Duncan A. Christie

Rain Forest Islands in the Chilean Semiarid Region: Fog-dependency, Ecosystem Persistence and Tree Regeneration

Tree presence in semiarid ecosystems is generally constrained by insufficient annual rainfall. However, in semiarid Chile, rainforest patches dominated by Aextoxicon punctatum are unexpectedly found on coastal mountaintops (450–600 m) at 30°S, surrounded by a xerophytic vegetation matrix that receives only 147 mm of annual precipitation. It has been proposed that these forests persist as a result of fog-water inputs. If so, then because fog-water deposition is spatially heterogeneous and shows strong edge effects, the potential environmental gradient created by the direction of fog input should determine forest structure and tree regeneration patterns. To investigate this hypothesis, we measured fog inputs, forest structural attributes (age and size distribution, basal area, and coarse woody debris), and tree regeneration in three different habitats: the windward edges (WE), leeward edges (LE), and the interior (center) of rainforest patches varying in area from 0.2 to 22 ha. Mean fog-water input was estimated from passive collectors over 1 year in WE and LE of patches. Tree regeneration was greater in the WE and forest interior (FI) and decreased toward the LE of patches, following a marked pattern of decline in fog inputs. Older trees and coarse woody debris were concentrated in the FI and LE of patches. Tree regeneration and patch structure appear to be largely controlled by fog-input direction and edge effects. We propose that forest patches may be slowly growing toward the incoming fog edge, while dying at the opposite edge.

Continental-Scale Temperature Variability during the Past Two Millennia: Supplementary Information

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

Facing unprecedented drying of the Central Andes? Precipitation variability over the period AD 1000–2100

Projected future trends in water availability are associated with large uncertainties in many regions of the globe. In mountain areas with complex topography, climate models have often limited capabilities to adequately simulate the precipitation variability on small spatial scales. Also, their validation is hampered by typically very low station density. In the Central Andes of South America, a semi-arid high-mountain region with strong seasonality, zonal wind in the upper troposphere is a good proxy for interannual precipitation variability. Here, we combine instrumental measurements, reanalysis and paleoclimate data, and a 57-member ensemble of CMIP5 model simulations to assess changes in Central Andes precipitation over the period AD 1000–2100. This new database allows us to put future projections of precipitation into a previously missing multi-centennial and pre-industrial context. Our results confirm the relationship between regional summer precipitation and 200 hPa zonal wind in the Central Andes, with stronger Westerly winds leading to decreased precipitation. The period of instrumental coverage (1965–2010) is slightly dryer compared to pre-industrial times as represented by control simulations, simulations from the past Millennium, ice core data from Quelccaya ice cap and a tree-ring based precipitation reconstruction. The model ensemble identifies a clear reduction in precipitation already in the early 21st century: the 10 year running mean model uncertainty range (ensemble 16–84% spread) is continuously above the pre-industrial mean after AD 2023 (AD 2028) until the end of the 21st century in the RCP2.6 (RCP8.5) emission scenario. Average precipitation over AD 2071–2100 is outside the range of natural pre-industrial variability in 47 of the 57 model simulations for both emission scenarios. The ensemble median fraction of dry years (defined by the 5th percentile in pre-industrial conditions) is projected to increase by a factor of 4 until 2071–2100 in the RCP8.5 scenario. Even under the strong reduction of greenhouse gas emissions projected by the RCP2.6 scenario, the Central Andes will experience a reduction in precipitation outside pre-industrial natural variability. This is of concern for the Central Andes, because society and economy are highly vulnerable to changes in the hydrological cycle and already have to face decreases in fresh water availability caused by glacier retreat.

Streamflow variability in the Chilean Temperate-Mediterranean climate transition (35°S–42°S) during the last 400 years inferred from tree-ring records

Abstract As rainfall in South-Central Chile has decreased in recent decades, local communities and industries have developed an understandable concern about their threatened water supply. Reconstructing streamflows from tree-ring data has been recognized as a useful paleoclimatic tool in providing long-term perspectives on the temporal characteristics of hydroclimate systems. Multi-century long streamflow reconstructions can be compared to relatively short instrumental observations in order to analyze the frequency of low and high water availability through time. In this work, we have developed a Biobío River streamflow reconstruction to explore the long-term hydroclimate variability at the confluence of the Mediterranean-subtropical and the Temperate-humid climate zones, two regions represented by previous reconstructions of the Maule and Puelo Rivers, respectively. In a suite of analyses, the Biobío River reconstruction proves to be more similar to the Puelo River than the Maule River, despite its closer geographic proximity to the latter. This finding corroborates other studies with instrumental data that identify 37.5°S as a latitudinal confluence of two climate zones. The analyzed rivers are affected by climate forcings on interannual and interdecadal time-scales, Tropical (El Niño Southern Oscillation) and Antarctic (Southern Annular Mode; SAM). Longer cycles found, around 80-years, are well correlated only with SAM variation, which explains most of the variance in the Biobío and Puelo rivers. This cycle also has been attributed to orbital forcing by other authors. All three rivers showed an increase in the frequency of extreme high and low flow events in the twentieth century. The most extreme dry and wet years in the instrumental record (1943–2000) were not the most extreme of the past 400-years reconstructed for the three rivers (1600–2000), yet both instrumental record years did rank in the five most extreme of the streamflow reconstructions as a whole. These findings suggest a high level of natural variability in the hydro-climatic conditions of the region, where extremes characterized the twentieth century. This information is particularly useful when evaluating and improving a wide variety of water management models that apply to water resources that are sensitive to agricultural and hydropower industries.

5.14 Recent and Historic Andean Snowpack and Streamflow Variations and Vulnerability to Water Shortages in Central-Western Argentina

The accumulation of snow during winter and its subsequent melting during warmer months provide most of the water needed for the human populations located along the semiarid western and eastern slopes of the Andes in central Chile and central-western Argentina. The societies in these regions can be characterized as ‘hydraulic societies,’ as social tissues are strongly associated with intensive use of water resources that historically have been adapted to ‘control’ a hostile natural environment. This chapter first discusses various empirical analyses of snowpack and streamflow records that demonstrate (1) the dominant influence of snowmelt on the hydrologic regimes of the main rivers of the region, (2) the impressive similarities in these records at interannual and interdecadal timescales, and (3) the strong relationships that exist with El Nino–Southern Oscillation (ENSO) features in the tropical Pacific. The authors also use the snowpack and streamflow records available to identify the most severe dry and wet periods in this portion of the Andes over the past 100 years. Two recently developed snowpack reconstructions that extend the instrumental records for several centuries are subsequently discussed in an attempt to provide evidence that may help assess the recent patterns observed in the instrumental records in a long-term perspective. This evidence may also be used to test the time stability of the relationships with large-scale ocean–atmosphere features and to validate the results from global and local modeling exercises intended to project future hydroclimatic changes in this region. The final discussion is on the inherent vulnerabilities associated with the scarce water resources of the inhabitants of the Rio Mendoza Basin in Argentina. This exercise allows an interesting analysis to better understand the historic, current, and possibly future socioeconomic situation of the different players of this hydraulic society. Comprehensive assessments integrating results from natural and social studies are suggested as an innovative approach to anticipate future vulnerabilities to water shortages and to develop adaptation strategies toward resilience.

Spatiotemporal Variations in Hydroclimate across the Mediterranean Andes (30°–37°S) since the Early Twentieth Century

AbstractIn the Mediterranean Andes region (MA; 30°–37°S), the main rivers are largely fed by melting snowpack and provide freshwater to around 10 million people on both sides of the Andes Mountains. Water resources in the MA are under pressure because of the extensive development of industrial agriculture and mining activities. This pressure is increasing as the region faces one of its worst recorded droughts. Previous studies have pointed to El Nino–Southern Oscillation (ENSO) as the main climatic force impacting the MA. However, the role of decadal and multidecadal climate variability, their spatial patterns, and the recurrence of long-term droughts remains poorly studied. In an attempt to better understand these factors, spatial and temporal patterns of hydroclimatic variability are analyzed using an extensive database of streamflow, precipitation, and snowpack covering the period between 1910 and 2011. These analyses are based on the combination of correlation, principal components, and kernel estimat...

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

Polylepis tarapacana forms the worlds highest forest, being able to grow up to 5,200 m a.s.l. At such elevations, low temperatures, high solar radiation and water scarcity severely restrict plant survival. Our study was focused on the photosynthetic responses of Polylepis species and how they are able to cope with such a challenging environment. We performed all measurements and samplings in their natural environment. This strategy allowed us to observe unexpected patterns of daily adjustments in photosynthetic pigments, which reflect major changes in the structure and organization of the photosynthetic apparatus.

The First Millennium-Age Araucaria Araucana in Patagonia

ISABELLA AGUILERA-BETTI1*, ARIEL A. MUÑOZ1, DANIEL STAHLE2, GINO FIGUEROA1,3, FERNANDO DUARTE1, ÁLVARO GONZÁLEZ-REYES4,5, DUNCAN CHRISTIE6, ANTONIO LARA6, MAURO E. GONZÁLEZ6, PAUL R. SHEPPARD7, DAVID SAUCHYN8, ANDRÉS MOREIRA-MUÑOZ9, ISADORA TOLEDO-GUERRERO1, MATÍAS OLEA1, PABLO APAZ1,10, and ALFONSO FERNANDEZ11 1Laboratorio de Dendrocronología y Estudios Ambientales, Instituto de Geografía, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile

Recuperación de bosques de Pilgerodendron uviferum (D. Don) Florin luego de perturbaciones antrópicas en la Cordillera de la Costa de Valdivia, Chile

Los cambios provocados por sucesivas y/o severas alteraciones pueden causar la transformacion o perdida de un sistema ecologico. En el presente trabajo se cuantifica la perdida estructural y su posterior recuperacion despues de alteraciones antropicas en dos fragmentos de Pilgerodendron uviferum (D. Don) Florin ubicadas en la Reserva Nacional Valdivia. Se estudio la estructura y composicion de los fragmentos, y las evidencias de alteraciones antropicas. La presencia de abundantes arboles quemados y tocones indica que el fuego y la extraccion de madera han sido los principales agentes que han determinado la estructura y composicion actual de dichos fragmentos. Para ambos casos, el 86 % del area basal corresponde a individuos muertos y el 14 % a individuos vivos. Se cuantifico una abundante regeneracion natural postalteracion, con una alta riqueza de especies en el sotobosque caracteristica de estos bosques. No obstante, actualmente ambos fragmentos presentan amenazas que podrian alterar el curso de la sucesion secundaria de este fragil ecosistema ubicado en la Cordillera de la Costa valdiviana.

Water availability reconstructions using tree-rings in the Valdivian rainforest ecoregion, Chile

Water availability can be considered as one of the main restrictions for future development in South-Central Chile, due to the reported decreasing trends in precipitation in the last decades and the increasing demand for this resource. This issue makes the study of past water availability fundamental for the understanding of present and future variations. This paper presents a comparison of two water availability reconstructions within the Valdivian rainforest ecoregion (35o-48oS), one corresponding to a precipitation (37o-39.5o S) and the other to a streamflow reconstruction (41o S). This study shows that there are fundamental differences between them especially in the long term variability. However, there are also coincidences, mainly at higher frequency variations, such as at a bidecadal, decadal and annual scale. Another important finding is that these reconstructions show significant correlations with different climatic forcings in this area. The northern reconstruction presents a significant relationship with ENSO (El Nino Southern Oscillation), while the southern does the same with the AAO (Antarctic Oscillation Index).