Browsing by Autor "Ricardo Villalba"

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Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across the Western Americas
(Springer Nature (Netherlands), 2010) Ricardo Villalba; Brian H. Luckman; José A. Boninsegna; Rosanne D’Arrigo; Antonio Lara; José Villanueva‐Díaz; Mariano Masiokas; Jaime Argollo; Claudia Solíz; Carlos LeQuesne
Determining the annual periodicity of growth rings in seven tree species of a tropical moist forest in Santa Cruz, Bolivia
(Spanish National Research Council, 2012) Lidio López; Ricardo Villalba; Marielos Peña‐Claros
To determine the annual periodicity of growth rings in seven tree species from a tropical moist forest in Santa Cruz, Bolivia, a fire scar was used as a marker point to verify the annual nature of tree rings. The number of tree rings formed between the 1995 fire scar and the collection of the cross sections in 2002 was visually identified. The seven species showed annual growth rings. In most cases, boundaries between rings were marked by the presence of marginal parenchyma and wall-thicked fibers formed at the end of the growing season. Growth lenses and false rings were recorded in some species. Tree rings can be carefully used in Santa Cruz forests to determine rates of growth. This information is crucial for defining forest management practices in tropical regions.
Inventory and recent changes of small glaciers on the northeast margin of the Southern Patagonia Icefield, Argentina
(Cambridge University Press, 2015) Mariano Masiokas; Silvia M. Delgado; Pierre Pitte; Étienne Berthier; Ricardo Villalba; Pedro Skvarca; Lucas Ruiz; Jinro Ukita; Tsutomu Yamanokuchi; Takeo Tadono
Abstract Most glaciological studies in Argentina have focused on the large outlet glaciers of the Southern Patagonia Icefield (SPI); the numerous smaller neighboring glaciers have received significantly less attention. We present an inventory of 248 medium- to small-size glaciers (0.01–25 km 2 ) adjacent to the northeast margin of the SPI, describe their change over the period 1979–2005 and assess local and regional climatic variations in an attempt to explain the observed glacier changes. Based on an ASTER mosaic from 20 February 2005 and the ASTER Global Digital Elevation Model, we identified a total glacier area of 187.2 ± 7.4 km 2 between 600 and 2870 m a.s.l. Glaciers are largely debris-free and are concentrated in the western, more humid sector adjacent to the SPI. Using a 20 March 1979 US military intelligence Hexagon KH-9 satellite photograph, we measured a total areal reduction of ∼33.7 km 2 (15.2%) between 1979 and 2005. Ablation season temperatures from the study area have followed a regional warming trend that could partly explain the observed glacier shrinkage. Annual precipitation estimates show a gradual decrease between 1979 and 2002 that may also have contributed to the ice mass loss.
Los anillos de crecimiento de Centrolobium microchaete (Fabaceae, Papilionoideae), una herramienta para evaluar el manejo forestal de los bosques secos tropicales del Cerrado boliviano
(2011) Lidio López; Ricardo Villalba; Marielos Peña‐Claros
La informacion obtenida a partir de los anillos de crecimiento de Centrolobium microchaete fue utilizada para proveer tasas de crecimiento, la edad y el tiempo requerido para alcanzar un determinado diametro en los distritos Chiquitano y Guarayos de la provincia biogeografica del cerrado Boliviano. Los crecimientos diametricos promedios de 0.4 cm para Chiquitos y 0.61cm en Guarayos observados en mas de 80 anos, indican que la especie tiene un crecimiento lento y variable entre sitios y distritos. Los tiempos necesarios para crecer de una clase diametrica a otra, reflejan que la especie necesita edades superiores a 100 y 80 anos, para alcanzar a los diametros minimos de corte (DMC) establecidos en Bolivia. Los resultados indican que el crecimiento de C. microchaete es lento, el tiempo necesario para alcanzar los DMC es alto y variable dentro de la region del Cerrado, por lo que imponer pautas fijas dentro de regiones para todas las especies, no seria factible en el tiempo para sostener el manejo forestal de los bosques tropicales de Bolivia
Potencialidad dendrocronológica de Polylepis tarapacana en los Andes Centrales de Bolivia
(2004) Jaime Argollo; Claudia Solíz; Ricardo Villalba
Precipitation changes in the South American Altiplano since 1300 AD reconstructed by tree-rings
(2011) Mariano S. Morales; Duncan A. Christie; Ricardo Villalba; Jaime Argollo; Jeanette Pacajes; J. S. Silva; Claudio Ã lvarez; J. C. Llancabure; Claudia Solíz
Abstract. During the second half of the 20th century, the Central Andes has experienced significant climatic and environmental changes characterized by a persistent warming trend, an increase in elevation of the 0 °C isotherm, and a sustained shrinkage of glaciers. These changes have occurred in conjunction with a steady growing demand for water resources. Given the short span of instrumental hidroclimatic records in this region, longer records are needed to understand the nature of climate variability and improve the predictability of precipitation, a key factor modulating the socio-economic development in the South American Altiplano and the adjacent arid lowlands. In this study we present the first quasi-millennial, tree-ring based precipitation reconstruction for the South American Altiplano. This annual (November–October) precipitation reconstruction is based on Polylepis tarapacana tree-ring series and represents the closest dendroclimatological record to the Equator in South America. This high-resolution reconstruction covers the past 707 yr and provides a unique record to characterize the occurrence of extreme events and consistent oscillations in precipitation, as well as to check the spatial and temporal stabilities of the teleconnections between rainfall in the Altiplano and hemispheric forcings such as El Niño-Southern Oscillation. Since the 1930s up to present a persistent negative trend in precipitation is recorded in the reconstruction, with the three driest years since 1300 AD occurring in the last 70 yr. The reconstruction contains a clear ENSO-like pattern at interannual to multicentennial time scales which determines inter-hemispheric linkages between our reconstruction and other precipitation-sensitive records modulated by ENSO in North America. Our reconstruction points out that century-scale dry periods are a recurrent feature in the Altiplano climate, and that the potential coupling of natural and anthropogenic-induced droughts in the future would have a severe impact on current socio-economical activities in the region. Water resource managers must anticipate these changes to adapt for future climate change, reduce vulnerability and provide water equitably to all users.
Precipitation changes in the South American Altiplano since 1300 AD reconstructed by tree-rings
(Copernicus Publications, 2012) Mariano S. Morales; Duncan A. Christie; Ricardo Villalba; Jaime Argollo; Jeanette Pacajes; J. S. Silva; Claudio Álvarez; J. C. Llancabure; C. C. Soliz Gamboa
Abstract. Throughout the second half of the 20th century, the Central Andes has experienced significant climatic and environmental changes characterized by a persistent warming trend, an increase in elevation of the 0 °C isotherm, and sustained glacier shrinkage. These changes have occurred in conjunction with a steadily growing demand for water resources. Given the short span of instrumental hydroclimatic records in this region, longer time span records are needed to understand the nature of climate variability and to improve the predictability of precipitation, a key factor modulating the socio-economic development in the South American Altiplano and adjacent arid lowlands. In this study we present the first quasi-millennial, tree-ring based precipitation reconstruction for the South American Altiplano. This annual (November–October) precipitation reconstruction is based on the Polylepis tarapacana tree-ring width series and represents the closest dendroclimatological record to the Equator in South America. This high-resolution reconstruction covers the past 707 yr and provides a unique record characterizing the occurrence of extreme events and consistent oscillations in precipitation. It also allows an assessment of the spatial and temporal stabilities of the teleconnections between rainfall in the Altiplano and hemispheric forcings such as El Niño-Southern Oscillation. Since the 1930s to present, a persistent negative trend in precipitation has been recorded in the reconstruction, with the three driest years since 1300 AD occurring in the last 70 yr. Throughout the 707 yr, the reconstruction contains a clear ENSO-like pattern at interannual to multidecadal time scales, which determines inter-hemispheric linkages between our reconstruction and other precipitation sensitive records modulated by ENSO in North America. Our reconstruction points out that century-scale dry periods are a recurrent feature in the Altiplano climate, and that the future potential coupling of natural and anthropogenic-induced droughts may have a severe impact on socio-economic activities in the region. Water resource managers must anticipate these changes in order to adapt to future climate change, reduce vulnerability and provide water equitably to all users.
Regional Differences in South American Monsoon Precipitation Inferred from the Growth and Isotopic Composition of Tropical Trees*
(American Meteorological Society, 2010) Ashley P. Ballantyne; Paul A. Baker; Jeffrey Q. Chambers; Ricardo Villalba; Jaime Argollo
Abstract The authors present results on the relationship between tree-ring proxies and regional precipitation for several sites in tropical South America. The responsiveness of oxygen isotopes (δ18O) and seasonal growth as precipitation proxies was first validated by high-resolution sampling of a Tachigali myrmecophila from Manaus, Brazil (3.1°S, 60.0°W). Monthly growth of Tachigali spp. was significantly correlated with monthly precipitation. Intra-annual measurements of cellulose δ18O in Tachigali spp. were also significantly correlated with monthly precipitation at a lag of approximately one month. The annual ring widths of two tropical tree taxa, Cedrela odorata growing in the Amazon (12.6°S, 69.2°W) and Polylepis tarapacana growing in the Altiplano (22.0°S, 66.0°W), were validated using bomb-derived radiocarbon 14C. Estimated dates were within two to three years of bomb-inferred 14C dates, indicating that these species exhibit annual rings but uncertainties in our chronologies remain. A multiproxy record spanning 180 years from Cedrela spp. showed a significant negative relationship between cellulose δ18O and January precipitation. A 150-yr record obtained from Polylepis spp. also showed a significant negative relationship between δ18O and March precipitation, whereas annual ring width showed a significant positive correlation with December precipitation. These proxies were combined in a multivariate framework to reconstruct past precipitation, revealing a significant increase in monsoon precipitation at the Amazon site since 1890 and a significant decrease in monsoon precipitation at the Altiplano since 1880. Proxy time series also showed spatial and temporal coherence with precipitation variability due to El Niño forcing, suggesting that oxygen isotopes and ring widths in tropical trees may be important diagnostics for identifying regional differences in the response of the tropical hydrologic cycle to anthropogenic warming.
Ritmos de crecimiento diamétrico en los bosques secos tropicales: aportes al manejo sostenible de los bosques de la provincia biogeográfica del Cerrado Boliviano
(Austral University of Chile, 2012) Lidio López; Ricardo Villalba; Marielos Peña‐Claros
Growth ring variations were used to provide the rates in diameter growth for seven tree species in the Bolivian Cerrado biogeographical province. Ten to 50 trees were measured per species. Ring width measurements provided accurate data on the rates of tree growth. Variations in growth rates were determined among species and among sites for the same species over a common period of 100 years. Diametric increases range from 0.43 to 0.56 cm year -1 in Chiquitano biogeographical district. For species in Guarayos district, diametric increments range from 0.51 to 1.06 cm year -1 . For Centrolobium microchaete growing in both districts, the annual diametric increments oscillate between 0.35 to 0.40 cm year -1 and 0.55 to 0.65 cm year -1 in Chiquitano and Guarayos districts, respectively. Diametric increases in Chiquitano district were not significantly different among sites, whereas in Guarayos district, annual increases differ among species and from the same species growing in Chiquitano district. Observed diameter growth rates indicate that diametrical increments are generally slower than commonly assumed, with considerable variation among species and between districts. Therefore, the idea of applying similar rules for the management of different species across different sites without considering actual growth rates is not recommended, with long-term consequences for the sustainability of forests at the tropical dry Bolivian Cerrado.
Spatio-temporal variations in Polylepis tarapacana radial growth across the Bolivian Altiplano during the 20th century
(Elsevier BV, 2008) Claudia Solíz; Ricardo Villalba; Jaime Argollo; Mariano S. Morales; Duncan A. Christie; Jorge Moya; Jeanette Pacajes