Vegetatio 110: 1-17, 1994.@ 1994 Kluwer Academicifublishers. Printed in Belgium. 1

The phytogeography of the Chamaecytisus proliferus (L. fil.) Link(Fabaceae: Genisteae) complex in the Canary Islands: a multivariateanalysis

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J. Francisco-Ortega 1, M. T. Jackson 1 *, A. Santos-Guerra 2, M. Fernandez-Galvan 2 &B. V. Ford-Lloyd 1 **1 School of Biological Sciences, The University of Birmingham, P.O. Box 363, Birmingham, B15 2TT,UK 2 Jardin de Aclimatacion de La Orotava, Calle Retama Num. 2, 38400, Puerto de La Cruz, Tenerife

Canary Islands, Spain * Present address: International Rice Research Institute, P.O. Box 993, 1099Manila, Philippines; ** Author for correspondence

Accepted

7.9.1992

Keywords: Ecogeography, Fodder-legumes, In-situ-conservation, Biodiversity, Germplasm, Tagasaste

Abstract

Chamaecytisusproliferus (L.til.) Link (Fabaceae: Genisteae) represents a species complex in the CanaryIslands. Floristic data from 147 releves from the whole complex were collected and analysed by clas-sification (TWINSP AN) and ordination (DECORANA) methods. Results indicate that white escobonof Tenerife, escobon of El Hierro, white escobon of Gran Canaria and typical tagasaste in La Palmaare associated with those plant communities from the north of these islands which are under the influ-ence of the north-eastern trade winds. Narrow-leaved escobon in Tenerife and La Gomera, escobon ofsouthern Gran Canaria and white tagasaste of La Palma are found in those areas which are not underthe direct influence of these winds. Morphological forms from the more easterly islands (Gran Canariaand Tenerife-La Gomera) have the broadest ecological range and they have played an important rolein the floristic changes which have taken place after the destruction of the forests in these islands. Thehighest priorities for in situ conservation should be given to wild populations of typical tagasaste, whiteescobon of Tenerife and escobon of El Hierro.

Abbreviations: International Board for Plant Genetic Resources (IBPGR), Detrended CorrespondenceAnalysis (DECORANA), Operational Taxonomic Unit (OTU), Two Way Indicator Species Analysis(TWINSP AN)

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Nomenclature: Hansen, A. & Sunding, P. 1985. Flora of Macaronesia. Checklist of vascular plants. 3rded. Sommerfeltia 1: 1-167; Acebes-Ginoves, J.R., Del Arco, M. & Wildpret, W. 1991. Revision taxo-nomic a del genera Chamaecytisus (t. fil.) Link en Canarias. Vieraea 20: 191-202.

Introduction truly domesticated species (Harlan 1983). Noclear morphological and agronomic differencesexist between typical tagasaste plants from wildand from cultivated populations. This means thatunlike many other more domesticated crops, ta-gasaste germplasm collected in the wild is of valueas in many instances it can be used without hav-ing to resort to complex plant breeding proce-dures. The importance of germplasm from wildpopulations of this fodder species determines thatecogeographical studies within its distribution areextremely useful in the establishment of strategiesfor subsequent evaluation and utilisation of itsplant genetic resources. Furthermore as the cen-tre of origin and diversity of tagasaste is foundwithin an archipelago, it is essential to considerthe general patterns of island biogeography priorto any study on the phytogeography and plantgenetic resources of this species.

Studies concerning the biogeography of the Ca-nary Islands have been reported extensively else-where (e.g. Webb & Berthelot 1836-1850; Kunkel1976; Bramwell 1979; Santos-Guerra 1983a;Rivas- Martinez 1987). Due to the oceanic posi-tion of the archipelago and the influence of thecold north-eastern and the hot north-westerntrade winds there is a stratification of differentclimates in the archipelago both in terms of alti-tude and orientation. This stratification is alsoreflected by the patterns of distribution of thevegetation of the Canary Islands in five differentlife-zones namely, infra-canarian zone (semi-desert scrub), thermo-canarian zone (arid scrub,Laurus azorica wood and heath belt), meso-canarian zone (Pinus canariensis forest), supra-canarian zone (high altitude scrub) and oro-canarian zone (only Viola cheiranthifolia). Withinthis ecological framework the other two factorswhich determine the patterns of biogeographicalvariation found in the Canary Islands are the ob-vious geographical isolation which exists betweeneach island and the abrupt topography.

Habitat stratification in life-zones has pro-duced several examples of adaptive radiation inthe genera Aeonium (Lems 1960), Argyranthemum(Humphries 1976) and Sonchus (Alridge 1980).On the other hand geographical isolation due to

The genus Chamaecytisus Link (Fabaceae:Genisteae) comprises approximately 28 species.The centre of highest diversity occurs in the Bal-kans where more than 15 species can be found(Cristofolini 1991). The number of species de-creases towards the rest of Europe, the Near East,North Africa and the Canary Islands. Chamae-cytisus proliferus (L.ftl.) Link forms a taxonomicspecies complex in the Canary Islands (Fig. 1).Both Acebes-Ginoves (1990) and Francisco-Ortega (1992) reported seven morphologicalforms within this complex namely, white escobonof Tenerife (C. proliferus ssp. proliferus sensustricto), narrow-leaved escobon (C. proliferus ssp.angustifolius (Kuntze) Kunkel), typical tagasaste(C. proliferus ssp. proliferus var. palmensis (Christ)Hansen & Sunding), white tagasaste (C. proliferusssp. proliferus var. calderae J .R. Acebes), escobonof southern Gran Canaria (C. proliferus ssp. me-ridionalis J .R. Acebes), white escobon of GranCanaria (C. proliferus ssp. proliferus var. canariae(Christ) Kunkel) and escobon of El Hierro (C.proliferus ssp. proliferus var. hierrensis (Pitard)J .R. Acebes).

Both kinds of tagasaste are endemic to the is-land of La Palma. Escobon ofEl Hierro, escobonof southern Gran Canaria, white escobon of GranCanaria and white escobon of Tenerife are onlyfound in their respective islands whereas narrow-leaved escobon occurs in Tenerife and La Go-mera (Fig. 1).

Although originally from La Palma, typical ta-gasaste is also cultivated in El Hierro, La Go-mera, Tenerife and Gran Canaria. The other sixmorphological forms are not cultivated but heavilypruned and grazed in their wild habitats (Perez dePaz et al. 1986; Francisco-Ortega et al. 1990).White escobon of Gran Canaria has been reportedto be semi-cultivated in some areas of north-western Gran Canaria (Hernandez-Gonzalez1987; Francisco-Ortega et al. 1990) where it isused to feed livestock.

Tagasaste appears to follow the same patternof domestication of other fodder species and al-though it is cultivated it cannot be regarded as a

3

J 10 20, , ,km

iW

~~ ~m

EI Hierro 20~; !2 ~m

Fig. 1. The distribution of the seven morphological forms of C. proliferus (based on Acebes-Ginoves et al. (1991) and Francisco-Ortega (1992». Taxa are coded as follows: 0 C. proliferus ssp. proliferus var. proliferus; .C. proliferus ssp. angustifolius; f,. C.proliferus ssp. proliferus var. canariae; ..C. proliferus ssp. meridionalis; .C. proliferus ssp. proliferus var. palmensis; 0 C. proliferusssp. proliferus var. calderae and .C. proliferus ssp. proliferus var. hierrensis.

island topography and/or insular isolation has ledto vicariance, examples of this evolutionary pro-cess being the patterns of morphological variationand ecology in the genera Cheirolophus, Crambeand Limonium (Bramwell 1972).

Previous reports on the phytogeography of C.proliferns (Ceballos & Ortufio 1951; Esteve-Chueca 1969; Sun ding 1972; Rivas-Martinez1987) were imprecise, as firstly they did not in-clude the whole distribution range of the species,

4

and secondly they were more concerned with theecology of the life-zones of the archipelago ratherthan with the ecological characteristics andtaxonomy of C. proliferns itself. Only recently hasit been proposed (Acebes-Ginoves 1990) thattypical tagasaste, white escobon of Gran Canaria,white escobon of Tenerife and escobon of ElHierro were linked to the laurel (Laurns azorica)wood and the heath (Erica arborea) forma-tions from the north of these islands, whereas theother three morphological forms were in associ-ation with the plant communities of P. canarien-sis.

and in zones with low and high rainfall of 175 and1200 mm respectively.

For each locality cover values of vascular plantspecies were estimated using the Braun-Blanquetscale. Special emphasis was placed upon thecompilation of Canarian and Macaronesian en-demics and of those species reported in previousworks (e.g. Santos-Guerra 1983b; Rivas-Mar-tinez 1987) as characteristic of each life-zone,since they are clearly related with both the ecol-ogy and historical biogeography of the CanaryIslands. Numerical analyses were carried out ona matrix in which each quadrat was regarded asan OTU. Data from the Braun-Blanquet scalewere transformed following Feoli-Chiapella &Feoli (1977). A classification of releves was ob-tained by the polythetic divisive method ofTWINSPAN (Hill 1979a). Ordination of reI eveswas accomplished using DECORANA (Hill1979b) which avoids the curvilinear distortionknown as "arch effect" which is produced withother techniques (e.g. Principal ComponentAnalysis, Non-Metric Multidimensional Scaling,Reciprocal Averaging), when species diversityamong sites follows environmental gradients(Jackson & Somers 1991). The CEP-PC package(Mohler 1987) was utilised to accomplish thesemultivariate analyses. In order to avoid between-island floristic vicariance effects, separate analy-ses were carried out for each island except for EIHierro where data were collected from only threepopulations. Simple descriptions of floristic com-positions of these stands were used for interpre-tation of the ecological features of escobon of EIHierro.

No multivariate analyses on the phytogeogra-phy of this species have been reported previously,and from our study both herbarium specimensand germplasm were collected from most of thelocalities of C. proliferus in the Canary Islandswith the objective that an understanding of thephytogeography of this species would lead to abetter interpretation of its patterns of morpho-logical ,variation. In turn, it was anticipated thatthis would contribute to the ecogeographicalcharacterization of the plant genetic resources ofthis fodder legume with a view to future conser-vation strategies.

Materials

and methods

Floristic data from 147 wild populations of C.proliferns sensu laID from El Hierro, La Palma, LaGomera, Tenerife and Gran Canaria were col-lected from quadrats of approximately 40 x 40 mbetween March and September 1989. Populationsfrom the whole distribution range of the specieswere sampled. They were separated by 3 km andwere chosen following the north-south climaticgradient which exist within each island (Santos-Guerra 1984). Table 1 shows localities for whichfloristic lists were compiled. Further ecologicalinformation concerning each of these localitieswas given previously (IBPGR internal report 90/1), and indicated that the species thrives better onsandy soils with low salinity and pH values be-tween 5 and 7. Furthermore populations wereidentified in areas where periodical frosts occur

Results

Tenerife

The hierarchical division of plant communitiesfrom TWINSP AN end groups, is given in Fig. 2a.Eight groups were recognised at the fifth division.These groups with their TWINSP AN indicatorspecies are given in Table 2. Stands identifiedwithin each group are shown in Fig. 3.

6

0

@

0

Fig. 2. TWINSPAN classification obtained for floristic data from Tenerife (a), Gran Canaria (b) and La Palma (c). The char-acteristic indicator species are also given (see species code number in Appendix A).

End group A comprises those scrubs situatedon northern and southern areas of the island ata mean altitude of 1850 m. Groups B, C, E andF were found both on northern and southernslopes ofTenerife and with an average altitude of1600 m. Stands from end group D were only

recorded on southern slopes at a mean altitude of900 m. Both end groups G and H were locatedin northern Tenerife. The mean altitude for groupG was of 1350 m whereas stands from group Hwere recorded at a mean altitude of 950 m.

An ecological interpretation of stands obtained

1

transition between the plant communities fromthe centre of the island, towards the Canary pineforest zone found at low altitudes. It is notewor-thy that it is likely that in the past the plant com-munities of central Gran Canaria also had P. ca-nariensis as a common species. However intensivedeforestation has meant that it has vanished fromthis area (Santos-Guerra & Fernandez-Galvan

1980).

La Palma

reflected by the species scores on this axis whichare summarised in Table 5, as those species linkedto the laurel wood zone (e.g. Laurus azorica) hadpositive values along this axis whilst speciesmainly found on the scrubs of La Caldera deTaburiente gorges (e.g. Bystropogon origanifolius)had negative scores. Stands which had typicaltagasaste showed the highest scores on the firstDECORANA axis. The separation of standsalong this axis was associated with a gradientwhich ran from northern La Palma towards theinterior of La Caldera de Taburiente.

The second DECORANA axis was relatedwith changes in the floristic composition of theCanary pine communities. Stand 26 had the high-est positive value on this axis and it was recordedon a cliff, in an area where the pine forest was notso dense. This was confirmed by the fact thatspecies such as Festuca agustini and Gonosper-mum canariensis had positive values along thesecond axis (Table 5). Stands 254 and 255 werefound in those areas of the pine forest of LaCaldera de Taburiente, which meant that speciesrelated to the thermo-canarian zone such as Ericaarborea had low values on this axis (Table 5).

The hierarchical classification yielded five TWIN-SPAN end groups at the third division (Fig. 2cand Table 2). Releves which fell within each endgroup are illustrated in Fig. 5.

A scatter diagram with values along the firsttwo DECORANA axes is shown in Fig. 5. Standsrecorded within the laurel wood-heath belt zonehad high positive values on the first axis. Popu-lations sampled on the bottom of some of thewide gorges of La Caldera de Taburiente N a-tional Park had high negative values along thefirst DECORANA axis. This situation was also

300l D'026 -', ,

E/-',

.238218!~-:13~OIB

A,---:/ 014'

,O16 O17

0222;---'

1001

c',

8217)~/

0255-at

;;<

0254

A"IS I 100 200 300 400 ..10 800

Fig. 5. DECORANA ordination for La Palma. The five TWINSPAN end groups are also given. Stands with typical tagasasteare represented by closed circles; stands with white tagasaste are represented by open circles. Stands with intermediate plantsare represented by open circle plus dot.

12

Table 5. Ten species which had the highest positive and negative values along the first two DECORANA axes in releves fromLa Palma.

DECORANAI DECORANA2

Laurus azoricaTeline stenopetala

Hypericum grandifoliumMyrica fayaErica arboreaParonychia canariensisLobularia palmensis

Spartocytisus filipesBystropogon origanifoliusSenecio palmensis

66655

'-r"

-.1

33333

"'!

J--1

Tinguarra montanaFestuca agustiniSilene pogonocalyxGonospermum canarienseHelianthemum broussonetiiLotus hillebrandiiAndryala webbiiErica arboreaRubus ulmifoliusSideritis bolleana

Eigenvalue 0.821 0.401

Four stands froqI La Caldera de Taburientehad plants of white tagasaste and typical taga-saste growing together (Francisco-Ortega 1992).However in these localities white tagasaste wasalways dominant. Furthermore, this morphologi-cal form was never detected within the laurelwood life-zone.

La Gomera

All the stands of narrow-leaved escobon from LaGomera were associated with Cistus monspelien-sis, and were similar to the scrubs from low alti-

tude zones of southern Tenerife. The hierarchicalclassification yielded two end groups at the firstdivision.

The first end group (TWINSP AN end groupA) had Erica arborea as characteristic specieswhereas the second (TWINSPAN end group B)had Artemisia thuscula and Micromeria lepida. Thetwo releves from end group A had also othercharacteristic species from the heath-belt and lau-rel wood plant communities (e.g. Myricafaya andflex canariensis) however these two sites were notwithin the limits of the actual laurel wood or heathbelt.

A scatter diagram for the first two DECO-

Table 6. Ten species which had the highest positive and negative values along the first two DECORANA axes in releves CrOffLa Gomera.

DECORANA DECORANA2

Micromeria lepida

Euphorbia obtusifoliaKleinia neriifoliaArtemisia thusculaPolycarpaea divaricata

Bystropogon origanifoliusBituminaria bituminosa/lex canariensis

Myrica JayaErica arborea

258238201194169

-165-221

-234

-234

-250

Sonchus ortunoiPhagnalon saxatile

Adenocarpus foliolosusPhagnalon saxatile

Hypericum grandifoliumHyparrhenia hirtaCarlina salicifolia

Andryala pinnatifidaDittrichia viscosaMicromeria varia

34822018812599

-35

-98

-159

-178

-317

Eigenvalue 0.233 0.101

73737390

8582828991

11

83836658353939859004

13

It was difficult from the data set to obtain anecological interpretation for the second DECO-RANA axis, which separated stands 139 and 142at one end and stands 138 and 140 at the other(Fig. 6). However floristic species scores(Table 6) indicate that the legume shrub Adeno-carpus foliolosus which is also a member of theGenisteae had high positive scores along the sec-ond axis whereas Micromeria varia had low nega-tive values on this axis.

RAN A. axes (Fig. 6) showed that populationsfrom TWINSP AN end group A had low valuesalong the second axis and were regarded as beingmore influenced by the northern trade winds. Allthe localities, with the exception of one (popula-tion 165), were below 1200 m altitude, and in thesouthern areas of the island. Population 165 wasin the north west of the island but at an altitudeof 450 m. This distribution was in agreement withthe species scores along the first axis (Table 6).Those species usually found in areas which havethe influence of the trade winds (e.g. Myricafaya)had large negative scores on the first axis. Highpositive values were only obtained for arid areas(e.g. Kleinia neriifolia or Euphorbia obtusifolia).This axis showed a transition within the Cistusmonspeliensis scrub from semi-arid areas to thosewhich receive the effect of the trade winds.

El Hierro

The three stands of escobon of EI Hierro werelocated on the cliffs of EI Golfo caldera in thenorth of this island at an altitude of 1000 m.These stands were clearly linked to the heath belt

SOl

Fig. 6. DECORANA ordination for La Gomera. The two TWINSPAN end groups are also indicated

14

and species usually found on cliff plant commu-nities such as Greenovia aurea, Silene sabinosae orToipis proustii were also recorded. It was neverobserved forming dense scrubs and could not beregarded as a common species. No populationsof C. proliferus were associated with the pine for-est, despite the extensive floristic survey carriedout in the south of the island.

Discussion

Chamaecytisus proliferus should be regarded as aspecies which grows under a broad range of eco-logical conditions. Previous reports (Ceballos &Ortufio 1951; Esteve-Chueca 1969; Sunding 1972and Rivas-Martinez 1987) which indicated thatthe whole complex is restricted to the Canary pinelife-zone have been misleading. The differentmorphological forms of the complex are alsofound in the thermo-s:anarian zone, and somepopulations were also identified towards the highaltitude scrub ofTenerife or in the semi-arid infra-canarian zone from the south of Tenerife andGran Canaria. The classification and ordinationof the stands demonstrate that the species followsan ecological cline through Tenerife, Gran Ca-naria and La Palma, with distinct morphologicalforms in the extremes of this cline. Typical taga-saste in La Palma, white escobon of Tenerife andwhite escobon of Gran Canaria are only locatedin laurel wood/heath belt zones of these islands,whereas white tagasaste in La Palma, narrow-leaved escobon in Tenerife and escobon of south-ern Gran Canaria have their distribution rangelinked with the Canary pine forest area.

Such a gradient was not detected in El Hierro,where C. proliferus was restricted to the cliffs ofthe heath belt of El Golfo. A similar situation wasfound in La Gomera, where narrow-leaved esco-bon was always associated with Cistus monspe-liensis, forming a kind of scrub which also oc-curred in localities of southern T enerife. However,some of the stands from La Gomera had speciessuch as Erica arborea or Myrica faya which werenot found in their homologues from the south ofTenerife. These species usually occur in northern

areas which are under the influence of the tradewinds (Santos-Guerra 1984), a situation previ-ously described by Fernandez-Galvan (1983), inLa Gomera, an island with lower altitude than LaPalma, Tenerife and Gran Canaria, and wherethe trade winds can have a great influence onsome slopes of the south. This factor coupledwith the fact that there are no real pine forestformations in the island, means that in the souththere are zones which reflect a transition betweenthe heath belt and plant communities from aridzones. In relation to that, one of the main featuresof C. prolifelUs in La Gomera is that it was neverlocated within the true laurel wood zone. Acebes-Ginoves (pers. comm.) considers it likely that aform of C. prolifelUs similar to the white escobonof Tenerife or Gran Canaria could exist on thecliffs of the laurel wood of this island. Despite thesurvey carried out during field studies and inter-views with farmers and forest rangers from thearea, such a morphological form was never found.The fact that narrow-leaved escobon was neverobserved within the limits of the laurel wood ofLa Gomera confirms that this morphological formhas achieved ecological differentiation, and isclearly adapted to dry areas which were not underthe influence of the north-eastern trade winds.

Chamaecytisus prolifelUs does not conform tothe same ecological trends in each island. Thetwo morphological forms from Gran Canariawere observed colonising and forming massivescrubs in all areas where both the pine forest andthe laurel wood have vanished. On some occa-sions, this colonising ability has led to the forma-tion of dense scrubs in which escobon of south-ern Gran Canaria or white escobon of GranCanaria are the dominant species. Furthermore,these two morphological forms also exhibit aweedy habit, being detected on abandonedcultivated sites. This ability to thrive under vari-ous ecological conditions was only shown bynarrow-leaved escobon in Tenerife where thismorphological type also forms dense scrubs(TWINSP AN end group E) and grows on aban-doned cultivated sites. All the other morphologi-cal forms have a more restricted ecological range;white escobon of EI Hierro, white escobon of

15

forms have played an important role during thefloristic changes which the pine forests ofTenerifeand Gran Canaria and the laurel wood/heath beltof Gran Canaria have suffered because of humanimpact since the conquest of the Canary Islands,late in the 14th century. Then intense pastoralismand agriculture resulted in large-scale deforesta-tion (Parsons 1981). Once such forests were cutdown these forms of C. proliferus colonised thearea and formed scrub, as the habitats becamesunnier and competition with other species wasdramatically reduced. Furthermore, wild C. pro-liferus is broadly utilised as a fodder plant. In ourstudy, 80 % of the stands were found to haveheavily pruned escobon shrubs (Francisco-Or-tega 1992). This means that only in exceptionalcases can C. proliferus form a dense shrub. Itscompetition with other species of the scrub andits colonisation ability and its density is severelyreduced by its utilisation as fodder by peasantfarmers. Eventually the scrub is not so dense anda ground layer is mainly formed by Micromeriaspp., Bystropogon origanifolius or Sideritis spp. Inthe few places where escobon is not pruned it hasbecome the dominant species, and even in somesituations other shrubs, such as Adenocarpus spp.which have similar ecological requirements to C.proliferus could barely compete with escobon. Ourobservations indicate that prior to the massivedestruction of the Canary pine forest and the lau-rel wood, C. proliferus may have been foundmainly in those areas where the forest was not sodense, such as along the small and numerousravines which dissected the forest, or on cliffswhere taller trees are not dominant. It is alsoperceived that due to the abrupt and rough geog-raphy of the islands the species could find manyecological niches because of these features whereit thrived in association with other species of theforest.

We also find that C. proliferus should be re-garded as a pyrophytic species. Many youngplants of narrow-leaved escobon, tagasaste andescobon of southern Gran Canaria were observedgrowing in stands which had been burnt recentlyand this is confirmed by Perez de Paz et al. (1986).Being a pyrophyte C. proliferus grows better on

Tenerife and typical tagasaste were only observedon cliffs and sunny areas of the laurel wood/heathbelt.

White tagasaste was confined to the pine for-est of northern La Palma and to La Caldera deTaburiente and did not show the weedy habit ofits ecologically homologous narrow-leaved esco-bon and escobon of southern Gran Canaria. Al-though it was observed as an under storey speciesof the pine forest it shows a tendency to formdense scrubs along the bottoms of the numerousgullies which dissect the huge eroded caldera ofthe La Caldera de Taburiente. This morphologi-cal form was observed neither in the pine forestof southern La Palma nor linked to low altitudeplant communities of Euphorbia obtusifolia orKleinia neriifolia. These distribution patterns re-present a more restricted ecological range thanescobon of southern Gran Canaria or narrow-leaved escobon.

Results shown here indicate that the ability ofthe species to grow under wider ecological con-ditions is demonstrated more in the eastern is-lands (Gran Canaria and Tenerife-La Gomera)than in the western islands (La Palma and ElHierro). This accords with previous studies ofgenetic diversity, based on results from tenisozyme loci, where only populations from theeastern islands had unique alleles and also thehighest values of Nei's index of genetic diversity(Francisco-Ortega 1992). Similarly, it was also inthose islands where a greater number of morpho-logical variants were detected (i.e. morphologicalclines for seed colour, juvenile characters, leafshape and keel petal length in Gran Canaria andfor leaf hairiness, leaf shape and keel petal lengthin Tenerife). These results suggest that there is arelationship between germplasm provenance andecogeographical variation measured in terms ofecology, morphology and allozymes. In this rela-tionship, germplasm from the eastern islands wasmore variable than that collected in the westernislands.

There is another major consequence of the highcolonising ability of narrow-leaved escobon, es-cobon of southern Gran Canaria and white es-cobon of Gran Canaria. These morphological

16

Appendix A

TWINSPAN characteristic species for Tenerife, Gran Ca.naria and La Palma.

1. Adenocarpus foliolosus 14. LaulUs azorica.2. Adenocarpus viscosus 15. Micromeria benthamii3. Bystropogon origanifolius 16. Nepeta teydea4. Carlina xeranthemoides 17. Phyllis nabla5. Chamaecytisus prolifelUs s.l. 18. Pinus canariensis6. Cistus monspeliensis 19. Rumex lunaria7. Cistus symphytifolius 20. Senecio webbii8. Echium onosmifolium 21. Sideritis cretica9. Erica arborea 22. Sideritis dasygnaphalla

10. Erysimum scoparium 23. Spartocytisus supranubius11. Euphorbia obtusifolia 24. Teline micropylla12. flex canariensis 25. Festuca agustini13. Kleinia neriifolia

habitats which become sunnier with less compe-tition from other species. Furthermore, as P. ca-nariensis is able to continue growth after a fire, areal scrub has not actually replaced the pine for-est, and only some young plants of C. proliferushave survived in competition with the Canarypine. Therefore an equilibrium, in which fire isone of the regulators, is established between C.proliferus and P. canariensis.

From a combined ecogeographical and geneticresource perspective the seven morphologicaltypes of C. proliferus have different ecological re-quirements and effective in situ conservation andutilisation of the plant genetic resources of thespecies needs to take account of its phytogeog-raphy. The two morphological forms endemic inGran Canaria, and narrow-leaved escobon inTenerife and La Gomera are not endangered spe-cies. Also they can withstand continuous pruningby farmers and many of their plant communitieshave arisen as a result of human intervention uponthe forest. As a consequence of the rather limiteddistribution range of white tagasaste most of itspopulations are confined to La Caldera de Tabur-iente National Park where they correctly have anin situ conservation status. Other priorities for insitu conservation should be focused towards theother three morphological forms, namely typicaltagasaste, white escobon ofTenerife and escobonof EI Hierro. They have restricted ecological re-quirements and also have lower adaptation tothose disturbed habitats which have arisen afterdeforestation.

References

Acknowledgements

Financial support for this work was receivedthrough a personal grant (JFO) from the Minis-terio de Educacion y Ciencia (Spain), Plan Na-cional de Formacion de Personal Investigador(grant no. PG88 42044506) and from the IBPGR.Thanks are due to J .R. Acebes-Ginoves (Univer-sidad de La Laguna, Tenerife) for critical readingof this manuscript. P.O. Machin (Universidad deLa Laguna, Tenerife) provided technical assis-tance.

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