Vegetation history of the western Rif mountains (NW Morocco): origin, late-Holocene dynamics and human impact

O R I G I N A L A R T I C L E

Vegetation history of the western Rif mountains (NW Morocco):

origin, late-Holocene dynamics and human impact

Serge D. Muller^•Laila Rhazi^•Benjamin Andrieux^• Marion Bottollier-Curtet^•Se´verine Fauquette^•

Er-Riyahi Saber^•Nabil Rifai ^•Amina Daoud-Bouattour

Received: 15 August 2014 / Accepted: 17 November 2014 ÓSpringer-Verlag Berlin Heidelberg 2014

Abstract

Unlike southern Spain, northern Morocco has been little investigated for palaeoecological purposes.

Consequently, the origin and history of the Rifan vegeta- tion is largely unknown, as well as the past role of human activities. A review of the Plio-Pleistocene fossil data available from North Africa clearly reveals the ancient origin of much of the present-day flora and vegetation structures of the region. A well-dated pollen record cov- ering the last 5,000 years, obtained from a fen, is compared to previous regional pollen data in order to understand the late-Holocene vegetation dynamics and the influence of anthropogenic disturbances. Modern pollen spectra have allowed the calibration of pollen diversity and evenness as

indicators of tree-cover density. The results obtained show the long-term persistence of regional forests until the onset of Arab Sharifian dynasties in the 16th century, with a surprising lack of human impact during the late Neolithic, and little impact during Roman colonisation. The increas- ing density of deciduous forests recorded from 3,800 to 1,900 cal

BP

, concomitant with the expansion of cedar in the Middle Atlas, could reveal the onset of widespread cooler and moister climatic conditions. The weak and late human impact in the Rifan mountains explains, at least in part, their high diversity and the conservation of their forest ecosystems. Anthropogenic activities however have led to severe modification of the understorey structure of these forests during the four last centuries, and to the worrying on-going deforestation that presently threatens the survival of this invaluable biological heritage.

Communicated by J.-L. de Beaulieu.

Electronic supplementary material The online version of this article (doi:10.1007/s00334-014-0504-9) contains supplementary material, which is available to authorized users.

S. D. Muller (&)B. AndrieuxS. Fauquette

Institut des Sciences de l’Evolution, Universite´ Montpellier 2, CNRS, IRD, case 061, Place Euge`ne Bataillon,

34095 Montpellier Cedex 05, France e-mail: smuller@univ-montp2.fr L. Rhazi

Laboratoire de botanique, mycologie et environnement, Faculte´

des Sciences de Rabat, Universite´ Mohammed V, 4 Avenue Ibn Battouta, BP 1014 RP, Rabat, Morocco

M. Bottollier-Curtet

Les Ecologistes de l’Euzie`re, Domaine de Restinclie`res, 34730 Prades-le-Lez, France

E.-R. Saber

De´partement de Ge´ographie, Faculte´ des Lettres et Sciences Humaines, Universite´ Moulay Ismail,

BP 11202, Zitoune Mekne`s, Morocco

N. Rifai

Direction Re´gionale des Eaux et Foreˆts et de la Lutte contre la De´sertification du Rif, BP 722, Te´touan, Morocco

N. Rifai

Laboratoire d’Ecologie Aquatique et Environnement, Faculte´

des Sciences Aı¨n Chock, Universite´ Hassan II Casablanca, BP 5366, Maarif, Casablanca, Morocco

A. Daoud-Bouattour

De´partement de Biologie, Faculte´ des Sciences de Tunis, Universite´ de Tunis El Manar, Campus universitaire, 2092 Tunis, Tunisia

A. Daoud-Bouattour

Faculte´ des Lettres, des Arts et des Humanite´s de Manouba, UR99/UR/02-04 BiCADE, Universite´ de la Manouba, Campus universitaire de Manouba, 2010 Manouba, Tunisia

DOI 10.1007/s00334-014-0504-9

Keywords

Late Cenozoic North Africa Palynology Anthropisation Climate Mediterranean forest

Introduction

The regions of southern Spain and north-western Morocco, bordering the Strait of Gibraltar, have been identified as a major hotspot for plant diversity within the Mediterranean basin (Me´dail and Que´zel

1997). The exceptional plant

diversity of this so-called Betic–Rifan hotspot is due to a conjunction of factors, including a complex history from the Neogene, a variety of substrates, climates, exposures and altitudes, and the proximity of both the Mediterranean and the Atlantic. The region harbours disjunct populations of endangered Tertiary relict species, including Abies marocana/pinsapo (sometimes considered to constitute two ssp. of A. pinsapo; Alba-Sa´nchez et al.

2010; Linares 2011),

Frangula dodonei ssp. baetica (F. alnus ssp. bae- tica; Hampe and Arroyo

2002; Hampe 2005),

Rhododen- dron ponticum ssp. baeticum (Mejı´as et al.

2007), and

Prunus lusitanica (Calleja et al.

2009). Despite the simi-

larity of plant communities within this geographical unit (Arroyo

1997; Rodrı´guez-Sa´nchez et al. 2008), northern

Morocco has a lower richness in species and endemics compared to southern Spain (Ojeda et al.

1996; Maran˜o´n

et al.

1999). These authors interpret these differences as

mainly caused by higher human pressure (slashing and browsing) in Morocco. While this is clearly the case today, the origin and history of such anthropogenic disturbances of the Rifan ecosystems are largely unknown. Indeed, contrary to Andalusia that has been thoroughly investigated for palaeoecological purposes since the pioneer works of Menendez Amor and Florschu¨tz (1962,

1964), the past

history of vegetation is only known in the Rif mountains from a single investigation (Reille

1977), carried out in the

southernmost external reliefs of the Jebala Range.

This publication presents a regional survey based on 12 poorly dated pollen diagrams, among which only one undated sequence (Daya Arbatete) was considered to cover the last ten millennia, and was consequently used to reconstruct the vegetation dynamics through the Holocene.

However a radiocarbon date recently obtained from a new core taken in this site revealed that the sediment accumu- lation began around 3,000 years ago (2,350

±

35

BP

at 190 cm, Poz-51919), and not in the Boreal period as pro- posed by Reille (1977). Consequently, Reille’s publication is not likely to present any diagram exceeding 4,500 years.

It nevertheless provides invaluable information about late- Holocene vegetation dynamics in the Rif, evidencing a relatively stable regional vegetation cover, the past abun- dance of alder swamps, and the late general decline of

semi-deciduous oak forests composed of Quercus canari- ensis (zeen oak) and Q. pyrenaica (Pyrenean oak).

We present here the palynological analysis of a 5,000 year-long sedimentary sequence from the Rif mountains, in order to (1) provide the first well-dated ref- erence sequence for northern Morocco, (2) discuss the origin and history of the regional flora by comparing the observed pollen assemblages with older North African records, (3) specify the past climatic and human influences that have controlled the late-Holocene history of vegetation in the Jebala Range, and (4) provide a historical back- ground for the conservation management of regional ecosystems.

Materials and methods

Biogeographical setting

The Rif, which is an Oligo-Miocene Alpine orogenic belt continuing southward to the Betic range around the Albo- ran Sea, comprises two main geological units: an internal coastal zone essentially composed of limestone rocks, and an external continental zone, the so-called Jebala Range, consisting of fragmentary sandstone flysch deposits (Fig.

1). The Jbel Bou Hachem, located near Chefchaouen

(sometimes abbreviated as Chaouen), constitutes the highest relief of the siliceous Jebala Range (1,602 m a.s.l.).

The major phytogeographic interest of this massif (Sau- vage

1958), in particular the diversity of its forests and the

abundance of its wetlands, including several Sphagnum fens (Dahlgren and Lassen

1972; Muller et al.2011), has

motivated its election as a Site of Biological and Ecolog- ical Interest (SBEI) in 1996, as an Important Plant Area (IPA) in 2004, and its inclusion within the Intercontinental Mediterranean Biosphere Reserve (IMBR) in 2006 (Ben- abid

2000; Taleb and Fennane2011).

Characterised by a humid to sub-humid bioclimate, the

Rif harbours a variety of fragmentary forest ecosystems

(Sauvage

1958; Benabid2000; Ajbilou et al.2006; Fig.2),

organised in a mosaic with deforested zones mainly

occupied by Mediterranean shrublands (matorrals), degra-

ded therophytic meadows and cultivated lands, including

the production of Cannabis sativa (kif), the expansion of

which is a cause of the on-going forest decline (Que´zel and

Barbero

1990; Taiqui1997). The most abundant tree spe-

cies of the region is Quercus suber (cork oak), which

constitutes extensive evergreen forests on the siliceous

substrates of the Jebala Range at low altitudes within the

Meso-Mediterranean belt. These open forests are charac-

terised by a light-demanding understorey of Arbutus unedo,

Erica arborea and Cistus spp. On eroded valley surfaces,

they are locally replaced by open xerophytic formations of

Tetraclinis articulata (arartree). Evergreen Thermo-Medi- terranean forests of Olea europaea (olive), Pistacia len- tiscus (mastic) and Ceratonia siliqua (carob) trees, thought to have dominated the alluvial valleys prior to anthropo- genic deforestation (Que´zel and Me´dail

2003), are now

preserved around holy monuments (marabous) and can elsewhere be observed only as scattered patches (Deil et al.

2009). The mid-altitude aspects of the Supra-Mediterra-

nean belt are covered by extensive forests of the semi-

deciduous Quercus canariensis, locally mixed with Q.

pyrenaica and Pinus pinaster ssp. hamiltonii (maritime pine). In the upper part of this belt, these species are associated with Cedrus atlantica (cedar), which dominates the Mediterranean Montane belt on the crests and summits of the Jebala Range. The sclerophyllous Q. ilex ssp. ro- tundifolia (holm oak) and Q. coccifera (kermes oak) are much less abundant than other oaks, and have developed mainly in the internal zone, respectively in rocky altitudi- nal places and in coastal lowland environments. The endemic Abies marocana (Moroccan fir) forms impressive mountain forests on the limestone reliefs of Chefchaouen and Tazaot. Original riparian ecosystems are constituted by a tetraploid form of Alnus glutinosa (Lepais et al.

2013),

locally associated with Betula pendula var. fontqueri, Frangula dodonei ssp. baetica and Prunus lusitanica.

Finally, the sandstone reliefs harbour numerous rich and diversified wetlands with a rare and endangered flora, from temporary pools with Isoe¨tes velata and Gratiola officinalis to fens with Sphagnum auriculatum and Eleocharis mul- ticaulis (Dahlgren and Lassen

1972; Muller et al.2011).

Study sites and fieldwork

Modern pollen spectra were obtained from surface sedi- ments collected in 2009 and 2011 from 11 wetlands (pools, marshes and fens; Fig.

1; Table1) that strongly differ by

both their hydrophytic cover and their environmental characteristics. A sediment core was taken for fossil pollen analysis in 2011 from the fen of Maison Forestie`re-1 (MF1;

Table

1), which lies on the northeastern flank of the Jbel

Bou Hachem, 300 m below the forest house. The present- day environment of MF1 is an open area colonised by Pteridium aquilinum (bracken), after the local Q. canari- ensis forest was cut down ca. 10 years ago. This recent clearing separates the upper Q. canariensis forest from the Q. suber forest developed at lower altitudes. MF1 is a roughly circular fen of 0.2 ha, with a small outlet at its northern extremity. It is covered by a dense lawn of El- eocharis multicaulis, Anthoxanthum odoratum and Bal- dellia ranunculoides, which has developed on a continuous carpet of Sphagnum auriculatum (Muller et al.

2011). This

unusual plant community provides a habitat for a number of rare species with Atlantic and Northern biogeographical affinities, including Carex echinata, Danthonia decumbens, Juncus bulbosus, Lotus pedunculatus, Potamogeton po- lygonifolius and Potentilla erecta, along with some en- demics (Dactylorhiza maurusia, Myosotis welwitschii).

The margins of the fen are occupied by low shrublands of Calluna vulgaris, Erica ciliaris, Genista anglica ssp.

ancistrocarpa, Myrtus communis and Pteridium aquilinum.

The 130 cm-long core was taken a few meters from the southern margin of the fen MF1, with a 50

9

5 cm

Fig. 1 Location of the study zone (a) and of the study sites on the

topographic map of the region (b). The meaning of the site codes is given in Table1

Fig. 2 Distribution of the main forest trees of the studied region (source: National Forest Inventory, 2003–2004). The sites previously studied (white dots) are located approximately, based on the indications furnished by Reille (1977)

modified Russian sampler, and conserved within plastic film until sampling in the laboratory.

The botanical nomenclature follows Fennane et al.

(1999,

2007), Valde`s et al. (2002), Que´zel and Me´dail

(2003), Fennane and Ibn Tattou (2005), and Ibn Tattou and Fennane (2008). However, when these authors have dif- ferent taxonomical points of view (e.g., about oaks, cedar and fir), we follow Que´zel and Me´dail (2003).

Laboratory work and data analysis Coring

Non-destructive elemental analyses were first carried out on the MF1 core every 2 cm with a X-ray fluorescence portable spectrometer (Delta

^Ò

Olympus); afterwards 1 cm

³

samples were taken every 2 cm for loss-on-ignition and every 4 cm for pollen analysis. LOI measurements were made after re-weighing the samples after five hours at 550

°C in an oven (Heiri et al.2001). The chronology is

based on radiocarbon dating, obtained from sediment samples and macrocharcoal. Calibrated ages (cal

BP

, i.e.

calendar years before present) were computed with Calib 7.0.2 (Stuiver and Reimer

1993), using the calibration

dataset IntCal13 (Reimer et al.

2013). Palynological

analyses of sediments were completed after chemical treatments (Berglund and Ralska-Jasiewiczowa

1986),

including a 36 h-long digestion with 70 % HF. Pollen percentages were based on sums excluding Pteridophyte spores. Pollen sums exceed 500 grains, except for the two poorest levels, where pollen sums are respectively 489 grains (surface) and 133 (bottom). Pollen nomenclature follows Birks and Birks (1980) and Fægri and Iversen (1989). Pollen diagrams were constructed with GPalWin (Goeury

1997) and Polpal (Walanus and Nalepka 1999).

Pollen zonation, based on hierarchical classification (paired group, Euclidean similarity measure) was carried out with Past 2.17c (Hammer et al.

2001).

Surface sediments

After chemical treatment (see above), the 11 surface sediments were used (1) to identify the regional pollen input and (2) to test the hypothesis of a filtering effect on

Table 1 Studied sites

Jbel Code Site name Nature Altitude (m a.s.l.)

Longitude W

Latitude N

Environment Reference

Bou Hachem

BH1* Bou Hachem-1 Fen 1,100 n.a. n.a. Boundary of zeen oak forest Reille (1977) MF1* Maison

Forestie`re-1

Fen 1,064 05°25⁰14⁰⁰ 35°15⁰12⁰⁰ Recently cleared zeen oak forest (bracken fern)

This study MF2 Maison

Forestie`re-2

Fen 1,092 05°25⁰40⁰⁰ 35°15⁰22⁰⁰ Recently cleared zeen oak forest (bracken fern)

This study MF3 Maison

Forestie`re-3

Fen 1,096 05°25⁰54⁰⁰ 35°15⁰32⁰⁰ Recently cleared zeen oak forest (bracken fern)

This study MF4 Maison

Forestie`re-4

Pool 1,213 05°25⁰58⁰⁰ 35°15⁰13⁰⁰ Zeen oak forest This study TAY1 Tayenza-1 Pool 980 05°26⁰09⁰⁰ 35°16⁰11⁰⁰ Dense pine wood This study Sougna MAR* Marzine Pool 720 05°20⁰09⁰⁰ 35°06⁰02⁰⁰ Pine woods and Mediterranean

scrublands

Reille (1977);

this study

TAN* Tanakob Lake 840 n.a. n.a. Mediterranean scrublands Reille (1977)

Khesana ABF Al-Bayda Fen Fen 1,125 05°12⁰33⁰⁰ 35°01⁰46⁰⁰ Mediterranean scrublands This study BAR* Bartete Fen 1,249 05°14⁰59⁰⁰ 35°01⁰51⁰⁰ Cultures and degraded zeen oak

forest

Reille (1977);

this study BAZ Bazoukout Fen 1,143 05°14⁰43⁰⁰ 35°02⁰10⁰⁰ Cultures and Mediterranean

scrublands

This study BOU Boujdayem Pool 1,202 05°12⁰24⁰⁰ 35°01⁰22⁰⁰ Degraded Pyrenean oak forest This study

RHE* Rhezana Fen 1,300 n.a. n.a. Zeen oak forest Reille (1977)

Tizirene DAY2 Dayla-2 Marsh 1,300 04°59⁰30⁰⁰ 35°01⁰02⁰⁰ Cultures and Mediterranean scrublands

This study

TIZ* Tizire`ne Lake 1,350 n.a. n.a. Zeen oak forest? Reille (1977)

Note that the site Bartete was previously named Arbate`te by Reille (1977) n.a.not available

* Fossil pollen analyses

the regional pollen input by the surrounding tree canopy (Tauber

1965). First, the regional pollen input was identi-

fied from comparison between modern pollen spectra and associated vegetation releve´s: it excludes strictly hydro- phytic taxa (e.g., Anagallis tenella-type, Isoe¨tes, Myrio- phyllum, Osmunda, Potamogeton) and taxa with wider ecological requirements that were systematically recorded within the local vegetation (e.g. Fabaceae, Poaceae, Potentilla). In particular, Poaceae include the hydrophytic species Anthoxanthum odoratum and Danthonia decum- bens, which may be abundant on the studied wetlands, with regular occurrences of agglutinated pollen masses in the sediment samples indicating the deposition of stamens from plants growing locally. Second, in order to identify the possible filtering effect of trees, we compared (linear regressions, with R; R Development Core Team

2005) the

pollen diversity, richness and evenness with the surround- ing tree cover measured from aerial photographs (source:

Google Earth 2003–2013). The calculation of Evenness and Shannon indexes was carried out with Past 2.17c (Hammer et al.

2001). The percentages of tree cover were

measured within circular surfaces of increasing diameter (each 50 m from 50 to 350 m) around sampling sites with ImageJ 1.47v (Abramoff et al.

2004).

Results

Chronology and lithology

Five radiocarbon dates (Table

2) were obtained from three

sediment and two macrocharcoal samples. The age-depth

model (Fig.

3) reveals continuous sedimentation for the last

ca. 5,000 years and allows the calculation of the sediment accumulation rate, which varies from 0.15–0.19 to 0.76–1.17 mm year

^-1

. The sediments (Fig.

3) show a

decreasing granulometry from the bottom (133 cm) to the surface. Sandy clay occurs in the deepest part of the core (133–103 cm); the presence of a sand layer (127–125 cm) and of a reworked macrocharcoal fragment dating from the Late-Glacial (117 cm) suggests the detrital origin of this deposit. The orange colour of the sediment reveals the pre- sence of iron oxides that are particularly abundant below 122 cm depth. The middle part of the sequence (103–36 cm) consists of clays, first rather mineral, then more and more organic, with a visual shift around 73 cm. These sediment changes indicate decreasing runoff and the local existence of standing water. This is moreover supported by the occur- rence of an autochthonous macrocharcoal fragment of Frangula dodonei found at 65 cm depth. Finally, a strongly decomposed peat layer occupies the upper part of the core, from 33 cm to the surface. Elementary analyses and loss-on- ignition measurements reveal the progressive nature of that change, which occurs from 50 to 36 cm. The progressive increase in organic matter results from the establishment of the present-day peat-forming vegetation, and corresponds to a change in sedimentation mode, with a decrease in the detrital input supplied by runoff.

Surface pollen analysis and present-day tree cover around the study sites

Diversity, Richness and Evenness indexes calculated from modern pollen spectra (ESM) were compared to

Table 2 Radiocarbon ages presently available in the Rif (this study for Maison-Forestie`re 1 and Bartete 1 bis; Reille1977for all other ages) Site Core Depth (cm) Lab. code ¹⁴C age (BP) Cal age, 2rrange

(calBP)

Dated material No in

Fig.6

Maison Forestie`re-1 MF1b 35–36 Poz-61157 315±30 460–300 Sediment 1

65 Poz-51918 2,060±30 2,120–1,950 Charcoal:Frangula dodonei 2

83–84 Poz-57995 2,125±30 2,300–2,000 Sediment 3

117 Poz-51917 11,070±60 13,070–12,780 Charcoal: decid.Quercus

131.5–132 Poz-57997 4,480±60 5,310–4,960 Sediment 4

Bou Hachem 1 BH1 75–80 Lv-633 810±50 900–670 Sediment 5

135–140 Lv-634 1,140±55 1,180–930 Sediment 6

Bartete-1bis BAR1bis 190 Poz-51919 2,350±35 2,490–2,320 Charcoal: cf. Lamiaceae 7

Bartete-3 (Arbatete-3) BAR3 125–130 Lv-635 1,010±50 1,050–790 Sediment 8

Rhesana-1 RHE1 155–160 Lv-632 1,670±65 1,720–1,410 Sediment 9

Marzine-1 MAR1 85–90 Lv-592 1,070±60 1,170–800 Sediment 10

Tanakob TAN 30–35 Lv-648 \130 Sediment

65–70 Lv-649 300±55 500–150 Sediment 11

115–120 Lv-650 1,080±55 1,170–910 Sediment 12

Tizire`ne 2 TIZ2 135–140 Lv-1233 1,390±140 1,560–980 Sediment 13

Tizire`ne 3 TIZ3 145–150 Lv-647 \280 Sediment

surrounding tree cover that varies from 0 to 65 % on cir- cular surfaces corresponding to diameters ranging between 50 and 350 m (Table

3). The diversity presents highly

significant regressions with the density of surrounding tree cover, with the highest regression for a surface corre- sponding to a diameter of 200 m around the sampling site (Table

3). This feature, associated with regressions that are

significant for evenness but not for richness, indicates that the presence of dense forests around wetlands does not qualitatively modify the pollen record (unchanged rich- ness), but induces an extra-local pollen input that over- whelms the regional one. Consequently, fossil pollen diversity and evenness can be used for evaluating the past density of the surrounding tree cover.

Fossil pollen analysis

Fossil pollen data from the core MF1b are presented in Figs.

4

(percentages) and

5

(concentrations). Based on the main regional taxa, the HCA [hierarchical cluster analysis]

allows the identification of five pollen zones:

Zone 1 (128–110 cm; ca. 4,870–3,840 cal

BP

) is char- acterised by very low pollen concentrations (3,000–80,000 grains cm

^-3

) and by pollen assemblages dominated by Q.

canariensis-type, with good representation of Cedrus and Q. suber. Cerealia-type and possibly Asteraceae are the only anthropogenic indicators showing continuous records from the bottom of the core.

Zone 2 (110–62 cm; 3,840–1,860 cal

BP

) is character- ised by a progressive increase in pollen concentrations which rise to ca. 860,000 grains cm

^-3

in the upper part of the zone. Quercus canariensis-type reaches in this zone its highest percentages (64 %), although Q. suber decreases and Cedrus remains stable.

Zone 3 (62–42 cm; 1,860–1,260 cal

BP

) is characterised by high but variable pollen concentrations, ranging from 400,000 to 1,600,000 grains cm

^-3

. After an increase ini- tiated in the upper part of PZ2, pollen percentages of Q.

suber rise to a maximum of 16 %, at the expense of Q.

canariensis-type and Cedrus, which show a slight decrease.

Some maquis indicators appear: this is notably the case of Arbutus and Erica-type, together with Olea partly coming from wild olive.

Zone 4 (42–30 cm; 1,260–900 cal

BP

) is also character- ised by high, variable concentrations (350,000–1,000,000 grains cm

^-3

). Quercus canariensis-type continues to decrease and Cedrus almost disappears from pollen assemblages, whereas mesophilous herbs including some indicators of anthropisation (Asteraceae, Plantago) and maquis indicators (Arbustus, Cistus, Erica-type, Pistacia) increase.

Zone 5 (30–0 cm; 900–0 cal

BP

), finally, is characterised by a progressive decrease in pollen concentrations from 430,000 to 80,000 grains cm

^-3

. The main regional forest trees show marked declines: Q. canariensis-type and Q.

suber decrease strongly, respectively around 34 and 38 cm depths, and reach in this zone their lowest values; Cedrus only presents discontinuous occurrences less than 1 %.

These declines correspond to two major events: at the regional scale, the expansion of pine forests and open Mediterranean scrub (Arbutus, Cistus-type, Erica-type, Asteroideae, Cichorioideae, Plantago lanceolata-type), and at the local scale, the onset of the present-day peat- forming hydrophytic plant community (Cyperaceae and other aquatics). We can also note the appearance of Can- nabis/Humulus that certainly indicates the onset of Can- nabis cultivation.

The low abundance of Alnus glutinosa through the entire sequence distinguishes our diagram from the one

Fig. 3 Age-depth model and

mineralogical content of the core MF1b (Maison Forestie`re 1, Jbel Bou Hachem, Rif, Morocco).OMorganic matter

Table3Linearregressionsbetweensurrounding-treecoveronsurfacesofdifferentdiametersaroundthe11studiedsitesandpollendiversitycomponents(Shannonindex,evennessand richness) Diameters(m)50100150200250300350 Treecover(%)ABF10.4512.489.6618.2122.8121.9722.59 BAR1.523.467.43 BAZ0.100.721.242.08 BOU13.5435.5252.1257.6960.5762.8265.27 DAY21.094.977.638.32 MAR2.048.5815.5924.23 MF19.1728.1933.8535.1138.2739.4939.93 MF26.7728.6243.8855.4260.2561.96 MF318.569.7816.0927.0932.5437.6839.29 MF436.5353.4162.5663.5863.1563.2865.16 TAY14.2940.6450.6552.8552.8551.3549.46 Shannonindexr2 0.580.710.860.880.850.840.83 Slope-20.45±5.86-38.36±8.14-52.42±6.94-55.10±6.66-53.91±7.46-52.87±7.56-51.20±7.74 p************ Evennessr20.620.690.830.840.80.80.8 Slope-75.86±19.84-135.46±30.01-183.62±27.82-191.73±28.23-186.95±30.94-183.98±30.71-179.67±30.05 p************ Richnessr20.010.090.180.240.270.240.18 Slope0.45±1.77-2.77±2.85-4.74±3.36-5.68±3.36-5.94±3.30-5.58±3.30-4.71±3.35 pnsnsnsnsnsnsns Ther2 andtheslopeweretestedseparately,butbecausetheobtainedp-valuesgivesimilarinformation,weonlyindicateone nsnotsignificant *p\0.01;**p\0.0001

obtained by Reille (1977) in a ‘Sphagnum pool of Jbel Bou Hachem’ (so-called Bou Hachem fen), where alder exceeds 30 % in most of the pollen spectra. This indicates

that, while presenting similar vegetation histories (Fig.

6),

the two studies have been carried out in two contrasting sites.

Fig. 4 Percentage pollen diagram of Maison Forestie`re 1 (core MF1b), Jbel Bou Hachem, Rif, Morocco

Fig. 5 Concentration pollen diagram for selected taxa of Maison Forestie`re 1 (core MF1b), Jbel Bou Hachem, Rif, Morocco. Concentration curves are represented bygrey-filled continuous lines(91,000 grains cm^-3) and percentage curves are added indashed lines. Note that the four concentration curves on the rightare exaggerated910 compared to the four curves on theleft. Pollen richness, Shannon index and Evenness index are calculated by excluding hydrophytic taxa.

Histograms at thetopof the diagram represent modern pollen spectra. The meaning of the site codes is given in Table1

Cultivated plants are only scarcely recorded in the present study, as well as in Reille (1977). The most abundant ones are Cerealia-type, which occur in more or less continuous curves from the base of all sequences, with abundances around 1 % in MF1b, while Olea shows a percentage increase around 1,000 cal

BP

at two sites (Mar1 and MF1b). Other taxa were only sparsely observed, almost exclusively from the last millennium: Juglans, Vitis and Linum are only represented by a few occurrences at two sites (undated sequence on Jbel Khezana and MF1b), whereas Cannabis/Humulus is only recorded in our study from 1,000 cal

BP

(with a single occurrence around 1,700 cal

BP

).

Since similar vegetations are likely to produce similar pollen influxes (Davis et al.

1973), pollen concentrations

are likely to reflect both the rate and the mode of sediment accumulation. The pollen concentrations presented in Fig.

5

may be used in comparison with the sedimentolog- ical analyses (Fig.

3) to infer information about the mode

of pollen deposition. The roughly constant sediment accumulation rate from the bottom of the core to 35 cm depth suggests that the progressive increase in pollen concentration result from changes in the depositional environment: in the deepest sandy part of the core, the low pollen concentrations suggest a weak pollen deposition in a running-water environment, while in the organic clay, the highly variable concentrations suggest a mosaic of vege- tation patches composed of heath and Cyperaceae, with small rivulets. In contrast, the decrease in concentrations occurring within the upper peat layer is clearly related to the contemporaneous increase in sediment accumulation rate, and maybe also to the formation of a continuous herbaceous carpet likely to filtrate the runoff-mediated pollen input. Pollen diversity, richness and evenness give similar increasing trends for Zone 2, which appear related to the Q. canariensis-type pollen abundance.

Discussion

Origin and long-term history of Rifan flora

Comparisons of floristic distribution patterns between both sides of the Strait of Gibraltar (Rodrı´guez-Sa´nchez et al.

2008; Jaramillo-Correa et al. 2010) reveal the strong

inherited similarity between both regions, as well as the role of the geographic barrier of the strait, which appears less marked for pioneer short-lived herbs than for trees, and independent of the dispersion mode. It moreover empha- sises the important regional endemism that occurs on the poor acid soils of the Oligo-Miocene Numidian Flysch, which constitutes a discontinuous crescent along the south- western Mediterranean side, from Andalusia through

Maghreb to Sicily and Calabria (Wildi

1983; Guerrera

et al.

1993). While the ancestral or derivative nature of this

pedological endemism is not definitely resolved, the fact that these acid substrates result from the Neogene Mag- hrebian orogeny and are contemporaneous with the indi- vidualisation of the Mediterranean flora suggests a pre- Quaternary origin. Such Neogene roots of a significant part of the Maghrebian flora are well supported by biogeo- graphical data, and notably by the occurrence of numerous Tertiary relict species (Que´zel and Me´dail

2003). More-

over, the existence in Morocco and Andalusia of genetic variants of some plant species also present in central Eur- ope, such as Alnus glutinosa (tetraploid populations; Lepais et al.

2013; M. Bohumil, pers. comm.),

Frangula dodonei (Hampe and Arroyo

2002; Hampe 2005), and

Juniperus thurifera (Terrab et al.

2008), attests that the Gibraltar

Strait and the Iberian Peninsula constituted barriers to gene flux, sufficient to allow speciation processes to occur within widely-distributed long-lived species.

The rarity and scarcity of fossil records in North Africa, already noted by Arambourg et al. (1953), is a serious limiting factor for testing this ‘pre-Quaternary origin’

hypothesis. However, the few available palaeobotanical studies provide some clues regarding the origin of the modern North-African Mediterranean flora in general, and of the Rifan one in particular. On the one hand, they attest the ancient expansion of numerous Eurasiatic taxa south- wards to NW Sahara and S Algeria (Ahaggar Mountains) from the Pliocene to the late Pleistocene (Van Campo

1964; Beucher1967a,b). Pollen grains of Maghrebian and

Eurasiatic taxa have also been found within Mid-Holocene Saharan fossil archives, such as hyrax middens from Ahaggar (Pons and Que´zel

1958) and mineral sediments

from Tassili n’Ajjer, SE Algeria (Que´zel and Martinez

1958). A more recent study (Thinon et al.1996) concluded

that these pollen assemblages resulted from long-distance southwards pollen transportation by wind or migratory birds, and cast some doubt on the reality of such a past Saharan boreal flora. However, the fossil leaf assemblages studied by Ducellier (1925) and Arambourg et al. (1953) clearly demonstrate the existence in NE Maghreb, from the Pliocene to the Mid-Pleistocene, of most of this flora, including several species now extinct from North Africa:

Carpinus betulus, Fagus cf. sylvatica, Pterocarya cf.

fraxinifolia and Ulmus scabra. The presence of such taxa,

at the genus level, is also attested by Neogene pollen floras

recorded in marine sediments (Suc et al.

1999; Bachiri

Taoufiq et al.

2001; Feddi et al. 2011), which are repre-

sentative of all the vegetation belts from the catchment

area, as demonstrated on modern sediments of the Rhone

River (Beaudouin et al.

2005,2007). These palaeobotanical

and palynological data, completed by Tunisian pollen

analyses (Van Campo

1977, 1978), finally confirm the

Neogene origin of a significant part of the modern flora of the Rif and Numidia, including Mediterranean elements (Cistus salviifolius, Fraxinus, Juglans regia, Laurus nobi- lis, Olea europaea, Phillyrea, Quercus canariensis, Q.

coccifera, Q. ilex, Rubus ulmifolius, Smilax aspera and Tamarix) and Euro-Siberian ones (Alnus, Frangula dodonei, Populus alba, Salix alba and S. atrocinerea).

These data, along with the few Pleni- and Late-glacial pollen records available from Numidia and the Middle Atlas (Ben Tiba and Reille

1982; Stambouli-Essassi et al.

2007; Benslama et al. 2010; Rhoujjati et al. 2010), that

show past vegetation similar to the present-day, support the hypothesis of a rather unchanged North African flora over the successive glacial-interglacial cycles that affected

Europe since the late Pliocene. Such a long-term vegetation stability is supported in the Rif by the age of 13,070–12,780 cal

BP

of a reworked charcoal found in the MF1 sequence (Fig.

3; Table2), which attests the regional

occurrence of deciduous Quercus since the end of Late- Glacial. Moreover, only slight geographical displacements of species were reported at the North African scale since the last glaciation, such as the retreat of Cedrus atlantica and Abies numidica from NW Tunisia and NE Algeria at the beginning of the Holocene (Ben Tiba and Reille

1982;

Salamani

1993; Stambouli-Essassi et al. 2007) or the

expansion of C. atlantica in the Middle Atlas between six and four millennia ago (Lamb et al.

1989,1999; Lamb and

van der Kaars

1995; Cheddadi et al.2009).

Late-Holocene climate and anthropogenic impacts on the Rifan vegetation

Neolithic occupation and cereal cultivation are attested for more than 7,000 years in northern Rif (Ballouche and Marinval

2003; Zielhofer and Linsta¨dter2006), and for the

last 5,000 years in the alluvial deposits of the Rharb region (Gartet et al.

2001) and in the present study area. However,

the vegetation history of the Jbel Bou Hachem and other Jebala reliefs shows little change and remains dominated until now by forest ecosystems, respectively composed of cedar on summits, semi-deciduous oaks (mainly Q. ca- nariensis) at mid altitudes, cork oak at low altitudes, and alder in wet habitats. The higher pollen abundance of all these trees compared to today indicates the wider extension of past forests that certainly occupied most of the currently open zones. The high percentages of Q. canariensis recorded in all pollen sequences (Fig.

6) indicate that this

tree extended from below 700 up to above 1,400 m a.s.l.,

bFig. 6 Simplified pollen diagrams of dated sites in the Rif for the three main forest taxa (from Reille 1977 and this study). The diagrams presented are: MF1b (Maison-Foretie`re 1; Jbel Bou Hachem), BH1 (Bou Hachem fen; Jbel Bou Hachem), BAR1 and BAR3 (Bartete, named Arbatete in Reille1977; Jbel Khesana), RHE1 (Rhesana; Jbel Khesana), MAR1 (Marzine; Jbel Sougna), TAN (Tanakob, Jbel Sougna), TIZ2 (Tizire`ne, Jbel Tizire`ne). The black curvesof the BH1 diagram correspond to a total pollen sum excluding Alnus. The taxon ‘Quercus canariensis-type’ regroups the taxa Q.

faginea and Q. pyrenaica of Reille (1977). Calibrated radiocarbon ages with 2r-uncertainty ranges are given below diagrams (numbers refer to Table2). Historical periods correspond to: P Phoenicians including Carthaginians (2,900–2,300 calBP),MBerber kingdom of Mauretania (2,300–1,910 cal BP), R Roman administration of the Province of Mauretania Tingitana (1,910–1,550 calBP), vb Unsub- dued mountain areas during the weak dominance of Vandals, Visigoths, then Byzantines (1,550–1,160 cal BP), I Idrisid dynasty (ca. 1,160–1,050 cal BP), f Zenata chieftainship during Fatimid anarchy (ca. 1,050–890 cal BP), B Berber dynasties (Almoravids, Almohads, Marinids and Wattasids) (890–400 cal BP), A Arab Sharifian dynasties (Saadi and Alaouite) (400 cal BP–today) (from Park and Boum2005)

and certainly constituted mixed forests with cork oak and cedar at both extremities of its altitudinal range.

A marked lowering of cork oak pollen percentage was recorded in the two sequences studied on Jbel Bou Hachem from ca. 3,800 cal

BP

, contemporaneously with a pollen increase of semi-deciduous oak (Fig.

6). This event was at

first interpreted as the regional abandonment of a putative older Neolithic agriculture on the plains that would have previously favoured sclerophyllous oaks at the expense of semi-deciduous ones, and used as evidence for the anthropogenic nature of the Rifan cork-oak forests (Reille

1977). However, the constant pollen concentrations of

Q.

suber in the MF1b record, along with the low pollen diversity and evenness (Fig.

5; Table3), do not support

this hypothesis: on the contrary, they suggest that cork-oak forests remained stable and that the decrease in Q. suber pollen percentages resulted rather from the local densifi- cation of the surrounding Q. canariensis canopy over- whelming the pollen input from lower altitudes (Tauber

1965; Muller et al. 2006). This implies that the montane

forests of Jbel Bou Hachem, and more generally of the whole Jebala Range, not only did not decline at the end or after the Neolithic, but even became denser. The densifi- cation of Q. canariensis forests in the Rif coincides with the spread of cedar in the Middle Atlas (Lamb et al.

1989;

Lamb and van der Kaars

1995; Cheddadi et al. 2009),

supporting the onset of moister climatic conditions (Cheddadi et al.

1998; Lamb et al. 1999) favourable to

forest development, and suggesting a surprisingly low forest impact by local Berber populations.

The further opening of the Q. canariensis forest, evi- denced around ca. 1,900 cal

BP

(

AD

50) by the pollen record of cork-oak forests developed at lower altitudes, the onset of heliophilous heaths and the increase in pollen diversity and evenness, coincides with the beginning of cedar decline on the reliefs. This period corresponds to the Roman colonisation of northern Morocco and to the foundation of the Roman province of Mauretania Tingitana (

AD

40). The contemporaneous vegetation disturbances recorded in the Middle Atlas (Lamb et al.

1991) confirm

that the changes observed in the Rif mountains resulted from large-scale anthropogenic forest disturbances, which nevertheless appear very weak in comparison to those occurring at the same time in Europe. Indeed, the activities of Roman populations triggered almost everywhere in southern Europe dramatic deforestation, accompanied by severe ecosystem modification. Well-documented exam- ples of such modifications are given by the Roman-induced decline of Abies alba (European fir) and Alnus glutinosa in the Southern Alps, which affected the structure, composi- tion and functioning of montane and wetland plant com- munities, respectively (Nakagawa et al.

2000; Muller et al.

2007, 2012). The much lower human impact recorded

during the Roman Period in the mountains of northern Morocco suggests that the life mode of people in the mountainous hinterland was probably traditional and only based on subsistence agriculture (Taiqui and Cantarino

1997). While this region has been poorly investigated

archaeologically, the few data obtained along the Medi- terranean coast have revealed almost exclusively medieval sites. However, on-going studies conducted in the Al- Hoceima vicinity have begun to detect a diffuse Punic and Roman presence on the coast (P. Cressier, pers. comm.).

The Jbel Bou Hachem and conterminous reliefs of the Je- bala Range occupy an intermediate position between the Romanised Morocco, mainly restricted within the eco- nomically-important area of the north-western coastal plains and valleys between Fez, Rabat and Larache (Re- buffat

1986; Callegarin 2008), and the long-marginalised

Rifan region bounded by the Wady Laou (north of Chef- chaouen) in the west, and the Nador peninsula (Cap des Trois Fourches) in the east. The weak and discontinuous record of Olea in the Jebela Range (Reille

1977; Fig.4)

indicates that the olive cultivation reported from archaeo- logical findings in the Tangier Region (Ponsich

1964) did

not extend eastwards within the Rif.

While initiated during Roman times, the decline of Ri-

fan forests really began several centuries later. Although

the rather insecure chronological control of the previously

published pollen sequences (Reille

1977) precludes

reconstructing accurately the dynamics of forest decline

over the Jebala Range, our tentative correlation (Fig.

6)

suggests that deforestation could have increased at mid-

altitudes during the Byzantine dominance or the Idrisid

dynasty from ca. 1,300 to 1,050 cal

BP

(ca.

AD

650–900),

before extending upwards after the Almoravid conquest of

the Rif between 890 and 870 cal

BP

(

AD

1060–1080) to

culminate with the onset of Arab Sharifian dynasties in the

16th century. The first recorded landscape changes coin-

cide with both drier climate conditions during the Medieval

Climate Anomaly in the western Mediterranean (Moreno

et al.

2012; Puy et al.2014) and the Idrisid dynasty, known

for having played a major role in the historical develop-

ment of northern Morocco, by reinforcing ancient trade

routes and founding several urban centres (Taiqui and

Cantarino

1997).

Cedrus almost disappears during medie-

val times from most of the pollen records, which clearly

indicates its regression to its present-day stands on moun-

tain crests. Similarly, Q. canariensis forests declined, but

remained dominant on mountain aspects above 1,000 m

a.s.l. (Fig.

6). The contemporaneous expansion of herbs,

including grazing-favoured plants (Asphodelus, Astera-

ceae, Plantago) and the local disappearance of certain

forest taxa such as Acer (a well-known under-represented

taxon; David and Barbero

2001) attest the accentuation of

the human-driven modification of the structure of montane

forests. While it is not possible to identify the annual plant component in pollen records, the late spread of herbs within open woodlands could reveal the progressive therophytisation of the forest understorey, widely observed today throughout the entire Maghreb (Que´zel

2000). The

herbaceous component favoured at this time probably originates at least partly from the open herbaceous envi- ronments that existed at low altitudes in northern Africa since the Neogene (Suc et al.

1999; Warny 1999; Bachiri

Taoufiq et al.

2001; Feddi et al. 2011).

Quercus suber forests also declined, but less markedly and probably less simultaneously than montane ones. In comparison to such a late decline in Rifan mountains, the Q. suber forest of Krimda, close to the antique city of Lixus (Larache) on the Atlantic coast, seems to have been weakly exploited since the Carthaginian period (Grau-Almero

2011) before its

marked decline at the 11–13th century (Damblon

1991).

The cultivation of Cannabis is attested during the Middle Ages by archaeological findings of pipes. The pollen record suggests that this cultivation began in the Chefchaouen region around 400 cal

BP

(

AD

1550). Such ecosystem modifications reveal the changes affecting the regional economy, and probably correspond to the emergence of modern landscapes that can be dated to the onset of the Arab Sharifian dynasties, just after the foundation of Chefchaouen in

AD

1471.

Indeed, the pollen records unambiguously attest unchanged landscapes over the whole Jebala Range at least since this period. Written sources moreover provide com- plementary information concerning cultivated species and human activities. The Andalous diplomat, Hassan Al- Wazzan, so-called Leo Africanus or Jean-Le´on l’Africain, has left accurate descriptions of the region of Chefchaouen in his book written in the first third of the 16th century (Jean-Le´on l’Africain

1956). Notably he reported in several

Jebala villages the important cultivation of fruit trees (including olive and figs), as well as Linum (flax) and Vitis (grapevine), suggesting an externalised economy. The very sparse pollen record of these cultivated plants in the available pollen records could be due both to the low pollen production and dispersion of these insect-pollinated plants, and to the altitudinal location of the studied wetlands.

Moreover, the fact that some of these cultivated species, such as fig trees and grapevines, grow naturally in the region, implies that only ‘‘high’’ percentages should be interpreted as reliable indicators of anthropogenic activi- ties. Al-Wazzan also noted the cultivation of cereals, specifying that this was unequal between the different tribes, some being rich while others poor. He finally underlined the importance of the forest cover and of its exploitation, unfortunately without mentioning the species concerned. Further writings (see Taiqui and Cantarino

1997)

attested a self-sufficient economy based on

subsistence farming in the Jebala populations until the onset of the colonial period: in 1900, the region was characterised by a communication network limited to tracks, few cities, lack of resource exportation, and egali- tarian social organisations. These descriptions fit well with the pollen record, which confirms the regional presence but not great abundance of crops including cereal cultivation, and the late continuance of a widespread forest cover.

Conclusion

The late persistence of forested landscapes in the Moroccan mountains is perceptible over the entire Jebala Range (Reille

1977; Fig.6), as well as in the Middle

Atlas, where human-induced changes also occurred for less than 2,000 years (Lamb et al.

1991). This constitutes

a highly original feature compared with the vegetation history of southern Europe, widely marked by landscape clearance since the Late Neolithic (e.g., Reille et al.

1996). Even the closest European region (southern Spain)

had experienced human-induced forest loss and xerophy- tization from sea level to high altitudes for the last 5,000 years (van den Brink and Janssen

1985; Rodrı´guez-

Ariza

1992; Carrio´n et al. 2010). The original history of

the Rifan vegetation may be partly attributed to the savage-looking appearance of the region, and to its steep topography and poor soils, which are likely to have pre- vented the regional expansion of agriculture. These dif- ferences in long-term human histories between both sides of the Mediterranean explain, at least in part, their recent divergent trends: (1) decreasing rural populations and agricultural abandonment in Mediterranean Europe, lead- ing to a recovery of pre-forest and forest ecosystems, and (2) increasing populations and enhanced human distur- bance in North Africa, leading to desertification of mountain zones through matorral-forming, steppe-form- ing, then therophytization (Que´zel

2000).

Such a recent impact of human populations probably played a role in the conservation until today of the exceptional richness of the Rifan flora, which otherwise resulted from a long history with its origins in the Neogene and the variety of soils and microclimates (Que´zel

2000).

However, this natural heritage preserved for so long has

shown a worrying decline during the last few decades due

to rapidly increasing human disturbance, such as illegal

cutting and clearing, unsustainable forestry practices,

anarchic urbanisation, uncontrolled fires and overgrazing

(Que´zel and Barbero

1990; Taiqui1997). As an example,

the Q. canariensis forests of the northern aspect of Jbel

Bou Hachem, while benefiting from protection statuses

(SBEI, IMBR), have been partially burned and cut down

within the last decade. The present study highlights both

the invaluable historical value of the present-day forests of Rif and their modification that has occurred during the last millennium, notably grazing-triggered impoverishment of understorey vegetation. Consequently, the recent acceler- ation of forest degradation appears particularly of concern as it impacts already weakened ecosystems and species.

Acknowledgments We thank Lucie Chabal for charcoal identifi- cation, Laurent Callegarin and Patrice Cressier for helpful comments on an earlier version of the manuscript, Mandak Bohumil for infor- mation about recently found tetraploid alder populations in southern Spain, and Alex Chepstow-Lusty for editing. We also address our grateful thanks to the two anonymous reviewers and the copy editor, whose comments were greatly appreciated. The present work is part of the project Medyna (FP7-PEOPLE-2013-IRSES). This publication is the contribution ISE-M no 2014-157.

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