Fire Effects and Fuel Management in
Mediterranean Ecosystems in Spain1
Ricardo Vélez2
The 1977 forest fire season was considered a
successful one in Spain. The number of fires did
not reach 50 percent of the average for the 3 previous years and the total area burned was less
than 40 percent of that burned in each of the
previous years (table 1). In contrast, 1978 presented an extremely prolonged fire season. Over
150,000 ha of forest and nearly 300,000 ha of
brushland and pastureland were burned by 8,324
fires (table 1). These contrasting years reemphasized the fire danger in the Mediterranean
ecosystems of Spain. They revealed the necessity
for a fire prevention program which considers the
factors determining the magnitude of the fire
hazard (Vélez 1980a).
In 1976 and 1977 the Forestry Service (ICONA)
was able to carry out pruning and clearing on over
120,000 ha of reforestation areas. This was
achieved with special funds provided to reduce
unemployment amongst agricultural workers. Moreover, in 1977 Spanish foresters had two opportunities to compare techniques with experts from
other countries and thus to reflect on their fire
prevention policy. These were the Technical Consultation (FAO/UNESCO) on Forest Fires in the
Mediterranean Region, held in France (ICONA 1978a),
and the Symposium on the Environmental Consequences
of Fire and Fuel Management in Mediterranean Ecosystems, held in Palo Alto, California (Mooney
and Conrad 1977). The concern over the need to
protect Spanish forests, together with exposure
to the ideas and practices of other countries led
to an active program of fuel management and research. In this paper I review the progress and
development of the early years of this program.
DEVELOPMENT OF A FUEL MANAGEMENT ACTION AND
RESEARCH PROGRAM
A fuel management plan for all danger areas as
well as a program of research on the effects of
1
Presented at the Symposium on Dynamics and
Management of Mediterranean-type Ecosystems,
June 22-26, 1981, San Diego, California.
2
Doctor Ingeniero de Montes, ICONA - Forest
Fire Section, Madrid Spain.
458
Abstract: Forest fuels in the Mediterranean ecosystems of Spain are characterized by generalized
pyrophytism and large accumulations of woody shrub
vegetation. The Forest Service prepared in 1978 a
fuel management plan and a program of surveys including: A study on the vegetation's evolution in
forests after fires; the experimental use of prescribed burning and grazing to reduce forest fuel
accumulations; a study of the evolution of fuel
accumulations in areas treated in 1976 and 1977
in Southern Spain; and a study of economics of
slash chipping.
fire and preventive silviculture techniques has
been developed (ICONA 1978b). The goal is to enable forest treatment methods to be perfected
through an improved knowledge of fire's role in
Mediterranean ecosystems.
Fuel Management In The Forests
The fuel management plan developed for Spain
can be summarized as follows: Fire prevention
(Vélez 1977) has the basic purpose of controlling
the fuel load in strategically important places,
either by reducing or removing it. The technique
used most commonly is that of fuel breaks, areas
from 60 to 100 m wide which divide the forest into
300 to 1,000 ha stands and on which natural vegetation is modified to reduce biomass and flammability. To the extent possible, fuel breaks
should link up with agricultural crops, recreational areas, campsites and natural barriers, so
as to form a system dividing the forest into compartments, making it easier to stop fires from
spreading.
Preventive work projects are designed to reduce
fire danger. They must specify the work to be
done, techniques used, the area to be treated
and the area to be protected. The work to be
included in such projects is varied. It must be
remembered, however, that unlike extensive forest
treatments directed towards improving production,
the intent of fuel management is to establish fire
barriers. This means intense action in small
areas, strategically located to prevent ignition
and contain the fire from spreading. The work
includes pruning, thinning and clearing in auxiliary strips along roads, and removing slash. It
may involve construction of roads and lanes,
accompanied by the relevant auxiliary strips, as
well as the preparation and maintenance of areas
with a humid microclimate, such as watercourses
and gullies. This may include the restoration,
on a small scale, of mesic vegetation. Reduction
of brushland by hand or mechanical clearing or
by controlled fire, and the opening up of spaces,
including the improvement of natural pasture for
use by cattle and wildlife are also involved.
Fuel management also includes the removal of
slash by burning or chipping. Classifying an
area as protected does not by itself assure that
it is fire proof. It does mean it is less likely
for a fire to start, and should a fire be started,
damage should be kept to a minimum.
Gen. Tech. Rep. PSW-58. Berkeley, CA: Pacific Southwest Forest and Range
Experiment Station, Forest Service, U.S. Department of Agriculture; 1982.
Table 1--History of forest fires in Spain, 1961-1980.
Burned area (ha)
Year
No. fires
Forested
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
............
1,680
2,022
1,302
1,645
1,686
1,443
2,229
2,109
1,494
3,203
1,714
2,148
3,765
3,980
4,242
4,596
2,148
8,324
7,167
7,000
34,506
23,911
13,279
17,671
21,777
24,644
33,930
20,547
19,296
34,330
13,194
18,048
40,559
58,789
111,091
79,853
26,454
159,264
119,579
101,086
UnForested
12,195
31,571
9,400
13,727
16,241
24,710
42,645
36,081
34,423
52,994
21,751
39,235
54,698
81,422
76,223
82,447
41,086
275,603
152,139
156,638
In the last two years fuel management work has
accomplished the following:
Action:
Fuel Break Preparation
Fire Break Maintenance
Road Building
Area Protected
Losses (millions pesetas)
1979
31,050 ha
-375 km
1980
17,356 ha
2,661 ha
140 km
500,000 ha
200,000 ha
Research on Fire Effects and Prevention Techniques
The research program on fire effects and preventive silviculture comprises these projects:
A.
A study of forest succession following fire.
Its aims are to study the effect of summer
fires on forest soils, to analyze the effect
of fire on regeneration, and to establish
the grounds for future prescribed burning.
Work on this project commenced in 1978, with
data being collected from burned areas in
the provinces of Gerona, Tarragona, Valencia,
Madrid, Avila and Pontevedra.
B.
Experimental use of prescribed burning to reduce forest fuel accumulations. Work on this
project began in Galicia (NW Spain) in 1978
and has progressed from initial burning of
plots less than 1 ha in size to burns of over
200 ha in pine plantations. Objectives include perfecting prescribed burning techniques as a means of controlling brushland
and for forest fire prevention, and understanding the atmospheric and vegetation features most suited to prescribed burning.
TOTAL
Commercial
46,701
55,482
22,679
31,398
38,018
49,354
76,575
56,628
53,719
87,324
34,945
57,283
95,257
140,211
187,314
162,330
67,541
434,867
271,718
257,724
C.
D.
928
598
311
372
412
446
575
549
484
764
334
559
1,118
1,992
4,121
3,974
981
9,205
6,790
6,000
Environmental
575
507
312
546
599
700
858
695
656
1,176
657
1,016
1,574
7,709
13,855
12,575
3,393
17,639
16,819
12,000
TOTAL
1,503
1,105
623
918
1,011
1,146
1,433
1,244
1,140
1,940
991
1,575
2,692
9,701
17,976
16,549
4,374
26,844
23,609
18,000
Experimental use of grazing to reduce fuel
accumulations. Work on this project began
in Galicia in eucalyptus plantations. The
idea was to use goats to remove Ulex and
Erica brush. The goal is to determine the
possibilities of using grazing to reduce fuel
accumulations in areas covered with brush and
in pine, eucalyptus and hardwood forests.
Study of fuel accumulation in Andalusia (South
of Spain). The aims of this project are to
determine the rate of brush regeneration, including the time at which it reaches a level
at which brush removal is needed, determining
the effectiveness of different methods of
destroying brush, and comparing success in
reducing fuel buildup by mechanical or manual
clearing, and prescribed burning. These
studies are being carried out in pruned and
cleared forest areas where debris has been
burned in piles, in unforested areas where
fire and grazing have maintained the herbaceous vegetation, and in pruned and cleared
forests where the branches have either been
left on the ground for weathering or have
been burned.
PRELIMINARY RESULTS
Fire Effects
Plant Survival
Surface fires that consume brush and herbaceous
vegetation without reaching tree tops make up 70
459
percent of all fires in Spain (ICONA 1968-1979).
The fire generally consumes the herbaceous vegetation and destroys most of the above ground brush,
with only the thickest lignified stems left standing. These fires usually burn the soil, reducing
litter to cinders and forming a layer of ash of
variable thickness. Tree damage is a function of
fire intensity and the amount of fuel accumulated
on the ground. In general, the bark is burned on
the outside but this does not necessarily signify
cambium damage. The thermal effect on leaves seems
more important. If the fire is rapid and the trees
have been pruned, only the lower levels of foliage
will be burned and the upper branches will survive.
If the fire is slow burning and the hot air envelopes the crown, survival is unlikely. Isolated
trees frequently survive fires in pine groves.
Unfortunately, it is difficult to collect this
type of information since to simplify forestry
operations, surviving trees are usually felled
wherever fires have occurred.
Data is being collected on tree survival in pine
groves after fires. In Lanjaron (Granada), where
there were fires in successive years (1973, 1974),
all the pine trees died in areas which burned
during the daytime. On the other hand, on areas
which burned at night, the fire became less intense as the wind dropped and humidity increased,
and only litter was burnt. A stand of Pinus
sylvestris with diameters of 5 to 10 cm and
branches from the base of the trunk survived the
fire as only the lower branches dried up. In
Musques (Vizcaya) incendiary fire in an unpruned
stand of P. radiata, with diameters of 10-15 cm,
burned at night, with high atmospheric humidity.
The fire slowly consumed the Ulex brush, leaving
the pine grove clean, as if it had been a prescribed fire.
In evaluating the effects of fire on broadleaved species we must distinguish between the
typically summer-drought Mediterranean (Quercus
ilex, Q. suber, etc.) and the more mesic species
(Q. robur, Castanea sativa, Fagus sylvatica, Betula
sp., Populus sp. etc.). The former usually grow
in sites similar to pine forests, forming either
open "dehesas" (the typical case of Q. ilex) or
closed formations as in Q. suber. In the "dehesas" fire is the creeping, rapid type, burning
the dry grass, often allowing the oaks to survive.
In closed formations there is usually a large
amount of brush and branches so that the fire
easily gets to the tree tops, defoliating the
trees.
Statistics indicate that on a scale from 1 to
10 the flammability of hygrophytic broad-leaved
species equals 1 while that of conifers equals 10
(Vélez 1980a). Thus the former are considered
as species which "do not burn". Indeed, on a
yearly basis formations of hygrophytic broadleaved species suffer little from fire, both in
numbers of fires and area burned. But, what happens when fire does occur? Without exception, the
above ground part of oaks (Quercus robur), chestnuts (Castanea sativa), and beech (Fagus sylvatica) die. Their tender leaves cannot withstand
460
the heat and the bark is not sufficiently thick to
insulate the cambium. However, it is noted that
these trees generally form a fire barrier. The
plants that are in front have perished, but the
forest has been saved. The reason is that these
species exist only in areas with abundant moisture. The fire is stopped because it spends its
heat evaporating water, and in the end there is
more water than heat. Naturally, if the fires
were to occur often enough these stands could be
eliminated. But, more commonly, they serve as an
effective fire barrier.
Plant Regeneration
Observations made in recent years indicate
that, contrary to public opinion, fire does not
sterilize an area but instead stimulates the
sprouting of vegetation after the first rainfall.
These sprouts usually consist of a larger number
of species than that present before the fire.
Subsequently, the variety of species diminishes or
at least is masked as some predominate over
3
others . The case of spurge flax (Daphne gnidium)
is typical in that it appears on all kinds of
burned ground with enormous vitality (it grows up
to 50 cm in a year) but becomes much less obvious
in later years. Woody brush also regenerates
strongly, sometimes sprouting from a stump (Erica,
Calluna, Ulex, Genista, Quercus coccifera, Juniperus, Chamaerops, etc.), and sometimes from seeds
(Cistus).
Pines seem to regenerate from seed easily after
fire as long as the stand was sufficiently old to
have fertile cones. In the Ayora-Enguera fire
(July 17-21, 1979 which burned 22,796 ha of pine
forest in Valencia (the most extensive fire recorded in Spain to date) regeneration of Pinus
pinaster and P. halepensis was abundant one year
later. The autumn following the fire was quite
favorable with frequent, non-torrential rainfall,
so that seeds had germinated when spring arrived.
They rooted well with that seasons rain and most
were able to survive the summer. Pine trees 20 cm
high were found in November, 1980, together with
others which had just germinated. All the burned
area had been logged, as the burned timber could
be commercially exploited. Over a 4,000 ha area
of Pinus pinaster was burned in 1976, near the
Ayora-Enguera fire. Total regeneration of the
pines was observed, reaching over 50 cm in height
after 4 years. Regeneration is at present being
aided by manually cleaning out around each tree.
In a drier area of Valencia, (Serra, Portaceli
fire, 1978), a lag of approximately one year in
regeneration has been observed. In addition,
little if any regeneration occurs on the driest,
3
1980 Internal Report by Ruiz del Castillo
on the study on fire effects in vegetation, Inst.
Nac. Investigaciones Agrarias, Madrid.
stoniest sites, which have a steep slope. The influence of exposure is not clear but sunny slopes
seem to be less favorable than shaded ones.
Regeneration appears to be greatest where the most
ash has accumulated. This might be because of the
high carbon content which retains a greater amount
of water, and thus favours seed germination. In
areas where former charcoal furnaces were located
regeneration is noticeably better, both in terms
of the number of trees and the height reached in
one year.
For certain species, used for reforestation,
like Pinus radiata, fire seems almost necessary
for regeneration, since the cones require heat to
open. In some reforested areas, mainly P. pinaster
and P. halepensis, little regeneration occurs. It
is not clear whether or how this might be related
to site quality.
Among the broad-leaved species, Quercus ilex
and Q. suber regenerate by crown sprouting.
Chestnuts are weakened as they may suffer wounds
in their roots when the fire goes deep into the
surrounding thick litter. Poplars sprout readily
and even withstand repeated, low intensity fires.
Birches disseminate their seeds better after fire.
In any event, not much information is available on
these species since they are seldom burned.
Introduced eucalyptus trees are able to withstand fire. Even when the above ground part is
killed, they sprout readily, often growing more
than 2 m the next year. They also disseminate
seed readily after fire. In Galicia E. globulus
is extending its area due to the large number of
fires occurring in that region (Dalda 1978a).
In light of these preliminary observations,
generalized pyrophitism of the Mediterranean
forest vegetation seems to be confirmed. In
truth, the story of our forest formations would be
incomplete if the role of fire was not included.
Fire is not and never has been a rare event in
these forests. It is now, apparently, more frequent than a few years ago and has more intense
effects. However, it has always been there. The
vegetation can tell us whether fire burned recently in an area. Chestnut and beech are clear
signs that there have been no fires for a prolonged period. A pine grove or Cistus shrub are,
on the other hand, probable indications of a
relatively recent fire (Martín Bolaños 1949). The
very name of the forest sometimes gives an indication of fire history. Magnificent pine stands
are known as "El quemado" (the burnt one) in many
places.
Controlled Fires
Experimental fires were burned on test plots in
unforested areas and eucalyptus plantations with
2
dry matter accumulation over 2 kg/m in the former
2
and 1 kg/m in the latter (Vega 1978). The slope
varied between 10 and 15 percent. In some cases
brush height came to 3 m. Burning was carried out
several days after rain in the spring. The majority of the fires were started with no brush preparation. Only on one eucalyptus plot was the
brush cut first and left on the ground. In the
first fire fuel reduction ranged from 55 percent
in the unforested areas to 50 percent in the
eucalyptus groves. In the latter, all trees over
10 cm in diameter survived without damage. The
influence of fire intensity on the trees was also
studied. The second burning, one year later,
produced less fuel reduction, but the effects on
the trees were similar. It was not found that the
increased cost of cutting the brush significantly
increased fuel reduction. Birch and oak (Q.
robur), with diameters less than 10 cm, were
common on the plots. Practically all survived or
sprouted after the fires. The same happened to
the few pines that were associated with the eucalyptus grove.
Fires were used on a greater scale in 1980 on
pruned Pinus pinaster and P. radiata plantations
with diameters of 10 to 40 cm and where brush
cover was from 1 to 4 m high. In one case, the
flash fuel was a thick layer of pine needles.
Burning was carried out in March and April, several days after rain. The burned areas varied
between 3 and 170 ha in size.
The following are presented as tentative conclusions. Additional studies will extend these
findings and check future effects:
a) Six months after fire the forest is easy to
travel through and little fuel is on the
ground. This makes it difficult for fire to
start as well as facilitates the suppression
thereof.
b) It does not appear that P. pinaster or P.
radiata with diameters over 10 cm suffered
appreciable damage.
c) Burning should be carried out so that brush
is consumed as completely as possible. If
the brush is thick, it may be advisable to
first fire under high moisture conditions and
then remove the rest with a second burning.
d) Trees should be pruned to a height above 2 m.
The low branches dry and drop a large number
of pine needles. If there is a large accumulation of needles they should be raked away
from the base before burning.
e) Burning should be carried out with the support of roads or fuel breaks at the top and
bottom. Butane lighters or diesel torches
are good ignition tools. Stirring up the
pine needles with rakes aids fire spread.
f) An average of 1 ha can be burned per day in
mountainous terrain. This is notably
cheaper than clearing by manual methods.
g) The possibility of keeping the burned land
clear by introducing horses, cattle or goats
should be considered.
h) A survey should be started on the effects of
burning on tree growth since these are basically plantations for timber production.
i) Apart from surveys on the effects of fire
prevention, it would be of interest to study
the effects of fire on the natural regenera-
461
tion of pines. It is probable that the lack
of regeneration in many stands is due to the
absence of fire.
be removed as soon as possible. The burying of
slash calls for the use of machinery which is not
easy in forested stands. Combining the manual
fuel removal system with other techniques appears
more promising.
Use Of Grazing
The first grazing experiments were carried out
in eucalyptus plantations (E. globulus) in Galicia.
Goats were the primary animal used although some
horses and cows were included. The plantations
consisted of mature trees with diameters over 10
cm. The understory is mainly Ulex, Erica and
Calluna.
The vegetation removal capacity of goats is
such that at certain times of the year natural
pasture does not suffice and their intake has to
be supplemented with concentrated feed. Animal
densities needed to keep the forest clean without
erosion are estimated at one goat per 1 to 1.5 ha
or one horse for each 4 ha (Rigueiro 1979).
Impacts on the flora are being studied since the
animals eat selectively, leaving the least appetizing species alone. For example, removal of
leguminous species may influence nitrogen fixation. The influence of fertilization from manure
must also be considered.
It is interesting to connect this work with
that of using controlled fire, bearing in mind
results from Santander where efforts are being
made to rationalize the traditional practice of
burning meadows and brush in order to "renew the
pasture" (Montserrat 1978). The intention is to
avoid extensive controlled burning which makes
the vegetation uniform, creating a continuous fire
danger. It has been recommended that mosaics of
2
small areas (maximum 200 m ) he burned by shepherds and grazed over the following years.
Fuel Management
It must he recognized that the budget for fuel
management has also had the aim of reducing unemployment. This forced manual methods to be employed wherever feasible. The common approach has
been pruning and clearing with hand tools, followed by piling of brush and branches for burning.
In areas with young trees and sparse canopy cover
it is estimated that further clearing will be
required every 2 to 3 years. If the trees are
older and give more shade brush regeneration is
less important. Some species, like Pinus sylvestris, inhibit brush growth in mature stands. In
any event, sufficient information is not yet
available to establish clearing rotation periods.
This system involves very high costs. To
reduce costs in areas with poor access it was
decided to deposit slash on the ground and leave
it for humification. In dry areas, this process
is slow and the danger arising from the fuel is
much greater than before, although it is true that
the branches prevent development of new brush.
The conclusion is that the slash should generally
462
In the province of Jaen fire breaks are combined with roads and open spaces in burning brushland. Wildlife comes down to eat the sprouting
brush, thus keeping biomass low. Burning may be
needed every five years in such situations.
Another possibility is to find a commercial use
for slash in order to make removing it from the
forest profitable. This has been studied for
Pinus sylvestris forests (Puig 1980). It requires
a chipper drawn by a tractor and a second tractor
to drag away the slash and pile it in strips along
the forest road. The potential profits are variable since the conditions in the forest and slash
to be chipped are heterogeneous. Products derived
include chips for particle board (pine) and chips
for fuel briquettes (oak, pine or brush). This
use is limited by the chip market which is low at
this time, and by the fact that there is only one
briquette factory in Spain. In any event, it is
an interesting alternative to the burning of
piles.
RECOMMENDATIONS
Observations on fire effects indicate that to
protect the forests (Vélez 1980b) it is necessary
to: a) recognize that fire is a natural ecological process that is only harmful in excess or
when it conflicts with man-created values: b)
recognize that genetic diversity produces morphologically diverse ecosystems which in turn are the
most apt to be perpetuated by fire; and c) recognize that fire must be managed as a recurring
process. In short, forest fire protection and
management requires the bringing together of a
variety of principles and types of knowledge.
This must consider the advisability of mixing
species, introducing hygrophytic species and
alternating forest and grazing lands (Gonzalez
Vazquez 1950).
In some places fire can be controlled with
hygrophytic species. They should be respected
where found and introduced where ecologically
desirable in order to create "fire resistant
places." Generally, the areas available for
forest restoration are degraded, dry and stony,
and are hardly suitable for hygrophytic species.
But there will always be watercourses nearby and
often scattered broad-leaved species of trees.
Respect for them and promotion thereof must prevail. The practice of planting birch trees in
water courses and at the side of forest roads is
being practiced in Galicia. Birch does not resist
fire but it does retain moisture and contributes
to retarding the fire's advance (Dalda 1978b).
Poplars, willows (Salix) and ash (Fraxinus) are
common wherever there is moisture and may also be
used. We must not hesitate to promote mixed
stands which in addition to being more natural,
defend themselves better from fire.
In areas with high fire danger it is not advisable, for instance, to replace cork oaks (Quercus
suber) since their thick bark makes them fire
resistant, as well as being able to sprout back
after burning. On the other hand, there is some
evidence that the eucalyptus plantations in
Galicia are turning out to be more and more attractive in view of the recent wave of incendiary
fires. They suffer little from fire, vigorously
sprouting from the stump. In any event, defense
against fire cannot be based primarily on replacing species with other less combustible ones.
Indeed, pyrophytism, so generalized in the Mediterranean area, reveals that natural fire defense
includes the mechanisms that stimulate reproduction after fire.
Forest fuel management should be directed
primarily towards the idea of reducing flammability.
This should be based on the creation of breaks
which transform the forest into a mosaic of species
and biomass, conifers mixing with broad-leaved
species, mixed ages, spaces being opened up between forest areas, etc. The even aged single
species stand, ideal for exploitation, is only
ecologically possible in limited areas of this
country due to its high susceptibility to fire.
Thus, the traditional concept of fire breaks,
which are costly to preserve, should be replaced
by the idea of fuel breaks as defined above (Vélez
1977). Likewise, low cost practices like controlled fires, and techniques which produce an
economic yield like grazing and slash chipping,
must be brought into forest fire preventive
treatment.
The development of these programs must bear in
mind criticism (Folch 1977) against the removal of
fuel from forests for ecological reasons. Experience up to now shows that those areas where fuel
has been reduced are less liable to suffer from
wildfires. In addition, if fire occurs, the
intensity is noticeably decreased, facilitating
suppression. Nevertheless, it is necessary for
the "ecology + economy" binomial to be carefully
analyzed in order to obtain valid results based on
scientific findings.
Literature Cited
Dalda González, J. Los efectos del fuego en la
vegetación forestal de Galicia. Madrid: ICONA;
Naturalia Hispanica; 1978a. 53 p.
Dalda González, J. Conveniencia y utilidad del
abedul para diversificar la cubierta forestal
del noroeste ibérico. Madrid: ICONA; Técnicas
españolas de lucha contra incendios forestales;
1978b; 65-68.
Folch Guillén, R. Sobre ecologismo y ecología
aplicada. Barcelona: Ketres, Ed.; 1977. 309 p.
González Vázquez, E. La riqueza forestal española.
Madrid: Dossat, Ed.; 1950. 63 p.
ICONA. Técnicas españolas de lucha contra incendios forestales. Madrid. 1978a. 91 p.
ICONA. Programa de estudios sobre ordenación y
control del combustible forestal para prevención
de incendios. Madrid: Bol. Est. Cent. Ecología
(14). 1978b; 93-97.
ICONA. Los indencios forestales en España durante
1968-1979. Reports published yearly from 1968
to 1979. Madrid. 1968-1979. 75 p. each.
Montserrat Recoder, P. El incendio de pastizales
y sus peligros. Madrid. Rev. Pastos (8), 1978;
31-36.
Martín Bolaños, M. Jaras y jarales. Madrid:
Instituto Forestal de Investigaciones y
Experiencias; 1949. 228 p.
Mooney H. A. and Conrad, C. E. (Eds). Proceedings
of the Symposium on the Environmental Consequences of Fire and Fuel Management in Mediterranean Ecosystems: USDA Forest Service Gen.
Tech. Report WO-3; 1977. 498 p.
Puig Sales, R. Aprovechamiento de residuos
forestales. Soria: Seminario sobre recuperación de recursos de los residuos; 1980. 73 p.
Rigueiro Rodríguez, A. Control de la vegetación
mediante pastoreo. Madrid: Rev. Agricultura;
1979; 871-873.
Vega Hidalgo, J. A. Utilización del fuego controlado en las comunidades vegetales de Galicia.
Madrid: Bol. Est. Cent. Ecología, (14). 1978;
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