GEOMORPHIC PROCESSES ABOVE TIMBERLlNE IN THE SPANISH PYRENEES

ABSTRACT This paper prcsents a general account of geomorphic processes effective aboye timberline in the Spanish Pyrenees with emphasis on the central section of the range. Climatic and environmental factors are discussed in detail as well as thc geomorphic responses to lowering of the upper timberline, especially betwecn the sixteenth and ninetcenth centuries. During thi8 periad expansion of livestock grazing reduced the forest cover extensively and caused a substantiallowering of the lower altitudinallimit of periglacial activity. Relic periglacial forms are attributable to the Late Quaternary Period, although many active forms are present today. These include rock glaciers, solifluction lobes and tcrracettes, and various types of patterned ground. Altitude, exposure, slope gradient, and lithology are shown to be important determinant factors, together with the increasing degree of continentality in the Central Pyrenees compared with areas further west and east respectively. The high mountain region is divided into two altitudinal belts with the 2,400 m level forming the general boundary. RÉSUMÉ Processus géomorphiques au-dessus de la limite des arbres dans les Pyrénées espagnoles. Cet article donne un apen;u général des processus géomorphiques qui se produisent au-dessus de la limite des arbres dans les Pyrénées espagnoles, en particulier dans la partic centrale de la ehalne. Les facteurs climatiques et environnementaux sont examinés en détail, ainsi que les réponses géomorphiques a la descente de la limite supérieure des arbres, en particulier entre le seizieme et le dix-neuvieme siecles. Au cours de cette période, l'expansion du paturage de bétail a c::msldérablement réduit la converture fOrestiere et a causé une descente sensible de la limite altitudinale inférieure de l'activité périglaciaire. Les formes périglaciaires héritées peuvent etre attribuées a la fin de l'ere quaternaire