My group is studying plant-herbivore interactions in coastal terrestrial environments in the Arctic and in northern California. We are determining how herbivores affect the structure and function of plant and soil communities via different feedback processes. In northern California a nitrogen-fixing lupine species is invading the Californian coastal prairie which is rich in native plant species.
Insects kill the lupine and the nitrogen is released into the soil.
Invasive, fast growing alien grasses replace the lupine and utilize the nitrogen-enriched soil until a new lupine crop establishes. Under these conditions the majority of the native species are unable to compete either with the lupine or with the fast growing grasses, hence species diversity declines. In the Arctic the soils are nitrogen-limited. Faecal nitrogen produced by geese increases the turnover of nitrogen in these systems. A series of feedbacks has led to habitat destruction as a result of foraging by the birds which are colonial.