Impacts of invasive biota in forest ecosystems in an aboveground–belowground context

Abstract

Forest ecosystems world-wide are being subjected to invasion by organisms representing all domains of life. Here we use a combined aboveground-belowground approach to provide a conceptual framework for assessing how forests respond to biological invasions. We first address mechanisms by which invasive plants and aboveground and belowground consumers impact on forests, and highlight that although we have a growing understanding of the determinants of the effects of invasive plants, for invasive consumers we have yet to move from a series of iconic case studies to the development of general principles. We also address the effects of invasive biota in the context of the drivers of invasion, coinvasion and invasional meltdown, the issue of simultaneous species gains and losses, and forest restoration and recovery post-invasion. We then highlight areas that would benefit from further work, particularly regarding underlying mechanisms, determinants of context-dependency of invader effects, and linkages between causes and consequences of invasion. In concluding, we emphasize that biological invaders have the potential for largescale and long-term impacts on forest processes, and consideration of these impacts in an abovegroundbelowground context will enable better prediction of future responses of forests to invaders and their management as well as of restoration efforts.

Towards a framework for understanding the context dependence of impacts of non‐native tree species

“…We define legacies as effects of non‐native species that remain after the species has been removed through changes in soil biological, chemical or physical conditions and subsequent plant communities (Corbin & D'Antonio, ). Legacies can be difficult to reverse and can make restoration of an ecosystem difficult or unattainable (Wardle & Peltzer, ). The context‐dependent nature of legacy effects is often related to non‐native species density and net per capita effect at the time of removal (Figure ).…”

“…Such secondary invasions are widespread (Corbin & D'Antonio, ), and some evidence suggests that removal of non‐native pines can facilitate secondary invasion by grasses or other woody non‐native species (Dickie et al, ). Knowledge of management legacies is thus an important aspect of the context dependence of non‐native species impacts and is critical for informing decisions on both management effectiveness in mitigating invasion impacts, and on whether additional activities such as active restoration following removal of the non‐native species are needed (Wardle & Peltzer, ).…”

“…abiotic and biotic environment) factors. Understanding what drives context‐dependent non‐native species impacts can improve our ability to quantify and predict impacts (Pyšek et al, ; Wardle & Peltzer, ), which will help optimize management efforts.…”

Endemic trees in a tropical biodiversity hotspot imperilled by an invasive tree

“…2; Wardle et al, 2015) and may cause changes to the soil that further accelerates its invasion through a positive feedback process. Plant-soil feedbacks are well recognised as processes that accompany invasions by non-native trees (Ehrenfeld, 2010;Vitousek and Walker, 1989;Wardle and Peltzer, 2017). Conservation policy in Jamaica aims to prevent deforestation and to maintain the forest cover in protected areas, including the Blue and John Crow Mountains National Park (Chai et al, 2009).…”

Plant-soil interactions of range-expanding plants

“…On the other hand, plant litter of exotic plant species has been shown to decompose more readily than that of surrounding natives because it contains higher nutrient concentrations, and thus has overall higher quality Vitousek 2004, Ashton et al 2005). Exotics plant species may, therefore, increase soil nutrient availability through their litter inputs to the soil (Wardle and Peltzer 2017), which can create a positive feedback to their own growth. In general, high nutrient availability in the soil, both via pre-existing soil condition or via litter effects, may become even more important when exotic plant species are released from their specialized enemies as shown by Blumenthal et al (2009).…”