Acer negundo invasion along a successional gradient: early direct facilitation by native pioneers and late indirect facilitation by conspecifics

Abstract

Summary Here, we analysed the role of direct and indirect plant interactions in the invasion process of Acer negundo along a natural successional gradient in the Middle Rhone floodplain (France). We addressed two questions: What are the responses of the invasive Acer seedlings to native communities’ effects along the successional gradient? What are the effects of the invasive Acer adult trees on the native communities? In the three communities (Salix, Acer and Fraxinus stands) we transplanted juveniles of the invasive and juveniles of the natives within the forest and in experimental gaps, and with and without the herb layer. We also quantified changes in understory functional composition, light, nitrogen and moisture among treatments. Acer seedlings were directly facilitated for survival in the Salix and Acer communities and indirectly facilitated for growth by adult Acer through the reduction of the abundance of highly competitive herbaceous competitors. We conclude that direct facilitation by the tree canopy of the native pioneer Salix is very likely the main biotic process that induced colonization of the invasive Acer in the floodplain and that indirect facilitation by adult conspecifics contributed to population establishment.

Experimental evidence for indirect facilitation among invasive plants

“…However, further experimental work is needed to determine the relative contributions of different mechanisms for facilitation of Alliaria by Microstegium, including the possible roles of alteration of microbial or herbivore (Parker, Burkepile & Hay 2006) communities. For example, invasive plants can alter soil microbial communities or nutrient availability, thereby providing more suitable conditions for conspecific (Lee, Flory & Phillips 2012) Maron & Connors 1996;Saccone et al 2010) or facilitation across trophic levels such as when animals facilitate invasive plants (Nuzzo, Maerz & Blossey 2009). Despite the lack of examples thus far, ongoing introductions of species to novel habitats may increase the co-occurrence of species with different phenologies or resource requirements (Fridley 2012) and promote indirect facilitation among invasive plant species (Kuebbing, Nuñez & Simberloff 2013).…”

“…Similarly, intraspecific facilitation can occur when adult invasive plants provide favourable abiotic conditions for offspring (Reinhart, Maestre & Callaway 2006;Saccone et al 2010). Facilitation across trophic levels may also occur, such as when an invasive plant provides habitat for consumers that feed on native species (Orrock, Witter & Reichman 2008).…”

Planted forests and invasive alien trees in Europe: A Code for managing existing and future plantings to mitigate the risk of negative impacts from invasions

“…Ailanthus altissima, mainly used as an ornamental or for roadside plantings, is one of the most widespread invasive plant species in Europe (Sladonja et al 2015). Acer negundo (Saccone et al 2010, Erfmeier et al 2011 (Starfinger 1997, 2010, Starfinger et al 2003, Pairon et al 2010, Vanhellemont et al 2010) are both ranked third and are invasive in several European countries (Forest Europe 2011.…”

Killing it Softly: Girdling as an Efficient Eco-friendly Method to Locally Remove InvasiveAcer negundo

“…Moreover, individuals have the ability to produce new vegetative sprouts following human cuttings or natural disturbances. Locally, this species may form monospecific stands (Lamarque et al 2012), reducing both native species richness and abundance by decreasing light availability (Saccone et al 2010, BottollierCurtet et al 2012. In France, A. negundo invasion leads to replacement of economically important trees such as Salix alba (white willow) (Bottollier-Curtet et al 2012) and Populus spp., to river bank collapses and reduces bird nesting (L. Degrave, Parc Naturel Régional des Landes de Gascogne and S. Buyle, Réserve Naturelle des Marais de Bruges, pers.…”