Due to the current predatory exploitation and consequent extinction of native medicinal plants around the world, strategies have been proposed aiming at the sustainable use of these resources. Accordingly, this study aims at verifying the differences in tannin compounds content in the bark of eleven species with high use value (UV) and also relating the amounts of tannins with their therapeutic indications. To quantify the total phenolic content in the samples the Folin-Ciocalteu reagent was used, and for total tannins chemical casein precipitation was applied. The amount of tannins ranged intra-specifically and the greater variation was found for Anadenanthera colubrina(angico) that displayed between 157.57 and 107.39 mg/g. The lowest variation occurred in Lafoensia replicata(mangabeira) with values ranging between 76.55 and 68.96 mg/g. There were significant differences between several of the eleven species and according to the simple regression analysis, the quantities of tannins found failed to justify their UV. Thus, it was not possible to establish whether the amount of total tannins influenced to a greater or lesser degree in the accumulation of knowledge. Moreover, this is the first study to investigate the relationship between the amount of total tannins and local botanical knowledge expressed by the UV.

Examinou-se a influência da sazonalidade climática sobre as concentrações de taninos em duas espécies da Caatinga: Myracrodruon urundeuva (Engl.) Fr. All. e Anadenanthera colubrina (Vell.) Brenan. Empregou-se o método Folin-Ciocalteau para quantificar os fenóis totais e o método de precipitação da caseína para taninos. De maneira geral, existe uma forte relação entre os teores de taninos e a pluviosidade, apesar das espécies parecerem adotar diferentes estratégias de produção de compostos tânicos em resposta aos períodos de seca e chuva na caatinga.

The influence of seasonal climatic changes on tannin concentrations was examined in two caatinga (semi-arid) plant species (Myracrodruon urundeuva (Engl.) Fr. All. and Anadenanthera colubrina (Vell.) Brenan). The Folin-Ciocalteau method was used to quantify total phenols, and the casein precipitation method was used for tannins. In general, there is a close relationship between tannin levels and rainfall, although species seem to adopt different strategies of tannin compound production in response to periods of drought and rainfall in the caatinga.