California Sea Grant College Program
What Makes an Island Green? Plant Communities at Multiple Spatial and Temporal Scales
- Author(s): Danner, Eric M.
- et al.
I investigated the spatiotemporal dynamics of plant communities on islands in the Aleutian archipelago, Alaska, using small scale plots and landscape level remote sensing. Islands of the Aleutian archipelago are a model system for vegetation studies: there is no significant variation in island size, geology, soil type, or plant composition for hundreds of islands spanning 1600km of longitude. There is variation in two important factors: nutrients and climate. Past fox introductions onto some of the islands substantially reduced seabird populations that formerly vectored nutrients from the sea to land. Previous field studies have documented significant differences in vegetation composition and biomass between fox infested and fox-free islands using small scale field measurements. I examined the landscape level vegetation response to nutrient subsidies on individual islands and to a regional climate gradient across the entire archipelago. There was also evidence of a climate gradient of gradual cooling from east to west. In order to capture the full extent of the spatial and temporal variation in the system, I developed a method of using high temporal frequency, moderate spatial resolution remote sensing data to measure the landscapes of entire islands across the archipelago through time. Using this technique I calculated the seasonal phenological profiles of every island, including descriptive parameters such as length, width, and peak of the growing season. With this information I was able to show that the plot level results scaled-up to the landscape level. I documented difference in the vegetation dynamics between nutrient subsidized and non-subsidized islands, demonstrating the landscape level impact of an apex predator. I also documented a regional cooling trend in climate and associated trends in vegetation dynamics. Overall, there was lower production from east to west on fox-infested islands. However, this longitudinal trend was not always present for the vegetation parameters on fox-free islands. This suggests that the significant nutrient subsidies can override the effect of climate in this system; a pattern that is driven by an introduced apex predator.