Grass Patches Research Articles

Turbulence structure and flow field of shallow water with a submerged eel grass patch

A flume experiment was conducted to investigate the effect of the aquatic herbaceous plant patch on the turbulent structure and flow field of shallow water. The eel grass that is widely distributed in the shallow lakes in China was chosen as the targeted plant. The plants were settled in patch form with three groups of densities and flow velocities. The three-dimensional instantaneous velocities were measured using an Audio Doppler Velocitimeter (ADV). The results indicate that the vertical velocity profile in the plant patch exhibits an S-shape from the canopy to the root of the eel grass. A secondary maximum in the vertical profile of velocity near the plant root is observed. The turbulent intensity increases from the water surface to the canopy, then decreases to the plant root; there is an inflection point around canopy, where the turbulent intensity deceases from the inner region to the side boundary of the patch. The vertical profiles of the eel grass resistance coefficient CP have different forms at different positions in the patch in general, but the forms of the CP profiles are similar along the boundary of the patch, and the forms of the CP profiles are similar in the inner part of the patch. In the patch area, the turbulent flow corresponds to the Quadrant 2 event (ejection event) above the canopy, the turbulent flow corresponds to the Quadrant 4 event (sweep event) below the canopy, but near the bed the Quadrant 1 event (outward interaction), the Quadrant 2 event and the Quadrant 4 event coexist. In the lateral boundary area of the patch the Quadrant 2 event and the Quadrant 3 event (inward interaction event) coexist due to presence of a strong shear layer.

Forage patch use by grazing herbivores in a South African grazing ecosystem

Understanding how different herbivores make forage patch use choices explains how they maintain an adequate nutritional status, which is important for effective conservation management of grazing ecosystems. Using telemetry data, we investigated nonruminant zebra (Equus burchelli) and ruminant red hartebeest (Alcelaphus buselaphus subspecies camaa), use of burnt patches in a landscape mosaic of nutrient-poor, old grassland interspersed with young, recently burnt, nutrient-rich grass patches. The Mkambati Nature Reserve landscape on the east coast of South Africa provided large grazers with a challenge in finding and using appropriate patches in which to forage to meet their nutritional requirements. In Mkambati, grassland fires, mostly ignited by poachers, induce regrowth of young nutrient-rich grass, which subsequently attract grazers. We tested if the study animals foraged more in burnt patches than in the unburned grassland and whether burnt patch use was related to the distance to the previously visited burnt patch, burnt patch size, burnt patch age, and distance to areas with high poaching risk using MANOVA. In general, zebra moved faster than red hartebeest, and both species moved faster in unburnt grassland than in burnt patches. Red hartebeest and zebra patch selection were influenced by interpatch distance, patch age, patch size, and poaching risk. A limited set of intrinsic traits, i.e., body mass, digestion strategy, and muzzle width, yielded different patch use rules for the two species. Large ungulates patch use behaviour varied among species and across conditions and was influenced by anthropogenic impacts such as poaching and changed fire regimes. This could potentially affect biodiversity negatively and needs to be factored into management of conservation areas.

Nematode consumption by mite communities varies in different forest microhabitats as indicated by molecular gut content analysis

Soil animals live in complex and heterogeneous habitats including litter of various types but also microhabitats such as mosses, fungal mats and grass patches. Soil food webs have been separated into a slow fungal and a fast bacterial energy channel. Bacterial-feeding nematodes are an important component of the bacterial energy channel by consuming bacteria and forming prey for higher trophic levels such as soil microarthropods. Investigating the role of nematodes as prey for higher trophic level consumers has been hampered by methodological problems related to their small body size and lack in skeletal structures which can be traced in the gut of consumers. Recent studies using molecular gut content analyses suggest that nematodes form major prey of soil microarthropods including those previously assumed to live as detritivores. Using molecular markers we traced nematode prey in fourteen abundant soil microarthropod taxa of Mesostigmata and Oribatida (both Acari) from three different microhabitats (litter, grass and moss). Consumption of nematodes varied between mite species indicating that trophic niche variation contributes to the high diversity of microarthropods in deciduous forests. Further, consumption of nematodes by Mesostigmata (but not Oribatida) differed between microhabitats indicating that trophic niches vary with habitat characteristics. Overall, the results suggest that free-living bacterial-feeding nematodes form important prey for soil microarthropods including those previously assumed to live as detritivores.

Effects of soil density on grass-induced suction distributions in compacted soil subjected to rainfall

Grass is recognized as being beneficial in reducing rainfall infiltration in some kinds of surface cover systems such as landfill cover, because rainwater discharges as surface runoff due to reduced water permeability caused by evapotranspiration-induced soil suction as well as foliage interception. However, the distributions of grass-induced suction in various compacted soils during rainfall are rarely reported. Moreover, it is not straightforward to determine an optimum soil dry density for minimizing rainfall infiltration and at the same time encouraging plant growth. This is because there are conflicting requirements for vegetated cover systems, i.e., compacted soil should not be too dense as to impede root growth, while on the other hand to minimize infiltration. This study thus aims to investigate, quantify, and compare grass-induced suction distributions in silty sand compacted at different densities when subjected to artificial rainfall in the laboratory. A grass species, Cynodon dactylon, which is common in many parts of Asia, was selected for testing. Compacted soil with and without a growing grass patch was tested at three relative compactions (RCs) of 70%, 80%, and 95%, in six test boxes. Test results reveal that at an RC of 95%, suction (40 kPa) retained in vegetated soil after rainfall is 100% higher than that (20 kPa) in bare soil. Among the vegetated soil compacted at the three RCs, suction retained was the highest at an RC of 95% (40 kPa), whereas suction decreased to 0 kPa at an RC of 70% after rainfall. As the average depth of grass roots decreased by 36% due to an increase in RC from 70% to 95%, the depth of influence of suction for vegetated soil at an RC of 95% reduced to less than half of root depth, which was the shallowest among the three compacted soil specimens.

Diversity, Abundance and Habitat Utilisation of Birds in Periphery of the Mihintale Sanctuary

Mihintale sanctuary is one of the important forest reserve located in Sri Lanka with scarceinformation on avifauna. Although this area has been subjected to anthropogenic activities,periphery areas provide more suitable habitats for different species of birds includingmigrants. Current study is carried from July 2010 to end of February 2012 in the Faculty ofApplied Science premises (disturbed) and remnant grass patch habitats locates adjacent to theMihintale forest to investigate the abundance species diversity, and habitat utilisation of birdspecies in two different habitats. Belt transect method (500 x 50 m), point counts and theopportunistic observation method were used for data collection. Vegetation analysis weredone by using quadrates sampling method and habitat utilisation data were gather by scansampling method. Shannon-Wiener Diversity Index and Margalef’s Diversity Indices werecalculated in order to determine the species diversity and richness.A total of 68 and 99 species belonging to 34 and 42 families were recorded from bothdisturbed and remnant grass patch nearby Mihintale Sanctuary. Among them 64 (94.2%)breeding residents and 4 (5.8%) winter visitors recorded in disturbed habitat while 87(87.8%) breeding residents and 12 (12.2%) winter visitors recorded in grass patch. In bothhabitats 7 endemic species were recorded. Out of the total species 45 species from grass patchand 69 species from disturbed area were common.Shannon Diversity Index (H') for disturbed and grass patch habitat were 2.48 and 2.76respectively. The results indicated that the diversity avifauna significantly (p=0.0237) higherin the grass patch. Mainly the observed bird species in the study area can be categorized intoseven trophic guilds. The majority was insectivores in both habitats (54% and 41.96%). 22and 19 species of plant were predominantly utilised by the birds inhabited the grass patch andin disturbed area respectively. During the breeding period majority of birds utilised all theplant species in grass patch for nesting while disturbed habitat used for collecting nestingmaterials. Ficus species were recorded as common feeding tree in both habitats. As birds areuseful indicator species of the health of an ecosystem they can be used as focal species togather data on status of habitat and disturbances. This will lead to conservation of birds andtheir habitats.

Temporal asynchrony in fine‐root biomass may contribute to shrub and grass coexistence in mixed patches

AbstractWe described seasonal changes in fine‐root biomass of a grass and a shrub dominant species in a plant community characteristic of the arid Patagonian Monte and then we inferred to want extent the observed differences could contribute to the species coexistence. We selected representative plant patches of the natural vegetation arrangement consisting of one isolated plant of the dominant shrub Larrea divaricata (Ld), grass patches formed by one or more bunches of the dominant grass Nassella tenuis (Nt), and mixed patches consisting of one individual of L. divaricata with bunches of N. tenuis under its canopy (LdNt). We assessed the biomass and temporal changes in fine roots of each species in the upper soil (50 cm depth) of each patch type at three‐month intervals during 2 years. The temporal series of fine‐root biomass were compared among patch types and in relation to above‐ground phenology, as well as climate variables (precipitation, arid index and air temperature). Seasonal changes in fine‐root biomass showed similar cycles in the three plant patches with a maximum in spring. The maximum increase in root biomass in Ld and Nt patches occurred during the onset of reproductive growth in winter and spring, respectively. Fine‐root changes in LdNt patches mimicked that in Ld patches. Precipitation inputs were significantly positively and temperature negatively related to fine‐root changes in Nt patches. Fine‐root changes in Ld and LdNt patches were related to the aridity index (positively) and temperature (negatively). We concluded that the observed asynchronies in the date of the largest increases in root biomass and its climate control between the studied grass and shrub species could contribute to the coexistence of plants of both life forms when they overlap their root systems growing in mixed patches. Mechanisms underlying the root patterns observed should be further explored.

内蒙古典型草原小叶锦鸡儿灌丛化对水分再分配和利用的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 内蒙古典型草原小叶锦鸡儿灌丛化对水分再分配和利用的影响 DOI: 10.5846/stxb201306051359 作者: 作者单位: 云南财经大学,北京师范大学,云南财经大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家杰出青年科学基金（41025001）；云南财经大学科研基金引进人才科研启动费项目（YC2013D15）；中央高校基本科研业务费和长江学者和创新团队计划（IRT1108）；中央高校基本科研业务费专项资助（2012CXQT07） Effects of shrub (Caragana microphalla Lam.) encroachment on water redistribution and utilization in the typical steppe of Inner Mongolia Author: Affiliation: Yunnan University of Finance and Economics,Beijing Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:灌丛化是全球草原地区存在的主要环境问题。通过对内蒙古典型草原区小叶锦鸡儿灌丛和草地斑块冠层降雨再分配、地表径流、土壤含水量的对比观测，研究了小叶锦鸡儿灌丛化对该区水分再分配和利用的影响。结果表明，灌丛和草地斑块的冠层截留量分别占降雨量的20.86%和7.88%，灌丛和草地斑块的平均地表径流系数分别为5.95%和17.19%。土壤含水量观测结果显示，0-60 cm土层中，降雨事件过程中，灌丛斑块较草地斑块能捕获更多水分，灌丛斑块植被冠层下方土壤含水量高于草地斑块；而在雨后无有效降水补充土壤水分的前提下，0-60 cm土层中，灌丛斑块土壤水分蒸散发量高于草地斑块，其中0-10 cm 土层中灌丛斑块土壤水分蒸散发速率低于草地斑块，10-60 cm 土层中灌丛斑块土壤水分蒸散发速率高于草地斑块。研究认为，在水分为关键性限制因子的干旱半干旱区，小叶锦鸡儿灌丛化过程增加草原生态系统中水分分布的空间异质性，灌丛斑块能捕获、利用更多水分以维持更多的生物量。 Abstract:Shrub encroachment is the main environment problem at the steppe region on the earth. This study observed rainfall redistribution composition of plant canopy, surface runoff, and soil moisture content at the shrub and interspace grass patches respectively, analyzed effects of shrub encroachment on water redistribution and utilization in the typical steppe which encroached by Caragana microphalla Lam. (C. microphalla) in Inner Mongolia. Results showed that the average canopy interception was 20.86% and 7.88% for shrub and interspace grass patches respectively, and the average surface runoff coefficient was 5.95% and 17.19% at shrub and interspace grass patches respectively. Shrub patches had greater water capability than intersapce grass patches in the same rainfall event, so soil moisture content under the canopy of shrub patches was much greater than intersapce grass patches after rainfall events in the 0-60 cm soil layers; soil evapotranspiration below the canopy of shrub patches was much greater than grass patches in the 0-60 cm soil layers, the evapotranspiration rate below the canopy of shrub patches was much lower than interspace grass patches in the 0-10 cm soil layers, but it was much greater than intersapce grass patches in the 10-60 cm soil layers. This study suggested that that shrub encroachment increased spatial heterogeneity of water distribution in grassland ecosystem at the arid and semiarid region where water was one of the key restriction factor, shrub patches could capture and utilize more water to produce more biomass than interspace grass patches. 参考文献 相似文献 引证文献

Investigation of off-site airborne transport of lead from a superfund removal action site using lead isotope ratios and concentrations

Lead (Pb) concentration and Pb isotopic composition of surface and subsurface soil samples were used to investigate the potential for off-site air transport of Pb from a former white Pb processing facility to neighboring residential homes in a six block area on Staten Island, NY. Surface and subsurface soil samples collected on the Jewett White Pb site were found to range from 1.122 to 1.138 for 206Pb/207Pb and 2.393 to 2.411 for 208Pb/207Pb. The off-site surface soil samples collected from residential backyards, train trestle, near site grass patches and background areas varied from 1.144 to 1.196 for 206Pb/207Pb and 2.427 to 2.464 for 208Pb/207Pb. Two soil samples collected along Richmond Terrace, where Jewett site soils accumulated after major rain events, varied from 1.136 to 1.147 for 206Pb/207Pb and 2.407 to 2.419 for 208Pb/207Pb. Lead concentration for on-site surface soil samples ranged from 450 to 8000ug/g, on-site subsurface soil samples ranged from 90,000 to 240,000ug/g and off-site samples varied from 380 to 3500ug/g. Lead concentration and isotopic composition for the Staten Island off-site samples were similar to previously published data for other northeastern US cities and reflect re-suspension and re-mobilization of local accumulated Pb. The considerable differences in both the Pb isotopic composition and Pb concentration of on-site and off-site samples resulted in the ability to geochemically trace the transport of particulate Pb. Data in this study indicate minimal off-site surface transport of Pb from the Jewett site into the neighboring residential area.

Woody Cover and Grass Production in a Mesquite Savanna: Geospatial Relationships and Precipitation

Woody plant effects on grass production at specific points in some rangeland savannas may be a function of numerous surrounding woody plants with lateral roots that extend into those patches of grass. This study determined the effects of increasing zones of honey mesquite (Prosopis glandulosa Torr.) influence on the production of three perennial grass types (C4 shortgrasses, C3 midgrasses, and C4 midgrasses) at specific points in gaps between mesquite trees in each of five years. Mesquite canopy cover was determined by geospatial analysis of aerial images for progressively increasing zones (0–5, 0–10, 0–15, and 0–20m radius) surrounding each grass production point. The woody cover/grass production relationships were mostly linear for C4 shortgrasses and C3 midgrasses, and mostly a declining exponential curve for C4 midgrasses in all canopy zones, indicating that C4 midgrasses were most sensitive to increasing mesquite cover, especially at covers >30%. The relationship between mesquite cover and C4 shortgrass production was strongest (i.e., highest r2) when the smallest woody cover zones (0–5 and 0–10 m) were included. In contrast, the relationship between cover and C4 midgrass production was strongest when the largest zones (0–15 and 0–20 m) were included. These differences were attributed to an inability of C4 midgrasses to persist in smaller intercanopy gaps resulting from increases in mesquite density and infilling. Annual precipitation and C3 annual grass invasions played a large role in determining the woody cover/grass production relationship for each grass type. This study illustrates the complexity involved in quantifying woody cover/grass production relationships in savanna ecosystems. Maintaining productive stands of C4 midgrasses may be facilitated by maintaining woody cover below 30% threshold levels and possibly by limiting grazing during episodic high rainfall events in midsummer when this grass type becomes somewhat decoupled from woody cover effects.

Shrub Hydropedology: Preferential Water Availability to Deep Soil Layer

The complex interactions between shrub traits, soil structure, and soil water dynamics are not well understood yet. This study investigated rainfall partition byC. microphyllaL., spatial soil water pattern, soil hydraulic conductivity, and soil macropores to ascertain preferential water flow to deep soil layer by shrub. Results indicated that high variability in throughfall existed within individual shrub stand: average coefficient of variation was 0.36 ± 0.13 for shrub and 0.15 ± 0.13 for interspace grass. Throughfall was less at the center of the shrub patch (30–60% of rainfall) than the outward positions at the edges of the canopy (70–90% of rainfall). Soil water responded differently to rainfall, soil depth, and vegetation type and showed high variability within shrub patches and on the slope. Greater and deeper infiltration was observed beneathC. microphyllaL. canopy than interspaces grass after rainfall with large amount and high intensity, suggesting that macropore flow dominated in shrub patches. X‐ray CT showed that macroporosity was over six times greater in soil underC. microphyllaL. than interspace grass. Soil hydraulic conductivity for shrub at saturation and the pressure heads of −30, −60, and −150 mm were 3, 2, 2.5, and 2 times than those of grass, respectively. Shrub patches had a significant lower bulk density and higher porosity than grass patches at the top 0‐ to 30‐cm depth. Soil hydraulic conductivity was significantly correlated to organic matter content, total N, bulk density, and porosity. This study suggests that rainfall partition by shrub's canopy and subsurface soil macropores induced by root architecture results in preferential water flow into deep soil layer, which might favor competitive advantages for water by shrubs under arid conditions.

Effects of heterogeneous competitor distribution and ramet aggregation on the growth and size structure of a clonal plant.

Spatially heterogeneous distribution of interspecific competitors and intraspecific aggregation of offspring ramets may affect the growth and size structure of clonal plant populations, but these have been rarely studied. We conducted a greenhouse experiment in which we grew a population of eight offspring ramets (plants) of the stoloniferous clonal plant Hydrocotyle vulgaris aggregately or segregately in two homogeneous treatments with or without a competing grass Festuca elata and a heterogeneous treatment with a patchy distribution of the grass. In patchy grass treatments, H. vulgaris produced markedly more biomass, ramets and stolons in open patches (without grasses) than in grass patches, but displayed lower size variations as measured by coefficient of variation of biomass, ramets and stolons among the eight plants. In open areas, H. vulgaris produced statistically the same amounts of biomass and even more stolons and showed higher size variations in patchy grass treatments than in open (no grass) treatments. In grass areas, H. vulgaris grew much worse and displayed higher size variations in patchy grass treatments than in full grass treatments. Ramet aggregation decreased the growth of H. vulgaris in open treatments and in both open and grass patches in patchy grass treatments, but had little effect in full grass treatments. Ramet aggregation had little effect on size variations. Therefore, heterogeneous distribution of competitors can affect the growth and size structure of clonal plant populations, and ramet aggregation may decrease population growth when they grow in open environments or heterogeneous environments with a patchy distribution of interspecific competitors.

Antecedent Conditions Influence Soil Respiration Differences in Shrub and Grass Patches

Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of this study was to characterize the effect of antecedent moisture and temperature conditions on soil respiration in a grassland now dominated by shrubs. Continuous measurements of soil respiration, soil temperature, and soil moisture were made over the entire summer of 2005 within distinct vegetation microsites in this shrubland community—under grasses, shrubs, and in open spaces. We analyzed these data within a Bayesian framework that allowed us to evaluate the time-scale over which antecedent conditions influence soil respiration. The addition of antecedent conditions explained an additional 16% of the variation in soil respiration. High soil moisture during the preceding month increased respiration rates in both the grass and shrub microsites. However, the time period over which antecedent soil moisture influenced the temperature sensitivity of soil respiration was shorter in the shrub compared to the grass microsites (1 vs. 2 weeks, respectively). The depth of moisture was important; for example, for respiration under shrubs, near-surface moisture was more influential on the day of the respiration measurement but subsurface moisture was more influential on the antecedent time scale. Although more mechanistic studies are required, this study is the first to reveal that shrub encroachment changes the time scales over which soil moisture and temperature affect soil respiration.

Shrub encroachment with increasing anthropogenic disturbance in the semiarid Inner Mongolian grasslands of China

Abstract Many arid grasslands around the world are affected by shrub encroachment. However, the transition states of shrub-encroached ecosystems are still poorly known, and the effects of human disturbances are difficult to quantify during the transition process. This study investigated plant biomass, community characteristics, and water capturing capability of the shrub and interspace grass patches during the different transition states of Caragana microphylla Lam-encroached grassland in response to the intensity of anthropogenic disturbances. The results indicate that the number of plant species increased with the disturbance intensity at the shrub patches and that the total aboveground biomass (AB) significantly decreased from the slightly disturbed site to the moderately disturbed site, then significantly increased from the moderately disturbed site to the seriously disturbed site. The total belowground biomass (BB) was much greater in the shrub patches than the interspace grass patches at the above three sites. The results also suggest that grass or shrub dominance were alternative stable states in the processes of shrub encroachment but that a threshold existed during state transition. Dye tracing experiments showed that shrubs had higher water capturing capability than grass. The shrubs could capture and transport water to the deeper soil layers in the shrub patches. We speculate that the competitive advantage for biomass and water by shrubs could be reversed for grass if the disturbance intensity does not exceed a threshold value. A continual increase of anthropogenic disturbance would further lower the water capturing capability of grasses, leading to an increase of biomass and the size of shrub patches and a shift in the landscape to a shrub-dominated state, which would be irreversible.

Small-scale patch structure in North American and South African grasslands responds differently to fire and grazing

Fire and grazing significantly impact small-scale patch structure and dynamics in savanna grasslands. We assessed small-scale grass-forb associations in long-term fire and grazing experiments in North America (NA) and Southern Africa (SA). Transects of 128 0.25 m2 contiguous quadrats were sampled in areas with different combinations of grazing (ungrazed, single grazer, or multiple grazers) and fire frequency (unburned or annually burned). We predicted that (1) the patch structure of each of the dominant grasses in NA and SA would respond similarly to fire and grazing, and (2) that forb richness would be correlated to grass patch structure. Semi-variance analysis was used to determine patch structure of dominant grasses and forb cover. Community structure responded similarly in NA and SA to fire, grazing, and fire-grazing interactions. Species richness, diversity, and community heterogeneity were significantly higher in unburned-grazed sites. Grazing significantly increased forb cover and decreased cover of the dominant grasses, and the effects of fire on community structure depended on the grazing regime. Contrary to our prediction, we found that small-scale patch structure of the dominant grass species in NA and SA responded differently to grazing and fire. We found strong grass patch structure in unburned-ungrazed grasslands in both sites; however, grazing and fire reduced patch structure in NA but not SA, and in no instance did grass patch structure influence forb community structure. We conclude that fire and grazing have larger impacts on small-scale patch structure in NA than they do in SA even though overall community structure responded similarly on both continents.

Performance evaluation of multiple ground based sensors mounted on a commercial wild blueberry harvester to sense plant height, fruit yield and topographic features in real-time

Site-specific crop management can increase profitability and reduce environmental risks of wild blueberry crop having large spatial variation in soil/plant characteristics and topographic features which may affect fruit yield. An integrated automated system comprising of an ultrasonic sensor, a digital color camera, a slope sensor, a real-time kinematics GPS (RTK-GPS), custom software and ruggedized computer was developed. The system was incorporated onto a commercial wild blueberry harvester, to measure plant height, fruit yield, slope and elevation simultaneously while harvesting. Two wild blueberry fields were selected in central Nova Scotia, Canada to evaluate the performance of the system. Field boundaries, bare spots, weeds and grass patches were mapped with a RTK-GPS prior to start the experiment.Linear regression was used to calibrate the actual fruit yield with the percentage of blue pixels (R2=0.91–0.92; P<0.001; n=40) using a 0.91×0.70m quadrat at selected points from both fields. The output voltage of the ultrasonic sensor was significantly correlated with manually measured plant height (R2=0.94; P<0.001; n=13). Comprehensive surveys were conducted in both fields to measure plant height, fruit yield, slope and elevation rapidly in real-time at the same time of harvest. The maps for the measured parameters were developed in ArcGIS 10. Maps showed substantial variability in measured parameters across the fields, suggesting more fruit yield and lower plant height in low lying areas (mild slope) and vice versa. A negative relationship among fruit yield and plant height and the results of zonal statistics in ArcGIS 10 also supported the results identified by the maps. Overall, the results of calibration and mapping indicated that the developed system was an accurate, reliable and efficient to map plant height, fruit yield, slope and elevation in real-time. This information can be used to develop site-specific fertilization, based on easily measured field parameters, to optimize productivity while minimizing the environmental impacts.

Patch identity and the spatial heterogeneity of woody encroachment in exotic-dominated old-field grasslands

Most grassland communities in agricultural landscapes comprise a mix of exotic and native plants, where grasses and forbs are disposed in low diversity patches conforming a heterogeneous matrix of vegetation. Within these “novel” ecosystems, woody encroachment is one of the principal causes of ecosystem degradation. Here, we examined the resistance to exotic woody establishment (Gleditsia triacanthos) into four different monospecific patches characteristics of old-field grasslands in Inland Pampa: an annual forb (Conium maculatum), an annual grass (Lolium multiflorum), and two perennial grasses (Cynodon dactylon and Festuca arundinacea). We evaluated the filter to tree recruitment by rodent seed removal and survival and growth of Gleditsia seedlings transplanted into undisturbed and disturbed microsites, within each patch. Beneath intact vegetation seed removal was an important biotic filter to woody establishment whereas disturbances facilitated seed survival in patches of perennial grasses. Patch identity affected tree growth, and Cynodon reduced the final biomass compared to forbs. Disturbance enhanced tree performance independently of patch type. After 2 years, tree survival was independent of disturbance and patch identity. As patch identity may regulate granivory and growth of tree saplings, community susceptibility or resistance to woody invasion rather than representing a static community attribute could vary according to the dynamic changes in the proportion of susceptible-resistant patches. Broadly, our work reinforces the concept that mechanisms regulating vegetation heterogeneity add a component of stochasticity to biotic resistance to community plant invasion.

Soil water and temperature dynamics in shrub-encroached grasslands and climatic implications: Results from Inner Mongolia steppe ecosystem of north China

Shrub encroachment occurs in arid grasslands worldwide, however, little experimental works on shrub encroachment has been conducted in China. Moreover, interactions and feedbacks between soil moisture/temperature and woody plants remain poorly investigated in arid and semiarid regions. We continuously measured soil water content and soil temperature at 10-min intervals beneath shrub canopy and inter-space grass at different topographic positions of a hillslope in Caragana microphylla encroached grassland of Inner Mongolia in north China from June 2009 to April 2011. The findings of this study revealed that, contrary to most previous results, soil moisture was not always greater in shrub patches than that in the inter-space grass patches, but was strongly affected by precipitation size and calcic layers. Significant higher soil water content and quicker response to summer rainstorm in the shallow soil layer (0–20cm) for grass patches than the adjacent shrub patches, however, spatial distribution of the deeper soil water (40–100cm) in the profile was controlled by the position of calcic horizon functioned as a ‘dam’ to store water in wet period and release water to plant in drought period, highlighting positive feedbacks between shrub establishment and CaCO3 horizons. Diurnal soil temperature and daily soil temperature was significantly higher for shrub than grass in winter, but the trend was reversed in summer. The summer soil cooling and winter soil warming effects would favor shrub to resist drought and freeze damage ensuring continuing shrub growth and survival under arid and clod conditions. These evidences suggest that feedbacks between C. microphylla and soil moisture/temperatur were overall positive.

内蒙古典型草原灌丛化对生物量和生物多样性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 内蒙古典型草原灌丛化对生物量和生物多样性的影响 DOI: 10.5846/stxb201208101131 作者: 作者单位: 北京师范大学资源学院,地表过程与资源生态国家重点实验室;北京师范大学资源学院,云南财经大学国土资源与持续发展研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家杰出青年科学基金资助项目（41025001）；长江学者和创新团队计划资助项目（IRT1108）；中央高校基本科研业务费资助项目；云南财经大学科研基金引进人才科研启动费资助项目（YC2013D15） Effects of shrub encroachment on biomass and biodiversity in the typical steppe of Inner Mongolia Author: Affiliation: College of Resources Sciences and Technology,Beijing Normal University,State Key Laboratory of Earth Surface Processes and Resource Ecology,Institute of Land Resources;College of Resources Sciences and Technology,Beijing Normal University,Institute of Land Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过样方调查，研究了内蒙古典型草原不同退化程度草地中小叶锦鸡儿 （Caragana microphylla Lam.）灌丛斑块空间分布格局、草地生物量及生物多样性特征。结果表明，从轻度到中度、重度退化草地，草本植物生物量呈减少趋势，小叶锦鸡儿生物量呈增加趋势，总生物量呈先减少后增加趋势；灌丛斑块生物多样性呈增加趋势，草地斑块生物多样性呈先减少后增加趋势，其中轻度退化草地中灌丛斑块生物多样性低于草地斑块，中度和重度退化草地中灌丛斑块生物多样性高于草地斑块。研究认为，内蒙古典型草原灌丛化过程中，生态系统可能存在草本植物占优势或小叶锦鸡儿占优势这样两种稳定状态，这两种状态能维持较高生物量和生物多样性，而在由草本植物占优势向小叶锦鸡儿占优势转化的过渡阶段，系统不稳定，仅能维持较低生物量和生物多样性。 Abstract:This study investigated spatial pattern, plant biomass and community characteristics of the shrub and interspace grass patches in Caragana microphylla Lam.(C. microphylla) encroached grassland of Inner Mongolia. Field quadrat surveys were conducted at three sites with lightly, moderately and seriously degradation states mainly resulting from overgrazing. Results indicated that the aboveground biomass of grass patches decreased with the increasing intensity of degradation, but C. microphylla showed reversed trend. The total aboveground biomass including grasses and C. microphylla decreased from the lightly to the moderately degradation sites and then increased from the moderately to the seriously degradation sites. Biodiversity increased at shrub patches with increasing degradation intensity from the lightly to the seriously degradation sites, but decreased from the lightly to the moderately degradation sites and then reversed from the moderately to the seriously degradation sites at the interspace grass patches. We noted that biodiversity of shrub patches was much less than that of the interspace grass patches at the lightly degradation site, while it was greater than the interspace grass patches at the moderately and seriously degradation sites. The above results suggest that two stable states might exist in the process of shrub encroachment, i.e., grasses dominated and C. microphylla dominated. Ecosystem was stable with more biodiversity and biomass when grasses or C. microphylla dominated, but it was unstable with less biodiversity and biomass at the transitional stage from grasses to shrubs. 参考文献 相似文献 引证文献

Spatial and temporal dynamics of Meloidogyne minor on creeping bentgrass in golf greens

Meloidogyne minor, first reported on potatoes in the Netherlands in 2004, is an emerging nematode pest in Europe. It damages turfgrass, particularly creeping bentgrass (Agrostis stolonifera) grown on sandy soils such as those of golf greens. However, little is known of the nematode's life history and pathology. In this study, the spatial and temporal distribution of M. minor on a creeping bentgrass green in Ireland was determined over a 15 month period. Cores were taken on transects across yellowing patches of grass caused by nematode damage. Second‐stage juveniles (J2) were absent from the soil from November to February, when soil temperatures were below 10°C. Both galls and egg masses were present throughout the year but were more abundant in late summer and early autumn. More J2, galls and egg masses were present in the top 10 cm of soil than at a depth of 11–20 cm. The nematode population tended to decrease as distance from the centre of the yellow patches increased. The diameter of visual symptoms (yellow patches) was also recorded over the 15 months. The mean diameter of five sampled patches increased from 23·7 cm in June 2003 to 45·2 cm in August 2004. There were 158–193 galls per 100 cm3 soil at the margin of the visible infested area, indicating that this could be the threshold level for visible symptoms.

Fuel Conditions Associated with Native and Exotic Grasses in a Subtropical Dry Forest in Puerto Rico

AbstractExotic grasses capable of increasing frequency and intensity of anthropogenic fire have invaded subtropical and tropical dry forests worldwide. Since many dry forest trees are susceptible to fire, this can result in decline of native species and loss of forest cover. While the contribution of exotic grasses to altered fire regimes has been well documented, the role of native grasses in contributing to fuel loads in dry forest has received little attention. We assessed differences in fuel conditions among native and exotic grasses within a subtropical dry forest preserve in Puerto Rico. We quantified fine fuel loads, fuel continuity, and seasonal changes in percent dead grass among the following grass patch types: (1) native grass with no known history of recent fire, (2) exotic grass that had burned once (single burn), and (3) exotic grass that burns frequently. Sampling was conducted during one wet season (August to October 2008) and again in the following dry season (February to March 2009). Overall, fine fuel loading was highest in native grass, but this was due to woody fuels rather than grass fuels. Percent of dead grass fuels increased with the transition from wet to dry season, and this increase was more pronounced for exotic grasses. Fuel continuity was highest in frequently burned exotic grass. Differences in grass phenology and fuel continuity may contribute to differences in fire frequency among native and exotic grass patches. Fuel management focused on prescribed fire should be used in conjunction with restoration of tree canopy to reduce fuels and limit development of a grass-fire cycle.