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1.
The purpose of this greenhouse experiment was to examine the short-term effects of competition between pine seedlings and the soil microbial biomass in sandy oligotrophic pine barrens upland forest soils subjected to varying levels of prescribed fire severity. Pine seedling growth performance, microbial biomass nitrogen, extractable soil nutrients and leaching loss from the soil were determined, throughout a single growing season following fire treatment. Replicate soil cores exposed to three levels of fire severity were maintained in a greenhouse with or without a pine seedling. Throughout the following growing season replicate cores from each treatment were harvested and analyzed monthly. The data allowed testing for two main effects: soil fire treatment and tree presence/absence. In no instance was a significant fire treatment X tree presence/absence interaction found. Our results indicate that biological activity strongly influences soil conditions. Reduced microbial activity resulted from the interaction of soil microbial biomass and an individual pine seedling. Increased plant growth performance correlates with reduced soil mineral nitrogen concentration and decreased pH. At the levels of fire severity utilized in this experiment immobilization due to biological uptake and abiotic soil fixation prevented significant leaching losses above that of unburned control samples. In the oligotrophic, pine barrens soils, nitrogen and phosphorus mineralized by fire are largely conserved by biological processes. These results also suggest that plant growth is subject to limitation by phosphorus availability in these soils.  相似文献   

2.
Summary Densities of the different taxa of microarthropods per gram of litter in litter bags varied widely from the rainy to the dry season. Collembola and Acarina constituted more than 86% of the total microarthropods, and occurred in significantly greater numbers in the coarse-mesh bags than the fine-mesh bags. There were no fauna in the litter of suspended bags. The average weight loss was greater in the coarse-mesh bags (50.4%) than in the fine-mesh bags (44.5%), and the suspended bags (7.4%). Similarly, the concentrations of N and Ca were greater in the litter of coarse-mesh bags compared to that of the fine-mesh bags. In contrast, the concentrations of P and K were comparatively lower in coarse-mesh bags. The mass loss of litter showed a negative linear correlation with the total Collembola and with litter temperature. The N concentrations in the litter in both the mesh bags showed negative correlations with the abundance of total Collembola, and with that of Lepidocyrtus sp. and Sminthuridae, and rainfall. The N concentration in the litter in the coarse-mesh bags was positively correlated with the total number of arthropods but, surprisingly, was negatively correlated with the total number of Acarina. The concentration of Ca showed negative correlations with rainfall and litter moisture only. The P concentration showed positive correlations with total Collembola, with Lepidocyrtus sp. and Sminthuridae in both the mesh bags, with rainfall in the fine-mesh bags, and with total microarthropods in the coarse-mesh bags.  相似文献   

3.
The importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species’ litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols).  相似文献   

4.
Pollination by insects in forests is an extremely important process that should be conserved. Not only do pollinating insects help to maintain a diversity of plants within forests, but they also aid in pollinating crops found near forested land. Currently, the effects of various forest management practices on floral visiting insect abundance or diversity is unknown, so we investigated how prescribed burning, mechanical shrub control, and combination of the two affected abundance of floral visiting insects. We caught 7921 floral visitors from four orders and 21 families. Hymenoptera was the most abundant and diverse order, with Halictidae being the most abundant family. A total of 45 species of Hymenoptera representing six families were captured. We caught seven families and 35 species of Lepidoptera, six families and 33 species of Coleoptera, and two families and 13 species of Diptera. Most floral visitors were captured in the mechanical shrub control plus prescribed burn treatments, while lower numbers were caught on the mechanical shrub control only, prescribed burn only and control treatments. Overall species richness was also higher on mechanical plus burn treatments. Total pollinator abundance and the abundance of most orders and families was correlated with decreased tree basal area and increased percent herbaceous plant cover. Our study shows that floral visitors increased in abundance and species richness most from forest disturbance that reduced the density of overstory trees and increased the amount of herbaceous plant growth.  相似文献   

5.
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   

6.
Loss of base cations from soils of the northeastern US may adversely influence forest health. A watershed-level calcium (as wollastonite, CaSiO3) addition experiment was initiated at the Hubbard Brook Experimental Forest, NH, USA, in fall 1999 to examine responses of forest ecosystem structure and function to restoration of exchangeable Ca that was lost over previous decades. We quantified the response of soil microarthropods to Ca addition as part of this larger study, and we also quantified microarthropod response to smaller scale (1×2 m plots) wollastonite additions within one site in an untreated reference watershed. We observed a small increase in pH in the surface organic horizon, accompanied by a decline in microarthropod abundance per gram organic matter three years following wollastonite application. However, responses varied among microarthropod groups, across years, and among study plots that were distributed along an elevation gradient in treatment and reference watersheds. Collembola declined in the treatment relative to the reference watershed in the second year but recovered in the third year following wollastonite application, whereas oribatid, prostigmatid, and mesostigmatid mites all declined in the treatment relative to the reference watershed by the third year following treatment. The largest treatment responses were observed in two base-poor hardwood stands, whereas at a slightly less poor hardwood site we found the least abundant and least variable microarthropod populations, and no response was observed to either the watershed or the plot-level treatments. Our results demonstrate that soil microarthropods are sensitive to relatively small changes in soil Ca, but that landscape position must be considered in testing responses of these soil biota to soil base status.  相似文献   

7.
We aimed to identify patterns of diversity in a below-ground community of microarthropods (mites and Collembola) after 15 months of a nutrient (calcium and nitrogen) manipulation experiment, located at the Natural Environment Research Council (NERC) Soil Biodiversity Site in Scotland, UK. We found that microarthropod densities increased with elevated soil fertility, but we detected no concurrent change in the diversity of soil microarthropods (mites and Collembola combined). That microarthropod density increased concurrently with improvements in soil fertility and plant productivity suggests that soil microarthropod communities are predominately regulated by bottom-up forces, driven by increased energy transfer via plant inputs to soil, providing increased food resources for fauna. However, that we found no concurrent change in the diversity of soil microarthropods provides little support for the idea that the diversity of soil fauna is positively related to their population density, primary productivity or improvements in soil conditions resulting from nutrient manipulations. However, we did find that microarthropod communities of more fertile sites contained a greater proportion of predators suggesting that more energy was transferred to higher trophic levels under elevated soil fertility. Our findings suggest that unlike plant communities, soil faunal diversity may not be strongly regulated by competition in productive situations, since competitive exclusion might not occur due to increased predation. Whilst we conclude that soil microarthropod diversity at our study site has not been affected by the nutrient additions to date, in the longer term we predict that changes in community composition and diversity could arise, most likely through top-down regulation of the soil food web.  相似文献   

8.
A long-term prescribed burning experiment, incorporating replicated plots that receive burning biennially (2 yr burn) or quadrennially (4 yr burn) and unburned controls, has been maintained in a wet sclerophyll forest at Peachester, Queensland, Australia since 1972. In 2003 we extracted DNA from soil collected from the experimental plots and investigated the influence of the burning on the soil fungal community by comparing denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified partial rDNA internal transcribed spacer regions (ITS1). Canonical analysis of principal coordinates (CAP) of the DGGE profiles of the upper 10 cm of the soil profile grouped the data strongly according to treatment, indicating that both burning regimes significantly altered fungal community structure compared to the unburned controls. In contrast, no obvious trend was observed for soil from a depth of 10-20 cm of the profile. Sequencing of selected DGGE bands found no obvious patterns of presence/absence of taxonomic groups between the treatments. Analysis of soil nitrogen and carbon by mass spectrometry indicated that total soil C and N, along with both gross and net N mineralisation, were significantly lower in 2 yr plots compared to control and 4 yr plots.  相似文献   

9.
Our study compared decomposition and litter microarthropod abundance among five plant communities in a mountain floodplain/fen complex located in the southern Appalachian Mountains, USA. We found that the least disturbed plant communities, red maple in particular, have the quickest decomposition, the greatest number of litter microarthropods, the highest soil organic carbon, and the lowest soil pH. Positive correlations were shown between soil organic carbon and total microarthropods; negative correlations were found between soil pH and total microarthropods. No correlations were found between soil moisture and decomposition or total microarthropod numbers. We conclude that soil characteristics related to disturbance, rather than to the presence of a closed canopy, are the main influences on decomposition and litter microarthropods.  相似文献   

10.
The effects of a range of fertilizer applications and of repeated low-intensity prescribed fires on microbial biomass C and N, and in situ N mineralization were studied in an acid soil under subalpine Eucalyptus pauciflora forest near Canberra, Australia. Fertilizer treatments (N, P, N+P, line + P, sucrose + P), and P in particular, tended to lower biomass N. The fertilizer effects were greatest in spring and smaller in summer and late actumn. Low-intensity prescribed fire lowered biomass N at a soil depth of 0–5 cm with the effect being greater in the most frequently burnt soils. No interactions between fire treatments, season, and depth were significant. Only the lime + P and N+P treatments significantly affected soil microbial biomass C contents. The N+P treatment increased biomass C only at 0–2.5 cm in depth, but the soil depth of entire 0–10 cm had much higher (>doubled) biomass C values in the line + P treatment. Frequent (two or three times a year) burning reduced microbial boomass C, but the reverse was true in soils under forest burn at intervals of 7 years. Soil N mineralization was increased by the addition of N and P (alone or in combination), line + P, and sucrose + P to the soil. The same was true for the ratio of N mineralization to biomass N. Soil N mineralization was retarded by repeated fire treatments, especially the more frequent fire treatment where rates were only about half those measured in unburnt soils. There was no relationship between microbial biomass N (kg N ha-1) and the field rates of soil N mineralization (kg N ha-1 month-1). The results suggest that although soil microbial biomass N represents a distinct pool of N, it is not a useful measure of N turnover.  相似文献   

11.
北京西山地区林火对土壤性质的影响   总被引:10,自引:0,他引:10  
 为进行火烧迹地的管理,采用调查取样和室内分析方法,对北京西山地区不同林火强度下油松林土壤物理和化学性质的变化进行了研究。结果表明:与未火烧相比,中度火烧会显著提高土壤密度,显著降低土壤总孔隙度、土壤黏粒含量和田间持水量,而毛管孔隙和非毛管孔隙的变化却不明显;轻度火烧对土壤物理性质的影响不显著。轻度火烧会显著地提高0~5cm范围的土壤有机质含量,而中度火烧会显著降低土壤有机质和全氮含量。轻度火烧使土壤pH值增加,其中0~2cm的差异达到显著水平;另外,0~5 cm土层Ca2+和Mg2+的含量比中度火烧和未火烧土壤有明显的提高。因此,轻度火烧有利于改善土壤的性质。  相似文献   

12.
Dry weight accumulation in blades for the trifoliolate leaf as well as the concentration per gram of dry weight and accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined during the vegetative and reproductive phases at different leaf positions of soybean [Glycine max (L) Merrill, var. Halle] grown in the field without fertilization. The leaf blades at each position were sampled three times at seven day intervals. Mature (middle) leaves showed a higher rate of dry weight accumulation particularly during the vegetative stage in comparison to the older (lower) and younger (upper) leaves. These differences increased with the progress of plant growth. The minimization to zero of the rate of dry weight accumulation in blades after the development of pods is differentiated in leaves of different age. The N, P, and K concentration in leaf blades increase and those of Ca and Mg decrease from older (lower) to mature (middle) and younger (upper) leaves. Rates of N and P accumulation at the vegetative stage are greater than the rate of dry weight accumulation. During the reproductive stage, P mobilization and transport to reproductive sinks was observed. Older and mature leaves sustain significant levels of N and P up to the end of the plant life cycle. In the upper leaves, the decline of N and P concentration during the same period is ascribed to dilution and change of the carbon/nitrogen (C/N) ratio due to the late increase of dry weight. Potassium in blades of mature and upper leaves seems to be mobilized to reproductive sinks. This did not seem likely for the lower leaves. High Ca concentration in the blades was attributed to the high level of available Ca in the soil, combined with the prevalence of dry growth conditions during the summer. The rate of Ca accumulation is smaller than the rate of dry weight accumulation during the vegetative stage and greater during the reproductive one. The Mg fluctuations indicate a small influence of reproductive sinks on Mg concentration in the blades. The older leaves have the greatest Ca and Mg concentrations compared to the mature and upper leaves. In lower leaves, indications of faster Mg redistribution are found. Iron, Cu, and Zn concentrations in the blades are higher before flowering, then afterwards in a contrary manner than that for Mn. A decline of Fe, Cu, Zn, and Mn concentration in blades from the lower to the mature and upper leaves was determined. Iron shows the greatest change with the highest concentration being during the early vegetative stage and a rapid decline shortly afterwards. Older leaves were found to be significant Fe reserves during the vegetative stage, while after pod development, they present an impressive accumulation of Zn and Mn.  相似文献   

13.
庐山旅游区森林防火技术体系研究   总被引:6,自引:0,他引:6  
通过庐山以黄山松为主的11个主要树种的野外燃烧试验与含水率、脂肪、灰分、热值测定,筛选出易燃、可燃、难燃树种,木荷、茶叶为难燃树种,应用于防火林带建设可起到阻隔周边荒水蔓延的作用。绘制了林火发生图,区划出轻、低、中、高4个火险等级,并配置了防火力量和防火设备图。确定了对林火有影响的气象、地形、植被类型指标,提出群众性防火、建立森林防火“信息高速公路”、生物防火、化学防火、建立防火池、人工降雨等措施。应用该研究可把火灾降到最低程度,既保护庐山的优美环境,又可产生显著的经济效益。1999-2000年应用该防火技术体系使庐山旅游区新增产值18万元,节省开支4.5万元,新培利税2.6万元。  相似文献   

14.
基于空间Logistic的黑龙江省林火风险模型与火险区划   总被引:5,自引:0,他引:5  
林火风险分析和森林火险区划是林火管理的重要组成部分。该文利用黑龙江省2000-2010年MODIS火烧迹地遥感数据集MCD45A1,在RS和GIS技术支持下构建林火空间分布与林火影响因子间的空间Logistic林火风险模型,在较大时间尺度和省域空间尺度上进行了森林火险区划研究,结果表明:通过空间采样构建的Logistic林火风险模型拟合效果很好,在显著性水平为0.05的情况下,通过模型系数的混合检验和Wald检验;相对运行特征(relative operating characteristic,ROC)值为0.753;经图层运算得到森林火险概率分布图,并将黑龙江省分为无火险区、低火险区、中火险区、高火险区和极高火险区。大兴安岭山地集中了极高火险区和高火险区;小兴安岭基本上属于高火险区和中火险区;东部山地小部分地区属于中火险区;其它地区属于低火险区和无火险区。黑龙江省森林火险的定量定位评价可为林火的预防、扑救以及防火指挥员进行防火规划和部署扑火力量、指导森林防火工作提供科学依据。  相似文献   

15.
Afforestation often causes direct habitat losses for farmland birds of conservation concern, but it is uncertain whether negative effects also extend significantly into adjacent open land. Information is thus required on how these species react to wooded edges, and how their responses are affected by edge and landscape characteristics. These issues were examined in Mediterranean arable farmland, using bird counts at 0, 100, 200, 300 and >300 m from oak, pine and eucalyptus edges, embedded in landscapes with variable amounts and spatial configurations of forest plantations. Bird diversity declined away from edges, including that of woodland, farmland and ground-nesting birds. Positive edge responses were also found for overall and woodland bird abundances, and for five of the nine most widespread and abundant species (Galerida larks, stonechat, linnet, goldfinch and corn bunting). Strong negative edge effects were only recorded for steppe birds, with reduced abundances near edges of calandra larks and short-toed larks, but not of little bustards and tawny pipits. Edge contrast affected the magnitude of edge effects, with a tendency for stronger responses to old and tall eucalyptus plantations (hard edges) than to young and short oak plantations (soft edges). There were also species-specific interactions between edge and fragmentation effects, with positive edge responses tending to be strongest in less fragmented landscapes, whereas steppe birds tended to increase faster away from edges and to reach the highest species richness and abundances in large arable patches. Results suggest that forest plantations may increase overall bird diversity and abundance in adjacent farmland, at the expenses of steppe birds of conservation concern. Clustering forest plantations in a few large patches and thus reducing the density of wooded edges at the landscape-scale might reduce such negative impacts.  相似文献   

16.
Soil microarthropod responses to long-term soil warming and increased fertilisation by addition of NKP or litter were assessed in three subarctic ecosystems. The experiment was carried out at three different field sites, where temperature and fertilisation manipulations had been running for 3–5 years (glade), 11 years (fellfield), and 12 years (heath) at the time of sampling. In the glade soil, warming led to decreases in Collembola and Gamasida, and increases in Oribatida, although effects were inconsistent between years. Actinedida densities were increased by fertilization, while Acaridida had higher densities in the treatment with both fertilisation and warming. In the fellfield, we found increased densities of Oribatida, Gamasida and Actinedida in the fertilised treatments, and some increases in Oribatida and decreases in Collembola and Gamasida in warming treatments. In the heath, there were increased densities of Collembola, Oribatida and Actinedida in the fertilised treatments, but we found no strong effects of warming. We suggest that the responses found in this study comply with the assumption that soil microarthropods are bottom-up controlled, and the observed changes are probably linked to changes in food availability more than direct climatic influences.  相似文献   

17.
Using the abundance and distribution of small mammals at 26 sites in an Atlantic forest landscape, we investigated how species abundance and alpha and beta diversity are affected by fragment size and the presence of corridors. To account for the variability in forest structure among fragments, we described and minimized the influence of foliage density and stratification on small mammal data. Sites were distributed among three categories of fragment size and in continuous forest. For small and medium-sized categories, we considered isolated fragments and fragments connected by corridors to larger remnants. Small mammal abundance and alpha and beta diversity were regressed against site scores from the first axis of a Principal Component Analysis on forest structure variables. Residuals were used in analyses of variance to compare fragment size and connectivity categories. Forest structure influenced total abundance and abundance of some species individually, but not the diversity of small mammal communities. Total abundance and alpha diversity were lower in small and medium-sized fragments than in large fragments and continuous forest, and in isolated compared to connected fragments. Three species were less common, but none was more abundant in smaller fragments. At least one species was more abundant in connected compared to isolated fragments. Beta diversity showed an opposite relationship to fragment size and corridors, increasing in small and isolated fragments. Results highlight the importance of secondary forest for the conservation of tropical fauna, the hyper-dynamism of small isolated fragments and the potential of corridors to buffer habitat fragmentation effects in tropical landscapes.  相似文献   

18.
Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations.  相似文献   

19.
Remaining patches of semi-natural grasslands are hot spots for biodiversity in modern agricultural landscapes. In Sweden semi-natural pastures cover approximately 500,000 ha. However, power-line corridors, road verges and clear-cuts cover larger areas (in total about 2,000,000 ha), and these open, less intensively managed habitats are potentially important for species associated with taller vegetation and flower resources (e.g. pollinating insects). The aim of the present study was to evaluate the relative importance of semi-natural pastures and the other three open habitats for butterflies in 12 forest-farmland mosaic landscapes in south central Sweden. Species composition differed significantly between habitats in multivariate analyses. Power-line corridors and semi-natural pastures harbored several species that were disproportionally abundant in these habitats (13 and 8 species, respectively), and power-line corridors also harbored several species that were classified as typical in indicator species analyses. There were more butterfly species, higher abundances and a tendency for more individuals of red-listed species in power-line corridors than in the other three habitats. Effects of the surrounding landscape composition seemed to be weaker than that of the local habitat. However, species composition was significantly associated with landscape composition and species with intermediate and low mobility were more abundant in forested landscapes than in landscapes dominated by arable fields. Analyses of flying time and host plants for larvae suggest that early flying species and species associated with dwarf shrubs were more common in power-line corridors than in the other habitats. A landscape perspective, which takes several habitats into account, is needed for conservation of butterfly communities in forest-farmland landscapes. Power-line corridors and road verges offer possibilities for creating habitats that are suitable for pollinating insects through conservation-oriented management.  相似文献   

20.
Summary The microarthropod community response to season, change in foliage litter quality during decomposition, and manipulated canopy herbivory by insects was measured in litterbags under 10-year-old Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, in western Oregon. Collembola accounted for 35% of the total fauna, oribatid mites for 29%, and fungivorous actinedids for 22%.The community structure was affected by responses to canopy defoliation, season, and changes in litter quality. Of 33 taxa, three were significantly more abundant under trees subject to lepidopteran defoliation (20% foliage removal), compared to other treatments, indicating responses to defoliator-induced changes in litter environment. Most taxa (23) showed seasonal fluctuations in abundance related to the seasonal pattern of temperature and precipitation and to the pattern of N and Ca mobilization from litterbags. Five taxa showed significant longterm trends in abundance, indicating responses to changes in litter quality, perhaps a loss of P and K.These data indicate that microarthropod communities respond qualitatively to environmental changes, including canopy defoliation. The qualitative changes can affeet decomposition processes.  相似文献   

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