The tree fern Alsophila setosa, occurs in primary and secondary forests of southern and southeastern Brazil. Two populations in secondary forest formations in the northeastern part of the State of Rio Grande do Sul, in the municipalities of Morro Reuter (45 plants) and Sapiranga (48 plants), were studied to estimate the ages of the plants. Two approaches were tested, one based on the total length in relation to the yearly growth rate of the caudex, and the second on the total number of scars and remains of stipe bases along the caudex in relation to the yearly frond production. Estimates based on growth rates and total length did not agree with the information and records of the past land use, whereas frond production over a longer time period presented acceptable estimates. The development of a new plant formed through vegetative reproduction was observed during three years. A brief discussion of the problems of age estimates in tree ferns is presented.