Identifying the mechanisms that prevent competitive exclusion in tropical forests is a key goal of tropical ecology. Because trees are long-lived organisms, it is complicated to test theory related to coexistence. However, the seedling stage, during which tree mortality is the highest, offers an ideal proxy to evaluate mechanisms that promote or hinder tree species coexistence. This dissertation utilizes both theory and empirical approaches to investigate two mechanisms thought to influence seedling dynamics and tree species coexistence: negative feedbacks from tree natural enemies and positive feedbacks from arbuscular mycorrhizal (AM) fungi. Tree natural enemies might promote tropical tree species coexistence by acting as agents of negative density-dependent mortality. Simultaneously, tropical seedlings associate with arbuscular mycorrhizal (AM) fungi, which can increase seedling growth and survival through enhanced nutrient and water uptake. However, little is known about the effects of AM fungi on tropical tree community dynamics. In chapter 1, I developed a theoretical model that combines competition between trees, predation by tree natural enemies, and mutualism with AM fungi, and showed that a subtle balance between negative and positive feedbacks is required to reach tree species coexistence. In chapters 2 and 3, I used empirical data collected from El Yunque (Puerto Rico) to gain a better understanding of the distribution of soil fungi and tree natural enemies in a secondary tropical forest and to test some of the assumptions of my theoretical model. In chapter 2, I found evidence that soil characteristics and the tree community were important to structure soil fungal communities, and I demonstrated long-lasting effects of past human land use. If AM fungi are important to promote tropical tree species coexistence as suggested by my theoretical model, past land use could influence tree species coexistence by altering AM fungal communities, emphasizing the need for additional studies about land use legacy effects on AM fungal communities. In chapter 3, I showed that seedlings at intermediate conspecific density and from intermediate abundance tree species, hosted the richest community of natural enemies, suggesting that negative density-dependent processes might be non-linear, and partially supporting my theoretical model. Finally in chapter 4, I investigated seedling mortality and showed that natural enemies increase seedling mortality, whereas AM fungal diversity decreases seedling mortality, counteracting the local effects of natural enemies. I also found evidence that AM fungal diversity rescues rare tree species, and natural enemies reduce survivorship of more abundant species, thereby preventing competitive exclusion. Therefore, at the community scale, AM fungal diversity and natural enemies act in the same direction, promoting tropical tree species coexistence, which is consistent with the findings of my theoretical model. In conclusion, this dissertation jointly investigated the effects of negative and positive feedbacks on tropical tree species coexistence, and demonstrated the importance of combining demographic processes that are known to occur simultaneously.

This research focuses on the spatial analysis of the habitat of two vulnerable species, the one-horn rhinoceros in the grasslands of southern Nepal, and the red-cockaded woodpecker in the Piney woods of southeast Texas, in the USA. A study sites relevant for biodiversity conservation was selected in each country: Chitwan National Park in Nepal, and areas near the Big Thicket National Preserve in Texas. Land-use differs in the two study areas: the first is still undergoing agrarian development while the second is in a technological phase and undergoing urbanization processes. Satellite remote sensing images were used to derive land-cover maps by supervised classification. These maps were then processed by Geographic Information Systems methods to apply habitat models based on basic resources (food and cover) and obtain habitat suitability maps. Several landscape metrics were computed to quantify the habitat characteristics especially the composition and configuration of suitable habitat patches. Sensitivity analyses were performed as the nominal values of some of the model parameters were arbitrary. Development potential probability models were used to hypothesize changes in land-use of the second study site. Various scenarios were employed to examine the impact of development on the habitat of red-cockaded woodpecker. The method derived in this study would prove beneficial to guide management and conservation of wildlife habitats.

Call number: LD2668 .T4 1978 B87 / Master of Regional and Community Planning

Prepared by James Silliman, Peter Hazelwood, Arid Lands Information Center.

The need for housing developments in South Africa has grown significantly over that last 12 years. On the one end of the scale there is the desperate need for housing by the homeless and on the other end there is substantial growth of the middleclass indicating better buying power and the explosion of the property market that made investment in housing very attractive. Examples of these two parallel levels of housing are the Sipumulele low cost housing development that is situated in the eThekwini Municipality and was developed by government. On the other side of the scale is the upmarket Koelwaters residential development situated on the South Coast of KwaZulu Natal in the Hibiscus Municipality and was developed by a private developer. In conjunction with this demand for housing there is also international pressure to comply with sustainable develop guidelines and approaches. Both these developments are situated on ecological sensitive land. As legal requirements both these developments were required to do scoping reports to assess their environmental impacts. In South African, Environmental Impact Assessments (EIA) for various new developments has been formally required in terms of Legislation for the last 8 years, although the legislation has been in place for the last 16 years. Is this legislation assisting in securing more sustainable development? It is agued that sustainable development should be founded on ecological justice principles. This research explores the concept of ecological justice and how it is linked with sustainable development. It identifies ecological justice principles that should be used in the compilation and assessment of EIAs. The field research explored how decision makers in practise are using the current legislation and if they are at all considering ecological justice in their decision making. This is done though a serious of interviews with the critical decision makers with regard to EIA's and key role players in the development process of specifically the two above mentioned housing projects. During the interviews qualitative questions were asked relating to the developments, the EIA process and ecological justice. There was a focus on interpreting the awareness of decision makers regarding development and layout and on improving developments to determine to what level they follow ecological justice principles. In the broader sense this research is contributing to the understanding of ecological justice and the clarifications of ecological justice principles. It also contributes to understanding the South African housing development context and the movement of South African Developments towards sustainability. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2006

There is convergence at the international level that conserving biodiversity can contribute to poverty alleviation, but empirical evidence for this relationship is scarce. In this thesis I assess the relationship between poverty and biodiversity, within the context of land use change, using a case-study from the Solomon Islands. This interdisciplinary study is based on both social and ecological data, primarily collected through focus groups, household surveys and avian line transect surveys. Poor households in Kahua were characterised by fewer members of a working age and fewer male members. They were also found to own fewer assets, which were correlated to lower land tenure. Natural resources, including wild foods, were a crucial resource for the consumption and income for poor households, with evidence of wild foods buffering shortfalls in household consumption. The livelihoods of poor households were dependent on natural resources, whereas wealthier households relied on cash crops. The lower involvement of poor households in cash cropping suggests that the poor have less access to such income sources, possibly through a lack of initial land holding assets. Cash crop areas of monoculture cocoa were the most intensive land use in Kahua and were found to be a poor habitat for many bird species, including most endemics. Overall, the relationship between poverty and biodiversity was found to be complex, context dependent and influenced by various social and institutional factors. Household inequalities in access to land and resources indicate that a social-ecological trap may be occurring for poorer households in Kahua, possibly perpetuated by the livelihoods of wealthier households. More research is required in translating the concept of social-ecological traps into management actions, but this thesis concludes that this could be a useful concept for improving poverty alleviation and biodiversity conservation initiatives.

Climate models predict changes to the frequency and intensity of extreme events, with large effects on tropical forests likely. Predicting these impacts requires understanding how landscape configuration and land-use change influence the susceptibility of forests to disturbances such as wind, drought, and fire. This is important because most tropical forests are regenerating from anthropogenic disturbance, and are located in landscape mosaics of forest, agriculture, and other land use. This dissertation consists of four chapters that combine remote sensing and field data to examine causes and consequences of disturbance and land-use change in tropical second-growth forests. In Chapter 1, I use satellite data to identify factors associated with permanence of second-growth forest, and assess how estimates of carbon sequestration vary under different assumptions about second-growth forest permanence. I show that most second-growth forest is cleared when young, limiting carbon sequestration. In Chapter 2, I combine data from weather stations, remote sensing, and landowner surveys to model fire activity on 732 farms in the study area over ten years. The relative importance of these factors differs across scales and depending on the metric of fire activity being considered, illustrating how implications for fire prevention and mitigation can be different depending on the metric considered. Chapter 3 combines Landsat imagery and field data to map wind damage from a severe convective storm, providing strong empirical evidence that vulnerability to wind disturbance is elevated in tropical forest fragments. Finally, in Chapter 4 I integrate annual forest census data with LiDAR-derived topography metrics and tree functional traits in a hierarchical Bayesian modeling framework to explore how drought, topography, and neighborhood crowding affect tree growth, and how functional traits modulate those effects. The results from these studies demonstrate innovative approaches to understanding spatial variation in forest vulnerability to disturbance at multiple scales, and the results have implications for managing forests in a changing climate.

In an effort to protect key environmental assets in the Outer West Region of the eThekwini Municipal area, the Environmental Management Department has embarked on a process to better align environmental concerns into the Consolidated Outer West Town Planning Scheme. The intention is to create sustainable living environments by recognising the importance and value of the environment and its open spaces. Ultimately the research is attempting to understand the difficulties in implementing sustainable development. Sustainable development has been acknowledged at a policy level in the eThekwini Municipality’s Integrated Development Plan; however the translation of sustainable development into implementation is more difficult. Part of the complexity relates to different sectors within the Municipality such as the Environmental Sector and the Economic Sector viewing sustainable development differently. The research focuses on the rapid densification in the Outer West adjacent to environmental resources by private land owners which highlights the lack of understanding by the public on the importance of the environment. Further, the conflicts between the need for economic development and environmental conservation in the context of the Giba Gorge area, show that historical zoning ‘rights’ operate against the protection of bio-diversity. This reinforces the need for better alignment between the environmental protection and land use management. / Thesis (M.T.R.P.)-University of KwaZulu-Natal, Durban, 2008.

The biology of the red-winged blackbird (Agelaius phoeniceus) was studied in relation to variations in agricultural landscapes of southwestern Quebec, eastern Ontario, and southwestern Ontario by examining the relationships between corn (Zea mays) production and population size, distribution of territorial males, and morphology. Dietary studies showed consistent use of corn during their 6-9 month residency in these regions, and during winter months. / A positive correlation was found between independent estimates of the density of males and counts of red-wings obtained from the North American breeding bird survey (BBS). Density of males was a useful indicator of the number of red-wings in an area, whereas the BBS was a useful indicator of change in regional population level. / Historical increases in populations of red-wings in these regions were correlated with increases in waste grain (corn) following harvest. Greater rates of population increase in Quebec (compared with Ontario) corresponded to higher rates of increase in waste corn abundance and landscape heterogeneity. In Quebec, cultivation (mainly corn) was the most important habitat influencing density of males. Wetland and hay field abundance were also important. Heterogeneous landscapes incorporating crops, wetlands and hay fields attracted the most male red-wings regardless of population level, and breeding males preferred wetlands and hay fields for territory establishment. Fields were used in proportion to abundance, whereas forest, crops and areas of human occupation were avoided. At high population density, proportionately more males settled in areas of human occupation and in fields; these habitats were less suitable than wetlands or hay fields. Packing of males into a preferred hay field habitat occurred. / Overwinter mortality did not favor small body size in male red-wings but evidence of stabilizing selection on female body size was found. Sexual dimorphism was slightly more pronounced in spring than in fall. Historical changes in the body size of red-wings were not clearly related to increasing abundance of food (corn). If population size tracks increases in food abundance, then inter-male competition for breeding space may intensity; thus, large size may be limited by energy contraints imposed on males by sexual selection pressure regardless of food availability.

No description available.