The United States has arbitrary weather criteria for a prescribed burn day to happen. This arbitrary criteria gives prescribed-burn managers a limited amount of days they can burn. To solve this, I established a 30-year climatology based on daily mixing height (m). I then calculated burn-day thresholds based on different mixing heights. I found seasonal and spatial patterns of the amount of days that are prescribed burns. Southeastern United States was my study area. A small decrease in threshold values will lead to large increases in prescribed burn days. Digital maps were created to show the spatial variability of prescribed burn days and the effects of lowering thresholds for prescribed burn days. This research will aid policy makers in lessening the criteria for burn days.

Prescribed burning is a commonly used wildlife management tool. While most of the available data have evaluated short term effects of fire on wildlife (< 3 years), the present study addresses longer term effects (0 to 7 years). This enables a more thorough investigation of fire management affects on herpetofaunal communities at the landscape level. Ten sites, stratified by 0 to 7 years post-burn, were randomly selected on Big Oaks National Wildlife Refuge in southeastern Indiana and monitored for 2 field seasons. Within each site, several trapping methods were utilized including a sampling array of drift fences, pitfall traps, single and double ended funnel traps, PVC pipes, and cover boards. Burning caused immediate stand level effects and changed vegetation characteristics, which affected the species assemblages of herpetofauna and small mammals. Data collected identified the spatial and temporal variables that explained the patterns of occurrence and abundance of herpetofaunal species and small mammal species, and how community vegetation characteristics such as structure, resource availability, and plant species assemblages, correlated with and affected those patterns. Burn regimes of 2-5 years were found to be optimal when managing herpetofauna and small mammals. Constrictor coluber priapus and Peromyscus leucopus were captured frequently in the study area and the effects of a properly timed prescribed burn could have positive effects on the numbers of generalist species. Akaike information criterion was used to determine the habitat variables that were most important in habitat selection of the herpetofaunal and small mammal classes and species. While this study was limited to one wildlife refuge, in the central hardwoods its findings may have ramifications for herpetofauna in other areas where prescribed fire can be used as a management tool.

<p><b></b>Passive acoustic monitoring (PAM) is a tool with immense potential to evaluate the response of wildlife to ecosystem disturbances. PAM allows to evaluate wildlife dynamics by means of acoustic indices that estimate the diversity or complexity of sounds in a recording, as well as to study ecological aspects at the species level by training machine learning-based automatic acoustic detector. In this study, five deep learning approaches for automatic song detection were evaluated of the near-threatened Bachman's Sparrow in data scarcity scenarios, and then used this classifier to study the response of this bird to the number of days following a prescribed burn in six subtropical habitats in central Florida. At the same time, the response of avifauna acoustic activity to prescribed burning was quantified by means of three of the most used acoustic indices used in the literature (Acoustic Complexity Index, Acoustic Diversity Index and Bioacoustic Index). I found that it is possible to construct competitive birdsong detectors with small datasets using pre-trained models regardless. Furthermore, the use of data augmentation can lead to a detriment of the detector performance, especially of lower quality recordings, and that increasing the dataset does not necessarily increase the generalizability of the model. On the other hand, I found that unlike Acoustic Diversity Index, the Bioacoustic and Acoustic Complexity indices are negatively correlated with time after a burn, the same trend that Bachman's Sparrow presence showed, even though it was more influenced by habitat type than by the effect of the prescribed burns. This study shows the potential of tools including automatic song detection and acoustic indices to model at different scales the dynamics of avifauna in response to ecosystem disturbances. Their development can provide efficient tools for the study and conservation of both threatened wildlife species and the ecosystems they inhabit.</p>

A new one-dimensional heat conduction model for predicting stem heating during fires is presented. The model makes use of moisture and temperature dependent thermal properties for bark and wood. Also, the thermal aspects of the processes of bark swelling, desiccation, and devolatilization are treated in an approximate fashion. Simulation with a surface flux boundary condition requires that these phenomena be accounted for. Previous models have used temperature-time boundary conditions, which prevents them from being directly coupled to fire behavior models. This model uses a flux-time profile for its boundary condition, making it possible to eventually couple it to fire behavior models. Cambial mortality predictions are made through the incorporation of a cell mortality model. The model was developed and validated with laboratory experiments on four species.

This thesis includes two studies: The first examined developmental changes that take place in the physiology of aspen (Populus tremuloides Michx.) and to characterize developmental influences on patterns of phenotypic trait variation among different aged ramets within the aspen clones. We surveyed eight clones, each with 8 distinct age classes ranging from 1 to 170 yrs in age. Using regression analysis we examined the relationships between ramet age and expression of functional phenotypes. Eight of the phenotypic traits demonstrated a non-linear relationship in which large changes in phenotype occurred in the early stages of ramet development and stabilized thereafter. Water and nutrient concentration, leaf gas exchange and phenolic glycosides tended to decrease from early to late development, while sucrose and condensed tannin concentrations and water use efficiency increased with ramet age. We hypothesize that ontogenetically derived phenotypic variation leads to fitness differentials among different aged ramets, which may have important implications for clone fitness. Age-related increases in phenotypic diversity may partially underlie aspen's ability as a species to tolerate the large environmental gradients that span its broad geographical range. Fire is an essential component of many forest ecosystems and fire exclusion policies and other anthropogenic factors have significantly altered disturbance regimes, which has lead to increased aspen succession to conifers. The second study examined how post-fire aspen regeneration success is influenced by increasing conifer abundance under longer fire return intervals. 66 sites were selected from the Sanford prescribed fire complex located in the Dixie National Forest. Slope, aspect, sucker regeneration heights, soil samples, and post and prefire stand densities were measured. Results from this study demonstrated that pre-disturbance conifer abundance and aspen densities are good predictors of aspen sucker regeneration success. Results also found that although conifer densities don't change across aspects, aspen densities are different on north facing slopes. We hypothesize the high levels of aspen regeneration came from a large disturbance size which overwhelmed the high levels of herbivores.

In Valencia region (SE Spain), many post-fire communities are dominated by non-resprouting (seeder) species, because of the long history of land exploitation and subsequent abandonment during the last half of 20th century. These communities accumulate fine dry biomass and, therefore, can burn again easily. In fact, Mediterranean forests are suffering from an increase in wildfire frequency since the early 1970s. Wildfires shape the composition and functioning of Mediterranean ecosystems, but we do not know how these ecosystems respond to both the higher fire recurrence and shorter recovery times expected for future climatic scenarios. In this sense, Aleppo pine forest (Pinus halepensis) is one of the most fire affected vegetation of this type in the Mediterranean Basin and to know how it respond to fire is fundamental to design management plans. After fire, regeneration of this forest can be highly variable, and it can go from extremely dense tree stands (overstocked pine) to treeless shrublands dominated by seeder species. All these regenerated stands are fire prone with limited ability to deliver multiple ecosystem services. Although several management techniques are applied to redirect these post-fire ecosystems towards less vulnerable and more functional communities, we do not know yet which amongst them could serve to foster more diverse and multifunctional landscapes. Therefore, the general objective of this thesis is to investigate the functioning of these Mediterranean ecosystems as consequence of shifts in fire regime and forest management application, using different techniques, in different post-fire regenerated ecosystems (overstocked pine forests and dense shrublands). To do so, we calculate, within Mediterranean Pinus halepensis forests affected by wildfires, the supply of multiple ecosystem services (biodiversity conservation, carbon sequestration, disturbance regulation, food production, supporting services, and multifunctionality), through up to 25 aboveground and belowground attributes. Our main findings are (1) High fire recurrence and time since last fire interacted to determine ecosystem services but did not affect their synergies and trade-offs between them. Their combined effects reduced carbon sequestration and multifunctionality. Disturbance regulation diminished drastically with the first fire, with no effect of further fires. However, their effects dampened, and even became positive, for biodiversity conservation and food production services if provided enough time to recover. (2) Thinning in overstocked pine stands enhances ecosystem attributes associated with biodiversity conservation without compromising the provision of carbon sequestration. After 10 years, two levels of thinning, (600 and 1200 trees·ha-1), similarly affected ecosystem attributes, which suggest that 1200 trees·ha-1 suffice to enhance individual ecosystem attributes. (3) Clearing within dense shrubland dominated by seeder species enhances ecosystem attributes associated with biodiversity conservation without compromising the capacity of ecosystem to sequester carbon. (4) Plantation of resprouting species combined with thinning and clearing, in overstocked pine forests and dense shrublands respectively, can enhance the provision of ecosystem services of disturbance regulation, food production and ecosystem multifunctionality. (5) Prescribed burning reduces the amount of dead fuel, increases biodiversity conservation, and improves food production. However, these effects become negative, in addition to the decline in disturbance regulation and multifunctionality, if prescribed burning is applied frequently. (6) Combining different management activities can enhance the supply of multiple ecosystem services simultaneously by reducing the trade-offs in between them and therefore, establish multifunctional Mediterranean landscapes.