Holocene Dynamics of Temperate Rainforests in West-Central Patagonia

Analyses of long-term ecosystem dynamics offer insights into the conditions that have led to stability vs. rapid change in the past and the importance of disturbance in regulating community composition. In this study, we (1) used lithology, pollen, and charcoal data from Mallín Casanova (47°S) to reconstruct the wetland, vegetation, and fire history of west-central Patagonia; and (2) compared the records with independent paleoenvironmental and archeological information to assess the effects of past climate and human activity on ecosystem dynamics. Pollen data indicate that Nothofagus-Pilgerodendronforests were established by 9,000 cal yr BP. Although the biodiversity of the understory increased between 8,480 and 5,630 cal yr BP, forests remained relatively unchanged from 9,000 to 2,000 cal yr BP. The charcoal record registers high fire-episode frequency in the early Holocene followed by low biomass burning between 6,500 and 2,000 cal yr BP. Covarying trends in charcoal, bog development, and Neoglacial advances suggest that climate was the primary driver of these changes. After 2,000 cal yr BP, the proxy data indicate (a) increased fire-episode frequency; (b) centennial-scale shifts in bog and forest composition; (c) the emergence of vegetation-fire linkages not recorded in previous times; and (d) paludification in the last 500 years possibly associated with forest loss. Our results therefore suggest that Nothofagus-Pilgerodendrondominance was maintained through much of the Holocene despite long-term changes in climate and fire. Unparalleled fluctuations in local ecosystems during the last two millennia were governed by disturbance-vegetation-hydrology feedbacks likely triggered by greater climate variability and deforestation

Holocene Dynamics of Temperate Rainforests in West-Central Patagonia

Analyses of long-term ecosystem dynamics offer insights into the conditions that have led to stability vs. rapid change in the past and the importance of disturbance in regulating community composition. In this study, we (1) used lithology, pollen, and charcoal data from Mallín Casanova (47°S) to reconstruct the wetland, vegetation, and fire history of west-central Patagonia; and (2) compared the records with independent paleoenvironmental and archeological information to assess the effects of past climate and human activity on ecosystem dynamics. Pollen data indicate that Nothofagus-Pilgerodendron forests were established by 9,000 cal yr BP. Although the biodiversity of the understory increased between 8,480 and 5,630 cal yr BP, forests remained relatively unchanged from 9,000 to 2,000 cal yr BP. The charcoal record registers high fire-episode frequency in the early Holocene followed by low biomass burning between 6,500 and 2,000 cal yr BP. Covarying trends in charcoal, bog development, and Neoglacial advances suggest that climate was the primary driver of these changes. After 2,000 cal yr BP, the proxy data indicate (a) increased fire-episode frequency; (b) centennial-scale shifts in bog and forest composition; (c) the emergence of vegetation-fire linkages not recorded in previous times; and (d) paludification in the last 500 years possibly associated with forest loss. Our results therefore suggest that Nothofagus-Pilgerodendron dominance was maintained through much of the Holocene despite long-term changes in climate and fire. Unparalleled fluctuations in local ecosystems during the last two millennia were governed by disturbance-vegetation-hydrology feedbacks likely triggered by greater climate variability and deforestation.This work was supported by grants from the National Science Foundation (0966472, 0956552, 0602166), the National Geographic Society (7988-06), and the Department of Archaeology and Natural History at the Australian National University

Habitat distribution modeling reveals vegetation flammability and land use as drivers of wildfire in SW Patagonia

Despite important recent advances in modeling current and future global fire activity in relation to biophysical predictors there remain important uncertainties about finer-scale spatial heterogeneity of fire and especially about human influences which are typically assessed at coarse-spatial resolutions. The purpose of the current study is to quantify the influence of biophysical and anthropogenic variables on the spatial distribution of wildfire activity between 1984 and 2010 over an extensive southern Patagonian-Andean region from ca. 43° to 53° S extending from coastal rainforests to xeric woodland and steppe. We used satellite imagery to map all detectable fires > 5 ha from 1984 to 2010 in four study areas (each of 13,100 to 36,635 km2) and field checked 65 of these burns for accuracy of burned vegetation class and fire perimeters. Then, we used the MaxEnt modeling technique to assess the relationships of wildfire distributions to biophysical and human environmental variables in each of the four regions. The 232 fires > 5 ha mapped in the four study areas accounted for an area of 1,314 km2 indicating that at least 1.8% of the total area burned between 1984 and 2010. In general, areas with intermediate productivity levels (e.g. shrublands) have higher fire probability compared with areas of low and high productivity levels, such as steppe and wet forests, respectively. There is a marked contrast in the flammability of broad vegetation classes in determining fire activity at a regional scale, as well as a strong spatial relationship of wildfires to anthropogenic variables. The juxtaposition of fire-resistant tall forests with fire-prone shrublands and woodlands creates the potential for positive feedbacks from human-set fires to gradually increase the flammability of extensive landscapes through repeated burning. Distance to roads and settlements were also strong predictors, suggesting that fire in all regions is ignition-limited. However, these anthropogenic predictors influenced probability of fire differently among study regions depending on their main land-use practices and their past and present socioeconomic contexts.Fil: Paritsis, Juan. State University Of Colorado-boulder; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Holz, Andrés. State University Of Colorado-boulder; Estados UnidosFil: Veblen, Thomas T.. State University Of Colorado-boulder; Estados UnidosFil: Kitzberger, Thomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentin

Studies on vegetation-, fire-, climate- and human history in the mid- to late Holocene - a contribution to protection and management of the forest-steppe-biome in the Mongolian Altai

In this thesis, several sedimentological archives from Altai Tavan Bogd National Park are studied to reconstruct the vegetation-, fire-, climate- and human history of the forest-steppe biome in the Mongolian Altai. The research is carried out to improve the understanding of the dynamics and variability of this sensitive ecosystem and its unique biodiversity. Previous palynological or palaeoecological work from the Mongolian Altai is sparse, yet important for an implementation of sustainable land use as well as protection and management of the species-rich vegetation in the Altai region. The main goals of this research are to reconstruct past vegetation and to investigate the role and extent of climate, fire and anthropogenic impact on environmental change. A multi-site approach of five environmental archives (lacustrine and peat) from different locations and elevations within the forest-steppe biome (below, within and above the forest belt) is applied to obtain as much information as possible. Multi-proxy analyses including palynological and sedimentological proxies (pollen, NPPs, charcoal, diatoms and XRF-scanning) were used on the radiocarbon dated sediment archives. During the mid- and the beginning of the late Holocene (4,300 to 1,000 (2,000) cal yr BP) the vegetation in the area was characterized by open coniferous forest and high-mountain steppe indicating rather warm and humid conditions. In the further course of the late Holocene, steppe communities expanded noticeably favoring a colder and more arid climate. During the last approx. 70 years an increase in tree and shrub vegetation indicates a warming climate and a higher availability of water due to permafrost and glacier degradation in the high mountains. Regarding the human history in the Mongolian Altai, the period from 2,000 to 1,000 cal yr BP represents a transition phase from hunters and gatherers to a nomadic herding lifestyle. Coprophilous fungi reconstructions show that grazing intensified around 1,000 cal yr BP, possibly also favoring the expansion of steppe. High-resolution data show that changes in human occupation due to political shifts and changing Mongolian settlements had an impact on the vegetation in the area, especially during Mongol Empire (744 to 582 cal yr BP). Regardless of specific settlement periods, short-term changes in climatic conditions favored shifts in grazing activities. In the Mongolian Altai, fires play a tangential role. However, at around 1,000 cal yr BP the fire frequency increased in accord with growing anthropogenic impact and climate aridity. An episode of low fire activity persists since around 150 cal yr BP. Major local variances occurred regarding the time frame and extent of steppe expansion and grazing activities in the soil archive within the forest belt and with respect to the fire frequency in the peat archive above the upper forest line. The applied multi-proxy approach highlights the value of the reconstruction of several independent proxies to examine various aspects of an ecosystem in the same archive, despite of that the interpretation of results is challenging. Additionally, the multi-site study offers the best possibility to distinguish between local environmental signals and regional trends

A paleolimnological reconstruction of Late-Quaternary environmental change along a transect from South America to the Antarctic Peninsula = Een paleolimnologische reconstructie van Laat-Kwartaire milieuveranderingen langsheen een transect van Zuid-Amerika tot het Antarctisch Schiereiland

In order to frame the recent global climatic changes, climate and oceanic models need to be tested against known climatic variations in the past. Recently, deglacial and Holocene paleo-environmental related research has shifted its main focus from the North-Atlantic region to the Southern Hemispheric high latitudes, as Antarctica and the Southern Ocean have shown to play an important role in global climate regulation (e.g. Knorr & Lohman, 2003). Very recently, the tropical (mainly Pacific) latitudes have been evenly recognized as potentially playing a large role in global climate modulation, both at interannual- decadal (e.g. El Niño Southern Oscillation) and century to millennial time scales (e.g. long-term changes in ENSO variability; Shulmeister et al., 2006; Pena & Cacho, 2009). Pacific tropical and Antarctic climate anomalies are physically linked with each other through the strength and the position of the Antarctic Circumpolar Current (ACC) and Southern Westerly Wind belt (SWW). Therefore, recent climate reconstructions are focused on past changes in position and strength of these winds, which have a direct impact on local and/or regional weather patterns along the westcoast of South America, and the Antarctic Peninsula. In this thesis, lake sediments were analyzed for biological, sedimentological and geochemical proxies, in order to infer past climatic changes at two key sites along a latitudinal transect from southern South America (40°S) through the Antarctic Peninsula (63°S). The first two chapters of this thesis are dedicated to postglacial paleoenvironmental and related paleoclimatic changes, inferred from an 11.22 m sediment core from Lake Puyehue (Chilean Lake District, 40°S), located at the northern boundary of the Southern Westerly Wind belt

Oribatid mite (Acari: Oribatida) and Chironomid (Diptera: Chironomidae) communities from a high-Andean cushion peatland in Peru (14°S) and their use for palaeoenvironmental reconstruction during the Nasca cultural period

The edaphic Oribatid mites and Chironomid larvae of five different successional stages of a high-Andean cushion peatland in southern Peru (14°S) were investigated. In total, 17 Oribatid mite taxa, belonging to eight families could be identified. Taxonomic remarks for the species found and an analysis of community structures are provided. The investigation shows significantly higher Oribatid mite densities in the early and medium successional stages in comparison to the successional climax ecotope. From the Chironomids, 11 taxa belonging to three subfamilies could be identified. For the taxa found, taxonomic descriptions and an analysis of community structures are also provided. Within the successional rank order of the peatland, the abundance of Chironomids is highest in pioneer soils, followed by mid-successional and degraded soils. Subsequently, a biogeographical investigation is presented of the Oribatid mite fauna from the high Andes is. Only 39 sampling sites, ranging from 3000-5200 m altitude from southern Ecuador (4°S) to mid-Argentina (34°S), have been sampled before. Only seven of these sampling sites can be assigned to cushion peatlands. For all available sampling sites, a diversity analysis was carried out, which revealed 219 species from 116 genera, comprising 51 families from the high Andes >3000 m a.s.l.. For cushion peatlands, 48 species from 34 genera, comprising 18 families were identified, of which only nine species were found in two or more sampling sites. In the high Andes, the γ-diversity of Oribatid mites shows evident fluctuations with latitude. At low latitudes 30 species. With increasing latitude, the richness declines to seven species at 19°S before it increases again to 14 species at >30°S. This fluctuation is probably associated with changes in precipitation. The analysis reveals that the high Andean Oribatid mite community is highly nested at both the genus- and species-level, and shows a zonal character for the community in contrast to the azonal occurrence of cushion peatlands; a significant change in the taxonomic composition of the community is indicated at about 4-7°S. In a subsequent geochemical investigation, the soil conditions (water content, C/N ratios, conductivity, pH and element content) of 38 samples from five ecotopes of the selected peatland in southern Peru were analysed. The data reveal the ecological heterogeneity of the peatland with strong variations in nutrient availability (very poorly oligotrophic - strongly mesotrophic), soil wetness (dry - saturated) and element content (e.g. in As, Cr, Cu, Fe, K, Pb and Rb). On the basis of these results, an advanced succession model is proposed for the different peatland ecotopes. Furthermore, the geochemical data were used to reveal microhabitat descriptions, community responses and the soil condition indicator potential of the Oribatid mite and Chironomid communities. From the Oribatid mites, seven indicators were assessed, with six species indicating low soil wetness 73%. From the Chironomids, five indicator taxa were revealed, with four taxa indicating soil wetness of 80-81%, and a single taxon indicating soil wetness >81%. Finally, to apply the autecological data to the palaeoecological record, the Oribatid mite and Chironomid subfossil assemblages were investigated in a 152 cm-long core, retrieved from the cushion peatland, which represents a record covering 1064 years (1924-860 cal yr BP; 26-1090 AD). 16 Oribatid mite species and 12 Chironomid taxa were identified, with five significant indicator taxa from each being used to reconstruct soil wetness quantitatively, by employing a modern analogue technique (MAT) model. The model predicts a humid period from 1924-1426±22 yr BP (26-524±22 AD) with a significant dry spell occurring from 1601±35-1543±24 yr BP (349±35-407±24 AD), and which was fully established by 1567 yr BP (383 AD). After 1426±22 yr BP (524±22 AD), the soil wetness shifted to drier conditions and remained stable until 860 yr BP (1090 AD). The reconstructed soil wetness fluctuations are supported by supra-regional signals revealed by other studies and coincide with migration movements and cultural changes of the Nasca people in the Peruvian costal area. This investigation confirms the sensitivity of the high-Andean cushion peatlands for climate fluctuations and highlights the strong dependency of the foothill region and the local population on the water supply from the high Andes. The water supply is essentially controlled by the peatlands in the headwaters, which basically act as water storages and drainage controllers. The results emphasise the need for a sustained conservation effort to protect the high-Andean cushion peatlands, which are nowadays endangered by mining activities and overgrazing

Dynamics of north Patagonian rainforests from fine-resolution pollen, charcoal and tree-ring analysis, Chonos Archipelago, Southern Chile.

Fine-resolution palaeoecological and dendrochronological methods were used to investigate the impacts of climate change, and natural and anthropogenic disturbances on vegetation in the North Patagonian rainforest of southern Chile at decadal to century timescales during the late Holocene. A lake sediment mud-water interface core was collected from the northern Chonos Archipelago and analysed for pollen and charcoal. Dendrochronological analysis of tree cores collected from stands of Pilgerodendron uviferum close to the lake site was incorporated into the study. The combined analysis showed that the present mosaic of vegetation types in this region is a function of environmental changes across a range of timescales: millennial climate change, more recent natural and anthropogenic disturbances, and possibly short-term climatic variations. Of particular interest is the spatiotemporal distribution of Pilgerodendron uviferum dieback/burning in the Chonos Archipelago region