wAbstract
@Wildfires increased dramatically in frequency and extent in the
European Mediterranean region from the 1960s, aided by a general
warming and drying trend, but driven primarily by socio-economic
changes, including rural depopulation, land abandonment and afforestation
with flammable species. Published research into post-wildfire
hydrology and soil erosion, beginning during the 1980s in Spain,
has been followed by studies in other European Mediterranean countries
together with Israel and has now attained a sufficiently large
critical mass to warrant a major review. Although variations in
climate, vegetation, soil, topography and fore severity cause
differences in Mediterranean post-wildfire erosion, the long history
of human landscape impact up to the present day is responsible
for some its distinctive characteristics. This paper highlights
these characteristics in reviewing wildfire impacts on hydrology,
soil properties and soil erosion by water. The emosaicf nature
of many Mediterranean landscapes (e.g. an intricate land-use pattern,
abandoned terraces and tracks interrupting slopes) may explain
sometimes conflicting post-fire hydrological and erosional responses
at different sites and spatial scales. First-tear post-wildfire
soil losses at point- (average, 45-56 t ha-1) and plot-scales
(many1 t ha-1 and the majority 10 t ha-1
in the first year) are similar to or even lower than those reported
for fire-affected land elsewhere or other disturbed (e.g. cultivated)
and natural poorly-vegetated (e.g. badlands, rangeland) land in
the Mediterranean, The few published losses at larger-scales (hillslope
and catchment) are variable. This soil and high stone content
can explain supply-limited erosion preceding significant protection
by recovering vegetation. Peak erosion can sometimes be delayed
for years, largely through slow vegetation recovery and temporal
variability of erosive storms. Preferential removal of organic
matter and nutrients in the commonly thin, degraded soils is arguably
just as if not more important than the total soil loss. Aspect
is important, with more erosion reported for south- than north-facing
slopes, which is attributed to greater fire frequency, slower
vegetation recovery on the former and with soil characteristics
more prone to erosion (e.g. lower aggregate stability). Post-fire
wind erosion is a potentially important but largely neglected
process. Gauging the degradational significance of wildfires has
relied on comparison with unburnt land, but the focus for comparison
should be switched to other agents of soil disturbance and/or
currently poorly understood soil renewal rates. human impact on
land use and vegetation may alter expected effects (increased
fire activity and post-wildfire erosion) arising from future climatic
change. Different future wildfire mitigation responses and likely
erosional consequences are outlined. Research gaps are identified,
and more research effort is suggested to: (1) improve assessment
of post-wildfire erosion impact on soil fertility, through further
quantification of soil nutrient depletion resulting from single
and multiple fire cycles, and on soil longevity; (2) investigate
prescribed fire impacts on carbon release, air pollution and nutrient
losses as well as on soil loss; (3) isolate hillslope- and catchment-scale
impacts of soil water repellency under Mediterranean post-wildfire
conditions; (4) test and refine application of cosmogenic radionuclides
to post-wildfire hillslope-scale soil redistribution at different
temporal scales; (5) use better temporal resolution of sedimentary
sequences to understand palaeofire-erosion-sedimentation links;
(6) quantify post-wildfire wind erosion; (7) improve the integration
of wildfire into an overall assessment of the processes and impacts
of land degradation in the Mediterranean; and (8) raise public
awareness of wildfire impact on soil degradation.
Keywords: wildfire; Mediterranean; soil erosion; erosion plot;
soil water repellency; soil renewal ratex
Contents
1. Introduction
2. Wildfire impacts on soil and soil erosion: a brief background
3. The Mediterranean region and the post-wildfire erosion context
4. Fire regimes in prehistory and history: relationship to climate,
vegetation and sedimentation
5. Post-wildfire hydrological impacts in the Mediterranean region
@5.1. Wildfire effects on the structural and hydrological
properties of the soil
@5.2. Wildfire effects on overland flow and catchment runoff in
the Mediterranean
6. Post-wildfire soil erosion in the Mediterranean Basin
7. Is post-wildfire soil erosion in the Mediterranean distinctive?
8. Assessing the significance of post-wildfire erosion in the
Mediterranean
9. Wildfires and future climatic change in the Mediterranean
10. Conclusions: retrospect and prospect
Acknowledgements
References