Vegetation:environment relationships and water management in Shark Slough, Everglades National Park

The hydrologic regime of Shark Slough, the most extensive long hydroperiod marsh in Everglades National Park, is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. In this paper, we use data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. Analysis of vegetation:environment relationships yielded estimates of both mean and variance in soil depth, as well as annual hydroperiod, mean water depth, and 30-day maximum water depth within each cover type during the 1990’s. We found that rank abundances of the three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) were identical in all portions of Shark Slough, but regional trends in the relative abundance of individual communities were present. Analysis also indicated clear and consistent differences in the hydrologic regime of three marsh cover types, with hydroperiod and water depths increasing in the order Tall Sawgrass , Sparse Sawgrass , Spikerush Marsh. In contrast, soil depth decreased in the same order. Locally, these differences were quite subtle; within a management unit of Shark Slough, mean annual values for the two water depth parameters varied less than 15 cm among types, and hydroperiods varied by 65 days or less. More significantly, regional variation in hydrology equaled or exceeded the variation attributable to cover type within a small area. For instance, estimated hydroperiods for Tall Sawgrass in Northern Shark Slough were longer than for Spikerush Marsh in any of the other regions. Although some of this regional variation may reflect a natural gradient within the Slough, a large proportion is the result of compartmentalization due to current water management practices within the marsh.We conclude that hydroperiod or water depth are the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades.

Ecological indicators for assessing and communicating seagrass status and trends in Florida Bay

A suite of seagrass indicator metrics is developed to evaluate four essential measures of seagrass community status for Florida Bay. The measures are based on several years of monitoring data using the Braun-Blanquet Cover Abundance (BBCA) scale to derive information about seagrass spatial extent, abundance, species diversity and presence of target species. As ecosystem restoration proceeds in south Florida, additional freshwater will be discharged to Florida Bay as a means to restore the bay's hydrology and salinity regime. Primary hypotheses about restoring ecological function of the keystone seagrass community are based on the premise that hydrologic restoration will increase environmental variability and reduce hypersalinity. This will create greater niche space and permit multiple seagrass species to co-exist while maintaining good environmental conditions for Thalassia testudinum, the dominant climax seagrass species. Greater species diversity is considered beneficial to habitat for desired higher trophic level species such as forage fish and shrimp. It is also important to maintenance of a viable seagrass community that will avoid die-off events observed in the past. Indicator metrics are assigned values at the basin spatial scale and are aggregated to five larger zones. Three index metrics are derived by combining the four indicators through logic gates at the zone spatial scale and aggregated to derive a single bay-wide system status score standardized on the System-wide Indicator protocol. The indicators will provide a way to assess progress toward restoration goals or reveal areas of concern. Reporting for each indicator, index and overall system status score is presented in a red–yellow–green format that summarizes information in a readily accessible form for mangers, policy-makers and stakeholders in planning and implementing an adaptive management strategy.

Examining the process of regime change in the North Atlantic Treaty Organization: The divide between rhetoric and reality

The North Atlantic Treaty Organization (NATO) is a product of the Cold War through which its members organized their military forces for the purpose of collective defense against the common threat of Soviet-backed aggression. Employing the terminology of regime theory, the creation of NATO can be viewed as the introduction of an international security regime. Throughout the Cold War, NATO member states preserved their commitment to mutual defense while increasingly engaging in activities aimed at overcoming the division of Europe and promoting regional stability. The end of the Cold War has served as the catalyst for a new period of regime change as the Alliance introduced elements of a collective security regime by expanding its mandate to address new security challenges and reorganizing both its political and military organizational structures. ^ This research involves an interpretive analysis of NATO's evolution applying ideal theoretical constructs associated with distinct approaches to regime analysis. The process of regime change is investigated over several periods throughout the history of the Alliance in an effort to understand the Alliance's changing commitment to collective security. This research involves a review of regime theory literature, consisting of an examination of primary source documentation, including official documents and treaties, as well as a review of numerous secondary sources. This review is organized around a typology of power-based, organization-based, and norm-based approaches to regime analysis. This dissertation argues that the process of regime change within NATO is best understood by examining factors associated with multiple theoretical constructs. Relevant factors provide insights into the practice of collective security among NATO member states within Europe, while accounting for the inability of the NATO allies to build on the experience gained within Europe to play a more central role in operations outside of this region. This research contributes to a greater understanding of the nature of international regimes and the process of regime change, while offering recommendations aimed at increasing NATO's viability as a source of greater security and more meaningful international cooperation.^

Disturbance regime and limits on benefits of refuge use for fishes in a fluctuating hydroscape

Refuge habitats increase survival rate and recovery time of populations experiencing environmental disturbance, but limits on the ability of refuges to buffer communities are poorly understood. We hypothesized that importance of refuges in preventing population declines and alteration in community structure has a non-linear relationship with severity of disturbance. In the Florida Everglades, alligator ponds are used as refuge habitat by fishes during seasonal drying of marsh habitats. Using an 11-year record of hydrological conditions and fish abundance in 10 marshes and 34 alligator ponds from two regions of the Everglades, we sought to characterize patterns of refuge use and temporal dynamics of fish abundance and community structure across changing intensity, duration, and frequency of drought disturbance. Abundance in alligator ponds was positively related to refuge size, distance from alternative refugia (e.g. canals), and abundance in surrounding marsh prior to hydrologic disturbance. Variables negatively related to abundance in alligator ponds included water level in surrounding marsh and abundance of disturbance-tolerant species. Refuge community structure did not differ between regions because the same subset of species in both regions used alligator ponds during droughts. When time between disturbances was short, fish abundance declined in marshes, and in the region with the most spatially extensive pattern of disturbance, community structure was altered in both marshes and alligator ponds because of an increased proportion of species more resistant to disturbance. These changes in community structure were associated with increases in both duration and frequency of hydrologic disturbance. Use of refuge habitat had a modal relationship with severity of disturbance regime. Spatial patterns of response suggest that decline in refuge use was because of decreased effectiveness of refuge habitat in reducing mortality and providing sufficient time for recovery for fish communities experiencing reduced time between disturbance events.