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Phylogeographic studies have repeatedly identified the southern European peninsulas (Iberian, Italian and Balkanic) as major refuges for the flora during Pleistocene glacial events. Due to the succession of cold and warm periods, a large number of frost—sensitive species became extinct or confined to isolated positions in the southern peninsulas, where specific physical conditions working at a local scale enabled the persistence of those frost-sensitive, relict species. The global purpose of this paper is to address the ecology and diversity of relict laurel—leaved scrublands in mainland Portugal (Southwest Europe), where geographic segregation gave rise to a floristic diversification of community types. These biogeographically isolated scrublands configure seven distinct associations, which are recognisable from both classical and numerical phyto- sociological approaches. The conservation of relict laurel—leaved scrublands in the territory is also assessed in the framework of the EEC “Habitats” Directive.
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Ecology, diversity and conservation
of relict laurel—leaved mesophytic
scrublands in mainland Portugal
João Honrado
a
b
, Paulo Alves
a
, Ângela Lomba
a
, João Torres
a
& Francisco Barreto Caldas
a
b
a
CIBIO—Centro de investigação em biodiversidade e recursos
genéticos , Universidade do Porto , Rua do Campo Alegre,
1191, P-4150-181 , Porto E-mail:
b
Faculdade de Ciências , Universidade do Porto , Rua do
Campo Alegre 1191, P-4150-181 , Porto
Published online: 26 Apr 2013.
To cite this article: João Honrado , Paulo Alves , Ângela Lomba , João Torres & Francisco
Barreto Caldas (2007) Ecology, diversity and conservation of relict laurel—leaved
mesophytic scrublands in mainland Portugal, Acta Botanica Gallica, 154:1, 63-77, DOI:
10.1080/12538078.2007.10516045
To link to this article: http://dx.doi.org/10.1080/12538078.2007.10516045
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Acta Bot. Gallica, 2007, 154 (1), 63-77.
Ecology, diversity and conservation of relict laurel-leaved mesophytic
scrublands in mainland Portugal
by João Honrado(
1,2
), Paulo Alves(
1
), Ângela Lomba(
1
), João Torres(
1
) and Francisco
Barreto Caldas(
1,2
)
(1) CIBIO - Centro de investigação em biodiversidade e recursos genéticos, Universidade do Porto
Rua do Campo Alegre, 1191, P-4150-181 Porto ; jhonrado@fc.up.pt
(2) Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 1191, P-4150-181 Porto
Abstract.- Phylogeographic studies have repeatedly identified the southern
European peninsulas (Iberian, Italian and Balkanic) as major refuges for the flora
during Pleistocene glacial events. Due to the succession of cold and warm per-
iods, a large number of frost-sensitive species became extinct or confined to iso-
lated positions in the southern peninsulas, where specific physical conditions
working at a local scale enabled the persistence of those frost-sensitive, relict
species. The global purpose of this paper is to address the ecology and diversi-
ty of relict laurel-leaved scrublands in mainland Portugal (Southwest Europe),
where geographic segregation gave rise to a floristic diversification of communi-
ty types. These biogeographically isolated scrublands configure seven distinct
associations, which are recognisable from both classical and numerical phyto-
sociological approaches. The conservation of relict laurel-leaved scrublands in
the territory is also assessed in the framework of the EEC “Habitats” Directive.
Key words : conservation - diversity - phytosociology - Portugal - relict vegeta-
tion.
Résumé.- Des études phylogéographiques ont souvent identifié les péninsules
européenes du Sud (ibérique, italienne et balkanique) comme d’importants
refuges pour la flore pendant les épisodes glacièrs du Pléistocène. À cause de
cette succession de périodes chaudes et froides, un grand nombre d’espèces
sensibles au froid extrême se sont éteintes ou confinées à des sites isolés dans
ces péninsules méridionales, les conditions physiques particulières ont per-
mis la persistence de ces espèces relictuelles. L´objectif de ce travail est la des-
cription de l’écologie et la diversité des formations arbustives laurifoliées
relictuelles au Portugal continental (sud-ouest de l’Europe), l’isolement géo-
graphique des populations a donné lieu à une diversification floristique des types
de communautés. Ces groupes de populations biogéographiquement séparées
définissent sept associations végétales, reconnues par des analyses phytoso-
ciologiques classiques et numériques. La conservation de ces formations arbus-
tives relictuelles dans le territoire est aussi discutée dans le contexte de la
Directive “Habitats”.
Mots clés : conservation - diversité - phytosociologie - Portugal - végétation
relictuelle.
arrivé le 30 novembre 2005, accepté le 14 avril 2006
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I. INTRODUCTION
Climate (both past and current) is generally considered the main factor determining the
distribution of plant species and communities, so that, in the absence of significant anthro-
pic disturbance, vegetation in a given biogeographical context mainly depends on climate
conditions, even in areas where substrate properties induce local variations (Comes &
Kadereit, 1998; Honrado et al., 2001).
Many studies concerning Quaternary palaeoecology in Europe have established the
occurrence of southward contractions of distribution ranges of plant species during
Pleistocene cold periods glaciations »), followed by rapid northward expansions at the
end of each cold period (Bennet et al., 1991; Ferris et al., 1993, 1995, 1998; Axelrod,
1996; Dumolin-Lapègue et al., 1997). This succession of cold and warm periods caused a
significant redistribution of the flora (Muñoz et al., 1996; Ramil-Rego et al., 1996). A large
number of mesophilic and thermophilic species became extinct or confined, within
Europe, to rather isolated positions in southern territories (mostly the current
Mediterranean Region). Plant families that were diverse and widespread (e.g. Palmaceae,
Lauraceae, Myrtaceae) became represented in Europe by few, narrowly distributed taxa
(sometimes only one taxon). Phylogeographic studies using both palinological and mole-
cular data (e.g. Bennet et al., 1991; Ferris et al., 1993, 1995, 1998; Dumolin-Lapègue et
al., 1997) have repeatedly identified the southern peninsulas (Iberian, Italian and Balkanic)
as major refuges for the flora during glacial periods.
Depending on their rapidity and intensity, climate changes can give rise to events that
range from genetic bottlenecks to local, regional or global extinction of taxa. However,
specific physical conditions working at a local scale, such as those that can be found in
rocky cliffs, along water courses or on special types of rock, can enable the persistence of
species in territories where macro-mesoclimate conditions are no longer appropriate for
their occurrence. If these species are common extant taxa elsewhere, they are called cli-
matic disjunctions (Pielou, 1992), but if their distribution is nowadays very restricted, they
are known as climatic relicts (Cox & Moore, 1993; Honrado et al., 2001). The same clas-
sification can obviously be applied to vegetation types.
Within this context, the global purpose of this paper is to address the ecology and diver-
sity of relict laurel-leaved scrublands in mainland Portugal (Western Iberian Peninsula,
Southwest Europe). Only relict vegetation types were addressed since, as will be descri-
bed, they raise specific questions regarding their persistence in the territory. A classical
phytosociological approach is complemented with numerical analyses of 56 relevés.
Moreover, two new, still unreported, endemic vegetation types are described, and the
conservation of relict laurel-leaved scrublands in the territory is assessed in the framework
of the EEC « Habitats » Directive.
II. METHODS
A. Study area
The study area (mainland Portugal) includes the westernmost areas of the Iberian
Peninsula, in Southwest Europe (Fig. 1).
Previous studies have shown that climate and lithology play a major role in the distri-
bution of vegetation types in Mainland Portugal (e.g. Costa et al., 1998), so the major cli-
matic and lithologic features of the country are indicated in Figure 2. It is a climatically
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oceanic territory, with mild temperatures both in summer and in winter, increasingly war-
mer southwards; winter frost is rare, except in interior mountains. In the north-western part
of the territory, where many of the mountain areas are located, there is heavy rainfall and
a small dry period in summer, so the climate is generally of the Temperate type (Rivas-
Martínez et al., 2002). In Central-western and South-western Portugal, there is less rain-
fall and the dry summer period ranges from three to five months (Mediterranean climate).
Lithology ranges from acid rocks (granites and schist) in the Northwest and most of the
interior areas to limestone and sedimentary substrates in the central-western and south-
western parts of the country.
B. Phytosociology and phytogeography
Vegetation types were studied according to the concepts and methods of Braun-
Blanquet’s phytosociology (Géhu & Rivas-Martínez, 1981; Rivas-Martínez, 2002). In
short, phytosociological relevés were performed in representative formations with widely
repeatable (i.e. stable) physiognomy, ecology and floristic composition. Relevés were later
surveyed for similarity and classified within the syntaxonomic scheme of Rivas-Martínez
et al. (2001).
Phytosociological data regarding relict laurel-leaved scrublands in mainland Portugal
(56 relevés) were collected from the following sources: Capelo & Mesquita (1998) for
Myrico fayae-Arbutetum unedonis (6 relevés), Costa et al. (2000) for Frangulo alni-
Prunetum lusitanicae (19) and Vinco difformis-Lauretum nobilis (10), Honrado (2003) for
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Fig. 1. The study area (mainland Portugal) within an European context.
Fig. 1.- L’aire d’étude (Portugal continental) dans le contexte européen.
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a
b
c
d
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Luzulo henriquesii-Prunetum lusitanicae (5) and Pruno lusitanicae-Arbutetum unedonis
(4) and Honrado et al. (2004) for Omphalodo nitidae-Lauretum nobilis (6). From the six
relevés of Calluno vulgaris-Rhododendretum baetici, two were collected from Braun-
Blanquet et al. (1956) and the other four are original relevés reported here for the first time.
The nomenclature of plant taxa is mostly according to standard Iberian floras
(Castroviejo et al. (1986-2003) for published volumes, Franco (1971, 1984) and Franco &
Afonso (1994, 1998, 2003) for other groups). Bioclimatic indices and typologies and phy-
togeographic units are those of Rivas-Martínez et al. (2002).
C. Numerical analyses
In order to perform statistical analyses (cluster analysis and ordination), a global data
matrix was constructed from the 56 available relevés.
Cluster analysis consists in grouping the vegetation samples into classes, based on their
attributes (Kent & Coker, 1992). Hierarchical cluster analysis has been referred as a sui-
table approach in the analysis of plant communities, allowing the grouping of phytosocio-
logical relevés based on their floristic composition (Capelo, 2003). In this research a
hierarchical cluster analysis was performed with the Community Analysis Package 3.1
®
(Pisces Conservation) software. Relevés were grouped according to Ward’s method using
Euclidean distance.
Ordination techniques are considered to be complementary to cluster analysis.
Specifically, indirect ordination techniques consist in the arrangement of vegetation
samples according to their similarity in terms of floristic composition (Kent & Coker,
1992). Ordination analyses were performed with Canoco 4.5
®
for Windows (Ter Braak &
Smilauer, 2002). A detrended correspondence analysis (DCA) was first performed to deter-
mine the length of the gradient within the dataset. Given the length of the gradient, a uni-
modal response was assumed and therefore a correspondence analysis (CA) (Ter Braak &
Smilauer, 2002; Van Den Brink et al., 2003) was performed.
III. RESULTS AND DISCUSSION
A. Relict laurel-leaved mesophytic species in mainland Portugal
In mainland Portugal, two major floristic elements come together. The territory is the
south-westernmost area for many eurosiberian temperate species, which predominate in
mountain areas and in lowland areas of the Northwest with high annual rainfall. The
Fig. 2.- Main climatic (a-c) and lithologic (d) features of mainland Portugal. Maps a to c were
obtained by kriging interpolation of the following bioclimatic indices: a, thermicity index: It
= 10(T+M+m), where T is the mean annual temperature, and M and m are, respectively,
the mean maximum and mean minimum temperatures of the coldest month of the year;
b, continentality index: Ic = T
max
-T
min
, where T
max
and T
min
are the mean temperatures
of the hottest and coldest months, respectively; c, annual ombrothermic index: Io =
Pp/Tp, where Pp and Tp are the sums of, respectively, the total rainfall and the mean tem-
perature of all months with positive mean temperature. Map d is a simplification of the
lithologic map of mainland Portugal available at the site of the Portuguese Institute of
Environment (www.iambiente.pt/).
Fig. 2.- Données climatiques (a-c) et lithologiques (d) pour le Portugal continental.
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Mediterranean element predominates in the central, southern and north-eastern parts of the
country and in lowland areas of the Northwest with at least two dry months in summer.
The vast majority of tropical and subtropical Tertiary vegetation was eliminated from
the territory by Pleistocene glaciations (Honrado et al., 2001). However, several kinds of
evidence suggest that some forest remains could have survived Pleistocene glaciations in
topographically sheltered valleys of Western Iberian Peninsula (Coudé-Gaussen, 1981).
The presence of these woodland environments would have provided shelter for Tertiary
(sub)tropical flora, allowing the persistence of the isolated populations we can nowadays
find in the flora of mainland Portugal.
The mild temperatures and abundant (though seasonal) rainfall that characterise the cur-
rent climate of North and Central Portugal favour the regular occurrence of those relict
(sub)tropical taxa. Among the climatic relicts that can be found in the territory, three are to
be highlighted since they are usually dominant elements in relict laurel-leaved scrublands:
the Common-laurel (Laurus nobilis), the Portuguese-laurel (Prunus lusitanica subsp. lusi-
tanica) and the west-mediterranean subspecies of Pontic-rhododendron (Rhododendron
ponticum subsp. baeticum). There are, however, several other relict mesophytic taxa that
regularly occur in these laurel-leaved formations, like Dryopteris guanchica, Smilax aspe-
ra, Woodwardia radicans, etc. There is still another group of laurel-leaved taxa which
became adapted to (sub)mediterranean climate conditions and cannot, therefore, be consi-
dered true relicts: Arbutus unedo, Myrtus communis, Phillyrea latifolia, Rubia peregrina
subsp. longifolia, Viburnum tinus subsp. tinus, Vinca difformis and others.
Laurus nobilis, Prunus lusitanica subsp. lusitanica and Rhododendron ponticum subsp.
baeticum are usually dominant in permanent relict formations, occupying either shaded
sites on steep slopes or biotopes with seasonal disturbance by running water, generally in
sheltered positions in valleys. The Strawberry-tree (Arbutus unedo) is a frequent dominant
in mesophytic low scrublands that replace disturbed climactic woodlands under (sub)medi-
terranean climate; these formations are not includable in the concept of « relict vegeta-
tion » used here, since they are at an equilibrium with current mesoclimatic conditions.
However, in the Gerês mountain range, a heavily rainy territory in Northwestern Portugal,
there are highly resilient arborescent scrublands dominated by Arbutus unedo and with
regular occurrence of Prunus lusitanica subsp. lusitanica (Honrado, 2003) that were inclu-
ded in this study; arborescent Arbutus scrublands which are considered a relict climax on
central-western palaeodunes (Capelo & Mesquita, 1998) were also included.
B. Laurel-leaved vegetation types in mainland Portugal
1. Classical and numerical syntaxonomy
Seven phytosociological associations of relict laurel-leaved scrublands are recognised
in mainland Portugal from a classical phytosociological approach (see Syntaxonomical
checklist), two of which (Luzulo henriquesii-Prunetum lusitanicae and Calluno vulgaris-
Rhododendretum baetici) are reported here for the first time. All seven associations are
included in alliance Arbuto unedonis-Laurion nobilis (Rivas-Martínez et al., 2001).
According to the predominant species, four groups of scrubland types are recognisable
(see description below): i) Laurus nobilis scrublands (in Portuguese: louriçais):
Omphalodo nitidae-Lauretum nobilis and Vinco difformis-Lauretum nobilis; ii) Prunus
lusitanica galleries (azerais): Frangulo alni-Prunetum lusitanicae and Luzulo henriquesii-
Prunetum lusitanicae; iii) Arbutus unedo arborescent scrublands (medronhais): Pruno
lusitanicae-Arbutetum unedonis and Myrico fayae-Arbutetum unedonis; and iv)
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Rhododendron ponticum subsp. baeticum galleries (adelfeirais): Calluno vulgaris-
Rhododendretum baetici.
Numerical analyses (both ordination and cluster analysis) of the total set of relevés were
performed to assess the validity of both new and previously reported associations (Fig. 3
and 4).
The CA ordination diagram (Fig. 3) discriminates three major groups of relevés: i) the
six species-poor Calluno vulgaris-Rhododendretum baetici relevés; ii) the 16 relevés of the
central-western basophilous Laurus nobilis (Vinco difformis-Lauretum nobilis) and
Arbutus unedo (Myrico fayae-Arbutetum unedonis) scrublands, with the latter in an inter-
mediate position regarding the third group; and iii) the relevés of the four species-rich aci-
dophilous associations (Frangulo alni-Prunetum lusitanicae, Luzulo
henriquesii-Prunetum lusitanicae, Omphalodo nitidae-Lauretum nobilis and Pruno lusita-
nicae-Arbutetum unedonis). Within this group, relevés of each of the four associations tend
to form discrete (though closely related) groups.
In the dendrogram of Figure 4, the relevés of the seven associations are clearly discri-
minated, demonstrating the statistical validity of results from the classical phytosociologi-
cal approach at the association level. At the first dichotomy, cluster analysis segregates the
central-western basophilous Myrico fayae-Arbutetum unedonis and Vinco difformis-
Lauretum nobilis from the five acidophilous associations. Within this group, relevés of the
species-poor Calluno vulgaris-Rhododendretum baetici are separated from a group com-
posed of the species-rich acidophilous scrublands dominated by Laurus nobilis, Arbutus
unedo and Prunus lusitanica subsp. lusitanica. Mediterranean Prunus lusitanica subsp.
lusitanica formations (Frangulo alni-Arbutetum unedonis) are then segregated from the
Fig. 3.- CA ordination dia-
gram for the total set of
reles. (CALROD =
Calluno vulgaris-
Rhododendretum baetici,
FRAPRU = Frangulo alni-
Prunetum lusitanicae,
LUZPRU = Luzulo henri-
quesii-Prunetum lusitani-
cae, MYRARB = Myrico
fayae-Arbutetum unedo-
nis, OMPLAU =
Omphalodo nitidae-
Lauretum nobilis,
PRUARB = Pruno lusitani-
cae-Arbutetum unedonis,
VINLAU = Vinco unedo-
nis-Lauretum nobilis).
Fig. 3.- Diagramme CA pour
l’ensemble des relevés.
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three temperate associations of the Northwest. Finally, thermotemperate Laurus nobilis
scrublands are separated from mesotemperate formations with Prunus lusitanica subsp.
lusitanica (both Arbutus and Prunus-dominated scrublands).
These results stress the importance of both climate and lithology in determining the flo-
ristic composition of relict laurel-leaved scrublands in the territory. In fact, laurel-leaved
vegetation tends to occur in areas with (highly) oceanic and moderate to heavily rainy cli-
mate in the north-western and central-western areas of Portugal, on soils derived from
limestone, sand or acid rocks (Fig. 2 and 5).
2. Description of vegetation types (associations)
Laurus nobilis scrublands
Tall scrublands dominated by the Common-laurel, typical of the north-western and cen-
tral-western parts of the territory. They usually occupy sheltered positions in the edge of
both Quercus robur or Q. faginea subsp. broteroi forests. Two associations are recognised
in the territory:
- Omphalodo nitidae-Lauretum nobilis, silicicolous laurel-thickets rich in temperate taxa
(Hedera hibernica, Omphalodes nitida, Saxifraga spathularis) occurring along rocky
margins of seasonal rivulets within forest landscapes dominated by Quercus robur
(Honrado et al., 2004);
- Vinco difformis-Lauretum nobilis, calcicolous laurel-thickets with abundant thermo-
philous taxa (Viburnum tinus subsp. tinus, Pistacia lentiscus, Rosa sempervirens,
Fig. 4.- Cluster diagram for the total set of relevés (see Fig. 3 for abbreviations).
Fig. 4.- Dendrogramme sur l’ensemble des relevés.
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Lonicera etrusca), colonising moist lime-
rich soils with seasonally flowing waters
within forest landscapes dominated by
Quercus faginea subsp. broteroi (Costa et
al., 2000).
Prunus lusitanica subsp. lusitanica scru-
blands
Tall scrublands dominated by Prunus
lusitanica subsp. lusitanica, occurring in
small areas in the north-western and central
parts of the territory, always on siliceous
soils. These formations occupy sheltered
positions in the bottom of deep valleys near-
by seasonally running water within forest
landscapes dominated by Quercus robur.
Two associations are recognised in the terri-
tory:
- Frangulo alni-Prunetum lusitanicae,
silicicolous mediterranean Prunus lusita-
nica subsp. lusitanica galleries with abun-
dant thermophilous laurel-leaved shrubs
(e.g. Viburnum tinus subsp. tinus) and
vines (e.g. Rubia peregrina), colonising
river beds with seasonally flowing waters
(Costa et al., 2000);
- Luzulo henriquesii-Prunetum lusitani-
cae ass. nova hoc loco (syntype: Table I,
relevé n. 4), silicicolous temperate Prunus
lusitanica subsp. lusitanica galleries, rich in temperate nemoral taxa (Ilex aquifolium,
Saxifraga spathularis, Luzula sylvatica subsp. henriquesii) typical of rocky river beds
with seasonally flowing waters (Honrado, 2003).
Arbutus unedo arborescent scrublands
Dense arborescent scrublands dominated by the Strawberry-tree, occurring in small
areas of the north-western and central-western parts of the territory, on either siliceous
soils or palaeodunes. Two associations are recognised in the territory:
- Pruno lusitanicae-Arbutetum unedonis, relict silicicolous Strawberry-tree formations,
occurring in the north-western areas of the territory (Costa et al., 2000; Honrado, 2003);
these formations are very stable in time and are dominated by arborescent specimens of
Arbutus unedo, colonising shaded slopes in deep valleys with frequent mist, within
forest landscapes dominated by Quercus robur;
- Myrico fayae-Arbutetum unedonis, relict arborescent Strawberry-tree formations,
occurring on litter-rich soils of palaeodunes in the coastal areas of the central-western
part of the territory; they are usually dominated by Arbutus unedo, Myrica faya and
Laurus nobilis (Capelo & Mesquita 1998).
Fig. 5.- Geographic location of the sites
where the 56 relevés were collected (com-
pare with the climatic and lithologic maps
of Fig. 2).
Fig. 5.- Localisation géographique des sites
où les 56 relevés furent effectués.
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Rhododendron ponticum subsp. baeticum mesophytic scrublands
Calluno vulgaris-Rhododendretum baetici ass. nova hoc loco (syntype: Table II, relevé
n. 6), temperate silicicolous low scrublands, absolutely dominated by Rhododendron pon-
ticum subsp. baeticum, occurring in a very restricted area of Northwest Portugal and colo-
nising the heads of small river beds with seasonally flowing waters. This is the most
narrowly distributed of all seven associations, with most formations located within the
Cambarinho botanical Reserve (Vouzela, Northwest Portugal). Both climatic changes and
human disturbance history are believed to be responsible for this narrow distribution.
Table I, Tableau I.- Luzulo henriquesii-Prunetum
lusitanicae ass. nova.
R
elevé n. 123 4 5
A
ltitude (m) 620 650 710 630 570
N
. of taxa 16 19 25 29 37
Characteristic taxa
Prunus lusitanica subsp. lusitanica 455 4 4
Erica arborea 12 1 2
R
uscus aculeatus 1+ 1 +
A
rbutus unedo 11
Rubia peregrina 1
D
ifferential taxa
D
ryopteris affinis subsp. borreri 111 1 1
Ilex aquifolium 211 1 1
Saxifraga spathularis 212 1 1
Luzula sylvatica subsp. henriquesii 211
Omphalodes nitida 11+
Pyrus cordata 111
Vaccinium myrtillus 21 2
Sanicula europaea ++
Betula celtiberica 1
Eryngium juresianum 1
Taxus baccata +
Companion taxa
Blechnum spicant 211 1 1
Hedera hibernica 234 3 1
Lonicera periclymenum 111 1 1
Rubus sp. 122 2 2
Teucrium scorodonia 11 1 1
Brachypodium sylvaticum 111
Frangula alnus 111
Polypodium interjectum 11 1
Viola palustris 111
Aquilegia vulgaris subsp. dichroa +1
Athyrium filix-femina 21
Brachypodium pinnatum subsp. rupestre 21
Carex elata subsp. reuteriana 11
Crepis lampsanoides 1+
Euphorbia dulcis 11
Festuca elegans +1
Primula acaulis ++
Osmunda regalis +
Potentilla erecta 1
Quercus robur 11
Salix atrocinerea 1
Companion taxa present in one relevé: Rel. 2:
1 Agrostis xfouilladei, + Angelica sylvestris,
+ Veronica officinalis; Rel. 3: + Anemone tri-
folia subsp. albida, + Hypericum androsae-
mum, 1 Polystichum setiferum; Rel. 4: 1
Carex remota, 1 Prunella grandiflora subsp.
pyrenaica; Rel. 5: 1 Arenaria montana, 1
Clinopodium vulgare, 1 Cytisus scoparius, 1
Fraxinus angustifolia, 1 Galium broterianum,
+ Hieracium vulgatum, + Laserpitium eliasii
subsp. thalictrifolium, + Linaria triornitho-
phora, 1 Peucedanum gallicum, 1 Picris hie-
racioides subsp. longifolia, + Vincetoxicum
hirundinaria subsp. lusitanicum, 1 Viola rivi-
niana.
Relevé sites
1 - Terras de Bouro: Serra do Gerês, Near
Bouça da Mó, to Albergaria, 29TNG6926.
2 - Terras de Bouro: Serra do Gerês,
Albergaria, Rio Maceira, 29TNG7127.
3 - Terras de Bouro: Serra do Gerês, Ribeira
da Laja, 29TNG7023.
4 - Terras de Bouro: Serra do Gerês, Rio
Gerês, near Curral da Laja, 29TNG7023.
5 - Terras de Bouro: Serra do Gerês, Ribeira
da Figueira, 29TNG7022.
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Braun-Blanquet et al. (1956) had already reported two relevés of a « groupement à
Rhododendron ponticum ssp. baeticum », which were included in Table II and in the nume-
rical analyses. Agrostis xfouilladei, Calluna vulgaris and Quercus robur are differential
taxa regarding the southern-Spain mediterranean association Scrophulario laxiflorae-
Rhododendretum baetici, which in turn is characterised by the occurrence of Frangula
alnus subsp. baetica, Scrophularia laxiflora, Viburnum tinus subsp. tinus and Quercus
canariensis (Pérez Latorre et al., 2000).
Table III synthesizes the most important biogeographical, bioclimatical and floristical
features of the seven associations of laurel-leaved relict scrublands in mainland Portugal.
IV. CONCLUSIONS
A. The importance of phylogeographical data in phytosociology
The Quaternary succession of cold and warm periods caused a significant redistribution
of the coenozoic flora, with a large number of frost-sensitive species becoming extinct or
confined to rather isolated positions in Southern Europe. Plant families once diverse and
widespread became represented only by few, narrowly distributed taxa.
Phylogeographic studies have repeatedly identified the southern peninsulas (Iberian,
Italian and Balkanic) as major refuges for the flora during glacial periods. Local ecologi-
cal conditions have enabled the persistence of species and vegetation types in territories
where mesoclimatical conditions are no longer appropriate for their occurrence. If those
Table II, Tableau II.- Calluno vulgaris-
Rhododendretum baetici ass. nova.
R
elevé nº 12 34 5 6
A
ltitude (m) 500 500 500 538 498 517
N
º of taxa 88 812 12 20
Characteristic taxa
Erica arborea +1 +1 + +
Rhododendron ponticum subsp. baeticum 54 54 5 5
D
ifferential taxa
Q
uercus robur 11 ++ 1 +
Agrostis xfouilladei +++1
Calluna vulgaris 1+ +
Companion taxa
P
teridium aquilinum 12 +1 2 1
D
actylis glomerata subsp. lusitanica ++++
Lonicera periclymenum ++ ++
Rubus sp. +111
Blechnum spicant ++ +
Salix atrocinerea +21
Teucrium scorodonia ++
Cistus psilosepalus ++
Digitalis purpurea ++
Osmunda regalis +
Potentilla erecta +
Tamus communis ++
Ulex minor ++
Companion taxa present in one relevé:
Rel. 2: + Pterospartum tridentatum
subsp. cantabricum; Rel. 4: 1 Cytisus
striatus, + Ulex europaeus subsp. late-
bracteatus; Rel. 5: 1 Quercus xandega-
vensis; Rel. 6: + Carex ovalis, + Carex
pilulifera, + Ranunculus repens.
Relevé sites:
1 to 6 - Vouzela: Cambarinho,
29TNF6702 (relevés 2 and 3 from
Braun-Blanquet et al., 1956).
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species or vegetation types have a restricted distribution, they are known as climatic
relicts. The mild temperatures and abundant rainfall that characterise the current climate of
North and Central Portugal favour the occurrence of relict taxa, like the Common-laurel
(Laurus nobilis), the Portuguese-laurel (Prunus lusitanica subsp. lusitanica) and the west-
mediterranean subspecies of Pontic-rhododendron (Rhododendron ponticum subsp. baeti-
cum). These taxa are usually dominant in relict formations, occupying shaded sites on
steep slopes with either topographic or edaphic constraints, or then biotopes with seasonal
disturbance by running water, generally in sheltered positions in valleys or in sub-coastal
areas.
The relict character of vegetation types dominated by these shrubs and small trees is lar-
gely responsible for the fragmentary distribution pattern that can nowadays be observed.
Biogeographical segregation gave rise to a floristic diversification of community types,
with climate and lithology playing a central role in that discrimination. Therefore, biogeo-
graphically isolated groups of scrublands configured distinct, narrowly distributed asso-
ciations which are recognisable from both classical and numerical phytosociological
approaches.
B. Conservation issues and final remarks
Table III.- Synthesis of the biogeographical, bioclimatical and floristical features of the seven
relict laurel-leaved scrubland associations in mainland Portugal.
Tableau III.- Synthèse des données biogéographiques, bioclimatiques et floristiques des
sept associations arbustives laurifoliées relictuelles du Portugal continental.
Associations Biogeographical sectors Thermoclimates Ombroclimates Characteristic combination
Calluno vulgaris- Galician-Portuguese Meso-temperate Humid Rhododendron ponticum subsp. baetic.
Rhododendretum baetici Erica arborea
P
teridium aquilinum
C
alluna vulgaris
Frangulo alni- Dividing-Portuguese Meso-mediterranean Sub-humid Prunus lusitanica subsp. lusitanica
Prunetum lusitanicae Estrelensean Humid Viburnum tinus subsp. tinus
Frangula alnus
Luzulo henriquesii- Juresian Meso-temperate Humid Prunus lusitanica subsp. lusitanica
Prunetum lusitanicae Hyper-humid Saxifraga spathularis
L
uzula sylvatica subsp. henriquesii
Pruno lusitanicae- Juresian Meso-temperate Humid Prunus lusitanica subsp. lusitanica
Arbutetum unedonis Arbutus unedo
Ilex aquifolium
Myrico fayae- Dividing-Portuguese Meso-mediterranean Sub-humid Arbutus unedo
Arbutetum unedonis Myrica faya
Laurus nobilis
Omphalodo nitidae- Galician-Portuguese Thermo-temperate Sub-humid Laurus nobilis
Lauretum nobilis Meso-temperate Humid Hedera hibernica
Meso-mediterranean Omphalodes nítida
Vinco difformis- Dividing-Portuguese Meso-mediterranean Sub-humid Laurus nobilis
Lauretum nobilis Vinca difformis
Smilax aspera
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The conservation of relict species and vegetation types is one of the most sensitive and
urgent tasks in conservation biology, for three main reasons: i) their current distribution
patterns provide important insights on the recent environmental evolution of their territo-
ries; ii) they are usually found at or near the limits of physiologic tolerance for one or more
ecological factors; and iii) they exhibit poor recovering capacity after destruction by any
kind of disturbance. Therefore relict vegetation types are usually rare (or even absent) in
landscape mosaics exhibiting moderate to intensive disturbance related to human activities
such as agriculture or forestry.
Relict mesophytic laurel-leaved scrublands occurring in mainland Portugal are classi-
fied as a priority habitat for conservation by the 92/43/EEC Council Directive (« Habitats »
Directive), namely within habitat 5230* (see the Directive’s Annex I). In a recent survey
of habitat types occurring in mainland Portugal, the Portuguese phytosociological
Association provided a set of individual characterisation files for 98 habitat types, which
can be found at the site of the National Institute for Nature Conservation (www.icn.pt).
Within habitat 5230*, five subtypes were considered to occur in mainland Portugal, sho-
wing a remarkable resemblance to the classification proposed in this paper (see
Syntaxonomical checklist and Table IV).
Many of the 56 relevés presented in this paper were collected within either EU Natura
2000 sites and/or national protected areas, so most of the best representations of these nar-
rowly endemic vegetation types are under some kind of formal protection. However, their
relict character and their (palaeo)botanical peculiarity should justify the elaboration of spe-
cific conservation plans in order to promote their long-term presence in the territory.
Table IV.- Comparison of the subtypes of habitat 5230* (Annex I of 92/43/EEC Council
Directive) occurring in mainland Portugal with the seven associations presented in this
paper.
Tableau IV.- Comparaison entre les sous-types de l’habitat 5230* présents au Portugal
continental et les sept associations décrites ici.
S
ubtype of habitat 5230 Associations
Laurus nobilis scrublands Omphalodo nitidae-Lauretum nobilis
Vinco difformis-Lauretum nobilis
P
runus lusitanica subsp. lusitanica scrublands Frangulo alni-Prunetum lusitanicae
L
uzulo henriquesii-Prunetum lusitanicae
Arbutus unedo-Prunus lusitanica subsp. lusitanica scrublands Pruno lusitanicae-Arbutetum unedonis
Arbutus unedo-Myrica faya scrublands Myrico fayae-Arbutetum unedonis
R
hododendron ponticum subsp. baeticum scrublands Calluno vulgaris-Rhododendretum baetici
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Syntaxonomical checklist of relict laurel-leaved mesophytic scrublands
in Mainland Portugal
Class QUERCETEA ILICIS Br.-Bl. ex A. & O. Bolòs 1950
Order Pistacio lentisci-Rhamnetalia alaterni Rivas-Martínez 1975
Alliance Arbuto unedonis-Laurion nobilis Rivas-Martínez, Fernández-González &
Loidi 1999
Sub-alliance Arbuto unedonis-Laurenion nobilis Rivas-Martínez & Sánchez-
Mata 2001
Association Frangulo alni-Prunetum lusitanicae Lopes, J.C. Costa, Lousã &
Capelo in J.C. Costa, Lopes, Capelo & Lousã 2000
Association Luzulo henriquesii-Prunetum lusitanicae J. Honrado, P. Alves, A.
Lomba, J. Torres & F. B. Caldas ass. nova
Association Myrico fayae-Arbutetum unedonis Capelo & Mesquita 1998
Association Omphalodo nitidae-Lauretum nobilis J. Honrado, P. Alves & F.B.
Caldas in J. Honrado, P. Alves, H.N. Alves & F.B. Caldas 2004
Association Pruno lusitanicae-Arbutetum unedonis (Aguiar & Capelo 1995)
J.C. Costa, Capelo & Lousã in J.C. Costa, Lopes, Capelo & Lousã 2000
Association Vinco difformis-Lauretum nobilis Capelo & J.C. Costa in J.C.
Costa, Lopes, Capelo & Lousã 2000
Sub-alliance Rhododendrenion baetici Rivas-Martínez & Sánchez-Mata 2001
Association Calluno vulgaris-Rhododendretum baetici J. Honrado, P. Alves,
A. Lomba, J. Torres & F. B. Caldas ass. nova
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... Frangulo alni-Prunetum lusitanicae C. Lopes, J.C. Costa, Lousã & Capelo in J.C. Costa, C. Lopes, Capelo & Lousã 2000 is an association found in the Montemuro and Estrela Sierran sector (Costa et al. 2015). Luzulo henriquesii-Prunetum lusitanicae Honrado, P. Alves, Lomba, Torres & B. Caldas 2007 is an association found in the territories of the Northern Lusitanian Sierra Sector (Honrado et al. 2007). Viburno tini-Prunetum lusitanicae Ladero 1976 is an association of mountain ranges in the center of the Iberian Peninsula (Ladero, 1976). ...
... For numerical analysis, we collected 12 field relevés, which were compared with another 22 relevés from literature review, in order to obtain a representative sample of communities dominated by P. lusitanica (Table 1). For the Portuguese territories, we followed Honrado et al. (2007), Costa et al. (2015) and we carried out two relevés in the Municipality of Mação (only known places). For the communities in the center of Spain we used data from Ladero (1976). ...
... The P. lusitanica communities in the Iberian Peninsula and France live mainly in a temporihygrophilic position and in some favorable conditions in a mesophilic position. In the Iberian Peninsula, these communities live their ecological optimum in locations with a humid to hyperhumid mesosubmediterranean bioclimate, enriched by plants of the Quercetea ilicis, such as Erica arborea, Ruscus aculeatus and Rubia peregrina (Costa et al. 2001;Honrado et al. 2007;Pulgar and Manso 2010;Kondraskov et al. 2015), appearing to be absent in the rivers and streams of southern mainland Portugal (Raposo et al. 2020). In order to differentiate the characteristic plants of each syntaxon studied, a synthetic table is presented (Table 6). ...
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The relict communities of Prunus lusitanica are globally threatened, mainly by climatic and anthropic factors. Solid knowledge about floristic composition and serial dynamics provides a valuable basis for the implementation of management and conservation measures. This article focuses on peculiar communities that occur in hydric-compensated areas of the Iberian Peninsula and south of France, a submediterranean ecotonal area. A hierarchical cluster analysis allowed to identify two new syntaxa. For the first time an association of Prunus lusitanica, Lonicero periclymeni-Prunetum lusitanicae ass. nova, is reported for France, representing the mature stage of a minoriseries of vegetation, attributed to Lonicerion periclymeni. The discovery of populations of P. lusitanica in valleys embedded in the Municipality of Mação (Portugal), represent the new association Smilaco asperae-Prunetum lusitanicae ass. nova, enriched by thermophilous taxa. This relict association occurs in the South Beira District and corresponds to the southern limit of the natural distribution area in mainland Portugal, integrated in the suballiance Fraxino angustifoliae-Ulmenion minoris. Additional notes on the occurrence of P. lusitanica in other areas of the Iberian Peninsula are provided.
... The type of the alliance is the association Frangulo baeticae-Rhododendretum pontici Rivas Goday et al. ex Rivas-Martínez et al. 1986. These formations occur not only in the southwest part of the Peninsula, but also in small areas spread out throughout its territory, including in the north, with more temperate climate (Pérez Latorre et al. 1999;Honrado et al. 2007;Biurrun et al. 2016;Portela-Pereira & Rodríguez-González 2021). In particular riparian Portuguese laurel forests have already been included in different taxonomic positions: Arbuto unedonis-Laurion nobilis (Quercetea ilicis) (Rivas-Martínez et al. 2001) (together with rododendron formations), Populion albae (Rivas-Martínez 2011;Costa et al. 2012) and also Osmundo-Alnion (Biurrun et al. 2016). ...
... Regarding the climate, they occur in a Mediterranean and temperate sub-Mediterranean climate, in termo-to mesomediterranean or mesotemperate thermotype level and in semi-hyperoceanic to semi-continental territories (Pérez Latorre et al. 2000;Honrado et al. 2007;Costa et al. 2012;Biurrun et al. 2016). ...
... The type of the alliance is the association Frangulo baeticae-Rhododendretum pontici Rivas Goday et al. ex Rivas-Martínez et al. 1986. These formations occur not only in the southwest part of the Peninsula, but also in small areas spread out throughout its territory, including in the north, with more temperate climate (Pérez Honrado et al. 2007;. In particular riparian Portuguese laurel forests have already been included in different taxonomic positions: Arbuto unedonis-Laurion nobilis (Quercetea ilicis) ) (together with rododendron formations), Populion albae ) and also Osmundo-Alnion . ...
... Regarding the climate, they occur in a Mediterranean and temperate sub-Mediterranean climate, in termo-to mesomediterranean or mesotemperate thermotype level and in semi-hyperoceanic to semi-continental territories (Pérez Latorre et al. 2000;Honrado et al. 2007;. ...
Book
Full-text available
This paper comprises an overview of the riverine, swamp, floodplain forests and scrub throughout the continent. The team of researchers from various European countries has considered most of the forest habitats from the Canary Islands to European Russia. It was a difficult task to gather all the knowledge about this type of vegetation across the continent as there are different approaches to the study and elaboration of forest vegeta- tion and the level of knowledge also varies. The backbone of the whole presentation is the work of Ladislav Mucina, a collaborator from 2016, who prepared the list of European alliances and in this way also prepared an overview of the river, swamp and floodplain forests and shrublands. We have considered this list and prepared the description of the majority of the forests and shrublands from the list. Unfortunately, we did not manage to cover all forests included in the list. The preparation of this paper was supported by the COST Knowledge conversion for en- hancing management of European riparian ecosystems and services (CONVERGES), which received financial support from the EU. The project itself was led by Simon Dufour of the University of Rennes and co-supervised by Patricia María Rodríguez-González of the University of Lisbon. This review is the result of WP1 led by Marta González del Tánago from the Politechnical University of Madrid. We owe special thanks to the leader of our subgroup, Dejan Mandžukovski of the Macedonian Forest State Agency, for his efforts in organizing our work. We also owe thanks to all our leaders for organizing this activity, inviting us to participate and leading us to the successful completion of this proj- ect. We enjoyed our friendship by sharing our experiences and knowledge about forests and preparing the results, including this book. Many thanks to all of you! In this booklet we give an overview of the forests and shrublands along European riv- ers, in their surroundings, on river islands, in depressions and oxbows. These forests are subject to constant change and are maintained by periodic/regular flooding or high groundwater. We call them paraclimatic because they are maintained by occasional ca- tastrophes caused by water. We may find one type of forest in one place, but after a flood it may move to another place the next year. Erosion and sedimentation, the destruction of the vegetation and new establishment alternate. We should keep in mind that these forests also contain different biota. They are very rich and dynamic ecosystems. We can admire this eternal dynamism of life caused by water and we should be aware that these ecosystems are endangered and need to be protected. Human impact on these ecosystems is quite extensive, as most habitats along rivers were converted to agricultural land or urbanized long ago. In addition to drainage, these habitats are also threatened by hydropower construction, river bank stabilization and regulation, gravel mining, groundwater extraction, and other pressures. These habitats are also among the most vulnerable to invasion by alien and invasive species because water flow is an effective vector for their spread. We find many invasive species in these habitats, such as Acer negundo, Helianthus tuberosus, Impatiens glandulifera, Rud- beckia laciniata, Solidago canadensis, Echinocystis lobata, Bidens frondosa, Deutzia scabra and many others. These are the reasons why many of these habitats are listed in Annex I of the Habitats Directive (Natura 2000), such as 3230 - Alpine rivers and their ligneous vegetation with Myricaria germanica, 3240 - Alpine rivers and their ligneous vegetation with Salix eleagnos, 91E0 - Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), 91F0 - Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angusti- folia, along the great rivers (Ulmenion minoris). There are many more types listed in the Annex I of the Habitats Directive: 92AO - Salix alba and Populus alba galleries, 91BO - Thermophilous Fraxinus angustifolia woods, 9280 - Riparian formations on intermittent Mediterranean water course with Rhododendron ponticum, Salix and others, 5230* - Arborescent matorral with Laurus no bilis, 92CO - Platanus orientalis and Liquidambar orientalis woods (Plantanion orien talis), 92DO - Southern riparian galleries and thickets (Nerio-Tamaricetea and Securi negion tinctoriae), 4080 - Rhodope Potentilla fruticosa thickets. We have treated the riverine, swamp and floodplain forests and scrubs in order as they were listed in the already mentioned list of European vegetation. The riverine, swamp and floodplain forests and scrub are divided into five groups: riverine gallery and flood- plain forests (Alno glutinosae-Populetea), willow and tamarisk forests and scrub (Salicetea purpureae), regularly flooded alder carrs and birch wooded mires (Alnetea glutinosae), scrubby willow carrs (Franguletea) and circum-Mediterranean and Maca- ronesian riparian scrub (Nerio-Tamaricetea). The overlook begins with the class Alno glutinosae-Populetea albae P. Fukarek et Fabijanić 1968. These forests occur under periodic or temporary flooding or are, oc- casionally, under high groundwater. Within this group we classify forests occurring on shallow gravel of the upper reaches, forests along small watercourses, and forests on river sediments in the lower reaches of rivers and forests occurring on the margins of swamps. Further division of this group shows that these forests appear in two biogeographical regions. Populetalia albae Br.-Bl. ex Tchou Yen-Tcheng 1949 presents Mediterranean and sub-Mediterranean gallery and floodplain forests, whereas forests from temperate and boreal regions are classified within Alno-Fraxinetalia excelsioris Passarge 1968. The Mediterranean and sub-Mediterranean forests of Populetalia albae are composed of two major groups. In western Mediterranean, we can find: riparian forests of the sub- Mediterranean regions of the southern France and Iberian Peninsula (Populion albae Br.-Bl. ex Tchou Yen-Tcheng 1949), riparian forests of the sub-Mediterranean regions of the northern and central Apennines (Ligustro vulgaris-Alnion glutinosae Poldini, Sburlino et Venanzoni in Biondi et al. 2015), alder and willow riparian forests of the western Mediterranean (Osmundo-Alnion glutinosae (Br.-Bl. et al. 1956) Dierschke et Rivas-Mart. in Rivas-Mart. 1975) and south Iberian Mediterranean riparian forests with relict laurisilva elements (Rhododendro pontici-Prunion lusitanicae A.V. Pérez, Galán et Cabezudo in A.V. Pérez et al. 1999). In the eastern Mediterranean, we can find: Platanus riparian gallery forests of the eastern Mediterranean (Platanion orientalis I. Kárpáti et V. Kárpáti 1961) and riparian gallery forests with relict laurisilva elements of the eastern sub-Mediterranean regions of the Apennine and Balkan Peninsulas (Lauro- Fraxinion angustifoliae I. Kárpáti et Kárpáti 1961). The temperate and boreal group of forests Alno-Fraxinetalia is composed of alder-ash and oak riparian floodplain forests on nutrient-rich alluvial soils in the nemoral zone (Alnion incanae Pawłowski et al. 1928), alder, ash and birch floodplain forests along streams of the Cantabrian region of the Iberian Peninsula (Hyperico androsaemi-Al- nion glutinosae (Amigo et al. 1987) Biurrun et al. 2016), elm-ash and oak riparian floodplain forests on nutrient-rich brown soils in the nemoral zone of Europe (Fraxino- Quercion roboris Passarge 1968, alder-oak riparian floodplain forests on nutrient-rich alluvial soils of the temperate regions of the Balkan Peninsula (Alno-Quercion roboris Horvat 1950) and oak-elm riparian floodplain forests on nutrient-rich alluvial soils in the steppe zone of southern Russia (Poo angustifoliae-Ulmion laevis Golub in Golub et Kuzmina 1997). The next group encompasses willow and tamarisk scrub and low open forests of ripar- ian habitats in the temperate to arctic zones (Salicetea purpureae Moor 1958), being divided into three subgroups as: willow scrub and low open forests of riparian habitats in the temperate to arctic zones of Europe (Salicetalia purpureae Moor 1958), tamarisk riverine scrub of the lowland rivers of the Balkan Peninsula and the Sarmatian region of southern Ukraine and Russia (Tamaricetalia ramosissimae Borza et Boşcaiu ex Dolţu et al. 1980) and willow woodlands on silt-rich alluvia, recent landslides and in beds of irregular streams of Madeira and the Canary Islands (Rubo bollei-Salicetalia canarien- sis Rivas-Mart. in Capelo et al. 2000). Willow scrub and low open forests of riparian habitats in the temperate to arctic zones of Europe (Salicetalia purpureae) can further be divided into willow scrub on the gravelly stream banks in the submontane to subalpine belts of the temperate and boreal Euro- pean mountains and the Caucasus (Salicion eleagno-daphnoidis /Moor 1958/ Grass 1993), willow and poplar low open forests of lowland to submontane rivers alluvia in the nemoral zone and at high altitudes of the Mediterranean (Salicion albae Soó 1951), wil- low scrub on loamy-sandy sedimentary river banks in the lowland to submontane belts of the nemoral zone (Salicion triandrae T. Müller et Görs 1958), willow scrub on riverine dunes of Central Ukraine (Artemisio dniproicae-Salicion acutifoliae Shevchyk et V. Solomakha in Shevchyk et al. 1996), western Iberian thermo- to supra-Mediterranean riparian alluvial willow scrub on the alluvia of mineral-poor rivers (Salicion salviifoliae Rivas-Martinez et al. 1984), eastern Iberian thermo- to supra-Mediterranean riparian al- luvial willow scrub on the alluvia of mineral-poor rivers (Salicion discolori-neotrichae Br.-Bl. et O. de Bolòs 1958 corr. Rivas-Martinez et al. 2002), Cantabrian sub-Mediter- ranean montane pioneer willow scrub on the alluvia of mineral-poor rivers (Salicion cantabricae Rivas-Martinez, T.E. Díaz et Penas in Rivas-Martinez et al. 2011), southern Iberian, Maghrebinian and Calabro-Sicilian thermo- to supra-Mediterranean riparian al- luvial willow scrub on the alluvia of mineral-poor rivers (Salicion pedicellatae Galán de Mera et al. in Pérez Latorre et al. 1999), Apennine sub-Mediterranean submontane- montane pioneer willow scrub on gravel alluvial riverine terraces (Salicion apennino- purpureae Biondi et Allegrezza in Biondi et al. 2014). Tamarisk riverine scrub Tamaricetalia ramosissimae can be further divided into tama- risk riverine scrub on coarse gravelly soils on lowland river banks of the western regions of the Balkan Peninsula (Tamaricion parviflorae I. Kárpáti et V. Kárpáti 1961) and tamarisk riverine scrub on coarse gravelly soils on lowland rivers banks of the eastern regions of the Balkan Peninsula and the Sarmatian region of Southern Ukraine and Rus- sia (Artemisio scopariae-Tamaricion ramosissimae Simon et Dihoru 1963). Willow woodlands of Madeira and the Canary Islands Rubo bollei-Salicetalia canarien- sis contain only a single group (Salicion canariensis Rivas-Mart., Wildpret, Del Arco, O. Rodríguez, Pérez de Paz, García Gallo, Acebes, T.E. Díaz et Fernández-González ex Rivas-Martinez et al. 1999). The third group encompasses mesotrophic regularly flooded alder carr and birch wood- ed mires (Alnetea glutinosae Br.-Bl. et Tx. ex Westhoff et al. 1946) encompassing me- sotrophic regularly flooded alder carr (Alnetalia glutinosae Tx. 1937), basiphilous birch forests on mesotrophic mires (Salici pentandrae-Betuletalia pubescentis Clausnitzer in Dengler et al. 2004) and acidophilous birch forests on mesotrophic mires (Sphagno- Betuletalia pubescentis Scamoni et Passarge 1959). As the overview does not deal with mire vegetation, we present only the mesotrophic carr. Mesotrophic regularly flooded alder carr (Alnetalia glutinosae) is divided into mesotro- phic regularly flooded alder carr (Alnion glutinosae Malcuit 1929) and amphiadriatic mesotrophic interdune and karstic ash carr (Frangulo alni-Fraxinion oxycarpae Pol- dini, Sburlino et Venanzoni in Biondi et al. 2015). The fourth group presents the willow carr of western Europe, Fennoscandia and the subatlantic regions of central Europe (Franguletea Doing ex Westhoff in Westhoff et Den Held 1969) with only one subgroup Salicetalia auritae Doing 1962, that is further divided into willow carr of western Europe and the sub-Atlantic regions of central Europe (Salicion cinereae T. Müller et Görs ex Passarge 1961) and alder-willow carr in the boreal zone of Fennoscandia and northern Russia (Alno incanae-Salicion pentandrae Kielland-Lund 1981). The last group encompasses circum-Mediterranean and Macaronesian riparian scrub (Nerio-Tamaricetea Br.-Bl. et O. de Bolos 1958) with only one subgroup (Tamaricetalia africanae Br.-Bl. et O. de Bolòs 1958). It can be divided into two parts. Western-Medi- terranean communities can be classified within infra- to supra-Mediterranean tamarisk riparian scrub in temporarily flooded brackish habitats (Tamaricion africanae Br.-Bl. et O. de Bolòs 1958), infra- to supra-Mediterranean tamarisk riparian scrub in temporarily flooded brackish habitats (Tamaricion boveano-canariensis Izco et al.1984), thermo- to supra-Mediterranean oleander riparian scrub (Rubo ulmifolii-Nerion oleandri O. de Bolòs 1958) and Luso-Estremadurean (Iberian Peninsula) thermo-mesomediterranean riparian thorny tamujal (Securinegion tinctoriae Rivas Goday ex Rivas-Martinez 1975). In the eastern Mediterranean, we can find thermo-meso-Mediterranean tamarisk scrub of the Balkan Adriatic seaboards (Tamaricion dalmaticae Jasprica in Jasprica et al. 2016). The present overview does not encompass some habitats due to unclear classification or lack of expertise within the project group, such as Ligustro-Alnion glutinosae, Rubo- Amorphion fruticosae, Artemisio-Tamariscion ramossisimae, Salicion canariensis, Fran- gulo-Fraxinion oxycarpae, Alno-Salicion pentandrae and Rubo sancti-Nerion oleandri. Nomenclature of plant species follows the Euro+Med Plantbase, unless the authorship is indicated [Available online: https://www.emplantbase.org]. The authors have listed also diagnostic, dominant and constant species that are of crucial importance for syntaxon (alliance) identification. Diagnostic species is a central concept in vegetation or habitat classification based on species composition. Diagnostic species (including character, differential and indicator species), can be broadly defined as species with a distinct con- centration of occurrence or abundance in a particular vegetation type (habitat, alliance). Species of high frequency (constant species) and species of high cover-abundance (dominant species) are also important for identification.
... These formations had previously been classified in the alliance Populion albae (Rivas-Mart ınez 2011; Costa et al. 2012), but cluster analysis placed them in the Osmundo-Alnion, due to the high constancy of diagnostic species of this alliance. Prunus lusitanica floodplain forests are of high conservation interest, as they are considered as relict formations typical of river-beds with seasonally flowing waters (Honrado et al. 2007). ...
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