A 2000 year history of vegetation and landscape change in Hawke's Bay, North Island, New Zealand

Sediment cores from four lakes in the Tutira and Putere districts of Hawke's Bay, North Island, New Zealand, are analysed for the remains of pollen, charcoal, tephra and erosion pulses to reconstruct a 2000 year history of vegetation and landscape change. The Hawke's Bay region is disturbed frequently by earthquakes, volcanic eruptions, cyclonic storms, droughts and fire. This thesis determines how the vegetation and soil stability have responded to some of these disturbances, through detailed palaeoecological investigations of lake sediment cores. Studies of surface pollen and differential pollen and spore preservation were undertaken to enhance the interpretations made from the palaeoecological record. Because New Zealand has only been settled by Polynesians relatively recently, the effects of natural disturbance on the vegetation and landscape can be assessed under similar climatic conditions to the present, but in the absence of cultural change. The effects of human settlement on a previously uninhabited landscape are assessed and compared with previously occurring natural disturbances

Floristic homogenization of South Pacific islands commenced with human arrival

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

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