A method by which a physical model of the solar radiation transfer in a vegetal medium is inverted to estimate the leaf area index (LAI) for different types of vegetation is presented here, as an alternative to the destructive experiments, which are a hard task to implement on the vegetation covers. Radiation data were obtained during the dry season - 1996, at the Embrapa Experimental Station, (BR 174 - km 54, 2º 31' S, 60º 01' W), Manaus, Brazil. The method yielded convergent values for the LAI between different adopted radiation classes with more stable estimates at time when there is a predominant diffuse radiation. The application of the inversion algorithm yields the following values for the leaf area index and respective annual foliage increments:3.5 (0.35 yr.-1) for the intact secondary forest; 2.0 (0.5 yr-1) for the palm agroforestry system; and 1.6 (0.4 yr-1) for the multi-layer ones.", 'en
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