Ann Se!For (1995) 52, 589-606© Elsevler/lNRA

Original article

Natural black pine (Pinus nigra subsp salzmanniJ)forests of the Iberian eastern mountains:development of the phytoecological basis

for their site evaluation *

P Regato-Pajares 1, R Elena-Rossell6 2

1 Centro de Investigacion Forestal, INIA, apartado 8111, Madrid;2 Departamento de Silvopascicultura, Universidad Politecnica de Madrid, 28040 Madrid, Spain

(Received 2 January 1994; accepted 2 January 1995)

Summary - A phytoecological study of the Pinus nigra subsp salzmannii forests in the dolomite­limestone mountains of eastern Spain was undertaken. Starting from several floristic and ecological datacollected from 355 releves, classification and ordination numerical analysis were realized. A typifica­tion of the different pine forest communities was thus obtained and a series of floristic groups wasdefined, which can be used as a basis for the classification of distinct sites. Following the phytosoci­ological method, 2 main groups, which can be considered as climax vegetation of the high supra- andmountain-Mediterranean levels, have been defined: a continental group, Thafictrotuberosi-Pinetum salz­mannii, and a subcontinental group, Lonicero xylostei-Pinetum salzmannii, which represents thesouthern range limit of Pinus nigra forests in the eastern Pyrenees.

Plnus nigra! numerical analysis! phytosociology I climax! floristic group

Resume - Typologie phytoecologique des stations torestleres : les forets naturelles de pin deSalzmann (Plnus nigra subsp salzmannii) des montagnes orientales Ibertquee. La presentefHudeconcerne la caracterisationphytoecologique des toret« de Pinus nigra subsp salzmannii des mon­tagnes orientales de I'Espagne. Des analyses numerlcuee de classification et ordination ont ete rea­lisees avec 355 releves comprenant des aonnees tloristt'ques et ecologiques. La typologie des diffe­rents groupements sitvatiques de Pinus salzmannii a permis d'etabJirplusieurs groupes tloristiques,susceptfbles d'etre utilises dans la caracterisation des stations torestieres de cetie essence. Selonla methode phyfosociologique, ont ete distfnguees 2 associations qui repreeentent sOrement la vege­tation climatique a I'horizon supetieur de I'etage suoremeattetreneen et aJ'etagemomeanerd.meat­teneneen : Thalictro tuberosi-Pinetum salzmannii dans la partie occidentale avec des conditions cfi-

* The present work complies with the nomenclature given in 8010s et al (1990), Castroviego et al(1986-1993) or Tulin etal(1964-1990).

590 P Regato·Pajares, R E!ena-Rosse1l6

mstiques meaitetreneo-corutnentees, etLonicero xylostei-Pinetum salzrnannf dans/apertie orientaleavecdes conditions cHmafiques sub-continenta/es. Lesforets depinde Salzmann quiappartiennentcl la aerntere association representent la limite meridicmele de ce groupement cerectettsttque desPyrenees orientates.

Plnus nigra / analyse numertoue I phytosocioJogie/climat / groupe ttortettque

INTRODUCTION

Pinus nigra subsp salzmannii has its cen­tral core of distribution in the dolomite-lime­stone mountain ranges of the eastern portionof the Iberian peninsula (Sistema lberico)(fig 1), the main forest region of Mediter­ranean Spain. Exceptionally a relict popula­tion stand isolated in areas of the central­western granitic range, representinga specialpaleogeographic and phytogenetic interest(Regato et et, 1992). The total natural pop­ulations of this species extend over approx­Imately 380 000 hectares.

The black pine forests found in the Sis­tema lberico account for two-thirds of thetotal black pine formations in the Iberianpeninsuia. Together with Pinus sylvestrtswoods, they represent the most extensiveforests of the eastern mountains. While Psylvestris forests have been easily managed,resuiting in good even-aged stands, P nigraforests actually have critical problems duein part to the lack of basic understandingabout the regeneration biology of this long lifespecies. Furthermore,disturbanceprocessesin the area (geomorphological dynamism,high frequency of storms, etc) generallyresulting in uneven-aged stands and the ran­dom exploitation of woods, carried out sincethe beginning of the century, contribute tothe present open-structured forests.

Historically, major problems have beenencountered when trying to establish a siteindex for the different types of forests. Inparticular, when stands are not even-aged,have mixed species compositions or havereceived severe growth damage, problemswith site index are greater (Monserud, 1977).

Therefore, a more ecologically oriented siteclassification, based on phytosociologicalconcepts and approaches, was developed inan attempt to solve some to these specificproblems. As a first attempt, Cajander'sapproach (1926) defines vegetation typesmeaningful to forest productivity. After thisvery early work, other vegetation-orientedstudies were conducted (Maycock, 1960;Pfister, 1977; Carieton, 1980; Jeglum et et,1982; Jones, 1984; Kotar, 1984). All effortshave been conducted to develop a betterunderstanding of natural vegetation patternsin order to establish an ecoiogical classifi­cation of forest types. This is the basis forcarrying out site evaluation in well-estab­lished stands inside each forest type.

In a first attempt to analyze the black pinewood area of Spain, Elena-Rosseil6 andSanchez-Palomares (1991) found a goodrelationship between yield and floristicgroups. Given the encouraging results ofthat early evaluation, a more in-depth anal­ysis in the largest territorial area of P nigra(Sistema lberico) was conducted (Regato,1992) In order to characterize the differenthabitat types of this species, an essentialelement to determine the potential produc­tivity of the different sites.

Geobotanlcal background

The most important geobotanic studies wereconducted by Wiilkomm (1844, 1852, 1896),and they provided very accurate descrip­tions of the main forests of this species.When describing black pine woods alongthe Sistema lberico, he mentioned the exis-

Phytoecological features ofblack pine forests 591

Fig 1. Distribution areaof Pinus nigra subps salzmannii inSpain.

tence of pristine forests, which he describedas a shady canopy of gigantic trees, includ­ing several specimens with an estimatedage of more than 1 000 years. As far as thestructure and degree of development areconcerned, he claimed these woods to beperfectly comparable to the best preservedones in Central Europe. Twenty years later,the same author regrettedthe serious degra­dation of these pine woods; today, it is diffi­cult to find mature formations with an aver­age age of more than 150 years.

Since the begining of phytosociologicalstudies in Spain, the role of Spanish Pinusnigra forests has been undervalued, if notneglected. Gaussen (1945) originallydefined a potential vegetation series for thePyrenees, headed by P nigra subsp salz­mermii, while Rivas-Goday (1946)described a vegetation level, Pinetum lari-

cionie, which is characteristic of the Sls­tema lberico, and located between theupper woods of Pinus sylvestris and themixed oak forests (Quercus faginea and Q

ilexsubsp ballota). Nevertheless, such con­siderations were eventually invalidated, andthe sites occupied by the Pinus nigra woodswere considered to be either potential oakforests (Quercus faginea, Q pubescens andQ ilex subsp ballota) or potential Juniperusthurifera steppic forests.

Under this prevailing theory, black pineis just an accessory species in such types offorests, and its populations are consideredas a consequence of anthropogenic expan­sion. Thus, a deep phytosociological andecological study of these pine woods waslargely neglected.

Recently, all over western Europe, woodsof Pinus n;gra subsp salzmanniiwere reval~

592 P Regato-Pajares, R Elena-Rossello

ued and given greater ecolcqical and phy­tosocloloqical importance ln France (Quezeland Barbero, 1988) and in Spain (Gamisansand Gruber, 1988; Gamisans et et, 1991;Elena-Hossello and Sanchez-Palornares,1991; Regato, 1992). Starting from a num­ber of historical elements, as well as theecological, biogeographic and bioloqlcal fea­tures of this species, it is thought that Pinusnigra subsp saJzmanniistands arean impor­tant element of the potential vegetation ofSpain, defining climatic forests which con­stitute a special vegetation level. It seemstherefore appropriate to revive the initial pro­posals of Gaussen and Rivas-Goday, and todetermine with greater precision the eco-

logical value of Pinus nigra in the Spanishvegetation landscape.

Ecological features

The Sistema lberico is a range of moun­tains with moderate high elevations oftenover 2 000 m, surrounded by high plateauswith an average height of 1 200 m. Most ofthe Pinus nigra forests are located in thesupra- and mountain-Mediterranean levels,between 1 000 to 1 500 m, ranging from thelowest points at roughly 400 m, to the high­est ones in the oro-Mediterranean level (fig2). Under particular conditions and in the

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Fig 2. Diagram of Pinus nigra subspeciesrelationships inelevation andlatitudinal terms.

Phytoecological features of black pine forests 593

southernmost mountains, Sierra deJavalambre, the species reaches the tirn­berline at 1 700-1 800 m.

WhHemost Spanish ranges have a westto east orientation, the Iberic Mountainscross the eastern part of the peninsula fromnorth to south, representing a barrier to themainnorthwestern rainfronts. As a conse­quence, the climate becomes highly conti­nental to the core of this mountainous regionand results in different characteristics of thewater regime between the Mediterranean­and the inner face of these mountains.

The physiography of these mountains isparticularly affected by the altemance of dif­ferent lithologlcal types. Karstic elevationsprevaH, and doline fields, laplaces and rivercanyons are frequent. Gravity slopes, uplandrocky plains and ridges are mainly made ofmore or less pure dolomites, whHe slopesand the floor of the valley are of differentiithologic types (limestone, dolomites, marls,sandstone and gypsum), which influencethe slope profile.

Soils are poorly developed and mostlysuperficial, with a prevalence of the rendz­ina-type (Sanchez-Palornares et ai, 1990).According to these authors, in spite of thedegree of soil evolution of the black pinewoods area, these should be considered asmainly mature, as they represent theedaphic potentiality of such mountains. Theabundance of dolomites, which typicallyhave a difficult chemical weathering, makessoil evolution even more difficult.

From the climatic point of view (Regato,1992), the areas where these pine woodsare mainly found have humid and subhu­mid types of bioclimates, in their "cold" and"very cold" variations (according to Emberg­er's classification in Daget, 1977) (fig 3).Exceptionally, they can also be found in asemi-arid superior cold bioclimate, corre­sponding to the lower and more continentalareas of its distribution range. According toAlIue-Andrade's classification (1990), blackpine woods are to be found mainly in the

nemoro-Mediterranean humid (V1(IV)2) andsubsteppic nemoral (VI(VII)) phytoclimatictypes. The most xeric nernoro-Medlter­ranean type (VI(iV)1) would roughly corre­spond with the semi-arid bioclimate typicalof the lower and most continental areas.

Continentality is remarkable, with wintermean minima temperature as low as -7°Cand absolute minima reaching values of-25°C. The frost-free season can be asshort as 1 mid-summer month, which alsotends to be characterized by a more or lessacute hydric deficiency. Under such extremeconditions, the vegetative period is consid­erabiy short and, as stated by Waiter (1968),evergreen coniferous species take the placeof broad-leaf marcescent species.

MATERIALS AND METHODS

Data from 355 forest sites were collected overthe full geographic range of Pinus nigra in theSistema lberlco (Regato, 1992). The samplingmethod used, that is, preferential sampling(Gauch, 1982),subjectively selects sample sitesthatappear tobe homogeneous anddistributesthemequitably throughout the black pinestudyarea according tothealtitudinal range andto thegeomorphological variability. The phytosoclo­logical releves weremade using theBraun-Blan­quet method (1951). Eachrelsve represented acomparatively homogeneous area, generallyfrom 200-400 m2 . Species' cover-abundancevalues were transformed according to Van derMaarel (1981).Elevation, slope, aspect andpro­portion of rocks in the surface were calculatedforeachreleve. Potential solar radiation wascal­culated using latitude, aspect and slope (Gan­dullo, 1974).

Polythetic divisive classification wasconducedwith TWINSPAN (Hill, 1979) on a data matrixcomprising 355 sites x 550 species (Regato,1992). Subsequently, all final TWINSPANdichotomies were explored by detrended corre­spondence analysis (DCA) (Hill andGauch, 1980)and canonical correspondence analysis (CCA)(Ter Braak, 1988) to determine to which extentthe dichotomies reflected a discontinuity in thesite fJoristic data and their relations with certainvariables (Regato, 1992).

594

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RESULTS

The TWINSPAN classification analysisresulted In 27 different ftoristicgroups. Sub­sequently, ali final TWINSPAN dichotomieswere explored using DCA and CCA. On thebasis of these ordination analyses, 13 f1oris­tic groups were definitively established. Thereduction from the Initial 27 group classifi­cation to the final 13 group classification isrepresented in figure 4.

The resulting 13 groups are ranked inthe dendrogram according to a xerothermicgradient. The first dichotomy in TWINSPANclassification hierarchy distinguishesbetween black pine forests associated with

sites of mesophilous conditions (cooler andwelter), and generaliy located at the highestaltitude (ranging between 1 100 to 1 500m), and black pine forest associated withmore xerothermic sites (ranging between900 to 1100 m).

Some typical spectes of the bushy for­mations of the area, Thymus vulgaris,Lavanduia latifolia and Koeleria vallesiana,appear as nonlndicative of the 2 groups thatresult in the first division (fig 4). This sug­gests a certain degradation of the under­story In most black pine woods, particularlythose that are subject to heavy timberexploitation. Furthermore, the subruplcu­lous nature of many of these woods also

Phytoecological features of black pine forests 595

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596 P Regato~Pajares, R Elena-Hossello

contributes to the presence of these speciescharacteristic ofopenscrub communities.

in the second division level of the classi­fication, both mesophytic and xerothermicsites are divided into 2 groups: a more con­tinental group typical of the inner mountains(western sector), and another group withsubcontinentai character typical of theranges closer to the Mediterranean Sea(eastern sector) (fig 4).

These 4 groups resultingfrom the secondtier are separately located in the 4 quartersof the DCA diagram, defined by the first 2axes.Axis 1 represents a xerothermic gra­dient, while axis 2 represents a continen­tality gradient Therefore, those black pineforesfs which have good mesophyllous con­ditions and are typical of the most advanced

AX2

phases appear towards the negative val­ues of the axis 1, while those forests whichhave a more sparse structure appeartowards the positive values of the axis (fig 5),being typical of lowest xerothermic areas,where P nigra is found at fhe iimits of itsdistribution, or of degraded areas wheremore xerophytic species coionize the sub­canopy.

In the CCA ordination anaiysis, groupsresuiting from subsequent divisions of theTWiNSPAN ciassification anaiysis are thebest defined. Such groups are associatedto sites with a high proportion of rocky sub­strates and steep si apes, both factorsstrongiy associated with axis 2. An altitudi­nai gradient becomes apparent aiong theaxis 1 (fig 6).

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Fig5. DCAanalysis diagram. Numbers indicate thesituation ofthe13TWINSPANsite groups. Arrowsshow the underlying ecological factors. Capital letters indicate the 4 site groups established at theTWiNSPAN second level.

Phytoecological features ofblack pine forests 597

Mesophytlc black pine woodsof the eastern sector: groups 1-3

This grouping includes 40 sites associatedto the highest aliitude zones of the easternmountains characterized by the lowest con­tinentality. Frequently, its sites are located inthe ubacs, where the comparatively higherair relative moisture attenuates their ther­mic continentality. Their phytoclimatic type,located between 1 000 and 1 700 m of alti­tude, is humid nemoro-Mediterranean(VI(IV)2) or substeppic nemoral (VI(VII».Dolomite substrates are predominant. Sitesin groups 1-3 are located mostly in the lowerleft quarter of the DCA diagram.

Group 1:includes forest formations well ver­tical-structured and developed, with nemoralunderstory, that can be considered as cli­max vegetation of the high supra- and lowmountain-Mediterranean level of the

dolomite-limestone mountains of the west­ern Iberian system (Puertos de Beceite,Maestrazgo and western stations of Gudarand Javalambre sierras). A group of sub­Mediterranean and eurosiberian speciescharacterizes both the scrub and the herba­ceous layers, belonging to Quercetaliapubescentis, orina wider scope, to Ouerco­Fagetea. Indicator and preferential speciesare Primula verissubsp columnae,Hepalicanobilis, Brachypodium sylvalicum, Fragariavesca, Pteridium aquilinum, Acer opalussubsp granatense, Sorbus aria, Buxus sem­pervirens, /lex aquifolium, among others.Mixed forest formationswith Pinussyives/ris,characteristic of the upper forest level, arevery often defined. Due to floristic similaritiesof black pine woods in this zone with thewoods described in the Pyrenees(Gamisans and Gruber, 1988), it can beconsidered that both belong to the sameassociation, Loniceroxylostei-Pine/um selz-

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Fig 6. CCAanalysis diagram. Thesituation ofthe13TWINSPAN site groups is indicated bya number.Arrows indicate environmental physical gradients. Theisolines suggest 3 groups ofsite quality: good(I): medium (11); and poor(tII).

598 P Regato-Pajares, R Elena-Hossellc

mannii (table I).Therefore, black pine woodsin this group may be a southern expansionfrom the Pyrenees formations, and repre­sent a transition from these tothemore con­tinental ones. Furthermore, some typicallyPyrenean species are found in the under­story, and they are representative of theirsouthern limit (Lavandula angustilolia andTeucrium pyrenaicum).

Group 2: comprises forest formations withan open structure that define the timberlineof the western slopes of Javalambre andCamarena sierras, towards Teruel, with cold

and xeric continental climate. These sitesare located in the transltionai zone from theforest of the more continental western sec­tor to the eastern sector, and therefore theircharacterization is sometimes difficult Fur­thermore, the lack of floristic elements inthe understory makes it difficult to deter­mine their phytosociology, Indicator and dif­ferential species show the orophylous char­acter of such forest formations: Juniperussabina, Astragalus granatensis, Thymusleptophyllus, etc. High mountain pastures,favored by human intervention, clearly have

Table I. Lonicero xy/ostei-Pinetum sa/zmannii (Gamisans andGruber, 1988) (eubassoclatlon genis­tetosum patentis; Regato, 1992).

Character- and differential species of theassociation:Pinus nigra subsp sa/zmanni VLonicera xyJosteum 11Helleborus foetidus V

Tanacetum corumbosumGeniste hispanicaCepha/anthera rubra

1I1I11

Differential species of subas genistetosum patentis:Genista patens IVLathyrus fi!iformis IIIJuniprus oxycedrus IIIJuniperus phoenicea IIITha/ictrum tuberosum n

Differential species vs Violo-Quercetum faginae:Avenu/a pratensis IVVa/eriana montana JJIJuniperus communis I1IPrunella grandifJora IIPteridium aquilinum JII

Character-species of Querco-Fagetea:Hedera helix IVHepatic nobilis IIIPinus sy/vestris IIIHieraclum aggreg murorum IVEuphorbia amygda/oides IVCruciata glabra IIIBrachypodium sy/vaticum II1Aquilegia vulgaris 11sentcute europaea 1IFragaria vesca IIGory/us avellana I/lexaquifoHum IGeum syfvaticum III

Character-species ofAceri-Quercion:Aceropa/us subsp granatensiPaeonia officinalis subsp humilViola willkommii

Character-species of Quercetalia pubescentis:Buxus sempervirensAme/anchier ovalisvtcte tenuifoliaPrimufa veris subsp columnaeSorbus ariaCoronilla emerusSorbus domestica

VIIIIII

VVIII11111111

Species of Querceta ilicis:Quercus ilexsubsp ballotaRubla peregrinaRhamnus a/aternus

Other species:Brachypodim retusumRosmarinus officinalisBup/eurum fruticescensEuphorbia characiasPo/ygala ca/carea

IVIIII

III111111III

---.--

Phytoecological features ofblack pine forests 599

contributed to the open-structure charac­teristic of forests of this group.

Group3: forests located on steepy sites withunstable substrates, and superficial rocksand boulder fields. These conditions favorthe establishment of certain subrupiculoustaxa, with the subsequent Impoverishmentofthe more sclophilous species. Preferentialspecies are Festucagauthieri, Ameianchieroveils, Thalictrum tuberosum, Sorbusdomestice, Paeonia Officinalis and Loniceraxylosteum. This community has beendefined as festucetosumgauthieri (Regato,1992) subassoclation of the climax typeLonicero-Pinetum (table 11).

Mesophytic bfack pine woodsof the western sector: groups 4-7

This grouping comprises 145 sites associ­ated with the most mesophilous conditions ofthe supra-Mediterranean and Mediterraneanmountain belts, between 900 and 1 500 m.The main phytoclimatic type Is humidnemoro-Mediterranean (VI(lV)2), with highvalues of thermic continentality (seasonalextremes of temperature). The characteris­tic substrate Is dolomite-limestone, with anabundant appearance of massive dolomitecovering the surface of a high plateau or flat­topped mountain. In the DCA diagram, sites

Table 11. Lonicero xylostei-Pinetum salzmannH (Gamisans andGruber, 1988) festucetosum gaufieri(Regate, 1992).

Character- anddifferential species oftheassociation: Cruciata glabra IIIPinus nigra subsp salzmannH V Hepatica nootue 11Lonicera xylosteum I1 Prunus spinosa IIHelleborus foetidus V Hedera helix 11

Differential species vs Violo-Quercetum valentinae: Species of Ononido-Rosmarinetea:Juniperus communis IV Euphorbia nicaensis IVAvenula pratensis IV Lavandula latifolia IIIKnautia arvensis III Genista scorpius III

Aphyllantes monspelUensis 11Differential species ofsubas festucetosum: Koeleria va/lesiana IIIFestuca gaufieri IV Helianthemum origanifoJium 11Lavandula angustifolia 11 Leuzea conifera ~ 11Teuonum pyrenaicum I Potentilla tabernaemontani 11Thalictrum tuberosum 11 Lotus corniculatus I

Medicago suffruficosa ICharacter-species of Quercetalia pubescentis: GaJium pumilum subsp pinetoru IIIAmelanchier ovelis VOnonis aragonensis 11 Other species:Quercus faginea 11 Quercus Hex subsp ballota IIITanacetum corymbosum III Brachypodium phoenicoides IIIBerberis vUlgaris subsp seroi 11 Arrhenatherum eteuue IIIBuxus sempervirens I Bromus erectus 11Paeonia officinalis subsp humili 11 Crepis albida IIIAcer opalus 11 Epipactis atrorubens IIILathyrus filiformis I Galium maritimum 11

Biscutella valentina IIICharacter-species of Querco-Fagetea: Sedum sediforme 11Pinus sylvestris III Laserpitium gallicum 11Hieracium aggrmurorum IV Centranthus lecoqH 11-_.,--

600 P Regato-Pajares, R Elena-Rossell6

included within these groups are located inboth higher and lower left quarters.

Group 4; includes all those black pine forestsin the western sector which have the beststructure and development and can thus beconsidered the climax or mature vegetationunder these specific ecological conditions.These are mainly located in ubacs, althoughit should be considered that this mightdepend on the fact that adrets tend to bemanaged by humans for cattle-raising andagriculturalpurposes. The understory is char­acterized by the abundance of sub-Mediter­ranean and central-European scrub andherbaceous species. Among indicator andpreferential species are Viburnum lanlana,Ligustrum vu/gare, Buxum sempervirens,Rosa pimpinellifoita, Thaitctrum tuberosum,Lalhyrus fiiiformis, Geranium sanguineumand Phyteuma orbiculare. Such pine forestshavebeendescribed as a newassociation,Thafictro tuberosi - Pinetum salzmannii(Regato, 1992), which is considered as thepotential vegetation type of the high supra­andlowmountain-Mediterrranean levels onthe mountains of the western Iberian Range(Serrania de Cuenca, Montes Universalesand westem side of Sierra de Gudar), (tableIll). The main phytoclimatic type is thenemoro-Mediterranean humid, VI(IV)2.

Group 5: includes those mesophytlc blackpine forests of a more steppic nature, whichare typical of the transitional mountainsbetween the western and eastern sectors.These are situated around the very cold andxeric depression of Teruel. Substeppicnemoral, VI(VII), is the main phytoclimatlctype and limestone-marl substrates prevail.In several sites, the sparse structure of theforest is due to intensive human manage­ment. The understory is poorer in sub­Mediterranean species, while species of thebushy formations are more frequently found.Among indicator and preferential species areAslragalus granalensis, Avenula pralensis,Festuca rubra, Scabiosa lurolensis, Brachy­podium phoenicoides and Avenula bro­moides. This can well be considered as a

variation of group 4 climatic wood, which hasbeen defined as the subassociation aslra­galelosum granalensis (Regato, 1992) of theclimax type Thaitctro-Pinelum (table IV).

Group 6: includes mesophytic black pineforests adapted to steppic conditions. Theseare typical of the highest areas of plateausand hilly uplands, which share with the step­plc Juniperus Ihurifera forests. Pine woodsare mainly placed on dolomite substrates,while Juniper formations tend to develop inlimestone-mar! areas. Juniperus thurifera isquite common in the pine wood subcanopytree layer, where the sub-Mediterraneanbushy element becomes rare. Among theirindicatorand preferential species are Brachy­podium syfvaticum, Geum sylvalicum, Lett»yrus fiiiformis, Prunus spinosa, Rosapimpinellifoita, Hepalica nobiits, Berberis vul­garis, Buxus sempervirens, Thymus bractea­Ius, elc. This can be considered as a geo­morphological variation of the typical maturepine woods of group 4, to more extreme cli­matic conditions in the upland plains andflat-topped mountains. This formation hasbeen defined as juniperetosum Ihuriferae(Regato, 1992) subassociation of the climaxtype Thelictro-Pinetum (table V).

Group 7: includes subrupicolous black pineforests of dolomitic gravity slopes and rockyplains, with abundant dolomite-limestoneindicator taxa. This is clearly differentiated inthe CCA diagram. The black pine has a veryirregular development, and hardly ever con­stitutes a proper canopy. Indicator and pref­erential species are Jasonia glutinosa,Junlperus phoenicea, Stipa ollneri, Fumanaericoides, Alyssum lapeyrousianum, etc.

Xerophytfc pine forestsof the western area: groups 8-10

This grouping comprises 140 sites found inthe lowest altitude ranges of the southernand western portion of the Serranfa deCuenca, where the xeric nemoro-Mediter-

Phytoecalagical features ofblackpineforests 601

ranean type (VI(IV)1) is the main phytocli­mate. Under such climatic conditions, Pinusnigra finds its ecological limit and gives ori­gin to moderately developed formations.These tend to have a sparse structure,mainly due to anthropic action as well as tothe subrupicolous features of several sites.Suchstructure favors a xerothermic natureof the wood understory. Quercus faginea

and Quercus ilex subsp bailota are fre­quently present In the tree layer, as the zoneis ecotonal with the woods of such oakspecies. Among indicator and preferentialspecies, only xerothermic taxa of bushy for­mations, such as Rosmarinus ottioinelis,Brachypodium retusum, Juniperusphoenicea, Saivia tavanduiifoiia, Saturejaintricataand Erinaceaanthyiiiscan be found.

Table Ill. Thalictro tuberosi-Pinetum sa/zmannii (Regato,1992).

Characterand differential species of the association:Pinus nigra subsp salzmannii VThalictrum tuberosum IVLathyrus tuuonnte IVSorbus aria IV

Differential species vs Cephalanthero-Quercetum {agineae:Rosa pimpinefli{ofia IVJuniperus communis IVOnonis aragonensis IIFilipendula vulgaris IIIAvenula pratensis III

Character-species of Quercion pubescenti-petreeee:Phyteuma orbiculare IIILeucanthemum vulgare IVRhamnus saxatilis lllCampanula rapunculoides 11Saponaria ocymoides ILonicera etrusca IBuxus sempervirens 11Sorbus domestica 11Helfeborus feotidus I

Character-species of Quercetalia pubeecemi-petreeee:Amelanchier ovafis VViburnum lantana IVLigustrum vulgare IVPrimula veris subsp columnae IVGeranium sanguineum IIIBerberis vulgaris subsp seroi IIITanacetum corymbosum IIIVicia onobrycioides 11Prunus mahaleb 11

Otherspecies:Arrhenatherum ela!fus IVBrachypodfum phoenicoldes IIIEuphorbia nieaensis IVTeucrium chamaedrys VRubia peregrina IVHippocrepis g/auea IIILavandula letitoli« IIIGenista scorpius IIBromus erectus JIKoe/eria vallesiana II

Species of Aphylfanfion:Catananche coerulea IVAphylfantes monspelfiensls IIILotus comiculatus 111Potentiffa tabernaemontani JIAnthyflis montana "

Character-species of Querco-Fagetea:Grataegus monogyna VHepatica nobilis VGeum sylvaticum VPo/ygonatum odoratum IIIGornus sanguinea IIIViola reichenbachiana IIILonicera xylosteum IIIAquilegla VUlgaris I1Gory/us avelfana 11Brachypodium sylvaticum 11Sanicula europaea 11Hedera helix 11Gephalanthera rubra 11Lonicera peryclimenum 11Glemafis vitalba IUlmus glabra 11Tilia plalhyphyllos IVic!a tenuiiolle ISifene nutans I

IVIII11III

Character-species of Aceri-Quercenion:AcermonspessulanumQuercus {agineaBupleurum rigidumPaeonia otttctnetis subsp humilis

602 P Heqato-Pajares, R Elena-Hossello

The almost complete absence of nemoralspecies in the understory and the frequentappearance of Quercus species make itvery difficult to characterize these ecotonalsites, where Pinus/Quercus mixed forest ismost likely their foreseeable forest type.

Xeromesophytic pine forestsof the eastern section: groups 1f-f3

This grouping includes 33 sites found in thelower elevation areas of the dolomitic ranges

Table IV. Thalictro tuberosi-Pinetum salzmannH astragaletosum granatensis (Regato, 1992).

Character-species of the association: Thymus leptophyllus 11Pinus nigrasubsp salzmannii V Potentilla cinerea 1IThafictrum tuberosum III Polygala ca/carea 11Lathyrus fiHformis 11 Festucahystrix 11

Juniperus sabina IDifferential species of subasastragaletosum:Astragalus granatensis IV Character-species of Ononido-Rosrnarinetea:Festuca gautieri 11 Lavandula latifolia VAstragalus hypoglottis III Koe/eria vetteetene IVJuniperus thurifera III Euphorbia nicaensis IV

Potentilla tabernaemontani IVDiffspecies vs Cephalanthero-Quercetum fagineae: AphyJlantes monspeJliensis IIIJuniperus communis V Sanguisorba minor IVRosa pimpinellifolia III Thymus vulgaris IVAvenula pratensis IV Genista scorpius 11Knautia arvensis III Scabiosa turolensis IV

Santolina chamaecyparisus IIICharacter-specles of Quercetalia pubescentis: Salvia lavandulifolia 11Amelanchier ovalis IV Avenula bromoides 11HeJleborus foetidus V Leuzea conifera IIITanacetum corymbosum III Catananche coeru/ea 11Ononis aragonensis III Medicago suffruticosa 11Leucanthemum vulgare 11 Digitalis obscura 11Si/ene nutans III Galium verum 11Aceropalus IVicia tenuifolia 11 Otherspecies:Teucrium chamaedrys V Arrhenatherum elatius V

Bromus erectus IVCharacter-species of Querco-Fagetea: Brachypodium phoenicoides IVPinus sylvestris III Ononis spinosa 11Crataegus monogyna III Garexhumilis 11Hieracium aggrmurorum 1I Hieracium pi/oseJla 11Gruciata glabra 11 Campanula hispanica 11Viola reichenbachiana III Dactylis g/omerata 11Rosa nitidula 11 Brachypodium retusum 1IHepatica nobilis I Festuca rubra I1

Asperula cynanchica IIISpeciesof Erinacetalia: Hieracium pi/oseJla 11Thymus bracteatus III Ononis tridentata IFestuca hystrix III Biscutella valentina 11Centaurea pinae 11 Erysimum granddolium 11Erinacea anthyllis 11

Phytoecological features of black pine forests 603

Table V. Thalictro buterosi-Pinetum salzmannii juniperetosum thutiteree (Regato, 1992).

Differential species vs Cephalanthero·Quercetum faginae:Juniperus communis VAvenula pretensis 11FiHpendula vulgaris IIIRosa pimpinellifolia 11 I

Differential species of the com with G mugronensis:Festuca hystrix 11Genista mugronensis 1Arenaria obtusiflora 11Cerastfum brachypetalum II

Differential species of the subas juniperetosum:Juniperus thurifera IIIThymus bracteatus IVBerberis vulgaris subsp seroi IVPrunus spinosa III

Character-species of Querco-Fagetea:Geum sylvatfcum IVCrataegus monogyna IVRosa sicula VBrachypodium sylvaficum IIIPinus sytvestris IHieracium aggr murorum IVViola reichembachiana JIHepatica nobilis JSanicula europaea +m~m~~ J

+II

Poa ligulataRanunculus gramineusStipa offneriDianthus hispanicusErinacea anthyllis

Species of Ononido·Rosmarinetea:Genista scorplus IIILavandula latifofia VEuphorbia nicaensis VPotentilla tabernaemontani IVHelianthemum cinereum IVCoronilla minima IIIKoelleria vallesiana IVMedicago suffritfcosa 11Aphyllantes monspelliensis II1Lotus corniculatus 11Helianthemum apenninum IISanguisorba minor JI

Other species:Arrhenatherum elatius VThymus vulgaris IVAnthyllis vulneraria IHippocrepis gfauca 11Teucrium chamaedrys JIIPolygala calcarea 11Trifolium campestre "Achillea odorata 11/Erysimum grandiflorum 1IBromus erectus IBrachypodium phoenicoides 1Dactylis glomerata 11Thapsia viffosa IIIAcinos alpinus 11Biscuteffa valentina ICarex hafferana 11Hieracium pifosella IGlobularia vulgaris IAsphodelus cerasifer 11

Phlomis Iychnitis "Marrubium supinum ICarduus assoi IEryngium campestre JIUthodora fruticosa ISantolina chamaecyparisus IVicia pyrenaica +

VIIIIII

Character-species of the association:Pinus nigra subsp salzmanniiThalictrum tuberosumLathyrus filiformis

Character-species of Quercetalia pubescentfs:Amelencnier ovalis IIIBuxus eempetvirene 11Paeonia otticlnelie subsp humilis 11Quercus faginea 11Cephalanthera damasonium ICephalanthera fongifolia IUmodorum abortivum 11Rhamnus saxatilis 11Acer monspessulanum Ivtce onobrychioides ILeucanthemum vulgare 1IOrchis mascula I

604 P Regato-Pajares, R EJena-Rossell6

in the proximity of the coast. Escarpmentsand canyons are common, producing veryheterogeneous site conditions. Group 11has the most nemoral conditions, and canbe considered as a xerothermic variation ofthe mature black pine woods of the easternsector, Lonicero-Pinetum subassociationgenistetosum patentis (Regato, 1992) (tableI). There is a considerable amount of rnes­ophytic taxa in the understory, but with alower abundance Index. The presence ofspecies such as Juniperus oxycedrus,Juniperus phoenicea, Bup/eurum fru­ticescens and Brachypodium retusum Indi­cates their xeromesophytic character.

Groups 12 and 13 are clearly differenti­ated in the CCA diagram. The formerincludes the most thermic sites of black pineformations in the Sistema lberico, and itshould be considered as azonai open com­munities with the worst growth potential.The latter group comprises the subrupi­colous sites, where the canopy hardly exists,and where trees have an Irregular distribu­tion over the rocky slopes.

DlSCUSSfON AND CONCLUSION

Black pine forests have their ecological opti­mum between the supra- and rnountain­Mediterranean levels of these dolomite-lirne­stone ranges, under a very cold humidnemoro-Mediterranean continental phyto­climate. Under these conditions, the poten­tial for growth of Pinus nigra Is better thanthat of other species. In the Sistema lberico,there are 2 climax communities, the morecontinental one, Thalictro-Pinetum salz­mannii, located In the western part (groups4-6) and the less continental one,Lonicero-Pinetum salzmannii, located inthe eastern part (groups 1, 3 and 11), sim­ilar to the black pine woods of the Pyrenees.

The indicator species group of the bestsites isa combination ofsub-Mediterraneanand central-European taxa. Some of themost common characteristics are:

Sorbus ariaHepatica nobilisRosa pimpineiiifoiiaLathyrus fiiiformisJuniperus communisThaiictrum tuberosumLonicera xylosteumPrimula veris ssp columnaeVibumum iantanaSanicufa europaeaAmeianchier ovalisGeum syivaticumBuxus sempervirensAvenula pratensisAcer opaius ssp granatensisBrachypodium syivaticum

These woods, Included in Cl Querco­Fagetea (or, Quercetalia pubescentis), rep­resent the ecological optimum (with realnemoral understory conditions and well ver­tical-structured canopy) of extensive areasthat were previously established as potentialsites of more xerophytic vegetation (Junipe­rus thurifera cotd stepplc woods and Quer­cus iiex subspbaiiota thermic woods).

Inthese climax communities, wecandis­tinguish 2 site types:

1) Those stands associated with the hillyuplands, where the subcanopy Is dominatedby the herbaceous layer. The arbustlve layeris poor and integrated by the most conti­nental species (Juniperus communis, Rosapimpineiiifolia and Berberis vuigaris subspseroii. This type has the best site quality,particularly over convex reliefs or plains. Inthe floor of some doline fields, the growthrate of Pinus nigra Is very high. Neverthe­less, soil conditions in thesesites have anunstable equilibrium, often broken by over­grazing and clear-cutting practices. Conse­quently, important soil losses and problemsIn tree regeneration will arise. The abun­dance of Juniperus thurifera In the tree layercan be considered a good Index for deter­mining the worst conditions of these kind ofsites. Such bad conditions are frequentlyrelated to the concave reliefs.

Phytoecological features ofblack pineforests 605

2) Those stands are associated with thesteepy sites on karstic valleys and canyons.The understory is dominated by the arbustivelayer. They have a good site quality despitetheir usuaily uneven-aged structure. Thisdepends on the heterogeneous conditionsof the substrate (rocks, boulder fields, steepslopes). Although the growth potential ofblack pine is good, the canopy structure maynot be uniform. The proportion of subrupi­colous taxa can be used as an indicatorvalue of the potential heterogeneous canopy.

The characteritics landform in the Sis­tema lberlco is the "cantil-talud" (gravityslope-pediment) system, where intense geo­morphologic dynamics occur (Calvo, 1987).The slope retreat maintains the verticalityof the cliff. The mixed pine/oak woods grow­ing in pediments with best edaphic condi­tions are modified by rock avalanches.These dolomitic blocks remove the soil,increasing dolomites and rock surface pro­portion. Under such conditions, black pineplays an important role in stabilizing andrestoring the site conditions.

At the oro-Mediterranean level of thesouthern mountains (Sierra Javalambre)(group 2), the characteristic cold climatebecomes more xeric, tending to steppic con­ditions. The indicator taxa are dwarf scrubs(eg Juniperus sebine, J hemlsphaerica,Prunus prostrata and Astragaiusgranatense), revealing an open structure ofthe wood. Nevertheless, these scrubs offerprotection to the black pine saplings and tothe few nemoral species that only growbelow them. Pines have a medium growthpotential and, according to Elena-Rosseil6and Sanchez-Palornares (1991), their sitequality appears to be average.

A high proportion of characteristic speciesof Ononldo-Rosmarlnetea bush communi­ties reveal a somewhat extensive under­story degradation. In the mountain-Mediter­ranean level, this usually reveals anthropicaldegradation (overgrazing; cleaning and thin­ning processes) and it is difficult to deter-

mine its site quality. Highest degradation isrevealed with the appearance of Festuco­poetaiia species (eg Festuca hystrix, Poaiiguiata, Arenarla erlnacea and Giobuiariarepens), which show strong soil denudation(groups 7 and 10). The black pine usuailyshows special growth limits with a charac­teristic table-shaped crown.

The presence of taxa typical of morexerothermic bush communities (Rosmarino­erlclon) (eg Rosmarinus otticinetis,Heiianthemum hirtum, Corls monspeiiensisand Brachypodium retusum) is consideredas being evidence of the lowest site qual­ity. This generally corresponds to siteswhere Pinus nigra has its ecological limiton the lowest xerothermic slopes (groups8 and 9). These species are also typical ofsites which correspond to rocky or erodedadrets at a higher elevationallevel.

In the eastern subcontinental sector, theworst site quality corresponds to the lowestsites, where azonal black pine communitiesare defined, having an open structure and apredominant QuerceteaIilc/sspecies under­story (group 12).

This phytoecologicai classification hasmade it possible to recognize Pinus nigraclimax communities, representing the poten­tial vegetation for this mountain region. Oncethe potential area and ecological optima forPinus nigra are established, a precise basisfor determining the quality of its differentsite types is available.

When analyzing the TWINSPAN dendro­gram, several interesting conclusions wereobtained. At the first division level, climaxPlnus nigra sites were separated from theazonal ones. In its second level, both sitetypes were divided into 2 groups according toregional climate reasons: the subcontinen­tal types, located in the eastern sector, andthe continental types in the western sector.Lower divisions can only be understood whentaken into account physiographic factors,showing the landform pattems of the regionalgeomorphological typical structure.

606 P Regato-Pajares, R Elena-Rossello

ACKNOWLEDGMENTS

We thank A lplestas and M Pagliani for their pre­cious help in the translation of the paper, and ALean for technical assistance. The urustrattonswere prepared by J De MigueJ. This study wassupported by an operating grant to PRP by theForestry Hesearch lnsfhute (CIFOR-INIA) of Spain.

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