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The increasing similarity of plant species composition among distinct areas is leading to the homogenization of ecosystems globally. Human actions such as ecosystem modification, the introduction of non-native plant species and the extinction or extirpation of endemic and native plant species are considered the main drivers of this trend. However, little is known about when floristic homogenization began or about pre-human patterns of floristic similarity. Here we investigate vegetation trends during the past 5,000 years across the tropical, sub-tropical and warm temperate South Pacific using fossil pollen records from 15 sites on 13 islands within the biogeographical realm of Oceania. The site comparisons show that floristic homogenization has increased over the past 5,000 years. Pairwise Bray-Curtis similarity results also show that when two islands were settled by people in a given time interval, their floristic similarity is greater than when one or neither of the islands were settled. Importantly, higher elevation sites, which are less likely to have experienced human impacts, tended to show less floristic homogenization. While biotic homogenization is often referred to as a contemporary issue, we have identified a much earlier trend, likely driven by human colonization of the islands and subsequent impacts., (© 2024. The Author(s).)

Islands are among the last regions on Earth settled and transformed by human activities, and they provide replicated model systems for analysis of how people affect ecological functions. By analyzing 27 representative fossil pollen sequences encompassing the past 5000 years from islands globally, we quantified the rates of vegetation compositional change before and after human arrival. After human arrival, rates of turnover accelerate by a median factor of 11, with faster rates on islands colonized in the past 1500 years than for those colonized earlier. This global anthropogenic acceleration in turnover suggests that islands are on trajectories of continuing change. Strategies for biodiversity conservation and ecosystem restoration must acknowledge the long duration of human impacts and the degree to which ecological changes today differ from prehuman dynamics., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Contrary to expectations, some human-modified landscapes are considered to sustain both human activities and biodiversity over the long-term. Agroforestry systems are among these landscapes where crops are planted under native shade trees. In this context, ancient agroforestry systems can provide insight into how farmers managed the landscape over time. Such insight can help to quantify the extent to which tropical forests (especially habitat-specialist trees) are responding to local and landscape-level management. Here, we extracted fossil pollen (indicator of past vegetation changes) and macroscopic charcoal (indicator of biomass burning) from four forest hollows’ sedimentary sequences in an ancient agroforestry system in Western Ghats, India. We used a mixed-modelling approach and a principal components analysis (PCA) to determine past trajectories of forest change and species composition dynamics for the last 900 years. In addition, we reconstructed the long-term forest canopy dynamics and examined the persistence of habitat-specialist trees over time. Our results show that the four sites diverged to a surprising degree in both taxa composition and dynamics. However, despite these differences, forest has persisted over 900 years under agricultural activities within agroforestry systems. This long-term analysis highlights the importance of different land-use legacies as a framework to increase the effectiveness of management across tropical agricultural lands. [ABSTRACT FROM AUTHOR]

This paper presents a study of phytoliths (opal silica bodies from plants) from sediment sequences obtained from two tropical forest patches in the Western Ghats of India: a sacred grove (sequence covers last 550 cal BP) and a forest patch in a plantation (sequence covers last 7500 cal BP). The sites are located at mid-elevation (c. 650–1400 m above sea level) in a mosaic landscape showing anthropogenic open habitats and plantations as well as some evergreen forests. The aim of this paper is to evaluate the landscape composition of grassland and forest over time in the region, grassland being invariably shaped by anthropogenic activities, particularly fire for cultivation. We identified and classified phytoliths into 34 morphotypes from five taxonomic groups: Poaceae (grasses), Cyperaceae (sedges), Arecaceae (palms), Pteridopsida (ferns) and woody dicotyledons (broad-leaved trees and shrubs). We also calculated the humidity–aridity index (Iph). First, our results show that grasses are the most represented phytolith types in both sites, followed by broad-leaved trees and shrubs, palms, sedges, and ferns. Second, the highly variable climatic index Iph over the last 1000 years suggest that changes in phytolith percentage (e.g. broad-leaved trees) might be caused by human agro-pastoral activities, such as clearing through fires and irrigation. Prior to these human activities, the phytolith signal for early Holocene climate is congruent with the existing literature. Finally, this study compares new phytolith results with previous pollen data from the same sites. We find good agreement between these two botanical proxies throughout, thus validating our findings. We provide important evidence regarding the history of environmental change due to anthropogenic activities in the Western Ghats. This has important implications because it provides insights into how tropical forest will respond to increased intensity of human activities. [ABSTRACT FROM AUTHOR]

Biological conservation and environmental management are increasingly focussing on the preservation and restoration of ecosystem services (i.e. the benefits that humans receive from the natural functioning of healthy ecosystems). Over the past decade there has been a rapid increase in the number of palaeoecological studies that have contributed to conservation of biodiversity and management of ecosystem processes; however, there are relatively few instances in which attempts have been made to estimate the continuity of ecosystem goods and services over time. How resistant is an ecosystem service to environmental perturbations? And, if damaged, how long it does it take an ecosystem service to recover? Both questions are highly relevant to conservation and management of landscapes that are important for ecosystem service provision and require an in-depth understanding of the way ecosystems function in space and time. An understanding of time is particularly relevant for those ecosystem services – be they supporting, provisioning, regulating or cultural services that involve processes that vary over a decadal (or longer) timeframe. Most trees, for example, have generation times >50 years. Understanding the response of forested ecosystems to environmental perturbations and therefore the continuity of the ecosystem services they provide for human well-being – be it for example, carbon draw-down (regulating service) or timber (provisioning service) – requires datasets that reflect the typical replacement rates in these systems and the lifecycle of processes that alter their trajectories of change. Therefore, data are required that span decadal to millennial time-scales. Very rarely, however, is this information available from neo-ecological datasets and in many ecosystem service assessments, this lack of a temporal record is acknowledged as a significant information gap. This review aims to address this knowledge gap by examining the type and nature of palaeoecological datasets that might be critical to assessing the persistence of ecosystem services across a variety of time scales. Specifically we examine the types of palaeoecological records that can inform on the dynamics of ecosystem processes and services over time – and their response to complex environmental changes. We focus on three key areas: a) exploring the suitability of palaeoecological records for examining variability in space and time of ecosystem processes; b) using palaeoecological data to determine the resilience and persistence of ecosystem services and goods over time in response to drivers of change; and c) how best to translate raw palaeoecological data into the relevant currencies required for ecosystem service assessments. [ABSTRACT FROM AUTHOR]

Aim The aim of the present study was to describe the diversity patterns along elevational gradients that are crucial for conservation management and for understanding diversification processes in montane environments. This article analyses the distributional range and elevation patterns of endemic and non-endemic (NE) vascular plants living on a unique set of Neotropical table mountains ( tepuis). To investigate the potential causes of the high degree of diversity and endemism we tested the role of elevation, area and the mid-domain effect (MDE). We also aimed to discuss the origin of the current tepuian biota. Location The Guayana Highlands (northern South America). Emphasis is placed on the mountaintops above 1500 m elevation, which form the highly biodiverse Pantepui biogeographical province. Methods We examined the distribution patterns of vascular plant species richness in relation to elevation, area, and the MDE using generalized additive models. We used Range Model for the MDE. Results We found that regional endemics richness show a hump-shaped curve in relation to elevation. Single-tepui endemics (STE) increase with elevation, whereas NE and total species richness decrease. Area and MDE influence this pattern for Pantepui and STE, but not for NE. We also observed that the spatial distribution of endemic richness displays a left-skewed distribution pattern due to the dominance of STE. Main conclusions Our results demonstrate that a combination of elevation, area and MDE provide a basic explanation for the diversity of vascular plants in Pantepui. In addition, the present study indicates that maxima of STE are located at the highest altitudes, where the possibility of biotic connection (via migration) and gene flux has been minimal, even during glacial phases when most migration pathways amongst the tepui mountains were open. We also suggest that climatic filtering due to the extreme conditions atop the tepuis and low dispersal capacity stand out as the main drivers of the decline in NE species richness with elevation. [ABSTRACT FROM AUTHOR]

Garajonay National Park in La Gomera (Canary Islands) contains one of the largest remnant areas of a forest formation once widespread throughout Europe and North Africa. Here, we aim to address the long-term dynamics (the last 9600 cal. years) of the monteverde forest (laurel forest and Morella-Erica heath) located close to the summit of the National Park (1487 m a.s.l.) and determine past environmental and human impacts., We used palaeoecological (fossil pollen, microscopic and macroscopic charcoal) and multivariate ecological techniques to identify compositional change in the monteverde forest in relation to potential climatic and human influences, based on the analysis of a core site at 1250-m elevation., The regional mid-Holocene change towards drier conditions was matched in this system by a fairly rapid shift in representation of key forest elements, with declines in Canarian palm tree ( Phoenix canariensis), Canarian willow ( Salix canariensis) and certain laurel forest taxa and an increase in representation of the Morella-Erica woody heath., Charcoal data suggest that humans arrived on the island between about 3000 and 1800 years ago, a period of minimal vegetation change. Levels of burning over the last 800 years are among the lowest of the entire 9600 years., Synthesis. A rapid climatic-induced shift of forest taxa occurred 5500 years ago, with a decrease in hygrophilous species in the pollen record. In contrast, we found no evidence of a significant response to human colonization. These findings support the idea that Garajonay National Park is protecting a truly ancient relict, comprising a largely natural rather than cultural legacy. [ABSTRACT FROM AUTHOR]

This work aims to estimate the potential effects of the global warming projected for the twenty-first century on the biodiversity of a remote and pristine region of the Neotropics called Pantepui. Habitat loss and fragmentation by upward migration of bioclimatic conditions is analyzed using Species-Area Relationships (SAR) and Altitudinal Range Displacement (ARD) analysis. The ARD is a tool that uses the present-day lapse rate to estimate the upward migration of the species based on the global warming predicted by the IPCC. The results show that around 80% of the vascular flora, ca. 1,700 species of which up to 400 would be Pantepui endemics, are threatened of extinction. These estimates should be considered preliminary, but the danger is real. Therefore, suitable conservation or mitigation strategies are needed. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented which discusses the bureaucratic challenges of conducting biodiversity research in the Guayana Highlands of Venezuela.