Population Ecology of Hybrid Mesquite (Prosopis Species) in Western Australia: How Does it Differ from Native Range Invasions and What are the Implications for Impacts and Management?

Abstract

Beneficial exotic trees and shrubs have been widely spread throughout semiarid and arid regions of the world. These trees and shrubs can however cause severe negative impacts. Mesquite (Prosopis species), native to the New World, is one example which continues to be promoted despite causing serious impacts both in its native and introduced ranges. We describe the population structure of the largest population of fire-tolerant hybrid mesquite (P. velutina  P. glandulosa var. glandulosa  P. pallida) in Australia, which was intentionally established in the 1930s. We compare it with invasive populations within its native range, and consider the implications for managing exotic mesquite invasions. We found relatively high juvenile densities at all levels of canopy cover (<30% to 90-100%), and low mortality rates for both juveniles and adults (<2%/y), which suggests that populations are still in an early phase of invasion. Exotic populations differed from native range populations in being more dense (average 4,859 adults/ha), having a sizable sapling (seedling and juvenile) bank that can remain quiescent under canopy cover (average 10,914 seedlings and juveniles/ha), failing to act as nurse plants for native shrubs (<8 native shrubs/ha), and almost totally excluding the herbaceous (grass) layer (average 0.3% cover). Our results suggest that ecosystem impacts in the introduced range are likely to be even worse, and management even more difficult, than has already been reported for invasions within its native range. The lack of feasible means for managing highly invasive, broad-scale mesquite populations need to be addressed, and needs to be considered explicitly when promoting mesquite as a beneficial plant.

Testing the discrimination and detection limits of WorldView-2 imagery on a challenging invasive plant target

“…The development of quantitative, repeatable mapping techniques is a priority for guiding management activities (Hennessy et al, 1983;Gibbens et al, 1992;Goslee et al, 2003). This can be challenging because mesquite often coexist with structurally similar shrubs, and invasions often begin as individual plants that form clumps before coalescing to form monocultures (Archer, 1995;van Klinken et al, 2006). Furthermore, the largest population in Australia, located in the Pilbara Region (north-western Australia) remains heavily defoliated since the release of a defoliating biocontrol agent in 1998 (van Klinken et al, 2003).…”

Detection of two intermixed invasive woody species using color infrared aerial imagery and the support vector machine classifier

“…Remote sensing techniques for accurate mapping of invasion offer a unique set of advantages including repeatability, large area coverage, and cost-effectiveness over ground-based methods over time and space. [34][35][36] Extent of mesquite distribution has been well reported from southwestern United States, South America, Australia, and India, [37][38][39][40] while that of juniper distribution is well recorded. 19,[41][42][43] As both species occupy a significant area of grasslands and rangelands, their invasion has raised several environmental concerns around the world.…”

Plant invasions in arid areas: special problems and solutions: a South African perspective

“…The wild spiny form, presumably originating from seeds and avoided by livestock, became invasive a century later (Annecke and Moran 1978). Similarly, Prosopis glandulosa, P. juliflora and P. velutina were introduced to South Africa during the late 1800s; large scale invasions began some 60 years later and involved mainly hybrids of P. glandulosa (Moran et al 1993) as did Prosopis invasions in arid Australia (van Klinken et al 2006).…”

“…They also form stands that are denser and less penetrable than those of indigenous trees or shrubs (van Klinken et al 2006) and therefore restrict access to animals, including large insects (Steenkamp and Chown 1996). On the other hand, architectural differences between indigenous trees and their alien equivalents lead indirectly to changes in vegetation structure.…”

“…Xerophytic and arid adapted plants such as succulents (Asphodelaceae, Cactaceae, Mesembryanthemaceae) and saltbushes (Atriplex species), have been widely exchanged among deserts for use in horticulture and agriculture, as have certain reeds (Arundo donax) and trees tolerant of wet and dry cycles (Eucalyptus, Prosopis) or saline water (Tamarix). The diversity of invasive alien plants invading arid South Africa may be relatively low ), but includes most of the species or genera that are globally recognised for transforming ecosystems, invading key resource areas and wetlands and having negative impacts on biodiversity, water resources and local economies (Fagg and Stewart 1994;van Klinken et al 2006).…”