The battle for suburbia: Japanese stilt-grass vs. garlic mustard – and deer

Abstract

Fragmented, suburban forests are essential for biodiversity and ecosystem services, and they offer many human communities a connection to nature. However, these forests are challenged by the dual problem of overabundant deer and invasion by multiple, potentially interacting non-native plant species. Two dominant herb layer invaders in eastern forests are garlic mustard (Alliaria petiolata) and Japanese stilt-grass (Microstegium vimineum). We have established a well-replicated factorial field experiment with all combinations of staged, novel invasions of one, both, or neither species, and exclusion or presence of deer (with fences), across six suburban New Jersey forests (224 4x4 m plots). These forests differ in ambient deer pressure, but all are in an area with about 30 deer/km2. We have measured invasion success as percent cover since the seed additions in November 2012, in order to test whether these species invade as ‘passengers’ on the ecosystem change caused by overabundant deer, and to determine if they facilitate each other’s invasion, setting the stage for a possible ‘invasional meltdown’ scenario.