Tropical plant canopies show abrupt changes in light conditions across small differences in spatial and temporal scales. Given the canopy light heterogeneity, plants in this stratum should express a high degree of plasticity, both in space (allocation to plant modules as a function of opportunity for resource access) and time (photosynthetic adjustment to temporal changes in the local environment). Using a construction crane for canopy access, we studied light acclimation of the liana Stigmaphyllon lindenianum to sun and shade environments in a tropical dry forest in Panama during the wet season. Measured branches were randomly distributed in one of four light sequences: high- to low-light branches started the experiment under sun and were transferred to shade during the second part of the experiment; low- to high-light branches (LH) were exposed to the opposite sequence of light treatments; and high-light and low-light controls , which were exposed only to sun and shade environments, respectively, throughout the experiment. Shade branches were set inside enclosures wrapped in 63% greenhouse shade cloth. After 2 months, we transferred experimental branches to opposite light conditions by relocating the enclosures. Leaf mortality was considerably higher under shade, both before and after the transfer. LH branches reversed the pattern of mortality by increasing new leaf production after the transfer. Rates of photosynthesis at light saturation, light compensation points, and dark respiration rates of transferred branches matched those of controls for the new light treatment, indicating rapid photochemical acclimation. The post-expansion acclimation of sun and shade foliage occurred with little modification of leaf structure. High photosynthetic plasticity was reflected in an almost immediate ability to respond to significant changes in light. This response did not depend on the initial light environment, but was determined by exposure to new light conditions. Stigmaphyllon responded rapidly to light changes through the functional adjustment of already expanded foliage and an increase in leaf production in places with high opportunity for carbon gain.
Lianas impose intense resource competition for light in the upper forest canopy by displaying dense foliage on top of tree crowns. Using repeated access with a construction crane, we studied the patterns of canopy colonization of the lianas Combretum fruticosum and Bonamia trichantha in a Neotropical dry forest in Panama. Combretum fruticosum flushed leaves just before the rainy season, and its standing leaf area quickly reached a peak in the early rainy season (May–June). In contrast, B. trichantha built up foliage area continuously throughout the rainy season and reached a peak in the late rainy season (November). Both species displayed the majority of leaves in full sun on the canopy surface, but C. fruticosum displayed a greater proportion of leaves (26%) in more shaded microsites than B. trichantha (12%). Self‐shading within patches of liana leaves within the uppermost 40–50 cm of the canopy reduced light levels measured with photodiodes placed directly on leaves to 4–9 percent of light levels received by sun leaves. Many leaves of C. fruticosum acclimated to shade within a month following the strongly synchronized leaf flushing and persisted in deep shade. In contrast, B. trichantha produced short‐lived leaves opportunistically in the sunniest locations. Species differences in degree of shade acclimation were also evident in terms of structural (leaf mass per area, and leaf toughness) and physiological characters (nitrogen content, leaf life span, and light compensation point). Contrasting leaf phenologies reflect differences in light exploitation and canopy colonization strategies of these two liana species.
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...
We present allometric models for estimating total carbon content and above ground carbon (AGC) for the Arecaceae family, and for seven abundant neotropical palm species: the canopy species Socratea exorrhiza (n = 10) and Iriartea deltoidea (n = 10), the sub-canopy palm Euterpe precatoria (n = 10), and the understory species Asterogyne martiana (n = 15), Prestoea decurrens (n = 10), Geonoma interrupta (n = 10), and Chamaedorea tepejilote (n = 22). Understanding the allometry of functional groups such as palms is critical for improving carbon stocks estimates in tropical forests and determining how allometric differences affect species functional diversity. The research was carried out in the tropical rainforests of the Caribbean slope of Costa Rica. We harvested 87 palms of a wide range of sizes, and separated them into roots, stems, and leaves, measured their fresh and dry biomass, and calculated their carbon content, tissue density, and dry mass fraction (dmf). Our general palm model estimating total carbon content based on these seven species and 87 samples accounted for 92% of the variation across species. We generated a similar model to estimate AGC and explained 91% of the variation. We compared our AGC model with two models used to estimate palm carbon content: Goodman et al. (2013)’s and Chave et al. (2014)’s models and found that all three converged on the estimation of AGC although our model was the most parsimonious because it achieved the same efficiency with only two variables, stem diameter and stem height. To improve the accuracy of allometric models we need to incorporate more species, a greater diversity of growth forms, a wider range of sizes, a larger sample size, and more diversity of habitats dominated by palms. Estimating carbon content using allometric approaches could benefit from more consistency in data collection across plant groups.
Illegal Palm Heart (Geonoma edulis) Harvest in Costa Rican National Parks: Patterns of Consumption and Extraction. Illegal extraction of non-timber forest products in the tropics is widespread, and many protected areas face the challenge of balancing conservation needs with cultural practices related to the use and extraction of animals and plants. We studied the illegal wild palm heart extraction of Geonoma edulis, locally known as súrtuba, in Volcán Poás and Braulio Carrillo National Parks in Costa Rica. Through 96 questionnaires administered in three communities bordering these national parks, and by semistructured interviews with poachers and park managers, this study examined extraction and consumption motives, patterns, and frequencies. This palm is sought out by the communities for use during Holy Week to satisfy cultural traditions, for its associated nutritive value, and because of its unique bitter flavor, not comparable to domesticated palm heart. Whereas the majority of the respondents consume it during Holy Week (55.2%), a substantial number (27.1%) consume G. edulis palm heart at least once a month. The majority extract once a year (58%); however, a minority (2.1%) rely on G. edulis for economic subsistence. This accounts for 72.6% of the reported extraction (over 4,500 palms per year) and is supplying a year-round market for nontraditional use. Our results show that what most likely began as a cultural tradition has become an uncontrolled, nontraditional source of income. Additional efforts should determine the feasibility of limited extraction outside protected areas to satisfy traditional use. Such an effort entails the decentralization of biodiversity policies and innovative methods to implement protective measures, as well as incentives for community involvement in the management of this palm heart species.
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