Ecophysiological traits associated with the competitive ability of invasive Australian acacias

Abstract

Aim We explored morphological and ecophysiological traits that enable invasive Australian acacias to compete with native species for resources (light, water and nutrients) necessary to support the substantial growth associated with successful invasions. Location Global. Results Invasive Australian acacias grow large and seed prolifically in invaded regions. The greater capacity for vegetative growth is underpinned by their ability to acquire and efficiently use resources in non‐native habitats. Key biological traits that enhance acquisition include (1) rapid and substantial allocation to root mass (up to 6‐fold more than co‐occurring native species) directed towards deep roots (at least 50% longer than those of natives) and to extensive shallow root networks; (2) heteroblasty, in most species, conferring high relative growth rates as bipinnate seedlings but long‐lived, nutrient‐conserving phyllodes as adults and (3) strong N2‐fixation abilities. Main conclusions The ecophysiological traits that govern the competitive interaction of invasive Australian acacias with native species are an important component of the recognized suite of factors including introduction history, human use and enemy release that combine to produce successful invasions. Traits interact to give Australian acacias competitive advantage over many native species. One such interaction is that of N2 fixation, which when coupled with slow decomposition of sclerophyllous phyllodes results in alteration of soil nutrient cycling. The lasting legacy of soil N‐enrichment hinders the competitive ability of native species and further enhances invasions. The importance of edaphic factors and competitive interactions in determining invasive success should be considered in predictive modelling of species distributions.

The Role of Plants in the Effects of Global Change on Nutrient Availability and Stoichiometry in the Plant-Soil System

“…The "weapon hypothesis" claims that the roots of alien plants exude allelopathic substances that inhibit the growth of native plants, alter soil microbial communities, and confer a competitive advantage to alien plants in the uptake of soil nutrients (Lorenzo et al, 2010;Weidenhamer and Callaway, 2010). N 2 -fixing plants can have an advantage in N-poor soils dominated by nonfixing plants (Londsdale et al, 1989;Yelenik et al, 2004;Hughes and Denslow, 2005;Morris et al, 2011). Communities dominated by legumes growing in soils with limited availabilities of soil P or water, however, are vulnerable to competition by nonfixing plants with high capacities of P uptake or stomatal control (Suriyagoda et al, 2011), and low availabilities of P reduce the chances of successful invasion by N 2 -fixing plants (Haubensak and D'Antonio, 2011).…”

Alien tree invasion into a South African montane grassland ecosystem: impact of Acacia species on rangeland condition and livestock carrying capacity

“…growth resources such as light, reducing the amount of precipitation that reaches the ground (Everson et al 2014). As a consequence, Acacia biomass can alter habitat suitability for indigenous vegetation by reducing light penetrability which changes the microclimate below the canopy tree canopy (Holmes and Cowling 1997;Morris et al 2011). Furthermore, high leaf litter content deposited under tree canopy, as evident in the densely and lightly invaded sites in this study, may change the nutrient status of the soil to be more suitable for the invading species.…”

Relationship between recruitment and mother plant vitality in the alien species Acacia cyclops A. Cunn. ex G. Don

“…The species is able to establish and survive in areas with low annual rainfall (250-300 mm: Gill, 1985;Witkowski, 1994). Like other Acacia species , A. cyclops is well adapted to Mediterranean climate and poor-nutrients environments, where it may regenerate and show a high competitive ability and a better acquisition of limiting resources, compared with that of native coexisting species (Morris et al, 2011). In particular, it is considered a transformer species in South Africa and in Portugal (Witkowski, 1994;Henderson, 2007;de Almeida and Freitas, 2006), where its invasiveness is mainly due to its large and persistent soil-stored seed bank (Milton and Hall, 1981;Richardson and Kluge, 2008).…”