Deciduous and Semi-Deciduous Oak Forests (Quercus Robur, Q

Home , Arenaria montana, Corylus avellana, Quercus petraea, Quercus robur

Biologia, Bratislava, 62/2: 163—172, 2007 Section Botany DOI: 10.2478/s11756-007-0025-4

Deciduous and semi-deciduous oak forests (Quercus robur, Q. petraea and Q. pyrenaica) ﬂoristic composition in the Northwest Iberian Peninsula

Ignacio J. Díaz-Maroto & P. Vila-Lameiro

Department of Agroforestry Engineering, University of Santiago de Compostela, Campus Universitario s/n, E–27002 Lugo, Spain; e-mail: [email protected]

Abstract: Oak forests in the Northwest Iberian Peninsula represent climax communities with a high floristic diversity of vascular plants. This study presents data from 189 botanical samples randomly collected in stands of deciduous and semi-deciduous oak as Quercus robur (98), Q. petraea (50) and Q. pyrenaica (41). Within these stands, 187 species or subspecies were identified, in addition to 20 genera and 68 families, all of them present in forests of Quercus robur. A total of 126 species occur in more than five relevés. The largest number of species corresponds to Poaceae (22), Fabaceae (19) and Rosaceae (14). The biological spectrum is dominated by hemicryptophytes, with mainly Atlantic and Sub-Atlantic floristic elements. The distribution of the stands has been studied by using Two-Way Indicator Species Analysis, obtaining like pseudo-species, with shrubby and arborea form, the following ones: Fagus sylvatica, Castanea sativa, Sorbus aucuparia, Corylus avellana, Crataegus monogyna, Pyrus cordata, Erica arborea, Frangula alnus and Cytisus scoparius. Key words: floristic diversity; Quercus; Iberian Peninsula; TWINSPAN

Introduction Rozeira 1956; 3) Blechno spicanti-Quercetum roboris Tx. & Oberdorfer 1958; 4) Linario triornithophorae- The genus Quercus dominates a large part of the forests Quercetum petraeae (Rivas-Martínez, Izco & Costa ex. in the temperate zone of the Northern hemisphere and F. Navarro 1974) F. Prieto & Vázquez 1987; 5) Luzulo in subtropical transition areas. At present, about 400 henriquesii-Quercetum petraeae (F. Prieto & Vázquez species are recognized, most of which occur in Mexico 1987) Díaz & F. Prieto 1994; 6) Linario triornithopho- andextendalloverNorthAmerica,Europeandmost rae-Quercetum pyrenaicae Rivas-Martínez et al., 1984; of Asia (Díaz-Maroto et al. 2005). In the Northwest 7) Holco molli-Quercetum pyrenaicae Br.-Bl., P. Silva Iberian Peninsula, the climax vegetation that currently & Rozeira 1956; 8) Genisto falcatae-Quercetum pyre- covers the largest area is the broad-leaved forest char- naicae Rivas-Martínez in Penas & Díaz 1985. According acterized by various oak species (Buide et al. 1998). to EU Directive 92/43/EEC, these forests are habitats According to palynological studies, these forests were of importance to conservation and, consequently, their established in the Northwest of the Peninsula between distribution and floristic diversity knowledge is essential five and seven thousand years ago, after the last glacia- (Díaz-Maroto et al. 2005, 2006). tion in the Quaternary (Guitián Rivera 1995). The surface area covered by these forests has grad- Historical factors, site conditions, and require- ually decreased over the historical period with con- ments of the species give rise to different forest types sequent forest fragmentation and decrease in species with various floristic compositions and structures (Pe- number (Amigo et al. 2001), as in other temperate terken & Game 1984; Díaz-Maroto 1997; Amigo et al. zones (Graae & Sunde 2000; Acar et al. 2004). The 2001). All the forests belong to Querco-Fagetea class main reasons for such a decrease were: land clearing for (Atlantic Province) with the maximum possible degree establishment of crops and pastures, timber and fire- of evolution, and they would remain in the current wood extraction, forest fires, unfortunate silvicultural state if environmental conditions did not change (Rivas- treatments or, more recently, massive reforestation with Martínez 1973, 1987). pine and eucalyptus (Guitián Rivera 1995). Recently, The forests correspond to the following phytosocio- these forests have increased substantially (DGCONA, logical associations (Fernández & Vázquez 1985; Rivas- 2001, 2003), native hardwood forests account for ap- Martínez 1987; Izco et al. 1990; Díaz & Fernández proximately 27% (375,922 ha) of the total woodland 1994; Rivas-Martínez et al. 2001) (Table 1): 1) Myrtillo- area of Galicia. Quercus robur stands cover an area of Quercetum roboris P. Silva, Rozeira & Fontes 1950; 2) 187,789 ha, representing almost 14% total woodland Rusco aculeati-Quercetum roboris Br.-Bl., P. Silva & area, and Quercus pyrenaica stands cover an area of

c 2007 Institute of Botany, Slovak Academy of Sciences 164 I. J. Díaz-Maroto & P. Vila-Lameiro

Asturias

A Coruńa Lugo

Pontevedra León

Ourense

Asturias

A Coruńa Lugo

Pont evedr a León

Ourense

Fig. 1. Location of the study area within the Iberian Peninsula.

100,504 ha, corresponding to more than 7%. In As- 1934), and the corresponding floristic elements were asturias, data for genus Quercus suggest that these cover signed (Rivas-Martínez 1973; Silva-Pando 1994; Buide et 76,871 ha, 7.25% total woodland area. al. 1998). Phytosociological studies about these forests are available (Fernández & Vázquez 1985; Izco et al. 1990; Statistical analysis Díaz & Fernández 1994; Silva-Pando 1994), and sev- Two-Way Indicator Species Analysis (TWINSPAN) (Hill eral authors, such as, Amigo et al. (2001), Díaz-Maroto 1979) available in Community Analysis Package version 3.0 (1997), Díaz-Maroto & Vila-Lameiro (2006) and Díaz- (Pisces Conservation LTD, 2004) was used for classifica- Maroto et al. (2005, 2006), reported phytosociological tion of relevés. TWINSPAN identifies at each step indicator species – “the set of most highly preferential species that re- and ecological data of oak forests in Spain NW. Pinto produce as good a refined ordination as possible” (Jongman Da Silva et al. (1950), Dantas (1958) and Carvalho et et al. 1995) – to distinguish between stands (Fernández- al. (2005) studied these forests in Portugal. The aim Alaez et al. 2005). Number of indicator species, number of of this study was 1) to describe the floristic diversity relevés per group, and levels of division can be modified of vascular species in deciduous (trees whose leaves fall in order to obtain the most suitable classification (Pisces every year) and semi-deciduous (trees whose leaves are Conservation LTD, 2004). The cover scale values (Braun- dried on the branches, without falling until the begin- Blanquet 1979) were grouped into six pseudo-species – “they ning of the new foliation) oak forests in Iberian Penin- represent ranks of relative abundance of a species, identified sula NW, and 2) to classify this oak forests according with the same name followed by a number” – (Vermeersch et al. 2003): zero (absence), one (up to 10% cover), two (10– to their overall species composition. 25%), three (25–50%), four (50–75%) and five (> 75%).

Material and methods Results

Study area and sampling design The study area is located in the Northwest Iberian Penin- A total of 187 species and 20 genera were identified. sula. For Quercus robur and Q. pyrenaica,theareacov- Table 2 shows the most frequent taxa, and Table 3 ers the whole Galicia, while for Quercus petraea the study presents the species number according to relevés num- area includes sites in Galicia, Asturias and León (Fig. 1). ber in which they occur, with a total of 126 species 189 botanical relevés (Braun-Blanquet 1979) were randomly that occur in more than five relevés. Sixty-eight fami- conducted in stands with varying size: 98 relevés in forests lies were identified within forests of Quercus robur,40 of Quercus robur,50inQ. petraea forests, and 41 in Q. with Q. pyrenaica but only 30 in Q. petraea forests. pyrenaica ones, with occurrence of hybrids in some cases. Families with the largest species number were: Poaceae The methodology of Braun-Blanquet school was followed (22), Fabaceae (19), Rosaceae (14), Apiaceae (13), Eri- (Braun-Blanquet 1979), so that each of present species was assigned a cover abundance index. The sampled area in caceae (11), Asteraceae (11), Lamiaceae (10), Liliaceae each stand was selected following the sampling minimum (8) and Scrophulariaceae (6). Figure 2 includes a com- area method (Muller-Dumbois & Ellemberg 1974). A min- parison of the most common families with data, from imum area of 100 m2 was used. Then, species were classi- the Iberian Peninsula NW, reported by other authors. fied according to Raunkiaer life form classes (Raunkiaer, The higher species richness occurred in Quercus robur, Deciduous and semi-deciduous oak forests 165

Table 1. Ecological status of the phytosociological associations presents in the study area.

Phytosociological association Ecological characteristics

Myrtillo-Quercetum roboris Present in the Galicia interior and the south, in zones with high continentality and Mediterranean inﬂuence. It is mainly developed on granites and schists in cambisol soils of average depth, locating in variable slopes with altitudes between 700–1300 m.

Rusco aculeati-Quercetum roboris Present in the west of Galicia, below the 550–600 m, in areas with a little period of summer drought. It developed on siliceous rocks that give rise to very acid oligotrophic soils.

Blechno spicanti-Quercetum roboris It is located in the north and east of Galicia and developed on granites, schists, quartzites, etc., that they give rise to deep and developed soils of type cambisol. Present in average slopes, increasing the stoniness with the altitude.

Linario triornithophorae-Quercetum petraeae These forests are located in eastern Galicia (Courel and Ancares), the moun- tainous area in the south of Asturias and the Leonese side of the Cantabrian Mountain with altitudes between 900–1400 m. They require a high environmental humidity and do not support the summer drought. It developed on siliceous rocks with acid soils and elevated OM %.

Luzulo henriquesii-Quercetum petraeae They are the typical ombrophilous oaks of high-mountain areas with altitudes > 1100 m and located in high slopes. They require a greater humidity than the previous association, and developed on cambisol soils.

Linario triornithophorae-Quercetum pyrenaicae Present in the Galician eastern mountain (Ancares and Courel) with altitudes between 600–1000 m and high precipitations (> 900 mm). They prefer zones of little slope with variable orientations. The soils are less acid and of variable depth from ranker to cambisols.

Holco molli-Quercetum pyrenaicae It is located in the east and the south of Ourense and in the Lugo southeastern on siliceous and limestone substrates that give rise to very diﬀerent soils. Present in variable slopes, in any exhibition with altitudes between 500–1300 m, in areas with an important Mediterranean inﬂuence and summer drought.

Genisto falcatae-Quercetum pyrenaicae Present in the valley of the Sil river, between 600–1200 m with a high Mediter- ranean inﬂuence. Topographically, it is similar to the previous association being developed also on variable substrates and types of soils.

with relevés that have more than 40 species. A maxi- Table 2. Taxa frequency, excluding oak species, present in more mumof52wereobtainedinamixedforestofQuercus than 40% of relevés. robur, Fagus sylvatica and Castanea sativa. Within the Number of occurrences Q. petraea and Q. pyrenaica forests, the largest species Most frequent taxa number per relevé was 15 and 20, respectively. Q. robur Q. petraea Q. pyrenaica The biological spectrum for all the relevés considered as a whole (Fig. 3) is dominated by hemicryp- Castanea sativa 62 0 17 tophytes, with 32%; followed by phanerophytes (26%) Sorbus aucuparia 0200 Corylus avellana 0250and chamaephytes (18%); therophytes account for 15%, Ilex aquifolium 56 35 0 although this life form corresponds more to the Eurosi- Pyrus cordata 00 20berian climate. The least common life forms were geo- Erica arborea 67 31 0 Rubus spp. 92 25 36 phytes (8%) and hydrophytes. If relevés are analyzed Ulex gallii 00 17separately for the three oaks (Fig. 3), the biological Vaccinium myrtillus 48 25 0 spectrum observed for forests of Quercus robur is very Pteridium aquilinum 83 35 37 similar to the spectrum of the relevés analyzed as a Blechnum spicant 47 0 0 Lonicera periclymenum 83 0 21 whole, and is dominated by hemicryptophytes (33%), Holcus mollis 62 20 0 followed by phanerophytes (27%), therophytes (16%), Teucrium scorodonia 77 0 21 chamaephytes (14%), geophytes (9%) and hydrophytes Asphodelus albus 00 20(1%). However, forests of Quercus petraea and Q. pyre- Hedera helix 82 0 20 Agrostis capillaris 00 36naica show a larger number of phanerophytes (38% and Polypodium vulgare 43 0 0 33%) than hemicryptophytes (24% and 22%, respec- Stellaria holostea 41 20 0 tively). Both forest types show a higher percentage of Arenaria montana 17 0 0 chamaephytes, and a lower percentage of therophytes and geophytes. 166 I. J. Díaz-Maroto & P. Vila-Lameiro

12 Silva-Pando, 1994 Buide et al., 1998 10 Amigo et al., 2001 Díaz Maroto et al., 2005

4 Percentage of sp. per family per sp. of Percentage

e e e e e e e e e a a a a a a a a a e e e e e e e e c c c ce c c c c c a a a a a la a ia a r o i b ili u s r i te P m a L c o la p s a F n R u A A L u h n p a o R cr S

Fig. 2. Botanical families in oak forests of the studied area according to diﬀerent authors.

Table 3. Number of species according to the number of relevés in dicator species and a minimum of fifteen relevés per which they occur. group, which resulted in six levels of dichotomous classification. As results, Simenthis planifolia, Melampyrum Number of relevés Number of species pratense, Asphodelus albus, Daboecia cantabrica, Cory- 191lus avellana, Quercus pyrenaica and Dactylis glomer- 242ata were considered as pseudo-species, characterized 336by their absence. The remaining pseudo-species de- 421 520fined according to presence (Fig. 5) were: Arenaria 6–10 46 montana and Viola riviniana (< 25%), Sorbus aucu- 11–20 38 paria and Pseudarrhenatherum longifolium (≤ 10%), 21–30 15 Lithodora postrata and Ruscus aculeatus (≥ 25%), 31–40 12 41–50 6 Daboecia cantabrica and Corylus avellana (any pres- 51–75 5 ence level), Quercus pyrenaica (≥ 10%), and Dactylis 76–100 4 glomerata (≥ 10%). Eleven final groups were obtained from dichotomous classification of the Quercus petraea relevés (Fig. 6). A maximum of four indicator species were con- The chorological spectrum (Fig. 4) shows that the sidered, with a minimum of eight relevés per group. largest groups observed in all the relevés considered as a Five levels of division were required. As in Quercus whole are: Atlantic (29%) and Sub-Atlantic (28%), fol- robur, several pseudo-species were characterized by the lowed by the Sub-Atlantic/Mediterranean (19%), Eu- absence (Fig. 6), like Pteridium aquilinum and Erica rosiberian (16%) and Mediterranean (8%). For sepa- arborea, Lonicera periclymenum and Fagus sylvatica, rate, Quercus robur and Q. petraea forests show a choro- Ilex aquifolium and Frangula alnus, Luzula sylvatica, logical spectrum with practically the same sequence as Deschampsia flexuosa, Erica arborea and Cytisus sco- observed in the forests as a whole, i.e., dominance of parius. In addition, the following species were defined Atlantic elements (32% in both cases), and low pres- as pseudo-species with several presence levels: Pyrus ence of Mediterranean (6% and 7%, respectively). In cordata (≤ 10%), Frangula alnus (10%), Corylus avel- forests of Quercus pyrenaica, Atlantic (35%) and Sub- lana (≥ 10%), Lonicera periclymenum and Fagus syl- Atlantic (29%) elements dominate, with more Mediter- vatica, Erica arborea and Cytisus scoparius (≥ 10%), ranean (12%) and Eurosiberian (6%). and Luzula sylvatica and Deschampsia flexuosa (10%). Figure 5 shows the final groups obtained by By applying TWINSPAN to Quercus pyrenaica TWINSPAN to the Quercus robur relevés. Eleven forests, fifteen final groups (Fig. 7) were obtained groups were obtained by using a maximum of two in- by using a maximum of three indicators species and Deciduous and semi-deciduous oak forests 167

Total inventarios Quercus pyrenaica

All surveys Quercus pyrenaica

1% 8% 1% 5% 9% 26% 15 % 33% Phanerophytes

Hemicryptophytes

Chamaephytes

30% 18 % Therophytes

Geophytes 32% 22%

Quercus robur Hydrophytes Quercus petraea Quercus robur Quercus petraea

1% 9% 7%

9% 27%

16% 38%

22%

14%

33% 24%

Fig. 3. Biological spectrum for all the species present in the relevés considered as a whole and considered separately according to forest type.

Total inventarios Quercus pyrenaica All surveys Quercus pyrenaica

8% 12 % Atlantic

29% 6% 16 % 35% Sub-Atlantic/Mediterranean

Sub-Atlantic

Eurosiberian

29% Mediterranean

28% 19 % 18 %

Quercus robur Quercus petraea Quercus robur Quercus petraea

6% 7%

12 % 17 % 32% 32%

23%

26%

19 % 26%

Fig. 4. Chorological spectrum for all the species present in the relevés considered as a whole and considered separately according to forest type. 168 I. J. Díaz-Maroto & P. Vila-Lameiro

A 9 samples Group 1

P < 2 4 samples Group 2

P 1 5 samples Group 3

Quercus pyrenaica A 11 samples Group 4

Simenthis planifolia Betula celtiberica Arenaria montana Cytisus striatus Viola riviniana Lithodora postrata Ruscus aculeatus

A 18 samples Group 5 Dactylis glomerata

P 1 6 samples Group 6 Vaccinium myrtillus Ilex aquifolium P 2 6 samples Group 7

P 1 6 samples Group 8

A 7 samples Group 9 Sorbus aucuparia Pseudorrenatherum longifolium

Daboecia cantabrica Melampyrum pratense Corylus avellana Asphodelus albus P > 0 14 samples Group 10

A 12 samples Group 11

Fig. 5. Groups and pseudo-species by TWINSPAN in Q. robur relevés (A – absence; P – presence).

P 1 5 samples Group I Holcus mollis Frangula alnus Stellaria holostea P > 0 5 samples Group II Lonicera periclymenum Fagus sylvatica Euphorbia dulcis Deschampsia flexuosa A 3 samples Group III Genisa florida ssp. polygaliphylla

P 1 4 samples Group IV Deschampsia flexuosa Pteridium aquilinum Luzula sylvatica Frangula alnus Cytisus scoparius Erica arborea A 7 samples Group V

Stellaria holostea Holcus mollis A Frangula alnus P = 1 1 sample Group VI 1 sample Group VII A 2 samples Group VIII Pteridium aquilinum P = 1 2 samples Group IX Ilex aquifolium Frangula alnus Deschampia flexuosa A 7 samples Group X Corylus avellana

Pteridium aquilinum Erica arborea

P 1 7 samples Group XI

A 6 samples Group XII

Fig. 6. Groups and pseudo-species by TWINSPAN in Q. petraea relevés (A – absence; P – presence). a minimum of five relevés per group, with six lev- Cytisus scoparius, Dactylis glomerata,andPyrus cor- els of classification. Like with the other two studied data. Other pseudo-species were defined according to species, pseudo-species characterized by their absence several presence levels: Quercus robur (≤ 10%), Pterid- appeared (Fig. 7): Arenaria montana, Castanea sativa, ium aquilinum and Castanea sativa (≥ 25%), Arenaria Deciduous and semi-deciduous oak forests 169

P 1 3 samples Group A

Quercus robur P = 1 3 samples Group B Castanea sativa

A 4 samples Group C

Rubus sp P = 1 1 sample Group D Erica arborea Arenaria montana Crataegus monogyna A Dactylus glomerata 3 samples Group E

Asphodelus albus P = 1 2 samples Group F Stellaria holostea Holcus mollis Cytisus striatus P 1 4 samples Group G

Hedera helix A 4 samples Group H Lonicera periclymenum Cytisus scoparius

P = 1 2 samples Group I

P 1 2 samples Group J

Pteridium aquilinum Frangula alnus Castanea sativa Pirus cordata A 4 samples Group K

Rosa canina Anemone nemorosa P 1 2 samples Group L

P 2 2 samples Group M

A Arenaria montana 4 samples Group N

P = 2 1 sample Group O

Fig. 7. Groups and pseudo-species by TWINSPAN in Q. pyrenaica relevés (A – absence; P – presence).

montana (25%), Castanea sativa (10%), Asphodelus al- Percentages of species per family practically co- bus (≥ 10%), Cytisus scoparius (10%), Frangula alnus incide with the data reported by Silva-Pando (1994), (≥ 10%), Crataegus monogyna (10%), Pyrus cordata Buide et al. (1998) and Amigo et al. (2001) for Poaceae (≥ 10%), and Dactylis glomerata (10%). and, to a lesser extent, for Liliaceae, Ranunculaceae and Rosaceae. However, the percentages obtained for Aster- Discussion aceae and Scrophulariaceae are lower and for Lamiaceae and Fabaceae are higher (Fig. 2). This pattern is similar The overall species number in the survey (Tables 2, 3) to that reported by Amigo et al. (2001). The number is higher than the number reported by Dantas (1958), of Apiaceae (13) and Ericaceae (11) species is higher very similar to the results by Díaz-Maroto (1997), and than reported by Silva-Pando (1994) and Buide et al. lower than reported by Amigo et al. (2001), since (1998). they suggest a total of 260 different species or sub- In general, the highest species richness is found species within the area of deciduous and semi-deciduous in the Galician montane bioclimatic belt oak forests, oaks in Galicia, but in their study, a higher num- located in zones with steep slopes where forests have ber of relevés were recorded. The most frequently oc- remained almost unaltered because environmental con- curring species (Table 2) were Rubus spp., Pteridium ditions have not allowed intensive forest exploitation aquilinum, Lonicera periclymenum, Hedera helix, Teu- (Díaz-Maroto et al. 2005, 2006). Regional endemics crium scorodonia, Agrostis capillaris, Ilex aquifolium, (Saxifraga spathularis, Eryngium duriaei), Quercus pe- Erica arborea, Corylus avellana and Vaccinium myr- traea and hybrid Quercus × rosacea Bechst were found tillus. This coincides closely with data reported by in these forests. Conversely, the lowest species richness Silva-Pando, (1994), Díaz-Maroto (1997) and Amigo occurs in stands of Quercus spp., highly altered by wood et al. (2001). Dantas (1958) suggested that the most extraction (Guitián Rivera 1995). An aspect of interest, frequent species were Erica arborea, Anemone trifo- well-known the floristic diversity, is to determine the lia ssp. albida and Pteridium aquilinum, while other area to conserve and the species number (Zacharias & species that occurred frequently were Rubus spp., Teu- Brandes 1990). In this sense, the effect of silviculture is crium scorodonia, Lonicera periclymenum and Hol- critical because thirty years without forest management cus mollis. With respect to the number of species are sufficient to change the forest floristic composition per relevé, results are similar to those obtained by (Aude & Lawesson 1998). Amigo et al. (2001), with 126 species. However, 91 Within the biological spectrum (Raunkiaer 1934), species occurred only in one relevé (Table 3), which the value for hemicryptophytes is lower than the is a higher value than the 62 species recorded by these value obtained by other authors, while it is higher for authors. phanerophytes (Fig. 3) (Silva-Pando 1994; Buide et al. 170 I. J. Díaz-Maroto & P. Vila-Lameiro

1998; Amigo et al. 2001). Similarities occur in geophytes 1987). The divisions that gave origin to the groups 1 and hydrophytes, with values that are close to those and 11 represent the most significant ones, estimated presented by Silva-Pando (1994), and lower than re- by the eigenvalue 0.24 and 0.26, respectively (Pisces ported by Buide et al. (1998) for Galician flora and Conservation LTD, 2004). This implicates the classifi- by Amigo et al. (2001). Therophytes are scarce be- cation of 21 samples that are most clearly located in cause most relevés were conducted in stands located in the TWINSPAN. A high eigenvalue was found at the the zones with Oceanic climate (Zacharias & Brandes level of the divisions of groups 2 and 3 (Fig. 5). How- 1990). With regard to the separate analyses of the three ever, the floristic diversity of these groups is not high, oak forests (Fig. 3), the values obtained for hemicryp- without any species with a 5 level (> 75%). tophytes are lower, while higher values were obtained In Quercus petraea forests, TWINSPAN has identi- for phanerophytes (Silva-Pando 1994; Buide et al. 1998; fied the following pseudo-species (Fig. 6): Fagus sylvat- Amigo et al. 2001). ica, Corylus avellana, Pyrus cordata, Frangula alnus, The chorological spectrum (Rivas-Martínez 1973) Cytisus scoparius, Erica arborea, Asphodelus albus, indicates that the Atlantic group was the largest one ob- Pteridium aquilinum, Lonicera periclymenum, Luzula served, with 29%, slightly higher than the percentage sylvatica and Deschampsia flexuosa. In addition, there obtained by Pinto Da Silva et al. (1950), Silva-Pando are others that define division levels, and not groups: (1994) and Amigo et al. (2001). The Eurosiberian (16%) Stellaria holostea and Holcus mollis. The frequency and Mediterranean (8%) elements are lower (Fig. 4). of Fagus sylvatica is very high in Quercus petraea However, Mediterranean elements in Quercus pyrenaica stands of Eastern Asturias, which can affect nega- forests are 12%, the same as reported by Silva-Pando tively the oak regeneration (Fernández & Vázquez (1994), similar to those calculated by Amigo et al. 1985). These forests belong to the association Linario (2001) and higher than obtained by Pinto Da Silva et al. triornithophorae-Quercetum petraeae,whereCorylus (1950), revealing their mesophile nature (Kanka 2001). avellana, Frangula alnus, Cytisus scoparius, Erica ar- Some of the pseudo-species that occur in Quer- borea, etc., are also characteristic in montane biocli- cus robur forests (Fig. 5) coincide with those listed matic series of sessile oak, present in the most eastern by Díaz-Maroto (1997): Q. pyrenaica, Ruscus aculea- zone of study area, with altitudes between 900–1400 m, tus, Daboecia cantabrica and Melampyrum pratense. high environmental humidity and absence of the sum- The other pseudo-species (Fig. 5) are Sorbus aucu- mer drought (Díaz & Fernández 1994) (Table 1). This paria, Corylus avellana, Asphodelus albus, Pseudar- analysis allows assigning this vegetation series to I, II, rhenatherum longifolium, Dactylis glomerata, Simen- IV and XI groups (Fig. 6). this planifolia, Lithodora postrata, Arenaria montana Luzula sylvatica is common in Sierra de Ancares and Viola riviniana. The presence of Quercus pyrenaica forests (Lugo-León), which are mixed oak forests with characterizes certain forests where both oak species large floristic diversity (Silva-Pando 1994). This species overlap, galician-portuguese coline acidophilous oak- is associated to orocantabric montane acidophilous se- lands stretching along a wide zone where they form ries of Quercus petraea, Luzulo henriquesii-Quercetum mixed forests and hybridize easily, giving rise to Quer- petraeae, ombrophilous oak forests of high-mountain cus × andegavensis Hy (Kanka 2001; Díaz-Maroto & with altitudes > 1100 m (Díaz & Fernández 1994) (Ta- Vila-Lameiro 2006). Ruscus aculeatus is the species in- ble 1). The presence of other index species of this asso- dex in this forests (Rusco aculeati-Quercetum roboris), ciation in the rest of relevés (i.e., Genista polygalihylla, located in the Atlantic zone of the study area, be- Erica arborea, Daboecia cantabrica, etc.) allows group- low 550–600 m, in areas with high precipitation (Izco ing them in this vegetation series (Buide et al. 1998; et al. 1990) (Table 1). Other pseudo-species (Sor- Rivas-Martínez et al. 2001). bus aucuparia and Corylus avellana) are present in TWINSPAN dendrogram in sessile oak (Fig. 6) is mid-mountain or high-mountain zones (Fig. 5), next less informative than with pedunculate oak. There is to Q. petraea and Quercus × rosacea Bechst (Fer- no significant difference between the floristic diversity nández & Vázquez 1985). These forests correspond and the dendrogram location of each sample. In fact, to galician-orocantabric coline-montane acidophilous the most significant divisions (higher eigenvalue) mean oaklands, Blechno spicanti-Quercetum roboris (Rivas- the classification of the groups VIII, IX and X, the last Martínez 1987), present in zones of complicated topog- ones in the extraction process by TWINSPAN and the raphy (Table 1). most clearly located. The TWINSPAN dendrogram (Fig. 5) showed At group level, the pseudo-species for Quercus that, the extreme groups (i.e., groups 1 and 11) re- pyrenaica (Fig. 7) are Q. robur, Castanea sativa, veal some common characteristics. The relevés of these Pyrus cordata, Frangula alnus, Crataegus monogyna, groups are located in the higher portion of the clas- Cytisus scoparius, Asphodelus albus, Pteridium aquil- sification and, all of them have at least one species inum, Dactylis glomerata and Arenaria montana,and with abundance equal to 5. The pseudo-species in these at division level Erica arborea, Rubus spp., Rosa can- groups are: Simenthis planifolia, Arenaria montana, Vi- ina, Hedera helix, Lonicera periclymenum and Anemone ola riviniana, Melampyrum pratensis and Asphodellus nemorosa. In some samples (specifically of the groups albus, all of them present in the floristic composition A, I and M), the following species are present: Quer- of Rusco aculeati-Quercetum roboris (Rivas-Martínez cus pyrenaica with Q. robur, Holcus mollis and Cytisus Deciduous and semi-deciduous oak forests 171 scoparius, index species of the orocantabric mon- factors, evaluated by variation partitioning. Plant Ecol. 134: tane acidophilous series of Q. pyrenaica: Linario 53–65. triornithophorae-Quercetum pyrenaicae,presentinthe Braun-Blanquet J. 1979. Fitosociología. Base para el estudio de las comunidades vegetales. Blume. Galician eastern mountain with altitudes between 600– Buide M.L., Sánchez J.M. & Guitián J. 1998. Ecological charac- 1000 m (Díaz-Maroto et al. 2006) (Table 1). teristics of the flora of the Northwest Iberian Peninsula. Plant Castanea sativa is the most outstanding indica- Ecol. 135: 1–8. tor species because its presence is important in many Carvalho J. (coord.) 2005. O Carvalho Negral. UTAD. Vila Real, Portugal. Quercus pyrenaica forests, located in the most south- Dantas R.R. 1958. Os carvalhais da Serra da Peneda. Estudo eastern zone of study area with important Mediter- fitosociológico. Agr. Lus. 20: 83–153. ranean influence on siliceous and limestone substrates DGCONA, 2001. Tercer Inventario Forestal Nacional. Galicia. (Carvalho et al. 2005) and, where the supramediter- Ministerio de Medio Ambiente. DGCONA, 2003. Tercer Inventario Forestal Nacional. Principado ranean carpetanian-iberian subhumid siliceous series of de Asturias. Ministeris de Medio Ambiente. Q. pyrenaica (Table 1), Holco molli-Quercetum pyre- Díaz T.E. & Fernández J.A. 1994. La vegetación de Asturias. naicae (Rivas-Martínez et al. 2001) is present. This Itinera Geobotanica 8: 243–528. series includes other index species present in the ma- Díaz-Maroto I.J. 1997. Estudio ecológico y dasométrico de las jority of relevés like Holcus mollis, Omphalodes nitida masas de carballo (Quercus robur L.) en el noroeste de la Península Ibérica. PhD Thesis. Polytechnic University of and Cytisus scoparius. In general, the number of sam- Madrid. ples within a group in Quercus pyrenaica is lower than Díaz-Maroto I.J., Vila-Lameiro P. & Silva-Pando F.J. 2005. Aute- within Q. robur and Q. petraea,withamaximumof cology of oaks (Quercus robur L.) in Galicia (Spain). Ann. Sci. 62: four samples (Fig. 7). The TWINSPAN dendrogram is For. 737–749. Díaz-Maroto I.J. & Vila-Lameiro P. 2006. Analysis of the dis- not especially significant, with results similar to those tribution of Quercus robur L. in Galicia, Spain. Ekológia, obtained for sessile oak. The eigenvalues are the highest Bratislava 25: 234–251. among the three oak species, with a maximum of 0.47. Díaz-Maroto I.J., Fernández-Parajes J. & Vila-Lameiro P. 2006. The most relevant conclusion that can be drawn Autecology of rebollo oak (Quercus pyrenaica Willd.) in Gali- cia (Spain). Ann. For. Sci. 63: 157–167. from this analysis of oak forests distribution in the Fernández J.A. & Vázquez V. 1985. Datos sobre los bosques as- Northwest Iberian Peninsula according to the presence turianos orocantábricos occidentales. Lazaroa 7: 363–382. or absence of certain floristic species is that, in agree- Fernández-Alaez C., Fernández-Alaez M. & García-Criado F. ment with other authors (Aude & Lawesson 1998; Acar 2005. Spatial distribution pattern of the riparian vegetation in a basin in the NW Spain. Plant Ecol. 179: 31–42. et al. 2004), the results confirm the need to describe a Graae B.J. & Sunde P.B. 2000. The impact of forest continu- larger number of relevés, avoiding zones in which the ity and management on forest floor vegetation evaluated by ground cover is altered due to grazing or other causes species traits. Ecography 23: 720–731. of anthropogenic nature. In addition, the study must be Guitián Rivera L. 1995. Origen y evolución de la cubierta forestal de Galicia. PhD Thesis. University of Santiago. limited to a scale that is smaller than the oak species Hill M.O. 1979. TWINSPAN: A fortran program for arranging area, for instance, the phytosociological association, or multivariate data in an ordered two-way table by classifica- even limited to a given mountain range or river basin tion of the individuals and attributes. Cornell Univ., New (Fernández-Alaez et al. 2005), trying to obtain a larger York. homogeneity of environmental conditions, because the Izco J., Amigo J. & Guitián J. 1990. Los robledales galaico- septentrionales. Act. Bot. Mal. 15: 267–276. study area represents a transition zone between Eu- Jongman R.H.G., ter Braak C.J.F. & Van Tongeren, O.F.R. 1995. rosiberian and Mediterranean regions (Rivas-Martínez Data analysis in Community and Landscape Ecology. Cam- 1987). bridge University Press. Kanka R. 2001. Phytocoenological characteristics of the ther- mophilous oak forests with Quercus pubescens in the Male Acknowledgements Karpaty Mts, Slovakia. Biologia 56: 85–101. Muller-Dombois D. & Ellenberg H. 1974. Aims and methods of This work was funded by the “Dirección Xeral de Inves- vegetation ecology. Willey Press. Peterken G.F. & Game M. 1984. Historical factors affecting tigación e Desenvolvemento da Xunta de Galicia”, within the number and distribution of vascular plant-species in the the framework of research projects PGIDT99MA29101 and woodlands of Central Lincolnshire. J. Ecol. 72: 155–182. PGIDIT02RFO29101PR, developed in the Department of Pinto Da Silva A.R., Rozeira A. & Fontes F. 1950. Os carval- Agroforestry Engineering of the University of Santiago de hais da Serra do Gerês. Esbo¸co Fitosociológico. Agronomia Compostela. Lusitana 12: 433–448. Pisces Conservation LTD, 2004. Community analysis package version 3.0. A program to search for structure in ecological References community data. England. Raunkiaer C. 1934. The life forms of plants and statistical plant Acar C., Acar H. & Altun L. 2004. The diversity of ground geography. Clarendon Press, Oxford. cover species in rocky, roadside and forest habitats in Tra- Rivas-Martínez S. 1973. Avances sobre una síntesis corológica de bzon (North-Eastern Turkey). Biologia 59: 477–491. la Península Ibérica, Baleares y Canarias. Anales del Instituto Amigo J., Silva-Pando F.J., González M.P., Rozados M.J., Rois Botánico A.J. Cavanilles Tomo XXX: 60–87. M. & Díaz-Maroto I.J. 2001. Diversidad florística en rob- Rivas-Martínez S. 1987. Memoria y mapas de series de vegetación ledales atlánticos del Noroeste de la Península Ibérica. Ponen- de España. 1:400.000. ICONA. cias y comunicaciones III Congreso Forestal Español, Mesa 7, Rivas-Martínez S., Fernández F., Loidi J., LousãM.&Penas Tomo IV: 169–175. A. 2001. Syntaxonomical checklist of vascular plants com- Aude E. & Lawesson J.E. 1998. Vegetation in Danish beech munities of Spain and Portugal to association level. Itinera forests: the importance of soil, microclimate and management Geobotanica 14: 5–341. 172 I. J. Díaz-Maroto & P. Vila-Lameiro

Silva-Pando F.J. 1994. Flora y series de vegetación de la Sierra Zacharias D. & Brandes D. 1990. Species area-relationships and de Ancares. Fontqueria 40: 233–388. frequency-floristical data analysis of 44 isolated woods in Vermeersch S., De Genst W., Vermoesen F. & Triest L. 2003. The northwestern Germany. Vegetatio 88: 21–29. influence of transformation of an ordinal scale of a floristic gradient, applied of a TWINSPAN classification. Flora 198: Received March 10, 2006 389–403. Accepted Jan. 15, 2007