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INTRODUCCIÓNEn este trabajo se realiza una aproximación a la caracterización fitoclimá-tica de un conjunto montañoso incluido en el sector palentino de las montañas cantábricas centrales y cuya culminación principal es el pico Curavacas (2.524 m, figura 1). En su mayor parte se asienta sobre una estructura sinclinoria dominada por conglomerados primarios y perteneciente a la región geológica del Pisuerga-Carrión (Rodríguez Fernández, 1994). La rigidez de los conglomerados westfalienses posibilita la existencia de un denso entramado de fracturación que determina una nítida compartimentación del macizo. Siguiendo las direcciones de las principales líneas de fractura el macizo se articula, especialmente en su vertiente septentrional, en diferentes umbrales y cubetas sobre los que ejerció su labor abrasiva el hielo pleistoceno (Frochoso & Castañón, 1996; Pellitero Ondicol, 2013a y 2013b.A la singularidad de las geoformas heredadas y las litologías que lo conforman se suma la peculiaridad de sus comunidades vegetales. Es un sector de

The Iberian populations of Juniperus oxycedrus L. subsp. oxycedrus have been studied by several authors who consider their condition as unfavourable. In the Madrid Region, current status, dynamic and distribution area are unknown even when their populations, specifically those who form arborescent shrubs, are included in the type 5210 (Habitat Directive 92/43/EEC). These formations are developed in austere Mediterranean mountain typical of agro ecosystems of high value that have interesting dynamics of recolonization, especially in those areas where agricultural and livestock systems have suffered a setback. This study aims to understand the distribution of juniper in the region of Madrid as the first step to identify and assess the dynamic changes in recent decades. To update the cartography of this species the available information has been checked and completed with photointerpretation and fieldwork. Based on this cartography and the information relating to the physical and biotic variables four types of juniper were differentiated by multivariate methods. On the other hand, two types of dynamics were recognized and it was studied in depth the genesis of changes produced in these forests in the last decades.