The successional dynamics of lightning-initiated canopy gaps in the mangrove forests of Shark River, Everglades National Park, USA

Gap succession is a significant determinant of structure and development in most forest communities. Lightning strikes are an important source of canopy gaps in the mangrove forest of Everglades National Park. I investigated the successional dynamics of lightning-initiated canopy gaps to determine their influence on forest stand structure of the mixed mangrove forests ( Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans ) of the Shark River. I measured gap size, gap shape, light environment, soil characteristics, woody debris, and fiddler crab abundance. I additionally measured the vegetative composition in a chronosequences of gap successional stages (new, recruiting, and growing gaps). I recorded survivorship, recruitment, growth and soil elevation dynamics within a subset of new and growing gaps. I determined the relationship between intact forest soil elevation and site hydrology in order to interpret the effects of lightning disturbance on soil elevation dynamics. ^ Gap size averaged 289 ± 20 m2 (± 1SE) and light transmittance decreased exponentially as gaps filled with saplings. Fine woody debris was highest in recruiting gaps. Soil strength was lower in the gaps than in the forest. The abundance of large and medium fiddler crab burrows increased linearly with total seedling abundance. Soil surface elevation declined in newly formed lightning gaps; this loss was due to a combination of superficial erosion (8.5 mm) and subsidence (60.9 mm). A distinct two-cohort recruitment pattern was evident in the seedling/sapling surveys, suggesting a partitioning of the succession between individuals present before and after lightning strike. In new gaps, the seedling recruitment rate was twice as high as in forest and the sapling population increased. At the growing gap stage, R. mangle seedling mortality was 10 times greater and sapling mortality was 13 times greater than recruitment. Growing gaps had reduced seedling stem elongation, sapling growth and adult growth. However, a few individuals (R. mangle saplings) were able to recruit into the adult life stage. In conclusion, the high density of R. mangle seedlings and saplings imply that lightning strike disturbances in these mangrove forests favor their recruitment over that of A. germinans and L. racemosa. ^

Development of test-based wind-driven rain intrusion model for hurricane-induced building interior and contents damage

Major portion of hurricane-induced economic loss originates from damages to building structures. The damages on building structures are typically grouped into three main categories: exterior, interior, and contents damage. Although the latter two types of damages, in most cases, cause more than 50% of the total loss, little has been done to investigate the physical damage process and unveil the interdependence of interior damage parameters. Building interior and contents damages are mainly due to wind-driven rain (WDR) intrusion through building envelope defects, breaches, and other functional openings. The limitation of research works and subsequent knowledge gaps, are in most part due to the complexity of damage phenomena during hurricanes and lack of established measurement methodologies to quantify rainwater intrusion. This dissertation focuses on devising methodologies for large-scale experimental simulation of tropical cyclone WDR and measurements of rainwater intrusion to acquire benchmark test-based data for the development of hurricane-induced building interior and contents damage model. Target WDR parameters derived from tropical cyclone rainfall data were used to simulate the WDR characteristics at the Wall of Wind (WOW) facility. The proposed WDR simulation methodology presents detailed procedures for selection of type and number of nozzles formulated based on tropical cyclone WDR study. The simulated WDR was later used to experimentally investigate the mechanisms of rainwater deposition/intrusion in buildings. Test-based dataset of two rainwater intrusion parameters that quantify the distribution of direct impinging raindrops and surface runoff rainwater over building surface — rain admittance factor (RAF) and surface runoff coefficient (SRC), respectively —were developed using common shapes of low-rise buildings. The dataset was applied to a newly formulated WDR estimation model to predict the volume of rainwater ingress through envelope openings such as wall and roof deck breaches and window sill cracks. The validation of the new model using experimental data indicated reasonable estimation of rainwater ingress through envelope defects and breaches during tropical cyclones. The WDR estimation model and experimental dataset of WDR parameters developed in this dissertation work can be used to enhance the prediction capabilities of existing interior damage models such as the Florida Public Hurricane Loss Model (FPHLM).^

Ethnic and American identity development: A developmental systems approach

Given the role ethnic identity has as a protective factor against the effects of marginalization and discrimination (Umaña-Taylor, 2011), research longitudinally examining ethnic identity has become of increased importance. However, successful identity development must incorporate elements from both one's ethnic group and from the United States (Berry, 1980). Despite this, relatively few studies have jointly evaluated ethnic and American identity (Schwartz et al., 2012). The current dissertation, guided by three objectives, sought to address this and several other gaps in the literature. First, psychometric properties of the Multigroup Ethnic Identity Measure (MEIM) and the American Identity Measure (AIM) were evaluated. Secondly, the dissertation examined growth trends in recently immigrated Hispanic adolescents' and their caregivers' ethnic and American identity. Lastly, the relationship between adolescents' and caregivers' ethnic and American identity was evaluated. The study used an archival sample consisting of 301 recently immigrated Hispanic families collected from Miami (N = 151) and Los Angeles (N = 150). Consistent with previous research, results in Study 1 indicated a two-factor model reliably provided better fit than a one-factor model and established longitudinal invariance for the MEIM and the AIM. Results from Study 2 found significant growth in adolescents' American identity. While some differences were found across site and nationality, evidence suggested recently immigrated Hispanic adolescents were becoming more bicultural. Counterintuitively, results found a significant decline in caregivers' ethnic identity which future studies should further examine. Finally, results from Study 3, found several significant positive relationships between adolescents' and their caregivers' ethnic and American identity. Findings provided preliminary evidence for the importance of examining identity development within a systemic lens. Despite several limitations, these three studies represented a step forward in addressing the current gaps in the cultural identity literature. Implications for future investigation are discussed.