Applying Ecological Concepts to the Management of Widespread Grass Invasions

Abstract

The management of plant invasions has typically focused on the removal of invading populations or control of existing widespread species to unspecified but lower levels. Invasive plant management typically has not involved active restoration of background vegetation to reduce the likelihood of invader reestablishment. Here, we argue that land managers could benefit from the ecological principles of biotic resistance and ecological resilience in their efforts to control invading plants and restore native species. We discuss two similar but contrasting case studies of grass invasion that demonstrate how these principles can be applied to control and management. In seasonally dry Hawaiian woodlands, management of invasive fire-promoting grasses has focused on seeding native species that are resilient to fire disturbance and can coexist with grasses. Resistance to grass invasions appears to be weak in unburned native habitats. Thus, the focus of management efforts has been to increase resilience of the native vegetation to inevitable disturbance. We contrast this with the Great Basin of the western USA where the annual Mediterranean grass, Bromus tectorum, also has promoted an increase in fire frequency in shrublands and woodlands. Here, a three-tiered approach has been employed in which preventative management in the form of fire or fire surrogates is used in the initial stages of invasion to increase the resilience and resistance of the native herbaceous vegetation. In transitional stages where B. tectorum is well established but not dominant, mechanical or herbicide treatments are used to open up dense and senescing shrub canopies, thereby increasing vigor of native perennial herbaceous species through competitive release. The released competitors (perennial grasses) are then assumed to provide resistance to B. tectorum invasion. Following complete B. tectorum dominance, the focus of management is intensive seeding of native species to create resistant plant communities that reduce the likelihood of reinvasion.