Acta Ecologica Sinica 33 (2013) 272–281

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Acta Ecologica Sinica

journal homepage: www.elsevier .com/ locate/chnaes

Implications of land-cover types for soil erosion on semiarid mountain slopes:Towards sustainable land use in problematic landscapes

Víctor Hugo Durán-Zuazo a,⇑, José Ramón Francia-Martínez b, Iván García-Tejero a, Simón Cuadros Tavira c

a IFAPA Centro ‘‘Las Torres-Tomejil’’, Carretera Sevilla-Cazalla km 12,2, 41200 Alcalá del Río, Sevilla, Spainb IFAPA Centro ‘‘Camino de Purchil’’, Apdo. 2027, 18080 Granada, Spainc Universidad de Córdoba, Campus de Rabanales Crta, Nacional IV A km 396, 14071 Córdoba, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 13 December 2011Revised 21 October 2012Accepted 17 July 2013

Keywords:Land-use typeRunoffSoil erosionSoil propertiesLanjarón

1872-2032/$ - see front matter � 2013 Ecological Sohttp://dx.doi.org/10.1016/j.chnaes.2013.07.007

⇑ Corresponding author.E-mail address: victorh.duran@juntadeandalucia.e

The impact of land-cover types on soil erosion and runoff, as well as on physico-chemical soil properties,was monitored. The study area, an agroforestry landscape was located in Sierra Nevada Mountains insouth-eastern Spain. Eight land-cover types were investigated: farmland planted with olive, almond,and cereals; forest with P. halepensis and P. sylvestris; shrubland; grassland; and abandoned farmland.The erosion plots replicated twice were located on hillslopes, where erosion and runoff were measuredafter 22 storm events. Forest dominated by Pinus stands exhibited significantly the lowest amounts oferosion and runoff, contrasting with abandoned farmland. Olive had higher erosion than did almond,cereals, or grasslands, but with the highest runoff rate under almond groves. The erosion and runoffresponse to shrubland showed an intermediate situation between forest and farmland–grassland uses.Under forest and shrubland, better soil properties were determined, especially higher organic C and totalN, and lower soil-bulk density. Erosion was highly dependent on runoff, bulk density, soil organic C, andthe degree of soil surface covered. Thus, the alteration in land cover is essential to an understanding ofproductivity of soil undergoing erosion, as sustainable planning can mitigate soil-degradation processesin the overall agroforestry landscape.

� 2013 Ecological Society of China. Published by Elsevier B.V. All rights reserved.

1. Introduction

Resource use and management has become an increasingly vitalissue in many countries, with an emphasis on improving forest aswell as agricultural management in mountain areas. Land-coveralteration significantly affects soil quality when major land-usechanges lead to land degradation [1–3]. Fire, deforestation, and in-creased agricultural activity intensify pressure, especially on frag-ile high-altitude ecosystems. The abandonment of farmlandshould eventually lead to regrowth of bushes and forests in thelong term, while the conversion of forest and grassland into farm-land is known to deteriorate soil properties, especially reducingsoil organic matter and changing the distribution and stability ofsoil aggregates [4–6]. Consequently, land-cover dynamics, particu-larly deforestation, forest fire, and abandoned farmlands, have be-come a critical concern, as the implications for systems involvinghuman livelihoods are vast [7–9]. On the other hand, as stated bymany authors [10–13], sustainable utilization and conservationof natural resources in agro-forestry systems is considered one ofthe fundamental components of sustainable rural development.

ciety of China. Published by Elsevie

s (V.H. Durán-Zuazo).

Plant covers play a significant role in regulating hydrologicalprocesses and changes in soil properties because of the destructiveforces of rainfall, which can cause erosion, soil sealing, and crusting[14–16]. The sediments that accumulate in lakes, peat bogs, andfluvial deposits have provided useful information on the relation-ships between land-use change and soil erosion [17,18]. Moreover,brief torrential thunderstorms are common in the European Med-iterranean area. In this context, severe soil erosion has been gener-ally regarded as a major cause of land degradation in mountainareas [19–22].

Land use and land cover strongly control carbon content and itsdistribution within ecosystems, which is governed by the nature ofthe vegetation, landforms, weather conditions, and soil texture[23,24]. In addition, soil physical and chemical alteration couldbe having far-reaching consequences for soil erosion and produc-tivity, the degraded areas being more susceptible to these pro-cesses [25,26]. Therefore, land covers play a key role inexacerbating the temporal dynamics of water erosion.

Thus, this study evaluates the impact of different land-covertypes on soil erosion and runoff in mountain slopes, characterizingtrends and relationships in soil properties under the semiarid Med-iterranean climate of south-eastern Spain.

r B.V. All rights reserved.

V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281 273

2. Material and methods

2.1. The study area

The study area was situated in Sierra Nevada Mountains, Lan-jarón, Granada (SE Spain). This agroforestry landscape bears fea-tures commonly found in the Mediterranean area, where cropsare confined to mountains and hills. The poor vegetation cover ofthe soil intensifies vulnerability to soil erosion, while rainfall inthese areas acts as a major factor in soil degradation.

Table 1 provides a brief description of plant species for eachland-use and land-cover type in the mountainous region under hillforest and upland cultivation.

The dominant soil parent material is colluvium and residuumderived from mica-schist, and the slopes are composed predomi-nantly of phyllites and mica-schist, with weathered regolith cover-ing only a few cm in depth. These phyllites may be overlain inplaces by limestones that have rafted downslope on top of the phyl-lites. In general, the soils of the watershed have loamy, sandy-loam,and silt-loam textures, which are classified as Chromic cambisols,Haplic phaenozems, Humic cambisols, Eutric cambisols, and Eutricregosols, among others, according to the FAO [27] (Table 3).

Mean annual precipitation over the hydrological years (Octoberto September) in the study area is a semiarid Mediterranean-typeclimate with about 490.4 mm with high inter-annual variabilityof rainfall intensity, most of which is concentrated in winter and au-tumn, while short-duration torrential storms occur frequently inspring but rarely in summer, with 15.0�, 20.8�, and 9.2 �C for aver-age annual, maximum, and minimum temperature, respectively.

2.2. Soil erosion and runoff measurement at land-cover types

Erosion and runoff were monitored in 16 closed erosion plotsdistributed in the study area with south-facing slopes (Fig. 1).

The plant-cover percentage was estimated three times using a1 m2 grid with 100 squares throughout the study period (Marchand November 2009, and March 2010). This consists of evaluatingthe different cover percentages estimated in each square on a scaleof 0–5, thus establishing a value matrix, the mean of which indi-cated the plot-cover percentage.

The following scheme was used to evaluate farmland and aban-doned land uses:

� 4 plots of 40 m2 in area with olive (Olea europaea) (36�5104400 Nand 3�2905000 W) and almond (Prunus amygdalus) (36�5505000 Nand 3�3000100 W), both with conventional tillage (at soil depthof 30–40 cm), and with 42% and 37% of vegetation cover onaverage, respectively.

Table 1Main plant species for each land-use type (LUT) in the study area.

LUT Dominant land-cover types

Forest Areas covered with pine stands (Pinus sylvestris, P. halepensis, P. pincategory included planted forests, mixed with regenerating indigedecorticans, Juniperus oxycedrus, J. versicolor,Castanea sativa,Ruscus a

Rainfedfarmland

Areas with cultivated crop tree: olive (Olea europaea), almond (Pru(hunting) feed, especially annual species winter wheat (Triticum aeL.), etc.

Irrigatedfarmland

Areas with irrigated tree crops such as walnut (Juglans regia L.), ch

Shrubland Areas covered with shrubs, scrubs, and small trees, with little usefdecorticans, Brachipodium sp., Cytisus scoparius, Retama sphaerocarpaDittrichia viscosa, Artemisia campestris, etc. Some areas with wild aroBoiss., Thymus zygis), sage (Salvia officinalis L.), lavender (Lavandula

Grassland/Pasture

Dry grassy areas used for grazing (goat and sheep) dominated by PAgrostis sp., Jurinea humilis, Dactylis sp., Bromus sp., etc., annual and pshrubs and bare land that has very little or no plant cover (expose

Abandonedland

Areas progressively recolonized with shrubs including herbaceous pPhlomis purpurea L., Bromus sp., Dactylis glomerata, Thapsia villosa L

� 4 plots of 24 m2 in area with cereals and grassland (36�5604800 Nand 3�2902500 W), with 61% and 72% of vegetation cover on aver-age, respectively.� 2 plots of 24 m2 in area with abandoned farmland (36�5604800 N

and 3�2902500 W) having 41% of vegetation cover on average.These plots had been left to grow without any human distur-bance since 2007, when the farmland was abandoned.

Forest and thicket land uses were assessed in the followingplots:

� 2 plots of 24 m2 in area with autochthonous shrubs (36�5604800

N and 3�2902500 W), gorse thicket with plants (Ulex parviflorus,Genista sp., Adenocarpus decorticans, Santolina sp., Thymus capit-atus, Thymus baeticus Boiss, and others) with 75% of vegetationcover on average.� 2 plots of 40 m2 in area with Aleppo pine (Pinus halepensis Mill.)

(36�5600500 N and 3�3001800 W) stands with 96% of vegetationcover on average (reforested less than 60 years earlier).� 2 plots of 40 m2 in area with Scots pine (Pinus sylvestris L.)

(36�5701000 N and 3�2805200 W) stands with 84% of vegetationcover on average (reforested less than 60 years earlier).

Soil erosion and runoff were collected in the drawer collectorof each closed erosion plot. The runoff was measured and sam-pled after each rainfall event and its sediment concentrationwas determined in aliquots, which were decanted and dried at105 �C.

In each transect with the land-cover types studied, a rain gauge(Thies Clima) (<60 m from the plots) was installed to collect rain-fall data and estimate the maximum intensity at 30 min (I30), andthe erosivity index (R factor) [28].

Plant-cover percentages in the cereal, grassland, shrub, andabandoned farmland plots were estimated visually by countingthe number of grid intersections which intercepted vegetationin a 1 m2 grid (1 m � 1 m) divided into squares 10 by 10 cm (a to-tal of 100 squares). Similar methodology was used to determinethe ground cover in almond, olive, P. sylvestris, and P. halepensisplots.

2.3. Physico-chemical soil properties under land-cover types

The soil was analyzed from disturbed (hand auger) and undis-turbed (100 cm3 cylinders) samples within the area of each se-lected land-cover type in order to represent the land useinvestigated. For replication, four adjacent subplots (5–10 m � 5–10 m) in the main plot were identified and sampled from different

aster, P. nigra, P. pinea, etc.) that formed nearly closed canopies (60–85%). Thisnous species of trees and bushes: Quercus rotundifolia, Q. ilex, Adenocarpusculeatus,Salix cinerea,Populus alba,P. nigra, etc.

nus amygdalus), and grapevine (Vitis vinifera L.). For livestock and wild-partridgestivum L.), oat (Avena sativa), barley (Hordeum vulgare L.), legumes (Lens esculenta

erry (Prunus cerasus), olive, and horticultural species

ul wood, mixed with some grasses: Ulex parviflorus, Genista sp., Adenocarpus, Lavandula pedunculata, Halimium viscosum, Psoralea bituminosa, Carlina vulgaris,matic and medicinal shrubs especially thyme (Thymus capitatus, Thymus baeticusstoechas), rosemary (Rosmarinus officinalis L.), Santolina sp., etc.oaceae species and other herbaceous plants (non-woody): Festuca granatensis,erennial forbs (Stipa tenacissima, Brachypodium soides, etc.) combined with dwarf

d rocks)lants, Ulex parviflorus Pourret , Santolina chamaecyparissus L., Stipa tenacissima L.,., etc.

Fig. 1. Erosion plots for each selected land-cover type located on the hillslopes of the Sierra Nevada Mountains in south-eastern Spain.

274 V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281

soil depths (25 and 50 cm), to enable comparison among selectedland-cover types. The soil samples were air-dried and passedthrough a 2-mm sieve, removing crop debris, root material, andstones. Soil texture, bulk density (BD), cation-exchange capacity(CEC), total nitrogen (TN), and plant-available phosphorus (P),and potassium (K) were determined using standard methods forsoil examination [29]. Soil pH was assessed using an electrodepH-meter on saturated soil paste (1:2.5). Soil organic carbon wasevaluated using the Walkey and Black method [30].

2.4. Statistical analyses

A one-way analysis of variance (ANOVA) was performed toascertain whether the various land-cover types differed in termsof runoff and soil erosion. Differences between individual meanswere tested using the least-significant difference test (LSD) atp < 0.05 using Statgraphics v. 5.1 package program. The soil prop-erties were grouped and summarized according to the land-covertypes and soil depths, and a statistical analysis was performed to

Table 3Soil characteristics for each land-cover type (LCT) at different soil depths.

LCT Slope Depth Sand Silt Clay SOC TN P K pH BD CEC ST(%) (cm) (g kg�1) (mg kg�1) (H2O) (Mg m�3) (cmolC

kg�1)

PHA 28 0–25 672 ± 22a 173 ± 21a 155 ± 8a 22.9 ± 4a 2.38 ± 0.08a 4.4 ± 2a 86.5 ± 19a 6.2 ± 0.4a 0.91 ± 0.03a 25.5 ± 8a I25–50

640 ± 18a 194 ± 17a 166 ± 10a 20.5 ± 3a 2.11 ± 0.10a 3.7 ± 4a 96.1 ± 25a 6.0 ± 0.5a 0.97 ± 0.07a 23.8 ± 11a

PSY 30 0–25 540 ± 28b 320 ± 39b 140 ± 8a 17.8 ± 6a 0.64 ± 0.04b 6.8 ± 3a 70.4 ± 22a 6.5 ± 0.3a 1.04 ± 0.04a 12.0 ± 5ab II25–50

552 ± 15b 297 ± 27ab 151 ± 11a 16.7 ± 9ab 0.59 ± 0.07b 6.1 ± 2a 68.4 ± 17a 6.3 ± 0.3a 1.08 ± 0.02a 11.0 ± 7ab

SHR 35 0–25 583 ± 52ab 349 ± 22b 68 ± 18b 13.5 ± 3ab 0.63 ± 0.04b 5.8 ± 1a 55.7 ± 25a 7.7 ± 0.2a 1.12 ± 0.05ab 7.2 ± 3b II25–50

612 ± 11ab 314 ± 18b 74 ± 14b 10.4 ± 1ab 0.58 ± 0.08b 6.0 ± 4a 61.4 ± 19a 7.4 ± 0.3a 1.10 ± 0.03ab 7.8 ± 5b

CER 35 0–25 654 ± 24a 250 ± 48ab 96 ± 10ab 10.0 ± 2ab 0.60 ± 0.02b 6.3 ± 3a 78.4 ± 31a 7.6 ± 0.5a 1.16 ± 0.06ab 7.9 ± 2b III25–50

625 ± 28a 271 ± 15ab 104 ± 19a 8.3 ± 8ab 0.55 ± 0.07b 6.7 ± 5a 82.8 ± 26a 7.0 ± 0.4a 1.13 ± 0.09ab 8.4 ± 4b

OLI 26 0–25 667 ± 31a 200 ± 17a 133 ± 9a 8.5 ± 3b 0.58 ± 0.02b 4.6 ± 1a 90.4 ± 12a 7.5 ± 0.2a 1.19 ± 0.04ab 10.2 ± 4ab IV25–50

611 ± 17ab 271 ± 22ab 118 ± 11a 8.9 ± 2b 0.62 ± 0.08b 5.2 ± 4a 94.7 ± 32a 7.7 ± 0.5a 1.17 ± 0.07ab 9.7 ± 7b

ALM 33 0–25 697 ± 65a 215 ± 32a 88 ± 12ab 8.4 ± 2b 0.45 ± 0.03c 6.4 ± 2a 68.7 ± 26a 7.4 ± 0.1a 1.17 ± 0.04ab 15.8 ± 4ab IV25–50

650 ± 41a 244 ± 19a 106 ± 15a 9.2 ± 3b 0.40 ± 0.05c 7.0 ± 3a 77.7 ± 16a 7.7 ± 0.2a 1.20 ± 0.02ab 15.7 ± 5ab

GRL 35 0–25 643 ± 33a 260 ± 42ab 97 ± 18ab 9.6 ± 2ab 0.85 ± 0.07b 5.8 ± 3a 60.8 ± 13a 7.9 ± 0.2a 1.11 ± 0.06a 7.4 ± 3b II25–50

622 ± 39a 255 ± 31ab 123 ± 22a 9.1 ± 2ab 0.79 ± 0.07b 5.0 ± 3a 57.3 ± 13a 7.4 ± 0.2a 1.10 ± 0.06a 7.0 ± 3b

ABF 25 0–25 705 ± 32a 224 ± 22a 71 ± 21b 6.7 ± 3b 0.58 ± 0.04b 4.1 ± 2a 65.7 ± 18a 8.2 ± 0.3b 1.27 ± 0.05b 7.0 ± 5b III25–50

680 ± 45a 237 ± 18a 83 ± 19ab 7.8 ± 3b 0.62 ± 0.05b 5.5 ± 3a 70.7 ± 22a 8.0 ± 0.2ab 1.23 ± 0.08b 7.8 ± 3b

CER, cereal; GRL, grassland; OLI, olive; ALM, almond; PHA, Pinus halepensis; PSY, Pinus sylvestris; SHR, shrub; ABF, abandoned farmland; Means in the column followed by thesame letter are not significantly different at p < 0.05; ±standard deviation; SOC, soil organic carbon; TN, total nitrogen; BD, bulk density; CEC, cation-exchange capacity; ST,soil type; I, Chromic cambisols; II, Haplic phaenozems; III, Eutric cambisols; IV, Eutric regosols [27].

Table 2Descriptive statistics for rainfall variables for each land-cover types during the study period with 22 events (from January 2009 to April 2010).

Olive-almond Cereal–grassland–shrub–abandoned farmland

P. halepensis P. sylvestris

R(mm)

I30

(mm h�1)R factor(MJ mmha�1 h�1)

R(mm)

I30

(mm h�1)R factor(MJ mmha�1 h�1)

R(mm)

I30

(mm h�1)R factor(MJ mmha�1 h�1)

R(mm)

I30

(mm h�1)R factor(MJ mm ha�1 h�1)

Average 44.5 9.2 106.6 59.0 9.0 99.7 50.4 7.0 83.2 42.5 9.4 103.2S.D. 51.4 5.1 166.2 61.3 4.7 145.9 59.7 4.4 147.2 53.4 4.2 190.9Max. 206.2 17.3 655.8 245.9 21.3 573.1 247.9 16.3 610.6 229.6 15.2 610.5Min. 6.6 2.5 3.6 16.5 3.0 14.8 5.1 1.5 1.0 3.8 4.6 16.5

S.D., Standard deviation; Max, Maximum; Min, Minimum; R, Rainfall depth; I30, Maximum intensity at 30 min.

V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281 275

determine the main differences. Finally, the data were analyzed bycorrelation analysis to evaluate the relationships among soil ero-sion and runoff with physico-chemical soil properties.

3. Results and discussion

3.1. Rainfall on selected mountain slopes

Table 2 shows characteristics of rainfall variables for eachlocation where the land-cover plots were established and studiedduring the monitoring period, which was characterized bywell-marked summer and winter seasons typically for aMediterranean-type climate. A total of 22 rainfall events were re-corded during the monitoring period (from January 2009 to April2010), the olive-almond, abandoned cereal–grassland–shrub–farmland, P. halepensis, and P. sylvestris plots accounting for a totalrainfall amount of 890.7, 944.2, 856.1, and 679.6 mm, respectively.Climatically, the monitoring period in the study area was charac-terized by brief torrential storms, which caused low infiltrationand consequently a high risk of runoff and soil erosion.

The average rainfall intensity at 30 min and the R factor(7.0 mm h�1 and 83.2 MJ mm ha�1 h�1, respectively) were the low-est for P. halepensis plots in contrast to the other land-cover types

(Table 2). However, these rainfall parameters were higher in the ol-ive and almond plots, showing its erosive potential. In this sense,soil erosion has long been recognized as being closely related tothe kinetic energy of rainfall in terms of the erosivity index inthe Mediterranean region [31–32]. From the rainfall registered inthe olive and almond plots over the study period, 91% of theseevents exceeded 10 mm of rain, with an average intensity I30 of9.1 mm h�1. For the group of cereal, grassland, shrub, and aban-doned farmland plots, 73% of events were higher than 10 mm, withan average intensity I30 of 9.0 mm h�1. For P. halepensis, it was 72%with an average intensity I30 of 7.4 mm h�1, while for the P. sylves-tris plot it was 64% with an average intensity I30 of 9.4 mm h�1. Thetemporal distribution of rainfall was also relevant in this type ofenvironment, being concentrated in a few days with heavy rainfallevents. The timing and intensity of rainfall regulated the degreeand annual fluctuation of soil erosion and runoff, rare erosive rain-fall events consistently accounting for a small portion of total rain-fall within a particular year but causing most of the damage. In thiscontext, high-intensity rainfall events are frequent in the Mediter-ranean semi-arid area. Such an event occurred on 25/12/2009, forthe olive and almond plots with 206.2 mm (I30 = 17.3 mm h�1), andon 28/12/2009 for the group cereal, grassland, shrub, and aban-doned farmland, with 245.9 mm (I30 = 13.2 mm h�1). Meanwhile,

Fig. 2. Average soil loss and runoff under each land-cover type. Vertical barsrepresent standard deviation; Different lower-case letters between columns arestatically different at the level of 0.05 by the LSD test.

276 V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281

the P. halepensis, and P. sylvestris plots registered 247.9 (I30 -= 13.7 mm h�1) and 229.6 mm (I30 = 15.2 mm h�1), respectively,representing a substantial part of the annual rainfall.

3.2. Water erosion in relation to land-cover types

Fig. 2 shows the weighted average hillslope soil-erosion andrunoff rates under different land-cover types at the plot scale. Dur-ing the study period (from January 2009 to April 2010) for olive-al-mond, abandoned cereal–grassland–shrub farmland, P. halepensis,and P. sylvestris, plots were evaluated after 20, 16, 14, and 13 runoffevents, and 14, 9, 8, and 9 erosion-producing events, respectively.In terms of the percentage of rainfall events that resulted in runoffunder olive, almond, cereals, abandoned farmland, grassland,shrubland, P. sylvestris, and P. halepensis was of 55%, 50%, 45%,59%, 82%, 59%, 55%, and 50%, and soil erosion of 82%, 41%, 41%,50%, 40%, 32%, 23%, and 18%, respectively.

Soil erosion and runoff varied spatially and temporally, increas-ing with rainfall intensity and land-cover types with open canopiesespecially for abandoned farmland, olive, almond, cereal, andgrassland. In this context, the highest runoff and erosion rates wererecorded with a maximum single-event intensity at 30 min and theR factor of 17.3 mm h�1 and 655.8 MJ mm ha�1 h�1 (25/12/2009),respectively, for both olive and almond plots; 21.3 mm h�1 and104.9 MJ mm ha�1 h�1 (17/09/2009) for group of cereal–grass-land–shrub–abandoned farmland plots; 16.3 mm h�1 and610.6 MJ mm ha�1 h�1 (28/12/2009) for the P. halepensis plots;and finally 15.2 mm h�1 and 610.5 MJ mm ha�1 h�1 (28/12/2009)for the P. sylvestris plots (Table 2). For farmland use, specifically al-mond, cereal, olive, and grassland plots recorded significantly low-er runoff rates than did abandoned farmland (30.4 mm), although,for soil erosion only grassland (0.13 Mg ha�1) registered signifi-cantly lower values than did the abandoned farmland plot(0.5 Mg ha�1; Fig. 2). For both P. halepensis, and P. sylvestris plots,the soil erosion and runoff values were significantly lower thanin shrubland, and therefore overall P. halepensis, P. sylvestris, andshrubland were the best land-cover types for reducing the soil-ero-sion and runoff rates in the study area. The lowest runoff coeffi-cients (RFC) were registered for P. halepensis, and P. sylvestris, andthe highest for abandoned farmland, olive, and almond, with inter-mediate values for grassland, cereal, and shrubland. Relatively highpositive correlations were found between RFC and maximum rain-fall intensity I30, showing the variability for each land-cover typethat influences the erosion rates (Fig. 3). In annual terms, the soilerosion for farmland in olive, almond, cereal, grassland, and aban-doned farmland was 5.18, 3.37, 2.76, 1.55, and 4.07 Mg ha�1 yr�1,and runoff 186.1, 158.7, 123.1, 150.9, and 220.4 mm yr�1, respec-tively. For forest, the soil erosion recorded under Pinus stands, inparticular for P. sylvestris and P. halepensis plots, were 0.19 and0.08 Mg ha�1 yr�1, and runoff of 24.0 and 18.7 mm yr�1, respec-tively; for shrubland, the soil erosion and runoff was1.24 Mg ha�1 yr�1 and 50.6 mm yr�1, respectively.

For the Mediterranean area, Cerdan et al. [22] recently reportederosion rates for different land uses, which are closely related tothose found in the present experiment — that is, for forest, grass-land, shrubland, farmland, and bare or abandoned farmland of0.18, 0.32, 0.54, 8.62, and 9.05 Mg ha�1 yr�1, respectively. How-ever, for semi-arid environments of Spain, Chirino et al. [33] in astudy based on erosion plots reported soil erosion for degradedopen land, grassland formation, and shrubland covers of 1.90,0.049, and 0.042 Mg ha�1 yr�1, and runoff coefficients of 4.4%,0.55%, and 0.60%, respectively. These data from short- to med-ium-term erosion rates confirm the great spatial variability in ero-sion rates in the Mediterranean area due to the nature ofexperiments (e.g. degree of soil cover, rock fragments, organicmulches, plant-cover species, slope gradient, length, etc.). The

main potential sources of variation were due to a lack of harmonybetween methodological conditions and the objectives of each spe-cific study.

3.3. Farmland and abandoned farmland

In a Mediterranean environment similar to our research area,Kosmas et al. [34] estimated lower soil erosion for rainfed cerealsat 0.176 Mg ha�1 yr�1. By contrast, Lasanta et al. [35] in mountainareas for cereals reported a higher soil-erosion rate and runoffcoefficient of 1.37 Mg ha�1 yr�1 and 19%, respectively. In addition,for hillside cereal plots sloped 35.5%, Durán et al. [36] reportedsoil-erosion rates ranging from 0.40 to 14.5 Mg ha�1 yr�1. In thissense, Casalí et al. [37] and Valcárcel et al. [38] reported that rillsdeveloped in the same place each year in cereal fields despite being

Fig. 3. Runoff coefficient (RFC) vs. maximum rainfall intensity at 30 min (I30) undereach land-cover type. ��, significant at p < 0.01.

V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281 277

eliminated annually by ploughing. De Santisteban et al. [39] dem-onstrated that soil loss from land with cereal crops resulted during1 or 2 rainfall events per year, usually at the end of autumn or evenin summer, with relatively high and variable erosion rates rangingfrom 2 to 115 Mg ha�1 yr�1. In general, the 2.76 Mg ha�1 yr�1 re-corded for rainfed cereals in the present study is within the erosionrates reported for the Mediterranean area.

Farmland cover is discontinuous with a significant area ofsparse land cover, especially in olive and almond orchards. The ero-sion rates for olive orchards with conventional tillage agree withFrancia et al. [40], who reported 5.7 Mg ha�1 yr�1, a rate similarto that for almond orchards with the same soil management wherethe soil erosion ranged from 1.3 to 10.5 Mg ha�1 yr�1 [41]. For oliveplots under conventional tillage, Gómez et al. [42] reported soilerosion and runoff coefficient of 4 Mg ha�1 yr�1 and 7.4%,respectively.

Van Wesemael et al. [43] for almond orchards with conven-tional tillage under even more extreme conditions than ours esti-mated higher erosion rates (26.6 Mg ha�1 yr�1) than those foundin the present experiment (3.37 Mg ha�1 yr�1). This demonstratesthe high variability in erosion rates for almond and olive orchardsunder Mediterranean conditions.

Overall, olive, almond, and cereal cultivation led to the higherrisk of breakdown of aggregate stability, loss of vegetative cover,export of nutrient-enrichment particles, exposure of the soil sur-face to direct impact of raindrops, and the resulting soil detach-ment (inter-rill erosive forces); all together, these factors madethe soil particles easily susceptible to runoff (rill erosive forces).

On the other hand, the results demonstrated that the areas ofthe greatest soil loss are associated with seriously discontinuousland cover, and that abandoned farmland causes significantshort-term increases in soil and runoff mobilization, as determinedin this study (4.07 Mg ha�1 yr�1). However, the risk of runoff andsoil erosion in abandoned lands after agricultural activities canbe decreased by natural and progressive growth of annual andperennial shrubs in the cleared site to maintain a stable and suit-able plant cover. This suggests that the expansion in the numberof native plant species could significantly reduce soil erosion andbolster soil stability by encouraging rootlets and the diversity ofroot-system characteristics inherent in a greater number of differ-ent species, as in the case of shrubland and grassland.

Farmland abandonment predominated especially in Mediterra-nean mountain areas, resulting in greater soil erosion during thefirst years after abandonment. This might be related to the distur-bance of the land when the farmland was abandoned, with de-creased canopy interception of rainfall drops and exposure toovergrazing for a period of time after cultivation ceased. Thus,higher average potential soil erosion and runoff were noted forabandoned agricultural soils and farmlands characterized bysparse vegetation and ground cover.

3.4. Shrubland and grassland

Land cover is an essential factor in mitigating soil erosion, itsprotective capacity being related to biomass and species diversity,as found in the present study for shrubland and grassland plots.Biomass converted to organic matter can protect against soil ero-sion by stabilizing aggregates and boosting soil structure in thesetypes of environments [44–45]. Cardinale et al. [46] reported thatmixtures of species can produce on average 1.7 times more bio-mass than monocultures produce; therefore, soil stability dependsalso on the above- and belowground structure of plant communi-ties. In addition, variability in the shoot and root architecture ofplants is capable of reducing both rainfall erosivity and soil erod-ibility, as the greater the diversity of root-growth forms, the lesslikely it is that extreme events will lead to soil erosion [47]. As sta-ted by Power and Follett [48] the loss of plant diversity in terms ofspecies number and structural complexity, and maintenance ofmonocultures can promote susceptibility to soil erosion, especiallyin high mountains. In this context, Kosmas et al. [34] reported asoil-erosion rate of 0.067 Mg ha�1 yr�1 for Mediterranean shrub-land, which is lower than 1.55 Mg ha�1 yr�1 recorded in ourexperiment.

Low soil erosion and runoff was found in land uses with higherplant diversity, e.g. shrubland and grassland, but not in others, asfor instance, cereals, which have a relatively high plant cover butalso high soil erosion. This is presumably due to the sparse canopyfailing to provide sufficient protection against soil erosion, espe-cially during early periods of seedling development.

After the abandonment of agricultural soils, the annual plantsthat become the dominant species (grasses and forbs) do not haveroot systems as extensive as those of shrubs. This might explainthe difference between the runoff rates in the grassland and shrub-land plots, grassland being an intermediate step to shrubland, re-lated strictly to development of plant diversity over the time. Inthis sense, Gyssels et al. [49] pointed out that plant roots penetrat-ing the soil macrospores improve water infiltration, reducing thevolume of surface runoff and consequently soil erosion.

Durán et al. [50,51] reported that runoff and soil erosion are sig-nificantly lower under shrubland as a result of the high infiltrationrate afforded by the increase in organic matter deposited over thesoil. Our findings confirmed that these characteristics of shrublandand grassland could have promoted a lower risk for soil erosion byinfluencing hydrological surface processes.

Table 4Correlation coefficients (Pearson) among soil erosion and runoff with rainfall and soil parameters.

SE RF BD SOC CEC C:N Sand Silt Clay RD I30 EI SSC

SE 1 0.833** 0.977** �0.713** �0.498* �0.556** �0.411* 0.191 �0.285 0.572** 0.455** 0.541** �0.925**

RF 1 0.834** �0.657** �0.305 �0.534** �0.216 0.212 0.018 0.437* 0.347 0.406* �0.847**

BD 1 �0.811** �0.638** �0.570** �0.360 0.283 0.112 0.618** 0.544** 0.579** �0.893**

SOC 1 0.850** 0.156 0.302 �0.421* 0.122 �0.275 �0.901** �0.854** 0.752**

CEC 1 0.138 0.086 �0.393 0.358 �0.364 �0.795** �0.634** 0.407*

C:N 1 0.070 0.076 �0.002 �0.840** 0.254 0.213 0.398Sand 1 �0.061 �0.460* �0.261 �0.366 �0.557** 0.543**

Silt 1 �0.360 0.375 0.432* 0.395 �0.231Clay 1 �0.119 �0.056 0.224 �0.401*

RD 1 �0.041 �0.035 �0.408*

I30 1 0.949** �0.575**

EI 1 �0.718**

SSC 1

SE, soil erosion; RF, runoff; RD, rainfall depth; I30, maximum intensity at 30 min; EI, erosivity index (R factor); SOC, soil organic carbon; BD, bulk density; CEC, cation-exchangecapacity; SSC, percentage of soil surface covered;* Significant at p < 0.05.** Significant at p < 0.01.

278 V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281

3.5. Forest

The annual erosion and runoff rates recorded under P. halepensisare similar to those reported by Topic et al. [52] of 0.04 Mg ha�1 -yr�1 and 6.2 mm yr�1, respectively. The lower average erosion un-der P. halepensis and P. sylvestris can clearly be attributed to thedense canopy structure and litterfall, which more effectively shieldagainst rainfall erosivity. Therefore, rainfall water that reaches thesoil infiltrates the soil profile, percolates to the groundwater, orflows downhill as runoff. The forest cover is one of the most com-mon methods for restoring degraded land and minimizing the riskof soil erosion [53]. The establishment of P. halepensis tree coverhas traditionally been encouraged in both natural and degradedecosystems in order to reduce soil erosion in Mediterranean areasduring the 20th century. Nevertheless, the role of P. halepensis inthe restoration of degraded semiarid lands has been questioned[54] and it has not been proved better at controlling runoff and soilerosion than the natural shrubland and grassland communitiesperceived as degraded where pine stands were planted [33]. Also,Bellot et al. [55] pointed out that the introduction of P. halepensiswith afforestation has a negative effect on native shrub perfor-mance in a Mediterranean semiarid area. According to the resultsof the present experiment, P. halepensis (0.08 Mg ha�1 yr�1) andP. sylvestris (0.19 Mg ha�1 yr�1) improve the soil conservation pri-marily by discouraging water-erosion processes.

In addition, our findings agree with Chirino et al. [33], who re-ported that soils with P. halepensis and native vegetation withouttrees result in the same amount of runoff, the interaction betweentrees and the annual understory reducing the runoff almost to zeroin the P. halepensis and P. sylvestris plots in our experiment. Gener-ally, the forests are well known for high soil-infiltration capacitiesand hydraulic conductivity, enhancing base flow [56]. This circum-stance at the watershed scale may have a positive influence onimportant hydrological functions such as infiltration, percolation,and base flow, which subsequently affect the water regime in awatershed.

Thus, soil-loss-tolerance rates may diverge according to landcover, climate, topography, and several soil characteristics. Inthe present study, the rates measured in all the land-cover types(from 0.08 to 5.18 Mg ha�1 yr�1 for olive and P. halepensis, respec-tively) did not exceed the tolerance rate of soil erosion of11.2 Mg ha�1 yr�1 [57], but exceeded the upper limit of soil for-mation (1.4 Mg ha�1 yr�1) especially in farmland (>1.55 Mg ha�1 -yr�1) for conditions prevalent in Europe, according to Verheijenet al. [58].

3.6. Soil properties under land-cover types and their relationship tosoil erosion

Table 3 lists the main physico-chemical soil properties undereach investigated land-cover type in the study area. The results re-veal differences in relation to the soil texture under different landuses, although it could also be attributed to the inherent character-istics of soil type. The soils planted with P. halepensis had the high-est amount of clay while shrubland and abandoned land had thelowest, which is probably linked to high erodibilty of silt andfine-sand fractions. In this context, at least for the upper soil sur-face layers, Lal [59] and Narain et al. [60] stated that soil erosionnormally increases with deforestation, leading to selective trans-port of clay particles. In addition, Hajabbasi et al. [61] reportedthe loss of clay associated with the transformation of forest soilsinto other land uses. This idea could be consistent with our results,where the clay content was negatively correlated (r = �0.285) withsoil erosion (Table 4).

The amount of organic carbon measured was significantly high-er in P. halepensis followed by P. sylvestris and shrubland, the levelswere lower in the respective farmland uses, and lowest in aban-doned farmland. A similar trend was recorded for soil-nitrogencontent and, in relation to plant-available phosphorus and potas-sium contents, no significant differences were found for land-covertypes (Table 3).

Because of the high organic carbon, the top 25 cm of the soil arelikely to be affected by land-use change and natural disturbances,such as cropping and wild fires. Loss of organic C is expected to re-sult in soil aggregates being easily broken down and the finer par-ticles being transported by erosion (r = �0.713) (Table 4). In thiscontext, soil organic carbon was significantly higher in P. halepen-sis, and P. sylvestris. These results appear to be related to the factthat the needles of the Pinus fell and decomposed underneaththe trees, adding high amounts of organic matter, especially in P.halepensis plots. This result agrees with Jeddi and Chaieb [62],who concluded that forests with P. halepensis improved the soilby increasing organic C, total N, and soil-available P, and facilitat-ing the colonization and development of understory vegetation. Inaddition, in shrubland dominated by diverse plants, the organiccarbon was high, presumably due to the incorporation of decom-posing plant litter [51,63].

Farmland had lower quantities of SOC probably due to the lossby water erosion from the soil surface. Similar results have beenreported by Fu et al. [64], who found the amount of SOC to be low-er in farmland than in land with native vegetation. In addition,

V.H. Durán-Zuazo et al. / Acta Ecologica Sinica 33 (2013) 272–281 279

depending on the tillage practices used in cultivation, the decom-position rate of organic matter may be increased. Also, a positiverelationship between SOC and total N contents was determined(Table 3). Similarly, previous studies state that if SOC increases,the total N increases [65,66], the dynamics of N in mineral soilbeing closely linked to C because most N exists in organic com-pounds and heterotrophic microbial biomass, which utilize organicC for energy.

The pH values of soils in land uses were within the range fornormal plant-growth conditions (6–7.5). The higher soil pH valuesfound in abandoned farmland might be related to low soil–watercontent and a low amount of organic carbon, as noted by Rezaeiand Gilkes [67]. Also, this fact, according to De Santis et al. [25],is a sign of eroded soil surfaces. As is well known, pine litter hasan acidifying effect on the soil, leading to slow decompositionand accumulation process of a thick organic horizon on the forestfloor, where large amounts of nutrients are stored.

The difference in bulk density among the land-cover types wascaused by the soil management, as the continual cultivation of thesoil in farmland caused the structure to decline (olive and almond).However, the shrubland and grassland area registered lower bulkdensity due to the minimal damage to the soil, as the vegetationfomented greater organic matter, pores, and higher microbial con-tent, all contributing to a healthier structure. The P. halepensis fol-lowed by P. sylvestris plots contained the lower bulk density due tominimal disturbance, this being in line with the highest organic-carbon accumulation on the soil surface (r = �0.811) (Table 4).

Table 4 shows the different correlation coefficients for soil ero-sion and runoff with soil and rainfall parameters. There were sig-nificant positive correlations for soil erosion with runoff, BD, RD,I30, and the R factor, while significant negative correlations werefound for SOC, CEC, the C:N ratio, and SSC. Runoff was correlatedpositively with BD and the R factor, being negatively with SOC,the C:N ratio, and SSC. This agrees with Kang et al. [68], who re-ported a significant relationship for soil erosion vs. bulk density(r = 0.86) and SOC (r = �0.76), respectively.

No significant correlations were found between SOC and tex-ture (sand, silt, and clay), in agreement with the findings of Honto-ria et al. [69] but in contrast to those of Kadeba [70], who reportedthat the effect of texture on carbon content varies depending onthe parent material. The close relation of CEC with clay and SOCcontent is well known, as confirmed in our study (r = 0.850; Ta-ble 4). Also, for SOC, bulk density, CEC, and the C:N ratio, the pres-ent study found significant correlations with average soil erosionand runoff. This is consistent with the findings of Guerra et al.[71] and Ritchie et al. [72], who reported the strongly significantrelationships between soil redistribution and SOC concentrationsin upland soils. Also, Massey and Jackson [73] and Sharpley [74],for many soils, reported higher selectivity of total N transport ineroding soil compared to that of SOC.

These results support the contention that the land use underfarmland and abandoned farmland in mountain areas degradedsoil properties, causing greater susceptibility to erosion and conse-quently its environmental impact [75]. Identifying and monitoringsuch soil-quality factors is the essential first step in counteringland degradation as well as in planning sustainable land use.

Overall, the soil health of land-use types follows the order: for-est, shrubland, grassland, farmland, and abandoned farmland.Thus, the continued land-use change and erosion will cause signif-icant degradation by altering land-cover types and soil properties.

4. Conclusions

The present study has shown the importance of human inter-vention regarding land-cover types, exploring its impact on erosion

process and soil properties, both of which connect to broader is-sues of land conservation.

The average rainfall events in the semiarid study area had ahigh volume, high intensity, and a short duration, and conse-quently acute erosion risk for the land-cover types analyzed. High-er average potential soil erosion and runoff was registered inabandoned farmlands, which are characterized by low plants andground cover. Less soil erosion and runoff was found in shrublandand grassland, with greater plant diversity, while cereal plots hadrelatively high plant cover but also serious soil erosion. This wasapparently because the reduced canopy fails to shield against soilerosion, especially during early periods of seedling development.Similarly, the conventional tillage on sloping lands with rainfedtree crops (olive and almond) promoted substantial soil erosionand runoff.

The lowest average erosion under forest with P. halepensis andP. sylvestris can be unequivocally attributed to the dense canopystructure, which more effectively reduced rainfall erosivity. Conse-quently, there is a clear need to focus greater attention on develop-ing sustainable land-use practices in management of thisagroforestry landscape. In addition, erosion processes in the studyarea were highly dependent on runoff, bulk density, soil organiccarbon, and the degree of soil surface cover, these parametersbeing directly related to the land-cover type. Subsequently, soilerosion is influenced by physico-chemical soil properties on whichsoil quality and productivity depend, posing a major threat to thesustainable use of soil and water resources. Thus, the main chal-lenge for agroforestry landscapes in the Mediterranean area is tointegrate the growing of forest trees and crops in harmonious com-binations that result in sustainable land use.

Acknowledgements

The research work that leads to this publication was sponsoredby the following research projects ‘‘Hydrological and erosive pro-cesses, biomass assessment, and organic carbon sequestering un-der different land uses in the Mediterranean agrarian watershedEl Salado, Lanjarón’’ (SE Spain) (RTA2007-00008-00-00) and ‘‘Con-servation agriculture techniques in rainfed-tree crops and Mediter-ranean climate: implications for sustainable productivity, erosioncontrol, and improvement of soil quality and biodiversity’’(RTA2011-00007-00-00) both granted by INIA Spain, and cofi-nanced by FEDER funds (European Union). Also the authors thanksto the Direction of Natural and National Park of Sierra Nevada.

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