Geomorphological approach for natural milieux analysis in humid tropical zone : the case of an agricultural frontier in north Colombia (South America ) Isopatterned areas were defined from a systemic point of view, from the texture climate/relief completed by land use data. Among five transects (i.e. reference areas), one alone is here studied. This 300km2 ares is a tropical, humid and mountainous one, with recent and unwary land use which has produced dilapidation for the milieu and worsening for the peasantry way of life. Slopes are of second importance, but morphodynamic processes are the best structuring factor. More often than not, the most swift morphodynamic evolution takes place during the first three years of farming and diminishes after rapidly ; versant becomes almost stable, but soil fertility lowers : after cropping by pioneers, great land-owners begin extensive ranching. After twenty yeats, fields are occupied by a little forest with clearings.