31 research outputs found
Self-Organized Criticality of Wildfires Ecologically Revisited.
Wildfire cumulative frequency¿area distributions of Mediterranean landscapes are examined for agreement with self-similar (fractal) behavior. Our results support landscape-specific restricted scaling regions of 1.5¿3.5 orders of magnitude in size, which are delimited by breakpoints or `cut-offs¿. By identifying the extent of such regions in the fractal frequency¿area distribution of wildfires, fractal statistics may give a deeper insight into the scale-invariant dynamics of fire spread, whereas the observed cut-offs may be related to changes in the process¿pattern interactions that control wildfire propagation at the landscape scale.Peer Reviewe
Reappraisal of Vipera aspis Venom Neurotoxicity
BACKGROUND: The variation of venom composition with geography is an important aspect of intraspecific variability in the Vipera genus, although causes of this variability remain unclear. The diversity of snake venom is important both for our understanding of venomous snake evolution and for the preparation of relevant antivenoms to treat envenomations. A geographic intraspecific variation in snake venom composition was recently reported for Vipera aspis aspis venom in France. Since 1992, cases of human envenomation after Vipera aspis aspis bites in south-east France involving unexpected neurological signs were regularly reported. The presence of genes encoding PLA(2) neurotoxins in the Vaa snake genome led us to investigate any neurological symptom associated with snake bites in other regions of France and in neighboring countries. In parallel, we used several approaches to characterize the venom PLA(2) composition of the snakes captured in the same areas. [br/]
METHODOLOGY/PRINCIPAL FINDINGS: We conducted an epidemiological survey of snake bites in various regions of France. In parallel, we carried out the analysis of the genes and the transcripts encoding venom PLA(2)s. We used SELDI technology to study the diversity of PLA(2) in various venom samples. Neurological signs (mainly cranial nerve disturbances) were reported after snake bites in three regions of France: Languedoc-Roussillon, Midi-Pyrénées and Provence-Alpes-Côte d'Azur. Genomes of Vipera aspis snakes from south-east France were shown to contain ammodytoxin isoforms never described in the genome of Vipera aspis from other French regions. Surprisingly, transcripts encoding venom neurotoxic PLA(2)s were found in snakes of Massif Central region. Accordingly, SELDI analysis of PLA(2) venom composition confirmed the existence of population of neurotoxic Vipera aspis snakes in the west part of the Massif Central mountains. [br/]
CONCLUSIONS/SIGNIFICANCE: The association of epidemiological studies to genetic, biochemical and immunochemical analyses of snake venoms allowed a good evaluation of the potential neurotoxicity of snake bites. A correlation was found between the expression of neurological symptoms in humans and the intensity of the cross-reaction of venoms with anti-ammodytoxin antibodies, which is correlated with the level of neurotoxin (vaspin and/or ammodytoxin) expression in the venom. The origin of the two recently identified neurotoxic snake populations is discussed according to venom PLA(2) genome and transcriptome data
C sequestration issues in the Mediterranean soils
The Mediterranean region has distinct characteristics resulting from its climate, land use history and landforms that may largely affect soil C balances. In this paper we present data on C storage in Mediterranean soils and how it can be affected by changes in land use and fire. We also discuss the sensitivity of organic matter levels in Mediterranean soils to land use and management in order to set the basis for increasing C sequestration in the Mediterranean
Land use and land cover change modelling
Forest fires result from a number of interacting factors
like ignitions, conditions amenable for fire initiation
and spread, and landscapes with vegetation
(i.e., fuels) that can support the combustion process.
In Europe, most fires occur in the southern countries
with a Mediterranean climate. But fires dominate
also in other parts of the world. Factors driving
fire have not been stable during the last decades,
mainly due to modifications in the territory caused
by socioeconomic changes. Climate has equally
not been stable. In looking at the future, changes
in climate and socioeconomics are projected to
continue. Understanding how such modifications
in the fire controlling factors affect fire activity is
utmost important for anticipating future fire risks.
In FUME we have come together 33 groups of scientists
from 17 countries and 5 continents to investigate
the relationships between the various drivers
of forest fires. The main focus was the southern
countries of Europe, although Northern Europe,
Northern and South Africa, Anatolia, California and
Chile were also investigated. The project addressed
the relationships between socioeconomic, landscape
and climate factors and fires across various
scales and countries during the last decades.
Additionally, future projections of these drivers
were used to anticipate future risks. Modeling and
experiments assessed impacts of future changes,
including extreme episodes like droughts, on the
vegetation and fuels. The effects of changes in fire
regime on the vegetation were also investigated.
Restoration needs under changing conditions and
for reducing fire hazard were also explored. Policy
needs and procedures used in a number of countries
were evaluated in regards coping with fire. Following
are some of the main results:
\u25b8 Fire activity has been changing in the Euro
Mediterranean countries (EUMed). Assessing fire
regimes and changes through time require longterm
databases that include more complete information
about fire characteristics and harmonized
data to permit comparisons among countries. Further
efforts are still needed to have harmonized
definitions, formats and methodologies in fire data
acquisition and assemblage across countries.
\u25b8 Mediterranean landscapes were dynamic in the
last decades, and fires responded to the changes
that occurred in them, independently of whether
they were planned (e.g., afforestation) or unplanned
(land abandonment). Fires often burned where
hazardous changes occurred. Changes driven by
socioeconomics are likely to continue in the future.
Because they operate on large time scales, anticipating
future risks should be possible.
\u25b8 Assessing impacts and future risks requires spatially
explicit information on burned areas, at least
for the fires above a certain size (a few hectares).
Reconstructing the near past and setting procedures
to gather this information for the future is
a requisite for a sound management of fire-prone
areas.
\u25b8 Fires do not burn equally all areas in a landscape,
and preferentially burn certain surfaces over others.
Furthermore, positive feedbacks driven by fire
have been documented across Southern Europe.
This is, fires favour burning again in a short time.
Understanding these positive feedbacks to prevent
certain areas entering into fire-driven degradation
loops is a necessity.
\u25b8 The rural-urban interface (RUI) is a particular area
of risk. Methods have been developed to map the
RUI and model fire risk in relation to RUI characteristics.
Furthermore, RUI development can be modeled
and taken into consideration in urban development
to reduce risk.
\u25b8 Socioeconomic factors were important for
explaining fire occurrence in EUMed countries, and
their knowledge should have an increasing role in
operational fire risk systems that focus on prevention
activities.
\u25b8 Fires are driven by weather, and dry spells and
other weather anomalies (heat waves, strong winds)
play a major role in determining fires. Extreme episodes,
like long dry spells, can be most relevant in
determining fire season severity. Improvements in
weather forecasting (seasonal, yearly) may allow
developments in fire danger and risk prediction.\u25b8 Attributing fires to climate change requires differentiating
the role of climate from other confounding
factors. Using the appropriate mathematical procedures
to relate climate and fires, while controlling
for the possible interference of other factors in this
relationship, a significant and positive relationship
was revealed between climate and fires during the
last three decades for the various EUMed regions.
This occurred despite the fact that, in recent years,
fires (numbers, area burned) were decreasing while
fire weather danger was increasing.
\u25b8 Anticipating future fire hazard and risk requires
that concurrent changes in climate and socioeconomy
are jointly analyzed to assess future allocations
to land use and land cover types, including RUI development.
Modelling at EUMed showed that land use
and land cover (LULC) will continue changing, but
changes can be affected by a priori decisions.
\u25b8 Wildfire simulators can be used with different
planning strategies, from tactical and strategic
planning of wildfire management, to firefighter
training, to even real-time firefighting. In a perspective
of climate and global changes, these tools can
assist policy makers and management agencies to
evaluate risks and needs to mitigate them.
\u25b8 With global warming, great increases are projected
in mean fire-weather indices, length of the
fire season and extreme values over large extensions
of Europe, including areas in which fires were
not prevalent until now. Procedures are now available
to make projections in the near future, in the
time when adaptation to changes in climate will be
needed.
\u25b8 Climate projections when used in fire models
under the assumptions of persisting current fire-climate
relationships and disregarding other limiting
factors project an important (up to 3 times) increase
in burned area in case-study areas like the Iberian
Peninsula.
\u25b8 Plant species differ in their seasonal variability
in live fuel moisture content and in their capacity
to produce necromass during drought periods.
Live fuel moisture content can be modeled using
drought indices, but improvements are possible
using adjustments based on actual vegetation and
soil.
\u25b8 Despite increased meteorological fire danger
with climate change, vegetation-fire models show
that under scenarios of high climate change low
productivity in parts of Southern Europe could limit
burned area.
\u25b8 Vegetation-fire models applied for contrasting
climate change scenarios indicate that fire would
enormously increase in Eastern Europe. This region
is identified as the main potential new fire-prone
area. Therefore, if climate change goes un-abated,
this region would require specific new developments
in fire research, management and protection.
\u25b8 Regeneration by germination of Mediterranean
species will suffer from changes in climate. However,
species and populations showed idiosyncratic
germination responses, which indicates that generalization
of impacts will be difficult to make.
\u25b8 Post-fire regeneration in field experiments simulating
future drought can lead to altered vegetation
due to the differential sensitivity of seeders (more
sensitive) than resprouters (less sensitive). Alterations
in ecosystem functioning are likely due to
downstream effects on the plant community and
nutrient cycling.
\u25b8 Changes in fire regime due to increased fire frequency
caused by climate change or other factors
can compromise vegetation stability to fire in low
fire-frequency areas but also in high-frequency
areas with resilient vegetation.
\u25b8 Pine woodlands burn frequently nowadays. The
post-fire vegetation in these systems is affected by
the interplay of previous management and geophysical
variables. Changes in vegetation can occur
due to fires, yet anticipating post-fire vegetation
characteristics is difficult. Site-specific, local information
is needed to identify possible vulnerable
areas subject to change due to fire.
\u25b8 Mediterranean pine forests require active management
to increase resilience. Pine thinning and
introduction of hardwood resprouting species are
recommended. Management actions have to be
adapted to each stage of the pine-stand dynamics
and site conditions, especially considering soil
moisture availability vs. light availability for selecting
drought-tolerant vs. shade-tolerant resprouter
species.
\u25b8 Post-fire restoration should consider fire-resilient,
drought-tolerant species in the perspective of climate
change. A structured approach has been
produced for post-fire impact assessment and restoration
under climate change, including technical
options for improving restoration success: seedling
acclimation to drought, soil preparation to increase
water supply, and microhabitat conditioners to
reduce water losses.
\u25b8 Increased fire load and costs are anticipated
under future scenarios of climate and other global
changes. This requires increased efficiency in
investments in wildfire management operations,
and resolving the disconnect problem between science,
policy and management
Self-organized criticality of wildfires ecologically revisited
Wildfire cumulative frequency-area distributions of Mediterranean landscapes are examined for agreement with self-similar (fractal) behavior. Our results support landscape-specific restricted scaling regions of 1.5-3.5 orders of magnitude in size, which are delimited by breakpoints or 'cut-offs'. By identifying the extent of such regions in the fractal frequency-area distribution of wildfires, fractal statistics may give a deeper insight into the scale-invariant dynamics of fire spread, whereas the observed cut-offs may be related to changes in the process-pattern interactions that control wildfire propagation at the landscape scale. © 2001 Elsevier Science B.V. All rights reserved