Fire is an important disturbance mechanism in big sagebrush (Artemisia tridentata) communities, yet little is known about wildlife population dynamics during post-fire habitat succession. I estimated the abundance of small mammals and birds in relation to fire history in mountain big sagebrush (A.t. spp. vaseyana) communities on the Sheldon National Wildlife Refuge in the northwestern Great Basin, USA. I employed a chronosequence approach that took advantage of multiple wildfires that had occurred in similar plant communities between 7 to 20 years prior to sampling. Belding’s ground squirrel (Spermophilus beldingii) were approximately 10 times as abundant in burned areas relative to adjacent unburned habitat regardless of the number of years since a burn occurred. Deer mouse (Peromyscus maniculatus) was more abundant on more recently burned sites, but not at sites closer to full vegetation recovery. Great basin pocket mouse (Perognathus parvus), sagebrush vole (Lemmiscus curtatus), and least chipmunk (Tamius minimus) abundance did not vary as a function of fire history, but some variance was explained by habitat features such as rocky areas and the canopy characteristics of sagebrush. Bird diversity was higher in unburned habitats irrespective of the number of years of recovery out to 20 years. Nine of the 12 most widely occurring species of birds in the study have population densities influenced by fire or post-fire habitat succession to at least 13 to 20 years following a burn. Sage Sparrow (Amphispiza belli), Black-throated Sparrow (Amphispiza bilineata), and Spotted Towhee (Pipilo maculatus) occurred at relatively low densities and were nearly restricted to unburned habitats. Green-tailed Towhee (Pipilo Chlorurus), Gray Flycatcher (Empidonax wrightii), American Robin (Turdus migratorius), and Brown-headed Cowbird (Molothus ater) occurred at lower densities in burned areas than adjacent unburned areas although the relationship was not strong for the latter two species. The magnitude of the difference in density between burned and unburned sites within a landscape diminished with the number of years of vegetation recovery for Green-tailed Towhee. Brewer’s Sparrow (Spizella brewerii) occurred at lower densities relative to adjacent habitat in the most recent burn, but occurred at higher densities after 20 years of habitat succession, suggesting a positive response with a multiple decade lag period. Horned Lark (Eremophila alpestris) and Vesper Sparrow (Pooecetes gramineus) respond positively to fire, but densities were similar to unburned areas after 20 years of habitat succession. An ordination analysis captured 86% of the variation in 12 bird species with 3 orthogonal axes. My research demonstrates that strong community structure exists for birds associated with mountain big sagebrush habitats, and that fire influences community structure for multiple decades. / Graduation date: 2011 / Access restricted to the OSU Community at author's request from Dec. 22, 2010 - Dec. 22, 2011.

Heathlands typically experience regimes consisting of frequent and intense fires. These fire regimes play important roles in the lifecycles and population dynamics of all species in these communities. Prescribed fire is commonly applied to heathlands to minimise the risk of wildfires as well as to promote biodiversity. Ignitions in heathlands tend to either be unsustainable, or quickly develop into rapidly spreading intense fires. This presents a major problem for the application of prescribed fire and is the primary focus of this thesis. Heathland ignition has been investigated in three sections; litter ignition; vertical development of fire into the shrub layer; and horizontal spread through the shrub layer. These were studied in laboratory experiments using miniature versions of field fuels. Ignition success in litter layers was related to the dead fuel moisture content. Litter type, ignition source, and presence of wind were found to affect the range of ignitable fuel moisture contents of a litter bed. The effect of litter type was best explained by density. Dense litter beds required drier conditions for ignition than low density litter beds. The vertical development of fire into shrubs was mostly dependent on live fuel moisture content, but crown base height, presence of wind, ignition source, shrub height and the percentage of dead elevated fuel were also important. Horizontal spread of fires through shrub layers was most affected by the presence of a litter layer, with nearly all ignitions successful when there was an underlying litter fire. Fire spread would only occur in shrubs without a litter layer when the shrub layer was dense and dry, or had a substantial dead fuel component. Spread was more likely to be sustained when there was wind. Models predicting the moisture content of dead fuels were tested in heathlands, and as would be expected those that can be calibrated for different fuel types were found to have the best performance. Fuel moisture content and fuel load models were reviewed for heathlands, and a number of recommendations for future research were made.

[Truncated abstract] Recovery of soil nutrients, microbial populations and carbon (C) and nitrogen (N) cycling processes are critical to the success of rehabilitation following major ecosystem disturbance. Bauxite mining represents a major ecosystem disturbance to the jarrah (Eucalyptus marginata) forest in the south-west of Western Australia. Mining has created a mosaic of mined areas in various stages of succession surrounded by non-mined forest areas. Initial site preparations within rehabilitation areas such as contour ripping alter soil structure (creation of mound and furrows) and over time also influence the distribution of vegetation and litter. Current performance criteria developed by industry, government and other stakeholders have determined that before post-bauxite mined areas of jarrah forest can be integrated back into normal forest management practises they should be functional and demonstrate resilience to normal forest disturbances such as fire. Furthermore, resilience should be of a manner comparable to non-mined analogue forest sites. Currently little is known of the resilience of microbial communities and C and N cycling in rehabilitation sites to normal forest disturbances such as prescription burning. As such, before rehabilitated jarrah forests can be successfully integrated into broad scale forest management regimes, a more thorough knowledge of the potential impacts of burning practises on the soil microbial community and C and N cycling processes in these systems is required. ... While there are similar rates of C and N cycling the underlying microbial community structure was distinctly different; implying a high degree of functional redundancy with respect to C and N cycling. Differences in the C and N cycling and structure of the microbial communities were likely to be due to differences in soil environmental conditions (i.e. soil alkalinity/acidity, soil moisture) and C substrate availability which influence the physiological status of the microbial community and in turn are related to successional age of the forests. Results also suggest that the measurement of CLPP can be a useful approach for assessment of changes in the functional ability of microbial communities. However, the interpretation of how well these rehabilitation forests have recovered heterotrophic abilities was greatly affected by the methodological approach used (e.g. MicroRespTM or Degens and Harris, 1997). Importantly, results from Chapter 4 and 5 suggested that the effects of a moderate prescription fire on C and N processes, CLPP and microbial community structure of 18 year old rehabilitation forests are likely to be short-lived (< 2 years). Furthermore, the effects of the moderate spring prescription fire were not large enough to decouple C and N cycling processes over the short-term (< 1 years) which suggests that by 18 years of age rehabilitation forests demonstrate comparable functional resilience to a moderate prescription burn.

Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2007. / The Agulhas Plain, an area rich in fynbos, was monitored within six months after the February 2006 fire. The potential of using medium resolution imagery, specifically from the Moderate Resolution Imaging Spectroradiometer (MODIS) in determining the re-growth rates of indigenous and alien vegetation types after fire was explored. Pixels representing dense areas of each vegetation type were selected. There was a significant difference in the pixels selected for each vegetation type. A time series of Normalized Difference Vegetation Index (NDVI) data was derived and fitted to functions, such as Double Logistics and Asymmetric Gaussian as implemented in the TIMESAT software. The results show that alien vegetation grows faster after a fire occurrence than in its absence. Within the specified months of monitoring, it was observed that fynbos grew faster than the alien vegetation. Also, the re-growth rates of vegetation on the coastal soils were higher than those of vegetation on the inland soils. The determination of the re-growth rate was necessary to assist resource managers determine the appropriate time for follow-up of clearing invaded sites after fire.

L'équilibre arbre-herbe dans la savane tropicale est reconnu comme l'une des principales<p>énigmes de l'écologie des plantes. Les origines du difficile équilibre entre ces formes de vie<p>sur des dizaines de millions de kilomètres carrés à l'échelle mondiale sont en partie attribuées<p>aux perturbations fréquentes induites par les feux de végétation dont les effets varient dans<p>l'espace et dans le temps selon les conditions environnementales. Les résultats de recherche<p>dépendent de l’échelle et les conclusions tirées d’études locales sont rarement transposables à<p>d’autres échelles. La question du transfert d'échelle s’avère donc cruciale dans l'étude des<p>effets du feu, et nécessite une approche transdisciplinaire.<p>En raison de la variété des échelles couvertes, cette étude constitue une première dans la<p>confrontation de données sur l’historique des feux dérivé de l'imagerie satellitaire à des<p>données de terrain incluant des mesures détaillées sur la structure et la composition de<p>végétation, ainsi que des propriétés édaphiques et topographiques. Elle s’est focalisée sur la<p>composante ligneuse de par son caractère pérenne et son influence sur les processus<p>écologiques majeurs. Sur une zone de plus de 2000 km², le Parc National du W du Niger<p>(PNWN), où le feu est utilisé comme outil pour la gestion et la conservation des écosystèmes<p>semi-arides, une carte de l'historique des feux a été élaborée à partir d'images MODIS de 250<p>m de résolution spatiale et de résolution temporelle journalière couvrant une période de sept<p>années (2002-2009). Pour comprendre la variabilité, à la fois dans l'espace et le temps, de la<p>propagation du feu dans la végétation, nous avons étudié les caractéristiques de distribution<p>des feux en termes de régime du feu (i.e. période d'occurrence et fréquence) et de structure<p>spatiale (métriques paysagères). Les relations causales plausibles entre les régimes du feu, les<p>conditions édaphiques et topographiques à l'échelle régionale comme locale, et les<p>caractéristiques de la végétation ligneuse (composition et structure) ont été examinées à<p>travers des analyses multivariées et des modèles d'équations structurales. Nous avons aussi<p>examiné plus en détails les stratégies adaptatives mises en oeuvre par les ligneux, et les<p>interactions biologiques qui sous-tendent l'organisation spatiale des ligneux à travers une<p>approche des processus ponctuels.<p>Les résultats montrent que l'activité du feu dans le PNWN se caractérise par une hétérogénéité<p>spatio-temporelle induite principalement par les conditions édapho-topographiques via la<p>structure de la végétation ligneuse. Les feux précoces de gestion créent des pare-feux<p>efficaces, limitant une large extension des feux de saison tardifs. Cependant, ces feux tardifs<p>pourraient ne pas être aussi destructifs comme qu’on le suppose généralement. En effet,<p>l'adaptation des espèces aux différents régimes defeu correspond à des stratégies de croissance<p>contrastées. Dans le cas des feux tardifs, les surfaces terrières et hauteurs moyennes les plus<p>fortes sont rencontrées, permettant aux arbres de résister au feu. Quant aux zones non<p>affectées par les feux l'analyse "patron-processus" désigne clairement la facilitation entre<p>ligneux comme un processus fondamental de l'organisation spatiale périodique du couvert, une<p>structure émergente qui empêche le passage du feu. Bien qu’ils ne se substituent pas aux<p>études expérimentales, ces résultats basés sur une expérimentation naturelle à large échelle<p>apportent des informations nouvelles précieuses tant au niveau fondamental que pour la mise<p>en place d'une gestion raisonnée du PNWN.<p><p><p>The tree-grass equilibrium in tropical savanna is recognized as one of plant ecology's main<p>conundrums. The origins of the difficult balance between these life forms over tens of millions<p>of square kilometers worldwide are in part attributed to the frequent disturbances caused by<p>vegetation fires effects of which vary in space and time depending on local environmental<p>factors. Research results are scale-dependent and findings from local studies are rarely<p>transposable to higher levels of ecosystem organization. The question of scaling (scale<p>transfer) is therefore crucial in the study of fire effects, and requires a multidisciplinary<p>approach.<p>Because of the variety of scales covered, this study is a premiere in the confrontation of<p>satellite-imagery derived fire history data with detailed field data including measurements of<p>vegetation parameters (structure and composition), as well as soil and topographic properties.<p>The study focuses on the woody component, because of its perennial character and its<p>influence on major ecological processes. On an area of more than 2000 km², the W National<p>Park of Niger (WNPN) where fire is used as a tool for the management and conservation of<p>semi-arid ecosystems, a fire history map was elaborated from MODIS images with a 250 m<p>spatial resolution and a daily temporal resolution over a period of seven years (2002-2009). To<p>understand the variability, both in space and time, of fire propagation in vegetation, we studied<p>the fire distribution characteristics in terms of fire regime (i.e. timing and frequency) and<p>spatial structure (landscape metrics). Plausible causal relationships at regional and local scales<p>between fire regimes, edaphic and topographic conditions, and the woody vegetation<p>(composition and structure) characteristics were examined through multivariate analyses and<p>structural equations models. We also examined in detail the woody species adaptive strategies<p>as well biological interactions, which underlie their spatial organization, using point statistics.<p>Results show that the WNPN fire's activity is characterized by spatial and temporal<p>heterogeneity induced mainly by edaphic and topographic conditions via the structure of the<p>ligneous component. Prescribed early season fires create effective firewalls, limiting wide late<p>season fires. However, these late fires might not be as destructive as is commonly assumed.<p>Indeed, species adaptation to different fire regimes corresponds to contrasting growth<p>strategies. In the case of late fires, increased basal areas and mean tree heights were<p>encountered, enabling trees to resist fire and escape flames. As for the unburned areas, the<p>"pattern-process" analysis clearly indicates that facilitation between shrubs is a fundamental<p>process determining the woody cover periodic spatial organization, an emergent structure that<p>prevents fire spread.<p>Although they do not replace experimental studies, these results based on a large-scale natural<p>experiment provide valuable new information both on a fundamental level and for setting up<p>the rational management of the WNPN. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished