Vegetation and landscape around Lake Montcortès ( Catalan pre-Pyrenees ) as a tool for palaeoecological studies of lake sediments

Vegetation and landscape around lake Montcortès (catalan pre-pyrenees) as a tool for palaeoecological studies of lake sediMents.— Lake Montcortès (42o 19′ N, 0o 59′ E; 1027 m elevation) is an excellent target for highresolution palaeoecological studies because its annually-laminated sediments extending back to the early-middle Holocene. The detailed knowledge of present vegetation patterns around the lake and the pollen they release to lake sediments is essential for a reliable interpretation of past vegetation dynamics. This study aims to identify and map the vegetation types currently growing around the lake. For this purpose, a quadrangular area of ca. 48 ha was defined. The floristic study resulted in a catalogue of 534 species. Vegetation analysis was based on 42 phytosociological inventories used to synthesise and map the relevant plant landscape units. As a result, we obtained 52 vegetation units as expressions of the CORINE habitats previously defined for Catalonia. Each of these habitats was described in floristic, physiognomic, phytogeographic, environmental and human-use terms. The next step will be the palynological study of the more representative species of the described vegetation types, as a means to optimise future palynological interpretations.


IntRoductIon
Lake Montcortès (Fig. 1) has become a favourite target for palaeoecological study after the finding of laminated sediments (varves) potentially useful to reconstruct Holocene palaeoenvironmental trends at annual or seasonal resolution (Corella et al., 2012).So far, past reconstructions based on Montcortès sediments using different indicators (proxies) such as sedimentology, geochemistry, pollen and diatoms, among others, have been conducted at centennial to millennial resolution (Corella et al., 2011;Rull et al., 2011;Scussolini et al., 2011).However, a project has been launched recently aimed to obtain the maximum resolution possible during the last millennium using a multiproxy approach (Vegas-Vilarrúbia, 2012).The annual varves consist of three laminae each (triplets) representing seasonal trends which biological nature is still under study (Corella et al., 2012).It is expected that some of these laminations coincide with the main flowering season and contain most of the sedimentary pollen.In order to properly interpret these sedimentary pollen assemblages in palaeoecological terms, it is necessary to know the source flora and the vegetation at different levels of spatial resolution.
The pollen that accumulates in a given sedimentary basin proceeds from three main sources, namely local, regional and long-distance (Birks & Birks, 1980;Faegri et al., 2000).In the case of Lake Montcortès, the flora and vegetation of the Catalan pre-Pyrenees is fairly well known thanks to numerous local and regional studies conducted so far (Bolòs, 1961(Bolòs, , 1976;;Vives, 1964;Lapraz, 1976;Romo, 1989;Conesa, 1991;Vigo et al., 2003;Sáez et al., 2004;Soriano & Devis, 2004, among others), as well as some synthetic works (Bolòs, 1979;Folch, 1981;Vigo & Ninot, 1987).The pollen coming from regional and long-distant sources, as for example the Mediterranean or interior lowlands, is easily detectable as well (Cañellas-Boltà et al., 2009).However, local sources need more detailed studies, as the ecological conditions created by the presence of the water body determine the occurrence of plants and plant associations that otherwise would not occur.
From a palaeoecological point of view, the detailed knowledge of the local component of pollen assemblages is essential as it allows reconstructing small-scale ecological successions influenced by local environmental factors, rather than regional or supra-regional shifts.This has several advantages, as for example the possibility of: (1) disentangling the effect of local features (flooding, landslides, etc.) from more general climatic events, (2) separating ecological shifts determined by human activities (more local in scope) from those induced by more general climate trends and events, and (3) reconstructing in detail local ecological successions over a long-term time scale useful for testing ecological hypotheses (Rull, 2012).These benefits are particularly useful in the case of annually laminated sediments, where several of the quoted drivers of change concur to shape the final pollen assemblage of each year.Without considering local drivers and phenomena in detail it is not possible to take advantage of all the temporal resolution captured in annual laminations.
The aim of this paper is to study in detail the vegetation occurring at present around Lake Montcortès and its area of influence.The next steps will be the study of pollen morphology of the more important species and habitats, and the study of present-day sedimentation patterns of these pollen types in the bottom lake sediments.

Study AReA
Lake Montcortès is situated on the southern flank of the Central Pyrenees, in the Pallars Sobirà region, at 42º 19′ N, 0º 59′ E and 1027 m altitude, with a surface of 12.36 ha.The lake lies in karstic terrain characterized mainly by Triassic limestones, marls and evaporites, and Oligocene carbonatic conglomerates.Triassic ophytes outcrop mainly at the south and Quaternary lacustrine sediments surround the present-day water body (Corella et al., 2011) (Fig. 1).The catchment is small and the lake is fed mainly by groundwater, with intermittent small creeks and scattered springs.The main water losses are due to evaporation and a small seasonal outlet at the north end.The lake is roughly kidneyshaped, with a diameter between 400 and 500 m and a maximum water depth of 30 m near the centre (Camps et al., 1976;Modamio et al., 1988).The annual average air temperature of the area is 10.6ºC, ranging from 1.9ºC in January to 20.3ºC in July.Total annual precipitation is 860 mm, with March as the driest month (46.6 mm) and May as the wettest month (99.2 mm) (Corella et al., 2012).
The lake lies near the altitudinal boundary corresponding to Sub-Montane belt, which in the Pyrenees Collectanea Botanica vol.32 (2013): 87-101, ISSN: 0010-0730, doi: 10.3989/collectbot.2013.v32.008 is situated around 800-1000 m elevation, depending on local conditions (Vigo & Ninot, 1987).Four major forest formations occur at the lake region, reflecting this boundary condition (Fig. 2): (1) Mediterranean sclerophyllous forests represented by Quercus rotundifolia Lam.woods; (2) Sub-Montane deciduous oak forests, submitted to higher precipitation, and dominated by Quercus pubescens Willd.and Q. subpyrenaica Villar; (3) conifer forests of Pinus nigra J. F. Arnold subsp.salzmannii (Dunal) Franco, usually secondary replacing the deciduous oak forests in lower and southern regions (Folch, 1981) but probably natural here (Bolòs et al., 2004); and (4) higher-elevation forests of Pinus sylvestris L. marking the transition between Sub-Montane and Montane belts.The possibility of part of these conifer woods to have been planted should not be dismissed.The vegetation around the lake has been poorly described.A belt of littoral vegetation dominated by Juncus, Scirpus, Phragmites, Typha and Sparganium has been mentioned by Camps et al. (1976).There is also an unpublished list of plants and other organisms in studies carried out by the Confederación Hidrográfica del Ebro, which is available online (www.chebro.es).
The region is fairly populated and the lake has been historically an important water source for the numerous surrounding villages and farmhouses.
There is also a project to build an artificial pond using the water of the lake for fire-fighting purposes.Cultivation (wheat, oat, barely, olives, rye, hemp and legumes) and livestock (cattle and sheep) have been also common practices during the last millennium and possibly earlier (Rull et al., 2011).At present, cereal and alfalfa fields intermingled with pastures (for cattle and horses) and hay meadows are common and heavily exploited.Protection practices should be focused on controlling water extraction and livestock overexploitation, as well as on avoiding tourism overcrowding and stimulating good environmental practices.The lake area lies within some protection figures, as for example the PEIN (Pla d'Espais d'Interès Natural), the Xarxa Natura 2000 and the ZEPA (Zona d'Especial Protecció per a les Aus).

MethodS
The vegetation map of Lake Montcortès was the result of a three-step progressive process, in which each step fed the next one.These phases were: (1) a detailed floristic survey of the vascular flora, (2) the identification of plant communities or phytocoenoses present, and (3) the definition of the cartographic units in terms of vegetation habitats.
Floristic studies supply the basic information needed to develop any sound botanic or ecological study, from the analysis of species-environment relationships to the definition of the corresponding phytocoenoses and habitats, or the interpretation of landscape dynamics, a key feature in palaeoecological inference using palynology.Without a solid floristic basis, any study of this type could be seriously questioned or overruled.Unfortunately, studies without a robust floristic support are not uncommon.For this study, a rectangular area of ca.48 ha around Lake Montcortès was explored in detail (Figs.1C and 3), including the flood basin and its neighbourhood, in order to account for both the vegetation influenced directly by the lake and a representative sample of the surrounding plant communities.Fieldwork was conducted systematically during 14 months (July 2012-September 2013) to include a complete annual cycle and, therefore, the different flowering seasons of the involved species.
The resulting floristic list can be considered virtually complete but not exhaustive due to the interference of harvesting and grazing, as well as eventual peculiarities of the particular annual cycle studied, as for example flowering irregularities due to unexpected climatic oscillations.To facilitate botanical and paly-nological study, all species bearing flowers during our field visits were collected and deposited in the herbarium of the Botanic Institute of Barcelona (BC).All these specimens were re-analysed to confirm or change preliminary field identifications.To elaborate a floristic list as complete as possible, we have also considered previous published records, despite their scarcity and bias towards aquatic macrophytes.Identifications were based on general guides for Catalonia (Bolòs & Vigo, 1984-2001;Bolòs et al., 2005) and the Iberian Peninsula (Castroviejo, 1986(Castroviejo, -2012)), as well as more specific taxonomic revisions, when necessary (e.g.Kerguélen & Plonka, 1989).
Plant communities were tentatively identified in the field and referred to their corresponding habitats.These preliminary communities were then inventoried and the corresponding inventories were analysed using the sigmatist system (Braun-Blanquet, 1951;Géhu & Rivas-Martínez, 1981) to define the preliminary vegetation types or phytocoenoses.These vegetation units were used as preliminary cartographic units in a vegetation map digitalized from orthophotomaps through ArcGis v10.0 (ESRI).These preliminary units were confirmed or modified again in the field to define the final cartographic units, which were a combination of the phytocoenoses and the European CORINE habitat classification adapted for Catalonia (Vigo et al., 2005(Vigo et al., -2008)).

ReSultS
The floristic study resulted in more than 1700 records of vascular plants including our own field observations and collections, the analysis of herbarium specimens and previously published records.Once carefully analysed, these records yielded a total of 534 species, corresponding to 291 genera and 76 families.The complete list of these taxa is beyond the objectives of the present paper and will be published separately.Concerning vegetation types, a total of 42 inventories were analysed to define 31 phytocoenoses.The combination of these plant communities and the habitats of Vigo et al. (2005Vigo et al. ( -2008) ) resulted in 52 units represented by an alphanumeric code.Each of these units has an additional code, given in brackets after the name of the unit, corresponding to the general habitat classification for Catalonia (Vigo et al., 2005(Vigo et al., -2008)).The suffix "bis" after the code of some of these units indicates that they slightly differ from the original ones.The CORINE units, which are the legend of the map (Fig. 3), are listed below.A more detailed description of these units is provided in Appendix, in both environmental and floristic terms.Some units do not appear in the map because they correspond to submerged vegetation (1a, 1b, 1c, 1e) or because they do not attain the minimum critical size to be represented (50 m 2 ) (5a, 8x, 8y, 8z).Exceptions are units considered to be of special significance.

habitat-vegetation units (based on the coRIne system)
A Aquatic and semi-aquatic habitats

FLORISTIC AND PHYTOGEOGRAPHIC NOTES
From a floristic perspective, the better represented family is Asteraceae (15.7%) followed by Poaceae (10.4%),Papilionaceae (9%) and Cyperaceae (3.9%).Of the five pteridophytes (0.9% of the flora) recorded, only the horsetail (Equisetum arvense L.) is associated to aquatic environments.Overall, the Montcortès flora is comparable to those found in similar pre-Pyrenean environments (Vigo & Ninot, 1987) but the micro-environmental particularities created by the lake results in a higher floristic diversity.
Phytogeographically, the Montcortès flora is mostly a combination of Euro-Siberian and Mediterranean elements, with some differences according to the vegetation type.Euro-Siberian species prevail in forests, meadows and pastures, particularly those of meridional and sub-Mediterranean character, whereas strictly Mediterranean elements dominate in drier environments.Figure 4  Beauv., as well as members of a varied array of other families (Carum carvi L., Geranium pratense L., Rhinanthus minor L. or Rumex acetosa L).In the mesophile pastures, the more common Euro-Siberian elements are Briza media L., Carex caryophyllea Latourr., Cirsium acaule (L.) Scop., Plantago media L. and Trifolium montanum L. It is worth mentioning the occurrence of species of Atlantic distribution as for example Centaurea nigra L. (hay meadows, mesophile pastures and forest edges) and Pulmonaria longifolia (Bast.)Boreau (forests).
A large part of the Montcortès flora is calcicolous due to the prevalence of calcareous substrates (Fig. 1C); however, the presence of acidic ophytes leads to the occurrence of silicicolous or acidophile species such as Chamaespartium sagittale (L.) P. E. Gibbs., Danthonia decumbens (L.) DC., Dianthus armeria L., Hieracium sabaudum L., Trifolium arvense L. and Trifolium glomeratum L.
Overall, the vegetation is mostly of sub-Mediterranean character, with some Mediterranean encroachments, and spiked by azonal communities linked to the lake and other moist areas.The aquatic vegetation is fairly rich, even if we consider only the vascular plants, and is constituted by a conspicuous belt of helophytic and hygrophyle plants subdivided into four (in the more complex case), clearly distinguishable fringes (from water to land): ( 1 The assumed natural vegetation beyond the direct influence of the lake is dominated by oak forests of Quercus pubescens Willd., Q. subpyrenaica Villar (possible hybrid between the first and Q. faginea Lam.) and Q. rotundifolia.The secondary vegetation is mostly characterised by shrubland formations of box (Buxus sempervirens L.) scrubs and Genista scorpius (L.) DC., as well as pastures of Euro-Siberian (Bromion erecti Koch alliance) or Mediterranean (Aphyllanthes grasslands) character.Thickets, forest edges, wetlands and annual grasslands grow on small areas.

FuRtheR StudIeS
The next step in this study will be the palynological characterisation of the more relevant species and the initiation of a pollen reference collection.The more interesting species will be selected according to their importance in the units defined in this study combined with the results of a monthly survey of modern pollen sedimentation on the bottom of the lake using traps.These procedures will help establish qualitative and quantitative relationships among the composition of modern pollen assemblages from lake sediments, the nature and location of their potential sources, and the more influential climatic parameters.These modern-analogue studies will be used to infer eventual vegetation and environmental changes occurred in the past by analysing ancient lake sediments, using the principle of uniformitarianism (Birks & Birks, 1980).

1a. Formations of smaller pondweeds and other submerged rooted plants
Not studied in detail in this paper, most of the information is from previous references (Font Quer, 1928;Margalef Mir, 1981;Montserrat Martí, 1981).This unit has been found until a water depth of at least 4 m and the main components are Myriophyllum spicatum L., Najas marina L., Potamogeton berchtoldii Fieber, Potamogeton crispus L. and Potamogeton pectinatus L.

1b. charophytes submerged carpets
Present in the lake and also in the artificial pond called Font Senta.The main species are Chara spp.and Nitellopsis obtusa (Desv.)J. Groves.
1c. Formations of Utricularia australis, Ranunculus trichophyllus..., with both submerged and floating leaves in shallow waters with fluctuating water levels Restricted to the western and south-western lake shores, favoured by the occurrence of more or less extensive shallowwaters due to the flat morphology of the substrate.

1d. Formations of rooted pondweeds with large floating leaves
This unit has not been recognised in detail but it is largely dominated by Potamogeton coloratus Hornem.

1e. Polygonum amphibium formations
In the north-western side, this unit occurs inside the reeds, whereas in the southernmost part, the unit is terrestrial and develops on moist soils.

2b. Reedmace (Typha domingensis) beds
Forming a narrow fringe along the eastern lake shore, close to the reed, from which is difficult to differentiate.

2c. Iris pseudacorus formations
Only present in a patch at the eastern lake shore.

2d. Flooded Phragmites beds
Forming an almost continuous belt along the entire lake perimeter, in contact with open waters.The taxonomic composition of this unit varies slightly according to the shore topography.In the more general case of fairly gradual shores, the more common species are Epilobium hirsutum L., Galium palustre L., Phragmites australis (Cav.)Steud., and Sparganium erectum L.

3a. Formations dominated by Carex riparia in permanently flooded areas
This is the second helophytic fringe, beyond the units of group 2, and is better developed at the western and southern shores, which are those with a more gradual topography.Important components are Agrostis stolonifera L., Carex riparia Curtis, Epilobium hirsutum L., Galium palustre L., Lythrum salicaria L., Mentha aquatica L., Phragmites australis (Cav.)Steud., Plantago major L., Poa trivialis L. and Ranunculus repens L.

3b. common spikerush (Eleocharis palustris) beds
Occasional formations occurring on some depressed zones of the north-western shore.

3c. Formations occupying the banks of small rivers or springs
The only patch found is situated in the northern side of the lake, close to the outlet.The unit is composed basically of Glyceria plicata Fr., with Carex hirta L., Lycopus europaeus L., Mentha longifolia (L.) Huds., Poa trivialis L. and Ranunculus repens L. Close to the Font Senta, there is a community of Scrophularia auriculata L subsp.pseudoauriculata (Sennen) O. Bolòs & Vigo of irregular appearance and not indicated in the map.

4aa. clubrush (Scirpus lacustris) beds
Besides the small patch represented in the map, this sedge occurs here and there within the helophytic and hygrophilous vegetation, mainly in the third fringe further on the flooded Phragmites bed.Scirpus lacustris L. subsp.tabernaemontani (C.C. Gmel.)Syme is dominant, accompanied by Agrostis stolonifera L., Carex lepidocarpa Tausch, Juncus articulatus L. and Juncus subnodulosus Schrank.