A meta-analysis of the effects of nitrogen additions on base cations: Implications for plants, soils, and streams

The dominant base cations (BC; i.e., Ca²⁺, Mg²⁺, K⁺, and Na⁺) are important in buffering soil and water acidity in both terrestrial and aquatic ecosystems. Ca²⁺, Mg²⁺, and K⁺ are also important in many plant physiological functions. Because BC availability is affected by changes in the nitrogen (N) cycle, we conducted a meta-analysis of previously published data to determine if N fertilization alters the availability of BC in terrestrial and stream ecosystems across biomes. We include data from 107 independent studies published in 62 different articles, taking a holistic perspective on BC by examining their responses to added N in plant foliage, bulk soil, soil solution, and stream water. Our results suggest N fertilization may accelerate BC loss from terrestrial ecosystems over time periods less than five years. We found that N additions resulted in an overall 24% decrease in the availability of exchangeable Ca²⁺, Mg²⁺, and K⁺ in the bulk soil of boreal forest, temperate forest, and grassland biomes. Collectively, responses of BC in boreal forest, temperate forest, tropical forest, and grassland biomes increased following N fertilization by about 71% in soil solution and 48% in stream waters. Additionally, BC responses in foliage decreased in boreal forest and temperate forest biomes following N additions over time periods less than five years, but there were no significant changes over longer time periods. Despite large short-term shifts in BC responses following N additions, we did not find evidence of widespread negative impacts on ecosystems over time periods greater than five years. This analysis suggests effects of N addition on the availability of exchangeable BC may diminish over time. Although the effects on BC can be substantial over periods less than five years, there is little available evidence that N fertilization has had large-scale detrimental effects on the availability of BC needed for plant growth within terrestrial or aquatic ecosystems.     

Differences in soil organic matter, extractable nutrients, and acidity in European beech (Fagus sylvatica L.) forest soils related to the presence of ground flora

Differences in soil organic matter (SOM) content, soil acidity, and soil exchangeable nutrients (NH₄–N, NO₃–N, Ca, K, Na, Mg) related to the presence of ground flora were studied. The study was carried out for a growing season in two different Fagus sylvatica L. forests in southern Sweden, and the differences in soil characteristics below naturally occurring patches of Deschampsia flexuosa (L.) Trin. or Anemone nemorosa L. were compared with those with no ground flora. Patches of D. flexuosa led to higher soil pH, but lower SOM, water content, base saturation, and NH₄–N concentration compared with adjacent zones without D. flexuosa. The lower SOM content suggested an increased rate of decomposition which caused soil pH to increase because of release of basic cations. In the presence of A. nemorosa, pH was higher and the exchangeable acidity lower than for patches without the herb. In early spring, when A. nemorosa emerged and flowered, the NH₄–N concentration was somewhat lower in the presence of the herb than when it was absent. For the evergreen grass D. flexuosa NH₄–N concentrations were lower in patches with the grass later in the summer season (July). This work indicates the presence of spatial and temporal differences in nutrient circulation and decomposition on the small ground flora scale, which should be considered when studying nutrient and carbon cycles of temperate forests.     

萧氏松茎象虫口密度与虫孔数的关系研究

萧氏松茎象Hylobitelus xiaoi Zhang(Coleoptera：Curculionidae)是我国近年来危害最为严重的松林钻蛀性害虫[1],主要危害湿地松(Pinus elliottii Engelmann),也危害火炬松(P.taeda L.)、马尾松(P.massoniana Lamb.)和华山松(P.armandi Franch.).     

Contribution of understory vegetation to minimizing nitrate leaching in a Japanese cedar plantation

Understory vegetation may affect nitrate (NO₃ ⁻) leaching, even in coniferous forests. Our objective was to estimate the contribution of understory vegetation to nutrient cycling, especially nitrogen, in a Japanese cedar (Cryptomeria japonica) stand. We therefore cut down and removed understory vegetation in one plot of the stand (the cutting plot) to compare nutrient budgets in the cutting plot with those in a control plot in which understory vegetation was allowed to grow. We also examined neutralization of the acid produced due to an increase in NO₃ ⁻ leaching. A monitoring study on precipitation and soil-percolated water was carried out in both plots. When the understory vegetation was cut down, NO₃ ⁻ flux at a soil depth of 10 cm increased remarkably in summer, with values significantly higher than those in the control plot. This resulted in an increase in proton load associated with N transformation ([H⁺]load). The increase in [H⁺]load enhanced mobilization of Ca²⁺, Mg²⁺, and SiO₂ ([SiO₂]mob). In addition, the correlations between [SiO₂]mob and mobilization of each base cation were distinct in the cutting plot. These results indicated that the acids produced because of N transformation were buffered not only by ion exchange but also by chemical weathering. The contribution of understory vegetation to minimizing NO₃ ⁻ leaching suggested that understory vegetation might reduce the risk of N saturation because of chronic atmospheric N inputs.