The study is the first integrated reconstruction of its kind for the Iberian Peninsula, and it tackles a question that has divided palaeoecologists for decades: were the treeless pastures of the Pyrenean subalpine belt opened by herders, or did climate do the heavy lifting? Traditional indicators of human activity in pollen records, such as cereal-type grains or plantain pollen, can be ambiguous in the Mediterranean region, because some of the same taxa also respond to natural climatic shifts. By layering multiple independent proxies from the same lake core, the researchers hoped to separate those signals with greater confidence than any single method allows.

The team retrieved two pairs of sediment cores from the lake’s deepest point in October 2020 and 2021, using a floating platform. Each core measured about nine metres long. The chronological backbone of the study rests on twenty-two radiocarbon dates processed at a laboratory in Seattle, woven into a Bayesian age-depth model that accounts for a sedimentary hiatus between roughly 20,000 and 15,000 years ago, when the lake appears to have been frozen for most of the year under glacial conditions. The uppermost two core sections showed signs of reworking and were excluded from the biological analyses to avoid distorting the record.

During the Last Glacial Maximum and the Lateglacial, the landscape around the lake was treeless and cold. Pollen from pine, wormwood, jointfir and goosefoot family plants dominated, consistent with other glacial-era records across the Pyrenees. When the Bølling warming arrived around 14,700 years ago, scattered pine formations persisted in an open steppe. The subsequent Allerød and Younger Dryas intervals are harder to read at this site because sedimentation rates were low, but the presence of deciduous oak and hazel pollen hints that tree populations survived nearby in regional refugia, supporting the idea that southern Europe served as a glacial sanctuary for temperate species.

The Early Holocene brought a dramatic transformation. As deglacial warming took hold, a mixed forest dominated by birch replaced the pine communities, an unusual pattern compared with other Pyrenean sites where hazel typically takes that role. The researchers propose that regular, low-intensity fires, probably ignited naturally by summer thunderstorms under a Mediterranean-influenced climate, gave pioneer birch an edge over hazel, which recovers more slowly after disturbance. Charcoal records show continuous fire occurrence through this period, yet the width-to-length ratio of charcoal particles indicates that grasses, not trees, were the main fuel, painting a picture of frequent but gentle ground fires in a landscape of high forest biomass.

The pivotal shift came around 8,200 years ago. An abrupt and sustained decline in plant biomass, recorded in pollen accumulation rates, coincides with a well-known cooling event that marks the start of the Mid-Holocene. Fire activity dropped sharply, and no fire episodes were detected for roughly seven centuries, suggesting cold, arid conditions had simply left too little fuel to burn. Crucially, no domestic animal DNA or clear anthropogenic indicators appear in the record at this stage, so the initial thinning of the forest cannot be blamed on people.

Then, between about 6,500 and 6,000 years ago, the story changes. Sedimentary ancient DNA from the cores revealed the first evidence of cattle and sheep around the lake, the earliest such continuous record of livestock in the Iberian Holocene. Runoff-dominated sediment layers signal increased erosion in the catchment, plant productivity declined across all vegetation types, and a cluster of fire episodes appeared precisely when a cave-based temperature reconstruction from the region shows its lowest Holocene values. The researchers interpret this conjunction as evidence that Neolithic pastoralists opportunistically exploited open ground created by climatic cooling, using fire to keep it open for grazing. Neither driver alone, they argue, explains the full pattern.

The Late Holocene deepened the human imprint. After about 4,000 years ago, charcoal accumulation reached its highest values around 2,100 years ago, and charcoal morphology shifted from herbaceous to woody fuel, indicating less frequent but more severe burns. Wild mammals such as red deer and brown bear, detected through DNA in older sediments, gave way to persistent livestock. Pollen of cereals and plantain climbed to their record highs. The authors also raise the possibility of selective management: deciduous oaks, whose acorns could have been valued as fodder, resist fire by resprouting and may have been deliberately spared, a practice echoing what landscape ecologists have called landscape fruiting. Meanwhile, the continued local presence of fire-sensitive fir suggests human impact never crossed the threshold that would have eliminated such vulnerable communities.

Perhaps the most methodologically interesting result is the comparison between pollen and sedimentary ancient DNA. The two proxies often disagreed. Anthropogenic taxa appear throughout the pollen record but only emerge in the DNA data around 6,000 years ago, implying that coarse pollen categories may overestimate early human influence by lumping in naturally occurring plants. Grasses, which dominate grazing diets, were underrepresented in the DNA record despite their prolific pollen, ruling out animal droppings as a major DNA source at this site. Tree taxa showed both convergent and divergent patterns depending on their pollen productivity. The researchers conclude that the two approaches are complementary, with DNA capturing local vegetation and pollen integrating the regional picture, though they caution that the taphonomy of lake sediment DNA still needs more study.

The implications reach into present-day conservation policy. The Pyrenean subalpine belt was grazed under transterminance, a system of short-distance seasonal livestock movement, until land abandonment in the last century triggered widespread reforestation. If these open landscapes are cultural artefacts sustained by millennia of low-intensity stewardship, as this study suggests, then protecting them may require deliberately emulating traditional grazing and burning practices rather than simply excluding human activity. The authors note that modern warming, rising atmospheric carbon dioxide and contemporary land-use pressures complicate direct translation of the past into management prescriptions. Still, their reconstruction supports the view that the Pyrenees host human-shaped biodiversity hotspots, and that without integrated management, rising temperatures could accelerate woody encroachment, elevate wildfire risk and quietly erase four millennia of ecological heritage.

Subject of Research: A 25,000-year multiproxy lake sediment reconstruction of climate and human interactions in the Pyrenean subalpine belt

Article Title: Human and climate-environment interactions in Pyrenean landscapes: a Lateglacial-Holocene multiproxy reconstruction

Article References: Julián-Posada, I., Gil-Romera, G., Moreno, A., Leys, B., Valero-Garcés, B., & González-Sampériz, P. (2026). Human and climate-environment interactions in Pyrenean landscapes: a Lateglacial-Holocene multiproxy reconstruction. Biogeosciences, 23(20), 7411-7446. https://doi.org/10.5194/bg-23-7411-2026

Image Credits: AI Generated

DOI: 10.5194/bg-23-7411-2026

Keywords: Pyrenees, palaeoecology, sedimentary ancient DNA, pollen analysis, charcoal, Holocene, Neolithic pastoralism, fire history, Tramacastilla Lake, landscape management, Biogeosciences, Human

Instead, the results support a coupled account in which biodiversity, resource availability, social hierarchy and resource-management practices could reinforce one another over centuries. The Society and Gambier Islands are unusually useful for comparison because both were settled by voyaging societies derived from a common Polynesian background and experienced broadly comparable cultural sequences before European contact. The researchers describe these as approximately 800 to 900 years long.

The pre-contact societies nevertheless differed substantially. The Society Islands supported hierarchical “complex” chiefdoms, an estimated population of 100,000 to 200,000 or more and a settlement pattern with five tiers of sites. The less hierarchical Gambier Islands probably had fewer than 10,000 people in aggregate and lacked strong centralized political authority.

The study compared the two archipelagos as whole historical socioecological systems, aggregating evidence from across the pre-contact era rather than tracking each interaction through time. Physical differences were equally pronounced. The Society archipelago consists of volcanic high islands with an aggregate area of 132.5 square kilometres and elevations reaching 2,241 metres.

Orographic rainfall and varied elevation create terrestrial habitats that support relatively high biodiversity. The Gambier Islands have one-fifth the aggregate land area, 24.3 square kilometres, and a maximum elevation of 441 metres. Their land-to-reef ratio of 1:7.2 provides extensive surrounding marine habitat, but fewer terrestrial species, limited productivity of some Polynesian cultigens and fewer opportunities for intensive husbandry of animals such as pigs and dogs.

The authors therefore treated the Gambiers as ecologically poorer on land but richer in marine surroundings. Earlier archaeo-ecological modeling cited by the study estimated that marine foods supplied only 15–18 percent of the Gambiers’ pre-contact diet, illustrating that access to a large marine area did not necessarily translate into a dominant subsistence contribution. Jennifer G.

Kahn, Stefani A. Crabtree, Patrick V. Kirch, Abigail Buffington, Spencer A.

Wood, Dieta Hanson, Evan Holt and Jennifer A. Dunne jointly compiled the underlying “Human Interactions with Other Species,” or HIOS, datasets from archaeological, archaeobotanical and zooarchaeological studies, modern botanical and ecological surveys, ethnographies, historical accounts, oral traditions and genealogies. The team first established a list of taxa known from each archipelago and resolved each identification to the finest taxonomic level supported by multiple sources.

Some records remain identified at genus, family or order level. Taxa were classified as native or as Polynesian introductions, while organisms introduced after European contact were excluded. Each documented interaction was assigned to one of 13 categories: artifact, clothing, companion, cosmology, food, fuel, housing, medicinal, ornamental, ritual, structural, trade and transportation.

Unlike a food web, which principally records feeding relationships, a HIOS network includes material, social, symbolic and relational uses. A species can therefore be represented not only as food but also as raw material for tools, an ingredient in housing, a companion, a component of cosmology, an ornament, a ritual offering or a means of transportation. The Society system included 1,749 taxa in total: 624 with documented human uses and 1,125 without them.

The corresponding Gambier totals were 850, comprising 252 taxa with documented uses and 598 without them. Native taxa greatly outnumbered Polynesian introductions among documented resources in both systems. In the Society Islands, 578 native taxa and 41 introduced taxa had recorded uses; in the Gambiers, the corresponding numbers were 224 and 28.

Bipartite network analysis converted the evidence into systems linking taxa to interaction categories. The Society network contained 690 nodes and 1,100 links, with an average of 1.6 links per taxon. The Gambier network contained 309 nodes and 393 links, averaging 1.3 links per taxon.

Food was the most connected category in both: 566 taxa linked to food in the Society system and 254 in the Gambier system. This high connectivity is consistent with the capacity to switch among food resources when availability changes, although the aggregated dataset does not directly measure how often such prey switching occurred. Most taxa used in either system had only a food relationship, with food accounting for approximately 84 percent of used taxa in the Society Islands and 93 percent in the Gambiers.

The network also distinguished taxa with many kinds of use from those serving only one or a few functions. Detrended correspondence analysis broadly reproduced the groupings identified by the networks, separating food from many other activities and clustering construction-related uses. It also showed that Polynesian introductions were associated with more interaction types in the Gambiers than in the Society Islands, consistent with the Gambiers’ lower native diversity.

Network analysis supplied additional structural information that the ordination did not reveal, including the positions of individual taxa and categories within the overall system. Introduced plants occupied especially central positions in both networks: breadfruit and coconut ranked among the most connected taxa in the Society Islands, while turmeric and noni were prominent in the Gambiers. The green sea turtle and screw pine were also highly ranked in their respective systems.

These central taxa often had ritual or cosmological importance, showing that network prominence was not confined to food production. Archaeological evidence indicates that pigs and dogs had been extirpated from the Gambiers by the time of European contact in 1797. In the HIOS records, turtles occupied a relatively larger role in the Gambiers than in the Societies, with uses including food, artifact production, ornament and cosmology.

The authors interpret the functional overlap between turtles and pigs as resource switching: replacing one taxon with another across food and non-food uses as environmental and cultural constraints changed. This interpretation is provisional. No turtle remains were recovered from ritual contexts in the Gambier archaeological record, so the comparison relies partly on ethnohistoric evidence rather than direct ritual assemblages.

Social hierarchy appears to have become more closely linked to ecological management in the Society Islands. Sixty-seven percent of mammal taxa in the Society HIOS dataset had ritual uses. Medium-sized terrestrial mammals, including pigs and dogs, served as tribute to chiefs and gods, objects of sacrifice and divination, and raw materials for prestige goods.

Pre-contact assemblages dated to 1650–1767 disproportionately contained pigs in elite ritual settings associated with temples. No Gambier mammal taxon had a recorded ritual use. The researchers propose that the larger, richer and more productive terrestrial environment facilitated animal husbandry and surplus production, after which specialized elites increasingly controlled access to valuable animals, resources and ceremonial roles.

The network pattern is consistent with feedback among ecological potential, status competition, restricted access and landscape management, but the static analysis cannot establish a direct causal sequence or show that environmental abundance alone produced social complexity. Several limitations constrain what the networks can reveal. They aggregate relationships across centuries, so they cannot establish when a particular species, use or social practice became important.

Interaction categories are discrete and unweighted, meaning that differences in the frequency, intensity or cultural salience of uses are not captured. The evidence base is also uneven: introduced and culturally prominent organisms are often more thoroughly documented, potentially increasing their apparent connectivity and centrality, while taxonomic resolution varies where multiple sources do not support species-level identification. These limitations prevent the study from separating environmental and cultural contributions cleanly.

The authors note that the comparative networks nevertheless provide a quantitative foundation for subsequent work, including analyses using 200-year chronological blocks, models that separate ecological, material and symbolic layers, and tests across additional Polynesian archipelagos. The present evidence supports a history of divergence shaped jointly by biodiversity, resource use, social decisions and changing ecological conditions, not a single prime mover.

Subject of Research: Comparative socioecological network analysis of human interactions with species in Eastern Polynesian chiefdoms

Article Title: Emergent socioecological dynamics in Eastern Polynesian chiefdoms: a comparative network analysis of the Society and Gambier Islands

Article References: Kahn, J. G., Crabtree, S. A., Kirch, P. V., Buffington, A., Wood, S. A., Hanson, D., Holt, E., & Dunne, J. A. (2026). Emergent socioecological dynamics in Eastern Polynesian chiefdoms: a comparative network analysis of the Society and Gambier Islands. Frontiers in Complex Systems, 4, Article 1887490. https://doi.org/10.3389/fcpxs.2026.1887490

Image Credits: AI Generated

DOI: 10.3389/fcpxs.2026.1887490

Keywords: Polynesian chiefdoms, socioecological networks, archaeology, Eastern Polynesia, biodiversity, resource switching, social complexity, network analysis, species interactions, landscape management, Emergent, socioecological

The macadamia is not an ordinary crop. Labour-intensive harvesting and complex post-harvest processing make it one of the costliest nuts in the global market, which means that every percentage point of yield lost to insects translates into substantial economic damage. Protecting the trees from pests is therefore a central concern for growers, and the conventional response has often been intensive chemical or mechanical intervention. The new research suggests that an alternative, ecologically grounded strategy may already be flying overhead every night. By examining how natural vegetation in and around plantations shapes the communities of birds and bats that forage among the trees, the team set out to quantify the pest control services these animals provide and to identify the landscape features that sustain them.

The study was conducted at ten intensively managed macadamia plantations in South Africa, a design that allowed the researchers to capture variation in both management intensity and surrounding land cover. At each site, the team compared trees growing at the edge of the plantation with trees in the centre, a comparison specifically chosen to analyse the influence of the surrounding vegetation on the animals visiting the crop. Edge trees sit closer to hedgerows, forest fragments and other natural features, while central trees are embedded more deeply within the monoculture, so any systematic differences in pest damage or animal communities between the two positions can reveal how strongly the wider landscape shapes what happens inside the orchard.

Surveying the fauna required two very different techniques. The researchers recorded 111 bird species through direct observation, walking the orchards and documenting the birds foraging among the trees. Bats, being nocturnal and difficult to observe visually, were detected through their echolocation calls, which were captured with acoustic recording equipment and used to identify 16 species. This acoustic monitoring allowed the team to build a detailed picture of which bat species were active over the plantations, how their activity varied between sites, and how that variation related to the structure of the surrounding landscape and the level of insect damage measured on the nuts.

The results pointed clearly to bats as the dominant pest control agents in the system. Bat activity was associated with reduced insect damage, and this effect was particularly pronounced in plantations that contained less natural habitat within their boundaries or were surrounded by natural habitat in the wider landscape. Natural habitat, in the sense used by the researchers, includes native forests, bushland and scrubland, the heterogeneous vegetation types that provide roosting sites, foraging grounds and refuge for insectivorous bats. In landscapes where these features persisted, the bats appeared to compensate for the scarcity of on-farm natural cover, patrolling the orchards and suppressing the insect populations that would otherwise feed on the developing nuts.

To test the contribution of flying vertebrates directly, the team conducted exclusion trials, a classic experimental approach in which nets are used to keep birds and bats away from the trees. The outcome was striking. When birds and bats were excluded, the proportion of nuts damaged by insects rose from 6.2 per cent to 10.7 per cent, an increase of roughly 70 per cent. This experiment provides some of the most direct evidence that these animals deliver a measurable, economically meaningful service to macadamia growers. Intriguingly, however, the researchers could not demonstrate a direct influence of bird numbers on pest infestation, suggesting that in this system the nocturnal bats, rather than the diurnal birds, carry the primary burden of biological pest control.

The landscape context proved to matter in more ways than one. As the proportion of natural habitats around the plantations increased, not only did the number of bats rise, but their diversity increased as well, indicating that intact vegetation supports a richer community of these aerial predators rather than merely a larger one dominated by a few generalist species. Even the yield of the macadamia trees was linked to the share of natural habitat in the landscape, reaching its highest level when natural habitats accounted for around 60 per cent of the surrounding area. This peak suggests a non-linear relationship in which a substantial but not exclusive share of natural cover best supports the ecological processes, from pest suppression to pollination, that underpin crop production.

Bird communities, by contrast, responded to fine-scale structure within the plantations rather than to the broader landscape. The researchers found that the species assemblages differed between the edges and the centres of the orchards: species that prefer dense and woody vegetation were more common at the plantation edges, while species of open habitats predominated in the interior. This edge-to-centre gradient shows that even within a single intensively managed plantation, the arrangement of vegetation creates distinct niches for different bird species, and it hints that the conservation value of an orchard depends not only on what surrounds it but also on how its own internal habitat mosaic is structured.

The implications extend well beyond macadamia. Lead author Dr Mina Anders of the Department of Functional Agrobiodiversity and Agroecology at the University of Göttingen emphasised the broader message of the findings. Natural habitats, she explained, are valuable refuges that support beneficial organisms providing pollination and pest control, which in turn benefits agricultural production and the farmers who depend on it. It is therefore essential, she argued, that natural habitats and their conservation are incorporated into the planning of agricultural land. In other words, the patches of native forest, bushland and scrubland that persist between and around fields should not be viewed as idle or expendable land, but as functional infrastructure that actively contributes to farm productivity.

For a crop as valuable as the macadamia, the economics of this ecological service are compelling. A 70 per cent increase in insect-damaged nuts when bats and birds are excluded illustrates how quickly quality, and with it market value, deteriorates without these natural allies. The study thus highlights a form of agriculture that combines biodiversity with production, in which conserving natural vegetation within and around farmland is not a concession to environmental ideals but a practical investment in yield and nut quality. As global demand for macadamias continues to grow, the research offers growers and land-use planners a concrete, evidence-based reason to protect the forests and scrublands that shelter the bats working the night shift over South Africa’s orchards, and it adds macadamia plantations to the growing list of cropping systems where the fate of the harvest is quietly tied to the health of the surrounding landscape.

Subject of Research: The role of bats, birds and natural habitat in biological pest control in macadamia orchards

Article Title: Bats as a form of biological pest control

Article References: Bats as a form of biological pest control. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: bats, biological pest control, macadamia, South Africa, agroecology, natural habitat, biodiversity, bird communities, echolocation, crop yield, landscape management, University of Göttingen