Browsing by Autor "Arturo Pacheco-Solana"

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Radial growth decline in a tropical Andean treeline in Bolivia
(2025) Rose Oelkers; Laia Andreu‐Hayles; Rosanne D’Arrigo; Arturo Pacheco-Solana; Milagros Rodríguez‐Catón; M. Eugenia Ferrero; Ernesto Tejedor; A C.; Carla Maldonado; Daniel Ruíz
Abstract. Relative to research efforts in higher latitiudes, the impact of climate shifts in the tropical treeline remains understudied. Little is known about the tree growth dynamics and climate response at this treeline over the past few centuries, and at present under a rapidly changing environment. Here we provide information on recent changes in tree-ring patterns of Polylepis pepei BB.Simpson, a tropical tree species that grows in a monospecific forest at the elevational treeline in the Andes-Amazon ecotone of Bolivia and identify factors that limit its radial growth. We first developed a ring width (RW) chronology spanning 1867–2018 C.E. using dendrochronological methods and independently verified annual periodicity with radiocarbon dating. The RW chronology indicates a significant (p < 0.01) radial growth decline in P. pepei since 1997, a trend that mirrors a decrease reported in other Polylepis species from the drier central Andes of South America. P. pepei tree-ring width (RW) was mostly limited by mean, minimum, and maximum temperature and precipitation during austral summer (November–January). Over the instrumental period (1981–2019) prior-year temperatures negatively affected current-year tree growth (p < 0.05), while prior-year wet conditions were associated with higher growth (p < 0.05). Gridded temperature records (1901–2019) showed a significant increase in minimum temperatures and a decline in the diurnal temperature range since 1967, which may reduce orographic convection and water availability at higher elevations where our forest is located. In situ daily measurements from dataloggers in the forest recorded higher temperatures and lower relative humidity values when data was available. Our results suggest less moisture availability associated with warming conditions was related to the observed tree-growth decline. If temperature continues to rise at current rates, one of the highest-elevation tree species on the globe, P. pepei, could face severe consequences. This work provides insights into the past and historical trends of a tropical Andean treeline, which shows a recent decline also observed in other high-elevation forests (4657–4800 m.a.s.l.) of tropical South America (>17° S).
Radiocarbon and wood anatomy as complementary tools for generating tree-ring records in Bolivia
(Frontiers Media, 2023) Arturo Pacheco-Solana; Rose Oelkers; Rosanne D’Arrigo; Guaciara M. Santos; Milagros Rodríguez‐Catón; Ernesto Tejedor; Eugenia Ferrero; Alfredo F. Fuentes; Carla Maldonado; Laia Andreu‐Hayles
The science of tropical dendrochronology is now emerging in regions where tree-ring dating had previously not been considered possible. Here, we combine wood anatomical microsectioning techniques and radiocarbon analysis to produce the first tree-ring chronology with verified annual periodicity for a new dendrochronological species, Neltuma alba (commonly known as "algarrobo blanco") in the tropical Andes of Bolivia. First, we generated a preliminary chronology composed of six trees using traditional dendrochronological methods (i.e., cross-dating). We then measured the 14C content on nine selected tree rings from two samples and compared them with the Southern Hemisphere (SH) atmospheric 14C curves, covering the period of the bomb 14C peak. We find consistent offsets of 5 and 12 years, respectively, in the calendar dates initially assigned, indicating that several tree rings were missing in the sequence. In order to identify the tree-ring boundaries of the unidentified rings we investigated further by analyzing stem wood microsections to examine anatomical characteristics. These anatomical microsections revealed the presence of very narrow terminal parenchyma defining several tree-ring boundaries within the sapwood, which was not visible in sanded samples under a stereomicroscope. Such newly identified tree rings were consistent with the offsets shown by the radiocarbon analysis and allowed us to correct the calendar dates of the initial chronology. Additional radiocarbon measurements over a new batch of rings of the corrected dated samples resulted in a perfect match between the dendrochronological calendar years and the 14C dating, which is based on good agreement between the tree-ring 14C content and the SH 14C curves. Correlations with prior season precipitation and temperature reveal a strong legacy effect of climate conditions prior to the current Neltuma alba growing season. Overall, our study highlights much potential to complement traditional dendrochronology in tree species with challenging tree-ring boundaries with wood anatomical methods and 14C analyses. Taken together, these approaches confirm that Neltuma alba can be accurately dated and thereby used in climatic and ecological studies in tropical and subtropical South America.
Recent growth increase in endemic Juglans boliviana from the tropical Andes
(Elsevier BV, 2023) Rose Oelkers; Laia Andreu‐Hayles; Rosanne D’Arrigo; Arturo Pacheco-Solana; Milagros Rodríguez‐Catón; Alfredo Fuentes; Guaciara M. Santos; Ernesto Tejedor; M. Eugenia Ferrero; Carla Maldonado
The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.