Microclimatic Preferences and Phenology of Terrestrial Xeric Ferns in Seasonally Dry Shrubland in Central Mexico

Plant phenology describes the response of plants to cyclic environmental fluctuations and is a powerful tool in the face of climate change. Most phenological studies in ferns have focused on humid environments, where water is not a limiting factor. However, Mexico has a great diversity of ferns growing in xeric environments (ca. 120 species). We studied the preference for slope aspects and phenological patterns of four of these desiccation-tolerant fern species in a seasonally dry shrubland of central Mexico for 18 months. South-facing rock surfaces and rock tops reached up to 6°C higher air temperatures and up to 24°C higher rock temperatures than North-facing rock surfaces. Myriopteris aurea grew most frequently on the hot rock tops, whereas M. myriophylla and Gaga kaulfussii were most common on cooler northern aspects, and Pellaea ternifolia was found on all lateral rock surfaces. Leaf production and growth of all species were positively correlated with rainfall, but the total leaf number was not seasonal because of their desiccation tolerance. Myriopteris aurea was the first to develop new leaves after the first rainfalls but its leaves dehydrated faster than in the other three species. Myriopteris myriophylla had scaly leaves with the longest life span (7.9 ± 1.1 months), whereas G. kaulfussii had the fastest rehydrating leaves and the highest leaf production during the rainy season. Pellaea ternifolia had glabrous leaves with the shortest life span (4.8 ± 0.2 months). We conclude that each fern species developed a different combination of xeric adaptations to survive under these extreme environmental conditions.