Abstract
Many invasive plants show evidence of trait-based evolutionary change, but these remain largely unexplored for invasive trees. The increasing number of invasive trees and their tremendous impacts worldwide, however, illustrates the urgent need to bridge this knowledge gap to apply efficient management. Consequently, an interdisciplinary workshop, held in 2015 at Stellenbosch University in Stellenbosch, South Africa, brought together international researchers to discuss our understanding of evolutionary dynamics in invasive trees. The main outcome of this workshop is this Special Issue of AoB PLANTS. The collection of papers in this issue has helped to identify and assess the evolutionary mechanisms that are likely to influence tree invasions. It also facilitated expansion of the unified framework for biological invasions to incorporate key evolutionary processes. The papers cover a wide range of evolutionary mechanisms in tree genomes (adaptation), epigenomes (phenotypic plasticity) and their second genomes (mutualists), and show how such mechanisms can impact tree invasion processes and management. The special issue provides a comprehensive overview of the factors that promote and mitigate the invasive success of tree species in many parts of the world. It also shows that incorporating evolutionary concepts is crucial for understanding the complex drivers of tree invasions and has much potential to improve management. The contributions of the special issue also highlight many priorities for further work in the face of ever-increasing tree invasions; the complexity of this research needs calls for expanded interdisciplinary research collaborations.
Highlights
Introduction to the special issueTree invasions: towards a better understanding of their complex evolutionary dynamicsHeidi Hirsch*, David M
The Special Issue highlights the multi-trophic aspects of tree invasions, in that trees might not arrive alone, but even worse, in time would attract an extensive array of non-native organisms that may or may not become invasive
Shorter-term experiments, comparing native and non-native tree populations under common environmental conditions, can shed light on potential evolutionary shifts in early life-cycle traits that are important for the successful colonization of new areas during the spread of an invasive tree species
Summary
Plants introduced by humans to areas well outside their native ranges must confront multiple selective barriers that influence their capacity to become invasive (Richardson et al 2000b, 2011; Blackburn et al 2011). An extensive body of literature shows that non-native plant species can undergo rapid evolutionary changes in response to novel selection pressures in their new ranges (Whitney and Gabler 2008; Buswell et al 2010; Lee 2010). Hirsch et al (2016) investigated shifts in seedling growth performance between native and non-native populations of the invasive elm, Ulmus pumila, under different water and temperature conditions Traits such as seedling growth, associated with the early parts of a plant’s life-cycle, can play an important role during the colonization of new sites. The authors argue that the positive effect of phenotypic integration on the plastic expression of morphological traits in shade is a key factor that allows C. equisetifolia to invade in the Brazilian sandy coastal plains
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