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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
811

Sapling growth and recruitment as affected by flooding and canopy gap formation in a river floodplain forest in southeast Texas

Hall, Rosine Blount Wilson January 1993 (has links)
I used sapling population data collected since 1980 to investigate how canopy disturbance interacts with chronic understory disturbance to determine regeneration patterns. I reconstructed flooding history using a combination of river gauging, a local water-level recorder, and contour maps. 1979 was an extreme flood year for this site, as was 1989. Reduction in flooding frequency since dam construction in 1965 was significant for all elevations, while reduction in flooding duration was significant only for the upper half of the site. Using constrained ordination, I showed that sapling occurrence varies primarily along a flooding/soil moisture gradient, and secondarily along a canopy-openness gradient. This confirms that both flooding and light influence local variation in species composition. Small sapling density increased by more than five times during the decade, while large sapling density increased over 70%. I suggest that this increase is related to the decline in frequency and duration of flooding, and specifically, to the pattern of flooding from 1979-1989, characterized by severe flooding in 1979 and 1989. Sapling survivorship also responded to temporal variation in flooding over the decade. A damage survey revealed a size component to flooding damage, with small individuals making up a disproportionate share of those in the highest damage classes. In addition, there is a relationship between river flow and the elevation of saplings that died, suggesting that the effects of elevation are not simply related to flooding, but perhaps to soil moisture as well. Analyses of sapling growth suggest that there is a trade-off between tolerating flooding in wet years and being subject to moisture stress in dry years. I presented evidence that canopy gaps play an important role in determining sapling growth. Gaps appear to be crucial to the continued success of large saplings, and the fastest-growing individuals are found in them. This may also confer a measure of flood-tolerance related to sapling size.
812

Effects of fire on vegetation in the Big Thicket of southeastern Texas, United States of America

Liu, Changxiang January 1995 (has links)
This study shows that fire had a strong short-term effect on the small-sized individuals in the understory of two dry upland vegetation types, sandhill and upland pine. Large trees were less affected than saplings and small trees. The changes in these types were mainly structural rather than compositional. The influence of fire diminished toward the wet end of the vegetation gradient. Post-fire recruitment via resprouting and germination from seeds was rapid. The interaction of fire and vegetation type was apparent in the comparison of the two dry upland types with slope types. Simulation of fuel and fire provided additional, although not very strong, support for the existence of differences in fire behavior corresponding to an environmental gradient from dry upland forests to mesic and wet slope forests. Ordination using pre- and post-fire data suggests that fire had limited effects on current vegetation patterns and there was no indication that any present pre-fire type would be converted to another type. Furthermore, there were no clear convergent or divergent patterns in overall vegetation change; hence it was difficult to predict long-term changes. An eight-year record of vegetation change at a tornado damaged savanna site in Hickory Creek Unit demonstrates that the tornado had resulted in the succession of the vegetation toward a midslope forest, but two prescribed fires partially reversed such a trend. Phytolith analysis revealed that upland pine and some upperslope forests had abundant grass phytoliths. This indicates that these types had a grass component in the past under an open canopy which might have disappeared as a result of fire suppression, logging, and encroachment of shrubs and hardwoods.
813

Fluctuations in abundance and mortality of Carpinus caroliniana (American hornbeam) and the invasion of Sapium sebiferum (Chinese tallow)

Mann, Lisa Erin January 2006 (has links)
A bottomland hardwood forest stand located in east Texas experienced a hurricane-related flood event in 1989. After this event, Carpinus caroliniana Walt. had a large pulse in mortality, decreasing dramatically in abundance (47%) over a 5-year period. The decline was greater at low elevations suggesting that at least part of the mortality was related to flooding. The flood was the longest summer flood on record. The duration of this growing season flood may have been partly a consequence of upstream dam management. Linear regression showed that in areas where Carpinus death was greater, several sapling species had increases in basal area growth. The invasive species Sapium sebiferum (L.) Roxb. had the greatest increase. This suggests that the Carpinus death and concomitant increase in light availability resulted in accelerated invasion of this forest by Sapium.
814

Vegetation change in response to a tornado and prescribed fire in the Hickory Creek unit of the Big Thicket National Preserve, Texas

Milton, Mikaila January 1998 (has links)
A mixed pine-oak forest in the Hickory Creek unit of the Big Thicket National Preserve was hit by a tornado in December of 1983. Subsequently the forest was subjected to three prescribed fires in an effort to restore this area to its former savanna state. The tornado has allowed for both pines and oaks to regenerate. Both groups have regained much of the basal area lost in the tornado. However, the biggest compositional change has occurred at the understory level. There has been a huge increase in the upland shrub Ilex vomitoria (yaupon). Vegetation composition and density seem to be involved in a positive feed-back loop with fire. Plots dense with shrubs experienced low flame heights, which has allowed for increased shrub growth. This process seems to be leading the tornado plots down a spiral towards unflammability. The current fire regime of periodic winter fires has only been able to slow this process in the most open plots. A more intense use of fire, such as repeated summer burns appears to be necessary to reclaim this area as a fire-dependent savanna.
815

Home range, habitat use and pup attendance of red wolves ( Canis rufus) during the pup rearing season

Hinton, Joseph William January 2006 (has links)
Despite a 20 year reintroduction effort into northeastern North Carolina, little is known about the natural history and ecology of red wolves (Canis rufus). In 2005, I studied home ranges, habitat use and pup attendance of red wolves during the pup rearing season. Data indicated that red wolves have home range sizes intermediate between those of coyotes (Canis latrans) and gray wolves (Canis lupus). Similar to other canids in the eastern United States, red wolves preferred to use extensive agricultural fields during the summer months rather than adjacent wooded areas. Red wolves abandoned dens early to move pups into adjacent agricultural fields. Consistent with pup rearing studies done on gray wolves, red wolf pups were rarely left alone indicating that red wolves share duties of pup rearing and that males play a significant role in the rearing of red wolf pups.
816

The influence of experimental Trichinella pseudospiralis infections on the reproduction and behaviour of captive American kestrels (Falco sparverius) /

Saumier, Michèle Dominique January 1986 (has links)
The reproductive success of American kestrels (Falco sparverius) infected with Trichinella pseudospiralis was significantly reduced when compared with uninfected controls. Egg laying was delayed, and infected females produced fewer eggs than uninfected controls. Infected females were more aggressive and copulated less frequently. Egg breakage among infected birds was greater than among controls. Infected females tended to lay eggs outside the nest box. Infected females did not incubate as frequently as the controls, thus accounting for the higher prevalence of embryo mortality among these birds. The above effects translated into a mean production of 2.1 hatchlings per control pair and 0.6 per infected pair of kestrel. Both in breeding and non-breeding kestrel, T. pseudospiralis infections gave rise to a general decline in mobility. Behavioural effects are primarily attributable to the presence of muscle larvae. The parasite showed no predilection for specific muscle groups.
817

Etude des endoparasites et plus spécialement du ver des méninges (Parelaphostrongylus tenuis) du cerf de Virginie (Odocoileus virginianus borealis) à l'ile d'Anticosti

Beaulieu-Goudreault, Michelle. January 1981 (has links)
No description available.
818

The UAV logger as a potential alternative for timber transportation in the Canadian boreal forest

Wychreschuk, Alena 14 August 2012 (has links)
The Canadian boreal forest has substantial natural resources located in remote isolated areas that are of economic interest. Requirements of the log extraction operation are to minimize impact on the ecosystem and its inhabitants. Transportation is one of the largest direct costs of forestry operations and many potential harvest areas are left untouched because of the high costs to build and maintain logging roads and water crossings. Alternatives to the traditional surface transportation system could benefit the industry, the residents and the ecosystem. The economics of a Lighter-Than-Air UAV Logger concept for log transportation is compared to the current truck and road build option using a cost comparison model and three harvest area case studies. At the engineered price estimate of $4.1 million, the results suggest that the UAV Logger is an uneconomic transportation alternative in the boreal forest at current product prices and supply availability. Conditions that favour the UAV Logger as a competitive economic alternative include small harvest volumes and high road build costs.
819

The UAV logger as a potential alternative for timber transportation in the Canadian boreal forest

Wychreschuk, Alena 14 August 2012 (has links)
The Canadian boreal forest has substantial natural resources located in remote isolated areas that are of economic interest. Requirements of the log extraction operation are to minimize impact on the ecosystem and its inhabitants. Transportation is one of the largest direct costs of forestry operations and many potential harvest areas are left untouched because of the high costs to build and maintain logging roads and water crossings. Alternatives to the traditional surface transportation system could benefit the industry, the residents and the ecosystem. The economics of a Lighter-Than-Air UAV Logger concept for log transportation is compared to the current truck and road build option using a cost comparison model and three harvest area case studies. At the engineered price estimate of $4.1 million, the results suggest that the UAV Logger is an uneconomic transportation alternative in the boreal forest at current product prices and supply availability. Conditions that favour the UAV Logger as a competitive economic alternative include small harvest volumes and high road build costs.
820

Assessment of two spectral reflectance techniques for the estimation of fuel moisture content, equivalent water thickness, and specific leaf weight in Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) needles

Visintini, Fabio 09 June 2011 (has links)
In the wildfire community fuel moisture content (FMC) is the quantity of choice when it comes to assess vegetation water status in relation to fire risk and fire behaviour. Field measurements of FMC are both expensive and time consuming and, in addition, sampling is often spatially inadequate. Remote sensing could represent an almost ideal solution both in terms of spatial and temporal coverage, if a consistent relationship between FMC and spectral reflectance could be established. A review of the literature suggests that it is difficult to retrieve FMC for dense forest canopies with remote sensing platforms. This study took a step back and explored the relationship between spectral reflectance and vegetation water content at the leaf level, where several confounding factors present at the canopy level are eliminated or controlled for. It also considered a conifer species, because relatively little research has been produced on this topic for this type of vegetation. The main goal was to establish if FMC can be derived directly from spectral reflectance in the solar spectrum using two well known approaches, such as spectral indices and continuum removal. It is also aimed at exploring if an alternative, indirect way to measure FMC as ratio of Equivalent Water Thickness (EWT) and Specific Leaf Weight (SLW) is feasible and accurate. The results derived from Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) needles used in this study suggested that FMC was not directly retrievable from spectral reflectance but vegetation water content could be assessed with sufficient accuracy in terms of EWT. Also the retrieval of SLW from reflectance of fresh foliage proved to be challenging. Finally, the study also highlighted several aspects in the relationships among foliar water content, dry matter content and reflectance that require additional research. / Graduate

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