An economic and ecological multi-criteria evaluation of reforestation methods to recover burned...

An economic and ecological multi-criteria evaluationof reforestation methods to recover burned

Pinus nigra forests in NE Spain

Josep Maria Espelta*, Javier Retana, Abdessamad HabroukCentre de Recerca Ecologica i Aplicacions Forestals (CREAF) i Unitat d’Ecologia, Facultat de Ciencies,

Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

Received 12 March 2002; received in revised form 9 August 2002; accepted 1 November 2002

Abstract

Recurrence of recent large wildfires is threatening the permanence of Pinus nigra Arnold (Black pine) forests in central

Catalonia (NE Spain), due to the almost nil post-fire regeneration of this non-serotinous pine. Potential practices to carry out

extensive reforestation programs with P. nigra may differ widely in terms of their final success, economic cost and undesired

ecological impact. In this framework, we have analysed different types of vegetation clearing (mechanical, controlled burning or

grazing), soil preparation (ripping or planting holes) and reforestation methods (broadcast seeding, spot seeding and planting) to

restore P. nigra forests. We have compared these practices in terms of seedling establishment, but also in the light of their

economic costs and ecological impact, through a new multi-criteria analysis. Seedling establishment after sowing was very poor

and not influenced by vegetation clearing. In plantations, seedling survival was higher in the ripper treatment than in planting

holes for all vegetation clearing treatments except the control one. Nevertheless, the higher economic cost of the planting holes

treatment and the negative impact of mechanical clearing and burning on the small mammals community made the stated

differences in seedling survival irrelevant. Thus, the multi-criteria analysis revealed that the two most preferred options were

planting in uncleared or lightly grazed areas with soil preparation through ripping. This study gives some valuable insights about

the use of new decision-support tools in restoration programs and provides practical guidelines concerning the restoration of

extensive burned P. nigra forests.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Post-fire restoration; Decision-support tools; Pinus nigra; Planting; Seeding

1. Introduction

Tree regeneration failure after large wildfires is

becoming one of the major factors threatening the

conservation of many forest ecosystems in the west

Mediterranean basin (Ferran and Vallejo, 1998).

Extensive and massive crown fires result in homo-

geneous burned landscapes where the absence of

surviving trees and the distance to the edge can

severely hinder the arrival of propagules and the

chances of a successful regeneration process (Retana

et al., 2002). In Catalonia (NE Spain), large wildfires

(>1000 ha) have accounted for 0.4% of the total

number of fires, but 75% of the total burned surface

from 1975 to 1999 (Salvador et al., 2000). Moreover,

since 1990, large wildfires have destroyed more than

Forest Ecology and Management 180 (2003) 185–198

* Corresponding author. Tel.: þ34-93-581-2028;

fax: þ34-93-581-1312.

E-mail address: [email protected] (J.M. Espelta).

0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0378-1127(02)00599-6

25% of the total area occupied by Pinus nigra Arnold

(Black pine) forests (Gracia et al., 2000). P. nigra does

not have serotinous cones and, due to the early release

of seeds at the beginning of spring, does not maintain a

seed bank when summer wildfires occur (Habrouk

et al., 1999). For these reasons, this species has very

low or nil post-fire regeneration (Trabaud and Camp-

mant, 1991; Retana et al., 2002).

P. nigra forests have both economic importance for

wood production and ecological significance (e.g. P.

nigra forests are included in the EU endangered

habitats directive), and the lack of successful regen-

eration has given rise to major concern about the best

alternatives to recover them through suitable artificial

reforestation programs (Espelta, 1999). In the west

Mediterranean basin, water stress has been envisaged

as the most limiting factor for ecosystem reconstruc-

tion, with soil fertility achieving secondary impor-

tance (Vallejo et al., 2000). Moreover, recently

established seedlings may be particularly prone to

water stress (Baeza et al., 1991), because they have

not yet developed a root system capable of replacing

water lost through transpiration. In that framework,

site preparation before reforestation, including both

vegetation clearing and soil preparation, may be of

paramount importance to enhance the outcome of

planted seedlings (Graham et al., 1989; Flemming

et al., 1996). Vegetation clearing has been reported

to diminish competition for water and nutrients, thus

ameliorating the survival rates of seedlings (Harvey

et al., 1996; Ashby, 1997). On the other hand, soil

preparation by ploughing may reduce runoff losses,

increase the total water stored in the profile and

decrease the penetration resistance of the soil (Ser-

rada, 1990; Querejeta et al., 2001).

Methods to clear vegetation and soil preparation

techniques may differ widely in their economic cost,

the effects on seedling survival and growth, and even

the promotion of undesired indirect ecological

impacts on the local fauna and flora (Peman and

Navarro, 1998). Although the benefits of different site

preparation techniques in reforestation programs have

been thoroughly documented elsewhere, very few

studies have at the same time taken into account their

effects on plantation performance, their economic

costs and their ecological consequences. Notwith-

standing, a general consensus has been growing up

about the need for insights from ecology and economy,

as well as social awareness about management of

natural resources, to be brought together if restoration

efforts are to succeed on a large-scale (Edwards and

Abivardi, 1997; Holl and Howarth, 2000). Elucidation

of the best way to increase plantation performance

with the minimum economic cost and ecological

impact, may benefit from advanced multi-criteria

decision-support tools. These methods facilitate the

comparison of different alternatives, and can contain

information arising from this complex system where

each criterion (plantation performance, economic cost

and ecological impact) may be expressed in a different

way (e.g. quantitative or non-quantitative) or sub-

jected to different types of uncertainty (e.g. stochastic

or fuzzy) (see, among others, Munda, 1995; Ducey

and Larson, 1999).

In the framework of assessing the best alternatives

to reforest extensive burned forests in Mediterranean

areas, the main objectives of this study are: (i) to

evaluate the combined effects of three different meth-

ods of vegetation clearing (controlled burning, live-

stock grazing and mechanical clearing), two types of

reforestation strategies (seeding, planting) and two

soil preparation techniques (ripping, planting holes)

in the establishment of P. nigra seedlings in burned

areas in Catalonia (NE Spain) and (ii) to compare this

array of contrasting alternatives in light of their eco-

nomic cost, plantation performance and ecological

impact, using a multi-criteria decision-support tool

(NAIADE: new approach to imprecise assessment and

decision environment; Munda, 1995). This compar-

ison includes two different analyses, one considering

financial cost and survival and growth of P. nigra

seedlings in the different reforestation practices, and

the second including other ecological criteria such as

the impact of those practices in the community of

small mammals.

2. Material and methods

2.1. Study area

This study was carried out in the regions of Bages

and Bergueda (418450–42860N; 18380–2810E, Catalo-

nia, NE Spain). The climatic conditions correspond to

the subhumid Mediterranean climate (according to the

Thornwaite index), with mean annual temperature of

186 J.M. Espelta et al. / Forest Ecology and Management 180 (2003) 185–198

12 8C and mean annual precipitation of 600 mm.

These regions were affected by the largest historically

recorded wildfire in NE Spain, which burned ca.

24,300 forested hectare in July 1994. According to

the data provided by the Forest Ecological Inventory

of Catalonia (IEFC), the area was covered extensively

by forests (71%). The main forest tree species before

the fire was P. nigra (75%) while other tree species

present in the area were Pinus halepensis Mill., Pinus

sylvestris L., Quercus ilex L. and Quercus cerrioides

Wk. et Costa (Gracia et al., 2000). After the fire event,

and due to the failure of P. nigra, 39% of the surface

previously covered by P. nigra forests became grass-

lands or open shrublands.

2.2. Experimental design and data analysis

The study was carried out from 1998 to 2000 in

three zones in the burned area: Can Armengol, Vila-

dases and Soler de Jaumas (Fig. 1A), the three located

in limestones. In each experimental zone, 14 plots of

1 ha each were established to test the combination of

different treatments of: (i) vegetation clearing, (ii)

reforestation and (iii) soil preparation. Treatments

were randomly assigned and combined in the 14

experimental plots in each zone (see Fig. 1B).

Before the start of the experimental treatments,

cover and height of the vegetation was determined

in each plot (sampling 1). To do so, 10 transects of

25 m each were laid per plot. In each transect, species

composition and vegetation height were measured

every metre. At this time, no significant differences

were found among experimental treatments for vege-

tation cover (range of mean values per plot: 83–86%)

and height (range 38–43 cm), while the three zones

differed in vegetation cover (ANOVA, F ¼ 15:9,

P < 0:05, mean � standard error: 91 � 1, 89 � 1

and 77 � 1%, for Viladasses, Can Armengol and Soler

de Jaumas, respectively), but not in vegetation height

(F ¼ 0:9, P ¼ 0:42, Viladasses: 48 � 2 cm; Can

Armengol: 41 � 2 cm; Soler de Jaumas: 33 � 2 cm).

In each study zone, four different treatments of

vegetation clearing were carried out:

� Livestock grazing (hereafter G). Four plots per site

were grazed by sheep and cattle during the spring

and fall of 1998. According to the observed levels

of tips and leaves consumption, as well as the light

browsing of low palatable shrubs, the grazing

pressure could be classified as moderate (following

Etienne et al., 1996).

� Controlled burning (hereafter B). The vegetation of

four plots per site was burned in December 1998 by

a controlled fire.

� Mechanical clearing (hereafter M). The vegetation

of three plots per site was cleared by rolling chains

pulled behind a tractor, leaving the debris scattered

about the site.

� Control (hereafter C). The vegetation of three plots

per site was kept intact.

To evaluate the effect of these clearing treatments,

the same 10 transects per plot of Sampling 1 were

monitored again after vegetation clearing, in March

1999 (Sampling 2), and 1 year later, in March 2000

(Sampling 3). The change in vegetation cover and

height per transect between Samplings 1 and 2 were

the variables used to analyse the ability of the different

clearing treatments to eliminate vegetation, while the

difference between Samplings 1 and 3 allowed us to

evaluate their ability to suppress vegetation re-growth

during a longer period. The effects of vegetation

elimination treatment and zone in these variables were

analysed by ANOVA models.

In the three experimental zones, the two reforesta-

tion methodologies contrasted consisted in planting

(1 þ 0) P. nigra seedlings or sowing P. nigra seeds. In

each zone P. nigra seedlings were planted in eight

plots combining randomly the four vegetation clearing

treatments and the two soil preparation methodologies

(Fig. 1B). The two soil preparation methods consisted

of:

� Ripping (hereafter R). In four plots, each one with a

different treatment of vegetation clearing, plough-

ing of planting lines where seedlings were subse-

quently planted, was carried out using a double

teeth subsoiler mounted at the rear of a bulldozer,

which opened two parallel rips of 70–90 cm depth.

� Planting holes (hereafter P). In four plots, each one

with a different treatment of vegetation clearing,

seedlings were planted in holes (40 cm � 40 cm) up

to 50 cm depth. These holes were carried out with

an excavator fitted with an articulated arm.

Initial seedling density planted in the different plots

was 1400 seedlings/ha regularly distributed. Survival

J.M. Espelta et al. / Forest Ecology and Management 180 (2003) 185–198 187

of seedlings was checked 1 and 2 years after planta-

tion, in six subplots of 25 seedlings (total 150 seed-

lings) per plot. Height growth of five seedlings per

subplot was also monitored in the six subplots per plot.

Height growth of seedlings was established as the

difference between their initial height (measured just

after plantation) and their height at the end of the first

and second year after the start of the experiment.

Fig. 1. (A) Geographical location of the area of Bages and Bergueda affected by the wildfire of 1994 in Catalonia (NE Spain) and the three

zones where the restoration practices were carried out. V: Viladases, SJ: Soler de Jaumas, CA: Can Armengol. (B) Experimental design of the

combined treatments of vegetation clearing, soil preparation and reforestation methods in each study zone.


The effects of the vegetation clearing treatment, soil

preparation, zone and time after plantation on seedling

survival and seedling height growth were analysed by

repeated measures ANOVA models. Inspection of

residuals was carried out to check for normality and

homoscedasticity. The sequential Bonferroni method

was employed to control the group-wide type I error

rate (Rice, 1989). The individual values of the differ-

ent levels of each variable were compared with a post-

hoc test (Fisher’s protected least significant differ-

ence).

Reforestation by seeding involved two different

methodologies to sow P. nigra seeds: broadcast dis-

tribution and spot distribution. In each experimental

zone, broadcast seeding was carried out in four plots

with the different vegetation clearing treatments pre-

viously described (Fig. 1B). On the other hand, spot

distribution was only applied in two plots per zone,

one grazed by livestock and another burned. We

specifically applied this type of seedling under these

two vegetation clearing methods, because they were

those which left the least debris above the soil, in

contrast with the mechanical clearing and the un-

cleared (control) plots. The aim was to compare the

possible benefits of a spot seed distribution to protect

seeds from predation and desiccation in contrast to a

broadcast seedling. The two seeding methodologies

consisted of:

� Broadcast distribution treatment. A total of 0.5 kg

of P. nigra seeds (cf. 25,000 seeds/ha) were broad-

cast over the whole surface of each 1 ha plot. This

treatment was applied in four plots per site, one per

treatment of vegetation elimination.

� Spot distribution treatment. In this case, 0.25 kg of

P. nigra seeds were used per 1 ha plot. A total

number of 1400–1500 small spots per ha were

regularly treated by hand in each plot, where 6–8

seeds were sown.

Prior to seeding, seeds were embedded in water

(12 h) and lightly dusted with two commercial and

widely used repellents (Morkit1 and Mesurol1) to

avoid or minimise predation by birds and insects after

sowing.

Since plots for all combinations of vegetation elim-

ination treatment � seeding methodologies were not

present in the field design, we were forced to carry

out two different complementary ANOVA analyses

instead of the complete design: a one-way ANOVA of

the effect of the four vegetation elimination treatments

on seedling establishment for the broadcast distribu-

tion treatment, and a two-way ANOVA of the effect of

the two seed distribution treatments and two of the

vegetation elimination treatments (grazed and burned

plots) on seedling establishment. To achieve normality

and homoscedasticity of residuals, seedling establish-

ment (density of seedlings per ha) was log-trans-

formed.

To assess a possible negative ecological impact of

the treatments applied, the dynamics of the small

mammals community were evaluated. We selected

this animal group as it can be considered highly

sensitive to the treatments used to clear vegetation

and prepare soil for planting (Barrett and Peles,

1999). Five surveys were carried out from November

1998 (before the experimental treatments) to January

2000. Two tramping transects were placed in each

plot. Each transect was composed of seven Sherman

traps at a distance of 10 m from one another. Captures

included two consecutive nights checked every 12 h.

An animal abundance index (number of animals

caught per trap and night) was obtained in each plot.

Two variables were used for describing the commu-

nity of small mammals in each plot: population

density (i.e., the total number of animals captured

per plot and survey), and diversity (computed as the

Shannon diversity index). More information on the

methodology used in this survey is described in

Comas et al. (2001).

2.3. Multi-criteria analysis of the different

reforestation practices

The evaluation of the different reforestation alter-

natives was carried out through a multi-criteria ana-

lysis. This analysis was done with the NAIADE

method (Munda, 1995). NAIADE is a multi-criteria

evaluation method which performs the comparison of

alternatives on the basis of a set of criteria. It allows

the use of information affected by different types and

degrees of uncertainty, thus the values assigned to the

criteria for each alternative may be expressed in the

form of either crisp, stochastic, fuzzy numbers or

linguistic expressions. This is a discrete method

(the set of alternatives is finite) which does not use

traditional weighting criteria and which generates a


ranking of alternatives using a pairwise comparison

technique (JRC-Ispra, 1996). NAIADE multi-criteria

analysis is based on a comparison algorithm made up

by the following steps:

(1) Completion of the criteria/alternatives matrix.

Values associated to each criteria for each

alternative are assigned in the form of pure

numbers or using a quantitative definition

affected by different levels and types of uncer-

tainty (either fuzzy or stochastic).

(2) Pairwise comparison of alternatives using pre-

ference relations. Comparison of criteria scores

(values) of each pair of alternatives is carried out

by means of their distance. In the case of numeric

evaluation, the distance is defined as the

difference between the two numbers. In the case

of fuzzy or stochastic evaluation, the semantic

distance is used, which measures the distance

between two functions, taking into account the

position and the shape of the two functions (see

for further details about this calculation JRC-

Ispra (1996)). The comparison by means of the

semantic distance is based on preference rela-

tions expressed by the user. These preference

relations are defined by means of six functions

that allow to express (depending on the distance

between alternatives), for each criterion, an index

of credibility of the statements that an alternative

is much better, better, approximately equal,

worse or much worse than another. The cred-

ibility index goes from 0 (definitely non-credible)

to 1 (definitely credible) increasing monotoni-

cally within this range.

(3) Criteria aggregation. Through an aggregation

algorithm of the credibility indexes, NAIADE

calculates a preference intensity index of one

alternative with respect to another, using the aparameter (see below) to express the minimum

requirements on the credibility indexes. Only

those criteria whose indexes are above the athreshold will be counted in the analysis.

(4) Ranking of alternatives. This ranking is based on

the preference intensity indexes. The final rank-

ing comes from the intersection of two separate

rankings. The first one (fþ) is based on the better

and much better preference relations, while the

second one (f�) is based on the worse and much

worse preference relations. Both rankings range

from 0 to 1 to express the intensity of the

relations (see for further details Munda (1995);

JRC-Ispra (1996)).

In this multi-criteria analysis, we only tested the

planting alternatives. We excluded the seeding treat-

ments; because their almost complete failure (see

Section 3) means that they were not worth comparing.

To evaluate each alternative, we used five criteria:

1. Financial cost. Monetary cost of the different

combinations of vegetation clearing and soil

preparation methods conducted.

2. Survival of P. nigra seedlings. Density of P. nigra

seedlings surviving at the end of the experiment.

3. Height growth of P. nigra seedlings. Absolute

mean height growth of P. nigra seedlings between

the start and the end of the experiment.

4. Density of small mammals. Computed as the

difference between the abundance of small

mammals captured per plot at the beginning and

at the end of the 2 years study.

5. Diversity of small mammals. Computed as the

difference in the Shannon diversity index of the

community of small mammals at the beginning

and at the end of the 2 years study.

This set of criteria had a different form. Financial

cost was a numerical criterion. P. nigra survival and P.

nigra growth were used as fuzzy criteria, because

there existed interactions on these variables among

vegetation clearing, soil preparation and zone (see

Section 3). For this reason we assigned to each cell

the mean observed value in the corresponding alter-

native, but instead of using a single value, we used a

fuzzy function shaped by the mean value and the

maximum range of variability observed among the

three zones. Thus, in the different simulations ran with

the model we could better integrate the spatial varia-

bility of survival and growth. For each criterion, four

thresholds delimiting indifference, weak indifference,

preference and strong preference were defined, after

discussion with landowners and governmental tech-

nical services in charge of restoration programs in the

area (Departament de Medi Ambient, Generalitat de

Catalunya). In NAIADE, the inclusion of such thresh-

olds is necessary to define the preference relations

that will allow the pairwise comparison of alternatives


(see above) taking into account the point of view of

stakeholders (see Munda, 1995). As it was impossible

to define realistically such thresholds for the density

and diversity of small mammals, we used a linguistic

expression of 9 degrees (ranging from perfect to extre-

mely bad) to define its situation in comparison with the

initial situation (before vegetation clearing and soil

preparation). In the analysis of alternatives, financial

cost was clearly considered a tendency to minimise,

while the remaining criteria were considered tendencies

to maximise. Table 1 summarises the form, thresholds

and tendencies of the different criteria used.

We ran two different analyses, the first one only

considered financial cost and survival and growth of

P. nigra seedlings, while the second also considered the

density and diversity of small mammals. Each analysis

included 1000 simulations to cover the variation arising

from fuzzy variables, such as survival and height of

seedlings, which are defined by a function. The mini-

mum requirement for the credibility indexes was

a ¼ 0:4. This means that in the aggregation process

only those criteria whose comparison resulted in an

index of credibility above the a threshold were included.

3. Results

3.1. Vegetation clearing

The different treatments to clear vegetation showed

significant differences in the reduction of vegetation

cover and height (Table 2). The highest reduction in

vegetation cover was obtained with the controlled

burning treatment, while the highest reduction in

height was obtained with the mechanical clearing

(Fig. 2). The reduction in vegetation cover (but not

height) varied with zone (41–33%). The interaction

between vegetation clearing treatment and zone was

also significant for vegetation height, because differ-

ences among zones were higher for the mechanical

clearing treatment.

One year after vegetation clearing, there were sig-

nificant differences in vegetation recovery among

experimental treatments (Table 3). The grazing treat-

Table 1

Expression, trend, units and thresholds of indifference (m ¼¼), slight indifference (m ¼), preference/rejection (m h&mi) and strong preference/

rejection (m hh&mii) for the criteria used in the multi-criteria analysisa

Criteria Expression Trend Unit m ¼¼ m ¼ m h&mi m hh&mii

Financial cost Numeric Minimise Euro 60 90 105 120

Survival of P. nigra Fuzzy Maximise Number 35 70 105 140

Height growth of P. nigra Fuzzy Maximise cm per year 2 4 6 8

Diversity of small mammals Linguistic Maximise – – – – –

Density of small mammals Linguistic Maximise – – – – –

a Note that preference or rejection will depend upon the trend of the criteria (respectively, maximise or minimise). Number, number of

seedlings/ha.

Table 2

F values from ANOVA tests of effects of vegetation clearing

treatment, zone and plot (nested within plot) on the decrease of

vegetation cover and height per transect just after the elimination

treatmenta

Factor d.f. Vegetation

cover

Vegetation

height

Vegetation clearing (VC) 2 119.3 52.7

Zone (Z) 2 8.3 1.6

VC � Z 4 2.1 3.8

Plot (zone) 3 7.1 1.6

a Significant coefficients (at a ¼ 0:05 after applying the

sequential Bonferroni method) are indicated in bold.

Table 3


treatment (grazing, fire, mechanical clearing and control), zone and

plot (nested within plot) on the decrease of vegetation cover and

height per transect 1 year after the elimination of vegetationa

Factor d.f. Vegetation

cover

Vegetation

height


Zone (Z) 2 11.0 1.1

VC � Z 4 3.3 0.9

Plot (zone) 3 8.6 0.2


sequential Bonferroni method) are indicated in bold. Data of

vegetation height were log-transformed.


ment showed the lowest reduction in vegetation cover,

and even an increase in vegetation height, in both cases

higher than control plots, while plots where the

mechanical clearing and burning treatments were

applied showed the lower recovery (Fig. 3). Zone

and the interaction between zone and clearing treat-

ment were significant for vegetation cover, because

vegetation recovery for the burning treatment was

higher in Can Armengol than in the other two zones.

3.2. Seedling survival and height growth in the

plantation plots

All factors and most of their interactions affected

seedling survival (Table 4). Percentage of seedling

survival was higher in mechanical cleared plots

(mean � standard error: 57:0 � 1:5%) and in control

plots (55:7 � 1:4%), than in grazed (52:1 � 1:2%) or

burned plots (50:0 � 1:3%). Moreover, seedling sur-

vival was higher in plots where ripping was conducted

(57:0 � 0:9%) than in those with planting holes

(50:3 � 1:0%), and was also different in the three

zones included in the study. Most of the interactions

between these factors were also significant. Thus,

according to the interaction vegetation clearing�soil preparation (Table 4) seedling survival was higher

in the ripper treatment than in planting holes for all

vegetation clearing treatments except the control

(Fig. 4). In the control treatment there were also

different patterns in the three zones of study. The

three zones also showed significant differences for

the two soil preparation treatments. Thus, seedling

survival decreased from 63:6 � 0:9% in 1999 to

43:7 � 1:0% in 2000, although this factor also showed

Fig. 2. Reduction of (A) vegetation cover and (B) vegetation

height after the three treatments used to eliminate vegetation.

Vertical bars extend over þ1S.E. of the mean. Different letters

indicate significant differences among treatments according to the

Fisher PSLD post-hoc test.

Fig. 3. Increment (or reduction) of (A) vegetation cover and (B)

vegetation height 1 year after the elimination of vegetation. Vertical

bars extend over þ1S.E. of the mean. Different letters indicate

significant differences among treatments according to the Fisher

PSLD post-hoc test.


significant interactions with the other three. Thus, the

highest survival was found in the mechanical clearing

treatment in the first year, and in the control treatment

in the second. The significant interactions of higher

order were of difficult interpretation.

Seedling height growth also varied for all the main

factors considered (Table 4). Seedling height growth was

lower in plots where vegetation had been cleared by

controlled burning (6:8 � 0:2 cm) than in the other three

types (M: 7:5 � 0:2 cm; G: 8:1 � 0:2 cm and C:

8:1 � 0:2 cm); it was also lower in plots where soil

preparation was carried out through ripping (7:2�0:1 cm) than in those which used planting holes

(8:1 � 0:2 cm), and was also different in the three zones.

There were also significant differences between years

(year 1999: 7:4 � 0:1 cm; year 2000: 7:8 � 10:2 cm).

3.3. Seedling density in the sowing plots

No significant differences were found among plots

with different type of vegetation clearing (two-way

ANOVA, P ¼ 0:41), among zones (P ¼ 0:15) or for

Table 4


treatment, soil preparation treatment, zone and year after

plantation (1999 and 2000) on seedling survival and seedling

height growtha

Factor d.f. Seedling

survival

Seedling height

growth


Soil preparation (SP) 1 32.4 9.0

Zone (Z) 2 228.2 6.3

Year after plantation (Y) 1 1101.1 8.2

VC � SP 3 33.7 0.1

VC � Z 6 16.3 2.8

SP � Z 2 15.9 1.7

VC � Y 3 12.2 0.6

SP � Y 1 1.9 4.7

Z � Y 2 52.4 3.4

VC � SP � Z 6 21.8 1.3

VC � SP � Y 3 16.3 3.8

VC � Z � Y 6 7.7 0.9

SP � Z � Y 2 11.1 0.1

VC � SP � Z � Y 6 2.1 0.4


sequential Bonferroni method) are indicated in bold.

Fig. 4. Variations in seedling survival in plots where vegetation had been eliminated by the different treatments according to the soil

preparation methodology used. Vertical bars extend over þ1S.E. of the mean.


the interaction between both factors (P ¼ 0:92) for

the broadcast sowing treatment. In these plots, seed-

ling establishment was very low (range: 0–200 seed-

lings/ha). Similar results were found for the

comparison between the two types of seed distribution

in plots with different type of vegetation clearing: no

differences were found between seed distribution

types (three-way ANOVA, P ¼ 0:10; broadcast dis-

tribution: 7 � 4 seedlings/ha; spot distribution: 80�36 seedlings/ha), vegetation clearing treatments (P ¼0:18) or zones (P ¼ 0:12). None of the interactions

between these variables was significant (P > 0:50 in

all cases).

3.4. Multi-criteria analysis of the different

reforestation practices

Table 5 shows the alternative � criteria matrix for

the NAIADE comparison of the different reforestation

methods. The analysis including only financial costs,

seedling survival and seedling growth (Fig. 5A), indi-

cated soil ripping and preserving vegetation (control)

(C þ R) or mechanical clearing (M þ R) as the best

alternatives, while mechanical clearing and planting

holes (M þ P) obtained the worst score. In spite of

differences on seedling survival, this ranking of alter-

natives was mainly driven by the economic differences

between treatments of ripping (cheaper) and planting

holes (much more expensive) (Table 5). Thus, all

alternatives including ripping as the soil preparation

method were placed at the top of the ranking list, while

those including planting holes were at the bottom.

When the impact of treatments on the density and

diversity of small mammals was included, some

important changes occurred in the ranking list

(Fig. 5B): (i) C þ R appeared as the most preferred

alternative, (ii) B þ R and M þ R went down in the

ranking list, due to their negative impact on small

mammals, (iii) C þ P raised to the third position in

spite of its high financial cost, and (iv) B þ P and

M þ P obtained again the worst scores, due to their

negative ecological impact and high costs.

4. Discussion

In most Mediterranean countries, reforestation is

the most widespread large-scale restoration practice

aimed at reducing fire effects (Vallejo and Alloza,

1998). Reforestation through seeding was the com-

monest way to restore pine forests until the mid-

seventies, when increased possibilities of mechanical

site preparation as well as improved seedling produc-

tion led to a shift towards plantation practices (Castell

and Castello, 1996). Notwithstanding, in recent years

the need to reforest extensive burned areas has

renewed interest in comparing different seeding and

planting strategies (Moreno and Vallejo, 1999).

In our study, the final establishment of P. nigra

seedlings 2 years after the experiment onset ranged

drastically from 7 � 4 seedlings/ha in the broadcast

seeding treatments to 610 � 40 seedlings/ha in the

plantations. Establishment after the seeding treatment

was much lower than the only comparable experience

we know in Catalonia: results obtained by Castell and

Castello (1996) in an aerial seeding experience with P.

halepensis immediately after the Garraf (Barcelona,

NE Spain) 1994 wildfire that gave densities of 830–

7200 seedlings/ha. The discrepancy observed may be

attributed to the fact we seeded 4 years after the fire,

Table 5

Alternative � criteria matrix used to compare the different reforestation methods essayed in the studya

G þ R G þ P B þ R B þ P M þ R M þ P C þ R C þ P

Financial costb 1020 1500 1200 1680 1320 1800 1020 1500

Survival of P. nigra a560 a630 a644 a490 a798 a434 a602 a728

Height growth of P. nigra a7 a8 a6 a7 A7 a9 a7 a8

Diversity of small mammals �Good �Good �Bad �Bad Bad Bad �Good �Good

Density of small mammals Good Good �Bad �Bad Moderate Moderate Good Good

a Numbers preceded by a symbol (a: approximately) indicate a fuzzy variable. G, livestock grazing; B, controlled burning; M, mechanical

clearing; C, control; R, ripping and P, planting holes.b Financial cost includes the costs of clearing vegetation (burning or mechanically), soil preparation (ripping or holes), cost of seedlings

and planting.


Fig. 5. Ranking of alternatives according to: (A) financial cost, survival and height growth of P. nigra seedlings and (B) adding the impact on the diversity and density of the

community of small mammals. Left values (fþ), ranking based on the better and much better relations (values range from 0 to 1, indicating how an alternative is better than the

rest). Right numbers (f�), ranking based on the worse and much worse relations (values range from 0 to 1, indicating how an alternative is worse than the rest).

J.M.

Esp

eltaet

al./F

orest

Eco

log

ya

nd

Ma

na

gem

ent

18

0(2

00

3)

18

5–

19

81

95

once ground vegetation had achieved a cover of

77–91%. Moreover, although seeds of P. nigra were

dusted with an insect repellent, we observed a great

amount of predation by granivorous ants (Messor

spp.), which had already massively colonised the area

(pers. observation). The failure of the broadcast seed-

ing assay points out that, although it may be recom-

mended to wait a precautionary time to observe

whether natural regeneration occurs after a wildfire

(Espelta, 1999), the fast recovery of ground vegeta-

tion, as well as some animal groups, severely threatens

the success of broadcast seeding treatments.

The establishment of seedlings of P. nigra obtained

in the plantation experiences is low in comparison to

the success of plantations reported in temperate and

boreal forests (Graham et al., 1989; Gemmel et al.,

1996; Archibold et al., 2000). However, they are in the

range of other experiences carried out in Mediterra-

nean environments (Vallejo and Alloza, 1998), where

the transplant-shock to a very harsh environment and

the following chronic water stress usually cause low

survival rates. Mortality linked to the early post-

transplant period is especially high in Mediterranean

environments, because of the poor ability of the root

system of the newly established seedlings to replace

water lost through transpiration (Baeza et al., 1991). In

addition, survival rates usually further decrease after

the first summer drought (Vallejo et al., 2000). For

these reasons, although global survival of P. nigra

accounted roughly for 50% of the initial density

(610 seedlings/ha), this result allows us to predict that

development of P. nigra forests in the area will be

possible at a medium term scale (see Retana et al.,

2002).

In our study, vegetation clearing prior to planting

showed a rather low impact, as survival after 2 years

was quite similar in all plots, with even slightly higher

values in control than in treated plots. This lack of

major effects of vegetation clearing could be linked to

two factors. First, the fast re-growth of the cleared

vegetation through resprouting led all plots to present

after 2 years a rather similar and high cover (more than

75%), the initial differences among treatments vanish-

ing (between 40% in the mechanical clearing and

100% in the control). Second, it is important to note

that in a harsh environment such as the Mediterranean

climate, rather than competing, vegetation could act as

a shelter for young seedlings, protecting them from

excessive solar radiation and water stress (see exam-

ples of this nursery effect in Jobidon et al. (1998)).

Notwithstanding this general trend, the type of vege-

tation clearing interacted with the soil preparation

method. Linear ripping has been reported as an excel-

lent way to ameliorate water availability and nutrient

release for seedlings by retaining runoff, increasing

the total water stored in the profile and enhancing the

possibilities of the root systems to penetrate and obtain

water and nutrients (Varelides and Kritikos, 1995;

Querejeta et al., 2001). However, to capture run off

losses it will be important to break soil crusts and

obtain regular and deep plowing rips in all the surface

(Peman and Navarro, 1998). In our study areas, rip-

ping was much more easily and regularly conducted in

plots where vegetation was previously burned or

mechanically cleared, in comparison to the grazed

or control areas, where shrubs obstructed ripping. In

contrast, in those areas the punctual planting holes

carried out by the excavator produced deep and regular

planting holes. We hypothesise that these differences

in soil preparation are responsible for the differences

in seedling survival.

The previous stated differences among reforestation

alternatives give us a first insight about the best way to

tackle recovery of extensively burned P. nigra forests.

However, possible emerging recommendations turn

over when considering differences in economic cost

and ecological impact throughout the NAIADE multi-

criteria analysis. Thus, combination of a low economic

cost and low ecological impact makes control plots

with soil preparation through ripping the top ranked

alternative, while burned and mechanical cleared plots

with planting holes would be the less recommended

ones. The two analysis run allowed us to note that

burning/mechanical clearing and ripping were top

ranked when only financial costs and survival and

growth of P. nigra seedlings were considered, but fell

down when the negative impact on small mammals

was included: in control plots, density of small mam-

mals increased 100% 2 years after the experiment

onset, but this increase only accounted for 30% in the

mechanically cleared plots and even decreased a 5% in

the burned plots (Comas et al., 2001). Moreover, in

these cleared plots, the community of small mammals

was dominated by a single species (Apodemus sylva-

ticus), while in control plots five different species

were found (Comas et al., 2001). These results allow


us to draw a major conclusion: vegetation clearing,

although a common sense practice extensively repor-

ted in reforestation projects, would be meaningless

in those sub-Mediterranean forests because of its

relative low importance in terms of seedling survival

but high economic cost and impact on the small

mammals community. Economic costs and ecological

values (e.g. protection of the community of small

mammals) have been usually placed at opposite

extremes (see Jackson et al., 1995). However, in our

case their optimisation involves similar reforestation

alternatives.

Restoration represents a long term dedication of

natural resources and a substantial financial commit-

ment (Ehrenfeld, 2000). Practitioners need to know

how to allocate this limited funding, labour and time

for maximum effect in the design of restoration pro-

grams of large-scale projects (Clewell and Rieger,

1997). In that framework, 4 years after the fire,

plantation rather than seeding arises as the most

suitable reforestation practice (with the present tech-

nological limitations of seeding). On the other hand,

vegetation clearing does not match the expected ben-

efits in the performance of young seedlings. Finally,

the multi-criteria analysis carried out provides a valu-

able example that although restoration activities are

inextricably embedded within an economic frame-

work (Edwards and Abivardi, 1997), it is possible

to reconcile such scope with ecological criteria (see

Holl and Howarth, 2000) when choosing among dif-

ferent alternatives.

Acknowledgements

Thanks are given to Giussepe Munda for helpful

comments and assistance in running the NAIADE

program, to Lluıs Comas for relevant information

about the dynamics of the small mammals community

in the study area and to Jose Luıs Ordonez for field

assistance. We are grateful to Anselm Rodrigo and

Ramon Vallejo and two anonymous reviewers for their

very useful comments on the manuscript. This

research was partly funded by INTERREG II (EU)

project Reconstruction of forest landscapes affected

by large wildfires events, the Department of Environ-

ment (Generalitat de Catalunya) and the INIA project

SC98-070.

References

Archibold, O.W., Acton, C., Ripley, E.A., 2000. Effect of site

preparation on soil properties and vegetation cover, and the

growth and survival of white spruce (Picea glauca) seedlings in

Saskatchewan. For. Ecol. Manage. 131, 127–141.

Ashby, W.C., 1997. Soil ripping and herbicides enhance tree and

shrub restoration on stripmines. Restor. Ecol. 5, 169–177.

Baeza, J.M., Pastor, A., Martın, J., Ibanez, M., 1991. Mortalidad

postimplantacion en repoblaciones de Pinus halepensis,

Quercus ilex, Ceratonia siliqua y Tetraclinis articulata en la

provincia de Alicante. Studia Oecolog. 8, 139–146.

Barrett, G.W., Peles, J.D., 1999. Landscape ecology of small

mammals. Springer, Heidelberg.

Castell, C., Castello, J.I., 1996. Metodologıa y resultados de la

siembra aerea efectuada en el Parque Natural del Garraf.

Montes 46, 51–57.

Clewell, A., Rieger, J.P., 1997. What practitioners need from

restoration ecologists. Restor. Ecol. 5, 350–354.

Comas, Ll., Retana, J., Espelta, J.M., 2001. Efecto de los

tratamientos silvıcolas para la reforestacion de zonas afectadas

por grandes incendios sobre las poblaciones de microma-

mıferos. V Jornadas de la Sociedad Espanola de Conservacion

y Estudio de Mamıferos, Vitoria-Gasteiz, Spain, December

6–10.

Ducey, M.J., Larson, B.C., 1999. A fuzzy set approach to the

problem of sustainability. For. Ecol. Manage. 115, 29–40.

Edwards, P.J., Abivardi, C., 1997. Ecological engineering and

sustainable development. In: Urbanska, K.M., Webb, N.R.,

Edwards, P.J. (Eds.), Restoration Ecology and Sustainable

Development. Cambridge University Press, New York, pp.

325–352.

Ehrenfeld, J.G., 2000. Defining the limits of restoration: the need

for realistic goals. Restor. Ecol. 8, 2–9.

Espelta, J.M., 1999. La reconstruccio de paisatges forestals afectats

per grans incendis. Projecte pilot a l’incendi del Bages-

Bergueda del 1994. Silvicultura 27, 6–9.

Etienne, M., Derzko, M., Rigolot, E., 1996. Browse impact in

silvopastoral systems participating in fire prevention in the

French Mediterranean region. In: Etienne, M. (Ed.), Western

European Silvopastoral Systems. INRA Editions, Paris, pp. 93–

102.

Ferran, A., Vallejo, V.R., 1998. Long-term plant regeneration after

wildfires in Mediterranean ecosystems of NE Spain. In:

Trabaud, L. (Ed.), Fire Management and Landscape Ecology.

International Association of Wildland Fire, pp. 155–165.

Flemming, R.L., Black, T.A., Adams, R.S., 1996. Site preparation

effects on Douglas-fir and lodgepole pine water relations

following planting in a pine-grass dominated clearcut. For.

Ecol. Manage. 83, 47–60.

Gemmel, P., Nilsson, U., Welander, T., 1996. Development of oak

and beech seedlings planted under varying shelterwood

densities and with different site preparation methods in

Sweden. New For. 12, 141–161.

Gracia, C., Burriel, J.A., Ibanez, J.J., Mata, T., Vayreda, J., 2000.

Inventari ecologic i forestal de Catalunya. Regio forestal IV.

Centre de Recerca Ecologica i Aplicacions Forestals, Barcelona.


Graham, R.T., Harvey, A.E., Jurgensen, M.F., 1989. Effects of site

preparation on survival and growth of Douglas-fir (Pseudotsuga

menziessi Mirb. Franco.) seedlings. New For. 3, 89–98.

Habrouk, A., Retana, J., Espelta, J.M., 1999. Role of heat tolerance

and cone protection of seeds in the response of three pine

species to wildfires. Plant Ecol. 145, 91–99.

Harvey, A.E., Page-Dumroese, D.S., Jurgensen, M.F., Graham,

R.T., Tonn, J.R., 1996. Site preparation alters biomass, root and

ectomycorrhizal development of outplanted western white pine

and Douglas-fir. New For. 11, 255–270.

Holl, K.D., Howarth, R.B., 2000. Paying for restoration. Restor.

Ecol. 8, 260–267.

Jackson, L., Lopoukhine, N., Hillyard, D., 1995. Ecological

restoration: a definition and options. Restor. Ecol. 3, 71–75.

Jobidon, R., Charette, L., Bernier, P.Y., 1998. Initial size and

competing vegetation effects on water stress and growth of

Picea mariana (Mill.) BSP seedlings planted in three different

environments. For. Ecol. Manage. 103, 293–305.

JRC-Ispra, 1996. NAIADE v. 1.0. Institute for Systems, Informatics

and Safety, Ispra.

Moreno, J.M., Vallejo, V.R., 1999. Fire impacts on the ecosystem

and restoration: summary of the main findings from the delfi-

fire database. In: Volume of Proceedings of Forest Fires: Needs

and Innovation. International Symposium. Athens, Greece,

pp. 239–261.

Munda, G., 1995. Multicriteria Evaluation in a Fuzzy Environment:

Theory and Applications in Ecological Economicals. Physica-

Verlag, Heidelberg.

Peman, J., Navarro, R., 1998. Repoblaciones forestales. Publ.

Universitat de Lleida, Lleida.

Querejeta, J.I., Roldan, A., Albadalejo, J., Castillo, V., 2001. Soil

water availability improved by site preparation in a Pinus

halepensis afforestation under semiarid climate. For. Ecol.

Manage. 149, 115–128.

Retana, J., Espelta, J.M., Habrouk, A., Ordonez, J.L., Sola-

Morales, F., 2002. Regeneration patterns of three Mediterra-

nean pines and forest changes after a large wildfire in

northeastern Spain. Ecoscience 9, 89–97.

Rice, W.R., 1989. Analyzing tables of statistical tests. Evolution

43, 223–225.

Salvador, R., Valeriano, J., Pons, X., Dıaz-Delgado, R., 2000. A

semi-automatic methodology to detect fire scars in shrubs and

evergreen forests with Landsat MSS time series. Int. J. Remote

Sens. 4, 655–671.

Serrada, R., 1990. Consideraciones sobre el impacto de la

repoblacion forestal en el suelo. Ecologıa 1, 435–462.

Trabaud, L., Campmant, C., 1991. Difficulte de recolonisation

naturelle du pin de Salzmann Pinus nigra ssp. salzmannii

(Dunal) Franco Apres incendie. Biol. Cons. 58, 329–343.

Vallejo, V.R., Alloza, J.A., 1998. The restoration of burned lands:

the case of eastern Spain. In: Moreno, J.M. (Ed.), Large Forest

Fires. Backhuys Publishers, Lieden, pp. 91–108.

Vallejo, V.R., Bautista, S., Cortina, J., 2000. Restoration for soil

protection after disturbances. In: Trabaud, L. (Ed.), Life and

Environment in the Mediterranean. WIT Press, Boston, pp. 301–

343.

Varelides, C., Kritikos, T., 1995. Effect of site preparation intensity

and fertilization on Pinus pinaster survival and height

growth on three sites in northern Greece. For. Ecol. Manage.

73, 111–115.


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