Given the short span of instrumental precipitation records in the South American Altiplano, longer-term hydroclimatic records are needed to understand the nature of climate variability and to improve the predictability of precipitation, a key natural resource for the socioeconomic development in the Altiplano and adjacent arid lowlands. In this region grows Polylepis tarapacana, a long-lived tree species that is very sensitive to hydroclimatic changes and has been widely used for tree-ring studies in the central and southern Altiplano. However, in the northern sector of the Peruvian and Chilean Altiplano (16–19^∘ S) still exists a gap of high-resolution hydroclimatic data based on tree-ring records. Our study provides an overview of the temporal evolution of the late-spring–mid-summer precipitation for the period 1625–2013 CE at the northern South American Altiplano, allowing for the identification of wet or dry periods based on a regional reconstruction from three P. tarapacana chronologies. An increase in the occurrence of extreme dry events, together with a decreasing trend in the reconstructed precipitation, has been recorded since the 1970s in the northern Altiplano within the context of the last ∼4 centuries. The average precipitation over the last 17 years stands out as the driest in our 389-year reconstruction. We reveal a temporal and spatial synchrony across the Altiplano region of dry conditions since the mid-1970s. Independent tree-ring-based hydroclimate reconstructions and several paleoclimatic records based on other proxies available for the tropical Andes record this synchrony. The influence of El Niño–Southern Oscillation (ENSO) on the northern Altiplano precipitation was detected by our rainfall reconstruction that showed past drier conditions in our study region associated with ENSO warm events. The spectral properties of the rainfall reconstruction showed strong imprints of ENSO variability at decadal, sub-decadal, and inter-annual timescales, in particular from the Pacific NIÑO 3 sector. Overall, the recent reduction in precipitation in comparison with previous centuries, the increase in extreme dry events and the coupling between precipitation and ENSO variability reported by this work is essential information in the context of the growing demand for water resources in the Altiplano. This study will contribute to a better understanding of the vulnerability and resilience of the region to the projected evapotranspiration increase for the 21st century associated with global warming.

Increasing drought pressure under anthropogenic climate change may jeopardize the potential of tropical forests to capture carbon in woody biomass and act as a long-term carbon dioxide sink. To evaluate this risk, we assessed drought impacts in 483 tree-ring chronologies from across the tropics and found an overall modest stem growth decline (2.5% with a 95% confidence interval of 2.2 to 2.7%) during the 10% driest years since 1930. Stem growth declines exceeded 10% in 25% of cases and were larger at hotter and drier sites and for gymnosperms compared with angiosperms. Growth declines generally did not outlast drought years and were partially mitigated by growth stimulation in wet years. Thus, pantropical forest carbon sequestration through stem growth has hitherto shown drought resilience that may, however, diminish under future climate change.

There is a significant dendrochronological gap in the Puna of the central Andes of Peru, which motivates research on new species. In this study, we present the first tree-ring chronologies of Escallonia myrtilloides. We collected samples at San Pedro Saño and Sapallanga in Peru, analyzed the anatomical characteristics that delimit the annual growth rings, and developed two tree-ring chronologies through conventional dendrochronological techniques. The tree-ring chronologies cover the period 1940–2015 (76 years) for San Pedro Saño and 1960–2015 (56 years) for Sapallanga. The E. myrtilloides chronologies presented similar values of mean sensitivity, Rbar and EPS to those recorded for Polylepis tarapacana, Polylepis pepei, and Polylepis rugulosa in the Puna region. The analysis of the climate-growth relationships indicated positive correlations with precipitation and negative correlations with temperature in particular months of the current growing season (October–April). This precipitation/temperature-sensitive record highlights the high value of E. myrtilloides for future studies on the influence of climate on tree growth in the central Andes.

Summary: Andean Walnut (Juglans neotropica Diels-Juglandaceae) is a long-lived, deciduous broadleaf Tropical Montane Cloud Forest (TMCF) tree species native to the Andes Cordillera; nevertheless, it has received limited attention for dendro-quantitative wood anatomical studies. Based on 70 increment cores from 50 Andean Walnut trees at two Peruvian TMCFs, two chronologies (from 1969 to 2020 and from 1964 to 2020) were developed. The xylem vessel parameters assessment allowed us to detect South American Monsoon System (SAMS) precipitation signals in the Andean Walnuts’ wood. Dendro-wood anatomical features can be assessed within an annual growth ring, which allows for assessing intra-annual past and present wood anatomy-function relationships and its climate vulnerability.