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.     

Soil CO2 concentration,efflux, and partitioning in a recently afforested grassland

Relatively few studies have documented the impacts of afforestation, particularly production forestry, on belowground carbon dioxide (CO₂) effluxes to the atmosphere. We evaluated the changes in the soil CO₂ efflux—a proxy for soil respiration (Rs)—for three years following a native grassland conversion to eucalypt plantations in southern Brazil where minimum tillage during site preparation created two distinct soil zones, within planting row (W) and between-row (B). We used root-exclusion and carbon (C)- isotopic approaches to distinguish Rs components (heterotrophic-Rh and autotrophic-Ra respirations), and a CO₂ profile tube (1-m deep) to determine the concentration ([CO₂]) and isotopic C signature of soil CO₂ (δ¹³[CO₂]). The soil CO₂ efflux in the afforested site averaged 0.37 g CO₂ m^?2 h^?1, which was 56% lower than the soil CO₂ efflux in the grassland. The δ¹³CO₂ in the afforested site ranged from ? 14.1‰ to ? 29.4‰, indicating a greater contribution of eucalypt-derived respiration (both Rh and Ra) over time. Higher soil CO₂ efflux and lower [CO₂] were observed in W than B, indicating that soil preparation creates two distinct soil functional zones with respect to C cycling. The [CO₂] and δ¹³[CO₂] decreased in both zonal positions with eucalypt stand development. Although the equilibrium in C fluxes and pools across multiple rotations is needed to fully account for the feedback of eucalypt planted forests to climate change, we provide quantitative information on soil CO₂ dynamics after afforestation and show how soil preparation can leverage the feedback of planted forests to climate change.

     

Soil N cycling in old-growth forests across an Andosol toposequence in Ecuador

Nitrogen (N) deposition in the tropics is predicted to increase drastically in the next decades. The sparse information on N cycling in tropical forests revealed that the soil N status of an ecosystem is the key to analyze its reactions to projected increase in N input. Our study was aimed at (1) comparing the soil N availability of forest sites across an Ecuadorian Andosol toposequence by quantifying gross rates of soil N cycling in situ, and (2) determining the factors controlling the differences in soil N cycling across sites. The toposequence was represented by five old-growth forest sites with elevations ranging from 300 m to 1500 m. Our results provide general insights into the role of elevation-mediated factors (i.e. degree of soil development and temperature) in driving patterns of soil N cycling. Gross rates of N transformations, microbial N turnover time, and δ¹⁵N signatures in soil and leaf litter decreased with increasing elevation, signifying a decreasing N availability across the toposequence. This was paralleled by a decreasing degree of soil development with increasing elevation, as indicated by declining clay contents, total C, total N, effective cation exchange capacity and increasing base saturation. Soil N-cycling rates and δ¹⁵N signatures were highly correlated with mean annual temperature but not with mean annual rainfall and soil moisture which did not systematically vary across the toposequence. Microbial immobilization was the largest fate of produced NH₄⁺ across all sites, and nitrification activity was only 5–11% of gross NH₄⁺ production. We observed a fast reaction of NO₃⁻ to organic N and its role for N retention deserves further attention. If projected increase in N deposition will occur, the timing and magnitude of gaseous N losses may follow the pattern of N availability across this Andosol toposequence.     

Changes of key soil parameters five years after forest harvesting suggest slow regeneration of disturbed soil

Forest soil is susceptible to changes in its top layers. These changes occur during ground-based forest harvesting and the rate of soil regeneration depends on the environmental conditions and the extent of the disturbance. This paper was focused on analyzing the changes of soil characteristics such as the depth of the erosion profile, bulk density of soil, its penetration resistance, and the subsurface concentration of CO₂ in soils five years after forest harvesting. The study took place in four forest stands harvested by a skidder and a harvester/forwarder combination. Statistical analyses did not prove significant changes of the characteristics of the disturbed soil after the five-year period without machine traffic: the profile depth did not change significantly, except for one stand, where the ruts became deeper. Other characteristics, such as the bulk density of soil also did not show any significant regeneration (1.29–1.36 g cm^?3 in the rut; initial measurements versus 1.34–1.38 g cm^?3 in the rut; repeated measurements). The penetration resistance, as well as the subsurface CO₂ concentration, were variable, and the results inconclusive. Our results suggest that five years was not enough time for soil to regenerate significantly after being disturbed by ground-based machinery.     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.     

Post-fire soil nitrogen content and vegetation composition in Sub-Boreal spruce forests of British Columbia's central interior,Canada

Forest fires are known to influence nutrient cycling, particularly soil nitrogen (N), as well as plant succession in northern forest ecosystems. However, few studies have addressed the dynamics of soil N and its relationship to vegetation composition after fire in these forests. To investigate soil N content and vegetation establishment after wildfire, 13 sites of varying age class were selected in the Sub-Boreal spruce zone of the central interior of British Columbia, Canada. Sites varied in time since the last forest fire and were grouped into three seral age classes: (a) early-seral (<14 years), (b) mid-seral (50–80 years) and (c) late-seral (>140 years). At each site, we estimated the percent cover occupied by trees, shrubs, herbs and mosses. In addition, the soil samples collected from the forest floor and mineral horizons were analyzed for the concentrations of total N, mineralizable N, available NO₃⁻-N and available NH₄⁺-N. Results indicated that soil N in both the forest floor and mineral horizons varied between the three seral age classes following wildfire. Significant differences in mineralizable N, available NO₃⁻-N and available NH₄⁺-N levels with respect to time indicated that available soil N content changes after forest fire. Percent tree and shrub cover was significantly correlated to the amount of available NH₄⁺-N and mineralizable N contents in the forest floor. In the mineral horizons, percent tree cover was significantly correlated to the available NH₄⁺-N, while herb cover was significantly correlated with available NO₃⁻-N. Moss cover was significantly correlated with total N, available NO₃⁻-N and mineralizable N in the forest floor and available NO₃⁻-N in the mineral horizons. We identified several unique species of shrubs and herbs for each seral age class and suggest that plant species are most likely influencing the soil N levels by their contributions to the chemical composition and physical characteristics of the organic matter.     

Soil-CO2 flux after patch scarification,harrowing and stump harvest in a hemi-boreal forest

Abstract

Stump harvesting is one way of increasing the amount of bioenergy, but little is known about the consequences of tree-stump harvesting on the carbon balance in the forest. Therefore, soil-surface CO₂ flux (soil respiration, R _s) was determined two years after clear-cutting for common soil disturbances occurring after patch scarification, harrowing and stump harvest in southern Sweden. R _s from intact soil was found to be of the same magnitude as emissions from areas of mixed humus, indicating only small effects of disturbance. Elevated mounds produced lower emissions than in the intact soil during the second year despite larger amounts of organic matter, probably due to low soil moisture. The lowest R _s was found in soil surfaces with exposed mineral soil. The treatment effects on R _s were estimated considering the actual area of different disturbances. During the first year, there was no difference in R _s among the treatments, whereas in the second year the flux was 10% higher after harrowing and stump harvesting than after patch scarification, implying that the effects on CO₂ flux after stump harvest were comparable to conventional harrowing. However, it is unclear whether this finding basically applies to regions where decomposition is limited by soil moisture during the summer.     

Influence of climate change,fire and harvest on the carbon dynamics of black spruce in Central Canada

The results of EFIMOD simulations for black spruce (Picea mariana [Miller]) forests in Central Canada show that climate warming, fire, harvesting and insects significantly influence net primary productivity (NPP), soil respiration (Rs), net ecosystem production (NEP) and pools of tree biomass and soil organic matter (SOM). The effects of six climate change scenarios demonstrated similar increasing trends of NPP and stand productivity. The disturbances led to a strong decrease in NPP, stand productivity, soil organic matter (SOM) and nitrogen (N) pools with an increase in CO₂ emission to the atmosphere. However the accumulated NEP for 150 years under harvest and fire fluctuated around zero. It becames negative only at a more frequent disturbance regime with four forest fires during the period of simulation. The results from this study show that changes in climate and disturbance regimes might substantially change the NPP as well as the C and N balance, resulting in major changes in the C pools of the vegetation and soil under black spruce forests.     

德国中部Soiling云杉-山毛榉混交林冠层组成对土壤CO2排放的影响

It was hypothesized that soil respiration can be affected by canopy composition. Hence, admixture of trees as a common forest management practice may cause significant change in the carbon cycling. This study was conducted in a mixed spruce-beech stand at Solling forest in central Germany to investigate the effect of canopy composition on soil respiration. The canopy cover was classified in four major canopy classes (pure beech, pure spruce, mixed and gap), and the area under each canopy class was identified as a sub-plot. Soil respiration in each sub-plot (n=4) was measured monthly from Jun 2005 to July 2006. Results show significant difference in annual soil respiration between the beech (359 g·m⁻²·a⁻¹ C) and gap (211 g·m⁻²·a⁻¹ C) sub-plots. The estimation of the total below-ground carbon allocation (TBCA) based on a model given by Raich and Nadelhoffer revealed considerably higher root CO₂ production in the beech sub-plot (231 g·m⁻²·a⁻¹ C) compare to the gap sub-plot (51 g·m⁻²·a⁻¹ C). The contribution of the root respiration to the total soil respiration was higher in the soil under the beech canopy (59%) compared with the soil in the gap (29%). The findings suggested that the condition under the beech canopy may cause more desirable micro-site for autotrophic respiration and consequently higher CO₂ release into the atmosphere.     

采伐对幕布山区毛竹林土壤呼吸的影响

利用LI-COR-8100土壤CO2通量自动测量系统测定了湖北赤壁幕布山区采伐毛竹林土壤表面CO2通量及5 cm深度的土壤温度、湿度,研究了采伐对毛竹林土壤呼吸的影响,并用壕沟法区分各组分呼吸。结果表明:采伐显著增加了毛竹林的土壤温度,但对土壤湿度无显著影响;采伐能增加土壤呼吸、凋落物呼吸与矿质呼吸,但降低了根系呼吸;土壤总呼吸及组分呼吸与土壤温度呈指数相关(R2=32.63%84.50%),与土壤湿度呈线性相关(R2=40.60%93.50%),运用土壤温度、湿度复合模型能提高预测土壤呼吸的准确性(R2=41.40%96.20%)。采伐毛竹林土壤呼吸的增加主要因为采伐后土壤温度升高所致。     

Reduced soil respiration in gaps in logged lowland dipterocarp forests

We studied the effects of forest composition and structure, and related biotic and abiotic factors on soil respiration rates in a tropical logged forest in Malaysian Borneo. Forest stands were classified into gap, pioneer, non-pioneer and mixed (pioneer, non-pioneer and unclassified trees) based on the species composition of trees >10 cm diameter breast height. Soil respiration rates did not differ significantly between non-gap sites (1290 ± 210 mg CO₂ m⁻² h⁻¹) but were double those in gap sites (640 ± 130 mg CO₂ m⁻² h⁻¹). Post hoc analyses found that an increase in soil temperature and a decrease in litterfall and fine root biomass explained 72% of the difference between gap and non-gap sites. The significant decrease of soil respiration rates in gaps, irrespective of day or night time, suggests that autotrophic respiration may be an important contributor to total soil respiration in logged forests. We conclude that biosphere-atmosphere carbon exchange models in tropical systems should incorporate gap frequency and that future research in tropical forest should emphasize the contribution of autotrophic respiration to total soil respiration.     

Soil respiration following site preparation treatments in boreal mixedwood forest

The effects of experimental site preparation treatments on soil respiration were studied in a boreal mixedwood forest. The treatments were: (1) intact forest (uncut); (2) clearcut without site preparation (cut); (3) clearcut followed by mixing of organic matter with mineral horizons (mixed); and (4) plots from which all organic matter was removed (screefed). Soil respiration was measured as carbon dioxide (CO₂) evolution from surface soil once a month from June to October, 1994 in the field using infra-red gas analyzer (IRGA). In addition, soil temperature and moisture content were determined once a month during the 1994 growing season and soil organic matter content was determined once in July 1994. Mixed plots had the highest soil respiration rates (0.86 to 0.98 g m⁻² h⁻¹), followed by the clearcut (0.68 to 0.84 g m⁻² h⁻¹) and uncut plots (0.56 to 0.82 g m⁻² h⁻¹), with screefed plots having the lowest respiration rates (0.24 to 0.52 g m⁻² h⁻¹) from June to September. Soil respiration of the cut plots was not significantly different from that of the uncut control. The site preparation treatments reduced soil moisture and soil organic matter contents significantly. Changes in soil temperature within treatment at 0, 5 and 10 cm depths and between the treatments were not significant. Observed soil respiration patterns were attributed to changes in soil moisture and organic matter content associated with the various treatments. A laboratory incubation experiment elucidated the effects of organic matter, soil moisture, and temperature on soil respiration rates. Site preparation treatments in boreal mixedwood forests affect soil respiration by modifying the moisture and organic matter content of the soil.     

Effects of parent material on soil microbial biomass carbon and basal respiration within young afforested areas

Afforestation is economically and ecologically important for protecting land and improving soil quality. This study evaluates how soil basal respiration, physicochemical and microbiological characteristics are affected by parent material variety in afforesting degraded areas. For this, some soil physical and chemical parameters, microbial respiration (MR), soil microbial biomass carbon and microbial indexes (C_mic/C_org and MR/C_mic) were determined. The results showed that the physical, chemical and microbiological properties of the soil formed from limestone were better than those of the basaltic-andesite soil. An independent samples t-test demonstrated that the afforested area on the limestone parent material had significantly higher microbial biomass C than the basaltic-andesite parent material. The microbial quotient (C_mic/C_org) of the limestone soil was positively affected by afforestation. In addition, the highest basal respiration value (1.01?±?0.33 CO₂–C 10^?2?µg?g^?1?h^?1) was observed for the limestone at the topsoil. The lowest metabolic quotient values were determined for the basaltic-andesite parent material on both topsoil and subsoil (1.99 and 1.42?μg CO₂-C mg C_mic^?1 h^?1, respectively). This study revealed the importance of determining the parent material and its soil characteristics for successfully managing forest applications in degraded areas. Limestone soil sequesters more carbon and promotes microbial activities with a higher C_mic/C_org than the basaltic-andesite soil. Furthermore, the microbial quotient remained low during the 10 years in which the forest was in its sapling stage.     

Tree age and soil phosphorus conditions influence N2-fixation rates and soil N dynamics in natural populations of Acacia senegal

Acacia senegal, an important leguminous tree in arid and semi-arid environments, has shown promise as a multipurpose species, including gum production and soil fertility improvement, linked with N₂-fixation capabilities. Of particular interest are ontogenetic and edaphic effects on A. senegal performance in natural populations. Our research objectives were to investigate the effect of tree age and site phosphorus conditions on (1) tree N₂-fixation and (2) soil N and C dynamics in natural stands of A. senegal var. senegal, Baringo District, in the Rift Valley, Kenya. Sites consisted of A. senegal saplings (9 months) and mature A. senegal trees (7 years) along an edaphic gradient of soil P availability. A single-tree neighborhood approach was employed using a two by two factorial design: site conditions [high and low soil P contents] and tree age class [juvenile and mature]. Soil (N and C pools and fluxes) and plant metrics were quantified. A soil transfer experiment was also employed to confirm age and site effects on soil N mineralization. On the high soil P site, A. senegal had significantly lower foliar (¹⁵N levels than neighboring non-leguminous species (Balanites aegyptiaca), while foliar δ¹⁵N values in A. senegal on the low P site exhibited no significant difference with our reference plant, B. aegyptiaca. Across P sites, B. aegyptiaca had similar foliar δ¹⁵N values. These results indicate that the rate of N₂-fixation of A. senegal trees, as determined with foliar ¹⁵N natural abundance methodology, increased with increasing soil P availability in these natural populations. However, N₂-fixation rates declined with age. Although soil texture and soil CO₂ efflux did not differ between sites or across ages, soils under mature A. senegal at the high P site exhibited significantly greater total N content and total C content in comparison to soils at the low P site and under juvenile plants. Furthermore, under mature A. senegal trees, soil N mineralization rates were significantly greater as compared to under saplings. Soil transplants confirmed that soil microbial activity may be stimulated under mature trees as N mineralization rates were 2-3 fold greater compared to under A. senegal saplings. Our findings suggest that tree age and soil P availability are important factors in the nitrogen budget of natural populations of A. senegal, determining N₂-fixation rates, and potentially influencing soil total N and C pools and soil mineral N. This study provides information regarding the adaptation of A. senegal under differing edaphic conditions thus increasing accuracy of management support for A. senegal populations as productive agroforests.     

不同干扰类型下的白桦次生林土壤理化性质研究

研究内蒙古大兴安岭地区不同干扰类型下白桦次生林土壤理化性质特征,在内蒙古根河市选取3种干扰类型的白桦次生林样地的不同土层土壤作为研究对象,对土壤理化性质进行测量分析,探究不同干扰类型对土壤理化性质的影响。研究结果表明,白桦次生林在不同干扰方式下土壤理化性质存在显著差异。其中人工条带改造后的白桦次生林土壤pH值增大,火烧后白桦次生林容重增大,土壤有机碳、全氮、全磷、全钾、速效磷、速效钾含量在人工条带改造后显著增高,采伐干扰样地白桦次生林样地土壤含水量、速效氮含量最高。不同干扰类型的白桦次生林样地土壤理化性质间相关性不同。人工条带改造干扰样地白桦次生林土壤综合指数较高,火干扰样地白桦次生林土壤综合指数较低。     

Topographical differences in soil N transformation using15N dilution method along a slope in a conifer plantation forest in Japan

Soil N transformation was investigated using¹⁵N dilution method along a slope on a conifer plantation forest. Although there was no significant difference in the net N mineralization rates by laboratory incubation, net nitrification rates increased downslope. Gross N transformation by¹⁵N dilution method showed a distinct difference not only on the rates, but also on the main process between the lower and the upper of the slope. Half of minelarized N was immobilized and the other half was left in NH ₄ ⁺ pool at the upper part of the slope, while all of mineralized N was used for immobilization or nitrification and NH ₄ ⁺ pool decreased at the lower of the slope. Soil N transformations were classified into two groups: one was shown below 773 m and the other was shown above 782 m. The incubation with nitrification inhibitor showed that nitrification was mainly conducted by autotrophs irrespective of the position of the slope. Microbial biomass and microbial C/N were similar among the sites. However, the gross mineralization rate was higher below 773 m than above 782 m under similar respiration rates. This suggests that the substrate quality may be one of the controlling factors for soil N transformation. Extractable organic C/N was similar to microbial C/N at the lower of the slope. It indicated that the substrate was more decomposable below 773 m. It is considered that soil N transformation is affected by topographical gradient of moisture and nutrient which makes plant growth and decomposition rate different.     

Tracing the fate of mineral N compounds under high ambient N deposition in a Norway spruce forest at Solling/Germany

The fate of high and equally distributed ammonium and nitrate deposition was followed in a 72-year-old roofed Norway spruce forest at Solling in central Germany by separately adding ¹⁵NH₄⁺ and ¹⁵NO₃⁻ to throughfall water since November 2001. The objective was to quantify the retention of atmospheric ammonium and nitrate in different ecosystem compartments as well as the leaching loss from the forest ecosystem. δ¹⁵N excess in tree tissues (needles, twigs, branches and bole woods) decreased with increased tissue age. Clear ¹⁵N signals in old tree tissues indicated that the added ¹⁵N was not only assimilated to newly produced tree tissues but also retranslocated to old ones. During a period of over 3-year ¹⁵N addition, 30% of ¹⁵NH₄⁺ and 36% of ¹⁵NO₃⁻ were found in tree compartments. For both ¹⁵N tracers, 15% of added ¹⁵N was found in needles, followed by woody tissues (twigs, branches and boles, 7–13%) and live fine roots (7%). The recovery of ¹⁵NH₄⁺ and ¹⁵NO₃⁻ in the live fine roots differed with soil depth. The recovery of ¹⁵NH₄⁺ tended to be higher in the live fine roots in the organic layer than in the upper mineral soil. In the live fine roots in deeper soil, the recovery of ¹⁵NO₃⁻ tended to be higher than that of ¹⁵NH₄⁺. Soil retained the largest proportion of ¹⁵N, accounting for 71% of ¹⁵NH₄⁺ and 42% of ¹⁵NO₃⁻. Most of ¹⁵NH₄⁺ was recovered in the organic layer (65%) and the recovery decreased with soil depth. Conversely, only 8% of ¹⁵NO₃⁻ was found in the organic layer and 34% of ¹⁵NO₃⁻ was evenly distributed throughout the mineral soil layers. Nitrate leaching accounted for 3% of ¹⁵NH₄⁺ and 19% of ¹⁵NO₃⁻. Only less than 1% of the both added ¹⁵N was leached as DON. These results suggested that trees had a high contribution to the retention of atmospheric N and soil retention capacity determined the loss of atmospheric N by nitrate leaching.     

Effects of winter selective tree harvest on soil microclimate and surface CO2 flux of a northern hardwood forest

Soil surface CO₂ flux (S_flux) is the second largest terrestrial ecosystem carbon flux, and may be affected by forest harvest. The effects of clearcutting on S_flux have been studied, but little is known about the effect of alternative harvesting methods such as selective tree harvest on S_flux. We measured S_flux before and after (i) the creation of forest canopy gaps (simulating group tree selection harvests) and (ii) mechanized winter harvest but no tree removal (simulating ground disturbance associated with logging). The experiment was carried out in a sugar maple dominated forest in the Flambeau River State Forest, Wisconsin. Pre-treatment measurements of soil moisture, temperature and S_flux were measured throughout the growing season of 2006. In January–February 2007, a harvester created the canopy gaps (200–380 m²). The mechanization treatment consisted of the harvester traveling through the plots for a similar amount of time as the gap plots, but no trees were cut. Soil moisture and temperature and S_flux were measured throughout the growing season for 1 year prior to harvest and for 2 years after harvest. Soil moisture and temperature were significantly greater in the gap than mechanized and control treatments. Instantaneous S_flux was positively correlated to soil moisture and soil temperature at 2 and 10 cm, but temperature at 10 cm was the single best predictor. Annual S_flux was not significantly different among treatments prior to winter 2007 harvest, and was not significantly different among treatments after harvest. Annual (+1 std. err.) S_flux averaged 967 + 72, 1011 + 72, and 1012 + 72 g C m⁻² year⁻¹ in the control, mechanized and gap treatments, respectively, for the 2-year post-treatment period. The results from this study suggest selective group tree harvest significantly increases soil moisture and temperature but does not significantly influence S_flux.     

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m^?2/16.06 mg m^?2) and autumn (9.7 m^?2/16.98 mg m^?2) and minimum in the summer (0.43 m^?2/1.26 mg m^?2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO₂–C g soil^?1 day^?1) and minimum in winter (0.24 mg CO₂–C g soil^?1 day^?1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.     

Soil and microbial respiration in a loblolly pine plantation in response to seven years of irrigation and fertilization

Because soil CO₂ efflux or soil respiration (R_S) is the major component of forest carbon fluxes, the effects of forest management on R_S and microbial biomass carbon (C), microbial respiration (R_H), microbial activity and fine root biomass were studied over two years in a loblolly pine (Pinus taeda L.) plantation located near Aiken, SC. Stands were six-years-old at the beginning of the study and were subjected to irrigation (no irrigation versus irrigation) and fertilization (no fertilization versus fertilization) treatments since planting. Soil respiration ranged from 2 to 6 μmol m⁻² s⁻¹ and was strongly and linearly related to soil temperature. Soil moisture and C inputs to the soil (coarse woody debris and litter mass) which may influence R_H were significantly but only weakly related to R_S. No interaction effects between irrigation and fertilization were observed for R_S and microbial variables. Irrigation increased R_S, fine root mass and microbial biomass C. In contrast, fertilization increased R_H, microbial biomass C and microbial activity but reduced fine root biomass and had no influence on R_S. Predicted annual soil C efflux ranged from 8.8 to 10.7 Mg C ha⁻¹ year⁻¹ and was lower than net primary productivity (NPP) in all stands except the non-fertilized treatment. The influence of forest management on R_S was small or insignificant relative to biomass accumulation suggesting that NPP controls the transition between a carbon source and sink in rapidly growing pine systems.