Applying Ecological Concepts to the Management of Widespread Grass Invasions - Management of Invasive Weeds - page 123

of the islands they have been found to enhance the occurrence of fire (Mueller-
Dombois 1981; Tunison et al. 2001). This has occurred largely to the detriment of
native species (Hughes et al. 1991), although there is some variation in the severity
of fire impacts across environmental gradients (D'Antonio et al. 2000). Some of the
perennial grasses are resilient to fire because of rapid resprouting from basal root
crowns (Smith 1985; D'Antonio et al. 2001a). Others, however, are killed by fire
but regenerate rapidly from seed (Tunison et al. 1994, 1995; D'Antonio et al. 2000,
2001a).
Nonnative, fire-enhancing grasses have also invaded xeric and semiarid portions
of the mainland USA with large-scale ecological consequences. The most wide-
spread of these is Bromus tectorum or cheatgrass, an annual species from the east-
ern Mediterranean region. B. tectorum was widespread throughout the intermountain
western USA by the 1930s (Mack 1986) and was associated with widespread
increases in fire frequency and size and declines in native species a few decades
later (e.g., Whisenant 1990). This species increases fire frequency and size by
increasing the homogeneity or horizontal continuity of fuels and the rate of fire
spread across what is otherwise a patchy shrub-steppe ecosystem that experiences
summer dry lightning (Link et al. 2006). Because of rapid spring growth and early
maturation, B. tectorum plants typically produce seeds prior to the fire season.
Populations recover rapidly after fire via dormant seeds not killed by fire and very
high seed output due to increased resource availability in the years following fire.
Many of the native shrub species in these ecosystems are killed by fire, and in areas
with depleted herbaceous understories, B. tectorum can rapidly dominate the
ecosystem (e.g., Whisenant 1990).
7.1.3 ChapterOverview
In this chapter, we use two case studies to emphasize a way to incorporate ecologi-
cal concepts into the management of persistent plant invaders. The example of grass
invasions in Hawaii that we describe is a case study of a situation in which ecologi-
cal resistance plays little role in the planning and implementation of control and
revegetation of grass-invaded, fire-prone ecosystems. In Hawaii Volcanoes National
Park's drier lowlands and mid-elevation habitats, exotic grasses have invaded virtu-
ally every place they could have invaded, and degradation and invader seed sources
are widespread. Management is focusing on creating resilient native plant assem-
blages that can coexist with the invasive grasses particularly after fire has already
occurred. Technically this is a restorative activity rather than ecosystem restoration
(sensu Jordan 2003). Nonetheless, the goal is to create communities with some of
the desired attributes of a restored ecosystem (http://www.ser.org/). By contrast with
the Hawai'i example, grass invasions in the Great Basin of the USA are not com-
plete and some potentially resilient native communities still exist. In sites that have
not converted to complete B. tectorum dominance, management is focusing on
maintaining native resilience while increasing resistance to invasion. In vast areas