Browsing by Author "Alloway, B. V."

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Development of a temperate rainforest zonation on the Pacific slopes of the North Patagonian Andes since-18 ka
    (2024) Moreno, P. I.; Alloway, B. V.; Valenzuela, M.; Villacis, L. A.; Villa-Martinez, R. P.
    Few studies along the western slopes of the Andes in Northwestern Patagonia (NWP: 40 degrees-44 degrees S) allow examining vegetation development through environmental gradients in latitude and elevation along a time continuum since the Last Glacial Termination (T1, -18-11 ka). This complete biostratigraphic context is necessary for assessing the sequence, timing, rates, and direction of compositional/structural changes of the former vegetation, and for deciphering their environmental drivers. Here we report palynological results from two NWP sites spaced -22 km apart on the western Andean slopes, Caleta Puelche roadside section located near sea level and Lago Reflejos at mid elevations (-800 m a.s.l.) and assess their continuous records since local ice-free conditions against other NWP sites. We find that cold-tolerant early successional trees dominated the initial stages of vegetation development in the Seno Reloncav & iacute; lowlands (-18-17 ka), followed by thermophilous shade-tolerant North Patagonian rainforest (NPRF) trees, which achieved their maxima between -17 and 15 ka at low-elevations. A spread of cold- and shade-tolerant hygrophilous NPRF conifers ensued (-14.8-13 ka) reaching similar magnitude at lowand mid-elevations, interrupted by increases in trees favored by canopy fragmentation linked to fire and explosive volcanism (-13-11 ka). Thermophilous, shade-intolerant, summer-drought tolerant Valdivian rainforest (VRF) trees increased and achieved maxima between -10 and 8 ka, most notably in the lowlands, coeval with peak abundance of the NPRF conifers Fitzroya/Pilgerodendron and Podocarpus nubigena in mid-elevation Lago Reflejos, contemporaneous with their virtual disappearance near sea level. Widespread increases in coldtolerant hygrophilous NPRF trees occurred after -8 ka, followed by mixing of NPRF and VRF elements in the lowlands after -6.3 ka with centennial-scale alternations. Inter-site and regional coherences of our findings suggest that variations in Southern Westerly Wind influence, along with disturbance regimes of natural and human origin, have driven the composition, structure, dynamics, and zonation of temperate rainforests in NWP since T1. We observe that Lago Reflejos features the highest abundance of Fitzroya cupressoides at regional scale since -12 ka, attesting to the importance of mid-elevation Andean environments for the persistence of these highly valued trees in the context of postglacial climate evolution, shifts in fire regimes, volcanic, and human disturbance in NWP.
  • No Thumbnail Available
    Item
    Multisequal aeolian deposition during the Holocene in southwestern Patagonia (51°S) was modulated by southern westerly wind intensity and vegetation type
    (2024) Flores-Aqueveque, V.; Villasenor, T.; Gomez-Fontealba, C.; Alloway, B. V.; Alfaro, S.; Pizarro, H.; Guerra, L.; Moreno, P. I.
    We studied a multisequal soil succession (MSS) just south of Torres del Paine National Park (51 degrees S), at the presentday core of the Southern Westerly Winds (SWW). The Rio Serrano Section comprises paleosol horizons with associated intervening loess and sandy loess beds formed during the Holocene. Our record suggests strong and stable aeolian activity between -9.3 -7.2 ka followed by a decline with centennial-scale variations until -5 ka. A strengthening commenced at -5 ka and culminated in a maximum between -2.2 -0.5 ka with millennial-scale variations. Subsequent weakening of aeolian activity between -0.5 and 0 ka was coeval with the deposition of a -40 cm-thick paleosol, after which aeolian activity increased abruptly and reached an unprecedented maximum starting in the mid-20th century. The inferred wind intensity variations from our data bear partial agreement with competing hypotheses of SWW evolution, which postulate minimum SWW influence in SW Patagonia during the early Holocene and maximum influence during the Late Holocene, or vice versa. When analyzed through the lens of vegetation physiognomy/distribution and associated hydrological balance inferences from neighboring sites, our results suggest a primary control by precipitation and wind speeds associated to SWW strength at regional scale, modulated by the position of the forest/steppe ecotone east of the austral Andes. Human activities during the mid-20th century (deforestation, fire -regime shifts, livestock grazing, land use changes) caused an unprecedented increase in aeolian activity through decreased vegetation cover that increased sediment availability for aeolian transport, marking a striking difference with the magnitude of natural processes before the Anthropocene. Our results highlight the importance of climate change and natural/human-driven changes in vegetation cover for deciphering wind intensity histories, particularly in the transition from humid to semiarid environments along the eastern slope of the southern Patagonian Andes.