Flora y vegetación de los Montes Obarenes (Burgos)

Abstract

The vegetation of an area located in the north-western part of the province of Burgos (Spain) is analysed. The area studied covers a series of parallel mountain ranges running north west to south east called Sierra de Oña, Montes Obarenes, Sierra de Pancorbo, Sierra La Llana and Macizo de Rumión. The mountains are between roughly 1,000 metres and 1,400 metres high. The ranges are separated by small valleys of an average of between 500 and 800 metres high. The land is largely limestone; siliceous outcrops are scarce and forro islets. The ranges are mainly composed of calcareous materials from the .Cretaceous period, while the valleys are rich in materials from the Tertiary. The terraces of the river Ebro and the quaternary glacis are also worthy of note.

In bioclimatic terms, the study area is a subhumid rainfall zone within a supra-Mediterranean  thermotype, with lower, middle and upper horizons distinguishable. The floristical study of the area has identified 1,301 taxons, of which we collected 1,247. The rest are citations from other authors we consider reliable. Forty-eight taxons were actually new to the province of Burgos. Owing to the transitional character of the area, a high percentage of Euro­Siberian elements can be seen in the vascular flora together with elements from the Mediterranean optimum. Plants with significant presence in the study area include:

- Taxons distributed in the Pyrenean-Cantabrian area: Dethawia tenuifolia, Alchemilla plicatula, Saxifraga hirsuta, Pritzelago alpina subsp. alpina, etc.

-  Taxons  of  the  Orocantabian optimum: Anemone  pavoniana,  Gentiana occidentalis, Androsace villosa, Saxifraga conifera, etc.

- Taxons more or less widely distributed throughout the lberian peninsular: Aster aragonensis, Aster willkommii, Campanula hispanica, Centaurea ornata, !nula langeana, Lavandula stoechas subsp. pedunculata, Saxifraga cuneata, Sesleria argentea, Sideritis guillonii subsp. brevispica, Silene legionensis, etc.

The Braun-Blanquet phytosociological method was followed for the study of vegetal communities, with 71 types of communities, grouped into 21 phytosociological classes, being identified in the area. The following sintaxons are described as new:

Festuco heterophyllae-Quercetum pyrenaicae Br.-Bl. 1947 populetosum tremulae subass. nova

Arctostaphylo crassifoliae-Genistetum occidentalis Rivas-Martínez, T.E. Díaz, F. Prieto, Loidi & Penas 1984 juniperetosum alpinae subass. nova

Koelerio vallesianae-Thymetum mastigophori García-Mijangos, Loidi & Herrera1994 brachypodietosum retusi subass. nova

Aveno-Seslerietum hispanicae Br.-BI. 1967 corr. Rivas-Martínez, Báscones, T.E. Díaz, F. Fernández-González & Loidi 1991 gentianetosum occidentalis subass. nova

Ericetum scopario-vagantis Loidi, García-Mijangos, M. Herrera, Berastegi & Darquistade 1997 lavanduletosum pedunculatae subass. nova

Drabo dedeanae-Saxifragetum cuneatae Romo 1988 dethawietosum tenuifoliae subass. nova

The following associations were validated:

Avenulo mirandanae-Brachypodietum phoenicoidis G. Mateo 1983 nom. inval. (art. 5 of the CPN)

 Scirpo holaschoeni-Molinietum (Br.-Bl. 1931) nom. nov.

(Molinietum mediterraneum Br.-BI. 1931 nom. ileg.) (Art. 34 of the CPN)

The vegetal landscape study facilitated the identification of the following vegetation series in the area studied:

- Cantabrian-Atlantic and Orocantabrian mountain, basophilous and rain-adapted series of the beech (Carici sylvaticae-Fageto sigmetum)

-  Mountain and  supramediterranean orocantabrian, cantabrian-basque and castilian-cantabrian basophilous and xerophilous series of the beech (Epipactido helleborines-Fageto sigmetum)

Iberian-sorian, supramediterranean, ayllonense and castilian-cantabrian silicicolous series of the oak (Quercus pyrenaica) (Festuco heterophyllae-Querceto pyrenaicae sigmetum)

- Meso-supraMediterranean Castilian-Cantabrian basophilous series of the oak

(Quercus faginea) (Spiraeo obovatae-Querceto fagineae sigmetum)

-  Meso-supraMediterranean Castilian-Cantabrian basophilous series  of  the evergreen oak (Quercus rotundifolia) (Spiraeo obovatae-Querceto rotundifoliae sigmetum)

- Edapho-hygrophilous Castilian-Cantabrian series of the alder (Humulo lupuli­ Alneto sigmetum