effects of 30-year-old aleppo pine plantations on runoff, soil erosion, and plant diversity in a...

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Catena 65 (200

Effects of 30-year-old Aleppo pine plantations on runoff, soil erosion,

and plant diversity in a semi-arid landscape in south eastern Spain

E. Chirino a,*, A. Bonet b, J. Bellot b, J.R. Sanchez b

a Fundacion Centro de Estudios Ambientales del Mediterraneo (CEAM), Spainb Department of Ecology, University of Alicante, Apdo. 99, 03080, Alicante, Spain

Received 9 March 2004; received in revised form 31 August 2005; accepted 13 September 2005

Abstract

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover

(Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation

structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5

vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15

hydrological plots (8�2 m), in the Ventos catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a

different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of

vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots

averaged 0.04 Mg ha�1 year�1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with

the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control

runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved

the stand’s vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey

of the plantations.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Runoff; Erosion rate; Afforestation; Semi-arid; Soil erosion

1. Introduction

During the 1950s and 1960s, Aleppo pine (Pinus

halepensis Miller) plantation over low cover formations

was the most widespread forest administration management

policy in most areas of Spain (Valle and Bocio, 1996;

Vallejo, 1997; Cortina et al., 2004). The medium and long-

term purpose of these afforestation policies was to recover

the vegetation cover for soil conservation and to reduce the

effects of soil erosion. With these aims, about 2.5 million

hectares in Spain, have been afforested over the last 50

years; that is approximately 5% of the national territory

0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.catena.2005.09.003

* Corresponding author. CEAM - Department of Ecology, University of

Alicante, Apdo. 99, 03080, Alicante, Spain. Tel.: +34 965903555; fax: +34

965909832.

E-mail address: [email protected] (E. Chirino).

(Vilagrosa et al., 1997). The II National Forest Inventory

(IFN) of the Ministerio de Medio Ambiente in Spain (1998)

reported that Aleppo pine forest had increased the woodland

surface over all in Spain by 75%. Aleppo pine forest

occupies practically all of the woodland surface of the

Spanish semi-arid region. Aleppo pine forest constitutes the

dominant forest species in the Alicante province covering

more than 90% of the forested area. As a consequence of

this forest policy the semi-arid lands have become a patch-

mosaic landscape of a mixed formation of grasslands and

shrublands with afforested woodlots, occupying the north-

facing slopes, where water availability is less restricted.

Whereas Alpha grass steppes of Stipa tenacissima L. are

widespread in south-facing slopes and the presence of pine

trees and other shrub species is less significant (Bonet et al.,

2001). Recently, the increase of abandoned land has

changed this patch-mosaic as described by Reynolds et al.

6) 19 – 29

E. Chirino et al. / Catena 65 (2006) 19–2920

(1999), introducing new patches for woodland connectivity

or for overall landscape fragmentation (Bonet et al., 2004).

The performance of Aleppo pine forest has been strongly

related to water balances and the disturbance regime in

Mediterranean conditions (Zavala et al., 2000). Moreover, it

has also been suggested that Aleppo pine plantations in

extreme water stressed arid conditions could not develop

self-persistent populations, mature and multi-layer commu-

nities, unlike the situation in other wetter Mediterranean

areas (Rivas-Martınez, 1987; De la Torre, 1988; De la Torre

and Alıas, 1996; Costa, 1987), in spite of their drought

resistant characteristics in dryer regions (Schiller and

Cohen, 1998; Atzmon et al., 2004). This is probably due

to low growth and unsuccessful regeneration dynamics in

extreme water stressed events (Raventos et al., 2001).

The objective of the work presented here is to evaluate

afforestation using Aleppo pine as the appropriate recovery

strategy in semi-arid regions, in contrast with the natural

recovery of these areas, considering the effects on the

magnitude of runoff, soil losses, plant cover, species

richness and plant diversity. This management strategy is

based on the hypotheses that erosion decreases exponen-

tially with vegetation cover (Elwell and Stocking, 1976),

despite the work of Francis and Thornes, which indicates

that this hypotheses is true but more-or-less independent of

cover type (Francis and Thornes, 1990a,b), and that the

advantages of Aleppo pine afforestations are only a little

above those of natural and anthropogenically degraded

shrubland and grassland (Francis and Thornes, 1990b).

From this perspective it was expected that the effects of an

Aleppo pine stratum planted 30 years ago, would signifi-

cantly reduce erosion, in contrast with the areas without

active management, where the regeneration of the plant

cover only took place slowly through natural vegetation

dynamics (Bonet, 2004). To evaluate the previous hypoth-

esis, we analysed five land-cover types that represented the

composition of the patch-mosaic landscape in north-facing

semi-arid environments (Bonet et al., 2001, 2004). In the

study area, north-facing afforestations with Aleppo pine

tress had been more successful in extent, growth and

survival than in south-facing aspects (Cortina et al., 2004;

Bonet et al., 2004). These cover types included a gradient

from more degraded (open areas without vegetation) to less

degraded (grassland and shrubland) landscape units and the

result of afforestation practices. The aim of this paper is to

evaluate the effectiveness of Aleppo pine afforestation as a

common technique to restore plant cover, facilitate the

establishment of other understorey species, and reduce the

effects of erosion in a semi-arid landscape.

2. Area description

The research was carried out in the Ventos-Agost

Catchment Experimental Station (University of Alicante),

located in the Municipality of Agost, Alicante Province, SE

Spain (38-28VN, 0-37VW). The study area covers approxi-

mately 537 ha, with altitudes ranging around 600 m a.s.l.,

and slopes between 23- and 26-. The climate is semi-arid

Mediterranean, with a very high inter-annual variability.

Mean annual temperature is 18.2 -C and annual rainfall is of

291.7 mm (mean of the 1961–1999 period), most of which

falls in autumn (Perez Cuevas, 1994). Lithology is loam and

loamy limestone supporting calcareous Cambisol (FAO-

UNESCO). The soils are characterised as shallow (0–30

cm), with a medium content of organic matter (5.7%),

between 48% and 58% of clay content, soil bulk density of

1246.0 kg m�3, and a soil particle density of 2352.0 kg

m�3. The hydraulic performance of the soil is determined

by a total porosity of 46.0%, field capacity of 25.0%, a

saturated soil hydraulic conductivity of 3.37 cm s�1, and

average infiltration rate of 512.6 L m�2 h�1. Resistance to

the penetration of a cone of 0–30 cm of depth (18%

humidity) varies between 31 and 97 kPa (Derouiche et al.,

1996; Bellot et al., 2001).

The plantation period lasted from 1960 to 1983, but was

especially intense during the first decade. The Forest

Service afforested the area with P. halepensis Miller

woodlots over land degraded grasslands and shrublands,

maintaining 30% of the territory managed with no inter-

vention. Afforestation was carried out by planting in holes

made by hand, with a mean plantation density of 5280T692trees ha�1 over grasslands and 3733T1097 trees ha�1 over

shrublands. In these areas forest management was restricted

to a minimum selective pruning, and no thinning was

carried out after the treatments.

The present vegetation landscape in the study area is

composed of different land cover types (patch-mosaic) that

can be situated in a successional and structural vegetation

complexity gradient: degraded open land or bare soil (B),

sometimes occupied by microphytic crusts (Maestre et al.,

2002); dry grassland formations (G) of Brachypodium

retusum Pers. Beauv., with dwarf scrubs (Anthyllis cyti-

soides L., Helianthemum syriacum (Jacq.) Dum.-Cours. and

Thymus vulgaris L.); and more mature landscape patches

composed of scattered thorn and sclerophyllous shrublands

(S) with Quercus coccifera L., Pistacia lentiscus L., Erica

multiflora L., Rhamnus lyciodes L. and Rosmarinus

officinalis L. (Bonet et al., 2001). Other anthropic compo-

nents of the present landscape mosaic are afforested dry

grasslands (AG) and afforested thorn shrublands (AS).

3. Methods and experimental design

The research was conducted over a 4-year period (1996–

1999) and 30 years after the plantation work. In each land-

cover type (B, G, S, AG and AS) we installed 3 hydrological

plots of 16 m2 (8�2 m) randomly distributed in each

landscape patch. After each rain event, the volumes of

runoff and soil loss were collected and measured in the

Gerlach box of 2 m width, installed at the bottom of each

E. Chirino et al. / Catena 65 (2006) 19–29 21

plot. The precipitation and other climatic variables (temper-

ature, radiation, wind, and air humidity) were measured and

registered continuously by means of an automatic meteoro-

logical station (Campbell CR10). The analysis of annual

runoff coefficient and erosion rates were calculated consid-

ering 4 years (1996–1999), and the one-way ANOVA was

used for statistical analyses of vegetation type responses

during 1998 and 1999. This analysis also was carried out in

two groups of rainfall events, those exceeding 10 mm and

those below 10 mm.

In order to determine the afforestation effect on

vegetation structure, the vegetation survey was performed

in two ways to characterise the hydrological plots and the

landscape patches, respectively. First, each hydrological plot

was divided into eight subplots (2 m2) to determine the

cover (%) of each plant species, stoniness, litter cover and

bare soil. As a functional indicator of vegetation community

structure, we also recorded the leaf area index (LAI), which

was estimated by means of a destructive analysis in 0.25 m2

plots close to hydrological plots. The second vegetation

survey was carried out on landscape patches over a wider

scale during the spring of 1998, using 5 stands (as

replicates) of 100 m2 in each land cover type. On each

stand, 10 squares (1 m�1 m) were placed in a random

procedure. A complete species list was recorded and the

species cover (%) was estimated in each through the

projection of each plant species in the soil horizontal plane

by means of a grid (5�5 cm unit). Species richness and

Shannon’s diversity index (HV), were calculated on each

plot. Species were grouped in life forms (trees, shrubs,

dwarf shrubs, and herbs: perennial grasses, perennial forbs

and annuals). The differences between the vegetation

characteristics in the hydrological plots and the landscape

patches surveys were analysed by using the Kruskall-Wallis

test and the posteriory Wilcoxon test. The statistical

analyses on plant diversity and hydrological variables were

carried out by doing a one-way ANOVA on log transformed

data. The statistical comparison of the vegetation cover

types in the hydrological plots was carried out by Principal

Components Analysis—PCA (Statistic, version 3.0). Vege-

tation composition and cover of hydrological plots was

analysed through means of Detrended Correspondences

Analysis—DCA (Ter Braak and Colin Prentice, 1988) using

CANOCO version 4 (Ter Braak and Smilauer, 1998).

Fig. 1. PCA ordination plot of cover type characteristics showing the

position of each hydrological plot in relation to the main ordination factors.

S, filled circle; AS, open circle; G, open square; AG, filled square.

4. Results and discussion

4.1. Analysis of the physical characteristics and vegetation

composition of hydrological plots

In order to prove the homogeneity of the characteristics of

the different hydrological plots in the cover types analysed,

we carried out a Principal Components Analysis (PCA)

using several variables that characterised the plots and the

accumulated values observed in runoff and soil loss treat-

ments. A correlation matrix between the 12 variables (runoff,

soil loss, slope, total LAI, total vegetation cover, trees

stratum cover, shrub stratum cover, herbaceous stratum

cover, moss stratum cover, bare soil surface, stones cover,

and litter cover), ratified the existence of significant

correlation ( p<0.05) between the variables runoff and soil

loss with the total vegetation cover and the bare soil

percentages. After this analysis we rejected those variables

that introduced redundant information in the PCA analysis.

The PCA results (Fig. 1), indicate eigenvalues (k) of 2.93,2.13 and 1.57 for factors 1, 2 and 3, respectively. The first

factor explains 36.6% of the variance and is composed of

vegetation cover, and trees and shrub stratum; factor 2

explains 26.7% and is made up of the LAI and the

herbaceous stratum and factor 3 explains the 19.6%

represented by the slope.

Grassland plots showed more variability in factors 1 and

2, regarding differences in vegetation cover (Fig. 1A). Shrub

plots also showed some variability in relation to factor 3

(Fig. 1B), as consequence of slope, which ratifies the effect

of this variable in the generation of greater runoff in S in

comparison to G. These results showed that the hydrolog-

ical response in the plots is a function of the vegetation

structure (vegetation strata) and physical characteristics,

mainly slope. The PCA ordination is consistent with the plot

selection by structure and vegetation cover types.

In order to verify the homogeneity of the vegetation of

hydrological plots, a DCA analysis on species composition

and cover was performed using an input matrix of 12

samples (plots with vegetation cover) by 52 species with

224 occurrence samples. DCAwas analysed with detrending


by segments and downweighting of rare species. Ordination

eigenvalues were higher for the first axis (k1=0.320) than

for the second (k2=0.139). Cumulative variances of species

data improve greatly through addition of the second and

third axis (c1=28.4; c2=40.3; c3=44.0). The DCA results

(Fig. 2) showed that ordination of vegetation composition is

consistent with the selected plot design. Ordination revealed

a close relationship of species cover between hydrological

plots pertaining to each land cover type. Meanwhile

Brachypodium retusum (Pers.) Beauv. was the most

abundant species in all plots, and specially in G, plots

under this land cover type also presented Coronilla juncea

L. and Fumana ericoides (Cav.) Gand. Cistus albidus L.

was recorded in pine understory of AS and AG, but other

dwarf shrubs were absent in forested plots (Globularia

alypum L., Helichrysum stoechas (L) Moench., Lithodora

fruticosa (L.) Griseb, and Thymus vulgaris L.). On the other

hand, Q. coccifera L. showed high cover values in S and

AS. Despite the existence of a P. halepensis Miller layer,

differences in composition and cover of hydrological plots

between S and AS were due mainly to the abundance of E.

multiflora L. in S and the abundance of P. lentiscus L. and

Rhamnus lycioides L. and the absence of dwarf shrubs in

AS. The first DCA axis is negatively correlated with LAI

(Kendall’s correlation coef. = 0.879, p <0.000, n =12),

meanwhile the second axis is negatively correlated with

tree cover (Kendall’s correlation coef.=�0.638, p=0.006,

n =12), and positively correlated with sediment yield

(Kendall’s correlation coef.=0.545, p =0.014, n=12), and

slope (Kendall’s correlation coef. =�0.450, p =0.045,

n =12).

4.2. Effects of afforestation on runoff and erosion

Many authors have studied the relationships between

vegetation cover, runoff and sediment yield (Elwell and

Stocking, 1976; Morgan, 1986; Trimble, 1988; Francis and

Thornes, 1990b; Teixeira and Misra, 1997; Albadalejo et al.,

1998). This relationship is a function of several factors:

Fig. 2. DCA ordination plot of the plant species cover showing the position

of each hydrological plots. S, filled circle; AS, open circle; G, open square;

AG, filled square.

rainfall characteristics (volume, intensity, duration and

frequency); soil parameters (physics and hydrophysics);

and also vegetation structure. All the research carried out in

the study zone (Derouiche et al., 1996; Bellot et al., 1998,

2001; Chirino et al., 2001) has indicated that the protective

effect of the vegetation cover controls runoff and soil

erosion. Vegetation cover diminishes the quantity of water

that reaches the soil through the effect of interception

(Bellot and Escarre, 1998), and also increases the hetero-

geneity of the spatial distribution of the rainwater toward the

soil, through the stemflow and throughfall (Lopez, 1989;

Bellot and Escarre, 1998).

According to the structure of vegetation cover, some

differences were expected in runoff and soil erosion between

AG, AS, G and S. Through the analysis of the entire research

period we observe the lower values of the annual runoff

coefficients in the vegetated plots (AS, AG, G and S), which

do not exceed 1.0% of precipitation (Table 1), and approx-

imately increased 8-fold in open land plots (B). In conse-

quence the calculated annual soil loss rates (through runoff)

are also low (Table 1). The average values of the annual soil

loss rates were calculated in all vegetated plots (less than 0.05

Mg ha�1 year�1). The open lands (B) obtained higher values

(1.90 Mg ha�1 year�1). Table 1 also expresses the sediment

yield as percentage of bare soil annual values. The result

appears to indicate that afforested communities (AG and AS)

show small mean values with respect to the non-afforested

ones (the half of the G and S, respectively), despite the high

inter annual variability of each cover type.

The statistical analysis of the runoff values and soil

losses (Table 2), detected significant differences only

between the accumulated runoff (FCover type = 8.105,

p =0.004, n =15), and soil loss (FCover type =16.554,

p =0.000, n =15), of the vegetated plots (AS, AG, S and

G) in comparison to the open lands (B). These results

indicate that in the aforementioned conditions, a 30-year-old

afforestation with Aleppo pine (AS and AG) does not

significantly reduce the runoff and erosion in comparison to

natural vegetation (S and G), which is very important for

management. In summary, these results are entirely consis-

tent with early expectations and we are relieved that there is

no significant difference between cover types.

These results are due to the high percentage of vegetation

cover in non-afforested plots. These values rise to 70–95%

in all (Table 1), which are enough to reduce the runoff and

soil loss in every type of vegetation cover analysed. If we

take into account the estimated values of net precipitation

using the hydrological model VENTOS (Bellot et al., 2001),

31–40% of the rainfall is intercepted by vegetation cover in

plots, reducing both the runoff by 85%, and the soil loss by

95%, with respect to the open lands. Several authors

(Francis and Thornes, 1990a; Cerda, 1998; Andreu et al.,

1998) have reported similar figures. In our study, shrublands

and grasslands with more than 70% of vegetation cover

protect the soil in the same way as the afforested

communities, however, the AS plots reveal higher protec-

Table 1

Annual runoff coefficient and soil loss in hydrological plots by vegetation type cover

Characteristics Slope and vegetation cover of hydrological plots

B G S AG AS

Slope (-) 22 26 29 23 21

Vegetation cover (%) 0 70 90.2 95.8 95.2

Years Acum. rainfall. (mm) Annual runoff coefficient (%)

B G S AG AS

1996 308.9 nda 0.60 0.46 0.45 0.29

1997 483.3 5.36 0.62 0.63 0.62 0.45

1998 288.3 3.80 0.45 0.52 0.80 0.39

1999 241.1 4.11 0.52 0.77 0.71 0.45

Mean 330.4 4.42 0.55 0.60 0.65 0.40

30/09/97b 134.6 12.54 0.59 0.86 1.02 0.56

Annual soil loss (Mg ha�1 year�1)

1997 483.3 2.070 0.100 0.055 0.088 0.036

1998 288.3 0.873 0.003 0.004 0.003 0.003

1999 241.1 2.761 0.004 0.067 0.014 0.019

Mean 337.6 1.901 0.049 0.042 0.035 0.019

30/09/97 134.6 1.70 0.07 0.05 0.10 0.03

Annual soil loss

(Mg ha�1 year�1)

Annual soil loss (% of bare soil)

1997 483.3 2.070 4.83 2.65 4.25 1.74

1998 288.3 0.873 0.34 0.46 0.34 0.34

1999 241.1 2.761 0.14 2.42 0.50 0.68

Mean 337.6 1.901 2.57 2.21 1.84 1.00

30/09/97 134.6 1.70 4.11 2.94 5.88 1.76

a Treatment not available.b Extraordinary event.


tion (0.40% of runoff and 0.019 Mg ha�1 year�1 of

erosion), but the difference was not statistically significant

from the other vegetated plots. Vacca et al. (2000) estimate

runoff coefficients of 0.65–1.59%, and erosion rates

between 0.03 and 0.05 Mg ha�1 in plots of 20 m2 covered

by herbaceous plants and shrubs, while in Eucalyptus sp.

plots (15 years old and 25% vegetation cover) the estimated

rates were 2.01% and 0.19 Mg ha�1, respectively. The

registered rates of soil erosion in our vegetated plots are

lower than those reported in other research works carried out

in semi-arid environments of Spain. Romero-Dıaz et al.

(1988) calculated annual soil losses of 0.08–2.55 Mg ha�1

year�1 in a catchment with 35% of vegetation cover with

marls as substrate. In a microcatchment with 60% of

vegetation cover, Albadalejo and Stocking (1989) deter-

mined rates between 0.5 and 1.2 Mg ha�1 year�1, and

Lopez Bermudez et al. (1991) reported annual losses of 0.1

Mg ha�1 year�1 in plots with 80% shrub cover. Areas with

reduced vegetation cover (lower than 50%) caused by

Table 2

Accumulated runoff and soil loss rates in hydrological plots by vegetation cover t

DMS post hoc)

B G

Runoff (L m�2) 20.85T15.46 a 2.56T0.36 b

Soil loss (Mg h�1) 3.64T2.23 a 0.05T0.00 b

Values of runoff and soil loss followed by same letter are not significantly differ

human interference or affected by wildfires can increase soil

loss in the first years after disturbance (Sanchez, 1997; Soto

and Dıaz-Fierros, 1997; Bautista, 1999). In our experimental

area, the bare soil (B) registered higher values of runoff

coefficient and soil loss (4.42% and 1.90 Mg ha�1 year�1,

respectively). Cerda (1998) obtained similar results when

comparing discontinuous Stipa tenacıssima steppes, herb

cover and dwarf shrub communities by means of rainfall

simulation experiments.

4.3. Effects of precipitation characteristics on runoff and

erosion

Besides the vegetation cover (%), rainfall characteristics

determine the runoff and erosion magnitude (Francis and

Thornes, 1990a; Cerda, 1997). Runoff and loss of soil

caused by rainfall events reflect small values in both

variables, as responses to the vegetation cover and to the

characteristics of the rain. 75% of events in vegetated plots

ype during 1998–1999 years (ANOVA—one way; averageTstandard error.

Vegetation type cover

S AG AS

3.36T0.75 b 4.01T3.12 b 2.20T0.15 b

0.07T0.01 b 0.02T0.01b 0.02T0.00 b

ent at p�0.05.

Fig. 3. Rainfall characteristics. Relationship between rainfall volume and

mean intensity, and between rainfall volume and rainfall duration for each

precipitation event (Ventos Meteorological Station, years 1996–1999).


and 53% in bare soils showed runoff values of �0.1 L

m�2. During the whole study period we registered 94

rainfall events, with an annual mean of 330.4 mm. 90% of

these events present volumes lower than 10 mm (Fig. 3),

with an average intensity lower than 5 mm h�1 and short

duration (less than 2 h). These characteristics of precipitation

and the vegetation cover (higher of 70%) may justify the

lower measured runoff and erosion rates. The temporal

distribution of rainfall events is also relevant in this region.

These are concentrated in a few days of very heavy rain. The

rainfall events with more than 10.1 mm (10% of the events)

represent 57% of accumulated annual precipitation volume,

with a mean maximum intensity (I15) of 18.9 mm h�1 and a

mean duration of 3 h. Also storm events are frequent in the

semi-arid area, called ‘‘flood’’, ‘‘cold drop’’ or ‘‘cut-off

low’’, similar to that which occurred on 30/09/97, with 134.6

mm in 7 h 30 min, which represented 24% of the annual

rainfall.

Table 3

Multiple regression by vegetation cover type

R2 F b0

Rainfall

AS 0.926 268,7838** �1.59e�02 5.404e�03**

AG 0.896 185,250*** 8.925e�05 1.014e�02**

S 0.942 353,265*** �1.20e�02 8.281e�03**

G 0.884 220,442*** �3.90e�02 4.224e�03**

B 0.968 395,198*** 6.089e�02 0.148***

y =runoff, b0=slope. x1= rainfall, x2=maximum intensity 15 min (Int15), x3=

***p <0.001, **p <0.01.

Considering that 90% of the precipitation events do not

exceed 10 mm, and that these events generated between

81% and 89% of the runoff, and between 92% and 96% of

soil loss in the different vegetation cover type; we carried

out a second statistical analysis considering two rainfall sets

(events until 10 mm and rainfall over 10 mm). The results

(not shown) reinforce the previous interpretations detecting

significant statistical differences between the means of the

accumulated runoff and soil loss of the vegetated plots (AS,

AG, S and G) and open land (B), but not between vegetation

communities (Table 2). The effects of the extraordinary

event of 30/09/97 only just increased the values of runoff

and soil loss (Table 1), but not the relationships between

different vegetation cover types.

Another aspect evaluated in this work has been the

contribution of rainfall intensity on runoff and soil losses.

Using multiple regressions to estimate runoff, through

rainfall amount, maximum intensity at 15 min, mean

weighted intensity, and rainfall duration, as independent

variables, we obtain significant correlation coefficients in all

vegetation cover types (Table 3). However, maximum

intensity seems to have made the major contribution,

together with the rainfall amount to explain the daily runoff

and soil loss variability.

4.4. Afforestation effects on vegetation structure, plant life

forms, species richness and diversity

Despite the observed changes in species composition and

cover (Fig. 2), the statistical analysis of the vegetation cover

structure of the hydrology plots (Table 4) indicates that

afforestation with Aleppo pine only modifies the previous

structure introducing the tree strata which was not present in

natural vegetation communities (G and S). The surface

occupied by the shrub stratum in the AS plots does not

significantly differ from the surface in the S plots, being

significantly smaller in AG. Nor does the surface occupied

by herbaceous stratum in AG differ from the plots with

natural vegetation (S and G), but the differences were

significant between these and AS. On the other hand, we did

not find differences in mosses and bare soil between the

different hydrology plots; but the difference exists with

regard to the surface covered by litter, being similar in AS,

AG and S, and different from G (Table 4).

Coefficient of the independent variable

Int15 mw_Int D

* 6.045e�03*** �6.07e�3*** �1.47e�03***

* 7.192e�03** �1.01e�02** �2.28e�03***

* 7.647e�03*** �8.91e�03*** �2.09e�03***

* 1.149e�02*** �1.149e02***

�0.111** 9.812e�02** �4.69e�02***

mean weigh intensity (mw_Int), and x4= rainfall duration (D); gl=86.

Table 4

Statistical significance of the differences between vegetation cover (%) of the hydrological plots

Mean cover (%)

G S AG AS X2 p-value

Layers

Trees 0.00 (0.00) 0.00 (0.00) 54.50 a (15.55) 44.05 a (14.40) 13.152 0.011*

Shrubs 9.71 b (8.13) 58.58 a (12.66) 5.10 b (3.82) 72.25 a (0.33) 12.300 0.015*

Herbs 60.92 a (13.72) 72.71 a (13.14) 69.54 a (15.21) 30.46 b (9.43) 10.267 0.036*

Mosses 0.42 (0.45) 0.00 (0.00) 0.27 (0.24) 0.13 (0.22) 5.777 0.216 ns

Bare 7.83 (7.49) 1.00 (1.31) 1.63 (2.06) 0.29 (0.40) 8.102 0.088 ns

Stones 44.29 a (19.62) 12.79 b (9.60) 2.54 c (0.95) 4.50 bc (3.15) 11.867 0.018*

Litter 16.11 b (6.43) 83.92 a (15.32) 95.61 a (3.15) 97.06 a (2.21) 11.583 0.021*

Total plant cover 70.02 c (3.22) 90.17 b (2.10) 95.83 a (2.40) 95.21 a (2.81) 9.359 0.025*

Vegetation characteristics

Species richness 24.33 a (1.15) 25.00 a (2.00) 19.00 b (6.00) 19.00 b (3.46) 9.862 0.043*

LAI 1.197 a (0.112) 2.303 a (0.135) 1.732 ac (0.038) 3.012 b (0.239) 13.233 0.010**

Mean values (s.d.) results of the Kruskall-Wallis test (X2) and post hoc Wilcoxon pairs comparison (values of mean cover followed by same letter are not

significantly different at p�0.05; the * in p-values indicates the significance of the Wilcoxon test: *p <0.05, **p <0.01).


The conflict between pine plantations and conservation

of pre-existing thorn shrublands is a relevant topic in the

management of the Mediterranean semi-arid ecosystem

(Esteve et al., 1990). From the medium to long-term,

Aleppo pine afforestation produces a positive effect in-

creasing the overall vegetation cover with respect to non

afforested cover; which implies similar results regarding

LAI (Table 4). On the other hand, a negative effect of the

afforestation is located in species richness values, being

higher in natural vegetation communities where the estab-

lishment of dwarf shrubs is facilitated, in contrast to the

afforested plots where the tree stratum reduces the presence

of other species in the understory. This effect is contrary to

one of the priorities of the EU Environmental Policy, which

Table 5

Vegetation characteristics of natural and afforested communities at landscape patch

species richness (S) and Shannon diversity index (HV) for all cover type and each

G AG

Mean (s.d.) Mean (s.d.) F

Overall community

Species richness (S) 37.00 (6.16) 19.80 (4.09) 27.04

Diversity (HV) 3.00 (0.15) 2.28 (0.18) 48.73

Plant cover (%) 71.00 (9.62) 72.60 (9.42) 0.90

Life forms

Species richness (S)

Shrubs 2.20 (1.64) 0.40 (0.55) 5.40

Dwarf shrubs 17.80 (1.30) 11.00 (1.41) 62.48

Grasses 5.20 (0.84) 1.00 (0.00) 126.00

Forbs 10.00 (3.46) 6.40 (3.05) 3.04

Annuals 1.80 (0.84) 1.00 (0.00) 4.57

Diversity (HV)Shrubs 0.86 (0.96) 0.00 (0.00) 4.08

Dwarf shrubs 3.44 (0.10) 2.86 (0.45) 8.08

Grasses 0.73 (0.24) 0.00 (0.00) 45.84

Forbs 2.72 (0.58) 2.36 (0.63) 0.88

Annuals 0.60 (0.60) 0.00 (0.00) 5.01

Means and standard deviations are calculated in 5-replicated 100 m2 plots. ANO

aims at the conservation of biodiversity of these Mediter-

ranean ecosystems (grassland and shrubland), through their

high rates of richness and species diversity (Peco et al.,

1983).

To evaluate the representativeness of these results on

structure, richness and diversity of species obtained in the

hydrology plots, we carried out another complementary

study in landscape patches on the same community types.

Table 5 shows the statistical results of the comparative

analysis between the natural vegetation communities with

their corresponding pairs of Aleppo pine afforestation (G –

AG and S–AS). Overall richness and diversity present lower

values in afforested than in natural communities. Some

shrubs like R. officinalis were present in S, but not in AS,

es in the north-facing slopes in the Ventos catchment: Plant cover (%), Mean

plant life form

S AS

p Mean (s.d.) Mean (s.d.) F p

** 34.20 (5.36) 26.20 (3.03) 8.44 *

*** 3.35 (0.22) 2.88 (0.17) 13.83 **

ns 85.60 (3.20) 99.20 (0.45) 120.71 ***

* 6.20 (2.17) 2.60 (1.14) 10.80 *

*** 15.40 (0.89) 15.20 (1.92) 0.04 ns

*** 3.60 (0.55) 1.80 (0.45) 32.40 ***

ns 8.40 (4.77) 6.20 (2.59) 0.82 ns

ns 0.60 (0.55) 0.00 (0.00) 6.00 ns

ns 1.51 (0.33) 0.77 (0.54) 6.81 *

* 3.70 (0.05) 3.55 (0.21) 2.54 ns

*** 0.97 (0.20) 0.10 (0.20) 45.92 ***

ns 2.68 (0.90) 2.32 (0.47) 0.67 ns

ns 0.00 (0.00) 0.00 (0.00) – –

VA (*p <0.05, **p <0.01, ***p <0.001).

Table 6

Mean cover (%) of dominant species in analysed vegetation type cover in landscape patches

S AS G AG

Mean (s.d.) Mean (s.d.) Mean (s.d.) Mean (s.d.)

Trees

Pinus halepensis 0.00 (0.00) 50.80 (11.78) 0.00 (0.00) 52.40 (7.60)

Shrubs

Erica multiflora 4.00 (2.92) 0.20 (0.45) 0.00 (0.00) 0.00 (0.00)

Pistacia lentiscus 2.20 (3.49) 9.60 (15.65) 0.20 (0.45) 0.00 (0.00)

Quercus coccifera 47.60 (16.74) 28.20 (6.53) 0.00 (0.00) 0.00 (0.00)

Rhamnus lycioides 1.40 (1.149) 1.20 (2.17) 0.60 (0.55) 0.40 (0.55)

Rosmarinus officinalis 9.00 (4.95) 0.00 (0.00) 0.60 (0.55) 0.00 (0.00)

Dwarf shrubs

Anthyllis cytisoides 1.00 (1.73) 1.40 (1.14) 10.80 (3.03) 1.80 (1.30)

Asparagus horridus 1.00 (0.71) 0.40 (0.42) 1.60 (0.89) 0.30 (0.45)

Atractylis humilis 0.70 (0.45) 1.00 (0.71) 1.40 (2.07) 2.40 (1.34)

Coronilla minima subsp lotoides 2.00 (1.58) 0.30 (0.45) 1.00 (1.22) 0.00 (0.00)

Fumana ericoides 0.80 (0.84) 1.80 (0.84) 0.80 (0.84) 0.00 (0.00)

Globularia alypum 2.00 (2.12) 1.40 (1.52) 0.60 (0.55) 0.40 (0.55)

Helianthemum syriacum 0.60 (0.55) 1.00 (0.71) 4.80 (3.11) 1.40 (1.52)

Helianthemum violaceum 0.60 (0.55) 0.80 (0.76) 1.20 (0.84) 1.40 (1.52)

Helichrysum decumbens 0.30 (0.45) 3.20 (1.64) 1.40 (0.55) 9.40 (7.64)

Phagnalon rupestre 0.00 (0.00) 0.20 (0.45) 1.00 (0.00) 1.80 (0.84)

Phagnalon saxatile 0.00 (0.00) 0.80 (1.30) 3.20 (0.84) 1.20 (1.10)

Teucrium homotrichum 1.00 (0.71) 2.60 (2.41) 0.24 (0.43) 0.40 (0.55)

Thymus vulgaris 1.20 (1.10) 3.40 (1.52) 3.00 (1.87) 1.60 (1.52)

Grasses

Brachypodium retusum 50.60 (18.94) 27.40 (16.15) 65.60 (12.82) 54.80 (9.42)

Lygeum spartum 0.60 (0.55) 0.00 (0.00) 2.40 (1.52) 0.00 (0.00)

Stipa parviflora 0.00 (0.00) 0.00 (0.00) 3.40 (1.95) 0.00 (0.00)

Forbs

Eryngium campestre 0.00 (0.00) 0.30 (0.45) 1.40 (0.89) 0.40 (0.55)

Pallenis spinosa 0.00 (0.00) 0.20 (0.27) 0.60 (0.55) 1.40 (1.67)

Teucrium pseudochamaepitys 0.70 (0.45) 0.60 (0.55) 0.50 (0.50) 0.80 (0.45)

Annuals

Reichardia tingitana 0.80 (0.84) 0.30 (0.45) 0.04 (0.09) 0.00 (0.00)


and the dominant Q. coccifera showed lower cover values

in afforested plots (Table 6). These effects were especially

evident in G, where mean richness values decreased near

50% in afforested plots AG (Table 5). Moreover, afforesta-

tion with pines increased plant cover values in AS,

increasing practically all the total available soil surface

whereas there was not such an effect on AG. However, plant

cover alone is not considered to be so important. There is a

threshold cover value above which there is no significant

impact on run-off and erosion.

The results indicate that afforested communities had a

different species composition when compared with non-

managed communities. Differences are clearer if we take into

account the plant life forms as crude functional groups (Table

5). We did not find variation in forbs and annuals richness

nor diversity in any of the cases that are compared. Grasses

demonstrate lower richness and diversity values with pine

afforestation in both cases, AG and AS. However, the

perennial grass B. retusum seems to be more constant than

other grasses (Table 6). Moreover, dwarf shrubs presented

lower richness and diversity values with afforestation only in

G. Shrub richness was lower in afforested communities than

in non-afforested ones, whereas we obtained statistically

significant differences in shrub diversity only between S and

AS due to the low shrub abundance in G (Table 4). Most

shrub species had fewer cover values in afforested plots,

except P. lentiscus (a bird-dispersed shrub), which could

have been facilitated through the presence of P. halepensis.

Verdu and Garcıa-Fayos (1996) described several examples

of facilitation pathways in colonisation dynamics of this

species by means of trees that can act as perches for

frugivorous birds disseminating seeds.

In summary, the grassland communities presented greater

shrub, dwarf shrub and grass species richness than in

grassland afforestation. On the other hand, shrubland

communities presented greater shrub and grass species

richness and overall species diversity, with no differences

in relation to dwarf shrubs. Several authors indicate similar


effects associated with afforestation management. Hartley

(2002) andWatson et al. (2000) detected the decrease of plant

diversity of pre-existing native species after the monospecific

afforestations with pines in non-degraded lands. Sometimes,

current management techniques like thinning or pruning, can

affect the composition of forest species (Freedman et al.,

1996; Wagner et al., 1998). In spite of this, it is recognised

that plantations can be of benefit to landscape composition by

increasing the ecotone density and landscape diversity

(Estades and Temple, 1999; Bonet et al., 2001).

4.5. Relationships between vegetation cover, runoff and soil

loss

In order to contrast these results with the so called 30%

rule (Francis and Thornes, 1990b), we carried out a

regression analysis between runoff and soil loss with

vegetation cover. The best equation obtained was the

negative exponential model (Fig. 4), as proposed by Elwell

and Stocking (1976), with R2>0.91. This function indicated

that in the presence of high vegetation cover percentages,

the responses in runoff and soil loss in the different

vegetation patches analysed tended to have little differen-

tiation. Obviously, small values of vegetation cover increase

Fig. 4. Exponential functions and regression coefficients for runoff and soil

loss as a function of vegetation type cover during the study period. Together

with hydrological plots studied in this paper, the data of Alfa grass plots

with 37% of soil cover is included to illustrate the relevance of the so called

‘‘30% rule’’.

soil losses, the most significant loss being for covers under

30% of surface. Further studies on Alpha grass steppe

(37.0% vegetation cover) reveal runoff and soil loss values

similar to the estimated ones using these equations (Fig. 4).

The response of the dry grassland is related to the

presence of B. retusum cover, that occupies 65.6% of the

surface of the plots (Table 6); being capable of intercepting

between 38% and 57% of the precipitation, according to

results of the rainfall simulations in laboratory (Derouiche et

al., 1996). Cerda (1997) reported runoff coefficients of

0.03–0.06% in herbaceous micro-plots (with B. retusum as

dominant species) and soil loss of 0.014 Mg ha�1. Gutierrez

and Hernandez (1996) in experiments with rainfall simulator

(137 mm h�1) and different herbaceous covers showed that

a cover of 50% of herbaceous (in growth phase) and 70%

(in dormancy phase) was sufficient to significantly reduce

the runoff.

Based on our results (Table 2), the runoff generated by

vegetation cover type should present the following order:

AS <AG <S<G <B, but the measured annual runoff coef-

ficients indicated a different order: AS <G <S <AG <B.

Moreover it was found to be significant that G formation

generated less runoff than S and AG. In this case the

difference between G and S may be because the mean slope

of the shrub plots (29.2-) exceeds the slope in the G plots

(26-), and despite the importance of soil surface roughness

(Lavee et al., 1995). The difference between G and AG, can

be related to the characteristics of the upper soil layer on the

surface. Both vegetation cover types present soil upon

loamy limestone substrate, but the AG plots are found

located in the medium third of the hillside, the zone of

greater erosion, for which the surface presents loamy

limestone horizon, with a certain degree of crusting that

reduces the infiltration and favours the generation of runoff.

Similar explanations are reported by Cerda (1999), which

obtained greater values of runoff and erosion in soil

supported by loamy limestone.

Most authors indicate that the soil loss tolerance rates

may differ according to several characteristics of the soils,

topography and vegetation cover. In our study area, the

values measured in all the vegetation cover types (afforested

and non-afforested vegetation communities) and bare soil

are lower than the 5.0 Mg ha�1 year�1 of annual rate of soil

loss indicated by Smith and Staney (1965) and Mitchell and

Bubenzer (1980). Only bare soil (in years 1997 and 1999)

presented annual soil losses that exceeded the rate of 2.0 Mg

ha�1 year�1 established by Arnoldus (1977) for soils whose

roots reach 25 cm depth, as in our case.

5. Conclusions

Our study provides basic information on runoff, sediment

yield and plant diversity in semi-arid natural and managed

communities and can be used to design effective recovery

strategies for degraded semi-arid ecosystems. Although 4


years is insufficient time in which to evaluate erosion

processes in semi-arid Mediterranean lands, due to high

climatic variability, this study reveals that dry grassland

formations (G) retained soil and runoff as efficiently as thorn

shrublands (S) and afforested communities (AG and AS).

The average rainfall event in the semi-arid study area had

low volume, low intensity and short duration, and conse-

quently low erosivity risk for the vegetation communities

analysed (more than 70% of land covered). When compar-

ing afforested communities (AS and AG) with natural

vegetation communities (G and S), the results reveal that

there were no differences in the runoff generation and soil

loss. Therefore, in the conditions under which the research

was conducted (semi-arid climate), afforestation with an

Aleppo pine stratum; does not significantly reduce erosion

on a long-term scale (30 years), in comparison to the natural

vegetation without trees. Consequently, this kind of

afforestation is not the most efficient procedure either in

the long-term or in the short-term to improve land cover in

non-degraded landscapes with the aim of soil and plant

conservation. Alternatively, the conservation of natural

communities, or the restoration of semi-arid ecosystems

with native shrub species can be an adequate method for

reducing the effects of erosion and improving plant diversity

and ecosystem resilience, especially when re-sprouting

species can be used.

In conclusion, afforestation, as a management practice

has improved the structure of the natural communities

through the addition of pine stratum in order to establish a

pluri-stratified forest; however species richness was reduced

as well as plant diversity in these afforested semi-arid areas.

Alternatively, these positive effects can be achieved through

recovery of the natural vegetation, which can be managed

with these aims.

Acknowledgements

This research was partially funded by the Spanish

Government, through the CICYT programmes (HID97-

1047 and REN2000-0592-HID), the LUCDEME pro-

gramme of MMA (RESEL network), and Generalitat

Valenciana Regional Program /GV97-RN-14-4.

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