A regional study of Holocene climate change and human occupation in Peruvian Amazonia

Aim  To investigate the influence of Holocene climatic and human-induced changes on a region of high biodiversity in southern Peruvian Amazonia.
Location  Four palaeoecological records from separate lakes within a lake district close to the modern city of Puerto Maldonado, Peru.
Results  The lakes provide a palaeoecological record spanning the last 8200 years. A mid-Holocene dry event is documented in all of the records that extend back > 6000 years. The dry event appears to have lasted from c . 7200 yr bp until c . 3300 yr bp . The onset of wetter conditions coincides with the formation of the youngest of the four lakes. The earliest occupation of these sites is inferred from the presence of charcoal at 7200 yr bp , and the first crop pollen is found at 3630 yr bp . Lakes that were regularly occupied were colonized soon after they formed. A reduction in charcoal concentration and the absence of crop pollen after c . 500  bp in all lakes is consistent with site abandonment following conquest.
Main conclusions  The mid-Holocene dry event is suggested to be part of a time-transgressive drying that tracked from north to south in both the Andes and the Amazon lowlands. The last millennium may represent the period of highest sustained lake levels within the Holocene. The proximity of the four lakes allows a landscape-scale analysis of the spatial extent of human disturbance centred on a known site of human occupation and reveals the highly localized nature of pre-Columbian anthropogenic disturbance in Amazonian landscapes. Inferences regarding widespread pre-Columbian landscape modification by indigenous peoples must take into account key site attributes, such as seasonality and proximity to rivers.     

From forest to farmland: pollen‐inferred land cover change across Europe using the pseudobiomization approach

Maps of continental‐scale land cover are utilized by a range of diverse users but whilst a range of products exist that describe present and recent land cover in Europe, there are currently no datasets that describe past variations over long time‐scales. User groups with an interest in past land cover include the climate modelling community, socio‐ecological historians and earth system scientists. Europe is one of the continents with the longest histories of land conversion from forest to farmland, thus understanding land cover change in this area is globally significant. This study applies the pseudobiomization method (PBM) to 982 pollen records from across Europe, taken from the European Pollen Database (EPD) to produce a first synthesis of pan‐European land cover change for the period 9000 bp to present, in contiguous 200 year time intervals. The PBM transforms pollen proportions from each site to one of eight land cover classes (LCCs) that are directly comparable to the CORINE land cover classification. The proportion of LCCs represented in each time window provides a spatially aggregated record of land cover change for temperate and northern Europe, and for a series of case study regions (western France, the western Alps, and the Czech Republic and Slovakia). At the European scale, the impact of Neolithic food producing economies appear to be detectable from 6000 bp through reduction in broad‐leaf forests resulting from human land use activities such as forest clearance. Total forest cover at a pan‐European scale moved outside the range of previous background variability from 4000 bp onwards. From 2200 bp land cover change intensified, and the broad pattern of land cover for preindustrial Europe was established by 1000 bp . Recognizing the timing of anthropogenic land cover change in Europe will further the understanding of land cover‐climate interactions, and the origins of the modern cultural landscape.     

Combining phylogeography and landscape genetics of Xenopipo atronitens (Aves: Pipridae), a white sand campina specialist,to understand Pleistocene landscape evolution in Amazonia

Open vegetation (campinas and campinaranas) associated with white sand patches occurs in the form of islands in a forested matrix throughout the Amazon basin. Bird species restricted to these habitats have patchy distributions, although connectivity may have been influenced by past glacial cycles as a result of the substitution of forest by savanna. Because these landscape changes are a matter of debate in the history of Amazonia, we studied the diversification of Xenopipo atronitens, a white sand specialist, aiming to infer the effects of past climate changes. The split of Xenopipo atronitens from its sister species, Xenopipo uniformis, may be related to Tepuis erosion and retreat of escarpments during the Miocene, or to a dispersal event. Compared with birds from terra firme forest, X. atronitens has low genetic structure. Low levels of unidirectional gene flow were found from the Guyana Shield to adjacent areas. Demographic expansion starting approximately 25 kyr BP was detected for some populations and is probably related to the Last Glacial Maximum and subsequent climate improvement. Landscape genetic analyses indicate that the forested (terra firme) matrix acts as a barrier for the dispersal of X. atronitens. The results of the present study indicate that glacial cycles have deeply influenced Amazonian biogeographical history, demonstrating a complex interaction between forest and nonforest habitats during the Pleistocene. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 60–76.     

A sediment-based history of medium altitude forest in central Africa: a record from Kabata Swamp, Ndale volcanic field, Uganda

1 Sedimentary data from a 6-m long core from Kabata Swamp, an in-filled crater in the Ndale volcanic field of western Uganda, provided evidence for a number of cycles of disturbance and recovery of medium altitude forest.
2 The date of formation of the crater was earlier than an Accelerator Mass Spectrometry (AMS) radiocarbon date of 11 460 ± 90  bp (11 699–11 209 bc cal.) and thus appears to predate volcanism farther north in the Fort Portal area.
3 A form of medium altitude forest was already present in western Uganda by the later stages of the last ice age. A more diverse form of medium altitude forest was present from 11 460 ± 90  bp .
4 Some phases of disturbance of this forest during the Holocene could be correlated with established political–economic changes in the study area. One dated c. 2500  bp (768–542 bc cal.) could be associated with the entry of Bantu-speaking people. A second at 400 ± 60  bp ( ad  1419–1648 cal.) coincides with significant shifts in the focus of settlement from drier grassland to wetter, more forested parts.
5 Levels of biodiversity in forests in western Uganda remain relatively high, even after substantial modifications of vegetation cover over an extended period of time. Many central African forest taxa may therefore be able to cope with environmental change, including prolonged human impact.     

A 7000‐year history of changing plant trait composition in an Amazonian landscape; the role of humans and climate

Tropical forests are shifting in species and trait composition, but the main underlying causes remain unclear because of the short temporal scales of most studies. Here, we develop a novel approach by linking functional trait data with 7000 years of forest dynamics from a fossil pollen record of Lake Sauce in the Peruvian Amazon. We evaluate how climate and human disturbances affect community trait composition. We found weak relationships between environmental conditions and traits at the taxon level, but strong effects for community‐mean traits. Overall, community‐mean traits were more responsive to human disturbances than to climate change; human‐induced erosion increased the dominance of dense‐wooded, non‐zoochorous species with compound leaves, and human‐induced fire increased the dominance of tall, zoochorous taxa with large seeds and simple leaves. This information can help to enhance our understanding of forest responses to past environmental changes, and improve predictions of future changes in tropical forest composition.     

Pike (Esox lucius) could have been an exclusive human introduction to Ireland after all: a comment on Pedreschi et al. (2014)

A recent publication (Pedreschi et al., 2014, Journal of Biogeography, 41 , 548–560) casts doubt over the status of pike (Esox lucius) as a non‐native species in Ireland by reporting two distinct genetic groups of pike present: one a human introduction in the Middle Ages, the other hypothesized to result from natural colonization after the Last Glacial Maximum (LGM). While the existence of two groups is not disputed, the hypothesized natural colonization scenario conflicts with the sequence in which the islands of Britain and Ireland became isolated from Europe after the LGM. An alternative natural colonization scenario raised herein was rejected, leaving an earlier, two‐phase, human introduction of pike from Britain or Europe to Ireland as a realistic alternative hypothesis explaining the results of Pedreschi et al. (2014). This leaves the debates on human introduction versus natural colonization, introduced versus native species status, and pike management in Ireland wide open.     

Out of Africa and into an ice age: on the role of global climate change in the late Pleistocene migration of early modern humans out of Africa

The results from two climate model simulations are used to explore the relationship between North Atlantic sea surface temperatures and the development of African aridity around 100,000 years ago. Through the use of illustrative simulations with an Earth System Climate Model, it is shown that freshwater fluxes associated with ice sheet surges into the North Atlantic, known as Heinrich events, lead to the southward shift of the intertropical convergence zone over Africa. This, combined with the overall increased aridity in the cooler mean climate, leads to substantial changes in simulated African vegetation cover, particularly in the Sahel. We suggest that Heinrich events, which occurred episodically throughout the last glacial cycle, led to abrupt changes in climate that may have rendered large parts of North, East, and West Africa unsuitable for hominin occupation, thus compelling early Homo sapiens to migrate out of Africa.     

How dung beetles respond to a human‐modified variegated landscape in Mexican cloud forest: a study of biodiversity integrating ecological and biogeographical perspectives

Aim To analyse how the dung beetles (Scarabaeinae) respond to a modified, variegated landscape, taking into account the biogeographical peculiarities of the Mexican Transition Zone. Location This study covers cloud forest (CF) of the Sierra Norte de Puebla mountain range and part of the Sierra Madre Oriental mountain range (Mexico). Methods We applied proportional sampling based on the landscape variegation model with Scarabaeinae as the indicator group, and using two approaches: structural units (vegetation type) and spatial units (windows). We used two measures – richness and Shannon diversity – and applied multiplicative diversity partitioning to obtain independent alpha and beta diversities for the landscape, windows and vegetation types. We grouped species by biogeographical distribution pattern for the biogeographical analysis and by whether they were originally from CF. Results The transformation of CF into secondary forest, pastures and other types of vegetation increases the Scarabaeinae diversity of the landscape, in vegetation types and windows. This increase is the result of species arriving from the tropical lowlands. However, the original dung beetle community of the CF dominates at different scales in the number of species, abundance and biomass. With increasing habitat modification, beta diversity increases in the windows, and species with the Tropical Palaeoamerican distribution pattern increase in abundance in vegetation types and windows. Main conclusions The variegated character of the landscape explains well the distribution and diversity of this dung beetle community. The peculiar characteristics of the Mexican Transition Zone have an effect owing to the overlap of fauna with different biogeographical origins. The conversion of fragmented landscapes to variegated landscapes could be a conservation goal in human‐modified mountain landscapes. Sampling proportional to the area of different types of vegetation and the use of windows offer an alternative experimental design in variegated landscapes.     

Assessing the effects of land-use change on plant traits, communities and ecosystem functioning in grasslands: a standardized methodology and lessons from an application to 11 European sites

BACKGROUND AND AIMS: A standardized methodology to assess the impacts of land-use changes on vegetation and ecosystem functioning is presented. It assumes that species traits are central to these impacts, and is designed to be applicable in different historical, climatic contexts and local settings. Preliminary results are presented to show its applicability. METHODS: Eleven sites, representative of various types of land-use changes occurring in marginal agro-ecosystems across Europe and Israel, were selected. Climatic data were obtained at the site level; soil data, disturbance and nutrition indices were described at the plot level within sites. Sixteen traits describing plant stature, leaf characteristics and reproductive phase were recorded on the most abundant species of each treatment. These data were combined with species abundance to calculate trait values weighed by the abundance of species in the communities. The ecosystem properties selected were components of above-ground net primary productivity and decomposition of litter. KEY RESULTS: The wide variety of land-use systems that characterize marginal landscapes across Europe was reflected by the different disturbance indices, and were also reflected in soil and/or nutrient availability gradients. The trait toolkit allowed us to describe adequately the functional response of vegetation to land-use changes, but we suggest that some traits (vegetative plant height, stem dry matter content) should be omitted in studies involving mainly herbaceous species. Using the example of the relationship between leaf dry matter content and above-ground dead material, we demonstrate how the data collected may be used to analyse direct effects of climate and land use on ecosystem properties vs. indirect effects via changes in plant traits. CONCLUSIONS: This work shows the applicability of a set of protocols that can be widely applied to assess the impacts of global change drivers on species, communities and ecosystems.