Conference PaperPDF Available

Appraising fuel and fire behaviour for prescribed burning application in heathlands of Northwest Italy

Authors:

Abstract and Figures

Calluna-heathlands are one of the most fire-prone vegetation types in NW Italy. Fire risk at the wildland urban interface is increasing. Moreover, frequent and large wildfires threat the Calluna-heathland, a Priority Habitat in Europe. Prescribed burning for fire hazard reduction could be a suitable tool to create fuel discontinuities in strategic areas so as to facilitate fire suppression. Nevertheless, its effectiveness has to be assessed and burn prescriptions need to be developed. The objective of the present work is to study the links between burning conditions, fire behaviour and fire effects on heathlands fuels of NW Italy. We carried out 25 experimental burns during the legal burning season in winter, both in unburnt (UB) heathlands stands of different ages (4-14 years) and recently burnt (BU) stands (1-3 yrs). The fuel complex load and structure was characterized before and after burning. Short-medium term post-treatment fuel dynamics were studied. The seasonal variation of fine fuels moisture was analysed. A linear regression model was developed to predict the dead fine fuel moisture as a function of weather variables. Fire behaviour was studied with a microplot scale approach. Rate of fire spread and fireline intensity were quantified for backfire (A), headfire in the acceleration phase (B), and headfire in the quasi steady state (C). Generalized linear models with Tukey's comparison were used to investigate differences in fuel load and structure vs. time since fire, and fire behaviour descriptors in BU vs. UB burns. Results evidenced that prescribed burning treatments significantly mitigated potential fire behaviour. In BU, observed fireline intensity in A, B, C behaviours was respectively the 26%, 38% and 20% of the UB values. Finally, operational windows (i.e. optimum moisture scenario; available days for burning) and technical recommendations (i.e. ignition techniques) to assist prescribed burning for fire hazard reduction in heath fuels of NW Italy were set out.
Content may be subject to copyright.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
Appraising fuel and fire behaviour for prescribed burning
application in heathlands of Northwest Italy
Ascoli D., Bovio G.
Dip. Agronomia, Selvicoltura e Gestione del Territorio, Università di Torino,
via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy
d.ascoli@unito.it, giovanni.bovio@unito.it
Abstract
Calluna-heathlands are one of the most fire-prone vegetation types in NW Italy. Fire risk
at the wildland urban interface is increasing. Moreover, frequent and large wildfires threat
the Calluna-heathland, a Priority Habitat in Europe. Prescribed burning for fire hazard
reduction could be a suitable tool to create fuel discontinuities in strategic areas so as to
facilitate fire suppression. Nevertheless, its effectiveness has to be assessed and burn
prescriptions need to be developed. The objective of the present work is to study the links
between burning conditions, fire behaviour and fire effects on heathlands fuels of NW
Italy. We carried out 25 experimental burns during the legal burning season in winter,
both in unburnt (UB) heathlands stands of different ages (4-14 years) and recently burnt
(BU) stands (1-3 yrs). The fuel complex load and structure was characterized before and
after burning. Short-medium term post-treatment fuel dynamics were studied. The
seasonal variation of fine fuels moisture was analysed. A linear regression model was
developed to predict the dead fine fuel moisture as a function of weather variables. Fire
behaviour was studied with a microplot scale approach. Rate of fire spread and fireline
intensity were quantified for backfire (A), headfire in the acceleration phase (B), and
headfire in the quasi steady state (C). Generalized linear models with Tukey’s comparison
were used to investigate differences in fuel load and structure vs. time since fire, and fire
behaviour descriptors in BU vs. UB burns. Results evidenced that prescribed burning
treatments significantly mitigated potential fire behaviour. In BU, observed fireline
intensity in A, B, C behaviours was respectively the 26%, 38% and 20% of the UB values.
Finally, operational windows (i.e. optimum moisture scenario; available days for burning)
and technical recommendations (i.e. ignition techniques) to assist prescribed burning for
fire hazard reduction in heath fuels of NW Italy were set out.
Keywords:
[Prescribed burning, fuel management, fire behaviour, fuel dynamics, heathland]
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
1. Introduction
Heathlands dominated by Calluna vulgaris Hull. are one of the most fire-prone
vegetation types in Northwest Italy (Regione Piemonte, 2007; Borghesio, 2009).
Uncontrolled surface fires of moderate intensity (500–6000 kW m
-1
), which spread
in late winter over relatively large areas (up to 400 ha), every 1–5 years, characterize the
fire regime of these heathlands. Ignition causes are human activities, such as the irrational
use of fire by shepherds, and the people negligence (Ascoli and Bovio, in press).
The heathland fire proneness in late winter is mainly due to fuel characteristics and
their interactions with seasonal weather patterns. In winter, the fuel complex is mainly
constituted by a tangle of live crowns of Calluna, which presents a reduced physiological
activity, and cured grasses, such as Molinia arundinacea Shrank; both species present high
values in surface area to volume ratio: 9650 m
2
m
-3
for Calluna foliage and shoots
(Fernandes and Rego, 1998), and 8000 m
2
m
-3
for Molinia cured leaves. Winter in NW Italy
presents a dry period of scarce precipitation (Mercalli et al., 2008) which is responsible of
low moisture contents of dead fine fuels (Cesti, 2005). Consequently, in correspondence of
the föhn wind, which blows more frequently in late winter with a speed up to 70-80 km h
-1
(Cesti, 1990), fire can spreads rapidly over extensive heathland areas characterized by
homogenous and continuous fuels. In these conditions, fire-fighting is difficult because the
distribution of the resources along the perimeter is slower than the growth of the wildfire
perimeter. Moreover, these wildfires present some critical aspects. As a consequence of the
urban growth, heathlands have been included within urban areas, thus the fire risk (sensu
Blanchi et al., 2003) at the wildland urban interface is increased. Finally, frequent fires are
responsible of the replacement of Calluna-heathlands, a Priority Habitat within the
European Union (EU 92/43/CEE), by grasslands or woodlands (Ascoli et al., 2009;
Borghesio, 2009; Ascoli and Bovio, in press).
For the above mentioned reasons, the reduction of wildfires extension and frequency
in heathlands of NW Italy is a management issue to be addressed.
Prescribed burning for fire hazard reduction could be a suitable tool to create fuel
discontinuities in strategic areas so as to facilitate fire suppression (Rigolot et al., 2009).
Strategic fuel management by prescribed burning has been thoroughly studied in European
shrublands dominated by broadleaf or heath species (Vega et al., 2001; Baeza et al., 2002;
Fernandes et al., 2002; Fernandes and Botelho, 2003; Davies et al., 2008), and is currently
applied in several European countries (Lázaro and Montiel, 2010). Nevertheless, its
effectiveness in reducing fire hazard in new areas has to be assessed (Rego et al., 2010),
above all in those countries where forest managers are interested in implementing
prescribed burning, but scientific and operational experiences are scarce, such as Italy
(Leone et al., 1999; Ascoli et al., 2009; Lázaro and Montiel, 2010). Burn prescriptions, to
translates burning conditions into fire behaviour, and fire behaviour into desired fire effects
on fuel load and structure (Fernandes and Botelho, 2003), need to be developed.
The objective of the present work is to assess prescribed burning effectiveness for
fire hazard reduction in heathlands of NW Italy. The links between burning conditions, fire
behaviour and fire effects on fuels were studied. In particular we analysed: i) the fuel
complex load and structure; ii) dead and live fine fuels moisture seasonal patterns; iii) fire
behaviour variability in relation to fuel loading, moisture scenarios and ignition techniques;
iv) short-medium term post-treatment fuel dynamics. Finally, operational windows and
technical recommendations to assist prescribed burning implementation were set out.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
2. Methods
Study site
The study was carried out within the Managed Nature Reserve of Vauda (Figure 1)
which include one of the most valuable heathlands of NW Italy (Mugion, 1996; Borghesio,
2009; Lonati et al., 2009; Ascoli and Bovio, in press). The Reserve is located 20 km NE of
Torino (7°41’17’’E, 45°13’13’’N), covers an area of 2635 ha on a stream terrace plateau at
an altitude ranging from 240 to 480 m. The soils are acidic, rich in silt and clay, with
limited water flow and plant root penetration. The climate is continental, with roughly 81%
of the mean annual rainfall (1000-1100 mm) falling between April and November. The
driest month is March with, on average, 35 mm of rain and 0.3 days of snow. The mean
annual temperature is 11.8°C, with monthly means ranging from 1.6°C in January to
21.9°C in August (Ascoli et al., 2009).
The fire regime of the study area was determined for the last two decades. The
wildfire statistics of the Corpo Forestale dello Stato (1986–2009 period) were analysed.
The geo-referenced wildfire perimeters provided both by the Regione Piemonte and by the
Land Managers of the MNR of Vauda for the period 1996–2009 are reported in Figure 1.
Figure 1 Map of the Managed Nature Reserve of Vauda showing the Reserve boundaries (green line) and the
areas burnt within 1996 and 2009 (red area) (Data source: Regione Piemonte).
Fuel characterization
The experiment design adopted to characterize fuel loading and structure consisted
in selecting 12 heathland stands which differed in time passed since the last fire. The map
of burnt areas (Figure 1) was used to choose stands locations. The stand age was
determined by counting rings of basal sections of 10 Calluna stems selected among the
largest stems found in each stand. The average stand fuel load was estimated by destructive
samplings in a 1-m
2
square (n=8 per stand). Dead and live fine fuels (<0.6 cm) were
separated, and oven-dried at 60°C for 24 hours to estimate the fuel load. The fuel structure
was assessed in linear transects, 10 m in length (n=4 per stand). Along each transect, every
50 cm, the height of Calluna and Molinia was collected. The average species height was
then calculated for each stand. The species cover was assessed along each transect
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
measuring the specific contribution according to Daget and Poissonet (1971). All samples
were randomly located. Field work was carried out in winter in 2008.
Fuel moisture was assessed along the winter season in 2009. A total of 30 days of
field sampling were carried out from November to March. Fuels were collected between
10.00 am and 14.00 pm. Each date, samples of ~50 g of fine dead fuels (Molinia cured leaves)
and live fuels (Calluna crowns) were collected (n=6); the fresh weight was determined in situ
using a field balance. Samples were oven-dried at 60°C for 24 hrs. The moisture content
was calculated as follow: M=(Wi-Wf)/Wi (where: Wi: initial weight; Wf: final weight).
Fire behaviour characterization
Experimental burns (n=25) were carried out from winter 2005 to winter 2010, both in
unburnt heathland stands (UB; n=9), whose age ranged between 6 to 14 years, and in recently
burnt stands (BU; n=16), whose time since fire ranged between 1 to 3 years. Plots dimensions
range was 1250-4000 m
-2
. Slope was <5%. Ignition techniques were backfires, headfires with
linear ignition (25-50 m), and strip head fires with strips at a distance of 15 m.
For each burn, fuel samples in a 1-m
2
square (n=6 per experiment) were collected
before and after the fire treatment to estimate fuel load before burning and fuel consumption
on a dry weight basis. On the burn dates, ~50 g of fine dead fuels (Molinia cured leaves) and
live fuels (Calluna crowns) were sampled (n=5) to measure fuel moisture.
Rate of spread (ROS; m min
-1
) was estimated with a microplot scale approach
(Smith et al., 1993; Fernandes et al., 2000) by timing the arrival of the fire front to 2 m high
aluminium rods placed within the fuel bed at the vertexes of a regular grid. This method
allows to distinguish, within the same burn, a backfire phase, headfire in the acceleration
phase (i.e. fire growth within 15 m from the ignition line) and headfire in the quasi steady
state (Cheney and Gould, 1995). Ascoli (2008) describes in detail the methodology used.
As the rods had height increment markers visual estimation of flame height was possible.
Fireline intensity (I; kW m
-1
), was calculated according to Byram (1959). High heat of
combustion of Calluna vulgaris was determined by Gillon et al. (1997) as 22940 kJ kg
-1
; a
value of 18000 kJ kg
-1
was used for grass fuels. Relative humidity, air temperature and
wind speed at 2 m above the ground were recorded every 30 seconds during each burning
using 2 mobile weather stations positioned upwind.
Data analysis
A generalized linear model with Tukey’s comparison was used to investigate
differences in fuel load between heathland class ages (fixed factor). Means were square root
transformed. Significant differences were tested at the 5% level. Data were examined for
homogeneity of variance (Levene test), and normality (K-S test). Correlation analysis was
used to test the relationships among dead and live fine fuels moisture and weather variables
taken from Front Malone (Arpa Piemonte), 4 km North from the study site. Regression
modelling was used to develop equations to predict the fuel moisture of dead fine fuels as a
function of weather variables. The best model fitted was used to plot the daily trend of dead
fine fuel moisture in winter for the period 1996-2008, entering weather data from F. Malone.
The microplot scale analysis allowed to have a consistent number of observations to
compare fire behaviour descriptors (ROS; I) between backfire (n=62), headfire in the
acceleration phase (n=57), and headfire in the quasi steady state (n=67), both in UB and BU
plots. The subset of data relative to the headfire behaviour was studied as a function of the fine
dead fuel moisture. Fuel moisture threshold values, respectively the moisture of extinction
above which fire sustainability is not guaranteed, and the moisture below which fire control
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
becomes difficult (I>500 kW m
-1
) (Andrews and Rothermel, 1982), were determined. These
threshold values were superimposed to the daily average fine dead fuel moisture in winter, as
estimated by the moisture model, to identify operational windows. Finally, the number of
available operative days to apply prescribed burning efficiently and safely was determined.
All analyses were performed using the SPSS v.16.0 statistical package (SPSS 2007).
3. Results and discussion
Fuel characteristics and dynamics
Stand age ranged from 1 to 15 years, that corresponds to the time passed since the
last fire. According to the Calluna developmental phases (Gimingham, 1988), the studied
stands were in the pioneer, building and late building phases. Stands were grouped in 5 age
classes (I: 1-3; II: 4-6; III: 7-9; IV: 10-12; V: 13-15 years).
The average total fine fuel load ranged
from 3.4 ± 0.2 t ha
-1
to 12.6 ± 0.8 t ha
-1
in the I and
V age classes respectively. Significant increases in
live fine fuel loads vs. age classes were observed
(Figure 2). Diversely, no significant differences
were found in dead fine fuel load. In the pioneer
phase, 1-6 years after fire, Calluna slowly
reconstitutes the cover (Lonati et al., 2009),
while Molinia dominates the short-term post-fire
succession (Ascoli and Bovio, in press).
Consequently, the fine dead fuel component in
heathland stands up to 6 years, constitutes most
of the fuel complex load (89% and 55%, in the I
and II age classes respectively). As Calluna ages,
its average height and cover increase (Figure 3),
up to 27 ± 2.7 cm in height and 50% of the total
cover in class V, thus becoming more competitive.
As Molinia is gradually dominated by Calluna, its
biomass does not step up, thus the rate of
accumulation of the dead fuel component is
balanced by degradation, and its load seems even to
slightly decrease, despite no significant differences
were found between age classes (Figure 2).
These results evidence that as time pass
since fire there are significant increases in fuel load
(up to 17.3 t ha
-1
) and fuel continuity (up to 100% in
cover): thus, the fuel complex becomes more
flammable; in fact, as demonstrated in previous
studies in similar fuel complexes (Ascoli, 2008;
Davies et al., 2009), and in others shrubland fuel
types (among others: Fernandes et al., 2000;
Fernandes, 2001; Baeza et al., 2002), increases in
fuel load, height and continuity are in part
responsible of the rise in rate of fire spread and fire
intensity.
Figure 2 Variation in fuel load vs. age classes.
(a) Total (live +dead) (b) live (Calluna) (c) dead
(Molinia) fuel load (t ha
-1
). Boxes show the 1
st
and 3
rd
quartiles; the black line is the median.
Whiskers show the general range of the data
with outliers shown as a dot. Significant
differences are evidenced by different letters.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
Figure 3 Variation in the fuel structure for five age classes. (a) Calluna height (cm), (b) Vegetation (Calluna
+ Molinia) cover (%). Significant differences are evidenced by different letters.
In winter 2009 the moisture content of live fuels (i.e. Calluna crowns) and dead
fuels (i.e. Molinia cured leaves) resulted significantly correlated (0.679; P < 0.01): ranges
were 37%-58% and 8%-54%, respectively (Figure 4). As dead fuels are present in all age
classes (Figure 2), and present a higher range of variation in the moisture content (Figure 4),
they play an important role in determining the fire behaviour of heathland fuels (i.e. fire
sustainability, or difficulties in fire control) (Ascoli, 2008). Consequently, to define suitable
burning conditions we deepened moisture dynamics of the fine dead fuel component.
The moisture of dead fine fuels (Mf) resulted significantly correlated to the average
air relative humidity (0.722; P < 0.01) and to the cumulative precipitation within the last 15
days (0.526; P < 0.01); diversely, no correlation was found with the air temperature (-0.37;
P = 0.845), and the dew point temperature (0.168; P = 0.325), probably as a consequence of
the low range of temperatures in winter. The first two variables were chosen as regression
predictors. Relative humidity (RH) is a commonly used variable in fuel moisture models
(Marsden-Smedley and Catchpole, 2001). It was assumed that the cumulative precipitation
(P15) plays also an important role in determining Mf: in heathlands of NW Italy soils are
rich in clay, consequently the cumulation of precipitation determines water stagnation,
which can last for several days after precipitation, affecting trough evaporation the Mf of
fuels close to the soil. The best model fitted was a linear regression:
Mf = 3.179 + 0.206*RH + 0.207*P15 [Equation 1]
Mf: fine dead fuel moisture;
RH: average air relative humidity;
P15: cumulative precipitation in the last 15 days;
The model had a R
2adj
= 0.86. Best predictions were between 5%-30% (Figure 4)
which is of interest for prescribed burning application. A brief consideration must be done
as RH and P15 were correlated (0.530; P < 0.01); consequently the use of these variables
could result in problems of multi-collinearity. Nevertheless, the risk of multi-collinearity is
low because the predictor variables are not highly correlated, and the standard errors of RH
and PG15 are low: 0.049 and 0.023 respectively (Quinn and Keough, 2002). Moreover, the
nearby weather station of Front Malone is placed in an area with no heathlands,
consequently RH should be marginally affected by the evaporation from heathlands soils.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
Figure 4 Moisture dynamics: (a) Variability in moisture content of live and dead fine fuels measured in
winter 2009; (b) Predicted versus observed dead fuel moisture from Equations 1.
Fire behaviour analysis
All experimental burns were carried out in collaboration with the Corpo
Volontari Antincendi Boschivi of the Piemonte Region, under the responsibility of the
State Forestry Corp, as regulated by the Regional Law 16/94. Two burns failed (n. 13
and n. 25) because fire sustainability was not guaranteed. All others burns achieved the
burn objective: total fine fuel load reduction higher than 80%. Wind speed ranged from
2 to 9 km h
-1
in all burns.
Significant differences in ROS [F (2, 126) = 0.865; P = 0.001)] were observed in
UB burns between behaviour types: backfire (A), headfire during the acceleration phase (B),
and the headfire of the quasi steady state (C) (Figure 5). The type of fire behaviour (A,
B, C) explained the 59% of the observed variability in ROS. All others factors which
affect fire behaviour, such as wind speed, dead fine fuel moisture and total fuel load
(Fernandes, 2001; Davies et al., 2009), were not significantly different between A, B
and C groups. Remarkable differences were also observed in fireline intensity, but it
was not possible to test significant differences, despite transformations, because the
homoscedasticity was not satisfied.
Figure 5 Variation in rate of spread (a), and fireline intensity (b), observed in UB experiment (n=9), for
backfire (A), headfire in the acceleration phase (B), and headfire of the quasi steady state (C). Significant
differneces are evidenced by different letters.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
On the basis of these results, as observed also in previous studies (Cheney and
Gould, 1995), it is possible to assert that the headfire during the acceleration phase
presents a behaviour remarkably milder in comparison with the subsequent phases, and
consequently can be controlled more easily. In fact, within 15 m from the line of ignition,
75% of the observed values of rate of spread and fireline intensity were respectively
below 5 m min
-1
and 1800 kW m
-1
. The strip head fire ignition technique, with strips
progressively distanced up to 15 m, should be suitable to implement prescribed burning to
reduce heathland fuels, both because it enables to maintain fire behaviour under control,
and allows to burn rapidly extensive areas in comparison with the backfire technique.
Experimental burns on 1250 m
2
in 2008 (n=4), carried out adopting the strip head fire
ignition technique, had an average (±SE) duration of 15 ± 2 minutes.
The average fireline intensity was significantly higher in UB vs. BU experimental
burns both for backfire, 381 kW m
-1
and 100 kW m
-1
[F (1, 62) = 7.6; P = 0.008)],
headfire in the acceleration phase, 1205 kW m
-1
and 463 kW m
-1
[F (1, 58) = 10.5;
P = 0.002)], and headfire in the quasi steady state, 3072 kW m
-1
and 619 kW m
-1
[F (1, 67) = 122.8; P = 0.001)], respectively.
These results evidence that fireline intensity can be remarkably mitigated in recently
burnt areas (1-3 years since fire) were the fuel load has been reduced by prescribed burning.
In fact, even the headfire behaviour in the quasi steady state showed a fireline intensity close
to the value of 500 kW m
-1
, which is commonly considered the upper limit for the direct
attack in fire control interventions on flat terrains (Andrews and Rothermel, 1982).
The fuel moisture effect on fire
behaviour was tested for the subset of
observations relative to headfires (both
in the acceleration and quasi steady
state) grouping together BU and UB
datasets. Significant differences in ROS
were found [F (2, 124) = 3.226; P =
0.043)] between moisture contents of
dead fine fuels below 15% and higher
than 25% (Figure 6). The average ROS
for moisture contents <15% was
7.6 ± 0.6 m min
-1
and values beyond
the direct attack capability (up to
20 m min
-1
) were observed. On the
other side, the 50% of observed values
of ROS for moisture content >25% was
below 2.2 m min
-1
, which implicates a
time-consuming job.
Figure 6 Variation in rate of spread (m min
-
1
) for moisture
classes of dead fine fuels, Significant differneces are
evidenced by different letters.
Additional information to set fine dead fuels moisture operational thresholds were
provided by experiments n. 13 and 25. In fact, these two fire experiments failed because
fire sustainability was not guaranteed as a consequence of the elevated dead fine fuel
moisture content, which was 29% and 32% respectively. Consequently, the optimum
moisture scenario appears to be the one whose values range between 15% and 25%
(average ROS equal to 4.4 ± 0.5 m min
-1
), because it guarantees a sustained fire behaviour
on one side, but does not exceed operative limits on the other.
In order to identify the prescribed burning operational period in winter, the optimum
burning windows of dead fine fuel moisture (15%-25%) were superimposed to the daily fine
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
dead fuel moisture estimated by Equation 1 for years 1996-2008 (Data source: Front Malone
weather station. Arpa Piemonte). The yearly variability of RH and P15 between 1996-2008
period was high. The difficulty to define the exact period in which is possible to apply
prescribed burning is evidenced in Figure 7 where the daily moisture content of dead fine
fuels is plotted for the year with minimum (2005) and maximum (2008) precipitation. Despite
the seasonal trend is verified in both curves, they differ remarkably in the distribution of
suitable periods to apply prescribed burning. Available days for burning within optimum
moisture windows between October and early February ranged from 39 to 111 days (from
middle February it starts the wildfire season and the use of prescribed burning is not
authorized in the Piemonte Region – R.L. 16/94).
Figure 7 Dead fine fuel moisture content in winter 2005 (black line) and 2008 (grey line) as predicted by
Equation 1. The white area represent the optimum of dead fine fuel moisture values (14%-26%) for prescribed
burning application; grey areas the lower (14%-10%) and upper (26%-30%) marginal conditions; lined areas
evidence moisture conditions (< 10%; > 30%) out of prescriptions.
4. Conclusions
The present study evidenced that prescribed burning can be an effective fuel
management technique to reduce fire hazard at the stand level in heathlands of NW Italy.
Prescribed burning treatments have to be implemented from October to the early February,
before the wildfire season starts. Fuel treatments are going to be effective not only the year of
the burn, where expected fuel reduction is higher than 80% of the total fine fuel load, but also
up to 3 years after the burn, as the fuel load remains below 5 t ha
-1
. The strip head fire
ignition technique is suitable to implement prescribed burning because gathers fire control
and efficiency. The optimum dead fine fuel moisture window is between 15% and 25%, as it
guarantees a sustained fire behaviour which does not exceed operative limits. The seasonal
distribution of available days for burning is extremely variable between years, consequently
the maximum flexibility is required; the authorization process should thus consider this issue.
Nevertheless, in Italy prescribed burning is still a controversial issues because of the lack of
knowledge, experiences and expertises (Leone et al., 1999; Ascoli 2008), consequently the
set of rules tends to protect itself from an unwise fire use. Muldisciplinary and long term
experimental studies carried out in Italy (Ascoli, 2008; Delogu, 2009; Catalanotti et al.,
Proceedings of this Conference) can thus help to improve knowledge of forest managers and
facilitate a more critical approach to prescribed burning.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
Reference list
Andrews P.L., Rothermel R.C., 1982. Charts for interpreting wildland fire
behaviour characteristics. USDA. General Technical Report INT-131. Pp. 24.
Ascoli D., 2008. Developing a prescribed burning expertise in Italy: learning fire
experiments. PhD thesis, Università degli Studi di Torino. Available at
http://www.eufirelab.org/toolbox2/library/upload/2552.pdf [Verified 25 May 2010].
Ascoli D., Beghin R., Ceccato R., Gorlier A., Lombardi G., Lonati M., Marzano R.,
Bovio G., Cavallero A., 2009. Developing an Adaptive Management approach to
prescribed burning: a long-term heathland conservation experiment in north-west Italy.
International Journal of Wildland Fire 18: 727-735.
Ascoli D., Bovio G., in press. Tree encroachment dynamics in heathlands of
Northwest Italy: the fire regime hypothesis. iForest (in press).
Baeza M.J., De Luís M., Raventós J., Escarré A., 2002. Factors influencing the
behaviour in shrublands of different stand ages and the implications for using prescribed
burning to reduce wildfire risk. Journal of Environmental Management 65: 199-208.
Blanchi R., Allgöwer B., Koutsias N., Salas J., Camia A., 2003 Fire risk mapping
(I): Methodology, selected examples and evaluation of user requirements.(E. CHUVIECO
ed.). Forest Fire Spread Prevention and Mitigation (SPREAD) Deliverable D161. Contract
number EVG1-CT-2001-00043. Pp. 46
Borghesio L., 2009. Effects of fire on the vegetation of a lowland heathland in
North-western Italy. Plant Ecology 201: 723-731.
Byram G.M., 1959. Combustion of forest fuels. In: Davis K.M. (Eds.). Forest Fire:
Control and Use. Mc Graw Hill. New York.
Cesti G., 1990. Il vento e gli incendi boschivi. Indagine sulla ventosità invernale in
Valle D’Aosta. Regione Autonoma Valle D’Aosta. Pp. 159.
Cesti G., 2005. I combustibili negli incendi di vegetazione. Monografia 1, Collana
di monografie sugli incendi boschivi e di vegetazione. De Rerum Natura: Pesaro.
Cheney N.P., Gould J.S., 1995. Fire growth in grassland fuels. International Journal
of Wildland Fire 5 (4): 237-247.
Daget P., Poissonet J., 1971. Une métode d’analyse phytologique des prairies.
Annales Agronomiques 22: 5-41.
Davies G.M., Gray A., Hamilton A., Legg C.J., 2008. The future of fire
management in the British uplands. International Journal of Biodiversity Science and
Management 4: 127–147.
Davies G.M., Legg C.J., Smith A.A., MacDonald A.J., 2009. Fire rate of spread in
Calluna vulgaris-dominated moorlands. Journal of Applied Ecology, 46, 1054-1063.
Delogu G., 2009. Esperienze di Prescribed Burning in Sardegna. In: Atti del Terzo
Congresso Nazionale di Selvicoltura. Taormina (ME), 16-19 ottobre 2008. Accademia
Italiana di Scienze Forestali, Firenze, p. 1293-1296.
Fernandes P.M., Rego F.C., 1998. A New Method to Estimate Fuel Surface Area-to-
Volume Ratio Using Water Immersion. International Journal of Wildland Fire 8(2): 59-66.
Fernandes P., Catchpole W.R., Rego F.C., 2000. Shrubland Fire Behaviour
Modelling with Microplot Data. Canadian Journal Forest Research 30: 889-899.
Fernandes P., Loureiro C., Botelho H., 2002. Guia de fogo controlado em matos.
Universidade de Trás os Montes e Slto Douro. Vila Real.
Fernandes P., 2001. Fire spread prediction in shrub fuels in Portugal. Forest Ecology
and Management 144: 67-74.
VI International Conference on Forest Fire Research
D. X. Viegas (Ed.), 2010
Fernandes P., Botelho H., 2003. A review of prescribed burning effectiveness in fire
hazard reduction. International Journal of Wildland Fire 12: 117-128.
Gimingham C.H., 1988. A reappraisal of cyclical processes in Calluna heath.
Vegetatio 77: 61–64.
Lázaro A., Montiel C., 2010. Overview of Prescribed Burning Policies and Practices
in Europe and Other Countries. In: Sande, J., Rego, F., Fernandes, P. and Rigolot, E. (Eds):
Towards Integrated Fire Management Outcomes of the European Project Fire Paradox.
European Forest Institute, Finland, Research Report 23. Pp. 137-150.
Leone V., Signorile A., Gouma V., Pangas N., Chronopoulous-Sereli, 1999.
Obstacles in prescribed fire use in Mediterrean countries: early remarks and results of the
Fire Torch project. In: Proceedings DELFI International Symposium. Forest Fires: Needs
and Innovations. Athens. Greece. November 18-19, 1999.
Lonati M., Gorlier A., Ascoli D., Marzano R., Lombardi G., 2009. Response of the
alien species Panicum acuminatum to disturbance in an Italian lowland heathland. Botanica
Helvetica 119 (2): 105-111.
Marsden-Smedley J.B., Catchpole W.R., 2001. Fire modelling in Tasmanian
buttongrass moorlands. III Dead fuel misture. International Journal of Wildland Fire 10:
241–253.
Mercalli L., Cat Berro D., Acordon V., Di Napoli G., 2008. Cambiamenti climatici
sulla montagna piemontese. Rapporto tecnico realizzato per la Società meteorologica
Subalpina. Pp. 143.
Mugion L.G., 1996. Vegetational aspects of Calluna heathlands in the western Po
Plain (Turin, NW Piedmont, Italy). Alliona 34: 343-348.
Quinn G.P., Keough M.J., 2002. Experimental design and data analysis for biologists.
Cambridge University Press. Pp. 537.
Regione Piemonte, 2007. Piano regionale per la programmazione delle attività di
previsione, prevenzione e lotta agli incendi boschivi 2007-2011. Regione Piemonte. Pp. 156.
Rego F.C., Silva J.S., Fernandes P., Rigolot E., 2010. Solving the Fire Paradox
Regulating the Wildfire Problem by the Wise Use of Fire. In: Sande, J., Rego, F., Fernandes,
P. and Rigolot, E. (Eds): Towards Integrated Fire ManagementOutcomes of the European
Project Fire Paradox. European Forest Institute, Finland, Research Report 23. Pp. 219-228.
Rigolot, E., Fernandes, P. and Rego, F. 2009. Managing Wildfire Risk, Prevention,
Suppression. In: Birot, Y. (ed.) Living with wildfires, what science can tell us. EFI
Discussion Paper 15. European Forest Institute. Pp. 49-52.
Smith J.K., Laven R.D., Omi P.N., 1993. Microplot sampling of fire behavior on
Populus tremuloides stand in North-central Colorado. International Journal of Wildland
Fire 3(2): 85-94.
SPSS (2007). SPSS for Windows, Rel. 16.0.1. SPSS Inc, Chicago.
Vega J.A., Pérez-Gorostiaga P., Cuiñas P., Fonturbel M.T., Fernández M.C., 2001.
Manual de queima prescrita para matogueiras de Galicia. Dirección General de Montes.
Consellería de Medio Ambiente. Xunta de Galicia. 215 pp.
... conservazione di particolari ambienti, è stato rivalutato il ruolo dell'incendio come strumento di gestione territoriale. Ne è prova il fatto che vari paesi europei, tra cui l'Italia, hanno sperimentato la tecnica del fuoco prescritto (Pyne et al., 1996) in progetti di ricerca volti innanzitutto alla prevenzione di incendi incontrollati ma anche mirati allo studio e alla conservazione di specie ed ecosistemi la cui distribuzione risultava frammentaria e/o compromessa (Botelho et al., 1999;Ascoli et al., 2006;Ascoli et al., 2007;Moretti & Conedera, 2005;Moretti et al., 2008;Montiel & Kraus, 2010;Ascoli & Bovio, 2010;2013). Scopo del presente lavoro è presentare e comparare due rilievi fitosociologici svolti in aree adiacenti (dalle simili caratteristiche stazionali e aventi la medesima potenzialità vegetazionale) di un versante montuoso delle Prealpi Orobie: uno dove si è originato e protratto l'incendio, l'altro dove la vegetazione non è stata colpita dal fuoco. ...
... L'elevata frequenza che assume molinia nelle comunità vegetali postincendio del settore esalpico è documentata da uno studio di Gallinaro et al. (2001) relativo agli effetti prodotti sulla vegetazione da incendi verificatisi in diverse aree montane della provincia di Lecco. Il fuoco avrebbe favorito Molinia arundinacea anche in alcune aree incendiate del Piemonte, dove è risultata essere la specie dominante negli stadi immediatamente successivi agli incendi (Ascoli & Bovio, 2010), e della Svizzera sudalpina (Moretti & Conedera, 2005). Ravazzi (1992) tratta ampiamente del ruolo che Molinia arundinacea può esercitare sui substrati calcareo-dolomitici delle Prealpi lombarde dove tale graminacea, oltre che a partecipare alla formazione di praterie basifile fresche (seslerio-molinieti), può divenire specie dominante nelle praterie su versanti ripidi ed aridi, esposti a sud, su suoli provvisti di orizzonte a tessitura fine, impermeabili, caratterizzati da buona ritenzione idrica e a pH neutro o acido. ...
Article
Full-text available
A floristic-vegetational analysis of a burned area of the Bergamasque Prealps was carried out in order to understand the effects of fire on vegetation. The results showed that the post-fire community contains many species (some of which are endemic) belonging to the Festuco valesiacae-Brometea erecti and Festuco- Seslerietea classes that were not present before the incident and that represent the vegetation's adaptation to the new ecological conditions of the area.
... (2) Assuming a homogeneous fuel bed (or a dead fuel bed), a low relative air humidity induces a low fuel moisture content [38]. ...
Article
Full-text available
Eruptive fires are one of the main causes of human losses in forest fire fighting. The sudden change in fire behaviour due to a fire eruption is extremely dangerous for fire-fighters because it is unpredictable. Very little literature is available to support either modelling or occurrence prediction for this phenomenon. In this study, an unsteady physical model of fire spread is detailed, which describes the initiation and development of eruptive fires with an induced wind sub-model. The latter phenomenon is proposed as the mainspring of fire eruptions. Induced wind is proportional to the rate of spread and the rate of spread is in a non-linear relationship with induced wind. This feedback can converge or diverge depending on the conditions. The model allows both explaining why an eruption can occur and predicting explicitly its occurrence according to meteorological conditions, topographic parameters, fuel bed properties and fire front width. The model is tested by comparing its results to a set of experiments carried out at laboratory scale and during an outdoor wildfire, the Kornati accident. Nomenclature A Model parameter, radiation contribution B Stefan-Boltzmann constant (W·m-2 ·K-4) b ∞ Asymptotic parameter for the rate of spread C p Specific heat of vegetative fuel (J·kg-1 ·K-1) C pa Specific heat of ambient air (J·kg-1 ·K-1) e Depth of fuel bed (m) H Flame height (m) l Flame length (m) L Flame base depth (m) m Moisture content (weight of water/total weight) p Slope of the straight-line from Eq. (17) (m·s-1) p ∞ Asymptotic parameter for the rate of spread (m·s-1) R Rate of spread (m·s-1) R' Non dimensional rate of spread R b Rate of spread due to the flame base radiation (m·s-1) R f Rate of spread due to the flame body radiation (m·s-1) R ∞ Asymptotic value of the rate of spread (m·s-1) R p Asymptotic parameter for the rate of spread (m·s-1) r 0 Rate of spread factor (m·s-1) r 00 Rate of spread factor (m 2 ·s-1
Thesis
Full-text available
Sebbene gran parte degli incendi boschivi che si verificano nel mondo sono contenuti tempestivamente da un settore antincendio sempre più efficiente e tecnologico, emergono con maggior frequenza eventi estremi che superano le capacità di controllo e divengono disastri ambientali, economici e sociali. La rilevanza del problema e la necessità di una risposta che vada oltre l’obiettivo di estinzione è appresa maggiormente a seguito di stagioni critiche come quella del 2017; anno in cui in Italia sono stati percorsi dal fuoco più di 140'000 ettari, circa 33% in più rispetto alla media del periodo 1980-2016. La presente tesi è stata indirizzata a rispondere alle esigenze provenienti sia dalle amministrazioni locali che dal mondo delle imprese nei confronti della gestione selvicolturale come opportunità di prevenzione al fenomeno degli incendi boschivi.
Article
Full-text available
A fast, simple, low cost and general technique for estimating fuel surface area-to-volume ratio was developed. It requires the knowledge of particle density, the determination of fuel weight before and after immersion in water, and theoretical thickness of the adsorbed water pellicle that is assumed constant. Estimates by the technique were consistent and in good agreement with published surface area-to-volume ratios for the same fuels obtained through commonly used methods, and its performance is judged appropriate for the cunent fire behaviour modeling needs. The water immersion technique was applied to five common shrub species in Portugal. Limitations and possibilities for improvement of the newly developed technique are discussed.
Article
Full-text available
This study focuses on the effect of fire on lowland heathlands at the extreme southern edge of their European distribution (Vauda Nature Reserve, NW Italy). Forty-nine plots (50 m radius) were surveyed between 1999 and 2006. Each year, fire occurrences were recorded and per cent cover of four vegetation types (grassland, heath, low shrubland, and tall shrubland) was estimated in each plot. Vascular plant species richness was also recorded in 255, 1-m2 quadrats. After a fire, grassland vegetation expanded, but then declined rapidly as heath and shrubland recovered: 7 years after a fire, tall shrubland encroached on to more than 40% of the plots, and grassland declined from 50% to 20% cover. Between 1999 and 2006, Betula pendula shrubland greatly expanded, while grassland decreased over most of the Reserve, even where fire frequency was high. Tall shrubland had low plant diversity and was dominated by widespread species of lower conservation value. By contrast, early successional vegetation (grassland and low shrubland) had higher richness and more narrowly distributed species, indication that the development of tall shrubland causes significant species loss in the heathland. Italian lowland heathlands are characterized by high rates of shrubland encroachment that threatens both habitat and species diversity. Burning frequencies of once in 3–6 years seem appropriate in this habitat, but burning alone might not suffice without actions to increase herbivore grazing.
Article
Full-text available
An experimental program was carried out in Tasmanian buttongrass moorlands to develop fire behaviour prediction models for improving fire management. This paper describes the results of the fuel moisture modelling section of this project. A range of previously developed fuel moisture prediction models are examined and three empirical dead fuel moisture prediction models are developed. McArthur’s grassland fuel moisture model gave equally good predictions as a linear regression model using humidity and dew-point temperature. The regression model was preferred as a prediction model as it is inherently more robust. A prediction model based on hazard sticks was found to have strong seasonal effects which need further investigation before hazard sticks can be used operationally.
Article
Rate of spread, heat per unit area, flame length, and fireline intensity are plotted on a fire behavior chart. Spread component, energy release component, and burning index are plotted on a National Fire Danger Rating System chart. -from Authors
Article
Calluna vulgaris-dominated heathlands are globally important habitats and extremely scarce outside of north-west Europe. Rotational fire, grazing and cutting by local farmers were dominant features of past heathland management throughout Europe but have been abandoned, altering the historical fire regime and habitat structure. We briefly review research on Calluna heathland conservation management and provide the background and methodology for a long-term research project that will be used to define prescribed fire regimes in combination with grazing and cutting, for management of Calluna heathlands in north-west Italy. We outline the ecological and research issues that drive the fire experiment, making explicit the experimental design and the hypotheses that will be tested. We demonstrate how Adaptive Management can be used to inform decisions about the nature of fire prescriptions where little formal knowledge exists. Experimental plots ranging from 600 to 2500 m2 are treated according to one of eight alternative treatments (various combinations of fire, grazing and cutting), each replicated four times. To date, all treatments have been applied for 4 years, from 2005 to 2008, and a continuation is planned. Detailed measurement of fire characteristics is made to help interpret ecological responses at a microplot scale. The results of the experiment will be fed back into the experimental design and used to inform heathland management practice in north-west Italy.