Composición y distribución espacial de la comunidad de bromelias epíficas (Bromeliaceae : Tellandsioideae) en un bosque húmedo premontano, con distintas etapas de sucesión ecológica Monteverde, Costa Rica, 2001-2002
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Fecha
2007
Autores
Duran Apuy, Alejandro
Sanahuja Rivera, Oscar
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Universidad Nacional (Costa Rica)
Resumen
distribución vertical y características de los sustratos utilizados en tres sitios con distinto grado de alteración: i) Vegetación Sucesional Temprana (VST), 15 años en regeneración; 1i) Bosque Secundario (30 — 40 años) el cual fue dividido en dos zonas: Interior (IBS) y Borde (BBS), y iii) Bosque Intervenido (BD), de más de 100 años. En cada uno de los sitios la comunidad de bromelias mostró diferencias en su comportamiento: de las 14909 plantas contabilizadas en el área de estudio, 68% se registraron en el BBS, 20% en la VST, 8% en el IBS y apenas 4% en el BI Asimismo de las 12 especies identificadas, 9 se presentaron en el BI, 3 en el BBS, 7 en el IBS, 6 en la VST. Catopsis nutans y Guzmania monostachia dominaron la composición en la VST y el IBS, y conjuntamente con Tillandsia fasciculata en el BBS, donde manifestaron altas tasas de reclutamiento y de individuos reproductivos. En el BI las especies más frecuentes fueron 7. fasciculata y T. tricolor, sin embargo, mostraron un pobre reclutamiento y escaso número de plantas reproductivas. La disminución en la riqueza de especies de bromelias desde el BI hacia la VST, la atribuimos en primer lugar a una reducción en la diversidad estructural de los fitóforos conforme aumentó la alteración del sitio. Hospederos menos complejos presentaron una menor diferenciación microclimática de los estratos, limitando su colonización a aquellas especies con requerimientos ecológicos similares. Sin embargo, en nuestro caso particular la estructura de la vegetación por si sola no podría explicar los patrones de colonización observados en los sitios. Por un lado, una disponibilidad desigual de semillas en los alrededores de los estadios, justificaría la poca ocurrencia o ausencia de algunas especies a pesar de contar con las adaptaciones necesarias para poblarlos, como fue el caso de 7. fasciculata y T. tricolor en la VST. Por otra parte, la mayor cantidad de semillas que lograron alcanzar las áreas correspondieron a especies que se desarrollan mejor bajo condiciones de alta incidencia luminosa, lo cual explicaría la pobre colonización del BI por especies propias de zonas boscosas, a pesar de que en esta área los fitóforos fueron estructuralmente más complejos y han estado expuestos a las semillas por mayor periodo de tiempo (más de 100 años). La abundancia de G. monostachia y C. nutans en la VST la atribuimos a las condiciones favorables de la corteza del fitóforo dominante (Acnistus arborescens), así como al abastecimiento interno de semillas por parte de plantas adultas. El aumento en el perfil vertical de la vegetación promovió un mayor grado de separación vertical de las bromelias, sin embargo, la poca preferencia de las especies dominantes por algún tipo de sustrato en particular refleja que su posicionamiento en el fitóforo esta en función de que los sustratos cuenten con condiciones microclimáticas adecuadas,.como lo evidencia claramente la mayor frecuencia de bromelias en el BBS, la cual es el resultado de un aumento en la cantidad de área colonizable, gracias a una mayor incidencia de luz a lo largo del perfil vertical de la vegetación, habilitando regiones del fitóforo como el tronco, sustrato poco utilizado en el IBS. El estadio sucesional del bosque parece no afectar la distribución espacial de las bromelias en cuanto a la inclinación del sustrato o a su localización en el mismo; en la mayoría de los casos se ubicaron con mayor frecuencia en ramas secundarias y terciarias las cuales se caracterizan por fuertes inclinaciones; de igual manera un mayor posicionamiento lateral parece ser una consecuencia del desprendimiento y arrastre de las semillas desde la parte superior de las ramas hacia las zonas laterales debido a las fuertes precipitaciones de la zona.
Vertical distribution and characteristics of the substrates used in three sites with different degrees of alteration: i) Early Successional Vegetation (ESV), 15 years in regeneration; 1i) Secondary Forest (30 — 40 years) which was divided into two zones: Interior (IBS) and Edge (BBS), and iii) Intervened Forest (BD), over 100 years old. In each of the sites, the bromeliad community showed differences in its behavior: of the 14,909 plants counted in the study area, 68% were registered in the BBS, 20% in the VST, 8% in the IBS and only 4% in the BI Likewise, of the 12 species identified, 9 were presented in the BI, 3 in the BBS, 7 in the IBS, 6 in the VST. Catopsis nutans and Guzmania monostachia dominated the composition in the VST and the IBS, and together with Tillandsia fasciculata in the BBS, where they showed high rates of recruitment and reproductive individuals. In BI, the most frequent species were 7. fasciculata and T. tricolor, however, they showed poor recruitment and few reproductive plants. The decrease in the richness of bromeliad species from the BI to the VST, we attributed in the first place to a reduction in the structural diversity of the phytophores as the alteration of the site increased. Less complex hosts showed less microclimatic differentiation of the strata, limiting their colonization to those species with similar ecological requirements. However, in our particular case, the vegetation structure alone could not explain the colonization patterns observed at the sites. On the one hand, an unequal availability of seeds in the surroundings of the stages would justify the low occurrence or absence of some species despite having the necessary adaptations to populate them, as was the case of 7. fasciculata and T. tricolor in the VST. On the other hand, the largest number of seeds that managed to reach the areas corresponded to species that develop better under conditions of high incidence of light, which would explain the poor colonization of the BI by species typical of forested areas, despite the fact that in this area phytophores were structurally more complex and have been exposed to seeds for a longer period of time (more than 100 years). We attribute the abundance of G. monostachia and C. nutans in the VST to the favorable conditions of the bark of the dominant phytophore (Acnistus arborescens), as well as to the internal supply of seeds by adult plants. The increase in the vertical profile of the vegetation promoted a greater degree of vertical separation of the bromeliads, however, the little preference of the dominant species for any type of substrate in particular reflects that their position in the phytophore is a function of the fact that the substrates have adequate microclimatic conditions, as clearly evidenced by the higher frequency of bromeliads in the BBS, which is the result of an increase in the amount of colonizable area, thanks to a greater incidence of light along the vertical profile of the vegetation, enabling regions of the phytophore such as the trunk, a substrate little used in the IBS. The successional stage of the forest does not seem to affect the spatial distribution of the bromeliads in terms of the inclination of the substrate or its location in it; in most cases they were located more frequently in secondary and tertiary branches which are characterized by strong inclinations; In the same way, a greater lateral positioning seems to be a consequence of the detachment and dragging of the seeds from the upper part of the branches towards the lateral zones due to the heavy rainfall in the area.
Vertical distribution and characteristics of the substrates used in three sites with different degrees of alteration: i) Early Successional Vegetation (ESV), 15 years in regeneration; 1i) Secondary Forest (30 — 40 years) which was divided into two zones: Interior (IBS) and Edge (BBS), and iii) Intervened Forest (BD), over 100 years old. In each of the sites, the bromeliad community showed differences in its behavior: of the 14,909 plants counted in the study area, 68% were registered in the BBS, 20% in the VST, 8% in the IBS and only 4% in the BI Likewise, of the 12 species identified, 9 were presented in the BI, 3 in the BBS, 7 in the IBS, 6 in the VST. Catopsis nutans and Guzmania monostachia dominated the composition in the VST and the IBS, and together with Tillandsia fasciculata in the BBS, where they showed high rates of recruitment and reproductive individuals. In BI, the most frequent species were 7. fasciculata and T. tricolor, however, they showed poor recruitment and few reproductive plants. The decrease in the richness of bromeliad species from the BI to the VST, we attributed in the first place to a reduction in the structural diversity of the phytophores as the alteration of the site increased. Less complex hosts showed less microclimatic differentiation of the strata, limiting their colonization to those species with similar ecological requirements. However, in our particular case, the vegetation structure alone could not explain the colonization patterns observed at the sites. On the one hand, an unequal availability of seeds in the surroundings of the stages would justify the low occurrence or absence of some species despite having the necessary adaptations to populate them, as was the case of 7. fasciculata and T. tricolor in the VST. On the other hand, the largest number of seeds that managed to reach the areas corresponded to species that develop better under conditions of high incidence of light, which would explain the poor colonization of the BI by species typical of forested areas, despite the fact that in this area phytophores were structurally more complex and have been exposed to seeds for a longer period of time (more than 100 years). We attribute the abundance of G. monostachia and C. nutans in the VST to the favorable conditions of the bark of the dominant phytophore (Acnistus arborescens), as well as to the internal supply of seeds by adult plants. The increase in the vertical profile of the vegetation promoted a greater degree of vertical separation of the bromeliads, however, the little preference of the dominant species for any type of substrate in particular reflects that their position in the phytophore is a function of the fact that the substrates have adequate microclimatic conditions, as clearly evidenced by the higher frequency of bromeliads in the BBS, which is the result of an increase in the amount of colonizable area, thanks to a greater incidence of light along the vertical profile of the vegetation, enabling regions of the phytophore such as the trunk, a substrate little used in the IBS. The successional stage of the forest does not seem to affect the spatial distribution of the bromeliads in terms of the inclination of the substrate or its location in it; in most cases they were located more frequently in secondary and tertiary branches which are characterized by strong inclinations; In the same way, a greater lateral positioning seems to be a consequence of the detachment and dragging of the seeds from the upper part of the branches towards the lateral zones due to the heavy rainfall in the area.
Descripción
Duran Apuy, A. & Sanahuja Rivera, O. (2007). Composición y distribución espacial de la comunidad de bromelias epíficas (Bromeliaceae: Tellandsioideae) en un bosque húmedo premontano, con distintas etapas de sucesión ecológica Monteverde, Costa Rica, 2001-2002. [Tesis de Licenciatura]. Universidad Nacional, Costa Rica.
Palabras clave
FLORA, BROMELIACEAE, BOSQUE NUBOSO MONTEVERDE (COSTA RICA), CLOUDY FOREST