Showing papers on "Vegetation (pathology) published in 1999"

Patch structure, dynamics and implications for the functioning of arid ecosystems

Abstract: Arid ecosystems present a two-phase mosaic structure of high- and low-cover patches. Vegetation patches differ among ecosystems in size and shape. However, recent studies indicate striking similarities in patch dynamics and in mechanisms explaining their origin and maintenance. Two major types of system, banded and spotted vegetation, which are characterized by patch shape, both originate from common mechanisms, although each is dominated by a different driver. Banded vegetation occurs when water is the dominant driver of the redistribution of materials and propagules, whereas spotted vegetation results when wind is the major redistribution driver. Model analysis indicates that patchy vegetation structure enhances primary production.

Enhancement of Interdecadal Climate Variability in the Sahel by Vegetation Interaction.

Abstract: The role of naturally varying vegetation in influencing the climate variability in the West African Sahel is explored in a coupled atmosphere-land-vegetation model. The Sahel rainfall variability is influenced by sea-surface temperature variations in the oceans. Land-surface feedback is found to increase this variability both on interannual and interdecadal time scales. Interactive vegetation enhances the interdecadal variation substantially but can reduce year-to-year variability because of a phase lag introduced by the relatively slow vegetation adjustment time. Variations in vegetation accompany the changes in rainfall, in particular the multidecadal drying trend from the 1950s to the 1980s.

A review of the scientific literature on riparian buffer width, extent and vegetation

Abstract: 2 The Office of Public Service and Outreach at the Institute of Ecology provides scientific and legal expertise to the citizens of Georgia in the development of policies and practices to protect our natural heritage. The goals of the office are to: • Develop and implement a research agenda to meet community needs; • Provide an opportunity for students, faculty and staff to work with other disciplines in integrated environmental decisionmaking and problem-solving to improve their ability to understand, communicate with, and influence other disciplines; • Build capacity for service learning in the sciences by providing students an opportunity to apply skills learned in the traditional classroom setting to pressing community concerns and problems; • Support high quality science education in K-12 schools by providing programs for students and instructional support and training for teachers; • Increase awareness of the importance of addressing environmental issues proactively within the university community and the greater community. Many local governments in Georgia are developing riparian buffer protection plans and ordinances without the benefit of scientifically-based guidelines. To address this problem, over 140 articles and books were reviewed to establish a legally-defensible basis for determining riparian buffer width, extent and vegetation. This document presents the results of this review and proposes several simple formulae for buffer delineation that can be applied on a municipal or county-wide scale. Sediment is the worst pollutant in many streams and rivers. Scientific research has shown that vegetative buffers are effective at trapping sediment from runoff and at reducing channel erosion. Studies have yielded a range of recommendations for buffer widths; buffers as narrow as 4.6 m (15 ft) have proven fairly effective in the short term, although wider buffers provide greater sediment control, especially on steeper slopes. Long-term studies suggest the need for much wider buffers. It appears that a 30 m (100 ft) buffer is sufficiently wide to trap sediments under most circumstances, although buffers should be extended for steeper slopes. An absolute minimum width would be 9 m (30 ft). To be most effective, buffers must extend along all streams, including intermittent and ephemeral channels. Buffers must be augmented by limits on impervious surfaces and strictly enforced on-site sediment controls. Both grassed and forested buffers are effective at trapping sediment, although forested buffers provide other benefits as well. Buffers are short-term sinks for phosphorus, but over the long term their effectiveness is limited. In many cases …

Survival, growth, and photosynthesis of tree seedlings competing with herbaceous vegetation along a water-light-nitrogen gradient

Abstract: In herbaceous dominated patches and ecosystems, tree establishment is influenced partly by the ability of woody seedlings to survive and grow in direct competition with herbaceous vegetation. We studied the importance of season long wet and dry spells on the competitive interactions between herbaceous vegetation and oak seedlings along a light and nitrogen gradient in an infertile secondary successional grassland in central North America. We conducted a field experiment in which seedlings of bur oak (Quercus macrocarpa) and northern pin oak (Q. ellipsoidalis) were exposed to two levels of light (full sun and 80% shade), three levels of nitrogen input (0, 5, 15 g m−1 yr−1), and three levels of water input (low, medium and high). In addition, seedlings were grown with and without the presence of surrounding herbaceous vegetation under both light and all three water levels. Seedling survival, growth, and rate of photosynthesis were significantly affected by competition with herbaceous vegetation and these effects varied along the multiple resource gradient. Overall, seedling survival of both species was significantly greater in wetter and shaded plots and when surrounding herbaceous vegetation was removed and was lower in nitrogen enriched plots. We found that soil water was significantly affected by varying inputs of water, light, and the presence or absence of herbaceous vegetation, and that seedling survival and rate of photosynthesis were highly correlated with available soil water. Our findings show that the impact of season long wet and dry spells on tree seedling success in grasslands can be affected by light and soil nitrogen availability.

Ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga menziesii establishment

Abstract: Chaparral on the central coast of California can occur as relatively stable patches of ectomycorrhizal Arctostaphylos directly adjacent to arbuscular mycorrhizal Adenostoma. Vegetation surveys and ...

Vegetation dynamics of Mongolia.

Abstract: Introduction to Studies on the Vegetation of Mongolia. Natural and Anthropogenic Factors and the Dynamics of Vegetation Distribution in Mongolia. 1.1. Introduction. 1.2. Natural Features of Mongolia. 1.3. Landscape-Ecological Regions. 1.4. Landscape and Ecological Factors of Vegetation Dynamics. 1.5. Conclusion. Late Quaternary Vegetation History of Mongolia. 2.1. Introduction. 2.2. An Overview of Previous Studies. 2.3. Data Used in this Study. 2.4. Regional Pollen Records from Individual Sites. 2.5. Holocene Changes in the Distribution of Tree and Shrub Taxa in Mongolia. 2.6. Spatial Reconstruction and Mapping of Mongolian Vegetation during the Last 15,000 Years. 2.7. General Discussion and Conclusions. Assessing Present-Day Plant Cover Dynamics. 3.1. Introduction. Modern Methods for Studying and Monitoring Plant Cover. 3.2. Mountain Plant Community Dynamics. 3.3. Plant Community Dynamics in Plains and Rocky Areas. 3.4. Dynamics of Water-Associated Vegetation. 3.5. Conclusions. Analysis of Present-Day Vegetation Dynamics. 4.1. Basic Changes in Vegetation. 4.2. Regressive Plant Community Successions. 4.3. Progressive Plant Community Regeneration. 4.4. Mapping Vegetation Dynamics. 4.5. Conclusions. Strategies for Nature Management and Vegetation Conservation. 5.1. Introduction. Methods for Vegetation Conservation. 5.2. Restoration and Conservation of Botanical Successions. 5.3. Systems for the Conservation of Botanical Diversity. 5.4. Conclusions. Summary Conclusions and Recommendations. References. Appendix 1. Appendix 2. Index.

Fluvial processes in streams with vegetation

Abstract: Recently, vegetation is a key of river management where environmental aspects should be taken care of as well as the safety against flood and the water resources utilization Then, the management of fluvial processes related to vegetation is inevitably important, and fluvial hydraulics and hydraulics of flow with vegetation must support it These two fields have been recently developed obviously, and coupling them must provide us answers to various emerging problems in new river engineering In this paper, after an explanation how to treat the flow with vegetation, 2D analysis of fluvial process related to flow with vegetation are introduced with typical processes Particular interests are paid on the topics of fluvial process related to flow with vegetation which concerns with changes of river landscape

Effect of Riparian Vegetation on Flow Resistance and Flood Potential

Abstract: An existing hydraulic model is modified to predict stage-discharge curves for channels with nonuniform cross sections, sand and gravel-bed materials, and flexible or nonflexible riparian vegetation. The model is based on a version of the flow momentum and continuity equations that account for lateral shear. The model accounts for the effects of vegetation using empirically calibrated flow resistance equations that incorporate measurable physical properties of vegetation. Separate flow resistance equations are used for flexible and nonflexible vegetation types. Simulated stage-discharge curves are compared with data obtained from three natural river channels. Discrepancies between simulated and observed data range between 2 and 45%, but most (∼70%) discrepancies were <15%. Sensitivity tests are performed to determine the effects of different types of riparian vegetation on friction factor and flood elevation. Surfaces covered by nonflexible vegetation are rougher than those covered with flexible riparian vegetation. Based on simulations at the three study sites, operational maintenance regimes are proposed that minimize flood risk, while maximizing the environmental benefits of a well-developed riparian vegetation cover.

Late Cretaceous and Cenozoic History of North American Vegetation: North of Mexico

Abstract: This book is a unique and integrated account of the history of North American vegetation and paleoenvironments over the past 70 million years. It includes discussions of the modern plant communities, causal factors for environmental change, biotic response, and methodologies. The history reveals a North American vegetation that is vast, immensely complex, and dynamic.

Hydrodynamics induced by wind waves in a vegetation field

Abstract: The wave-induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed. Using potential flow and an eigenfunction expansion, the problem is solved considering regular as well as irregular incident waves. The model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity. The model is validated against experimental laboratory data obtained by other authors, showing a much better agreement than previous theoretical models. In this paper the model is used to evaluate wave height evolution (damping), vegetation and fluid motion, and forces and moments on the vegetation. Furthermore, the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics.

Effects of grazing and topography on long-term vegetation changes in a Mediterranean ecosystem in Israel

Abstract: The dynamics of Mediterranean vegetation over 28 years was studied in the Northern Galilee Mountains, Israel, in order to identify and quantify the major factors affecting it at the landscape scale. Image analysis of historical and current aerial photographs was used to produce high resolution digital vegetation maps (pixel size = 30 cm) for an area of 4 km 2 in the Galilee Mountains, northern Israel. GIS tools were used to produce corresponding maps of grazing regime, topographic indices and other relevant environmental factors. The effects of those factors were quantified using a multiple regression analyses. Major changes in the vegetation occurred during the period studied (1964‐1992); tree cover increased from 2% in 1964 to 41% in 1992, while herbaceous vegetation cover decreased from 56% in 1964 to 24% in 1992. Grazing, topography and initial vegetation cover were found to significantly affect present vegetation patterns. Both cattle grazing and goat grazing reduced the rate of increase in tree cover, yet even intensive grazing did not halt the process. Grazing affected also the woody-herbaceous vegetation dynamics, reducing the expansion of woody vegetation. Slope, aspect, and the interaction term between these two factors, significantly affected vegetation pattern. Altogether, 56% and 72% of the variability in herbaceous and tree cover, respectively, was explained by the regression models. This study indicates that spatially explicit Mediterranean vegetation dynamics can be predicted with fair accuracy using few biologically important environmental variables.

Acetylsalicylic Acid Reduces Vegetation Bacterial Density, Hematogenous Bacterial Dissemination, and Frequency of Embolic Events in Experimental Staphylococcus aureus Endocarditis Through Antiplatelet and Antibacterial Effects

Abstract: Background—Platelets are integral to cardiac vegetations that evolve in infectious endocarditis. It has been postulated that the antiplatelet aggregation effect of aspirin (ASA) might diminish vegetation evolution and embolic rates. Methods and Results—Rabbits with Staphylococcus aureus endocarditis were given either no ASA (controls) or ASA at 4, 8, or 12 mg · kg−1 · d−1 IV for 3 days beginning 1 day after infection. Vegetation weights and serial echocardiographic vegetation size, vegetation and kidney bacterial densities, and extent of renal embolization were evaluated. In addition, the effect of ASA on early S aureus adherence to sterile vegetations was assessed. In vitro, bacterial adherence to platelets, fibrin matrices, or fibrin-platelet matrices was quantified with either platelets exposed to ASA or S aureus preexposed to salicylic acid (SAL). ASA at 8 mg · kg−1 · d−1 (but not at 4 or 12 mg · kg−1 · d−1) was associated with substantial decreases in vegetation weight (P<0.05), echocardiographic veg...

Understory vegetation, resource availability, and litterfall responses to pine thinning and woody vegetation control in longleaf pine plantations

Abstract: In six 8- to 11-year-old plantations of longleaf pine (Pinus palustris Mill.) near Aiken, S.C., responses of understory vegetation, light, and soil water availability and litterfall were studied in...

Vegetation management on grass-dominated clearcuts planted with Norway spruce in southern Sweden

Abstract: A field experiment was established between 1989 and 1993 to study the effects of competing vegetation on growth of planted Norway spruce (Picea abies (L.) Karst.) seedlings. Effects of clearcut age, scarification (mounding), herbicide treatment, and seedling stock type were investigated 5 years after planting. On fresh clearcuts, amounts of vegetation were negligible, whereas 2.1-3.7 Mg·ha-1 was found on 4-year-old and older clearcuts. Soil temperatures were about 10% higher in mounds than in undisturbed ground, while herbicide and clearcut age only marginally affected soil temperatures. Seedlings planted on old clearcuts showed significant reductions in growth due to interference from vegetation. Five years after planting, the reduction in growth corresponded to about 1 year's growth. Most of the interaction between seedlings and vegetation occurred during the first 2 years after planting. Thus, scarification was just as effective as repeated herbicide treatments in reducing competition from vegetation. ...

Potential high‐latitude vegetation feedbacks on CO2‐induced climate change

Abstract: We use a fully coupled climate-vegetation model to examine the potential effects of changes in vegetation cover on simulations of CO2-induced climate change. We find that vegetation feedbacks, acting mainly through changes in surface albedo, enhance greenhouse warming in the northern high latitudes during spring and summer months. In spring and summer, land surfaces north of 45°N are warmed by 3.3 and 1.7°C by a doubling of CO2 alone; vegetation feedbacks produce an additional warming of between 1.1–1.6 and 0.4–0.5°C, respectively. In winter, however, vegetation feedbacks appear to oppose the 5.6°C radiative warming, particularly over Eurasia. These results demonstrate that vegetation feedbacks are potentially significant and must be included in assessments of anthropogenic climate change.

A model for the explanation of vegetation stripes (tiger bush)

Abstract: Regular vegetation patterns appear on aerial views of plateaux in SW Niger where densely and sparsely popu- lated zones alternate with each other. This spatial organization of the vegetation is an endogenous phenomenon which is not limited to specific plants or soils; it is a characteristic land- scape of many arid regions throughout the world. The phe- nomenon is interpreted as the result of a spatial range differ- ence between two biologically distinct interactions operating at the plant population level. The proposed mechanism is independent of external heterogeneities deriving from soil geomorphology or meteorology. We present a model to simu- late the genesis of vegetation stripes. In addition, the model predicts the occurrence of vegetation hexagons corresponding to higher or lower density spots arranged in a hexagonal lattice. The distinction between the two spatial symmetries is discussed in terms of their Fourier transforms.

Variation in the effects of vegetation and litter on recruitment across productivity gradients

Abstract: 1 We tested predictions about how the effect of vegetation and litter on seedling establishment varies among sites and herbaceous community types (sand barrens, prairies, fens). For both vegetation and litter, we also separated direct interactions from indirect interactions and interaction modifications along the gradient. 2 Although the intensity of the effects varied across sites, the direct effects of vegetation or litter alone were consistently facilitative along the productivity gradient. Predominance of facilitative effects may be due to the focus on the seedling establishment phase. 3 However, inclusion of indirect interactions and interaction modifications caused the net effects of both vegetation and litter to become largely negative. While one layer of biomass may be advantageous to ameliorate some moisture stress, the addition of another layer may be disadvantageous if this layer limits light proportionally more than it relieves moisture stress. 4 One exception to this pattern occurred at high productivity when the net effect of vegetation, even in the presence of litter, remained facilitative. The net effect of vegetation was competitive at low productivity and grew increasingly facilitative with productivity. Thus, indirect effects of litter may alter interaction patterns across this gradient.

Evaluation of NDVI for monitoring live moisture in three vegetation types of the Western U.S.

Abstract: been estimated through empirically derived algorithms or The Normalized Dimence Vegetation Index (~~vr) is evalu- Was measured using intensive field methodology. ideally, inated for monitoring seasonal a Burgan et al., 1997). The Advanced Very High Resoluthan the conifer canopy was examined. Seasonal changes in tion sensor On the TIROS-N series vegetation moisture for all sites were statistically significant polar-orbiting weather satellites provides daily observations (p<0.05). Time-series profiles of the NDVI were functionally of the Earth's mrface at a nominal spatial resolution (at narelated to changes in vegetation moisture only for the grass dir) square lcrn. it was and forest understory vegetation. N~ significant relationships with natural resource observation objectives, several indices were observed for either the shrub or coniferous forest can- derived the AVHRR Vectral data provide meaningfu1 opy vegetation. This field experiment will improve our inter- measures of vegetation condition (Loveland and ~hlen, pretation of seasonal NDVI data with respect to fire potential. lgg3). The lIifference Index (NDvl)*