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.

The vanishing and the establishment of a new ecosystem on an oceanic island - Anthropogenic impacts with no return ticket.

A multiproxy approach was applied to a sediment core retrieved from the deep crater Lake Funda, located in the middle of the North Atlantic Ocean on Flores Island, Azores archipelago (Portugal). The purpose of this study was to determine how this ecosystem responded to natural and anthropogenic forces over the last millennium. We distinguished three main phases in lake evolution using multiproxy reconstructions and documentary sources. (A) Climate and lake catchment processes, as well as internal ones, were the main drivers of ecosystem variability before 1335 CE, when human disturbances were absent in the Lake Funda catchment. (B) The second phase is marked by unprecedented changes in all studied proxies between 1335 and 1560 CE, including abrupt changes in the composition and diversity of diatom and chironomid assemblages. Synergistic effects from high climate variability and the onset of human disturbances in the catchment (e.g., introduction of livestock) during the Medieval Climate Anomaly-Little Ice Age transition, led to an increase in lake trophic state from mesotrophic to eutrophic conditions. (C) In the last phase (1560 CE to the present), the eutrophic conditions in Lake Funda were maintained through a positive feedback loop between lake productivity and in-lake phosphorous recycling. Variability within the lake ecosystem was mainly associated with climate variability and internal lake dynamics (e.g., phosphorus remobilization). Our results show that a paleoecological approach is crucial to understanding lake ecological states in the present-day in order to develop locally adapted management and restoration strategies. A long-term perspective enables us to understand the harmful consequences of ongoing climate change and human disturbances on lake ecosystems.

Climate change facilitated the early colonization of the Azores Archipelago during medieval times.

Humans have made such dramatic and permanent changes to Earth's landscapes that much of it is now substantially and irreversibly altered from its preanthropogenic state. Remote islands, until recently isolated from humans, offer insights into how these landscapes evolved in response to human-induced perturbations. However, little is known about when and how remote systems were colonized because archaeological data and historical records are scarce and incomplete. Here, we use a multiproxy approach to reconstruct the initial colonization and subsequent environmental impacts on the Azores Archipelago. Our reconstructions provide unambiguous evidence for widespread human disturbance of this archipelago starting between 700-60+50 and 850-60+60 Common Era (CE), ca. 700 y earlier than historical records suggest the onset of Portuguese settlement of the islands. Settlement proceeded in three phases, during which human pressure on the terrestrial and aquatic ecosystems grew steadily (i.e., through livestock introductions, logging, and fire), resulting in irreversible changes. Our climate models suggest that the initial colonization at the end of the early Middle Ages (500 to 900 CE) occurred in conjunction with anomalous northeasterly winds and warmer Northern Hemisphere temperatures. These climate conditions likely inhibited exploration from southern Europe and facilitated human settlers from the northeast Atlantic. These results are consistent with recent archaeological and genetic data suggesting that the Norse were most likely the earliest settlers on the islands.

The human dimension of biodiversity changes on islands.

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.

Island biodiversity conservation needs palaeoecology.

The discovery and colonization of islands by humans has invariably resulted in their widespread ecological transformation. The small and isolated populations of many island taxa, and their evolution in the absence of humans and their introduced taxa, mean that they are particularly vulnerable to human activities. Consequently, even the most degraded islands are a focus for restoration, eradication, and monitoring programmes to protect the remaining endemic and/or relict populations. Here, we build a framework that incorporates an assessment of the degree of change from multiple baseline reference periods using long-term ecological data. The use of multiple reference points may provide information on both the variability of natural systems and responses to successive waves of cultural transformation of island ecosystems, involving, for example, the alteration of fire and grazing regimes and the introduction of non-native species. We provide exemplification of how such approaches can provide valuable information for biodiversity conservation managers of island ecosystems.