Browsing by Subject "landscape ecology"
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Item A comparison of the environmental effects of traditional intensive forestry and the sustainable forestry initiative: a modeling approach at the landscape level(Texas A&M University, 2004-09-30) Azevedo, Joao CarlosChanges in landscape pattern caused by changes in forest management, namely the Sustainable Forestry Initiative (SFI), and the implications of these structural changes on landscape processes were analyzed. Landscape structure was studied based upon the comparison of landscapes with different management histories. Ecological processes were analyzed based upon simulation of stand and landscape attributes of habitats for several vertebrate species and upon simulation of hydrological processes such as water and sediment yield. A methodology to integrate landscape and stand pattern and dynamics with landscape processes was developed for this work. It integrates a forest landscape structure model, several stand level growth and yield models, vertebrate habitat models, and a hydrological model. The comparisons among landscapes revealed that forest management has a strong influence on landscape structure. The SFI program increases fragmentation of the landscape indicated by the presence of more and smaller patches, more edges, more complex shapes, and less and smaller core areas. Traditional intensive and extensive management show comparable patterns characterized by high aggregation and connectivity. Landscapes managed according to the SFI program show higher Habitat Suitability Index (HSI) values for American woodcock, American beaver, wild turkey, fox squirrel, and gray squirrel. HSI is higher for pine warbler in the landscape not managed according to the SFI program. Downy woodpecker and barred owl present very reduced HSI values in either landscape. The SFI program induced fragmentation of the habitat of pine warbler and the establishment of narrow and elongated habitats in a network structure for the remaining species. Both patterns are determined by SMZs. The scenario representing management according to the SFI program presents higher sediment yield at the watershed level than the scenario representing management not according to the SFI program due to higher channel erosion related to the absence of buffer strips in the non-SFI scenario. In general, management according to the SFI program increases landscape diversity and evenness, habitat suitability for most species, potential vertebrate diversity, and provides habitat structure suitable for most species. This management also decreases sediment loss at the watershed level.Item Feral Africanized honey bee ecology in a coastal prairie landscape(Texas A&M University, 2004-09-30) Baum, Kristen AnneHoney bees, Apis mellifera, play an important role in many ecosystems, pollinating a wide variety of native, agricultural, and exotic plants. The recent decline in the number of feral and managed honey bee colonies in North America, as well as the arrival of Africanized honey bees, have caused concern about adequate pollination for agricultural crops and natural plant communities. However, little is known about feral colonies, and the feral population is the source for Africanized honey bees as they spread and infiltrate managed populations. The goal of my dissertation was to examine the ecology of feral honey bee colonies, adding the spatial context necessary to understand the population ecology and patterns of resource use by feral honey bees on the Welder Wildlife Refuge. I defined the functional heterogeneity of feral honey bee habitat by identifying the suitability of different habitats for feral colonies based on the distribution and abundance of important resources (cavities, nectar, and pollen). I evaluated the distribution and abundance of feral colonies by examining nest site characteristics, population trends, and spatial and temporal patterns in cavity use. Lastly, I examined resource use by evaluating patterns in pollen collection and identifying where and when honey bees searched for resources. Overall, the Welder Wildlife Refuge provided excellent habitat for feral honey bees, supporting a high density of feral colonies. The dense live oak habitat was the best overall source for cavities, nectar, and pollen. Nectar and pollen were abundant throughout the year, with the exception of December and January, when a large number of honey bees searched for resources. Cavities did not appear to vary in their suitability for feral colonies based on measured structural and environmental attributes, since no cavity attributes were correlated with indices of cavity quality. However, the cavity quality indices varied between cavities, suggesting some cavities were more suitable for feral honey bees than others. Colonies were aggregated within the study area, probably due to the distribution of resources. The invasion of Africanized honey bees appeared to fragment the existing European population, with Africanized colonies aggregated in distribution and European colonies random in distribution.