141 |
The management of tree replacement in mature urban landscapesParker, Matthew David January 2004 (has links) (PDF)
Amenity trees provide physical, social and economic benefits to people sharing their environment. To maintain the benefits that many people have come to expect of trees in their urban landscapes, a viable and dynamic tree population is required. To this end it is necessary to plant new trees or replace existing trees when they require removal. The challenge when replacing mature trees is not simply the process of planting a tree when one is removed, but of the continual replacement of the entire tree population in a planned and managed fashion. In urban landscapes this is not a natural process, and human intervention is required.
|
142 |
Contagious distributions in even aged forest stands : dynamics of spatial pattern and stand structure /Hamilton, Fiona C. January 1984 (has links)
Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 59-61). Also available on the World Wide Web.
|
143 |
Vattenkvalité i Märstaån : Igenväxning som indikator på närsaltläckage och vattenstatusKamperman, Jan-Erik January 2011 (has links)
The purpose of this study was to examine whether an inventory of the vegetation overgrowth could be used to indicate a locally nutritional impact. The study was conducted at Märstaån where the water runs through a number of agricultural lands that could lead to an increased amount of diffuse emissions of nutrients. The vegetation overgrowth in the water was also studied in relation to shade, meandering and water flow effects on the vegetation. With this method, no definitive conclusions could be drawn. Where the water was shaded, no vegetation overgrowth could be found. Therefor trees should be planted to prevent any future overgrowths. The majority of Märstaån is straightened and should get an increased meandering to lower the water flow. The water pond in Steningedalen could also be more effective by lowering the water flow. In the future, more extensive studies should be conducted in the purpose to find other substances in the water that comes from point sources in the area.
|
144 |
Laboratory experiments and numerical modeling of wave attenuation through artificial vegetationAugustin, Lauren Nicole 15 May 2009 (has links)
It is commonly known that coastal vegetation dissipates energy and aids in
shoreline protection by damping incoming waves and depositing sediment in vegetated
regions. However, this critical role of vegetation to dampen wave forces is not fully
understood at present. A series of laboratory experiments were conducted in the Haynes
Coastal Laboratory and 2-D flume at Texas A&M University to examine different
vegetative scenarios and analyze the wave damping effects of incident wave height, stem
density, wave period, plant type, and water depth with respect to stem length.
In wetland regions vegetation is one of the main factors influencing hydraulic
roughness. Traditional open-channel flow equations, including the Manning and Darcy-
Weisbach friction factor approach, have been successfully applied to determine bottom
friction coefficients for flows in the presence of vegetation. There have been numerous
relationships derived relating the friction factor to different flow regime boundary layers to try and derive a wave friction factor for estimating energy dissipation due to bottom
bed roughness. The boundary layer problem is fairly complex, and studies relating the
wave friction factor to vegetation roughness elements are sparse. In this thesis the
friction factor is being applied to estimate the energy dissipation under waves due to
artificial vegetation. The friction factor is tuned to the laboratory experiments through
the use of the numerical model COULWAVE so that the pipe flow formulation can be
reasonably applied to wave problems. A numerical friction factor is found for each case
through an iterative process and empirical relationships are derived relating the friction
factor for submerged and emergent plant conditions to the Ursell number. These
relationships can be used to reasonably estimate a wave friction factor for practical
engineering purposes.
This thesis quantitatively analyzes wave damping due to the effects of wave
period, incident wave height, horizontal stem density, water depth relative to stem
length, and plant type for a 6 m plant bed length. A friction factor is then determined
numerically for each of the laboratory experiments, and a set of equations is derived for
predicting a roughness coefficient for vegetation densities ranging between 97 stems/m2
and 162 stems/m2.
|
145 |
Raster based coastal marsh classification within the Galveston Bay ecosystem, TexasEdwards, Aron Shaun 15 May 2009 (has links)
A mapping study using remote sensing software called ENVI was conducted utilizing four
software algorithms to investigate whether these techniques could accurately classify habitat types and
vegetation communities along West Bay of the Galveston Bay Ecosystem from color infra-red (CIR)
imagery. The algorithms were used in a small-scale study to investigate which of these techniques could
most accurately distinguish habitat types and vegetation communities from the imagery at a site specific
location. The most accurate algorithm of the four was used in a large-scale classification study in which
entire images were classified utilizing the same data from the small-scale study.
Regions of interest (ROIs) were used within ENVI to specify areas of interest within each image
that was classified. The locations of ROIs were recorded using a GPS prior to classification, then each
was added into ENVI as data points, and each ROI polygon was digitized according to its respective pixel
color. Once all of the ROI polygons were completed, each software algorithm was employed.
After classification, each habitat type and vegetation community was ground-truthed in order to
verify the accuracy of the algorithms. The position points were added as ground truth points within ENVI
and an accuracy matrix was assessed. The technique with the greatest averaged accuracy within the smallscale
study was selected for the large-scale study. The ROIs and ground truth points used in the smallscale
study were used again in the large-scale study.
The small-scale study concluded that the Parallelepiped algorithm produced significantly less
accurate classifications than the other three. Although the Mahalanobis algorithm was not significantly
different from the other two algorithms, it yielded the highest overall average accuracy and was used in the
large-scale study. In both the small-scale and large-scale studies there was no significant difference in the
two different years of aerial imagery and there were no significant differences in accuracy for locations. None of the software algorithms were accurate at classifying habitat types and vegetation communities
using the imagery. The accuracy for the Mahalanobis algorithm was less than 60%. Inaccuracies were
largely due to overlapping spectral signatures among habitat types and vegetation communities.
|
146 |
Methoden zur Bewertung gradueller Unterschiede des Ausbreitungspotentials von Pflanzenarten : modellierung des Windausbreitungspotentials und regelbasierte Ableitung des Fernausbreitungspotentials /Tackenberg, Oliver. January 2001 (has links) (PDF)
Thesis (doctoral)--Universität Marburg, 2001. / Also available in PDF format. Includes bibliographical references (p. 89-102).
|
147 |
Tropical forest landscape dynamics: population consequences for neotropical lianas, genus PassifloraPlowes, Robert Merrick 28 August 2008 (has links)
Not available / text
|
148 |
Downscaling Climate and Vegetation Variability Associated with Global Climate Signals: a new Statistical Approach Applied to the Colorado River BasinCanon Barriga, Julio Eduardo January 2009 (has links)
This research presents a new multivariate statistical approach to downscale hydroclimatic variables associated with global climate signals, from low-resolution Global Climate Models (GCMs) to high-resolution grids that are appropriate for regional and local hydrologic analysis. The approach uses Principal Component Analysis (PCA) and Multichannel Singular Spectrum Analysis (MSSA) to: 1) evaluate significant variation modes among global climate signals and spatially distributed hydroclimatic variables within certain spatial domain; 2) downscale the GCMs' projections of the hydroclimatic variables using these significant modes of variation and 3) extend the results to other correlated variables in the space domain. The approach is applied to the Colorado River Basin to determine common oscillations among observed precipitation and temperature patterns in the basin and the global climate signals El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). These common oscillations serve as a basis to perform the downscaling of ENSO-related precipitation and temperature projections from GCMs, using a new gap-filling algorithm based on MSSA. The analysis of spatial and temporal correlations between observed precipitation, temperature and vegetation activity (represented by the Normalized Difference Vegetation Index, NDVI) is used to extend the downscaling of precipitation to vegetation responses in ten ecoregions within the basin. Results show significant common oscillations of five and 15-year between ENSO, PDO and annual precipitation in the basin, with wetter years during common ENSO and PDO positive phases and dryer years during common negative phases. Precipitation also shows an increase in variability in the last 20 years of record. Highly correlated responses between seasonally detrended NDVI and precipitation were also identified in each ecoregion, with distinctive delays in vegetation response ranging from one month in the southern deserts (in the fringe of the monsoon precipitation regime), to two months in the mid latitudes and three months to the north, affected by seasonal precipitation. These results were used to downscale precipitation and temperature from two GCMs that perform well in the basin and have a distinctive ENSO-like signal (MPI-ECHAM5 and UKMO-HADCM3) and to extend the downscaling to estimate vegetation responses based on their significant correlations with precipitation.
|
149 |
The effects of observed and experimental climate change and permafrost disturbance on tundra vegetation in the western Canadian High ArcticBOSQUET, LYNNE M 05 January 2011 (has links)
The response of vegetation to climate change and permafrost disturbance was studied at the Cape Bounty Arctic Watershed Observatory (CBAWO) on Melville Island, Nunavut. Climate change is expected to alter the terrestrial ecosystem of this area and cause non-linear responses. This study focussed on two predicted outcomes of climate change in the western Canadian High Arctic: the occurrence of a permafrost disturbance termed active layer detachments (ALDs), and increased air temperature and precipitation.
To study the effects of ALD formation twenty 1 m2 plots were established within two ALDs. One ALD (ALD05) was formed in July 2007 and represented the initial impact of slope failure caused by an exceptionally warm year. The other (ALD04) was formed at least sixty years ago and represented the long-term impact of slope failure. Physical soil measurements and vegetation surveys were completed in both disturbances.
ALD formation creates depressions on the landscape that increase snow accumulation. Snow accumulation was greater in the more recent ALD than in the older one and this resulted in greater changes to the physical environment. Vegetation was not significantly impacted by disturbance, although phenology was delayed due to snowcover retention.
To study the effects of increased air temperature and precipitation an International Tundra Experiment (ITEX) site was established at CBAWO in July 2008. Snow fences and open-top chambers (OTC) were erected to increase snow accumulation and air temperature. Physical soil measurements and vegetation surveys were completed through the summer of 2009. Soil temperature and active layer depth were affected by snow and phenology was delayed in plots with snow enhancement. Experimental warming also had some effects on the parameters measured but only in conjunction with snow enhancement. This study found that in the first year of experimentation snow enhancement has a greater effect than increased air temperature.
These studies represent the beginning of two long-term projects at CBAWO and the results from this study represent baseline data for future research. Continued monitoring will show the evolution of vegetation in the ALDs and the potential long-term effects of temperature and snow manipulation. / Thesis (Master, Geography) -- Queen's University, 2011-01-04 20:53:31.689
|
150 |
Saltanvändning i skidbackar : Utbredning och påverkan av natriumklorid i den lokala miljön / Salt use in ski slopes : Distribution and impact of sodium chloride in the local environmentLeidermark, Ida January 2014 (has links)
Natriumklorid sprids i ca. 20 skidbackar inom Åres skidsystem. Natriumklorid sänker vattens fryspunkt och gör att snön kan hållas hård under tävlingar, vilket ger de tävlande så lika förutsättningar som möjligt. Studiens främsta syfte var att undersöka om spridning av natriumklorid i Åres skidbackar är skadlig för vegetation i dess område och Indalsälvens vattenmiljö. Huvudsakligen utfördes detta genom en kartläggning av natriumkloridets väg via mark och vatten. Men hjälp av kartläggningen beräknades mängden kloridjoner som når Indalsälven från spridningen samt bidraget till koncentrationen av kloridjoner i Indalsälven. Genom en litteraturundersökning och fältstudie har natriumkloridets påverkan på vegetation och mark undersökts. Resultaten visar att de flesta kloridjoner från saltning med natriumklorid i skidbackarna når Indalsälven genom ytavrinning och att kloridjonernas uppehållstid i backarna är mindre än ett år. På grund av utspädningseffekten bedöms bidraget till koncentrationen av kloridjoner i Indalsälven vara försumbar. Ingen påverkan på markvegetation i eller nedanför backarna kunde identifieras. Markens fysikaliska egenskaper och struktur inom de saltade områdena och 25 m nedanför bedöms kunna försämras, vilket kan skapa ökad erosion. Det är däremot inte fastställt att så är fallet. Sammanfattningsvis indikerar resultaten i studien en begränsad påverkan på miljön av saltanvändningen i Åres skidbackar. Det fordras ytterligare undersökningar för att kunna få en djupare förståelse av saltningens miljöpåverkan på kort och lång sikt. / Sodium chloride is spread in approx. 20 ski slopes within the ski system of Åre. Sodium chloride lowers the waters freezing point and can keep the snow stable during ski competitions, which gives the contestants as similar conditions as possible. The primary purpose of the study were to examine if the distribution of sodium chloride in ski slopes is harmful to vegetation in the area and in the aquatic environment of Indalsälven. Mainly, this was done through a mapping of the sodium chloride transport through the soil and water. By using the mapping, calculations were done to know which amount of chloride ions that reaches Indalsälven from the spreading and the contribution to the concentration of chloride ions in Indalsälven. Through a literature- and field study, the sodium chloride impact on vegetation and soil were investigated. The results shows that the most of the chloride ions from the salting of sodium chloride in ski slopes reaches Indalsälven through surface runoff and the chloride ions residence time in the slopes is less than a year. Because of the dilution effect, the contribution to the concentration of chloride ions in Indalsälven deemed negligible. No impact on ground vegetation in or below the slopes were identified. The soil physical properties and structure within the salted area and 25 m below, is expected to deteriorate which can cause increased erosion. However, it is not established that this is the case. Summarize, the results of the study shows limited impact on the environment by the use of salt in the ski system of Åre. It requires further investigation in order to gain deeper understanding of the environmental impacts in short and long term of salt use.
|
Page generated in 0.0962 seconds