Biodiversity and invasive grass species: multiple-use or monoculture?

Abstract

Invasive plants are recognised as a major threat to biodiversity conservation worldwide. Despite this recognition, our understanding of the mechanisms controlling the invasion process and its impact on flora and fauna is often poor. We examined the impact of an invasive aquatic grass species, para grass (Urochloa mutica), on seasonally inundated wetlands in tropical northern Australia. Flora and avifauna were surveyed at sites invaded by para grass and in native vegetation. Spatial information systems were used to design surveys and determine environmental correlates of para grass distribution and so predict the potential future spread of para grass and infer impacts in the absence of control. Where para grass was present the median number of plant taxa was ~75% lower. Few birds showed preference for habitats invaded by para grass, and most birds were associated with areas of native vegetation or other habitats with little or no para grass. The study identified several wetland habitats that are at greater risk of invasion, based on the apparent habitat preferences of para grass. The degradation or loss of some of these 'at-risk' habitats, including Oryza meriodionalis grasslands that play an integral role in the wetland food chain, has important ramifications for the levels of biodiversity supported by the wetlands.

Unassisted invasions: understanding and responding to Australia’s high-impact environmental grass weeds

“…In some cases they were invading relatively empty niches such as mudflats (see above); in others they appeared better adapted to inundation regimes than native species, thereby becoming dominant (Ferdinands et al 2005).…”

Why non-native grasses pose a critical emerging threat to biodiversity conservation, habitat connectivity and agricultural production in multifunctional rural landscapes

“…The most obvious process is for infestations to form virtual monocultures in which other ground layer species (Ferdinands et al 2005) are excluded from the recipient assemblage. Most NNGs grow rapidly and produce large amounts of standing biomass, which generates intense competition for soil nutrients, water and light with smaller understory or riparian plants (e.g., McArdle et al 2004;Perna et al 2012).…”

Fire, landscape heterogeneity and wildlife management in Australia's tropical savannas: introduction and overview

“…The remaining papers in the volume focus on other anthropogenic drivers of change in the savannas, including invasive plants and harvest and how such influences might be better managed. Ferdinands et al (2005) describe a growing threat to ecologically and economically critical elements of the savanna landscape, namely pasture grasses invading seasonally inundated floodplain wetlands. These areas are particularly significant for pastoralism in the Top End, with large numbers of cattle being agisted there in the dry season, fattening before live export.…”

“…Particular implications are: (1) Interventions need to be focused on the highest-priority issues, so there must be an active process for setting and reviewing priorities. (2) Presently loose regulation of the introduction and use of exotic plants (Ferdinands et al 2005) and animals (especially those already present in the country) needs to be strengthened, preferably through legislation that establishes mechanisms for independent review. (3) The role of existing, and preferably expanded, reserve networks will be pivotal, and improved systems for reporting on the extent to which they have achieved operational and conservation goals will be critical (Price et al 2005a).…”

“…For example, in the case of granivorous birds, studies are most likely to be incisive in regions where rainfall variance is greatest and at sites with strongly contrasting grazing histories (Franklin et al 2005). (4) Well articulated models (preferably quantitative) should be developed to explore the implications of changed management practice on the hypothesised dependencies of wildlife on particular resources (Woinarski et al 2005;Bradstock et al 2005;Ferdinands et al 2005;Whitehead 2005a, 2005b). (5) There is an acute need for better understanding of realistic options for employment in regional (chiefly Aboriginal) communities, including natural and cultural resource management, and valuation of the ecosystem services that such work can deliver to the wider Australian community.…”