Direct and indirect effects of invasion by the alien tree Ailanthus altissima on riparian plant communities and ecosystem multifunctionality

Abstract

Most existing studies addressing the effects of invasive species on biodiversity focus on species richness ignoring better indicators of biodiversity and better predictors of ecosystem functioning such as the diversity of evolutionary histories (phylodiversity). Moreover, no previous study has separated the direct effect of alien plants on multiple ecosystem functions simultaneously (multifunctionality) from those indirect ones mediated by the decrease on biodiversity caused by alien plants. We aimed to analyze direct and indirect effects, mediated or not by its effect on biodiversity, of the invasive tree Ailanthus altissima on ecosystem multifunctionality of riparian habitats under Mediterranean climate. We measured vegetation attributes (species richness and phylodiversity) and several surrogates of ecosystem functioning (understory plant biomass, soil enzyme activities, available phosphorous and organic matter) in plots infested by A. altissima and in control (non-invaded) ones. We used structural equation modelling to tease apart the direct and indirect effects of A. altissima on ecosystem multifunctionality. Our results suggest that lower plant species richness, phylodiversity and multifunctionality were associated to the presence of A. altissima. When analyzing each function separately, we found that biodiversity has the opposite effect of the alien plant on all the different functions measured, therefore reducing the strength of the effect (either positive or negative) of A. altissima on them.Soraya Constán-Nava and Santiago Soliveres have contributed equally to this work. Electronic supplementary materialThe online version of this article (This is one of the few existing studies addressing the effect of invasive species on phylodiversity and also studying the effect of invasive species on multiple ecosystem functions simultaneously.

Impact of pine invasion on the taxonomic and phylogenetic diversity of a relict Mediterranean forest ecosystem

“…Loss of taxonomic diversity in the pine stands implied a parallel reduction of phylogenetic diversity, which confirms recent evidence showing the impact of invading tree species on Mediterranean plant communities (Lapiedra et al, 2015;Constán-Nava et al, 2015). As found in previous studies in different areas and ecosystems (Forest et al, 2007;Qian et al, 2014) these indices were distributed in a similar manner and positively associated (Fig.…”

“…According to Faith (1992), this can be defined as the total amount of evolutionary distance among plant species in a community, which is determined by how related species are to each other. Such a ''deep" component of diversity has been suggested to be relevant for ecosystem functioning (Srivastava et al, 2012) and services (Faith et al, 2010) as well as processes such as extinction (Purvis et al, 2000) and biotic invasion (Winter et al, 2009;Lapiedra et al, 2015;Constán-Nava et al, 2015). According to Winter et al (2009), the latter has the potential to cause dramatic changes of also the phylogenetic diversity of native plant assemblages.…”

A niche for ecosystem multifunctionality in global change research

“…Where present, hypotheses of abiotic mechanisms were most clearly stated in the case of invasive or domestic species that have physical effects on biogeochemical cycling (Constán‐Nava et al, ; Zhang et al, ). For example, in addition to altering local diversity, invasive plants may alter soil or sediment properties, such as water retention, stability, and biogeochemical cycling (Constán‐Nava et al, ; Quero, Maestre, Ochoa, García‐Gómez, & Delgado‐Baquerizo, ; Ramus et al, ). The activities of grazers may also impact soil properties and processes through trampling and dung and urine deposition (Allan et al, ; Peco, Navarro, Carmona, Medina, & Marques, ; Sircely & Naeem, ; Vandandorj et al, ; Zhang et al, ), resulting in altered EMF (Figure b).…”

“…Indeed, nearly half of the reviewed studies explicitly investigated the relative role of different mechanisms with a SEM approach. In some cases, abiotic‐mediated effects on EMF were generally stronger (though these were often not explicitly defined and more typically shown as “direct effects”; Constán‐Nava et al, ; Peco et al, ; Zhang et al, ), while biodiversity‐mediated effects were important in other cases (Delgado‐Baquerizo et al, ; Liu et al, ; Luo et al, ). Such discrepancies among studies are likely due to the different types of mechanisms tested, as well as variation in the measurement of EMF and the global change drivers in question.…”

Review on Invasive Tree of Heaven (Ailanthus altissima (Mill.) Swingle) Conflicting Values: Assessment of Its Ecosystem Services and Potential Biological Threat

“…Introduced species may become invasive and displace native species, modify habitats, change community structure, affect ecosystem processes or wider ecosystem functioning, impede the provision of ecosystem services, and cause substantial economic losses (Blackburn et al 2004;Pimentel et al 2005;Vilà et al 2010;Gatto et al 2013;Constán-Nava et al 2015). They are a product of human redistribution of species to support agriculture, forestry, mariculture, horticulture, and recreation, as well as the results of accidental introductions (van Wilgen et al 2008).…”