The Interaction of Fire Refugia and Climate Refugia: A Case Study within California’s Diablo Mountain Range

As climate change contributes to larger and more severe wildfires in California, areas of fire refugia – considered unburned and low-severity burn patches – are playing an increasingly important role in sustaining ecosystem resilience, maintaining biodiversity, and supporting post-disturbance recovery. At the same time, climate refugia – which are areas less impacted by climate change than the surrounding landscape – provide relatively stable habitats for at-risk species, as climate conditions around them continue to shift. Understanding where and why fire refugia and climate refugia occur and overlap as “super-refugia” are important for conservation and adaptation management. The diverse topography, high biodiversity, and frequent fire activity of California’s inland coastal mountain ranges offer an ideal location to study the interactions of fire refugia and climate refugia on the landscape. I took advantage of the 2020 SCU Lightning Complex Fire that occurred in California’s inland coastal Diablo Mountain range as an opportunistic case study. The primary objectives were to: (1) develop an understanding of the spatial patterns and mechanisms for the formation of fire refugia, (2) develop a simple, but novel index for the identification of high potential areas of climate refugia, and (3) develop an understanding of the spatial patterns and mechanisms for overlapping fire refugia and high-potential climate refugia as locations of super-refugia. For objective (1) I used a gradient-boosted machine learning model and focused on the biophysical factors that influenced the patterns of burn severity in wooded and forested areas, which comprised 79.9% of the study area landscape. For objective (2) I developed a data-derived synthetic index of climate refugia locations within the fire’s burn perimeter. For objective (3) I focused on the biophysical factors that influenced the formation of super-refugia, and mapped potential locations on the landscape where super-refugia may occur. Fire refugia were identified in 14.9% of the wooded and forested portion of the study area, with two daily fire weather indices (maximum temperatures and energy release component) identified as the most important factors associated with the occurrence of fire refugia; topographic and vegetation variables also contributed high explanatory power in the model. Pixels identified as high potential climate refugia – based on low levels of solar radiation, the presence of fire refugia, the availability of microclimates, relatively higher surface moisture, the presence of protected areas, and areas of high canopy cover – comprised 8.6% of the study area. Pixels identified as super-refugia covered 3.5% of the study area, with the topographic solar radiation index, and heat load index, identified as having the highest association with super-refugia occurrence. A detailed visual map analysis showed that valley bottoms, riparian areas, rugged terrain and north-aspect slopes had the highest proportion of super-refugia across the study area. My results illustrate that areas with low levels of insolation, high surface moisture, and diverse topography may be important conservation sites as both fire refugia and climate refugia. The integration of fire refugia and climate refugia metrics into land management planning may provide useful tools for fire risk mitigation, conservation, restoration, and other land-management decisions

Evaluating desiccated cyanobacteria Aphanizomenon flos-aquae for use as a biofertilizer on Swiss Chard

Non-toxic species of desiccated blue-green algae, or cyanobacteria, may offer potential for use as a fertilizer on irrigated crops. Here, the non-toxic cyanobacteria species Aphanizomenon flos-aquae (AFA), collected from Upper Klamath Lake, Oregon, was evaluated for use as a biofertilizer in a controlled experiment on Swiss chard “Bright Lights” (Beta vulgaris L. ssp. cicla L.). Two comparison groups were used in the study: group 1, fertilized with a commercially available synthetic fertilizer, and group 2, an unfertilized control. All plants were grown from seeds. With the exception of average root growth, the results found that both the synthetically fertilized and algae fertilized plants produced significantly higher growth rates than the unfertilized control group. These findings are consistent with other studies showing positive outcomes using live cyanobacteria in various cropping systems

Self-assembly and entropic effects in pear-shaped colloid systems. II. Depletion attraction of pear-shaped particles in a hard-sphere solvent

We consider depletion effects of a pear-shaped colloidal particle in a hard-sphere solvent for two different model realizations of the pear-shaped colloidal particle. The two models are the pear hard Gaussian overlap (PHGO) particles and the hard pears of revolution (HPR). The motivation for this study is to provide a microscopic understanding for the substantially different mesoscopic self-assembly properties of these pear-shaped colloids, in dense suspensions, that have been reported in the previous studies. This is done by determining their differing depletion attractions via Monte Carlo simulations of PHGO and HPR particles in a pool of hard spheres and comparing them with excluded volume calculations of numerically obtained ideal configurations on the microscopic level. While the HPR model behaves as predicted by the analysis of excluded volumes, the PHGO model showcases a preference for splay between neighboring particles, which can be attributed to the special non-additive characteristics of the PHGO contact function. Lastly, we propose a potentially experimentally realizable pear-shaped particle model, the non-additive hard pear of revolution model, which is based on the HPR model but also features non-additive traits similar to those of PHGO particles to mimic their depletion behavior

Self-assembly and entropic effects in pear-shaped colloid systems. I. Shape sensitivity of bilayer phases in colloidal pear-shaped particle systems

The role of particle shape in self-assembly processes is a double-edged sword. On the one hand, particle shape and particle elongation are often considered the most fundamental determinants of soft matter structure formation. On the other hand, structure formation is often highly sensitive to details of shape. Here, we address the question of particle shape sensitivity for the self-assembly of hard pear-shaped particles by studying two models for this system: (a) the pear hard Gaussian overlap (PHGO) and (b) the hard pears of revolution (HPR) model. Hard pear-shaped particles, given by the PHGO model, are known to form a bicontinuous gyroid phase spontaneously. However, this model does not replicate an additive object perfectly and, hence, varies slightly in shape from a “true” pear-shape. Therefore, we investigate in the first part of this series the stability of the gyroid phase in pear-shaped particle systems. We show, based on the HPR phase diagram, that the gyroid phase does not form in pears with such a “true” hard pear-shaped potential. Moreover, we acquire first indications from the HPR and PHGO pair-correlation functions that the formation of the gyroid is probably attributed to the small non-additive properties of the PHGO potential

Purely entropic self-assembly of the bicontinuous Ia3̅d gyroid phase in equilibrium hard-pear systems

We investigate a model of hard pear-shaped particles which forms the bicontinuous Ia3d structure by entropic self-assembly, extending the previous observations of Barmes et al. (2003 Phys. Rev. E 68, 021708. (doi:10.1103/PhysRevE.68.021708)) and Ellison et al. (2006 Phys. Rev. Lett. 97, 237801. (doi:10.1103/PhysRevLett.97.237801)). We specifically provide the complete phase diagram of this system, with global density and particle shape as the two variable parameters, incorporating the gyroid phase as well as disordered isotropic, smectic and nematic phases. The phase diagram is obtained by two methods, one being a compression–decompression study and the other being a continuous change of the particle shape parameter at constant density. Additionally, we probe the mechanism by which interdigitating sheets of pears in these systems create surfaces with negative Gauss curvature, which is needed to form the gyroid minimal surface. This is achieved by the use of Voronoi tessellation, whereby both the shape and volume of Voronoi cells can be assessed in regard to the local Gauss curvature of the gyroid minimal surface. Through this, we show that the mechanisms prevalent in this entropy-driven system differ from those found in systems which form gyroid structures in nature (lipid bilayers) and from synthesized materials (di-block copolymers) and where the formation of the gyroid is enthalpically driven. We further argue that the gyroid phase formed in these systems is a realization of a modulated splay-bend phase in which the conventional nematic has been predicted to be destabilized at the mesoscale due to molecular-scale coupling of polar and orientational degrees of freedo

Self-assembly and entropic effects in pear-shaped colloid systems. II. Depletion attraction of pear-shaped particles in a hard-sphere solvent

We consider depletion effects of a pear-shaped colloidal particle in a hard-sphere solvent for two different model realizations of the pear-shaped colloidal particle. The two models are the pear hard Gaussian overlap (PHGO) particles and the hard pears of revolution (HPR). The motivation for this study is to provide a microscopic understanding for the substantially different mesoscopic self-assembly properties of these pear-shaped colloids, in dense suspensions, that have been reported in the previous studies. This is done by determining their differing depletion attractions via Monte Carlo simulations of PHGO and HPR particles in a pool of hard spheres and comparing them with excluded volume calculations of numerically obtained ideal configurations on the microscopic level. While the HPR model behaves as predicted by the analysis of excluded volumes, the PHGO model showcases a preference for splay between neighboring particles, which can be attributed to the special non-additive characteristics of the PHGO contact function. Lastly, we propose a potentially experimentally realizable pear-shaped particle model, the non-additive hard pear of revolution model, which is based on the HPR model but also features non-additive traits similar to those of PHGO particles to mimic their depletion behavior.The authors thank Universities Australia and the German Academic Exchange Service (DAAD) for funds through a collaboration funding scheme, through the grant “Absorption and confinement of complex fluids.” They also thank the DFG through Grant No. ME1361/11-2 and through the research group “Geometry and Physics of Spatial Random Systems” (GPSRS) for funding. They gratefully acknowledge Klaus Mecke’s support and advice in useful discussions. P.W.A.S. acknowledges a Murdoch University Postgraduate Research Scholarship. G.E.S.-T. is grateful to the Food Science Department at the University of Copenhagen and the Physical Chemistry group at Lund University for their hospitality and to Copenhagen University, the Camurus Lipid Research Foundation, and the Danish National Bank for enabling a sabbatical stay in Denmark and Sweden

Self-assembly and entropic effects in pear-shaped colloid systems. I. Shape sensitivity of bilayer phases in colloidal pear-shaped particle systems

The role of particle shape in self-assembly processes is a double-edged sword. On the one hand, particle shape and particle elongation are often considered the most fundamental determinants of soft matter structure formation. On the other hand, structure formation is often highly sensitive to details of shape. Here, we address the question of particle shape sensitivity for the self-assembly of hard pear-shaped particles by studying two models for this system: (a) the pear hard Gaussian overlap (PHGO) and (b) the hard pears of revolution (HPR) model. Hard pear-shaped particles, given by the PHGO model, are known to form a bicontinuous gyroid phase spontaneously. However, this model does not replicate an additive object perfectly and, hence, varies slightly in shape from a "true" pear-shape. Therefore, we investigate in the first part of this series the stability of the gyroid phase in pear-shaped particle systems. We show, based on the HPR phase diagram, that the gyroid phase does not form in pears with such a "true" hard pear-shaped potential. Moreover, we acquire first indications from the HPR and PHGO pair-correlation functions that the formation of the gyroid is probably attributed to the small non-additive properties of the PHGO potential.We thank Universities Australia and the German Academic Exchange Service (DAAD) for funds through a collaboration funding scheme and through the grant “Absorption and confinement of complex fluids.” We also thank the DFG (Grant No. ME1361/11-2) and the research group “Geometry and Physics of Spatial Random Systems” (GPSRS) for funding. We gratefully acknowledge Klaus Mecke’s support and advice in useful discussions. P.W.A.S. acknowledges a Murdoch University Postgraduate Research Scholarship. G.E.S.-T. is grateful to the Food Science Department at the University of Copenhagen and the Physical Chemistry group at Lund University for their hospitality and to Copenhagen University, the Camurus Lipid Research Foundation, and the Danish National Bank for enabling a sabbatical stay in Denmark and Sweden

Temperature, Pressure, and Infrared Image Survey of an Axisymmetric Heated Exhaust Plume

The focus of this research is to numerically predict an infrared image of a jet engine exhaust plume, given field variables such as temperature, pressure, and exhaust plume constituents as a function of spatial position within the plume, and to compare this predicted image directly with measured data. This work is motivated by the need to validate computational fluid dynamic (CFD) codes through infrared imaging. The technique of reducing the three-dimensional field variable domain to a two-dimensional infrared image invokes the use of an inverse Monte Carlo ray trace algorithm and an infrared band model for exhaust gases. This report describes an experiment in which the above-mentioned field variables were carefully measured. Results from this experiment, namely tables of measured temperature and pressure data, as well as measured infrared images, are given. The inverse Monte Carlo ray trace technique is described. Finally, experimentally obtained infrared images are directly compared to infrared images predicted from the measured field variables