Elsevier

Dendrochronologia

Volume 62, August 2020, 125722
Dendrochronologia

Original Article
Dendroclimatological assessment of Polylepis rodolfo-vasquezii: A novel Polylepis species in the Peru highlands

https://doi.org/10.1016/j.dendro.2020.125722Get rights and content

Abstract

In spite of enormous diversity in tree species, dendrochronological records in the tropical Andes are very scarce. Therefore, it is necessary to increase the search for new tree species with high dendrochronological characteristics in the tropical Andes, including the humid Puna of Peru. We present the first tree-ring chronology from Polylepis rodolfo-vasquezii, a recently described tree species in the Central Andes of Peru between 4000 and 4400 m elevation. Fifty trees were sampled in the district of Comas, Peru. After establishing the anatomical characteristics that delimit the annual growth rings, we developed a ring-width chronology by applying conventional dendrochronological techniques. The chronology covers the period 1869–2015 (157 years) and is well replicated from 1920 to present (> 20 samples). The statistics used to evaluate the quality of the chronology indicate that the P. rodolfo-vasquezii has similar values of MS, RBAR and EPS to those shown by other Polylepis spp chronologies. To determine the main climatic factors controlling the growth of P. rodolfo-vasquezii, we compared our chronology with local and regional temperature and precipitation records. Growth season temperature (November to May) seems to be the main climatic factor modulating inter-annual variations in the growth of this species. The sensitivity to inter-annual temperature variations highlights the potential of P. rodolfo-vasquezii to provide climatically sensitive dendrochronological records in the Central Andes. To our knowledge, this is the first tree-ring record in South America displaying significant relationships with temperature over the tropical Atlantic Ocean.

Introduction

Nineteen species of Polylepis grow in the Peruvian Andes between 1800 and 5100 m elevation (Mendoza and Cano, 2011). Some Polylepis woodlands represent the highest elevation tree formations in the world, reaching up to 5000 m a.s.l. in the humid and arid Andes, respectively (Kessler and Schmidt-Lebuhn, 2006). The Polylepis woodlands provide ecosystem services to local montane communities including water regulation and soil nutrient conservation. These woodlands also represent important refuges for biodiversity and an important carbon sink at high elevations (Fjeldsá, 2002; Zutta et al., 2012).

Compared to the subtropical and temperate regions along the Andes, tree-ring records in the tropics are scarce (Boninsegna et al., 2009). The Central Andes of Peru (6°-15 °S) sustain one of the most diverse forests in the world (Josse et al., 2009); however, the development of well-replicated chronologies from tree species has been limited. One of the most important dendrochronological advances in South America during recent decades has been the development of the Polylepis spp. tree-ring chronologies. This achievement was possible due to the presence of well-defined annual rings in several Polylepis species, their high climatic sensitivity, the longevity of some species and their unique geographical locations (Boninsegna et al., 2009). From a dendrochronological point of view, Polylepis tarapacana is the species most studied of the genus (Argollo et al., 2004; Christie et al., 2009; Solíz et al., 2009; Morales et al., 2004, 2012, 2015; Moya and Lara, 2011). Other Polylepis species used in tree-ring research include Polylepis besseri (Gareca et al., 2010), Polylepis pepei (Roig et al., 2001), Polylepis subsericans (Jomelli et al., 2012), Polylepis rugulosa (Jomelli et al., 2012), and Polylepis australis (Chartier et al., 2016; Marcora et al., 2017; Suarez et al., 2008). Therefore, the exploration of the dendrochronological potential in Polylepis species in the Peruvian Andes is of high scientific value due to its possible applications in ecological and paleoclimatic studies, at both local and regional scales.

The Peruvian Andes, the home of an extraordinary biological and cultural diversity, encompass three phytogeographic regions: The Yungas, the Wet and the Xerophytic Puna (Josse et al., 2009). In the Wet Puna, the precipitation shows a marked seasonality with a prolonged dry interval from May to October. The marked dry season induces a period of vegetative dormancy with the fall of leaves in most species and the cease of biomass production (Josse et al., 2009).

In this study, we present the first chronology of Polylepis rodolfo-vasquezii, a species recently discovered in the central Andes of Peru (Valenzuela and Villalba, 2015). Based on standard dendrochronological statistics (Cook and Pederson, 2011), we evaluate the quality of the chronology in the context of tree-ring records from different Polylepis species. Finally, we compared the chronology of P. rodolfo-vasquezii with instrumental records of temperature and precipitation to determine the climatic variables that influence the growth of this species.

Section snippets

Climate

Climate variability at different temporal scales in the tropical Andes is modulated by oceanic and continental climatic forcings. Sea-surface temperature anomalies in the Pacific Ocean related to El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation, are major forcings of interannual- and decade-scale climatic variations, respectively, along the tropical Andes (Vuille et al., 2000; Garreaud et al., 2003). On the other hand, variations in the South American summer monsoon in

Results

The wood of Polylepis rodolfo-vasquezii shows clearly distinguishable growth rings (Fig. 3a) due to the presence of more abundant and large-diameter vessels at the beginning of the earlywood (semicircular porosity; Fig. 3b and c). Heterogeneous, uni-seriates and multi-seriates radii up to three-cell wide are observed (Fig. 3d and e). The delimitation of the growth rings is also facilitated by the occurrence of abundant fibers with thicker cell walls present at the end of the annual rings (Fig. 3

Discussion

We present here the first ring-width chronology of P. rodolfo-vasquezii from the humid Puna in the Central Andes of Peru. This tree-ring record, located in the tropics at 11 °S, extends towards the equator the coverage of dendrochronological records in the Andes. The P. rodolfo-vasquezii wood shows rings clearly demarcated by the semicircular arrangement with larger vessels at the beginning of the annual ring that contrast with abundant thick-wall fibers at the end of the latewood. The

Conclusions

The first P. rodolfo-vasquezii chronology at 4000 m elevation in the humid Puna of Peru represents a valuable record to infer past climate variability in the tropical Andes and their relationships with SST over the tropical Pacific and Atlantic oceans. This temperature-sensitive record provides climatic information of great paleoclimatic value in a region devoid of long-term instrumental records and tree-ring chronologies. Our tree-ring record shows significant relationships with SST variations

Declaration of Competing Interest

The authors whose names are listed immediately below certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in

Acknowledgments

The authors are grateful for the collaboration of Harol Quispe and Luis Salome in the field work and Ricardo Ortega and Luis Santin in the preparation of histological cuts. Pomamnta community for facilities and permission to work the woodlands. This study was financed by the National Council for Science, Technology and Technological Innovation; CONCYTEC, Peru (Project N° 147-2015-FONDECYT-DE, Proyect N° 039-2019-FONDECYT-BM-INC-INV). M.S.M. and R.V. have been partially support by CONICET,

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