湖南省森林公益效能的经济评价Ⅱ森林的固土保肥、改良土壤和净化大气效益

对湖南省森林的固土保肥、改良土壤和净化大气效益进行了计量评估,结果表明由于对森林的保护,每年,湖南省少流失的土壤234.37×10     

Soil water characteristics in glacial till at two forest sites in Sweden

Soil water characteristics were determined in 6 soil profiles along a Norway spruce forested sandy‐loamy till hillslope in Southern and Northern Sweden, respectively. The soil moisture class was mesic at both sites, i.e. having well drained soil water conditions. Two different Podzols; Leptic and Orthic, were developed at each site respectively. The vertical distribution of soil water retention capacity (SWRC) was similar in the different profiles at each site respectively. The SWRC of the mineral soil was significantly higher in the spodic B horizon compared to the other horizons. In concordance with the vertical distribution of SWRC, the largest amount of organic matter in the mineral soil, measured as ignition loss, was also found in the spodic B horizon. The significantly higher SWRC in the spodic B horizon, i.e. the ¡lluvial horizon, was suggested to depend on the accumulated organic‐sesquioxide material in this horizon. As SWRC reached maximum values in the spodic B horizon at all tensions applied, it was further suggested that soil formation in the studied profiles enhanced the formation of both micro‐ and macropores in the spodic B horizon. The variation of SWRC, at a certain level in the soil, was often larger within a profile than between the profiles at each site respectively.     

Converting conventional agriculture to poplar bioenergy crops: soil greenhouse gas flux

Conversion of agricultural fields to bioenergy crops can affect greenhouse gases (GHG) such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Soil GHG emissions were measured seasonally in poplar bioenergy and agricultural fields at three Northwestern US locations. A forest stand was also used at one location for comparison. A portable gas analyzer was used to measure CO₂ efflux and CH₄ and N₂O fluxes were first measured with chambers and later with gradients. Agricultural soil had 17% larger CO₂ efflux rates than poplar soil. Chamber fluxes showed no differences in CH₄ uptake but did show higher N₂O fluxes in poplar than agricultural soil. Gradient CH₄ uptake rates were highest in agricultural soil in the summer but showed no N₂O flux differences. Forest soils had smaller quarterly CO₂ efflux rates than agricultural soils and greater CH₄ uptake rates than poplar soils. The largest GHG contributor to soil GHG flux was CO₂, with those being ～1000 times larger than CH₄ flux rates and ～500 times larger than N₂O flux rates based on CO₂ equivalences. Converting conventional agricultural cropland to poplar bioenergy production does not have adverse effects on soil greenhouse gas flux and these results could be useful for modeling or life cycle analysis of land use conversion.     

Short-term effects of fire on soil properties inPinus densiflora stands

This study was performed to investigate a short time change (one week after fire) on soil properties due to the fire inPinus densiflora Sieb. et Zucc stands of the Kosung area in Kangwon Province in Korea. Twenty seven sampling plots [16 burned (8 low intensity fire, 8 high intensity fire) and 11 unburned plots] were chosen. Mineral soil samples from three depths (0–5, 5–15, and 15–25 cm) under the forest floor were collected. Forest fire in the area affected soil chemical properties. Soil pH, total nitrogen, available phosphorus, potassium, calcium, and magnesium in the surface soil (0–5 cm) of the burned area compared with the unburned area increased, but there was no marked change in the subsurface soil (5–25 cm). Organic matter, total nitrogen, available phosphorus, and exchangeable cations in the surface soil were generally lower in the high than in the low intensity fire areas. This indicates that these nutrients on the high intensity fire may be volatilized. The results suggest that change in soil chemical properties in the area was restricted mainly to the surface soil and was different between the high and the low intensity fire types.     

Extent and causes of site damage due to forestry traffic

Increased mechanization in the forestry means usually increased traffic on a ground which is also used as a growth substrate. In this state‐of‐the‐art article it is found that the traffic could have an areal extent of 10–30% of the site area mainly due to yarding at clear‐felling and thinning. In the future there could be up to 6 machine entries on the site till a stand age of 50 year.

Skidding is often recognized as the major cause of soil disturbance with 50–75% of the skid trails considered as apparently compacted. Rut formation after forwarders can also be a problem but harvesters seems to be forgotten or give minor problems.

In order to reduce soil compaction smaller machines must be considered on many sites. Maybe 5–10 tonnes machines with a real mean ground pressure of 60–70 kPa could give, thanks to good tyres, an acceptable level of soil disturbance.

High tractive forces and slip may contribute to the soil disturbance as much as double the ground pressure. Calculations show it is therefore better to carry the load than to skid. However, the change in weight balance of the machine due to the load is still a problem and maybe anti‐slip control could give the machine a better torque distribution.     

Seasonal response of soil enzyme activity to thinning intensity of aerial seeded Pinus tabulaeformis stands

Aerial seeding is one of the most important vegetation restoration patterns in remote hilly areas, and studies concerning soil quality and its management have practical value. In 2000, a study of the effect of thinning intensities at five different treatments levels, 0 (CK), 30% (slight thinning), 48.75% (medium thinning), 53.75% (intense thinning) and 65.6% (super intense thinning) on soil enzyme activity was carried out on 9-year-old aerial seeded Chinese pine (Pinus tabulaeformis Carr.) stands with an initial density of 8000 trees/hm², in the Wang-jiapu Aerail Seeding Center, Yanqing County, Beijing. Five years later, the activities of five kinds of soil enzymes, soil urease, alkaline phosphatase, inertase, catalase and polyphenol oxidase in the first 20 cm of soil layer were compared during four seasons. Relationships among soil enzymes and soil physiochemical properties were also analyzed to examine the possibility of using soil enzymes to evaluate thinning intensities. The results showed that the maximum enzyme activities of catalase and polyphenol oxidase occurred in June, those of soil urease and alkaline phosphatase occurred in October, and soil invetase had its maximum in April. In addition, the five soil enzymes were affected differently by thinning intensities. Soil catalase, urease and invertase showed the highest response to a slight thinning, followed by medium thinning, which is the opposite experienced with polyphenol oxidase and alkaline phosphatase. There are statistically significant and positive relationships between soil enzymes and organic matter and available K. It should be noted that soil water was a limiting factor to soil enzyme activity. Compared with soil physicochemical characteristics, soil enzymes were more sensitive to levels of thinning intensities. Among the enzymes, soil alkaline phosphatase and catalase could be regarded as indicators to assess soil quality. It is concluded that a suitable thinning intensity benefits the development of undergrowth and soil enzymes. Generally, when the stand with initial density of 8000 trees/hm² grows up to nine years old, the most suitable thinning intensity should be about 50%. __________ Translated from Journal of Beijing Forestry University, 2008, 30(2): 82–88 [译自: 北京林业大学学报]     

Evolution of soil microbial biomass in restoration process of Robinia pseudoacacia plantations in an eroded environment

Vegetation recovery is a key measure to improve ecosystems in the Loess Plateau in China. To understand the evolution of soil microorganisms in forest plantations in the hilly areas of the Loess Plateau, the soil microbial biomass, microbial respiration and physical and chemical properties of the soil of Robinia pseudoacacia plantations were studied. In this study, eight forest soils of different age classes were used to study the evolution of soil microbial biomass, while a farmland and a native forest community of Platycladus orientalis L. were chosen as controls. By measuring soil microbial biomass, metabolic quotient, and physical and chemical properties, it can be concluded that soil quality was improved steadily after planting. Soil microbial biomass of C, N and P (SMBC, SMBN and SMBP) increased significantly after 10 to 15 years of afforestation and vegetation recovery. A relatively stable state of soil microbial biomass was maintained in near-mature or mature plantations. There was an increase of soil microbial biomass appearing at the end of the mature stage. After 50 years of afforestation and vegetation recovery, compared with those in farmland, the soil microbial biomass of C, N and P increased by 213%, 201% and 83% respectively, but only accounting for 51%, 55% and 61% of the increase in P. orientalis forest. Microbial soil respiration was enhanced in the early stages, and then weakened in the later stage after restoration, which was different from the change of soil organic carbon. The metabolic quotient (qCO₂) was significantly higher in the soils of the P. orientalis forest than that in farmland at the early restoration stage and then decreased rapidly. After 25 years of afforestation and vegetation recovery, qCO₂ in soils of the R. pseudoacacia forest was lower than that in the farmland soil, and reached a minimum after 50 years, which was close to that of the P. orientalis forest. A significant relationship was found among soil microbial biomass, qCO₂ and physical and chemical properties and restoration duration. Therefore, we conclude that it is possible to artificially improve the ecological environment and soil quality in the hilly area of the Loess Plateau; a long time, even more than 100 years, is needed to reach the climax of the present natural forest. __________ Translated from Acta Ecologica Sinica, 2007, 27(3): 909–917 [译自: 生态学报]     

Photosynthetic physio-response of Taxodium ascendens seedlings to different soil water gradients

Four different kinds of water treatments were applied to study the photosynthetic eco-physiological characteristics of Taxodium ascendens seedlings in the environment of the Three Gorges hydro-fluctuation belt. The four kinds of water treatments were: normal growth water condition (CK), light drought stress (T1), soil water saturation (T2), and soil submersion (T3). The results showed that different water treatments could effectively influence the content of the photosynthetic pigment, leaf gas exchange and apparent resources use efficiency of T. ascendens seedlings. It was also demonstrated that the T. ascendens seedlings could not only tolerate water submersion and wet conditions but also endure a certain degree of drought. To establish a protection forest system in the hydro-fluctuation belt in the Three Gorges Reservoir Area, the species T. ascendens is suitable for planting in conditions of root submersion or water-saturated soil. In case it is planted in drought conditions, this tree species should be watered appropriately in order to keep its normal net photosynthetic rate. Translated from Forest Research, 2006, 19(1): 54–60 [译自: 林业科学研究]