Approche cartésienne pour le calcul du vent en terrain complexe avec application à la propagation des feux de forêt

La méthode de projection et l'approche variationnelle de Sasaki sont deux techniques permettant d'obtenir un champ vectoriel à divergence nulle à partir d'un champ initial quelconque. Pour une vitesse d'un vent en haute altitude, un champ de vitesse sur une grille décalée est généré au-dessus d'une topographie donnée par une fonction analytique. L'approche cartésienne nommée Embedded Boundary Method est utilisée pour résoudre une équation de Poisson découlant de la projection sur un domaine irrégulier avec des conditions aux limites mixtes. La solution obtenue permet de corriger le champ initial afin d'obtenir un champ respectant la loi de conservation de la masse et prenant également en compte les effets dûs à la géométrie du terrain. Le champ de vitesse ainsi généré permettra de propager un feu de forêt sur la topographie à l'aide de la méthode iso-niveaux. L'algorithme est décrit pour le cas en deux et trois dimensions et des tests de convergence sont effectués.

Modélisation de répartition d’espèces aviaires et de feux en forêt boréale du Québec dans un contexte de changement climatique

Les changements climatiques prennent une importance grandissante dans l’étude des phénomènes spatiaux à grande échelle. Plusieurs experts affirment que les changements climatiques seront un des principaux moteurs de changement écologique dans les prochaines décennies et que leurs conséquences seront inévitables. Ces changements se manifesteront sur le milieu physique par la fonte des calottes glaciaires, le dégel du pergélisol, l’instabilité des versants montagneux en zone de pergélisol, l’augmentation de l’intensité, de la sévérité et de la fréquence des événements climatiques extrêmes tels les feux de forêt. Les changements climatiques se manifesteront aussi sur le milieu biologique, tel la modification de la durée de la saison végétative, l’augmentation des espèces exotiques invasives et les changements dans la distribution en espèces vivantes. Deux aspects sont couverts par cette étude : 1) les changements dans la répartition spatiale de 39 espèces d’oiseaux et 2) les modifications dans les patrons spatiaux des feux, en forêt boréale québécoise, tous deux dans l’horizon climatique de 2100. Une approche de modélisation statistique démontre que la répartition spatiale des oiseaux de la forêt boréale est fortement liée à des variables bioclimatiques (R2adj = 0.53). Ces résultats permettent d’effectuer des modélisations bioclimatiques pour le gros-bec errant et la mésange à tête noire quivoient une augmentation de la limite nordique de distribution de l’espèce suivant l’intensité du réchauffement climatique. Finalement, une modélisation spatialement explicite par automate cellulaire permet de démontrer comment les changements climatiques induiront une augmentation dans la fréquence de feux de forêt et dans la superficie brûlée en forêt boréale du Québec.

Can salvage logging affect seed dispersal by birds into burned forests?

The recovery of vegetation in Mediterranean ecosystems after wildfire is mostly a result of direct regeneration, since the same species existing before the fire regenerate on-site by seeding or resprouting. However, the possibility of plant colonization by dispersal of seeds from unburned areas remains poorly studied. We addressed the role of the frugivorous, bird-dependent seed dispersal (seed rain) of fleshy-fruited plants in a burned and managed forest in the second winter after a fire, before on-site fruit production had begun. We also assessed the effect on seed rain of different microhabitats resulting from salvage logging (erosion barriers, standing snags, open areas), as well as the microhabitats of unlogged patches and an unburned control forest, taking account of the importance of perches as seed rain sites. We found considerable seed rain by birds in the burned area. Seeds, mostly from Olive trees Olea europaea and Evergreen pistaches Pistacia lentiscus, belonged to plants fruiting only in surrounding unburned areas. Seed rain was heterogeneous, and depended on microhabitat, with the highest seed density in the unburned control forest but closely followed by the wood piles of erosion barriers. In contrast, very low densities were found under perches of standing snags. Furthermore, frugivorous bird richness seemed to be higher in the erosion barriers than elsewhere. Our results highlight the importance of this specific post-fire management in bird-dependent seed rain and also may suggest a consequent heterogeneous distribution of fleshy-fruited plants in burned and managed areas. However, there needs to be more study of the establishment success of dispersed seeds before an accurate assessment can be made of the role of bird-mediated seed dispersal in post-fire regeneration

Developing a desertification indicator system for a small Mediterranean catchment: a case study from the Serra de Rodes, Alt Empordà, Catalunya, NE Spain

La desertificació és un problema de degradació de sòls de gran importància en regions àrides, semi-àrides i sub-humides, amb serioses conseqüències ambientals, socials i econòmiques com a resultat de l'impacte d'activitats humanes en combinació amb condicions físiques i medi ambientals desfavorables (UNEP, 1994). L'objectiu principal d'aquesta tesi va ser el desenvolupament d'una metodologia simple per tal de poder avaluar de forma precisa l'estat i l'evolució de la desertificació a escala local, a través de la creació d'un model anomenat sistema d'indicators de desertificació (DIS). En aquest mateix context, un dels dos objectius específics d'aquesta recerca es va centrar en l'estudi dels factors més importants de degradació de sòls a escala de parcel.la, comportant un extens treball de camp, analisi de laboratori i la corresponent interpretació i discussió dels resultats obtinguts. El segon objectiu específic es va basar en el desenvolupament i aplicació del DIS. L'àrea d'estudi seleccionada va ser la conca de la Serra de Rodes, un ambient típic Mediterràni inclòs en el Parc Natural del Cap de Creus, NE Espanya, el qual ha estat progressivament abandonat pels agricultors durant el segle passat. Actualment, els incendis forestals així com el canvi d'ús del sòl i especialment l'abandonament de terres són considerats els problemes ambientals més importants a l'àrea d'estudi (Dunjó et al., 2003). En primer lloc, es va realitzar l'estudi dels processos i causes de la degradació dels sòls a l'àrea d'interés. En base a aquest coneixement, es va dur a terme la identificació i selecció dels indicadors de desertificació més rellevants. Finalment, els indicadors de desertificació seleccionats a escala de conca, incloent l'erosió del sòl i l'escolament superficial, es van integrar en un model espaial de procés. Ja que el sòl és considerat el principal indicador dels processos d'erosió, segons la FAO/UNEP/UNESCO (1979), tant el paisatge original així com els dos escenaris d'ús del sòl desenvolupats, un centrat en el cas hipotétic del pas d'un incendi forestal, i l'altre un paisatge completament cultivat, poden ser ambients classificats sota baixa o moderada degradació. En comparació amb l'escenari original, els dos escenaris creats van revelar uns valors més elevats d'erosió i escolament superficial, i en particular l'escenari cultivat. Per tant, aquests dos hipotètic escenaris no semblen ser una alternativa sostenible vàlida als processos de degradació que es donen a l'àrea d'estudi. No obstant, un ampli ventall d'escenaris alternatius poden ser desenvolupats amb el DIS, tinguent en compte les polítiques d'especial interés per la regió de manera que puguin contribuir a determinar les conseqüències potencials de desertificació derivades d'aquestes polítiques aplicades en aquest escenari tan complexe espaialment. En conclusió, el model desenvolupat sembla ser un sistema força acurat per la identificació de riscs presents i futurs, així com per programar efectivament mesures per combatre la desertificació a escala de conca. No obstant, aquesta primera versió del model presenta varies limitacions i la necessitat de realitzar més recerca en cas de voler desenvolupar una versió futura i millor del DIS.

Forest Policy Scenario Analysis: Sensitivity of Songbird Community to Changes in Forest Cover Amount and Configuration

Changes in mature forest cover amount, composition, and configuration can be of significant consequence to wildlife populations. The response of wildlife to forest patterns is of concern to forest managers because it lies at the heart of such competing approaches to forest planning as aggregated vs. dispersed harvest block layouts. In this study, we developed a species assessment framework to evaluate the outcomes of forest management scenarios on biodiversity conservation objectives. Scenarios were assessed in the context of a broad range of forest structures and patterns that would be expected to occur under natural disturbance and succession processes. Spatial habitat models were used to predict the effects of varying degrees of mature forest cover amount, composition, and configuration on habitat occupancy for a set of 13 focal songbird species. We used a spatially explicit harvest scheduling program to model forest management options and simulate future forest conditions resulting from alternative forest management scenarios, and used a process-based fire-simulation model to simulate future forest conditions resulting from natural wildfire disturbance. Spatial pattern signatures were derived for both habitat occupancy and forest conditions, and these were placed in the context of the simulated range of natural variation. Strategic policy analyses were set in the context of current Ontario forest management policies. This included use of sequential time-restricted harvest blocks (created for Woodland caribou (Rangifer tarandus) conservation) and delayed harvest areas (created for American marten (Martes americana atrata) conservation). This approach increased the realism of the analysis, but reduced the generality of interpretations. We found that forest management options that create linear strips of old forest deviate the most from simulated natural patterns, and had the greatest negative effects on habitat occupancy, whereas policy options that specify deferment and timing of harvest for large blocks helped ensure the stable presence of an intact mature forest matrix over time. The management scenario that focused on maintaining compositional targets best supported biodiversity objectives by providing the composition patterns required by the 13 focal species, but this scenario may be improved by adding some broad-scale spatial objectives to better maintain large blocks of interior forest habitat through time.

Investigating Targets of Avian Habitat Management to Eliminate an Ecological Trap

Ecological traps are attractive population sinks created when anthropogenic habitat alteration inadvertently creates a mismatch between the attractiveness of a habitat based upon its settlement cues, and its current value for survival or reproduction. Traps represent a new threat to the conservation of native species, yet little attention has been given to developing practical approaches to eliminating them. In the northern Rocky Mountains of Montana, Olive-sided Flycatchers (Contopus cooperi) prefer to settle in patches of selectively harvested forest versus burned forest despite the lower reproductive success and higher nest predation risk associated with the former habitat. I investigated characteristics of preferred perch sites for this species and how these preferences varied between habitats and sexes. I then built on previous research to develop a range of management prescriptions for reducing the attractiveness of selectively harvested forest, thereby disarming the ecological trap. Female flycatchers preferred to forage from shorter perch trees than males, and females’ perches were shorter than other available perch trees. Both sexes preferred standing dead perch trees (snags) and these preferences were most obvious in harvested forest where snags are rarer. Because previous research shows that snag density is linked to habitat preference and spruce/fir trees are preferred nest substrate, my results suggest these two habitat components are focal habitat selection cues. I suggest alternative and complementary strategies for eliminating the ecological trap for Olive-sided Flycatchers including: (1) reduced retention and creation of snags, (2) avoiding selective harvest in spruce, fir, and larch stands, (3) avoiding retention of these tree species, and (4) selecting only even-aged canopy height trees for retention so as to reduce perch availability for female flycatchers. Because these strategies also have potential to negatively impact habitat suitability for other forest species or even create new ecological traps, we urge caution in the application of our management recommendations.

Northern hemisphere snow: measurement, modelling and predictability

Northern hemisphere snow water equivalent (SWE) distribution from remote sensing (SSM/I), the ERA40 reanalysis product and the HadCM3 general circulation model are compared. Large differences are seen in the February climatologies, particularly over Siberia. The SSM/I retrieval algorithm may be overestimating SWE in this region, while comparison with independent runoff estimates suggest that HadCM3 is underestimating SWE. Treatment of snow grain size and vegetation parameterizations are concerns with the remotely sensed data. For this reason, ERA40 is used as `truth' for the following experiments. Despite the climatology differences, HadCM3 is able to reproduce the distribution of ERA40 SWE anomalies when assimilating ERA40 anomaly fields of temperature, sea level pressure, atmospheric winds and ocean temperature and salinity. However when forecasts are released from these assimilated initial states, the SWE anomaly distribution diverges rapidly from that of ERA40. No predictability is seen from one season to another. Strong links between European SWE distribution and the North Atlantic Oscillation (NAO) are seen, but forecasts of this index by the assimilation scheme are poor. Longer term relationships between SWE and the NAO, and SWE and the El Ni\~no-Southern Oscillation (ENSO) are also investigated in a multi-century run of HadCM3. SWE is impacted by ENSO in the Himalayas and North America, while the NAO affects SWE in North America and Europe. While significant connections with the NAO index were only present in DJF (and to an extent SON), the link between ENSO and February SWE distribution was seen to exist from the previous JJA ENSO index onwards. This represents a long lead time for SWE prediction for hydrological applications such as flood and wildfire forecasting. Further work is required to develop reliable large scale observation-based SWE datasets with which to test these model-derived connections.

A climate change risk analysis for world ecosystems

We quantify the risks of climate-induced changes in key ecosystem processes during the 21st century by forcing a dynamic global vegetation model with multiple scenarios from 16 climate models and mapping the proportions of model runs showing forest/nonforest shifts or exceedance of natural variability in wildfire frequency and freshwater supply. Our analysis does not assign probabilities to scenarios or weights to models. Instead, we consider distribution of outcomes within three sets of model runs grouped by the amount of global warming they simulate: <2°C (including simulations in which atmospheric composition is held constant, i.e., in which the only climate change is due to greenhouse gases already emitted), 2–3°C, and >3°C. High risk of forest loss is shown for Eurasia, eastern China, Canada, Central America, and Amazonia, with forest extensions into the Arctic and semiarid savannas; more frequent wildfire in Amazonia, the far north, and many semiarid regions; more runoff north of 50°N and in tropical Africa and northwestern South America; and less runoff in West Africa, Central America, southern Europe, and the eastern U.S. Substantially larger areas are affected for global warming >3°C than for <2°C; some features appear only at higher warming levels. A land carbon sink of ≈1 Pg of C per yr is simulated for the late 20th century, but for >3°C this sink converts to a carbon source during the 21st century (implying a positive climate feedback) in 44% of cases. The risks continue increasing over the following 200 years, even with atmospheric composition held constant.

Climate and human influences on global biomass burning over the past two millennia

Large, well-documented wildfires have recently generated worldwide attention, and raised concerns about the impacts of humans and climate change on wildfire regimes. However, comparatively little is known about the patterns and driving forces of global fire activity before the twentieth century. Here we compile sedimentary charcoal records spanning six continents to document trends in both natural and anthropogenic biomass burning for the past two millennia. We find that global biomass burning declined from AD 1 to 1750, before rising sharply between 1750 and 1870. Global burning then declined abruptly after 1870. The early decline in biomass burning occurred in concert with a global cooling trend and despite a rise in the human population. We suggest the subsequent rise was linked to increasing human influences, such as population growth and land-use changes. Our compilation suggests that the final decline occurred despite increasing air temperatures and population. We attribute this reduction in the amount of biomass burned over the past 150 years to the global expansion of intensive grazing, agriculture and fire management.

Modelling fire and the terrestrial carbon balance

Four CO2 concentration inversions and the Global Fire Emissions Database (GFED) versions 2.1 and 3 are used to provide benchmarks for climate-driven modeling of the global land-atmosphere CO2 flux and the contribution of wildfire to this flux. The Land surface Processes and exchanges (LPX) model is introduced. LPX is based on the Lund-Potsdam-Jena Spread and Intensity of FIRE (LPJ-SPITFIRE) model with amended fire probability calculations. LPX omits human ignition sources yet simulates many aspects of global fire adequately. It captures the major features of observed geographic pattern in burnt area and its seasonal timing and the unimodal relationship of burnt area to precipitation. It simulates features of geographic variation in the sign of the interannual correlations of burnt area with antecedent dryness and precipitation. It simulates well the interannual variability of the global total land-atmosphere CO2 flux. There are differences among the global burnt area time series from GFED2.1, GFED3 and LPX, but some features are common to all. GFED3 fire CO2 fluxes account for only about 1/3 of the variation in total CO2 flux during 1997–2005. This relationship appears to be dominated by the strong climatic dependence of deforestation fires. The relationship of LPX-modeled fire CO2 fluxes to total CO2 fluxes is weak. Observed and modeled total CO2 fluxes track the El Niño–Southern Oscillation (ENSO) closely; GFED3 burnt area and global fire CO2 flux track the ENSO much less so. The GFED3 fire CO2 flux-ENSO connection is most prominent for the El Niño of 1997–1998, which produced exceptional burning conditions in several regions, especially equatorial Asia. The sign of the observed relationship between ENSO and fire varies regionally, and LPX captures the broad features of this variation. These complexities underscore the need for process-based modeling to assess the consequences of global change for fire and its implications for the carbon cycle.

Volatile profile of Spanish Cistus plants as sources of antimicrobials for industrial applications

Cistus is a plant genus traditionally used in folk medicine as remedy for several microbial disorders and infections. The abundance of Cistus spp. in the Iberian Peninsula together with their ability to renew after wildfire contribute to their profitability as suppliers of functional ingredients. The aim of this study was to provide a comprehensive characterization of the volatile profile of different Cistus plants grown in Spain:Cistus ladanifer L., Cistus albidus L., Cistus salviifolius L., and Cistus clusii Dunal (the latter has not been studied before). A system combining headspace solid-phase microextraction and gas chromatography coupled to mass spectrometry (HS-SPME-GC–MS) was implemented; thereby, the volatile compounds were extracted and analyzed in a fast, reliable and environment-friendly way. A total of 111 volatile compounds were identified, 28 of which were reported in Cistus for the first time. The most abundant components of the samples (mono and sesquiterpenes) have been previously reported as potent antimicrobial agents. Therefore, this work reveals the potential use of the Cistus spp. studied as natural sources of antimicrobial compounds for industrial production of cosmeceuticals, among other applications.

Effects of fragmented habitat and fire on the distribution and ecology of the swamp antechinus (Antechinus minimus maritimus) in the Eastern Otways, Victoria

This study investigated the distribution, habitat and population dynamics of the swamp antechinus (Antechinus minimus maritimus) in the eastern Otway Ranges. The species has a restricted, disjunct distribution and has been recorded at 25 sites between 1969 and 1999. All sites were located within 7 km of the coast, occurred at altitudes up to 80 m above sea level and within 10 m of a gully. Analysis of landscape site variables identified sun index as being significant in determination of the probability of occurrence of A. minimus. The presence of A. minimus is negatively associated with sun index, occuring at sites that have a southerly aspect and gentle slope. A. minimus was located in a range of structural vegetation including Open Forest, Low Woodland, Shrubland and Hummock Grassland and a number of floristic groups, some characterised by high frequencies of sclerophyll shrubs, others by high frequencies of Pteridium esculentum, hummock grasses and herbaceous species. A. minimus occurs in fragmented, small populations with maximum population densities of 1.1–18 ha^–1. Populations at inland sites became extinct after the 1983 wildfire which burnt 41 000 ha. These sites have not been recolonised since, while on the coast the species did not re-establish until 1993–97. One population that is restricted to a narrow coastal strip of habitat is characterised by high levels of transient animals. The species is subject to extinction in the region due to habitat fragmentation, coastal developments and fire. Management actions to secure the present populations and ensure long-term survival of the species in the area are required and include implementation of appropriate fire regimes, prevention of habitat fragmentation, revegetation of habitat, and establishment of corridor habitat.

Does firefighting foam affect the growth of some Australian native plants?

Firefighting foams (Class A foams) are an effective and widespread firefighting tool, and are frequently used in environmentally sensitive areas. They are known to be ecologically damaging in aquatic environments; however, their impacts at the plant species or ecosystem level are relatively unknown. Reports of shoot damage to plants, suppressed flowering and changes in plant community composition suggest that the environmental damage caused by their use may be unacceptable. Applications of four levels of foam to seedlings of seven Australian plant species, from five representative and widespread families, showed no detectable impacts on a range of vegetative growth characteristics. The results are encouraging for continued use of firefighting foam in sensitive natural habitats.

Effect of fire on Benthic Algal Assemblage structure and recolonisation in intermittent streams

Dry biofilm on rocks and other substrata forms an important drought refuge for benthic algae in intermittent streams following the cessation of flow. This dry biofilm is potentially susceptible to disturbance from bushfires, including direct burning and/or scorching and damage from radiant heat, particularly when streams are dry. Therefore, damage to dry biofilms by fire has the potential to influence algal recolonization and assemblage structure in intermittent streams following commencement of flow. The influence of fire on benthic algal assemblages and recolonization was examined in intermittent streams of the Grampians National Park, Victoria, Australia, using a field survey and manipulative field experiment. The field survey compared assemblages in two intermittent streams within a recently burnt area (within 5 months of the fire) with two intermittent streams within an unburnt area. The two burnt streams were still flowing during the fire so most biofilms were not likely to be directly exposed to flames. Considerable site-to-site and stream-to-stream variation was detected during the field survey, which may have obscured potential differences attributable to indirect effects of the fire. The manipulative field experiment occurred in two intermittent streams and consisted of five treatments chosen to replicate various characteristics of bushfires that may influence dry biofilms: dry biofilm exposed directly to fire; dry biofilm exposed to radiant heat; dry biofilm exposed to ash; and two procedural controls. After exposure to the different treatments, rocks were replaced in the streams and algae were sampled 7 days after flow commenced. Differences occurred across treatments, but treatment differences were inconsistent across the two streams. For example, direct exposure to fire reduced the abundance of recolonizing algae and altered assemblage structure in both streams, while radiant heat had an effect on assemblage structure in one stream only. The manipulative field experiment is likely to have represented the intensity of a small bushfire only. Nonetheless, significant differences across treatments were detected, so these experimental results suggest that fire can damage dry biofilms, and hence, influence algal recolonization and assemblage structure in intermittent streams.

Estimating population size of the black-eared miner, with an assessment of landscape-scale habitat requirements

The decline of the Black-eared Miner Manorina melanotis has been caused primarily by habitat degradation and vegetation clearance. To better direct conservation actions for this species there was a need to assess habitat requirements on a regional-scale and to estimate the population size using quantitative methods. We used vegetation mapping and the current distribution of the Black-eared Miner to determine regional-scale habitat requirements. These findings were combined with the results of distance sampling to provide population estimates. The species is restricted to large tracts of intact mallee in the Murray Mallee of southeastern Australia that have not been burnt for at least 45 years. The density· of Black-eared Miners is highest in areas that are dominated by mallee- Triodia associations and have not been intensively grazed. The Bookmark Biosphere Reserve supports an estimated 501 (270-927, 95% CI) colonies, containing 3758 (2026-6954) phenotypically pure Black-eared Miners, 2255 (1 215-4170) hybrids and small numbers of Yellow-throated Miners Manorina flavigula. However, the effective population size is considerably smaller (390 Black-eared Miners '(21 0-726) and 234 hybrids (126-433)), due to a skewed adult sex ratio (1 female: 1.81 males) and complex social organization. A smaller population also persists in the Murray Sunset National Park containing 53 (32-85) Black-eared Miner/hybrid colonies. Both populations face a high risk of extinction from large-scale wildfire. The endangered status of the species under IUCN criteria remains warranted.