Polylepis Tarapacana Research Articles

Hydroclimate variability in the Tropical Andes recorded by δ18O isotopes from a new network of Polylepis tarapacana tree-rings

Stable oxygen isotopes records (δ18O) in tree-rings are commonly used to assess the response of trees to environmental variability being a valuable tool for studying past climate at different temporal and spatial scales. This is particularly relevant in semi-arid regions like the southern Tropical Andes, where ongoing environmental changes coincide with a rapidly increasing demand for hydrological resources, presenting a challenge for ecosystem dynamics and water resource management. In this study, we aim to determine the main spatio-temporal variability of a new network of δ18O Polylepis tarapacana chronologies during the last century, and their relationships with hydroclimate and tropical circulation at local to subcontinental scales throughout the Tropical Andes. For this purpose, we develop six δ18O P. tarapacana tree-ring chronologies across a 450 km latitudinal moisture gradient in the southern Tropical Andes adjacent to the Atacama Desert, covering the period 1900–2007. Results show a clear latitudinal gradient in the δ18O values across the network and significant relationships are observed with other δ18O tree-ring chronologies in Tropical South America, demonstrating clear regional climate influences at a subcontinental scale. A principal component analysis of the δ18O tree-ring chronologies demonstrate a strong regional environmental signal contained in the network, exhibiting a main temporal pattern (PC1 δ18O) that explains 63% of the total variance during the period 1900–2007. Comparisons between PC1 δ18O and environmental variables showed significant negative relationships with precipitation and soil moisture, and positive relationships with temperature and vapor pressure deficit (VPD) during summer when the South American monsoon occurs. The main δ18O tree-ring network signal clearly records tropical atmospheric and circulation patterns across South America. The easterly wind flux conditions from the Amazon basin favor lower δ18O values, and the PC1 δ18O exhibit significant positive correlations with VPD across the entire Tropical Andes and the northern portion of the Amazon basin, and as well as outgoing longwave radiation across the southern Tropical Andes and part of the Amazon basin. The close relationships between the regional signals from our δ18O tree-ring network with the previously mentioned parameters, highlight the potential to develop future hydroclimatic-related reconstructions with these δ18O records to assess climate variability and change across the Tropical Andes.

A 300-year tree-ring δ18O-based precipitation reconstruction for the South American Altiplano highlights decadal hydroclimate teleconnections

Tropical South American climate is influenced by the South American Summer Monsoon and the El Niño Southern Oscillation. However, assessing natural hydroclimate variability in the region is hindered by the scarcity of long-term instrumental records. Here we present a tree-ring δ18O-based precipitation reconstruction for the South American Altiplano for 1700–2013 C.E., derived from Polylepis tarapacana tree rings. This record explains 56% of December–March instrumental precipitation variability in the Altiplano. The tree-ring δ18O chronology shows interannual (2–5 years) and decadal (~11 years) oscillations that are remarkably consistent with periodicities observed in Altiplano precipitation, central tropical Pacific sea surface temperatures, southern-tropical Andean ice core δ18O and tropical Pacific coral δ18O archives. These results demonstrate the value of annual-resolution tree-ring δ18O records to capture hydroclimate teleconnections and generate robust tropical climate reconstructions. This work contributes to a better understanding of global oxygen-isotope patterns, as well as atmospheric and oceanic processes across the tropics.

Characterization of Polylepis tarapacana Life Forms in the Highest-Elevation Altiplano in South America: Influence of the Topography, Climate and Human Uses.

In the upper vegetation limit of the Andes, trees change to shrub forms or other life forms, such as low scrubs. The diversity of life forms decreases with elevation; tree life forms generally decrease, and communities of shrubs and herbs increase in the Andean highlands. Most of treeline populations in the northwestern Argentina Altiplano are monospecific stands of Polylepis tarapacana, a cold-tolerant evergreen species that is able to withstand harsh climatic conditions under different life forms. There are no studies for P. tarapacana that analyze life forms across environmental and human impact gradients relating them with environmental factors. This study aims to determine the influence of topographic, climatic, geographic and proxies to human uses on the occurrence of life forms in P. tarapacana trees. We worked with 70 plots, and a new proposal of tree life form classification was presented for P. tarapacana (arborescent, dwarf trees, shrubs and brousse tigrée). We describe the forest biometry of each life form and evaluate the frequency of these life forms in relation to the environmental factors and human uses. The results show a consistency in the changes in the different life forms across the studied environmental gradients, where the main changes were related to elevation, slope and temperature.

Drought increase since the mid-20th century in the northern South American Altiplano revealed by a 389-year precipitation record

Abstract. 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.

CLIMATE CHANGE EFFECTS ON HIGH-ALTITUDE WOODS IN THE ALTIPLANO

The keñua tree (Polylepis tarapacana), found at 5200 m a.s.l. in the Andes Mountains, grows at the highest treeline in the world. We measured the thermal conduction coefficient of keñua bark samples taken from different locations within the Andes Mountains. These measurements were used to find a correlation between environmental inputs and high altitude plant defence mechanisms. We found a new classification method to identify the origin of plant samples.

Plantas medicinales asociadas a bosques de Polylepis tarapacana del altiplano jujeño: Riqueza y cobertura en gradientes geográficos, topográficos y de estructura forestal

The use of medicinal plants in traditional medicine is common among the peoples of the Argentinean highlands, where only one tree-like species grows: Polylepis tarapacana. Until now, this resource of medicinal plants has not been quantified, ignoring the richness and coverage throughout its distribution and in different environments. The objective was to quantify the richness and coverage of medicinal plants in geographic, topographic and forest structure gradients in P. tarapacana forests. The forests were categorized into 5 zones, where 93 plots were surveyed. In each forest, medicinal plants were sampled using the point-intercept method. Twenty-one medicinal species (16 genera and 8 botanical families) were recorded. The family with the highest representation is Asteraceae (12 species, 9 genera), while the species showing the highest frequency and coverage were Baccharis tola ssp. tola (97.8%, 2.37%), Azorella compacta (82.8%, 1.21%) and Parastrephia lucida (81.7%, 0.66%). The richness of medicinal plants showed differences depending on elevation and northern aspect (ExN), where richness decreases with increasing elevation and northern aspect. From the total of 21 medicinal plants found, 11 presented significant relationships between their coverage and geographic, topographic and forest structure variables. It was observed that within the wide distribution of P. tarapacana forests in Argentina, the medicinal plants found correspond to different plant associations from Bolivia and Chile. This information will facilitate the establishment of guidelines for adequate management and protection of these resources.

Optimal environmental drivers of high-mountains forest: Polylepis tarapacana cover evaluation in their southernmost distribution range of the Andes

The Andes Mountains are considered a global biodiversity hotspot, where Polylepis forests are one of the most threatened forests in the area. We evaluate the P. tarapacana forest's distribution and cover and relate this pattern with topographic, climatic and geographic environmental factors at the landscape level. Along 93 plots, forest structure data was conducted according to their homogeneity, accessibility, and size (patches up to > 1 ha each). Hexagon binning processes were used to estimate the forest cover, as the proportion of hexagon area covered by forests, and one-way ANOVAs were conducted to evaluate its variation according to the environmental factors. Our results show that P. tarapacana forests are widely distributed, occupying a forest area of 8519.8 ha among 2462 forest patches and an average of 6.7% of forest cover (1296 hexagons - 129600 ha). According to the findings, the entire forest distribution encompasses a wide range of environmental conditions. We identify that the slopes and elevations were the main environmental drivers that shaped P. tarapacana distribution and cover. Variations in forest area and cover indicate a strong preference for north and east-facing slopes (18 and 24°) and intermediate elevations (4400 - 4500 m a.s.l), with a life zone of Tropical subalpine dry scrub accounting for 62.1%. Our research shows that remote sensing mapping and geographic information systems are effective methods for identifying habitat variables linked to threatened forest cover and evidence of forest vulnerability in the face of continuous global change.

Particularities of the highest elevation treeline in the world: Polylepis tarapacana Phil. as a model to study ecophysiological adaptations to extreme environments

Polylepis tarapacana is an exceptional species, forming the highest treeline in the world. In this work, we compared the climatic conditions of the main highest treelines around the world and highlight the unique conditions of the treelines of the Andes’ Altiplano, the habitat of P. tarapacana. We review the current state of knowledge on the physiology of P. tarapacana and call for the urgent need of additional studies to assess the adaptive strategies of this species that allow it to withstand the harsh environments of high elevation climates.

Hydroclimate and ENSO Variability Recorded by Oxygen Isotopes From Tree Rings in the South American Altiplano

AbstractHydroclimate variability in tropical South America is strongly regulated by the South American Summer Monsoon (SASM). However, past precipitation changes are poorly constrained due to limited observations and high‐resolution paleoproxies. We found that summer precipitation and the El Niño‐Southern Oscillation (ENSO) variability are well registered in tree‐ring stable oxygen isotopes (δ18OTR) of Polylepis tarapacana in the Chilean and Bolivian Altiplano in the Central Andes (18–22°S, ∼4,500 m a.s.l.) with the northern forests having the strongest climate signal. More enriched δ18OTR values were found at the southern sites likely due to the increasing aridity toward the southwest of the Altiplano. The climate signal of P. tarapacana δ18OTR is the combined result of moisture transported from the Amazon Basin, modulated by the SASM, ENSO, and local evaporation, and emerges as a novel tree‐ring climate proxy for the southern tropical Andes.

High ENSO sensitivity in tree rings from a northern population of Polylepis tarapacana in the Peruvian Andes

Polylepis tarapacana is the highest-elevation tree species worldwide growing between 4000 and 5000 m a.s.l. along the South American Altiplano. P. tarapacana is adapted to live in harsh conditions and has been widely used for drought and precipitation tree-ring based reconstructions. Here, we present a 400-year tree-ring width (TRW) chronology located in southern Peru (17ºS; 69ºW) at the northernmost limit of P. tarapacana tree species distribution. The objectives of this study are to assess tree growth sensitivity of a northern P. tarapacana population to (1) precipitation, temperature and El Niño Southern Oscillation (ENSO) variability; (2) to compare its growth variability and ENSO sensitivity with southern P. tarapacana forests. Our results showed that this TRW record is highly sensitive to the prior summer season (Nov-Jan) precipitation (i.e. positive correlation) when the South American Summer Monsoon (SASM) reaches its maximum intensity in this region. We also found a positive relationship with current year temperature that suggests that radial growth may be enhanced by warm, less cloudy, conditions during the year of formation. A strong positive relationship was found between el Niño 3.4 and tree growth variability during the current growing season, but negative during the previous growth period. Growth variability in our northern study site was in agreement with other populations that represent almost the full range of P. tarapacana latitudinal distribution (~ 18ºS to 23ºS). Towards the south of the P. tarapacana TRW network there was a decrease in the strength of the agreement of growth variability with our site,with the exception of higher correlation with the two southeastern sites. Similarly, the TRW chronologies recorded higher sensitivity to ENSO influences in the north and southeastern locations, which are wetter, than the drier southwestern sites . These patterns hold for the entire period, as well as for periods of high and low ENSO activity. Overall, P. tarapacana tree growth at the north of its distribution is mostly influenced by prior year moisture availability and current year temperature that are linked to large-scale climate patterns such as the SASM and ENSO, respectively.

Assessing Dendrochronological Potential of Escallonia myrtilloides in the High Andes of Peru

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.

Conteo de marcas de yemas para estimar la edad en Polylepis tarapacana: Una técnica potencial

In forest species that present a determined growth, the buds generate marks that are used to estimate the ages along the apical shoots or branches, by counting the internodes. In order to estimate the age along the branches in threatened and slow-growing species, such as Polylepis tarapacana Phil., it is crucial to have non-destructive techniques that avoid the collection of branches, sapling or complete specimens. Therefore, the objective of this work was to evaluate the potentiality of the age estimation technique, which uses external marks along the branch in P. tarapacana. We worked with 13 apical branches collected in 13 forests in the town of Lagunillas del Farallón, Dpt. Rinconada. Shoot marks were counted on each branch using two methods: a) along the 20 cm length of the main branch and b) on a lateral shoot of the main branch, three marks were counted along the length of the shoot. It was analyzed if the mark count adjusts to age with a mixed generalized linear model (Glmm), including tree as a random factor (n=26). The results indicate that there is potential for applying this technique, but in order to generate a reliable model, it would be necessary to collect a larger number of samples in future research.

Different climate sensitivity for radial growth, but uniform for tree-ring stable isotopes along an aridity gradient in Polylepis tarapacana, the world's highest elevation tree species.

Tree growth is generally considered to be temperature limited at upper elevation treelines, yet climate factors controlling tree growth at semiarid treelines are poorly understood. We explored the influence of climate on stem growth and stable isotopes for Polylepis tarapacana Philipi, the world's highest elevation tree species, which is found only in the South American Altiplano. We developed tree-ring width index (RWI), oxygen (δ18O) and carbon (δ13C) chronologies for the last 60years at four P. tarapacana stands located above 4400 m in elevation, along a 500 km latitude aridity gradient. Total annual precipitation decreased from 300 to 200mm from the northern to the southern sites. We used RWI as a proxy of wood formation (carbon sink) and isotopic tree-ring signatures as proxies of leaf-level gas exchange processes (carbon source). We found distinct climatic conditions regulating carbon sink processes along the gradient. Current growing-season temperature regulated RWI at northern-wetter sites, while prior growing-season precipitation determined RWI at arid southern sites. This suggests that the relative importance of temperature to precipitation in regulating tree growth is driven by site water availability. By contrast, warm and dry growing seasons resulted in enriched tree-ring δ13C and δ18O at all study sites, suggesting that similar climate conditions control carbon-source processes along the gradient. Site-level δ13C and δ18O chronologies were significantly and positively related at all sites, with the strongest relationships among the southern drier stands. This indicates an overall regulation of intercellular carbon dioxide via stomatal conductance for the entire P. tarapacana network, with greater stomatal control when aridity increases. This manuscript also highlights a coupling (decoupling) between physiological processes at leaf level and wood formation as a function of similarities (differences) in their climatic sensitivity. This study contributes to a better understanding and prediction of the response of high-elevation Polylepis woodlands to rapid climate changes and projected drying in the Altiplano.

Phylogenetic placement of Leptosphaeria polylepidis, a pathogen of Andean endemic Polylepis tarapacana, and its newly discovered mycoparasite Sajamaea mycophila gen. et sp. nov.

Polylepis tarapacana forms one of the highest-altitude woodlands worldwide. Its populations are experiencing a decline due to unsustainable land-use practices, climate change, and fungal infection. In Sajama National Park in Bolivia, Polylepis tarapacana is affected by a disease caused by the pleosporalean fungus Leptosphaeria polylepidis, recently described in 2005. In this study, the integrative morphological and molecular analyses using sequences from multiple DNA loci showed that it belongs to the genus Paraleptosphaeria (Leptosphaeriaceae, Pleosporales). Accordingly, the appropriate new combination, Paraleptosphaeria polylepidis, is made. Pseudothecia of Pa. polylepidis were found to be overgrown by enigmatic conidiomata that were not reported in the original description of this fungus. Morphological and molecular analyses using sequences from two DNA loci revealed that they belong to an undescribed genus and species in the family Dictyosporiaceae (Pleosporales). The new generic and specific names, Sajamaea and S. mycophila, are introduced for this unusual fungus.

ECOLOGY OF POLYLEPIS SPP FORESTS, AND PROPOSAL FOR ITS CONSERVATION IN THE ANDEAN REGION OF TACNA, PERU

The forests of Polylepis (queñoales) is one of the most important Andean forest ecosystems and with the greatest impact due to human activities. The objectives of the study were to determine the distribution and diversity of queñoa forests in the Andean region of Tacna, Peru. With this information, We propose the restoration and conservation plan for the Polylepis spp. For this purpose plots of 500 m2 were established. The sampling was simple random, taking a population census in each of the sample units in the 4 provinces (Jorge Basadre, Tacna, Tarata and Candarave). The total evaluation area was 27,491 hectares. The presence of two Polylepis species was identified. Polylepis rugulosa Bitter was registered in 9 districts with an altitudinal range of 3050 to 4226 m.a.s.l. in 6 life zones. Polylepis tarapacana Phil is distributed in the provinces of Tarata and Tacna within 3 districts. P. tarapacana occurs in an altitudinal range between 4230 and 4750 m.a.s.l. in 5 life zones. The tall and diameter of tree were variable for two species. The human impact for P. rugulosa was recorded: Not Intervented (76%), Semi Intervening (21%) and Intervened (3%). For P. tarapacana it was: Not Intervented (77%), Semi Interventions (21%) and Intervened (2%). According to the data gathered, the conservation plan is proposed, consisting of 5 guidelines: 1) education, 2) communication and capacity building, 3) conservation and sustainable management, 4) policies and regulations, and 5) research and monitoring.

Climate change and the distribution and conservation of the world's highest elevation woodlands in the South American Altiplano

Climate change is becoming an increasing threat to biodiversity. Consequently, methods for delineation, establishment and management of protected areas must consider the species' future distribution in response to future climate conditions. Biodiversity in high altitude semiarid regions may be particularly threatened by future climate change. In this study we assess the main environmental variables that best explain present day presence of the world's highest elevation woodlands in the South American Altiplano, and model how climate change may affect the future distribution of this unique ecosystem under different climate change scenarios. These woodlands are dominated by Polylepis tarapacana (Rosaceae), a species that forms unique biological communities with important conservation value. Our results indicate that five environmental variables are responsible for 91% and 90.3% of the present and future P. tarapacana distribution models respectively, and suggest that at the end of the 21st century, there will be a significant reduction (56%) in the potential habitat for this species due to more arid conditions. Since it is predicted that P. tarapacana's potential distribution will be severely reduced in the future, we propose a new network of national protected areas across this species distribution range in order to insure the future conservation of this unique ecosystem. Based on an extensive literature review we identify research topics and recommendations for on-ground conservation and management of P. tarapacana woodlands.

Pleistocene climatic oscillations rather than recent human disturbance influence genetic diversity in one of the world's highest treeline species.

Biological responses to climatic change usually leave imprints on the genetic diversity and structure of plants. Information on the current genetic diversity and structure of dominant tree species has facilitated our general understanding of phylogeographical patterns. Using amplified fragment length polymorphism (AFLPs), we compared genetic diversity and structure of 384 adults of P. tarapacana with those of 384 seedlings across 32 forest sites spanning a latitudinal gradient of 600 km occurring between 4100 m and 5000 m a.s.l. in Polylepis tarapacana (Rosaceae), one of the world's highest treeline species endemic to the central Andes. Moderate to high levels of genetic diversity and low genetic differentiation were detected in both adults and seedlings, with levels of genetic diversity and differentiation being almost identical. Four slightly genetically divergent clusters were identified that accorded to differing geographical regions. Genetic diversity decreased from south to north and with increasing precipitation for adults and seedlings, but there was no relationship to elevation. Our study shows that, unlike the case for other Andean treeline species, recent human activities have not affected the genetic structure of P. tarapacana, possibly because its inhospitable habitat is unsuitable for agriculture. The current genetic pattern of P. tarapacana points to a historically more widespread distribution at lower altitudes, which allowed considerable gene flow possibly during the glacial periods of the Pleistocene epoch, and also suggests that the northern Argentinean Andes may have served as a refugium for historical populations.

Oxygen isotopes in tree rings show good coherence between species and sites in Bolivia

A tree ring oxygen isotope (δ18OTR) chronology developed from one species (Cedrela odorata) growing in a single site has been shown to be a sensitive proxy for rainfall over the Amazon Basin, thus allowing reconstructions of precipitation in a region where meteorological records are short and scarce. Although these results suggest that there should be large-scale (>100km) spatial coherence of δ18OTR records in the Amazon, this has not been tested. Furthermore, it is of interest to investigate whether other, possibly longer-lived, species similarly record interannual variation of Amazon precipitation, and can be used to develop climate sensitive isotope chronologies. In this study, we measured δ18O in tree rings from seven lowland and one highland tree species from Bolivia. We found that cross-dating with δ18OTR gave more accurate tree ring dates than using ring width. Our “isotope cross-dating approach” is confirmed with radiocarbon “bomb-peak” dates, and has the potential to greatly facilitate development of δ18OTR records in the tropics, identify dating errors, and check annual ring formation in tropical trees. Six of the seven lowland species correlated significantly with C. odorata, showing that variation in δ18OTR has a coherent imprint across very different species, most likely arising from a dominant influence of source water δ18O on δ18OTR. In addition we show that δ18OTR series cohere over large distances, within and between species. Comparison of two C. odorata δ18OTR chronologies from sites several hundreds of kilometres apart showed a very strong correlation (r=0.80, p<0.001, 1901–2001), and a significant (but weaker) relationship was found between lowland C. odorata trees and a Polylepis tarapacana tree growing in the distant Altiplano (r=0.39, p<0.01, 1931–2001). This large-scale coherence of δ18OTR records is probably triggered by a strong spatial coherence in precipitation δ18O due to large-scale controls. These results highlight the strength of δ18OTR as a precipitation proxy, and open the way for temporal and spatial expansion of precipitation reconstructions in South America.

Photosynthetic responses of trees in high-elevation forests: comparing evergreen species along an elevation gradient in the Central Andes.

Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18°S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long periods of unfavourable, winter conditions.

Lake Fluctuations, Plant Productivity, and Long-Term Variability in High-Elevation Tropical Andean Ecosystems

Environmental trends and ecosystems’ ranges of variability are little known in tropical very high elevation Andean ecosystems (above 4400 m a.s.l.). We combined satellite image analyses and dendrochronological methods with instrumental records at lower elevation to assess changes in lake size and indices of plant productivity of subtropical high-elevation ecosystems in northern Argentina and southern Bolivia. Between 1985 and 2009, interannual lake fluctuations assessed with Landsat images were positively correlated with interannual variations in regional precipitation and de Martonne’s aridity index, showing a decreasing trend in moisture availability during the period. Changes in lake size were positively correlated with radial growth of Polylepis tarapacana, and with MODIS-derived phenological parameters of enhanced vegetation index (EVI; an index of vegetation “greenness”) between 2001 and 2010. This indicates that water balance has a significant effect on ecosystem functioning, which is related to regional scale atmospheric circulation. A long-term tree ring chronology (starting in 1750) showed that tree growth during recent decades was lower than the last 180 years, and were comparable to growth patterns that occurred between 1775 and 1825. These results suggest that if recent climatic trends continue, long-term ranges of variability in ecosystem functioning could be exceeded.