Reproductive biology of Australian acacias: important mediator of invasiveness?

Abstract

Aim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life-history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness.Location Global.Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating an Acacia phylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non-invasive (129) species. We also explore the distribution of groups of trait 'syndromes' between invasive and non-invasive species.Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non-invasive species. These data suggest that invasives reach reproductive maturity earlier (10/ 13 within 2 years vs. 7/26 for non-invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire-, heat-or disturbance-triggered germination cues.Conclusions Invasive species respond quicker to disturbance than non-invasive taxa. Traits found to be significant in our study require more in-depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species-rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions.

Why so many flowers? A preliminary assessment of mixed pollination strategy enhancing sexual reproduction of the invasive <i>Acacia longifolia</i> in Portugal

“…In A. longifolia, Kenrick and Knox (1982) found up to 12 seeds per pod as a result of open pollination in Australia, while we found 10 seeds and Correia et al (2016) found less than 6 seeds in Portugal. Acacia is a genus that invests a lot of resources in massive flowering (Gibson et al, 2011). Acacia longifolia flowering branches are very abundant on a given plant, and number of inflorescences and flower heads and flowers are impressive (Tybirk, 1997;Fernandes et al, 2015).…”

<i>Acacia cyclops</i> A. Cunn. ex G. Don (Leguminosae) in Italy: first cases of naturalization

“…However, two insects have recently provided a significant reduction in Acacia cyclops seed production (Impson & al., 2004;Post & al., 2010), and biological control appears to be the most effective and cost-saving method for curbing the Acacias reproductive potential and related invasiveness (Richardson & Kluge, 2008). Because of the substantial absence of vegetative propagation (Gill, 1985;Gibson & al., 2011), A. cyclops establishment and invasive success is strongly dependant on a copious production of viable seeds and their subsequent dispersal (Milton & Hall, 1981;Holmes, 1988). In particular, its seeds with attractive arils are well adapted for bird dispersal whilst they are retained in the canopy (Glyphis & al., 1981), but once the seeds have fallen to the ground, ants and small rodents may also spread them or carry them into the deeper soil layers, thus increasing the likelihood of their being added to the soil seed-bank (Holmes, 1989;Richardson & Kluge, 2008 fery & al., 1988;Holmes, 1989), rather it depends upon chemical scarification, notably after the passage through the gut of birds, or to only moderate heating in order to break dormancy (Glyphis & al., 1981;Gill, 1985;Jeffery & al., 1988).…”

Invasive Acacia mearnsii De Wilde in Kunming, Yunnan Province, China: a new biogeographic distribution that Threatens Airport Safety

“…Meanwhile, interference by construction activities enhances invasion ability of A. mearnsii, because it can help break seed dormancy underground. Finally, the weedy characteristics are also key drivers of invasive success (Gibson et al 2011;Low 2012), such as long-lasting inflorescences, a variety of dispersal pathways, the ability to re-sprout and germinate in abundance following disturbance, and high growth rates. All result in the emergence of a large number of tree seedlings after environmental adaptation in grass-planting area at the airport.…”

“…The trees attract many birds to rest on them, which increases the opportunities for bird strike at the airport (Gallagher et al 2011;Gibson et al 2011;Li 2014;Li et al 2011;Xu et al 2011). We undertook an A. mearnsii invasion survey, which is the first time in China that a detailed monitoring investigation of this species has been performed.…”