Vol.:(0123456789) 1 3 Oecologia https://doi.org/10.1007/s00442-019-04452-7 PHYSIOLOGICAL ECOLOGY – ORIGINAL RESEARCH Scaling of stem diameter and height allometry in 14 neotropical palm species of diferent forest strata Gerardo Avalos 1,2  · Maga Gei 1  · Luis Diego Ríos 3  · Mauricio Fernández Otárola 1  · Milena Cambronero 1  · Carolina Alvarez‑Vergnani 1  · Olivia Sylvester 4  · Gustavo Rojas 1 Received: 9 November 2018 / Accepted: 27 June 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Tropical palms reach tree-like heights without a vascular cambium through sustained cell expansion and lignifcation of primary tissues, but only a fraction of palms have been explored in their allometric relationships. Here, our main question was to determine how palms depart from the traditional mechanical models developed for trees and how they approach the theoretical buckling limit. We analyzed the stem allometry of 1603 palms of 14 species from diferent strata at 10 sites in Costa Rica and Peru. We measured their ft to the stress, elastic, and geometric similarity models, and their position relative to the maximum theoretical buckling limit calculated for trees. We evaluated the slope of the linear and logarithmic regres- sions between stem diameter and height using logarithmic least squares, and standardized major axis regression (SMA), expecting segregation according to canopy position and geographic location. Seventeen out of 19 statistically signifcant models had SMA slopes > 1, and 11 had SMA slopes ≥ 2, departing from traditional mechanical models developed for trees. Many species varied their allometry relative to geographic location. Canopy palms showed the highest regression ft but had less steep slopes than understory and subcanopy species. Subcanopy and understory species were more underbuilt than canopy palms, increasing height faster than diameter. Some of the tallest canopy palms surpassed the maximum buckling limit whereas subcanopy and understory species were consistently below the buckling limit of record-size trees. Palm stem allometry changed in response to environmental conditions. Keywords Buckling limit · Mechanical stability · Palm architecture Introduction The palm family (Arecaceae) is one the most diverse, widely distributed, and utilized groups of monocots, with nearly 2400 species in approximately 200 genera (Dransfeld et al. 2008). This high level of species diversity is refected in varied architectural patterns, morphological structure, and regeneration and life history strategies (Kahn and De Gran- ville 2012). Palms develop very strong stems comparable in magnitude to those of trees without producing woody tissues generated by a vascular cambium. Instead, they undergo sustained primary growth, which consists of the division, expansion, and lignifcation of parenchyma cells [the “difuse secondary thickening” of Schoute (1912) and Waterhouse and Quinn (1978)] and can increase the cell wall thickness of vascular fbers (Rich et al. 1986; Rich 1987b; Niklas 1993; Tomlinson et al. 2011). These rein- forced primary tissues are concentrated close to the stem periphery and around vascular bundles, and in many spe- cies, their density decreases from the base toward the apex of the stem and from the stem periphery toward the core of the stem (Killmann 1983; Tomlinson et al. 2011). Ligni- fed tissues result in increased resistance to biomechanical strains, and thus, facilitate attaining considerable heights. Communicated by Fernando Valladares. * Gerardo Avalos gerardo.avalos@ucr.ac.cr 1 Escuela de Biología, Universidad de Costa Rica, San Pedro, San José 11501-2060, Costa Rica 2 The School for Field Studies, Center for Sustainable Development Studies, 100 Cummings Center, Suite 534G, Beverly, MA 01915, USA 3 Department of Biology, Indiana University, 1001 East Third Street, Bloomington, IN 47405, USA 4 Department of Environment and Development, University for Peace, Ciudad Colón, San José, Costa Rica