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1.
A shoreline cleaner was tested to determine its effectiveness in removing different types of oil from selected US Gulf coastal marsh macrophytes. Bulltongue (Sagittaria lancifolia L.), three cornered grass (Scirpus olneyi E. & G.) and broadleaf cattail (Typha latifolia L.) were subjected to oil application and cleaning in a greenhouse and the subsequent effects on plant functions were evaluated during the period immediately after treatment initiation. Plant stomatal functioning, photosynthesis, respiration, regeneration, growth and biomass were monitored. Two types of oil, South Louisiana Crude (SLC) or Arabian Medium Crude (AMC) were used. The treatments included: control (no oil or cleaner), cleaner only (COREXIT 9580 only, no oil), oiled with SLC or AMC only (no cleaner), and oiled using SLC or AMC and cleaned with COREXIT 9580 after two days. The existing leaves on the macrophytes at the time of treatment application directly subjected to oiling (but not cleaned) did not recover from the effects of oiling in all of the study species. However, leaves under oil+cleaner treatments or leaves developed during the post-oiling period (new leaves) showed a different pattern of response. For instance, in bulltongue plants, new leaves had stomatal conductances at or close to the values recorded for control plants. However, new leaves and leaves subjected to oil+cleaner treatment in cattail and three-cornered plants, had stomatal conductances significantly lower than their respective control plants. However, photosynthetic and respiration data indicated no overall significant differences within each species across treatments. Thus, the physiological functions of the study species had apparently recovered from the initial adverse effects of oiling within the experimental period. Based on photosynthetic and respiration data, the study species sensitivity ranking is similar. Furthermore, there were no significant differences in physiological responses of the study species to oil types. In addition, above-ground biomass was not affected significantly by the treatments in bulltongue or cattail but was reduced significantly in three-corner plants. Based on the overall physiological and biomass data, bulltongue was the least sensitive of the three species to SLC and AMC oil types than the other species while cattail appeared to be the most sensitive. Any beneficial effects of the cleaner may be more pronounced in plant species highly sensitive to specific oil types than the species studied.  相似文献   

2.
The first‐year effect of two different prescribed burning treatments on throughfall, runoff and soil erosion was evaluated in gorse shrubland (Ulex europaeus L.) in Galicia (NW Spain). The treatments compared were: intense burn, light burn and control (no burn). Accumulated annual throughfall represented between the 81 and 87 per cent of total rainfall in intensely burned and lightly burned areas, respectively, whereas in the unburnt areas it was 60 per cent. No significant differences between burning treatments were found for the annual throughfall. However, runoff was significantly greater in intensely burned plots (1·5‐times) than in lightly burned plots. Burning also resulted in a significant increase in runoff (between 2·5 and 1·7‐times, respectively) compared with controls. Total soil losses were small in all treatments, but the intense burn caused significantly greater soil erosion (5·8‐times) compared with the unburned areas. Soil losses after the light burn did not significantly differ from the control although they were higher (2·3‐times). The relationships obtained between erosion and several rainfall parameters were significantly different in burned areas compared to the control. The same response was observed for runoff. Annual erosion losses showed a strong dependence on percentage of bare soil even for small values of this variable. Litter thickness was also a very important variable influencing on erosion rates. This study indicated that by combining ignition techniques and high litter moisture content to maintain the percentage of bare soil below 85 per cent, soil erosion was low. Nevertheless, this result was constrained by the low rainfall that occurred during the study. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

3.
The effects of ecological restoration on belowground processes such as decomposition are generally unknown. To assess the immediate effects of prescribed fire and mechanical thinning on belowground processes, we measured the activities of five extracellular enzymes (phosphatase, β-glucosidase, β-N-acetylglucosaminidase, phenol oxidase, and lignin-peroxidase) in soils and on decomposing Quercus falcata leaf litter in unburned, burned, and burned and thinned plots in a mesic forest in northern Mississippi. Decomposition rates of Q. falcata leaf litter were also assessed at each plot. Soil phosphatase activity decreased after a prescribed burn and was related to an increase in soil organic matter in plots that had been burned. Soil β-N-acetylglucosaminidase activity increased after a burn, and was related to a decrease in leaf litter. Leaf litter enzyme activity showed no consistent patterns amongst treatments, or between individual enzymes, while decomposition rates of leaf litter were slightly accelerated in the treatment plots, but not significantly so. Decomposition rates were related to cumulative enzyme activity, with phenol oxidase and lignin-peroxidase having the highest apparent efficiencies in degrading the leaf material. Overall, the microbial degradation of Q. falcata leaf litter was more efficient in plots that were burned and thinned than in the other plots. Increases in the efficiency of litter decomposition coupled with reductions in litter inputs due to canopy thinning likely allows for increased solar penetration to the soil, and could promote the restoration of the shade-intolerant species that once dominated the understory. Post-burn increases in β-N-acetylglucosaminidase activity and decreases in phosphatase activity also suggest a potential shift in the soil community from phosphorus limitation to nitrogen limitation following a fire.  相似文献   

4.
Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (Cmic) was 52% (fumigation-extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of Cmic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24-85%) and nitrate (47-76%) in the soil until 90 d after burning, while soil NH4+-N was not affected to the same extent. The increase in soil NO3−-N but not NH4+-N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH4+-N to NO3−-N. In the subsequent rainy season, NO3−-N and, consequently, PDA were reduced by ash deposition. Further, Cmic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.  相似文献   

5.
Two oiling experiments were conducted from 1977–1979 on sea otters Enhydra lutris in Prince William Sound, Alaska. In the first experiment, four captured otters were fitted with radio-transmitters and released following contamination of their pelage with 25 cc of Prudoe Bay crude oil; a fifth individual was oiled and cleaned with detergent prior to being released. For all experimental animals activity increased dramatically during the first week following treatment; this effect was accentuated in the otter cleaned with detergent. Most of the increase in activity corresponded to increased grooming, whereas the feeding pattern (as measured by dive time analysis) did not change. It appeared that all experimental otters survived the first experiment, probably because only a small portion of the pelage was treated, and because food resources in the study area were abundant. In the second experiment we observed behavioural reactions of two otters in an above-ground swimming pool which was partly covered with crude oil. Both otters spent very little time on the oiled side of the pool (less than 1 minute per hour), but occasionally surfaced in it for brief periods and eventually became contaminated. One of these individuals was not cleaned and died within 24 h of first encounter with the oil; the other was cleaned and released with a radio-transmitter that failed shortly afterwards.  相似文献   

6.
Soil fungal species density and aggregation had changed 6 months after spring burning and raking in a Wisconsin prairie. Fungal species density had increased by 29% in burned relative to raked or undisturbed plots; species density was highest at the soil surface in burned and raked plots, and lowest at the surface in undisturbed plots. Fungal propagules of the same species were less aggregated in burned and raked plots than in undisturbed. These changes imply greater mixing of fungal propagules in soil of burned and raked plots than in undisturbed plots. The physical effects of burning and raking and the properties of fungal spores do not account for the changes. It is argued that soil invertebrates are responsible for the mixing because: (1) at any depth in soil, density of mites and collembola increased concurrently with fungal species density; and (2) path analysis shows that fungal species density is equally associated with microarthropod density and root biomass after burning, but after raking, fungal species density was more strongly associated with root biomass than microarthropods.  相似文献   

7.
The effect of crude oil on gas exchange functions of Juncus roemerianus and Spartina alterniflora, two important U.S. Gulf Coast plant species, were examined. Plants were exposed to petroleum hydrocarbons (Mexican Sour type) mixed with water at 4.4 mL L?1 (2 L m?2). Coating entire leaf with oil resulted in cessation of photosynthetic activity. Partial leaf exposure to oil resulted in net photosynthesis decrease in both species shortly after exposure. Net photosynthesis remained within 71 and 94% of control plants in J. roemerianus during the first four weeks of the experiment. In S. alterniflora, photosynthetic rates averaged between 53 to 80% of control plants during the same period. Four weeks following the partial oiling, net photosynthesis began to improve in both species. Partial oil coverage of leaves of both species resulted in reduction in normal photosynthetic activity with no lethal effects. By the end of the laboratory study, there was no significant reduction in production of new shoots or the overall growth of either species.  相似文献   

8.
Prescribed, biennial burning in forest understory started in Cuivre River State Park, Missouri, USA, in the late 1980s to help restore the forest to conditions that existed prior to European settlement. Bird surveys were started in 1996 on two burned and two unburned sections of the park to determine what effects the burning and subsequent changes in vegetation were having on bird populations. Birds were sampled at 17 60-m radius point counts on each study area; each point was sampled twice per year during the main breeding period from 1996 through 2002. Total abundance and species richness differed among the four areas but no differences could be attributed to burning. Some individual species, however, differed in abundance and frequency of occurrence between burned and unburned areas. For example, Indigo Bunting (Passerina cyanea), Kentucky Warbler (Oporornis formosus), and several species of woodpeckers were more abundant on burned areas; Ovenbird (Seiurus aurocapillus), Worm-eating Warbler (Helmitheros vermivorous), Wood Thrush (Hylocicla mustelina) and Acadian Flycatcher (Empidonax virescens) were among the species more abundant on unburned areas. As a consequence, overall community composition differed significantly between burned and unburned areas of the park, but did not differ between burned areas or between unburned areas. Prescribed burning was instituted to restore vegetation to presettlement conditions and has started to achieve that objective. Restoration also has affected and likely will continue to affect bird populations. Future maintenance of a full complement of bird species, including a number of neotropical migrants, will be dependent on presence of both burned and unburned forest habitat.  相似文献   

9.
After oil spills, oiled wildlife are regularly cleaned at considerable cost. Yet the conservation value of this intervention has been questioned, mostly because cleaned animals appear to have poor post-release survival. However, reliable long-term data are needed to judge the success of such programs. We used 16 ring recoveries to estimate survival of 932 Cape gannets (Morus capensis) that were oiled, cleaned and released in 1983. For the period 1989-2006, we further compared survival of 162 surviving cleaned gannets to that of 10,558 non-oiled gannets using capture-recapture data. We used modern statistical tools that account for recapture probabilities, recovery rates, transience, and temporary absence from the breeding colonies. Mean annual survival rates of de-oiled gannets ranged from 0.84 (se = 0.05) to 0.88 (se = 0.02), depending on analysis and colony. Between 1989 and 2006, rehabilitated gannets survived slightly less well than unoiled birds, but the difference was similar to the difference in survival between the two colonies where the birds were studied. Our results show subtle long-term effects of oiling and subsequent treatment. However, they also show that cleaned gannets can survive at almost the same rate as unoiled birds, at least if they survived the initial years after release. Rehabilitation of these birds may thus be a valuable conservation intervention for this localised species where a single spill can threaten a large proportion of the world population.  相似文献   

10.
多年连续计划烧除对云南松林坡面水土流失的影响   总被引：1，自引：0，他引：1  
龚顺清  陈奇伯    黄新会    杨建光  黎建强    钱靖 《水土保持研究》2022,29(3):18-24
为探讨多年连续计划烧除对云南松林坡面水土流失的影响,科学评价云南松林计划烧除后森林生态系统的服务功能,2019年在滇中新平县照壁山云南松林设置计划烧除区域和未烧除区域的径流小区,对降雨及产流产沙变化进行了定位观测,建立了降雨、径流和泥沙的数值关系,结果表明:(1)2019年研究区降雨量为568.6 mm,仅为多年平均降雨量939.79 mm的60.5%,降雨主要集中雨季5—10月,雨季降雨量占年降雨总量的73.8%。雨季降雨51场次,其中产流降雨28场,占雨季降雨总量的93.7%。(2)多年连续计划烧除增强了降雨转化为林地坡面径流的能力,且小雨量级最能凸显计划烧除促进林地坡面径流泥沙的产生。(3)计划烧除小区和未烧除小区的径流主要与降雨量显著相关,计划烧除小区的径流与降雨呈幂函数关系,未烧除小区的径流与降雨呈多项式关系。(4)计划烧除小区和未烧除小区的泥沙均与降雨量、径流量显著相关,且泥沙与降雨、径流的关系均呈幂函数形式。表明多年连续计划烧除改变林地水文特征,提高了降雨转化为林地坡面径流的能力,提高了径流挟带泥沙的能力,才使计划烧除林地的径流泥沙比未烧除林地多。  相似文献   

11.
《CATENA》2001,45(3):185-207
In northern Ecuador, soils of high altitude grasslands (páramos) are mainly non-allophanic Andisols developed on Holocenic volcanic ash. These soils have a high water retention capacity and are the “water tank” of central Ecuador. To assess the effect of land use (burning and tillage) on soil hydrodynamic properties, rainfall simulation was conducted at two different sites. At Pichincha near Quito, the simulation was conducted on a recent volcanic ash soil comparing natural, tilled and burned plots. At El Angel, the simulation was conducted on a mature non-allophanic Andisol comparing natural, recently tilled and formerly cultivated plots.On natural plots, the infiltration rate was very high and sediment loss very low. Results for infiltration rate and runoff indicated that land use change on páramos increased runoff flow and reduced saturated hydraulic conductivity. Superficial reorganisation of the soil surfaces occurred on tilled plots at both sites. This crusting process was fast and resulted in surfaces with very low conductivity at Pichincha. The same processes seemed to be slower at El Angel. The soil surface of recent Andisols at Pichincha was prone to crusting whereas the mature Andisol, at El Angel, with a lower bulk density, was compacted when the kinetic energy of raindrops was high. Water repellency occurred after burning at Pichincha and following long natural air drying after tillage in the non-allophanic A horizon at El Angel. Water repellency combined with the low bulk density of soil aggregates explain the intensity of sediment losses in the abandoned soils after cultivation (Bare fallow plots). Erosion occurred in these areas through floating hydrophobic and stable aggregates.  相似文献   

12.
Oil spills may detrimentally damage sensitive coastal habitats, such as coastal wetlands. Successful restoration of oiled habitats primarily depends on the tolerance of vegetation transplants to oil. In this study, tolerance limits of the dominant coastal brackish marsh plant Spartina patens to South Louisiana crude (SLC) oil and its phytoremediation effectiveness on petroleum hydrocarbons in wetland sediments were investigated in the greenhouse environment. Spartina patens was transplanted into brackish marsh sediments contaminated with SLC oil at concentrations of 0, 40, 80, 160, 320, 640 and 800 mg SLC oil g?1 dry sediment. High oil concentrations adversely affected plant stem density, aboveground biomass and belowground biomass even one year after transplantation. At the 320 mg g?1 oil dosage, plant belowground biomass was significantly lower than the control although aboveground variables were not significantly different from the control. All plant parameters mentioned above at the 640 mg g?1 oil dosage were less than 50% of the control. Spartina patens did not survive the 800 mg g?1 oil dosage. The tolerance limit of S. patens to SLC was estimated about 320 mg oil g?1 dry sediment. In addition, S. patens transplants enhanced oil degradation in the sediment; concentrations of residual total petroleum hydrocarbons (TPH) in the sediments vegetated by S. patens were significantly lower than those of un-vegetated sediments for both the surface and subsurface sediment at the 40 and 160 mg g?1 SLC oil dosages. Decreases in the concentrations of polycyclic aromatic hydrocarbons (PAHs) further demonstrated the capacity of S. patens to phytoremediate residual oil; residual total targeted PAHs in the phytoremediation treatment were less than 20% of the un-vegetated treatment at the 40 mg g?1 oil dosage. These results demonstrated the potential of phytoremediation with S. patens to simultaneously restore and remediate petroleum-contaminated coastal marsh habitats.  相似文献   

13.
In the Gilgel Gibe catchment in Ethiopia, local farmers intensify land use on Planosols by adjusting a traditional soil burning practice known as guie. The burning practice used to be applied in a cycle of shifting cultivation. However, more recently, farmers burn small plots to make fertile seedbeds for Eucalyptus seedlings in the first year before these trees are transplanted to larger plots. The purpose of this research was to assess the physico‐chemical properties of Planosols that have been subjected to burning over the last 10 yrs and evaluate the contribution of guie to land‐use intensification of these soils. Transect studies and interviews of local farmers, followed by chemical, physical and micromorphological analyses of samples from selected plots were used to compare the soil properties of recently (0–2 yrs) and formerly (3–10 yrs) burnt Planosols with those of unburnt Planosols. The analytical results show that the burning practice improved nutrient availability in the first 2 yrs after guie. Increased amounts of exchangeable aluminium (Al) were reported in the long term. Charge fingerprints illustrate that the nutrient‐buffering capacity of the soil was high shortly after the practice but subsequently decreased with time. Given the population pressure on the formerly extensively used Planosols, it is argued that the current application of guie on small, localized plots for raising Eucalyptus seedlings is well adapted to the local socio‐economic context and promotes land‐use intensification on the Planosols. The increased exchangeable Al content of former Eucalyptus seedbeds merits further in‐depth research into the biophysical sustainability of the burning practice.  相似文献   

14.
We examined patterns of microarthropod abundance in oak-hickory (Quercus-Carya) forest ecosystems in southern Ohio (USA) in relation to landscape position and fire frequency. Abundances of various suborders of Acari and Collembola were determined in samples taken in June 1999 in three forested watersheds, one that had been burned annually for four consecutive springs (1996-1999), one that had been burned periodically (1996 and 1999), and an unburned control. Microarthropod abundance was significantly lower in the annually burned watershed than the periodically burned and control watersheds. Since both the periodically burned and annually burned watersheds were burned in April 1999, the lower microarthropod abundance in the annually burned watershed was not simply an immediate effect of burning. At the landscape scale, the abundance of oribatid mites was greater in xeric than intermediate or mesic landscape positions. Within any single watershed, there was no significant linear relationship between litter mass and microarthropod abundance. However, when all three watersheds were combined, there was a significant, positive relationship between litter mass and microarthropod abundance, mainly due to the annually burned watershed where there was very low litter mass and low microarthropod abundance. Both fire frequency and landscape position have significant effects on microarthropod abundance; however, those effects cannot be robustly predicted based solely on forest floor litter mass differences.  相似文献   

15.
The effects of forest fires on the soil mycotlora were investigated in a Pinus contorta forest in Alberta, where it was found that species of Trichoderma and Penicillium were reduced in the burned plot, whereas Gelasinospora sp occurred only in the burned plot: Cylindrocarpon destructans appeared not to be affected by fire.The response of fungi to aqueous extracts of burned and unburned litter, measured as linear growth on agar, showed that, of the isolates tested, all but C. destructans were inhibited by the burned litter extract; C. destructans grew better on the burned litter extract. An examination of spore germination rates and growth in liquid culture showed that Trichoderma polysporum and Penicillium janthinellum were both inhibited by burned litter extracts whereas C. destructans was not. Gelasinospora sp did not grow in liquid culture, nor did it produce spores after being kept in culture for some time.It was concluded that species of Trichoderma and Penicillium were killed by the heat of the fire, and subsequently unable to rccolonize the upper layers of the soil, due to an inhibition of spore germination and growth by the chemical products of burning. C. destructans on the other hand may have been able to recolonize quickly as it appeared to be stimulated in its linear growth rate by the chemical products of burning, and its spore germination rate was only marginally lowered. The occurrence of Gelasinospora sp following fire is possibly explained by its extremely rapid growth rate, and the possibility of its ascospores being more able to withstand high temperatures in the soil.In the light of recent reports, indicating that some species of Trichoderma and Penicillium are actively antagonistic to other fungi, it is suggested that their absence after fire, in the area studied, may permit a high inoculum of C. destructans to develop in the soil, which could possibly result in a high incidence of disease in developing pine seedlings  相似文献   

16.
Fires in grasslands significantly alter nutrient cycling processes. Seasonal climatic changes can interact with fire to further modify nutrient cycling processes. To investigate the effects of fire on soil nitrogen transformation processes and their seasonal change and interannual variability in a typical steppe in Inner Mongolia, we determined the rates of net nitrogen mineralization and nitrification over two growing seasons and a winter following a prescribed spring fire in May 2006. Fire significantly decreased rates of both net nitrogen mineralization and net nitrification during the first growing season and winter following burning. Cumulative net nitrogen mineralization in unburned and burned plots in the 2006 growing season was 133% and 183% higher, respectively, than in the drier 2007 growing season. Nitrogen mineralization apparently occurred in winter and the cumulative net nitrogen mineralization from October 2, 2006, to April 27, 2007 in unburned and burned plots amounted to 1.18 ± 0.25 g N m−2 and 0.51 ± 0.08 g N m−2, respectively. Cumulative net nitrogen mineralization was higher in a wet 2006 than in a dry 2007 growing season, indicating that the net N mineralization rate was sensitive to soil moisture in a dry season. Our study demonstrated that a one-time prescribed fire decreased net N mineralization rates only for a short period of time after burning while interannual variation in climate had more significant effects on the process of nitrogen mineralization.  相似文献   

17.
Abstract

A field study evaluating the effects of gypsum and water management on the survival, yield, and protein content of selected species of marsh vegetation was conducted on an open area inundated by brackish water near Hackberry, Cameron Parish, Louisiana. The overall growth and yield response of four species of marsh vegetation: joint grass (Paspalum vaginatum SW.), marsh hay cordgrass (Spartina patens Muh L.), salt grass (Distichlis spicata L.), and American three square (Scirpus americanus Pers.) to gypsum addition (0 versus 7 Mg/ha) and water management (flooded versus non‐flooded plots) were statistically evaluated.

Soil drying was detrimental to the overall growth and yield of all marsh vegetation. There was zero plant survival in the non‐flooded plots except the marsh hay cordgrass with a survival rate of 32.8 %.

Plots receiving 7 Mg gypsum/ha had significantly higher dry matter production than the control. Gypsum application increased dry yield of joint grass (5.44 to 8.08 Mg/ha), marsh hay cordgrass (1.90 to 6.91 Mg/ha), salt grass (0.97 to 2.79 Mg/ha) and three‐square (1.55 to 2.84 Mg/ha) in flooded plots. The yield of marsh hay cordgrass, the only surviving species in the non‐flooded plots, produced a yield increase of 0.40 Mg/ha in response to gypsum. Significantly higher survival rates were observed in flooded plots treated with gypsum than in the non‐flooded plots receiving no gypsum. The mean survival rate for the gypsum‐ treated plots was 68.2%, as opposed to 21.9% for the untreated plots.  相似文献   

18.
In the traditional shifting cultivation system practiced by the Karen people in northern Thailand, the effects of burning on the content of extractable organic matter, microbial biomass, and N mineralization process of the soils were studied. Five plots (5×5 m2 quadrat) with 0, 10, 20, 50, and 100 Mg ha-1 of slashed materials were arranged and burned. Ten to 20 Mg ha-1 of slashed biomass corresponded to the amount commonly burned by the Karen people. During the burning process, the soil temperature at the depth of 2.5 cm in the 100 Mg ha-1 plot almost evenly increased to 300°C while the temperature in the 10 to 50 Mg ha-1 plots increased with large variations from 50 to 300°C. Burning caused a conspicuous increase in the contents of organic C and (organic + mineral)-N extracted at room temperature and a simultaneous decrease in the contents of microbial biomass C and N, especially in the soil of the 100 Mg ha-1 plot. In the rainy season, the values of the changes induced by burning reverted to the values recorded before burning, except for the microbial biomass in the 100 Mg ha-1 plot, which still remained lower. Based on an incubation experiment, N mineralization rate was higher in the soils taken just after burning, especially in the 100 Mg ha-1 plot, than in the soils taken during the rainy season. However, the soil in the 100 Mg ha-1 plot was considered to have the lowest ability to supply mineral N among the soils in the rainy season. Burning of 10 to 20 Mg ha-1 biomass corresponding to the values recorded in Karen peoples' shifting cultivation system was more compatible with soil ecology in terms of N supply at the initial stage of crop growth and of microbial biomass recovery during the rainy season, compared to the burning of 100 Mg ha-1 biomass corresponding to the value recorded in a natural forest. Thus, the shifting cultivation system implemented by the Karen people can be considered to be a well-balanced agricultural system.  相似文献   

19.
Tree thinning and harvesting produces large amounts of slash material which are typically disposed of by burning, often resulting in severe soil heating. We measured soil chemical properties and microbial community structure and function over time to determine effects of slash pile burning in a ponderosa pine forest soil. Real time data were collected for soil temperature, heat flux, and soil moisture contents in one of two slash piles burned in April 2004. During the burn, soil temperatures reached 300 °C beneath the pile center and 175 °C beneath the pile edge. Slash pile burning increased soil pH, extractable N and P, and decreased total C levels within the first 15 cm of soil. Burning reduced soil bacterial biovolumes within the first 15 cm of soil and fungal biovolumes within the first 5 cm of soil. One month after the burn, soil microbial communities under the pile center were enriched in Gram-positive bacterial fatty acid markers compared to communities from under the pile edge and control (nonburned) soil. Fifteen months later, soil chemical properties had not returned to background levels, and microbial community structure in fire-affected soil, regardless of pile location, was distinct from communities of control soil. In fire-affected soil, concentrations of fungal fatty acid biomarkers were low and arbuscular mycorrhizal fungal biomarkers were absent, regardless of pile location. Slash pile burning also reduced fungal and bacterial respiration and resulted in large fluctuations in microbial potential N mineralization and immobilization activities. By altering soil properties important to soil conservation and plant reestablishment, slash pile burning negatively impacts forest ecosystems at localized scales.  相似文献   

20.
The effects of burning on the levels of soil organic matter, soil nitrogen, and soil microbial biomass were studied by carrying out experimental shifting cultivation at two sites, Niah and Bakam in Sarawak, Malaysia. Vegetation biomass was burned in plots (10 × 10 m2) at the rates of 0 (control), 100, 200, and 300 Mg ha−1 at the Niah site and 0, 20, and 100 Mg ha−1 at the Bakam site. At the Niah site, the levels of total C and N of the soils did not change throughout the experiment in spite of enhanced soil respiration until 2 months after burning. Although burning induced an increase in the amount of NH4-N of the soils, the readily available pool of N (the sum of the NH4-N, NO3-N, microbial biomass N, and extractable organic N pools) in the burned plots was depleted appreciably at the end of rice cultivation. The effects of burning on these properties tended to be substantial with increasing amounts of the vegetation biomass burned. On the other hand, the levels of total C and N and the readily available N pool at the Bakam site were low before burning compared with those at the Niah site, and the burning treatments did not affect them appreciably. While the rice yield at the Niah site reached the average value obtained in traditional shifting cultivation in Sarawak, that at the Bakam site was much lower. It was suggested that the flush of NH4-N induced by burning was one of the major factors for rice growth.  相似文献   

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