Browsing by Autor "C. García‐Núñez"

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A Multi-Scale Ecological Approach for the Conservation and Restoration of Venezuelan Andean Cloud Forests
(2025) C. García‐Núñez; Fermín Rada; Ana Quevedo-Rojas; Mauricio Jeréz; Luis D. Llambí; C. Pacheco; Luis E. Gámez; Emilio Vilanova
Aspectos ecofisiológicos para la conservación de ecosistemas tropicales contrastantes
(Sociedad Botánica de México, A. C., 1999) Aura Azócar; Fermín Rada; C. García‐Núñez
The identification of plant functional groups allows to evaluate plant properties as: recovering capacity, regeneration and resistence to environmental changes. It is possible to define plant functional groups in the seasonal savana and the high barren plateau taking in to account the ecophysiological plant responses to water stress and daily temperature-water rythmn, respectively. In the savana, although the wooden component is constituted by evergreen and deciduous tree species, they make only a functional group taking in to account their responses to water stress, this is similar in the herbaceous component. Results suggest that a change in environmental factors may generate a floristic replace without major changes in the system function.However, in the high barren plateau, the different life forms also constitute different functional groups according to plant responses to temperature-water factor, suggesting that the substitution of any group will put in danger the preservation of this ecosystem.
Leaf Gas Exchange and Water Relations in Polylepis tarapacana at Extreme Altitudes in the Bolivian Andes
(Institute of Experimental Botany of the Czech Academy of Sciences, 2004) C. García‐Núñez; Fermín Rada; C. Boero; Juan Antonio González; M. Gallardo; A. Azócar; M. Liberman‐Cruz; Mirna Hilal; Fernando E. Prado
Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (PN). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (-1.67 and -1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m-2 s-1, respectively), while differences in mean PN (2.5 and 2.8 μmol m-2 s-1, respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations.
Low‐temperature resistance in <i>Polylepis tarapacana</i>, a tree growing at the highest altitudes in the world
(Wiley, 2001) Fermín Rada; C. García‐Núñez; C. Boero; M. Gallardo; Mirna Hilal; Juan Antonio González; Fernando E. Prado; M. Liberman‐Cruz; A. Azócar
ABSTRACT The Polylepis tarapacana forests found in Bolivia are unique with respect to their altitudinal distribution (4200–5200 m). Given the extreme environmental conditions that characterize these altitudes, this species has to rely on distinct mechanisms to survive stressful temperatures. The purpose of this study was to determine low‐temperature resistance mechanisms in P. tarapacana . Tissue was sampled for carbohydrate and proline contents and micro‐climatic measurements were made at two altitudes, 4300 and 4850 m, during both the dry cold and wet warm seasons. Supercooling capacity (−3 to −6 °C for the cold dry and −7 to −9 °C for the wet warm season) and injury temperatures (−18 to −23 °C for both seasons), determined in the laboratory, indicate that P. tarapacana is a frost‐tolerant species. On the other hand, an increase in supercooling capacity, as the result of significant increase in total soluble sugar and proline contents, occurs during the wet warm season as a consequence of higher metabolic activity. Hence, P. tarapacana , a frost‐tolerant species during the colder unfavourable season, is able to avoid freezing during the more favourable season when minimum night‐time temperatures are not as extreme.
Seasonal gas exchange and water relations in juveniles of two evergreen Neotropical savanna tree species with contrasting regeneration strategies
(Springer Science+Business Media, 2010) C. García‐Núñez; Aura Azócar; Fermín Rada
Spatial relations and population structure of a dominant tree along a treeline ecotone in the Tropical Andes: interactions at gradient and plant-neighbourhood scales
(Taylor & Francis, 2013) Luis D. Llambí; Johanna Puentes Aguilar; C. García‐Núñez
Background: Studies in temperate mountains suggest that plant–plant interactions modulate tree establishment above the forest line. In tropical mountains worldwide this issue remains largely unexplored. Aims: To analyse the population structure and local spatial relationships of a dominant tree at a species-rich tropical Andean forest line. Methods: We determined changes in the population structure of Diplostephium venezuelense along an elevation gradient between continuous forest and open páramo and analysed plant community structure and superficial rock cover in the neighbourhood of saplings and adults at the upper forest line. Results: Sapling and adult densities were highest in low-altitude páramos adjacent to the forest line and at the borders of small forest islands. Saplings showed local spatial aggregation, were positively associated with small boulders and low shrubs, and negatively associated with mosses and lichens. However, no spatial association was found between scattered adults in the páramo and saplings of other forest trees. Conclusions: Complex species-specific local spatial interactions, suggesting both facilitative and antagonistic effects, seem to modulate the establishment of the dominant tree D. venezuelense at and above the upper forest line. Nevertheless, the establishment of other tree species above continuous forests does not appear to be facilitated by the canopy cover offered by the isolated D. venezuelense individuals established in open páramo environments.