International Journal of Mediterranean Ecology - Ecologia ...

AMINE HABIB BORSALI, KHELOUFI BENABDELI, RAPHAËL GROS
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microbiological properties (basal respiration,
microbial biomass, enzymatic activities) of
burned soils. The soil properties were analysed
on 25 soil samples sampled in the Forest of
Fénouane (wilaya of Saïda, Algeria) along a
chonosequence 2, 4, 8, 13 and 20 years after the
last fire (i.e. 5 times since fire x 5 sampling
plots). Compared to an unburned soil since
20 years, the moisture content as well as urease
and FDA hydrolase activities were significantly
reduced 2 years after the last fire. A peak of
microbial activity, due to a stimulation of microbial
growth probably by manure, was measured
8 years after the last fire. These unburned soils
since 8 years are also characterized by very low
organic carbon contents (0.5 %) probably resulting
from a strong erosion concomitant to a
priming-effect of recalcitrant organic matter.
This study showed the vulnerability of semi-arid
forest soils to a frequency of fires over one fire
every 20 years.
Abridged english version
Since 1965, Algerian’s forest patrimony is
menaced by renewed fires that destroy
48,000 ha per year (i.e. 12% of the forest surfaces).
An increase in fire frequency associated
to climate warming (IPCC, 2007) could
affect the equilibrium between ecosystem
functioning and ancestral wildfire regime and
lead an instable state in which ecosystem
functions and services may to be not correctly
ensured. In Algeria, the studies about effects
of fire on soil quality are rare. The aim of this
study was to assess post-fire recovery at short
and long term of some soil physico-chemical
(water holding capacity and moisture content
at sampling time, contents in organic carbon,
total nitrogen, ammonium, nitrate and inorganic
phosphorus, pH) and microbiological
properties (microbial basal respiration and
biomass, FDA hydrolase, alkaline phosphomonoesterase,
urease and phenol oxydase
activities).
The study area was located in the forest of
Fénouane (Sidi M’barek, wilaya of Saïda,
Algeria). This forest of the southern foothills
of the Tell Atlas Mountain can be compared
to others semi-arid fresh bioclimatic stages of
Algeria with recurrent fires and difficulties to
reafforestation. In this region, the average fire
frequency is close to 1 fire every 25 years.
The study area (2,537 ha) presents an altitude
close to 850 m above sea level and is characterized
by a Mediterranean climate. The mean
annual temperature is 16,5 oC and the mean
annual precipitation is 350 mm. At the early
stage of succession (i.e. following forest
fires), plant communities are dominated by
herbaceous and fast growing species such as
Pistacia lentiscus, Stipa tenacissima and Cistus
villosus. At the later successional stage
(i.e. with no fire for at least 20 years), close
forest is dominated by a tree stratum of Pinus
halepensis and Tetraclinis articulata. In this
forest, 25 sampling plots (400 m2 ) were
selected taking into account the year of the
last fire. To assure five replicates of each
“time since fire”, 25 sampling plots (400 m2 )
were selected along a chronosequence of 2, 4,
8, 13 and 20 years since fire. Soils were sampled
at the top 5 cm and their physico-chemical
properties (water holding capacity and
moisture content at sampling time, contents
in organic carbon, total nitrogen, ammonium,
nitrate, inorganic phosphorus and CaCO3 , pH)
and microbial properties (basal respiration,
microbial biomass, enzymatic activities) were
analysed.
Our results showed lowest soil moisture content
(2 %) in the soils unburned since 2 years.
The destruction of arboreous vegetation and
it substitution two years after the fire by an
herbaceous stratum are hypothesized to
increase evapotranspiration and thus soil
drought. Similar organic carbon contents in
the recently burned soils and unburned soil
since 20 years suggested inputs of charred
material from carbonized vegetation. In comparison
with soils unburned since 20 years,
FDA hydrolase and phosphomonoestreases
activities remained weaker two years after the
last fire in spite of the recovery of microbial
biomass. These results are coherent with those
of Boerner and Brinkman (2003) who have
shown a decrease in the short term of
hydrolytic activities due to an alteration of the
quality of the organic matter. However, concomitant
increase in total nitrogen content to
black carbon also suggested inputs of inorganic
nitrogen of fresh organic matter. These
inputs of available resources, probably originated
from grazing sheep, have stimulated the
recovery 8 years after fire of microbial biomass
and some enzyme activities (FDA
hydrolase and phenol-oxydase). Indeed, fire
is frequently used by breeders to promote the
development of grasslands and thus allow the
grazing of sheep. Either traditional or intensive
grazing is then practiced for 5 years with,
in average, 20 or 150 sheep per hectare
respectively (DSA, 2010). The stimulation of
microbial growth and activities may have generated
a priming effect of the black carbon
ecologia mediterranea – Vol. 38 (1) – 2012