North Patagonian Rainforest Research Articles

Development of a temperate rainforest zonation on the Pacific slopes of the North Patagonian Andes since ∼18 ka

Few studies along the western slopes of the Andes in Northwestern Patagonia (NWP: 40°-44°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 Reloncaví 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 low- and 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 cold-tolerant 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.

The last glacial termination in northwestern Patagonia viewed from the Lago Fonk (∼40°S) record

The anatomy of the Last Glacial Termination (T1) in the southern mid-latitudes, and its relationship with changes in the Southern Westerly Winds (SWW), offers empirical constraints for understanding the mechanisms involved in the transition from the Last Glacial Maximum into the current interglacial. Northwestern Patagonia (40°-44°S) is a sensitive region for monitoring past changes in the SWW, the Patagonian Ice Sheet, terrestrial ecosystems, and fire regimes through T1. Here we present results from Lago Fonk (∼40°S) to examine the structure of T1 based on the palynological, macroscopic charcoal, elemental, and isotopic composition of organic lake sediments.We observe an instantaneous establishment of Nothofagus-dominated forests at the onset of T1, followed by a diversification and densification trend that culminated with the establishment of thermophilous, Myrtaceae-dominated North Patagonian rainforests between ∼15.6–14.7 cal ka BP. The expansion of the conifer Podocarpus nubigena marks a shift to cool-temperate and hyperhumid conditions, coeval with high lake levels and enhanced algal productivity between ∼14.7–11.9 cal ka BP. Stand-replacing fires, driven by enhanced seasonality or high-frequency rainfall variability, started at ∼12.4 cal ka BP and catalyzed the rapid spread of Weinmannia trichosperma. Subsequent warming and a decline in precipitation at ∼11.4 cal ka BP led to intense fire activity, lake-level lowering, and establishment of the Valdivian rainforest trees Eucryphia/Caldcluvia. Our results suggest a coherent linkage between changes documented in the amphi south Pacific region and Antarctic ice cores during T1. This implies a zonal and hemispheric response to changes in the position/intensity of the SWW that emphasizes their central role as a key driver of the hemispheric and global climate evolution through T1.

Vegetation, disturbance, and climate history since the onset of ice-free conditions in the Lago Rosselot sector of Chiloé continental (44°S), northwestern Patagonia

We present results from Lago Negro, a small closed-basin lake adjacent to Lago Rosselot, to examine the vegetation and environmental history of an insufficiently studied sector of Chiloé Continental (41°30′-44°S) in northwestern Patagonia. Lake sediment cores from Lago Negro reveal 27 tephra deposited since ∼12.7 ka, including two prominent rhyodacite tephra marker beds erupted from Volcán Melimoyu, and a stratified basal clastic unit we attribute to meltwater discharge from an ice tongue that originated from Monte Queulat and covered Lago Rosselot during its expanded position, presumably Antarctic Cold Reversal in age. The pollen record shows closed-canopy North Patagonian rainforests since ∼12.7 ka, with variations in species composition and structure that suggest dynamic responses of the vegetation to past environmental changes. Vegetation responses to climate in the Lago Negro record were modulated, sometimes interrupted, by high magnitude and frequent disturbance regimes, most notably during maxima in explosive volcanic activity (∼9.5–7.2 ka and ∼3.6–1.6 ka) and heightened fire activity.Since Lago Negro is the southernmost palynological site so far investigated in the region and is located within a volcanically active sector, it provides a valuable perspective for assessing past vegetation responses along environmental gradients since the last glaciation. When compared with other sites throughout northwestern Patagonia, our record reveals a distinct north-to-south gradient in temperature and precipitation, with peak temperature and rainfall seasonality in the north, and a west-to-east gradient in disturbance regimes, with maximum frequency and magnitude of explosive volcanic events in the east. These gradients have modulated the response of rainforest vegetation to climate forcing at regional scale since ∼12.7 ka. We identify negligible differences in timing for the majority of key vegetation signals during the initial phase of the Lago Negro record, and propose that plant colonization and expansion along the ∼360 km long corridor through the Pacific slope of the northwestern Patagonian Andes was a rapid process during the Last Glacial Termination.

The role of climate and disturbance regimes upon temperate rainforests during the Holocene: A stratigraphic perspective from Lago Fonk (∼40°S), northwestern Patagonia

Climate and disturbance regimes play key roles in shaping the structure, composition and functioning of terrestrial ecosystems. Despite this importance, very few stratigraphic studies in the temperate rainforests from northwestern Patagonia have explored this relationship in detail along a time continuum through the entire Holocene. Here we present a high-resolution fossil pollen and charcoal record from Lago Fonk (median resolution: 20 years), a small closed-basin lake in the lowlands of the Chilean Lake District (41°S), where wildfires and explosive volcanism have intermittently taken place during the Holocene, along with pronounced human-induced disturbance in post-colonial time. Our results show persistence of temperate rainforest throughout the Holocene, with changes in the composition and structure of Valdivian rainforests (VRF) at millennial timescales. We detect centennial-scale alternations in dominance between the VRF tree Eucryphia/Caldcluvia and generalist trees found in VRF and North Patagonian rainforests after ∼6.5 cal ka BP. Intervals dominated by VRF coincide with enhanced fire occurrence signaling negative hydroclimate anomalies with a mean duration of ∼150 years, which alternate with positive hydroclimate anomalies lasting ∼312 years on average.Our results suggest that the magnitude and rapidity of vegetation changes detected at 10.2–9.9, 4.0–3.0, ∼1.0, and ∼0.7 cal ka BP were amplified by disturbance regimes, and led to the establishment and maintenance of Eucryphia/Caldcluvia-dominated forests in the Longitudinal Valley of the Chilean Lake District. On several occasions the higher incidence of fire disturbance during warm/dry climate intervals coincided with episodes of heightened explosive volcanic activity from multiple eruptive centers within the Southern Andean Volcanic Zone.

Timing and structure of vegetation, fire, and climate changes on the Pacific slope of northwestern Patagonia since the last glacial termination

By virtue of its location in the southern mid-latitudes, northwestern Patagonia (40°-44°S) offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance. Of particular importance is deciphering the evolution of the Southern Westerly Winds (SWW) considering their influence at continental, zonal, hemispheric, and global scale. Here I present a multi-decadal record from Lago Proschle, a small closed-basin lake located on the Pacific slope of northwestern Patagonia, to examine the timing and structure of vegetation, fire, and climate change along a continuum since the onset of the Last Glacial Termination (T1). The record shows rapid glacier recession during T1, reaching the western Andean foothills in ∼400 years or less. Nothofagus-dominated forests established between ∼17.4–17 ka, followed by closed-canopy North Patagonian Rain Forests (NPRF) with shade-tolerant thermophilous trees between ∼16.3–15.4 ka. These changes suggest an abrupt warming trend and an increase in precipitation at ∼16.3 ka, associated with a northward shift of the SWW. Subsequent increases in cold-tolerant hygrophilous trees between ∼15.4–12.8 ka imply a shift to cold, more humid conditions during the Antarctic Cold Reversal, suggesting stronger SWW influence. This was followed by stand-replacing fires brought by a sudden decline in summer precipitation at ∼12.8 ka, associated with a millennial-scale southward shift of the SWW which was contemporaneous with the onset of the Younger Dryas. Dominance of thermophilous, summer-drought tolerant Valdivian rainforest trees and high fire activity ensued between ∼10.3–7.8 ka, suggesting peak warmth and overall decline in annual precipitation associated with weakening of the SWW during the early Holocene. A multi-millennial cooling and wetting trend started at ∼7.8 ka, brought by stronger SWW influence, followed by recurrent, centennial-scale variations in temperature and precipitation starting at ∼6.4 ka. Deforestation, fire, and spread of non-native herbs by Chilean/European settlers began during the late 18th century. Abrupt vegetation changes in the Lago Proschle record were driven by rapid climate changes over the last 17,400 years amplified, in some instances, by fire disturbance.

Revision of Tropopterus Solier: A disjunct South American component of the Australo-Pacific Moriomorphini (Coleoptera, Carabidae)

TropopterusSolier, 1849, precinctive to southern South America, is taxonomically revised. Six new species are described:T. peckorumsp. nov.,T. robustussp. nov.,T. canaliculussp. nov.,T. trisinuatussp. nov.,T. minimucrosp. nov., andT. fieldianussp. nov.Merizodus catapileanusJeannel, 1962, is synonymized withT. montagneiSolier, 1849. Lectotypes are designated forT. montagnei,T. giraudyiSolier,T. duponcheliiSolier, andT. nitidusSolier (=T. duponchelii).Tropopterus peruvianusStraneo is noted as anomen dubium, with its identity and taxonomic placement to be substantiated via neotype designation. Phylogenetic relationships amongTropopterusspp. are hypothesized based on 37 morphological characters, the distributions of which are analyzed under the parsimony criterion, with the cladogram root established betweenTropopterusand its adelphotaxon from New South Wales, Australia. Speciation in the group has occurred predominantly at a limited geographical scale relative to the overall generic distribution, with three pairs of sister species sympatric. However phylogenetic divergence between taxa in the more northern, sclerophyllous forest characterized byNothofagus obliqua(Brisseau de Mirbel) and those occupying the Valdivian and North Patagonian Rain Forest dominated byN. dombeyi(Brisseau de Mirbel) is observed in two instances of phylogenetic history. Using specific collecting locality records, it is shown thatTropopterusbeetles have been collected syntopically and synchronically with species ofGlypholomaJeannel (Coleoptera, Staphylinidae),AnaballetusNewton, Švec & Fikáček (Coleoptera, Leiodidae),AndotypusSpangler (Coleoptera, Hydrophilidae), andNovonothrusBalogh (Acari, Oribatida). These concordant ecological occurrences document a cohesiveNothofagusforest leaf-litter community. These genera plus other Valdivian Rain Forest invertebrate taxa all exhibit an Austral disjunct biogeographical pattern that corroborates trans-Antarctic vicariance between theNothofagusforests of southern South America and Australia. Male genitalic antisymmetry is shown to be a synapomorphy ofTropopterus, though the female reproductive tract retains the plesiomorphic orientation observed in all other moriomorphine taxa.

A continuous record of vegetation, fire-regime and climatic changes in northwestern Patagonia spanning the last 25,000 years

We present a high-resolution precisely dated terrestrial paleovegetation/paleoclimate record from Lago Pichilaguna, northwestern Patagonia (40°–44°S), which spans continuously from the Last Glacial Maximum (LGM) to the present. We find abundant and continuous presence of arboreal pollen (chiefly Nothofagus) during the LGM, accompanied by other trees, shrubs, and alpine herbs. These results suggest Subantarctic parkland and/or scattered woodlands under a cold and hyperhumid climate during the LGM (∼25,000–17,800 cal. yr BP) with expansion of Nothofagus under relatively warm interstadial conditions between 25,000 and 19,200 cal. yr BP. This was followed by cooling and a precipitation increase between 19,200 and 17,800 cal. yr BP, which was contemporaneous with the youngest LGM advance of Andean glaciers in the region and maximum influence of the Southern Westerly Wind (SWW). The Last Glacial Termination (T1) started at 17,800 cal. yr BP and featured the spread of thermophilous trees and ferns characteristic of North Patagonian rainforests, along with lake level lowering. These results suggest a warm pulse and southward shift of the SWW, concurrent with a rapid collapse of Andean glacier lobes. Subsequent changes led to the establishment of closed-canopy rainforests under peak interstadial warmth between ∼16,000 and 15,000 cal. yr BP. We detect a shift to cold/wet conditions during the Antarctic Cold Reversal (14,800–12,700 cal. yr BP) and a precipitation decline during Younger Dryas time, followed by maximum temperature, relatively lower lake level and minimum SWW influence between 11,300 and 7700 cal. yr BP. Precipitation then rose punctuated by centennial-scale variations since 6200 cal. yr BP. Chilean-European deforestation and spread of invasive exotic species started at ∼350 cal. yr BP aided by fire. We conclude that temperate rainforests have persisted with little interruption since T1, with major changes in floristic composition driven by climate change and fires. Rainforest composition and heterogeneity declined in response to Chilean/European disturbance during the 1600s and intensified since the 1800s. These events constitute the fastest/largest-magnitude vegetation changes of the last ∼25,000 years.

Fossil beetles from Pilauco, south-central Chile: An Upper Pleistocene paleoenvironmental reconstruction

A new assemblage of fossil beetles of Upper Pleistocene age, dated between 15,754 and 14,697 cal yr BP, is described and interpreted based on cluster analysis. In this study, we present an analysis on the taxonomic composition, and the paleoenvironmental implication of the fossil beetle assemblage in the archaeo- paleontological site of Pilauco in Osorno, south-central Chile (40°34′S-73°07′ W). Around 17,370 cal yr BP at the onset of deglaciation the old Damas River abandoned its alluvial plain; afterwards wetlands grew up by deposition of peat and colluvial sediments. The fossil beetles were deposited in the PB-7 layer where human artefacts and vertebrate remains have been found in the same spatial and temporal context. The assemblage includes 13 families, documented by 285 skeletal remains of fossil beetles. Ten ecological groups were identified and related to riparian, epigean, Nothofagus sp. forests, and lotic environments such as streams and ponds. Dung and fungi beetles were also part of the fossil assemblage. Pollen and carpological investigations in the same strata point towards the presence of wetlands and evergreen North Patagonian rainforest communities in the Pilauco site during the Upper Pleistocene. However, this study reveals that the Pilauco fossil beetles do not completely conform to any of the known modern assemblages. Therefore, we interpret that the fossil beetle assemblage from Pilauco is the result of the coexistence of different small pockets of habitats in a reduced spatial setting during a period of deep environmental/anthropic changes at the end of the last glaciation. The carabids and dung beetles from these beds indicate that the wetlands may have undergone dry conditions for undetermined periods of time. Finally, we compare nearly contemporaneous beetle assemblages of the sites Pilauco and Monte Verde II to discuss differences and similarities between the sites.

Increased drought impacts on temperate rainforests from southern South America: results of a process-based, dynamic forest model.

Increased droughts due to regional shifts in temperature and rainfall regimes are likely to affect forests in temperate regions in the coming decades. To assess their consequences for forest dynamics, we need predictive tools that couple hydrologic processes, soil moisture dynamics and plant productivity. Here, we developed and tested a dynamic forest model that predicts the hydrologic balance of North Patagonian rainforests on Chiloé Island, in temperate South America (42°S). The model incorporates the dynamic linkages between changing rainfall regimes, soil moisture and individual tree growth. Declining rainfall, as predicted for the study area, should mean up to 50% less summer rain by year 2100. We analysed forest responses to increased drought using the model proposed focusing on changes in evapotranspiration, soil moisture and forest structure (above-ground biomass and basal area). We compared the responses of a young stand (YS, ca. 60 years-old) and an old-growth forest (OG, >500 years-old) in the same area. Based on detailed field measurements of water fluxes, the model provides a reliable account of the hydrologic balance of these evergreen, broad-leaved rainforests. We found higher evapotranspiration in OG than YS under current climate. Increasing drought predicted for this century can reduce evapotranspiration by 15% in the OG compared to current values. Drier climate will alter forest structure, leading to decreases in above ground biomass by 27% of the current value in OG. The model presented here can be used to assess the potential impacts of climate change on forest hydrology and other threats of global change on future forests such as fragmentation, introduction of exotic tree species, and changes in fire regimes. Our study expands the applicability of forest dynamics models in remote and hitherto overlooked regions of the world, such as southern temperate rainforests.

Vegetation and climate changes during the last 22,000 yr from a marine core near Taitao Peninsula, southern Chile

High-temporal resolution of pollen analyses from marine core MD07-3088 (46°S) documents regional and coastal vegetation changes in the mid-latitude of southern Chile during the last 22kyr BP. The coastal margin was partly ice-free during the last glacial period with the presence of scattered vegetation. After~17.6kyr BP, the expansion of Nothofagus woodland highlights a warming trend and marks the beginning of the last deglaciation. The deglacial forest expansion is interrupted by the development of Magellanic moorland simultaneously with the Antarctic Cold Reversal. This vegetation change illustrates a pause in the warming trend with an abrupt increase in precipitation which is related to strong intensity of Southern Westerly Winds. After 12.8kyr BP, the retreat of Magellanic moorland illustrates a second-step warming that is strengthened after 11.5kyr at the onset of the Holocene. Expansion of heliophytic taxa illustrates warmest and driest conditions of the Holocene from 11 to 7.4kyr BP. Later, the decrease of heliophytic taxa shows a return to cooler and wetter conditions, illustrated by the presence of the North Patagonian rainforest that reaches modern condition after 5kyr. Climate changes inferred from the marine pollen record are consistent with geochemical data changes from the same samples and illustrate a clear synchronicity with δD variations of EPICA Dome C ice core during the last deglaciation and Holocene. Comparison between vegetation changes from the marine core and regional palaeoclimatic records highlights southward-northward shifts of the Southern Westerly Wind belt and supports a close link between Southern Westerly Wind belt and atmospheric CO2 variability during the last deglaciation.

Temperate rainforest response to climate change and disturbance agents in northwestern Patagonia (41°S) over the last 2600 years

We present detailed pollen and charcoal records from Lago Pichilafquén (~41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600yr. Here, temperate rainforests have dominated the landscape since 2600calyr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430calyr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690calyr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140calyr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340calyr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes.

Extensión del límite austral de Persea lingue (Lauraceae) al sur de la Provincia de Palena, Región de los Lagos, Chile

The finding of Persea lingue (Miers ex Bertero) Nees (Lauraceae) in the south of the province of Palena, Region X of Los Lagos, Chile, is reported. The new locality (Puerto Piedra: 43o 26' S, 72o 09' W) extends by some 250 km the southern limit previously described for the species in Chile. This is the first report of P. lingue from the North Patagonian rainforest. This species belonging to a mainly tropical genus had previously been associated with the warmer Valdivian, temperate-deciduous and sclerophyllous forests found in Chile further north.

Andes virus infections in the rodent reservoir and in humans vary across contrasting landscapes in Chile

Hantavirus cardiopulmonary syndrome (HCPS) is an emerging infectious disease first reported in Chile in 1995. Andes hantavirus (ANDV) is responsible for the more than 500 cases of HCPS reported in Chile. Previous work showed that ANDV is genetically differentiated in Chile across contrasting landscapes. To determine whether the reservoir rodent ( Oligoryzomys longicaudatus) populations are also geographically segregated, we conducted range-wide spatial genetic analyses of O. longicaudatus in Chile using the mitochondrial DNA cytochrome b gene. Given that landscape structure influences the incidence of hantavirus infections, we also tested 772 O. longicaudatus specimens for antibodies to ANDV captured during the period 2000–2006. Population genetic analyses of O. longicaudatus are largely congruent with those reported for ANDV, with the host primarily differentiated according to three defined ecoregions, Mediterranean, Valdivian rain forest and North Patagonian rain forest. Significant differences in the relative prevalence of anti-ANDV antibodies in rodent samples also were found across the three ecoregions. We relate these results to the number of reported human HCPS cases in Chile, and discuss the importance of landscape differences in light of ANDV transmission to humans and among rodent populations.

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

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

Effects of forest type and stand structure on coarse woody debris in old-growth rainforests in the Valdivian Andes, south-central Chile

Coarse woody debris (CWD) is an important structural and functional component of temperate forests. There are few studies that have estimated CWD biomass in temperate forests of the southern hemisphere. In Chile, this is the first study of CWD in Andean old-growth forests, where tree-fall is the most common type of disturbance and generates a mosaic of different structures within a forest stand, both conditions that must affect the quantity and quality of CWD. We estimated and analyzed CWD biomass in two differing old-growth forest stands, one composed mainly by Nothofagus dombeyi, Laureliopsis philippiana and Saxegothaea conspicua (Nothofagus-dominated stand) and another composed mainly by L. philippiana, S. conspicua and Dasyphyllum diancanthoides (Mixed-species stand). We set up 80 and 95 circular 0.05-ha plots in these stands, where we measured all live trees ≥5 cm diameter at breast height (dbh, 1.3 m), recorded diameters at the large and small ends of logs and snags, and total length of logs or total height of snags, and classified these within three decay classes. The Nothofagus-dominated forest stand had 88.8 Mg ha −1 of CWD biomass, compared to 59.6 Mg ha −1 in the Mixed-species stand, a difference that can be attributed basically to the greater biomass of snags in the former, where most biomass of CWD, logs and snags belonged to N. dombeyi. In both stands we found that most plots had a tree structure dominated by small trees; these plots had greater CWD biomass, of which most was in decay class III, likely reflecting past tree falls that reduced the numbers of large trees and increased CWD. At the stand level the only significant but low correlation occurred between log biomass in decay class III and mean diameter of the plots. However, there were strong relationships of mean diameter (QMD) of the different structural types and log biomass in decay class III in both stands, thus reflecting that diameter structure (or QMD) can be a good predictor of log biomass. CWD biomass in these Valdivian old-growth rainforests is in the range of values found for North Patagonian rainforests sampled with similar plot size, greater than biomass in deciduous forests in North America, and lower than temperate rainforests in the Pacific Northwest in North America, in New Zealand and Tasmania. Differences can be attributed to forest type, forest productivity, and successional phase.

A pollen-based record of late glacial–Holocene climatic variability in the southern lake district, Chile

A pollen record from Puyehue area (40°S; 72°W) in the southern Lake District, Chile, indicates that prior to 13,410 14C yr BP (ca. 16,500–15,200 cal yr BP), cold resistant and hygrophilous vegetation, particularly Nothofagus forest and myricaceous vegetation, covered the area. From ca. 15,000 cal yr BP onward, the forest became increasingly dense. Between 10,010 and 7450 14C yr BP (ca. 11,000–8000 cal yr BP), the expansion of Nothofagus obliqua and the spread of grasses suggests the climate became warmer and semi-arid. Lowland deciduous forest (Nothofagus obliqua, Aextoxicon punctatum, Laurelia sempervirens) and Valdivian rainforest (Nothofagus dombeyi, Eucryphia cordifolia, Caldcluvia paniculata, Aextoxicon punctatum, Laureliopsis philippiana) were abundant. During the next two thousand years, stable warm climatic conditions prevailed, and the diversity of the vegetation increased. From 5760 to 1040 14C yr BP (ca. 6500–900 cal yr BP), the North Patagonian rainforest expanded. The presence of Pilgerodendron/Fitzroya, together with Nothofagus forest, suggests that humid conditions prevailed. During the last millennium, human impact intensified and regional vegetation was disturbed, particularly the lowland deciduous forest and Valdivian rainforest. North-Patagonian and subantartic taxa, such as Podocarpus nubigena, Pilgerodendron/Fitzroya, Nothofagus dombeyi type, Austrocedrus chilensis and Drimys winteri, occupied the low and high-altitude parts of the Cordillera. Five hundred years ago, shrub and grasses expanded in the Nothofagus forest, suggesting that forest became more open under cool–cold, and humid climatic conditions. These conditions prevail to the present day.

Disturbance and regeneration dynamics of an old‐growth North Patagonian rain forest in Chiloé Island, Chile

Summary 1 Few studies have addressed the mechanisms of coexistence of shade-tolerant and intolerant tree species in the canopy of old-growth, lowland rain forests of southern South America. We explored the hypothesis that their forest dynamics result from frequent, single tree-fall gap episodes. 2 We analysed the disturbance regime and assessed the regeneration modes of shadetolerant and intolerant canopy trees in a lowland, old growth North Patagonian rain forest in Chiloe Island (42 ° S) using dendroecological methods. 3 Dominant canopy trees were the shade-intolerant Nothofagus nitida (Fagaceae), Drimys winteri (Winteraceae) and the tolerant Podocarpus nubigena (Podocarpaceae). The oldest individuals, however, were represented by Saxegothaea conspicua , Podocarpaceae (shade tolerant > 498 years) and Weinmannia trichosperma , Cunoniaceae (intolerant > 382 years). Shade-tolerant species have regenerated continuously for the past 400 years, but recruitment of shade-intolerant species has increased only in the past 50 years. These regeneration patterns suggest a lack of catastrophic disturbance, at least since 1650. 4 Analysis of tree radial growth patterns revealed frequent moderate releases of both shade-tolerant and intolerant tree species, consistent with frequent small-scale disturbances, such as individual tree-fall gaps. Increased releases, peaking in 1940 and followed by enhanced recruitment, may be a consequence of individual tree-falls induced by lowintensity windstorms or limited selective logging. Such disturbances have occurred for at least 250 years, but have had little overall effect on stand structure and canopy composition. 5 The replacement and coexistence of shade-tolerant and intolerant tree species in the canopy of this North Patagonian forest can be explained by frequent small-scale disturbances (i.e. gap-phase dynamics) and by the absence of large-scale natural or anthropogenic disturbances over the past four centuries.

Deglacial and postglacial climate history in east-central Isla Grande de Chiloé, southern Chile (43°S)

Palynologic and stratigraphic data from Laguna Tahui (42°50′S, 73°30′W) indicate cool–temperate and humid conditions there between 14,000 and 10,000 14C yr B.P., followed by warmer and drier-than-present conditions between 10,000 and 7000 14C yr B.P., and subsequent cooling and rise in precipitation over the last 5800 14C yr. The thermophilous Valdivian trees Eucryphia cordifolia and Caldcluvia paniculata reached their maximum abundance during the early Holocene warm–dry phase (10,000–7000 14C yr B.P.), followed by a rise in lake levels and reexpansion of North Patagonian conifers starting at 7000 and 5800 14C yr B.P., respectively. Variations in the stratigraphic and geographic distribution of temperate rainforests in southern Chile suggest multimillennial trends in temperature and westerly activity, which are spatially and temporally coherent with paleoclimate records from neighboring regions. Climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine-scale mosaics of Valdivian and North Patagonian rainforest species in low- to mid-elevation communities since ∼5800 14C yr B.P.

Postglacial formation and dynamics of North Patagonian Rainforest in the Chonos Archipelago, Southern Chile

Pollen analysis of continuous sediment cores from two lakes in the northern Chonos Archipelago (44°S) in southern Chile shows a complete postglacial record of vegetation change. The fossil records indicate that deglaciation was complete in the northern Chonos by at least 13,600 14C yr BP. Ericaceous heath and grassland persisted for more than 600 years after deglaciation under the influence of dry/cold climates and frequent burning. Nothofagus- Pilgerodendron- Podocarpus forest, with modern analogues in the southern Chonos Archipelago, was established across the northern islands by 12,400 14C yr BP under increasingly warm and wet climates. There is no evidence for a return to cooler climates during the Younger Dryas chronozone. The rise of Tepualia stipularis and Weinmannia trichosperma as important forest components between 10,600 and 6000 14C yr BP may be associated with climates that were warmer than present. The collapse of Pilgerodendron communities during this time may have been triggered by a combination of factors related to disturbance frequency including tephra deposition events, fire and climate change. After 6000 14C yr BP Pilgerodendron recovers and Nothofagus-Pilgerodendron-Tepualia forest persists until the present. European logging and burning activity may have increased the susceptibility of North Patagonian Rainforest to invasion by introduced species and to future collapse of the long-lived Pilgerodendron communities.

Abrupt vegetation changes during the last glacial to Holocene transition in mid‐latitude South America

AbstractA pollen record from the Huelmo site (ca. 41°30′S) shows that vegetation and climate changed at millennial time‐scales during the last glacial to Holocene transition in the mid‐latitude region of western South America. The record shows that a Nothofagus parkland dominated the landscape between 16 400 and 14 600 14C yr BP, along with Magellanic Moorland and cupressaceous conifers. Evergreen North Patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14C yr BP, following a prominent rise in Nothofagus at 14 600 14C yr BP. Highly diverse, closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14C yr BP, followed by the expansion of cold‐resistant podocarps and Nothofagus at ca. 12 500 and 11 500 14C yr BP. Local disturbance by fire favoured the expansion of shade‐intolerant opportunistic taxa between 10 900 and 10 200 14C yr BP. Subsequent warming pulses at 10 200 and 9100 14C yr BP led to the expansion of thermophilous, summer‐drought resistant Valdivian rainforest trees until 6900 14C yr BP.Our results suggest that cold and hyperhumid conditions characterised the final phase of the Last Glacial Maximum (LGM), between 16 400 and 14 600 14C yr BP. The last ice age Termination commenced with a prominent warming event that led to a rapid expansion of North Patagonian trees and the abrupt withdrawal of Andean ice lobes from their LGM positon at ca. 147 000 14C yr BP. Hyperhumid conditions prevailed between 16 400 and 13 000 14C yr BP, what we term the ‘extreme glacial mode’ of westerly activity. This condition was brought about by a northward shift and/or intensification of the southern westerlies. The warmest/driest conditions of the last glacial–interglacial transition occurred between 9100 and 6900 14C yr BP. During this period, the westerlies shifted to an ‘extreme interglacial mode’ of activity, via a poleward migration of stormtracks. Our results indicate that a highly variable climatic interval lasting 5500 14C years separate the opposite extremes of vegetation and climate during the last glacial‐interglacial cycle, i.e. the end of the LGM and the onset of the early Holocene warm and dry period. Copyright © 2003 John Wiley & Sons, Ltd.