Stilt Root Structure in the Neotropical Palms Iriartea deltoidea and Socratea exorrhiza¹

Abstract

Many arborescent palms develop a stilt root cone that provides increased mechanical support on steep hillsides, better root aeration under waterlogged conditions, resprouting after mechanical damage, and rapid stem elongation. However, for most species the role of stilt roots is not well understood. We determined how palm size and slope inclination affected the structure of stilt roots in the neotropical palms Iriartea deltoidea and Socratea exorrhiza. We expected palm height to be lower on steep slopes because the effectiveness of root support could decrease as slope inclination increases, and thus, the structure of the root cone would vary mostly with slope. Alternatively, if stilt root development is determined by palm size, their production should match stem height, with taller palms having larger cones. We measured the stilt root cone of 31 Iriartea and 36 Socratea palms in San Ramón Biological Reserve and Golfito Wildlife Refuge, Costa Rica. We divided the cone into five variables (horizontal projections of the cone base and stilt root height up and down the slope, and width of the cone base), from which we extracted the first two principal components and used them to measure the effects of slope and palm size on stilt root structure. We found stilt roots to be determined by palm size, not by slope conditions. Stilt roots matched palm size, with larger palms having taller and larger cones, maintaining stability under diverse slope conditions. RESUMENMuchas palmas arborescentes desarrollan un cono de raíces fúlcreas el cual provee mayor apoyo mecánico sobre pendientes pronunciadas, mejor aereación de raíces bajo condiciones de anegación, facilitan la capacidad de retoñar ante daños mecánicos, y favorecen una rápida elongación del tallo. Sin embargo, en la mayoría de las especies la función de las raíces fúlcreas no está bien comprendida. Determinamos cómo el tamaño de la palma y la inclinación de la pendiente afectaron la estructura de las raíces fúlcreas en las palmas Neotropicales Iriartea deltoidea y Socratea exorrhiza. Esperábamos que la altura de la palma fuera menor en mayor pendiente, ya que la efectividad del soporte de la raíz podría disminuir con el aumento de la inclinación de la pendiente, y por lo tanto, la estructura del cono de la raíz podría variar principalmente con la pendiente. Alternativamente, si el desarrollo de las raíces fúlcreas está determinado por el tamaño de la palma, su producción debería igualar la altura del tallo, con las palmas más altas teniendo mayores conos. Medimos el cono de las raíces fúlcreas en 31 palmas de Iriartea y 36 de Socratea en la Reserva Biológica de San Ramón y en el Refugio de Vida Silvestre Golfito, Costa Rica. Dividimos el cono en cinco variables (proyecciones horizontales de la base del cono y altura de las raíces fúlcreas a favor y en contra de la pendiente, y ancho de la base del cono), a partir de las cuales obtuvimos los dos primeros componentes principales, y los usamos para medir los efectos de la pendiente y el tamaño de la palma sobre la estruct...

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

“…However, stilt root architecture did not differ between trees on sloped and flat locations. This supports previous work that S. exorrhiza alters neither its physical structure nor its investment in stilt roots in relation to degree of slope (Avalos et al 2005). The difference in stilt root height between La Selva and BCI may reflect site-specific abiotic conditions or population characteristics; however, it is unlikely that the difference (<0.3 m) on trees averaging over 14 m height is of biomechanical significance.…”

“…The association of Iriarteoid palms with steep sloped habitats has led to the suggestion that stilt roots may be an adaptation to unstable conditions and provide mechanical stability against uprooting (Henderson 1990, Chiatante et al 2002. However, Avalos et al (2005) concluded that stilt roots do not provide enhanced stability on sloped locations, and found that stilt root architecture is instead a function of stem volume.In addition to hypotheses addressing enhanced structural stability, it has also been suggested that stilt roots allow for a unique vertical growth strategy. Hartshorn (1983) suggested that stilt roots in S. exorrhiza may facilitate rapid growth towards the canopy when light becomes available in the understory.…”

“…The association of Iriarteoid palms with steep sloped habitats has led to the suggestion that stilt roots may be an adaptation to unstable conditions and provide mechanical stability against uprooting (Henderson 1990, Chiatante et al 2002. However, Avalos et al (2005) concluded that stilt roots do not provide enhanced stability on sloped locations, and found that stilt root architecture is instead a function of stem volume.…”

Allometric estimation of total leaf area in the neotropical palm Euterpe oleracea at La Selva, Costa Rica

“…In contrast to our results, Kimura and Simbolon (2002) predicted that adult palms of Pinanga coronata should have a constant crown mass irrespective of stem height once the stem diameter has been fixed. Contrary to palms in which the stem diameter is fixed at an early stage, species like E. oleracea, E. precatoria and E. edulis, Prestoea decurrens, P. acuminata, Iriartea deltoidea and Socratea exorrhiza are able to exhibit a sustained increased in diameter with increasing stem height (Alves et al 2004;Avalos et al 2005;Avalos 2007;Avalos and Fernandez-Otarola 2010).…”

Allometric Equations for Estimating Biomass of Euterpe precatoria, the Most Abundant Palm Species in the Amazon

“…8 cm). It has been reported that some palm species including E. precatoria develop stilt roots to structurally support its slender-shaped stem [22,36]. Euterpe precatoria may need the large root portion accompanied by the stilt root development for support under physically unstable habitat conditions on sandy soils with seasonal inundation.…”