Browsing by Subject "disturbance"
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Item Ecology of Sandy Beach Intertidal Macroinfauna Along the Upper Texas Coast(2012-07-16) Witmer, Angela DawnOpen coastlines are dynamic environments which experience seasonal and long-term physical changes. Sandy beaches line much of this coastline. As part of the requirements for Ph.D., I conducted a study examining intertidal macrofaunal and sedimentological features along the upper Texas coastal from 2007-2009. Four sites near Sabine Pass, High Island, Jamaica Beach, and Surfside Beach were selected. Beach transects were established at each site with six intertidal stations identified for collecting macrofaunal sediment core samples. Although sandy beaches are low in species diversity, the taxa found survive under dynamic and harsh conditions. In disturbance dominated environments, sandy beach fauna tended to be influenced by physical factors, instead of biologically controlled ones. The taxa found in this study include primary and secondary successional organisms which are adapted to handle disturbances. 98% of the benthic specimens identified belonged to six taxa with 92% from two taxa, Scolelepis squamata (38%) and Haustoriidae (54%). Macrofaunal zonation varied between sites because of beach geomorphology. On September 13, 2008, Hurricane Ike made landfall on the upper Texas coast causing extensive damage and erosion. Roughly 0.5 m of vertical height was lost at each beach post-storm. Total macrofaunal abundance declined by 87% from pre-storm counts. During the recovery the dominant two taxa, Haustoriidae and Scolelepis squamata, made up 82.78% of the total benthic specimens identified with haustoriids making up 68% of the total benthic taxa. The beach community remained dominated by four of the previously identified, six most common and abundant taxa. Recovery of sandy beaches often was hindered by increased vehicular traffic, sand removal and cleaning. Beach ecosystems have shown a high natural ecological resilience, but do not preclude the possibilities of habitat extinction and/or catastrophic community regime shift. Beaches are highly susceptible to human exploitation and global climate change, such as sea level rise. Knowledge of beach macrofaunal diversity along the Texas coast, such as haustoriids, could be used to estimate beach health and better evaluate the upward effects of natural disturbance, pollution and human uses on an integral part of the coastal ecosystem.Item Is Salinity Variability a Benthic Disturbance?(2014-05-07) Van Diggelen, AmandaEstuaries are subjected to variable salinity regimes governed by variable freshwater inflow and tidal regimes. Estuaries are less saline near the river (source of fresh water); salinities increase towards the inlet of the adjacent sea or ocean. Freshwater inflow is a driver to the functioning of estuaries, and average salinity is usually measured to identify the effects of inflow. However, salinity variability could act as a disturbance by producing unstable habitats. The purpose of this research was to determine if salinity variance is an indicator of benthic disturbance, and therefore a driver of community stability. The macrofauna communities of the five most southern estuaries on the Texas coastline were analyzed using a long-term data set. The estuaries lie in a climatic gradient and have different long-term salinity dynamics, thus salinity variance within and between estuaries can be compared. Benthic diversity, evenness, and richness (i.e., total number of species) were calculated and compared to salinity average and salinity variance to determine the efficacy of each diversity measure for determining community changes within and between estuarine systems. Salinity variance, rather than salinity average, was found to be more correlated to benthic diversity for each estuarine system. Freshwater inflow acts as a benthic disturbance both within and between estuaries. As salinity variance decreased (i.e. reduced freshwater inflow) diversity levels of benthic communities increased, while areas with more freshwater inflow displayed lower levels of benthic diversity. These findings advance a general theory of diversity maintenance. When communities are not influenced by persistent stressors, such as salinity variance, multiple stages of succession may occur with more species available to occupy the resulting open niches, thereby increasing diversity.Item Post-fire recovery and successional dynamics of an old growth red spruce forest in the southern Appalachian Mountains(2009-05-15) Krustchinsky, Adam R.Red spruce is a shade-tolerant conifer whose distribution and abundance reflect Quaternary climate history as well as natural and anthropogenic disturbances. This species once extended further south than its present localities, because of natural and anthropogenic disturbances such as logging, windthrow, and fire. Little is known about the disturbance regime of this species, because long term stand dynamics are difficult to obtain. This-long lived species is hypothesized to be suffering a decline in radial growth, density and abundance at the present time. Recent research suggests pollution, biotic stresses, climate change and natural stand dynamics are the driving forces behind these decreases. The purpose of this study is to investigate the influence of fire in a mesic ecosystem, specifically a high-elevation red spruce (Picea rubens Sarg.) forest on Whitetop Mountain in the southern Appalachian Mountains. Six plots were established in a high elevation red spruce stand to characterize the stand composition. Tree ring data were collected to investigate radial growth relations to inter-annual climatic variability and cross-sections were used to investigate fire history. Red spruce continued to establish throughout the 19th century until a severe fire occurred in 1919 and caused a new cohort of yellow birch (Betula alleghaniensis Britt.) to establish within the stand. Logging and fire caused high mortality in the stand, yet many spruce remain that outdate the past disturbances. Red spruce saplings continue to persist in the stand, showing regeneration despite the abundant hardwoods. Moisture was the main contributing factor to red spruce growth in the dendroclimatic analysis. Red spruce radial growth was significantly correlated to high precipitation and low temperatures of the previous growing season, which is similar to recent research results. This study collaborates the current literature on red spruce growth along with the results found here in creating a model to represent the growth characteristics of red spruce when inter-mixed with hardwoods after a severe disturbance.