Effect of the clearfelling on the water quality: Example of a spruce forest on a small catchment in France



This paper presents the variation of the hydrology and the water quality of a spruce catchment, located at Mont-Lozére (France), in a mediterranean mountain climate area , in relation to the forest status during 12 years (1981-1993). Four situations were successively examined : healthy forest (1981-84), declining stand with pest (1984-87), gradual clearfelling (1987-89) and reforestation (1989-93). An undisturbed beech catchment was used to provide reference values. In the hydrological budgets, the P-Q value (as ETR) was slightly higher in the spruce catchment than in the beech one during the first period and decreased progressively in the following ones as a consequence of: (1) the declining stand of the forest and (2) the clearfelling. No change was observed for cations, and NO3 concentrations remained were very low during the whole period in the streamwater of the beech catchment , in relation to the steady state of that ecosystem. Iin the spruce catchment,the concentrations of cations and NO, were always higher, and increased slightly during the disease. During the clearfelling, NO3 was strongly related to Ca and Mg. Six months after the reforestation, NO,, Ca , Mg concentrations were respectively 11,9 , 2,6 and 3,6 higher than at the begiming of the clearfelling.They retumed to previous values at the end of 1993. The Input-Output budget of cations presented a continuous storage in the beech catchment and simultanously a permanent release in the spruce catchment . The mean loss, -expressed as the denudation cation rate, in keq.ha-1.year-1 was as follow: -0,41 (1981-84), -0,65 (1984-87), -1,60 (1987-89) and -0,82 (1989-93).The leaching was observed during more than 6 years after the clearfelling, resulting probably from the duration of the drought period , and from the mineralization of the remaining important organic matter comparhnent

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