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

Abstract

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. Tropical wet rain forest trees use several root architectural strategies to cope with a number of harsh edaphic conditions including waterlogging, poorly developed soil profiles, and unstable soils (Dransfield 1978). Jeník (1978) identifies at least 25 model root systems in tropical trees, of which the most striking are buttresses and stilt or aerial adventitious roots. Stilt roots have evolved in many plant families, but most species belong to the Arecaceae (Richards 1996). Iriarteoid palms, which include the genus Socratea H. Karst., have stilt roots that arise from the lower portion of the stem and grow freely in the air until they make contact with the ground and root (Kahn and de Granville 1992). In Socratea exorrhiza (Mart.) H. Wendl., a common lowland neotropical species, stilt roots begin establishing almost immediately following seedling germination (Kahn and de Granville 1992). Mature S. exorrhiza demonstrate great individual variation in stilt root patterns with respect to the number, size, and height of roots, such that their function has been debated extensively.Despite a number of proposed hypotheses, the function of stilt roots in palms remains poorly understood. In a now refuted hypothesis (Dransfield 1978, Kahn andde Granville 1992), Corner (1966) suggested that stilt root palms were associated with areas prone to water-logging and flooding. Bodley and Benson (1980) coined the term "walking palm" by observing saplings of S. exorrhiza 'escape' from beneath fallen debris by developing new roots on the opposing side of a disturbance and effectively righting themselves by allowing old roots to rot away. In turn, Swaine (1983) observed that stilt roots may allow individuals to est...

Tree Diversity Explains Variation in Ecosystem Function in a Neotropical Forest in Panama

“…For example, environment only affected the carbon storage in palms (Andersen et al . 2010), where slope (Svenning 1999, Goldsmith & Zahawi 2007) and soil texture (Costa et al . 2009) have been identified as the strong predictors.…”

Allometry and stilt root structure of the neotropical palm Euterpe precatoria (Arecaceae) across sites and successional stages

“…Stilt roots facilitate further height increases, enabling resprouting when the palm has been knocked down by falling trees, allowing to grow out of debris accumulation or after a disturbance (Bodley and Benson, 1980; Avalos, 2004). Relatively few palm species have been explored in terms of their stilt root structure (Dransfield, 1978; Schatz et al, 1985; Avalos et al, 2005; Goldsmith and Zahawi, 2007). Because palms are morphologically constrained to increase in height, we expect the structure of stilt roots in E. precatoria to scale with palm size, matching stem height, rather than local conditions of topography over a wide range of slope conditions.…”

Vegetative Propagation of Amazonian Indigenous Species for Restoration Practices Over a Riverscape Floodplain Disturbed by Silting

“…Although the substratum moisture was enough for the development of the species B. parviflora and F. insipida, E. oleracea and S. exorrhiza are hydrophytic species with pneumatophores which is essential for root respiration in wetlands areas, one of the reasons of its widespread predominance in the Amazonian swamps and floodplains (Avalos et al, 2005;De Oliveira & Schwartz, 2018;Goldsmith, Gregory & Zahawi, 2007;Schauss, 2016). Thus, the moisture content used in this experiment was not enough to provide an ideal condition for the development of palm trees.…”