Contribution to the knowledge of the flora and vegetation of the lower course of river Sabor

André Hoelzer1 & Carlos Aguiar2

I. INTRODUCTION

This communication aims to present preliminary results of the diploma project «Vegetation ecological studies at the lower course of river Sabor», at Department of Ecology and Evolutionary Biology, University of Bremen. It focuses on vegetation, landscape and floristic diversity of a river valley that still has not suffered from impacts of large hydroelectric power plants. The main objective is to elucidate an interrelationship between vegetation and human impact, namely agriculture. We intend hereby to give a brief vision of the area in study.

DESCRIPTION OF AREAPhysiography – characterized by the persistence of residual primitive plateaus (peneplains) dissected by an hydrographic network enclosed in deep and narrow valleys, with the valley of river Sabor and its tributaries (rivers Angueira, Maçãs, Azibo and Ribeira do Zacarias) standing out (Cabral, 1995). Lithology – Acid rocks, schists and quartzites are prevailing. Outcrops of granites appear within limits of parish of Larinho (not included in our area; cf. DGMSG, 1974). Soils – On the plateaus luvisols are most frequent. At the slopes towering the rivers, the soils are normally thin (leptosols). Punctually, along the margins of the rivers, exist small areas of fluvisols, in general of very coarse texture Biogeography – Costa et al. (1998) included all the area here concerned in Terra Quente Superdistrict of the Lusitano-Duriense Sector (Carpetan-Leonese Subprovince, Mediterranean Iberoatlantic Province, Eurosiberian Region)Bioclimatology – meso-mediterranean thermo-type which comprises punctually the semiarid stage up to the superior dry stage (Rivas-Martínez & Loidi, 1999)

IV. REFERENCES

Aguiar, C. 2001. Flora e vegetação da Serra de Nogueira e do Parque Natural de Montesinho. Dissert. Dout. Univ. Téc. Lisboa.

Cabral, J. 1985. Estudos de Neotectónica em Trás-os-Montes Oriental. Provas de Aptidão Pedagógica. Depart. Geol. Fac. Ciênc. Lisboa. Lisboa.

Costa, J. C., C. Aguiar, J. Capelo, M. Lousã & C. Neto. 1998. Biogeografia de Portugal Continental Quercetea 0: 5-56.Direcção Geral de Minas e Serviços Geológicos (DGMSG). 1974. Carte Géologique Schématique (NE de Portugal), Escala 1:200.000. Coordenada por A. Ribeiro. Serviços Geológicos de Portugal. Lisboa.

Géhu, J. M. & S. Rivas-Martínez.1981. Notions fondamentales de phytosociologie In: Syntaxonomie. J.Cramer. Vaduz.

Rivas-Martínez, S. & J. Loidi. 1999. Bioclimatology of the Iberian Peninsula. Itinera Geobot. 13: 41-47.

Theurillat, J.-P. 1992. Étude et Cartographie du Paysage Végétal (Symphytocoenologie) dans la Région D’Aletsch (Valais, Suisse). F. Flück-Wirth. Teufen.

V. REMARKDuring the field survey, some chorological news for the region were recorded:

Antirrhinum meonanthum Hoffm. & Link, Crepis foetida L., Gamochaeta pensylvanica (Willd.) Cabrera, Hesperis laciniata All., Linum strictum L. Lathyrus setifolius L., supposed to be extinct from our area, has been observed at few points of the river valley.

VEGETATION & LAND USE

The potential vegetation of the territory was identified in earlier works (Costa et al., 1998 and Aguiar, 2001). Three vegetation belts with straight correlation to altitude and physiography of territory were recognized.

Dry upper meso-mediterranean stage

Plateau

In climatophilous positions mixed forests of Quercus suber, Q. rotundifolia, Q. faginea ssp. faginea and Juniperus oxycedrus var. lagunae develop [Junipero lagunae-Quercetum suberis]. Substituting those forests frequently occur communities of Retama sphaerocarpa [Cytiso multiflori-Retametum sphaerocarpae] and Cistus ladanifer [Cisto-Lavanduletea]. The territory occupied by those communities presents a plateau physiography; here ancestral land use by man dates back at least to iron age. Most frequent crops, up to relatively short time ago, have been cereals, grape and olive trees. In depressionary areas once occupied by mixed woods of Fraxinus angustifolia and Quercus faginea [Fraxino angustifoliae-Ulmenion minoris] hay-meadows [Molinio-Arrhenatheretea] have been implanted, or they are used in a more intensive form in horticulture.

Upper & middle slope

Upstream the sector comprised between Picões and Felgar, the upper dry meso-mediterranean level descends half the slope down. Here the typical geoseries of this stage can be found: in climatophilous positions Junipero lagunae-Querco suberis S. and in edaphoxerophilous positions Junipero lagunae-Querco rotundifoliae S., dominated by mixed woods of Juniperus oxycedrus var. lagunae and Quercus rotundifolia. This space had traditionally an extensive pasturage use; the expansion of perennial crops down to the middle of the slope as well as the clearance of the woods became more generalized since the end of the 19 th century.

Dry inferior meso-mediterranean stage

This stage is localized at the lower portions and bottom of the valley slope. Its originality resides mainly in the vegetation of the floodplain. The vegetation catena of inundated areas, subjected to violent currents during the winter floods, is of utmost complexity. At the borders of the river, wherever currents are weak, woods of Alnus glutinosa [Scrophulario-Alnetum glutinosae] install, and where currents are stronger, willows of Salix salviifolia [Salicetum salviifoliae]. Sand deposits as well as rocky portions of the river bank are annually submersed, leading to sedimentation of significant quantities of organic matter which become quickly mineralized during summer. On the other hand, during summer this space is traditionally used as pasture for sheep and goats, contributing equally to fertilization of soil. For these reasons the vegetation of river bank is mostly nitrophilous (Solano-Polygonetalia and Echio-Galactition). Rocky outcrops in the floodplains of the river bed are dominated by mosaic communities of Buxus sempervirens with pioneer communities of chamaephytes. Land use in this stage is largely similar to the before mentioned stage.

Additionally, it is referred that within this position, where infiltrated water of the plateau reappears through geological faults, woody communities of Celtis australis of uncertain syntaxonomy are frequent.

Semiarid inferior meso-mediterranean stage

This stage enters within the sector comprised between villages Picões and Felgar. It is characterized by shrubby formations of Pistacio-Rhamnetalia alaterni [Asparago-Rhamnion oleoidis], marked by the species Asparagus albus and Rhamnus oleioides.

II. METHODOLOGY

Between May and July 2002, a vegetation survey has been conducted, along the river valley as circumscribed by village of Porrais (Council of Mogadouro) upstream and Felgar (Council of Torre de Moncorvo) downstream, comprising a total number of 109 sample plots with quadrate size of 10m x 10m, at both sides of the river and at different altitudes, from the river bed upward, to allow for sampling of very diversified vegetation mosaic; species were identified and their respective abundamce determined. An important parameter is the land use or abandonment of cropping of sampled areas. The data will be used for multivariate analysis. A more profound perception of the vegetation, its dynamic and its disposal along environmental gradients (vegetation catena) of the area in concern implies resort to classic phytosociologic methods as well as symphytosociological concepts and methods (Géhu & Rivas-Martínez, 1981; Theurilat, 1992). On the other hand, these methodological approaches are of widespread use among the Iberian vegetation researchers, and they have also been applied to the territory studied by Costa et al. (1998) and Aguiar (2001). The schematic presentation of local vegetation catenas follows the work of these authors.

III.RESULTS & DISCUSSIONIn all, 395 taxons from 65 families were recorded. Distribution among families as well as spectrum of life-forms are shown in the following figures.

1: University of Bremen, Germany 2: Escola Superior de Bragança, Portugal

Life-forms (Raunkaier)

phanerophytes14%

chamaephytes8%

hemicryptophytes26%

therophytes46%

cryptophytes1%

geophytes5%

distribution among families

13 12 12

6 5 4 4 4 3 3 3 2 2

28

0

5

10

15

20

25

30

CompositaeGramineaeLeguminosaeUmbeliferae

Caryophyllaceae

CruciferaeLabiataeLiliaceae

Scrophulariaceae

Rosaceae

RanunculaceaePolygonaceaeRubiacaea

others

percentage