Restauración ecológica de bosques tropicales en Costa Rica: efecto de varios modelos en la producción, acumulación y descomposición de hojarasca

Tropical forest restoration in Costa Rica: the effect of several strategies on litter production, accumulation and decomposition. Tropical forest restoration strategies have the potential to accelerate the recovery of the nutrient cycles in degraded lands. Litter production and its decomposition represent the main transfer of organic material and nutrients into the soil substrate. We evaluated litter production, accumulation on the forest floor, and its decomposition under three restoration strategies: plantation (entire area planted with trees), island (trees planted in patches of three different sizes) and control (natural regeneration) plots. We also compared restoration strategies to young secondary forest (7-9yr). Restoration treatments were established in 50x50m plots in June 2004 at six sites in Southern Costa Rica. Planted tree species included two native timber species (Terminalia amazonia and Vochysia guatemalensis) interplanted with two N fixers (Erythrina poeppigiana and Inga edulis). Litter was collected every 15 days between September 2008 and August 2009 in 12 0.25m² litter traps distributed within each plot; litter that accumulated on the soil surface was collected at four locations (0.25m² quadrats) within each plot in February and May 2009. Total litter production in plantation (6.3Mg/ha) and secondary forest (7.3Mg/ha) did not differ, but were greater than in islands (3.5Mg/ha) and control (1.4Mg/ha). Plantation had greatest accumulation of litter on the soil surface (10.6Mg/ha) as compared to the other treatments (SF=7.2; I=6.7; C=4.9). Secondary forest was the only treatment with a greater annual production of litter than litter accumulation on the soil surface. Carbon storage in litter was similar between plantation and secondary forest, and significantly greater than the other treatments. No differences were found for carbon concentration and storage in the soil among treatments. There was also high variability in the production and accumulation of litter and carbon among sites. Active restoration treatments accelerated the production of litter and carbon storage in comparison to areas under natural recovery. However, the nutrient cycle has not necessarily been restored under these conditions, as high litter accumulation on the soil surface indicates a low decomposition rate, which slows nutrient return to the soil. Rev. Biol. Trop. 59 (3): 1323-1336. Epub 2011 September 01.

Estrategias de restauración tienen el potencial de acelerar el restablecimiento del ciclo de nutrientes en áreas degradadas. En este estudio, se evaluó la producción de hojarasca, su acumulación y descomposición bajo tres tratamientos: plantación (toda la superficie plantada); islas (árboles sembrados en parches de tres tamaños) y testigo (regeneración natural). También se compararon bosques secundarios jóvenes (7-9 años). Los tratamientos fueron establecidos en parcelas de 50x50m en junio 2004 en seis sitios en el sur de Costa Rica. Las especies introducidas fueron dos maderables (Terminalia amazonia y Vochysia guatemalensis) intercaladas con dos fijadoras de nitrógeno (Erythrina poeppigiana e Inga edulis). La producción total de hojarasca en la plantación y bosque secundario no difirió significativamente, fue mayor que en las islas y el testigo. La plantación presentó mayor acumulación de hojarasca sobre el suelo. Los resultados indican una gran variabilidad entre los sitios. Ambas estrategias de restauración activas aceleraron la producción y acumulación de hojarasca en comparación con la regeneración. No obstante, eso no implica la restauración del ciclo de nutrientes. La elevada acumulación de hojarasca sobre el suelo indica baja tasa de descomposición y de retorno de nutrientes al suelo.

The function of stilt roots in the growth strategy of Socratea exorrhiza (Arecaceae) at two neotropical sites

Arboreal palms have developed a variety of structural root modifications and systems to adapt to the harsh abiotic conditions of tropical rain forests. Stilt roots have been proposed to serve a number of functions including the facilitation of rapid vertical growth to the canopy and enhanced mechanical stability. To examine whether stilt roots provide these functions, we compared stilt root characteristics of the neotropical palm tree Socratea exorrhiza on sloped (>20º) and flat locations at two lowland neotropical sites. S. exorrhiza (n=80 trees) did not demonstrate differences in number of roots, vertical stilt root height, root cone circumference, root cone volume, or location of roots as related to slope. However, we found positive relationships between allocation to vertical growth and stilt root architecture including root cone circumference, number of roots, and root cone volume. Accordingly, stilt roots may allow S. exorrhiza to increase height and maintain mechanical stability without having to concurrently invest in increased stem diameter and underground root structure. This strategy likely increases the species ability to rapidly exploit light gaps as compared to non-stilt root palms and may also enhance survival as mature trees approach the theoretical limits of their mechanical stability. Rev. Biol. Trop. 55 (3-4): 787-793. Epub 2007 December, 28.

Comparamos características físicas de raíces aéreas de la palmera Socratea exorrhiza en sitios inclinados (pendiente>20º) y sitios planos, en dos lugares neotropicales. S. exorrhiza (n=80 árboles) no muestra diferencias en el número de raíces, la altura vertical de las raíces, la circunferencia y la masa del cono de las raíces, o la posición de las raíces en los sitios con pendiente. Encontramos relaciones positivas entre el crecimiento vertical y la arquitectura de las raíces aéreas, incluso entre el número de raíces, la circunferencia del cono de las raíces, y la masa del cono de las raíces. Es posible que las raíces aéreas permitan a S. exorrhiza crecer en altura y mantener la estabilidad mecánica sin involucrar el diámetro del tallo y la estructura de las raíces subterráneas. Probablemente, esta estrategia incrementa la capacidad de la especie para usar claros de luz rápidamente, en comparación con palmeras carentes de raíces aéreas; posiblemente también exista un incremento en su supervivencia cuando las adultas palmeras se acercan a sus límites de estabilidad mecánica.