14,000 years of climatic and anthropogenic change in the Afromontane forest of São Tomé Island, Gulf of Guinea

São Tomé (Gulf of Guinea, Central Africa) is a 854 km2 tropical island that had a pivotal role in early European colonial expansion through the Atlantic between the 15th and 16th centuries. Historical sources suggest that native vegetation has been heavily impacted since human arrival (1470 CE) due to monoculture economies and the introduction of mammals and plants, some of which now have established wild populations. The Afromontane forest of São Tomé, located above 800 m.a.sl., is particularly rich in endemic plant species and has remained relatively unaffected by direct human impacts. Here, we explore how environmental change influenced this forest through the study of a sedimentary sequence from the volcanic crater of Lagoa Amélia (1340 m a.s.l.), a palustrine system located at the boundary between submontane (800–1400 m a.s.l.) and mist forest (above 1400 m a.s.l.). We used fossil pollen, non-pollen palynomorphs, sedimentology and charcoal to determine forest dynamics from the Late Pleistocene to the present. From 14,000 to 12,500 cal yr BP the forest was dominated by taxa from higher altitudes, adapted to cooler and drier climates (e.g. Afrocarpus mannii trees and Psychotria nubicola). After 12,500 cal yr BP, a potential uphill migration was identified by an increase in taxa like the trees Symphonia globulifera and Craterispermum cerinanthum. From 11,200 cal yr BP through the rest of the Holocene taxa from lower altitudes became dominant (e.g. Prunus africana, Polyscias, and Sabicea), except at c. 8500 cal yr BP when rapid cooling led to forest opening. Charcoal showed that fires were frequent during the Late Pleistocene (14,000 to 11,200 cal yr BP), becoming rare during the Holocene until anthropogenic fires started at c. 220 cal yr BP. Other recent anthropogenic impacts detected in Lagoa Amélia included the appearance of pollen of introduced plant species (e.g., Cestrum), and the increase in pollen of economically important species (Elaeis guineensis, Zea mays) and in fungal spores related to introduced herbivores. Our results reveal that climate changed the altitudinal distribution of the Afromontane forest in São Tomé during the Late Pleistocene, as observed on the African continent, and that this ecosystem was also strongly impacted by human arrival, through fire, farming, and introduced species.info:eu-repo/semantics/publishedVersio

Aprendre de les illes petites per entendre la dinàmica dels boscos afromuntans

Un grup d'investigadores i investigadors internacionals ha dut a terme un estudi a l'illa de Sao Tomé, Golf de Guinea, per a comprendre la dinàmica dels boscos afromuntans. Encara que aquests boscos tropicals van resistir canvis climàtics fa 12.500 anys, la introducció d'espècies vegetals en els últims 200 anys i l'augment de partícules de carbó assenyalen la seva vulnerabilitat a impactes humans i al canvi climàtic.Un grupo de investigadoras e investigadores internacionales ha llevado a cabo un estudio en la isla de Santo Tomé, Golfo de Guinea, para comprender la dinámica de los bosques afromontanos. Aunque estos bosques tropicales resistieron cambios climáticos hace 12.500 años, la introducción de especies vegetales en los últimos 200 años y el aumento de partículas de carbón señalan su vulnerabilidad a impactos humanos y al cambio climático.An international group of researchers conducted a study on the island of São Tomé, Gulf of Guinea, to understand the dynamics of the Afromontane forests. Although these tropical forests withstood climatic changes 12,500 years ago, the introduction of plant species in the last 200 years and the increase in charcoal particles suggest their vulnerability to human impacts and global climate change

Anthropogenic transitions from forested to human-dominated landscapes in southern Macaronesia

The extinction of iconic species such as the dodo and the deforestation of Easter Island are emblematic of the transformative impact of human colonization of many oceanic islands, especially those in the tropics and subtropics. Yet, the interaction of prehistoric and colonial-era colonists with the forests and forest resources they encountered can be complex, varies between islands, and remains poorly understood. Long-term ecological records (e.g., fossil pollen) provide the means to understand these human impacts in relation to natural change and variability pre- and postcolonization. Here we analyze paleoecological archives in forested landscapes of the Canary Islands and Cabo Verde, first colonized approximately 2,400 to 2,000 and 490 y ago, respectively. We demonstrate sensitivity to regional climate change prior to human colonization, followed by divergent but gradual impacts of early human settlement. These contrast with more rapid transformation in the colonial era, associated with significant increases in anthropogenic pressures. In the Canary Islands, at least two native tree taxa became extinct and lowland thermophilous woodlands were largely converted to agricultural land, yet relictual subtropical laurel forests persisted with limited incursion of nonnative species. In Cabo Verde, in contrast, thermophilous woodlands were depleted and substituted by open landscapes and introduced woodlands. Differences between these two archipelagos reflect the changing cultural practices and societal interactions with forests and illustrate the importance of long-term data series in understanding the human footprint on island ecosystems, information that will be critically important for current and future forest restoration and conservation management practices in these two biodiversity hotspots

Taming Fogo Island: Late-Holocene volcanism, natural fires and land use as recorded in a scoria-cone sediment sequence in Cabo Verde

Cabo Verde remained uninhabited until 1460 CE, when European sailors founded a settlement in Santiago, and soon after in Fogo island. The degree to which different island ecosystems in Cabo Verde have been transformed by humans remains uncertain because of a scarcity of historical information and archaeological evidence. Disentangling these processes from natural ones is complicated in islands with a history of volcanic impacts and other natural hazards. In this paper, we apply microfossil (pollen, non-pollen palynomorphs and phytoliths) and sedimentological analyses (granulometry, X-ray diffraction, loss on ignition and tephrostratigraphy) to a 2-m sediment sequence deposited in a scoria cone from 4100 cal year BP (calibrated years before 1950 CE) to the present. The organic-rich basal sediments indicate that between 4100 and 2600 cal year BP the pre-settlement landscape of Fogo was an open grassland, where fire was infrequent and/or small-scale. An increase in volcanic glass deposition after 2600 cal year BP, peaking ca. 1200 cal year BP, suggests that there was a progressive activation of Fogo’s volcanic activity, contemporaneous with increased fire frequency and erosion pulses, but with little impact on local grassland vegetation. While dating uncertainty is high, the first evidence of intensive local land use by early settlers was in the form of cultivation of Zea mays, abundant spores of coprophilous fungi (i.e. Sporormiella), and peaks in charcoal concentrations between 800 and 400 cal year BP. This was followed by large increases in pollen from pigeon pea (Cajanus), a diverse array of exotic trees (Cupressus, Grevillea), and invasive shrubs (Lantana). The introduction of these taxa is part of recent human effort to ‘tame’ this steep, dry and hazardous island by reducing erosion and providing firewood. An important outcome of these efforts, however, is a loss of fragile native biodiversity.</p

Effects of halocene climate change, volcanism and mass migration on the ecosystem of a small, dry island (Brava, Cabo Verde)

Research ArticleAim: Palaeoecological data provide an essential long-term perspective of ecological change and its drivers in oceanic islands. However, analysing the effects of multi-scalar and potentially co-occurring disturbances is particularly challenging in dry islands. Here, we aim to identify the ecological consequences of the integrated impacts of a regional drying trend, volcanic eruptions and human mass migrations in a spatially constrained environment—a small, dry oceanic island in Macaronesia. Location: Brava Island, Republic of Cabo Verde. Taxa: Terrestrial vegetation and fungi. Methods: We use palaeoecological analyses applied to a caldera soil profile that dates back to 9700 cal yr BP (calibrated years before the present). Analyses include pollen (vegetation history), non-pollen palynomorphs (changes in fern and fungal communities), grain-size distribution, loss-on- ignition and geochemistry (sedimentology and erosion regimes), microscopic tephra shards (volcanic ash deposition) and charcoal (fire regime). Results: A regional drying trend after c. 4000 cal yr BP caused increased erosion but had limited immediate impacts on highland grassland vegetation. The expansion of fern-rich woody scrubland was contemporaneous with significant deposition of volcanic ash and erosion between 1800 and 650 cal yr BP. About 300 cal yr BP, exogenous plants expanded, grazing and fires increased, and there was a decrease of native vegetation cover. Main conclusions: Throughout the Holocene, highland vegetation in Brava was characterized by the presence of open landscapes dominated by herbaceous species (e.g. Poaceae, Forsskaolea), with some presence of woody native taxa (e.g. Ficus, Dodonaea). A regional drying trend was a driver of erosion since the Mid Holocene but did not have an immediate influence on highland vegetation. Tephra deposition is a possible driver of vegetation change. Inter-island mass migration after volcanic events in Fogo Island c. 1680 CE potentially triggered land use change and intensification, causing a reduction of native vegetation in Bravainfo:eu-repo/semantics/publishedVersio

Effects of Holocene climate change, volcanism and mass migration on the ecosystem of a small, dry island (Brava, Cabo Verde)

Aim: palaeoecological data provide an essential long-term perspective of ecological change and its drivers in oceanic islands. However, analysing the effects of multi-scalar and potentially co-occurring disturbances is particularly challenging in dry islands. Here, we aim to identify the ecological consequences of the integrated impacts of a regional drying trend, volcanic eruptions and human mass migrations in a spatially constrained environment—a small, dry oceanic island in Macaronesia. Location: Brava Island, Republic of Cabo Verde. Taxa: Terrestrial vegetation and fungi. Methods: we use palaeoecological analyses applied to a caldera soil profile that dates back to 9700 cal yr BP (calibrated years before the present). Analyses include pollen (vegetation history), non-pollen palynomorphs (changes in fern and fungal communities), grain-size distribution, loss-on-ignition and geochemistry (sedimentology and erosion regimes), microscopic tephra shards (volcanic ash deposition) and charcoal (fire regime). Results: a regional drying trend after c. 4000 cal yr BP caused increased erosion but had limited immediate impacts on highland grassland vegetation. The expansion of fern-rich woody scrubland was contemporaneous with significant deposition of volcanic ash and erosion between 1800 and 650 cal yr BP. About 300 cal yr BP, exogenous plants expanded, grazing and fires increased, and there was a decrease of native vegetation cover. Main conclusions: throughout the Holocene, highland vegetation in Brava was characterized by the presence of open landscapes dominated by herbaceous species (e.g. Poaceae, Forsskaolea), with some presence of woody native taxa (e.g. Ficus, Dodonaea). A regional drying trend was a driver of erosion since the Mid Holocene but did not have an immediate influence on highland vegetation. Tephra deposition is a possible driver of vegetation change. Inter-island mass migration after volcanic events in Fogo Island c. 1680 CE potentially triggered land use change and intensification, causing a reduction of native vegetation in Brava.</p

Using multiple palaeoecological indicators to guide biodiversity conservation in tropical dry islands:the case of São Nicolau, Cabo Verde

Tropical dry islands are currently facing major challenges derived from anthropogenic and climatic pressures. However, their trajectories of environmental change, which could provide relevant information applicable to biodiversity conservation, remain understudied. This is mainly due to poor micro-fossil preservation and irregular sediment deposition. Multi-proxy palaeoecological analyses spanning decades to 1000s of years can add perspective as to how vegetation, fungal communities, and the fauna responded to previous natural and anthropogenic disturbances. In São Nicolau, Cabo Verde, we used palaeoecological methods to analyse a highland soil profile (1000 m asl) dated to 5900 cal yr BP. We analysed how vegetation (abundances in pollen of native and introduced species, and leaf wax n-alkanes), ferns and fungal communities (abundance of non-pollen palynomorphs) varied over time in relation to fire (charcoal concentration) and erosion regimes (grain sizes and elemental composition). Between 5000 and 400 cal yr BP the highlands held native woody taxa such as Euphorbia tuckeyana, Dracaena draco subsp. caboverdeana, and Ficus, taxa that can be used for future reforestation programmes. From 400 cal yr BP to the present day, replacement of native taxa by introduced and cultivated taxa (Pinus, Eucalyptus, Asystasia, Opuntia) has occurred. Vegetation burning and grazing caused loss of vegetation and erosion, acting as conjoined drivers of scrubland degradation. This dataset helps to set historically contextualised restoration goals such as the re-introduction of native species, monitoring of recently introduced species and control of free grazing. This can serve as a model system for the conservation of tropical dry islands' biodiversity

Ecological responses to land use change in the face of European colonization of Haytí island

Caribbean island ecosystems underwent significant landscape transformations in the centuries after Columbus landed in the archipelago in AD1492, but there is no agreement as to the degree and extent of pre-Columbian human impacts and the long-term trends of ecosystem disturbance and recovery. Here, we present an integrative analysis of three palaeoenvironmental records in the northern Caribbean island of Haytí (currently Dominican Republic and Haiti), to assess regional landscape transformation and human impacts in pre- and post-Columbian times. We examine biotic and abiotic indicators of landscape and ecosystem change along the Columbus’ Route, the first European extractive transport route built in the Americas. Our data show that indigenous populations transformed the landscape between 1000 and 450 cal yr BP through slash-and-burn agricultural practices. Depopulation and forced population displacement through relocation of indigenous people into Spanish mining areas triggered the recovery and expansion of forests in the valley, coastal plain and mountains. In contrast, mangroves near the first permanent European colonial outpost in the Americas (La Isabela) underwent no significant impacts related to climatic, indigenous, and early colonial pressures. All ecosystems studied have suffered degradation through deforestation during the last 200 years leading to the present fragmented landscapes. In islands with long histories of human settlement such as Haytí, reconstructing temporal and spatial aspects of human transformations and impacts on the environment is crucial to improving our understanding of the drivers and mechanisms of ecosystem degradation and recovery

Ecological responses to land use change in the face of European colonization of <i>Haytí</i> island

Caribbean island ecosystems underwent significant landscape transformations in the centuries after Columbus landed in the archipelago in AD1492, but there is no agreement as to the degree and extent of pre-Columbian human impacts and the long-term trends of ecosystem disturbance and recovery. Here, we present an integrative analysis of three palaeoenvironmental records in the northern Caribbean island of Haytí (currently Dominican Republic and Haiti), to assess regional landscape transformation and human impacts in pre- and post-Columbian times. We examine biotic and abiotic indicators of landscape and ecosystem change along the Columbus’ Route, the first European extractive transport route built in the Americas. Our data show that indigenous populations transformed the landscape between 1000 and 450 cal yr BP through slash-and-burn agricultural practices. Depopulation and forced population displacement through relocation of indigenous people into Spanish mining areas triggered the recovery and expansion of forests in the valley, coastal plain and mountains. In contrast, mangroves near the first permanent European colonial outpost in the Americas (La Isabela) underwent no significant impacts related to climatic, indigenous, and early colonial pressures. All ecosystems studied have suffered degradation through deforestation during the last 200 years leading to the present fragmented landscapes. In islands with long histories of human settlement such as Haytí, reconstructing temporal and spatial aspects of human transformations and impacts on the environment is crucial to improving our understanding of the drivers and mechanisms of ecosystem degradation and recovery

Long-term trajectories of non-native vegetation on islands globally

Human-mediated changes in island vegetation are, among others, largely caused by the introduction and establishment of non-native species. However, data on past changes in non-native plant species abundance that predate historical documentation and censuses are scarce. Islands are among the few places where we can track human arrival in natural systems allowing us to reveal changes in vegetation dynamics with the arrival of non-native species. We matched fossil pollen data with botanical status information (native, non-native), and quantified the timing, trajectories and magnitude of non-native plant vegetational change on 29 islands over the past 5000 years. We recorded a proportional increase in pollen of non-native plant taxa within the last 1000 years. Individual island trajectories are context-dependent and linked to island settlement histories. Our data show that non-native plant introductions have a longer and more dynamic history than is generally recognized, with critical implications for biodiversity baselines and invasion biology