Questions: Vascular epiphytes make up about 9% of all vascular plants globally but are clearly underrepresented in the temperate zones. The accidental epiphytic occurrence of terrestrial species, in contrast, is common at these latitudes and can provide important insights in the evolution of obligate epiphytes. Here, we present the results of the first two annual censuses of a planned long-term study on accidental epiphytes. We particularly aim to identify: (a) the abundance and species richness of accidental epiphytes; (b) the dynamics of accidental epiphytism; (c) occupied substrates and microsites; and (d) suitable host tree species. Location: Harz Mountains, Germany, Central Europe. Methods: We surveyed more than 1,200 trees in a low mountain range in two consecutive years for epiphytic individuals of vascular plants, considering host tree species and occupied microsites. Results: About one quarter of the surveyed trees hosted epiphytic plants, totalling 1 450 (2016) and 1 350 (2017) individuals, respectively. These belonged to more than 100 species and 39 different families. The majority of epiphytic individuals newly emerged in 2017, whereas one-third persisted since 2016 (or earlier) and a smaller proportion even reproduced in the epiphytic habitat. Accidental epiphytes were mostly restricted to host tree species providing water-storing substrates such as extensive moss pads or arboreal soil accumulated in crotches. Compared to tropical epiphyte communities, accidental epiphytes in the temperate zones show a higher turnover, as they are less consistent in species abundance and composition in time.Conclusion: For the majority of the observed species, epiphytism indeed is an accidental phenomenon. Undoubtedly, abiotic conditions limit the occurrence of obligate epiphytes at higher latitudes, but the presence and persistence of numerous epiphytic individuals illustrate that abiotic conditions do not per se preclude epiphytic occurrence of vascular plants in the north-temperate zone. Besides water shortage, the availability of suitable host trees is a decisive environmental factor that contributes to limit epiphytism of vascular plants in Central Europe.

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Although it has long been acknowledged that seed characteristics are of major importance to the conquest of tree crowns by vascular epiphytes, there is surprisingly little quantitative evidence on the aerodynamic properties of their diaspores. We used a custom-built device to determine the terminal velocity (Vterm) of falling seeds, a parameter that has been shown to have high predictive power for the wind dispersal potential of diaspores under natural conditions. We determined Vterm of 45 species of epiphytic and terrestrial Orchidaceae, which almost doubles the currently available database for this family. Although varying by a factor of five with values of 0.09–0.4 m s−1, Vterm was invariably very slow compared to plants in general. For each species, we also took morphological data and determined seed mass. None of these parameters was linearly correlated with Vterm and neither did the average Vterm differ between species found in the two habitats, although seeds of terrestrial taxa were significantly larger and heavier. Finally, we demonstrate the potential of our device to measure Vterm of even smaller diaspores by successfully quantifying Vterm of fern spores. This tool has much potential for the quantitative study of dispersal of plants with tiny diaspores, particularly in a conservation context in fragmented landscapes.

Antecedentes y Objetivos: Las especies de Araceae son conocidas por sus distintas formas de vida; sin embargo, la terminología relacionada con este grupo genera confusiones conceptuales dentro de la comunidad científica. Nuestro objetivo fue demostrar la confusión conceptual actual derivada de la literatura y ejemplares de herbario vs. observaciones y datos de campo. Métodos: Se realizó una revisión exhaustiva de fuentes de información relevantes sobre las formas de vida de aráceas, incluyendo floras y tratamientos taxonómicos, así como de ejemplares de herbario. Adicionalmente, se llevó a cabo un censo de seis especies de aráceas en la Estación de Biología Tropical “Los Tuxtlas”, Veracruz, México. Para cada individuo se buscaron las conexiones de sus raíces adventicias y tallos con el suelo, además se tomaron medidas de su longitud total y hojas para crear tres clases ontogénicas. Resultados clave: Se presentan las descripciones de formas de vida de 30 especies de Araceae trepadoras de Veracruz publicadas en nueve publicaciones, mostrando una marcada inconsistencia en el uso de la terminología. El análisis de los datos documentados en los ejemplares de herbario reveló para 17 especies, que todas fueron asignadas con al menos tres de ocho diferentes categorías de hábito, principalmente como epífita, hemiepífita y trepadora. De las seis especies censadas en campo, la mayoría de los individuos tiene conexión con el suelo. Conclusiones: Las asignaciones de formas de vida basadas en observaciones de campo sin tener datos cuantitativos sobre el contacto de las plantas con el suelo son problemáticas. Más bien, es necesario analizar y aclarar la ontogenia de las aráceas trepadoras, lo que puede contribuir a estructurar adecuadamente nuestros conceptos y evitar ambigüedades en la terminología. Asimismo, también se debería evitar que se agrupen a las especies de Araceae indistintamente en estudios sobre epífitas, lo cual lleva a sobreestimar la riqueza reportada.

As climate change leads to increasing temperatures, tropical dry seasons are expected to become more severe. An overall intensification of drought events may strongly affect vascular epiphytes. Especially at the community level, the response of epiphytes to intense drought events is still poorly understood. Therefore, the severe El Niño event of 2015/16 was used to assess the impact of prolonged drought on an epiphyte community on Annona glabra host trees, around Barro Colorado Island. Prior census data from 2002 and 2015 served as a reference for background community dynamics. Net species changes and net population changes at the species level were determined for both periods. While the total abundance of the community almost doubled during the 13 years of the reference period, individual numbers decreased by c. 17% within the year of the El Niño event. Overall, the El Niño event strongly affected the epiphyte community and led to a strong decrease in epiphyte numbers and species. These findings contrast with most previous studies in tropical lowlands that found epiphyte populations to be rather resistant to similarly severe drought events.

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