Patagonian Andean Region Research Articles

Changes in soil organic matter associated with afforestation affect erosion processes: The case of erodible volcanic soils from Patagonia

Large areas of the Patagonian Andean Region with high potential for planting fast-growing exotic conifers, based on the volcanic nature of its soils, are affected by erosion processes. This study aimed to analyse the effects of Pinus ponderosa afforestation on soil organic matter (OM) fractions in non-allophanic volcanic soils and to determine the relationship between organic matter, soil aggregates and erosion processes. The study was conducted along a forested hill slope showing different soil properties according to slope position. OM fractions and aggregate size fractions under different dispersion forces were analysed on 0–5 cm soil samples in rangelands and in 14- and 24-year old plantations on steep and gentle slopes. Simulated rainfall assays were performed to assess soil erodibility; OM and granulometry of sediments were also studied. Results showed that OM contents, mainly OM labile fractions (i.e., particulate OM, and OM associated with macro and large microaggregates), soil aggregation and the formation of very stable microaggregates were enhanced in the afforested soils. However, soil changes varied depending on the initial soil OM contents and on the age of the plantation, with more erratic and smaller changes in most fertile soils. Although potential erosion rates are lower in plantations than in rangeland soils, the high OM enrichment rates found in sediments imply a high OM loss when the soils remain uncovered. Erosion processes in afforestation involve the removal of microaggregates rich in OM and silt fractions, while in the rangelands, coarse and very coarse sand single particles are lost. Afforestation replacing degraded rangelands may be a way to control erosion in these highly erodible volcanic soils, as long as the soil remains covered. Otherwise, the loss of soil enriched in OM from the superficial soil could favour soil carbon depletion.

137Cs inventories along a climatic gradient in volcanic soils of Patagonia: Potential use for assessing medium term erosion processes

Fallout radionuclides, such as Caesium-137, were proven to be a valuable means for studying medium-term (c.a. 50 years) soil erosion processes. In order to gain knowledge on the spatial distribution of 137Cs in volcanic soils of Andean Patagonia, 137Cs reference inventories were established along a precipitation gradient. At the subhumid sector, patterns of 137Cs gain/loss associated with land use were also determined considering native forests under grazing, a degraded rangeland and a pine plantation.Along the rising rainfall gradient (750–1400 mm), pedogenesis of volcanic ash soils, non-crystalline mineral formation, organic matter content and soil porosity varied, increasing in moister areas. Radionuclide inventories varied along the edaphoclimatic gradient, reaching mean values of 192, 267 and 576 Bq m−2, at study areas with 750, 950 and 1400 mm of annual precipitation, respectively. The 137Cs inventory followed an exponential relationship with precipitation, which could be related to the presence of allophane as the colloidal material in the soils from the rainiest area. The penetration depth reached by 137Cs varied between 15 and 25 cm, according to rain amount and soil texture. Most of the 137Cs fallout was retained in the uppermost 10 cm of the profiles and an exponential decline of 137Cs with depth, highly related to organic matter contents, was found.At the subhumid study area, both 137Cs mass activity and inventory, significantly decreased under the different land uses, with respect to reference soils. Although the pattern of 137Cs gain/loss varied according to topography, soil properties (organic matter and porosity) and vegetation cover, showing eroding and aggrading profiles, most samples had 137Cs values lower than the reference value, suggesting loss of soil as a consequence of erosion processes. Furthermore, as much as 45%, 58% and 70% of sample points from native forests, plantation and rangeland, respectively, had 137Cs values below the limit of detection. In the study transects, the loss of the upper 15 cm of soil in the subhumid sector during the last 50 years, highly exceeding tolerable erosion rates, highlights the urgent need for applying effective soil conservation measures.Reference inventories, which vary according to the edaphoclimatic gradient, and the loss of the radionuclide in sites with anthropic intervention, show the potential for using 137Cs measurements for assessing erosion processes in the Patagonian Andean Region.

Obsidian Distribution of the Northern Patagonian Forest Area and Neighboring Sectors during the Late Holocene (Neuquén Province, Argentina)

AbstractAnalysis of 519 obsidian artifacts (pebbles, debitage, cores and small bifaces) by nondestructive X-ray fluorescence from forests and steppes of southern Lanín National Park in the northern Patagonian Andean region, from Lácar (chemical group QU/AP), Lolog (CP-LL 1), Filo Hua-Hum (FHH), Paillakura (Pk, former unknown 1 group), Meliquina (MQ, former unknown group 2) and Yuco (YC) sources. Neutron activation analysis was applied to 29 of the artifacts. We identified for the first time the presence of obsidian from distant Covunco (PC1) in the center of Neuquén. This paper is the first English language publication of our ongoing, ten-year-long research. In accordance with previous work, but using other analytical techniques, the most frequently used sources during the late Holocene remain CP/LL 1 and Pk, here we add YC, mainly by the incorporation of new sites recently surveyed in the islands and the coast of Lake Lácar, next to its source. Another result consistent with previous work is the absence of obsidian from Mendoza and Chilean sources; therefore, we suggest these obsidians circulate just to the east and northeast, allowing us to discuss issues of human territoriality during the Late Holocene.

A new species of predaceous midge in the Patagonian genus Austrosphaeromias with a redescription of A. chilensis (Diptera, Ceratopogonidae)

A new species of predaceous midge, Austrosphaeromias setosa sp. nov., is described and illustrated from adult males and females collected in the Patagonian-Andean region of Argentina and Chile. Based on examination of the type species of Austrosphaeromias Spinelli, 1997 and recently collected specimens from near the type-locality, the female and previously unknown male of Austrosphaeromias chilensis (Ingram & Macfie, 1931) are also described and illustrated. Descriptions are accompanied by color photographs and illustrations of key features of females and males of both species. We also provide a key to adult females and males of the four species of Austrosphaeromias.

Relationships between climate variability and radial growth of Nothofagus pumilio near altitudinal treeline in the Andes of northern Patagonia, Chile

Global warming is expected to enhance radial tree growth at alpine treeline sites worldwide. We developed a well-replicated tree-ring chronology from Nothofagus pumilio near treeline in a high precipitation climate on Choshuenco Volcano (40°S) in Chile to examine: (a) variation in tree radial growth in relation to interannual climatic variability; and (b) relationships of radial growth to variability in El Niño Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO) at interannual and decadal time scales. A tree-ring chronology based on 99 tree-ring series from 80 N. pumilio trees near treeline showed a high series intercorrelation (0.48) indicating a strong common environmental signal. Radial growth is negatively correlated with precipitation in late spring (November–December). Temperature and tree growth are positively correlated during late spring and early summer (November–January). Interannual variability in both seasonal climate and in tree growth is strongly teleconnected to ENSO and AAO variability. Radial growth of N. pumilio in this humid high-elevation forest does not show a positive trend over the past half century as predicted from global treeline theory and broadscale warming in the Patagonian-Andean region. Instead, tree growth increased sharply from the 1960s to a peak in the early 1980s but subsequently declined for c. 30years to its lowest level in >100years. The shift to higher radial growth after c. 1976 coincides with a shift towards warmer sea surface temperatures in the tropical Pacific which in turn are associated with warmer growing season temperatures. The decline in tree growth since the mid-1990s is coincident with the increasingly positive phase of the AAO and high spring precipitation periods associated with El Niño conditions. The recent shift towards reduced growth of N. pumilio at this humid high-elevation site coincident with rising AAO mirrors the reduced tree growth beginning in the 1960s for trees growing in relatively xeric, lower elevation sites throughout the Patagonian-Andean region. The current study indicates that N. pumilio growth response in humid high-elevation environments to recent broad-scale warming has been non-linear, and that AAO and ENSO are key climatic forcings of tree growth variability.

Fish distribution patterns and habitat availability in lakes Moreno Este and Moreno Oeste, Patagonia, Argentina

Andean Patagonian lakes are ultraoligotrophic and deep, have simple food webs and low fish diversity and abundance. In this work the distributional abundance data of fish was studied in two interconnected Andean Patagonian lakes with varying proportions of contrasting habitat types. Hydroacoustic data (120 kHz) were used to analyze fish abundance and habitat use during the mixis and stratification periods. Three types of habitat (near shore, surface pelagic and deep pelagic) and two groups of fish, based on size (Big Fish >12 cm total length and Fish Larvae and Small Fish <12 cm total length) were defined. The distribution of both fish groups in these lakes revealed differences in habitat use for each lake and period. Fish group abundance was related to the availability of habitat types, according to the morphology of each lake. The Big Fish group showed preference for the near shore habitat during lake stratification and always appeared as individual targets. The Fish Larvae and Small Fish group used mainly the pelagic habitat during mixis, where they formed dense sound scattering layers. However, during lake stratification many individual targets from this group were found both in pelagic and near shore habitats, which would seem to indicate a change in distributional behavior. This is possibly associated with niche changes in the Galaxiids ( Galaxias spp), a key component of Northern Patagonian lake food webs. Lakes like Moreno Oeste, which are morphologically and structurally more complex, could have more diverse fish ensembles with higher abundances. In contrast, lakes of simple morphology with low development of near shore habitats and ample deep zones, like Lake Moreno Este, could present lower Big Fish abundance. The contrasting habitat availability between lakes accounts for the abundances and distribution patterns of each fish group. While in these lakes fish assemblage species composition could depends on the environmental filter, the particular structure of a fish assemblage in terms of the proportional abundances of species depends on proportional habitat type availability. We can speculate that in Andean Patagonian lakes Galaxiids mediate a habitat coupling process critical for the transfer of energy and matter in oligotrophic lakes. We may also consider that the Small Puyen in this type of lake is a keystone prey species that relieves predation pressure on other potential prey. The existence of deep pelagic habitats in numerous deep lakes in the Northern Patagonian Andean region provides not only daytime refuge for Galaxiids, which allows them to maintain their high numbers in the lakes, but could also, in the long term, act as a Galaxiid source for other water bodies.

Endozoochory decreases environmental filtering imposed to seedlings

AbstractQuestionsRecruitment microsites are imposed on plants, first by seed dispersal and then by the environment. Different seed dispersal vectors could decrease or increase the environmental filtering imposed on seedlings, depending on their specificity to deliver seeds to suitable microsites for germination and establishment. We addressed the hypothesis that endozoochory reduces the environmental filtering imposed to seedlings to a larger extent than does anemochory. We predicted that seedlings from animal‐dispersed species should show a higher degree of environmental coupling.LocationNorthern Patagonian Andean region of Argentina, 40–42° S.MethodsWe characterized the relationship of seedlings, saplings and reproductive individuals to total radiation, air temperature and relative humidity for 16 woody species growing in 25 plant communities of different post‐fire ages in temperate forests of southern South America.ResultsSeedlings and saplings of endozoochorous species occurred under more similar environmental conditions than seedlings and saplings of anemochorous species. Basically, the mean difference in plant–environment correlation coefficients between saplings and seedlings was &lt;0.2 for all endozoochorous species and &gt;0.2 for all anemochorous species for all environmental variables. Comparisons between dispersal modes were also statistically significant before and after controlling for phylogenetic relationships among species. Even though saplings and seedlings of endozochorous species tended to occur under similar environmental conditions, we did not find evidence that saplings and seedlings co‐occur in the same physical microsites. Finally, we did not find evidence either that seedlings of endozoochorous species tended to occur differentially underneath reproductive individuals of the same species (i.e. more seeds falling by gravity beneath maternal plants).ConclusionsThe tighter coupling between seedlings of endozoochorous species and environmental factors persisting to the sapling stage suggests that relying on animals for seed dispersal reduces mortality costs during the early stages of recruitment by reducing the environmental filtering imposed on seedlings.

Adapting to global environmental change in Patagonia: What role for disturbance ecology?

Research from the Patagonian-Andean region is used to explore challenges and opportunities related to the integration of research on wildfire activity into a broader earth-system science framework that views the biosphere and atmosphere as a coupled interacting system for understanding the causes and consequences of future wildfire activity. We examine how research in disturbance ecology can inform land-use and other policy decisions in the context of probable future increases in wildfire activity driven by climate forcing. Climate research has related recent warming and drying trends in much of Patagonia to an upward trend in the Southern Annular Mode which is the leading pattern of extratropical climate variability in the southern hemisphere. Although still limited in spatial extent, tree-ring fire history studies are beginning to reveal regional patterns of the top-down climate influences on temporal and spatial pattern of wildfire occurrence in Patagonia. Knowledge of relationships of fire activity to climate variability in the context of predicted future warming leads to the hypothesis that wildfire activity in Patagonia will increase substantially during the first half of the 21st century. In addition to this anticipated increase in extreme fire events due to climate forcing, we further hypothesize that current land-use trends will increase the extent and/or severity of fire events through bottom-up (i.e. land surface) influences on wildfire potential. In particular, policy discussions of how to mitigate impacts of climate warming on fire potential need to consider research results from disturbance ecology on the implications of continued planting of flammable non-native trees and the role of introduced herbivores in favouring vegetation changes that may enhance landscape flammability.

Residential energy use in one-family households with natural gas provision in a city of the Patagonian Andean region

Residential energy use was studied in one-family houses in the city of Bariloche, in the Patagonian Andean region of Argentina. A survey was conducted of households connected to the natural gas network to correlate use of gas, living area and number of inhabitants per house. The annual average consumption of gas was found to be 169 GJ, and consumption of electricity 8 GJ. This total energy use per household per year is almost double the average value reported for Stockholm, Sweden, although both locations have similar heating requirements. The difference was mainly due to heating energy consumption per unit living space, which in Bariloche was 1530 MJ/m 2 per year, while in Stockholm the average is around 570 MJ/m 2 per year. The high energy consumption in Bariloche is explained primarily by the construction characteristics of the buildings, and secondarily by the efficiency of the heating devices used. We were able to conclude that subsidies on natural gas tariffs given to the residential sector do not promote a rational use of the resource. Furthermore, almost 40% of the population (mostly households in poverty) are not connected to the subsidised gas resource, but pay prices for alternative fuels that are between 10- and 15 times higher. Policies to improve buildings and appliances would reduce emissions and make access to energy more equitable.

Infection patterns of Tylodelphys barilochensis and T. crubensis (Trematoda: Diplostomatidae) metacercariae in Galaxias maculatus (Osmeriformes: Galaxiidae) from two Patagonian lakes and observations on their geographical distribution in the southern Andean region, Argentina.

In the Patagonian Andean region, 2 species of diplostomatids parasitize the brains of Galaxias maculatus. The purpose of this study was to evaluate seasonal variation, spatial variation, and association with host age in the transmission of Tylodelphys barilochensis and T. crubensis in several oligotrophic lakes in Argentinian Patagonia. Fishes were captured monthly in Lake Gutiérrez and bimonthly in Lake Escondido. One summer or autumn sample was also taken in several other Patagonian lakes. Infection parameters were calculated and compared using nonparametric tests. The 2 species co-occurred in most of the sampled lakes, with high values of prevalence and mean intensity. In Lake Gutiérrez and Lake Escondido, the intensity of both diplostomatid species did not show significant differences between sexes and co-varied with host length. All age classes were infected; maximum prevalence values were reached before maximum mean intensity values in the 1-yr age class. A seasonal pattern of prevalence and mean intensity of the 2 parasite species with autumn mean intensity values differing significantly from those of the other seasons was evident only in Lake Gutiérrez.

Light climate and plankton in the deep chlorophyll maxima in North Patagonian Andean lakes

The light climate at the deep chlorophyll maxima (DCM) was analysed in a set of lakes of the North Patagonian Andean region. Apparent and inherent optical properties in relation to the chlorophyll a vertical distribution were investigated in seven lakes including deep (Z max > 90 m) and shallow (Z max < 12 m) ones. Sampling was carried out during the thermal stratification period (summer) of the deep lakes since in the shallower lakes no stable thermal stratification was detected. The large deep lakes presented very low diffuse attenuation coefficients of photosynthetically active radiation (K dPAR ), and a DCM situated at 0.98-2% of surface PAR irradiance, coinciding with the maximum abundance of the mixotrophic ciliate Ophrydium naumanni and autotrophic picoplankton. Both fractions seemed to be favoured by dim light conditions of particular wavelengths, since at these DCM layers mainly green and blue wavelengths prevailed (<600 nm). In contrast, shallow lakes showed higher K dPAR values, with a higher concentration of dissolved yellow substances, which caused substantial differences in the spectral quality that may have contributed to explain the absence of this ciliate population in these lakes.

ENSO EFFECTS ON TEMPERATURE AND PRECIPITATION OF THE PATAGONIAN-ANDEAN REGION: IMPLICATIONS FOR BIOGEOGRAPHY

This study documents instabilities in the relationship between El Niño-Southern Oscillation (ENSO) and climate of the Patagonian-Andean region at spatial and temporal scales directly relevant to biogeographical research. Four temperature and four precipitation regions located south of 38°S were described using homogeneous climate records that were significantly correlated. Correlation function analysis evaluated the response of seasonal temperature and precipitation for each region relative to two indices of ENSO, the Southern Oscillation Index (SOI) and tropical Pacific sea surface temperatures (SSTs). Statistically significant correlations were observed for each region, although relationships varied among regions. Climatic responses to El Niño events were deduced from these relationships. The 30-year moving correlations of temperature and precipitation against SOI and SST showed substantial temporal instability of the ENSO-climate relationships during this century. These instabilities are explained by documented, multi-decadal variations in ENSO, the southeast Pacific anticyclone, and mean sea-level pressure (SLP) in the southern Atlantic Ocean. Despite significant relationships between ENSO and climate for particular regions and periods, we did not find that such relationships were consistent in space or time. ENSO-climate relationships often are useful for understanding temporal variability in ecological processes, but temporal instability in these relationships limits their predictive ability. [Key words: Argentina, Chile, climate variation, correlation analyses, El Niño, South America, southern oscillation.]

Curvas de índice de Sitio para Pinus ponderosa (Dougl.) Law de aplicación en la región Andino Patagónica de Chubut y Río Negro, Argentina

Anamorphic Site Index and Height-Growth Curves with application in Patagonian Andean Region were developed from a database formed by 57 stem analysis of dominant trees from 22 Ponderosa Pine stands.