Abstract
Alpine wetlands are one of the most at-risk ecosystems under future climate change scenarios; how these systems function and their biodiversity values have received little research attention in the temperate southern hemisphere. To contribute to this knowledge gap in current research, an alpine wetland in the Central Otago region of New Zealand was chosen to investigate water level fluctuation, standing vegetation, and the soil seed bank, in order to infer how these might respond to expected climatic changes. The End Peak wetland complex represents one of few Southern Hemisphere patterned wetlands, and is classified as a naturally uncommon ecosystem. Locally, deterioration or loss of the End Peak wetland complex would result in a loss of diversity and ecosystem function, with negative impacts on downstream communities.
This study examined two important components of wetland function: wetland hydrology and vegetation. The hydrological component involved measuring water level fluctuation across the wetland complex by setting up trail cameras to take daily photos recording water level change. There were consistent patterns across all sites; water levels gradually dropped during the summer drying phase, before rising and remaining steadily above the average for the recording period during the autumn recharge phase. However, each site had its own characteristics; some areas displayed large peaks in response to precipitation during certain parts of the season, while others had smaller peaks and were presumably better buffered hydrologically. This was attributed to the unique features of each site, in particular water body depth and below-ground processes.
Standing vegetation was investigated by setting up six transects throughout the wetland complex and recording vascular plant species and cover. This showed that the End Peak wetland complex provides a habitat for a unique plant community, including a high number of naturally uncommon species, endemics and wetland specialists. The wetland complex provides an important habitat for these species within the wider landscape, as there are few comparable wetlands that are likely to be within the dispersal range of most wetland plant species.
Finally, the soil seed bank was assessed by taking soil samples and carrying out seedling emergence trials ex situ. This showed a moderate level of similarity between the standing vegetation and the soil seed bank at the End Peak wetland complex, comparable to many other alpine or wetland soil seed bank studies. While there was no indication of seed bank taxa that had become extinct in the standing vegetation, it did highlight the high probability for invasion by exotic species such as Cirsium arvense that were not yet established in the wetland, but that were present in the soil seed bank. This likely indicates that current conditions are not yet suitable for the establishment of some exotic taxa, and that with climatic change the risk of invasion by exotic species is likely to increase, subsequently posing a significant threat to the integrity and function of this environment. The soil seed bank also allowed the identification of taxa most likely to become locally extinct in the wetland following disturbance or significant climatic changes due to their minor presence or absence in the soil seed bank.
This study has found that the End Peak wetland is both highly complex and variable in terms of both water regimes and vegetation, and it is suggested that negative impacts to the physical structure and biodiversity of the wetland are highly likely under future climate scenarios. These findings add to the current pool of knowledge regarding alpine wetlands, particularly seasonal patterns in water levels, plant community composition and soil seed bank dynamics, and relationships with the standing vegetation. With changes to ecosystems such as the End Peak wetland complex imminent, it is important to document their current state so that changes can be identified and better understood as they occur, and negative impacts to biodiversity and ecosystem function can be mitigated or prevented.