In the Chile's Choapa valley (4th Region), the small-scale irrigated agriculture found today was brought about by the changes in land tenure which occurred between 1965 and 1975. In the Chillepin district, an extensive holding that produced wheat and cattle was expropriated and, after a period of collective farming, small family holdings of vineyards and orchards took their place. These changes were studied over a 50 years period through the use of social enquiries, local history, vegetation measurements and aerial photographs so as to compare the effects of the successive agrarian systems on the environment. The most intense wood extraction occurred during the 8 years' period just after the expropriation. During 25 years of small family farming we observed that (i) diversity and number of cultivated plots in the irrigated area have increased and (ii) tree vegetation in the hinterland has partially recovered. Keywords: Social evolution, Land use, Vegetation, Deforestation, Family farming, Semi-arid climate, Environment, Northern Chile.