A spatiotemporal gradient in the anthropization of Pyrenean landscape. Preliminary report

A preliminary analysis of the timing of landscape anthropization in the southern-central Pyrenees shows the occurrence of an elevational gradient from the Bronze Age (basal belts) to the Middle Ages (alpine belts). This relationship is statistically significant and suggests an average anthropization rate of 40 m in elevation per century. The elevational gradient is most clear between the Bronze Age and the Roman occupation, suggesting a progressive upward anthropization trend from the south with the likely involvement of Iberian cultures. During the Middle Ages, a massive anthropization pattern of subalpine/alpine areas is observed; this pattern is chronologically consistent with the incursion of northern cultures crossing the Pyrenees and the development of extensive high-mountain pastoralism and horizontal transhumance. In general, the progression of upward anthropization has occurred during warm climatic phases. Further work is needed to confirm these observations, especially in areas with few available paleoecological studies, notably the basal and montane belts. It could be interesting to develop similar studies of other Pyrenean regions and other mountain ranges

Potential Responses of Vascular Plants from the Pristine 'Lost World' of the Neotropical Guayana Highlands to Global Warming: Review and New Perspectives

The neotropical Guayana Highlands (GH) are one of the few remaining pristine environments on Earth, and they host amazing biodiversity with a high degree endemism, especially among vascular plants. Despite the lack of direct human disturbance, GH plants and their communities are threatened with extinction from habitat loss due to global warming (GW). Geographic information systems simulations involving the entire known vascular GH flora (>2430 species) predict potential GW-driven extinctions on the order of 80% by the end of this century, including nearly half of the endemic species. These estimates and the assessment of an environmental impact value for each species led to the hierarchization of plants by their risk of habitat loss and the definition of priority conservation categories. However, the predictions assume that all species will respond to GW by migrating upward and at equal rates, which is unlikely, so current estimates should be considered preliminary and incomplete (although they represent the best that can be done with the existing information). Other potential environmental forcings (i.e., precipitation shifts, an increase in the atmospheric CO2 concentration) and idiosyncratic plant responses (i.e., resistance, phenotypic acclimation, rapid evolution) should also be considered, so detailed eco-physiological studies of the more threatened species are urgently needed. The main obstacles to developing such studies are the remoteness and inaccessibility of the GH and, especially, the difficulty in obtaining official permits for fieldwork

The neotropical Gran Sabana region: palaeoecology and conservation

The Gran Sabana (GS) is a key region for understanding the origin of neotropical savannas and is an ideal location to test ecological hypotheses on long-term vegetation dynamics under the action of natural and anthropogenic drivers. The conservation of the GS is a controversial issue because of the confluence of disparate cultural and socio-economic interests, with a strong debate surrounding fire practices by indigenous people. Late glacial to Holocene pollen and charcoal records obtained thus far in this region have documented the main palaeoecological trends along with the climatic and anthropogenic (mostly fire) drivers involved. Here we discuss how these records can be used to inform conservation and restoration practices in the GS. The main points of the discussion are the local vs. regional character of palaeoecological evidence, the support provided by this evidence for the existing fire management proposals and the role of spatiotemporal environmental and ecological heterogeneity in the definition and evaluation of realistic restoration targets. A general conclusion is that past ecological reconstructions do not fully support either of the current options for fire management, i.e., either total fire suppression or the continuity of indigenous fire practices. It is recommended to replace this dual and rigid conservation framework with a more diverse and flexible approach that considers the complex spatiotemporal heterogeneity documented in palaeoecological records

Undervalued impacts of sea-level rise: vanishing deltas

Current SLR might be considered a significant extinction force because of its high potential to degrade, reduce, or eliminate deltaic and coastal habitats, thereby promoting huge diversity losses. Nonetheless, the effects of SLR are still too frequently ignored in terms of designing biodiversity conservation strategies or developing urban/rural areas. SLR represents a serious threat to millions of people living in densely populated deltas. Almost 40% of major deltas, most of them already overpopulated, may increase their population density by >100 hab./km2 (2000-2050). Most adaptive measures to confront SLR in deltaic habitats will become more expensive and more difficult to execute with continued human growth. Growing populations also increasingly exploit biodiversity goods and services, adding stress to the deltaic ecosystems that strive to acclimatize to SLR. Beyond a certain point, additional pressure would favor their collapse. To achieve some degree of success, adaptive measures might be reinforced by specific policies and regulations, such as migration control and development restrictions. Biodiverse and sparsely populated deltas housing ethnic minorities may remain unattended and rely on their own resilience to SLR, whereas wealthy and densely populated deltas will be given priority. The selection of strategies to adequately address SLR in delta environments should be performed in the context of long-term planning. Because the long term is full of uncertainties, space- and time-specific research efforts should be devoted to address knowledge gaps before information demands become progressively too pressing

Neotropical vegetation responses to Younger Dryas climates as analogs for future climate change scenarios and lessons for conservation.

The Younger Dryas (YD) climatic reversal (12.86-11.65 cal ky BP), especially the warming initiated at ∼12.6 cal ky BP, and the associated vegetation changes have been proposed as past analogs to forecast the potential vegetation responses to future global warming. In this paper, we applied this model to highland and midland Neotropical localities. We used pollen analysis of lake sediments to record vegetation responses to YD climatic changes, which are reconstructed from independent paleoclimatic proxies such as the Mg/Ca ratio on foraminiferal tests and Equilibrium Line Altitude (ELA) for paleotemperature, and grayscale density and Titanium content for paleoprecipitation. Paleoclimatic reconstructions at both highlands and midlands showed a clear YD signal with a conspicuous warming extending into the early Holocene. A small percentage of taxa resulted to be sensitive to these YD climate changes. Response lags were negligible at the resolution of the study. However, changes in the sensitive taxa were relevant enough to determine changes in biodiversity and taxonomic composition. Highland vegetation experienced mainly intra-community reorganizations, whereas midland vegetation underwent major changes leading to community substitutions. This was explained in terms of threshold-crossing non-linear responses in which the coupling of climatic and other forcings (fire) was proposed as the main driving mechanism. Paleoecology provides meaningful insights on the responses of highland and midland Neotropical vegetation to the YD climatic reversal. Biotic responses at both individual (species) and collective (assemblage) levels showed patterns and processes of vegetation change useful to understand its ecological dynamics, as well as the mechanisms and external drivers involved. The use of paleoecological methods to document the biotic responses to the YD climate shifts can be useful to help forecasting the potential consequences of future global warming. Due to its quasi-global character, the YD reversal emerges as a well suited candidate for providing useful insights of global scope by analyzing the corresponding biotic responses virtually at any geographical and biological setting

Diatom and vegetation responses to Late Glacial and Early Holocene climate changes at Lake Estanya (Southern Pyrenees, NE Spain)

We investigate Lake Estanya's diatom and pollen records from the Late Glacial (LG) to the Early Holocene (EH), in order to compare limnological and vegetation responses to common climate forcing. The biotic changes recognized in this study largely agree with the hydrological evolution of the lake described previously for the same period. The diatom record shows high sensitivity to fluctuations in both lake level and salinity concentration as consequence of climate shifts. In addition vegetation results indicate that the area could have played an important role as regional vegetation refuge. Shallow lake conditions during the Last Glacial Maximum (LGM) were punctuated by relatively deeper freshwaters between 19.3 and 18.6 cal kyr BP and at 18.0 cal kyr BP, as recorded by diatom shifts. A subsequent increasing aridity trend, coinciding with the Mystery Interval (MI), affected the diatom accumulation rates, which dropped to its minimum values between 17.2 to 14.7 cal kyr BP. Particularly dry and cold conditions during the LGM and MI are supported by the largest values of steppic pollen taxa of the whole sequence, which account for up to 40%. However, relatively high values of Betula during the Heinrich Event 1 suggest a plausible regional vegetation refuge. Abrupt cooling and warming episodes within the LG triggered remarkable ecological threshold crossings in the diatom communities, especially during the stadial/interstadial episodes. At this point, the vegetation reflect the onset of warm conditions during the Bølling/Allerød with the partial substitution of Betula by Marcescent and Evergreen Quercus, what probably indicates the arrival of temperate taxa to the area and the likely migration of birch to higher altitudes. The Younger Dryas Stadial shows a complex ecological response. Diatoms are very poorly preserved, but aquatic taxa reach their highest values. An increase in Marcescent Quercus during this cold stage lends further support to the hypothesis that this is a regional vegetation refuge. Low lake levels recorded during the EH affected the development and preservation of diatom communities. A delay in the onset of humid conditions for the EH is also supported by the vegetation composition, characterized by the maximum expansion of Juniperus

Late-Holocene vegetation and fire dynamics on the summits of the Guayana Highlands: the Uei-tepui palynological record.

The summits of the tepuis (sandstone table mountains of the Neotropical Guayana region¿Guayana Highlands, GH) have been considered valuable for palaeoecological studies due to their pristine nature, which emphasizes the role of natural (i.e. non-human) factors on ecological change. Anthropogenic fires, very frequent in the surrounding Gran Sabana (GS) uplands, have very rarely been documented in the GH, and are therefore not considered an important ecological factor in the high-tepui biome. This paper reports the palynological and charcoal results of a Late Holocene sequence from the summit of Uei-tepui (2104 m elevation), where extensive signs of fire were recently observed. Since ~2000 cal yr BP, the landscape of the study site has been dominated by meadowswith occasional shrubs and cloud forests,which underwent expansions and contractions driven by climate changes and fire. A major vegetation shift occurred in the mid-18th century, when a sustained increase in local fires favoured the expansion of the low and spreading Cyrilla racemiflora shrublands at the expense of meadows and forests. Uei-tepui firesmost probably were the result of human activities and reached the summit under study from the GS uplands through the vegetated slopes that characterize this tepui. The mostly anthropogenic nature of these fires, especially themore recent ones, is supported by the initial occurrence of wetter conditions, and by its coincidence with significant social changes in the GS indigenous populations, mainly the European contact. The emergence of fire as a disturbing agent of theGH biome highlights the need for an effective management plan in the GS uplands, where the vast majority of present-day fires originate, and designed in collaboration with the indigenous communities. Proactive conservationmeasures are considered even more important under future warming projections in the area

Vegetation and landscape around Lake Montcortès (Catalan pre-Pyrenees) as a tool for palaeoecological studies of lake sediments

Vegetation and landscape around Lake Montcortès (Catalan pre-Pyrenees) as a tool for palynological studies of lake sediments. Lake Montcortès (42º 19′ N, 0º 59′ E; 1,027 m elevation) is an excellent target for high-resolution palaeoecological studies because its annually-laminated sediments extending back to the early-middle Holocene. The detailed knowledge of present vegetation patterns around the lake and the pollen they release to lake sediments is essential for a reliable interpretation of past vegetation dynamics. This study aims to identify and map the vegetation types currently growing around the lake. For this purpose, a quadrangular area of ca. 48 ha was defined. The floristic study resulted in a catalogue of 534 species. Vegetation analysis was based on 42 phytosociological inventories used to synthesise and map the relevant plant landscape units. As a result, we obtained 52 vegetation units as expressions of the CORINE habitats previously defined for Catalonia. Each of these habitats was described in floristic, physiognomic, phytogeographic, environmental and human-use terms. The next step will be the palynological study of the more representative species of the described vegetation types, as a means to optimise future palynological interpretations

Grazing activities in the southern central Pyrenees during the last millenium as deduced from the non-pollen palynomorphs (NPP) record of lake Montcortès

Human activities during the last millennium have shaped most of the present-day landscapes. During this time, in the southern central Pyrenees several climate periods and phases of variable human disturbance have driven varied landscape responses. In previous studies of the sediment deposits in Lake Montcortès (southern central Pyrenees) several climatic shifts (including the Medieval Climate Anomaly and the Little Ice Age), as well as forest clearance by fire, agriculture and cattle raising as the main human impacts were recorded since Medieval times. In this work we use non-pollen palynomorphs (NPP) on the same sequence to reconstruct the different human activities, with a special focus on grazing, at an average resolution of around 30 years per sample. Independent NPP proxies for fire and forest clearance were found, supporting former studies. Moreover, the NPP record shows four periods of high abundance of coprophilous fungi: 1) 830-865 CE; 2) 1120-1290 CE; 3) 1530-1795 CE; and 4) 1865-1880 CE. These four periods correspond to phases of increased livestock farming, as reported in historical documents. Comparison of pollen, historical documents, and NPP records show that the impact on landscape dynamics during the last millennium have been mostly related to variable human population density controlled by historical, political and cultural changes in the Pyrenean mountains. Moreover, the use and comparison of several independent proxies have highlighted the strength of the indicator value obtained

High-resolution (sub-decadal) pollen analysis of varved sediments from lake Montcortès (South-central pre-Pyrenees): a fine-tuned record of landscape dynamics and human impact during the last 500 years.

A high-resolution (average 6 years/sampling interval) palaeoenvironmental reconstruction using pollen, charcoal and non-pollen palynomorphs was carried out on annually laminated sediments of Lake Montcortès (southern Pyrenean flank). The results were combined with historical data to better understand landscape evolution and human interaction during the last 500 years. Our results show that human activities (cropping, livestock breeding and hemp cultivation and retting) have been the most important factors responsible for vegetation changes with highest intensity between 1530 and 1900 CE. By means of a sub-decadal study we have been able to evaluate short-lasting events at local and regional scales related to climate (heavy rainfall events and, high-land forest fluctuations) or to historical and well-dated and documented socio-economic events (i.e., crop promotions (hemp) or land abandonment-population emigration). The temporal extent (400 years) and continuity of Cannabis pollen peak have been confirmed, and new evidence of water quality changes, likely as a consequence of hemp retting practices between the mid-17th to late 19th century, are provided. This is the first high-resolution palaeoenvironmental study carried out in a varved lake on the Iberian Peninsula so far. With these data we hope to contribute to filling the gap in high-resolution palaeoenvironmental data