<p>Most demographic studies of ferns have been conducted in temperate or tropical humid environments. In this study, we examined the microhabitat preferences and population dynamics of <i>Myriopteris aurea</i> and <i>Pellaea ternifolia</i> in a seasonally dry environment. We conducted three annual censuses and used transition matrix models to estimate the stable population structure, reproductive value and finite growth rate (λ) of each fern population. We calculated the latter for three scenarios of different rainfall probabilities (25%, 50% and 75% rainy years) with a stochastic matrix. Although the two species differed in their microhabitat preferences, both had growing populations and with lower values in the second, drier year (λ_{<i>M. aurea</i>} = 1.53 and λ_{<i>P. ternifolia</i>} = 1.67) than in the first, wetter year (λ_{<i>M.</i> <i>aurea</i>} = 2.52 and λ_{<i>P.</i> <i>ternifolia</i>} = 2.29). During the dry year, the elasticities of growth decreased by 10%, whereas those of permanence increased by 25%. Consequently, both xeric fern species maintained a growing population by reducing growth and increasing permanence during the drier year. Even for rainfall scenarios with only 25% probability of rainy years, both species had λ &gt; 1. Rapid changes in vital parameters, such as reduced fertility and growth but higher permanence during the dry year, are part of the plasticity of these ferns and enable both species to thrive in xeric habitats with interannually variable precipitation.</p>