Assessing an exotic plant surveying program in the Mojave Desert, Clark County, Nevada, USA

Abstract

Exotic species can threaten native ecosystems and reduce services that ecosystems provide to humans. Early detection of incipient populations of exotic species is a key step in containing exotics before explosive population growth and corresponding impacts occur. We report the results of the first three years of an exotic plant early detection and treatment program conducted along more than 3,000 km of transportation corridors within an area >1.5 million ha in the Mojave Desert, USA. Incipient populations of 43 exotic plant species were mapped using global positioning and geographic information systems. Brassica tournefortii (Sahara mustard) infested the most soil types (47% of 256) surveyed in the study area, while Nicotiana glauca (tree tobacco) and others currently occupy less than 5% of soil types. Malcolmia africana (African mustard) was disproportionately detected on gypsum soils, occurring on 59% of gypsum soil types compared to 27% of all surveyed soils. Gypsum soils constitute unique rare plant habitat in this region, and by conventional wisdom were not previously considered prone to invasion. While this program has provided an initial assessment of the landscape-scale distribution of exotic species along transportation corridors, evaluations of both the survey methods and the effectiveness of treating incipient populations are needed. An exotic plant information system most useful to resource mangers will likely include integrating planning oriented coarse-scale surveys, more detailed monitoring of targeted locations, and research on species life histories, community invasibility, and treatment effectiveness.

Assessing the extent and the environmental drivers of Eucalyptus globulus wildling establishment in Portugal: results from a countrywide survey

“…Most eucalypt wildlings detected in this study were taller than 30-40 cm, as smaller seedlings were difficult to see (occasionally larger and already reproductive saplings, up to 5 m high, were also spotted). Other studies used similar approaches to detect alien species on roadsides (Abella et al 2009;Milton and Dean 1998;Shuster et al 2005;Wilson et al 1992). This method was chosen because it allows a fast assessment of large areas, facilitated in this case by the conspicuous nature of eucalypt wildlings (bluish colour), and because roadsides are public domain and not cultivated, which strongly increases the confidence that plants are wildlings (naturally established).…”

“…For example roadsides are often associated with a higher availability of light, water and nutrients (Gelbard and Belnap 2003), which may favour wildling establishment (Florence 1996). The preference of invasive exotic species for disturbed sites like roadsides has been referred by several authors (Abella et al 2009;Milton and Dean 1998;Wilson et al 1992). On the other hand, the fact that many roadsides are managed using mowing equipment, may counteract the higher suitability of these places for wildling establishment.…”

Responses of native and non-native Mojave Desert winter annuals to soil disturbance and water additions

“…We selected five sites based on land management records of non-native species occurrences (Abella et al 2009) to evaluate our experimental treatments. Field surveys of non-native species indicated that the populations we selected were in the early stages of establishment.…”

“…Brassica tournefortii is a winter annual native to the southern and eastern parts of the Mediterranean rim, where it establishes viable populations on sandy soils (Thanos et al 1991). In the Mojave Desert in southern Nevada, B. tournefortii has spread into a variety of habitats, including gypsum-derived soils (which are inhabited by numerous rare endemic plant species) (Abella et al 2009). As a winter annual, B. tournefortii seeds germinate after winter rainfall (October through April) and before many of the native annuals.…”

Factors affecting exotic annual plant cover and richness along roadsides in the eastern Mojave Desert, USA

“…In deserts, road verges may host relatively greater native-plant biomass because of increased water collection at road edges (Starr and Mefford, 2002). Consequently, monitoring programs for exotic plants have focused on roadside surveys in the Mojave Desert (Abella et al, 2009) even though there are no published documents indicating that distributions of exotic species in the Mojave Desert are limited to roadsides.…”