In September 2012, the Centre for Invasion Biology (C·I·B) organised a workshop in Patagonia, Argentina, that brought together 21 researchers from around
the world to discuss all aspects of alien tree invasions.
In the past few decades trees have become among the most widespread and damaging of all invasive species. Invasive trees, including escapees from alien tree plantations,
have huge impacts on biodiversity, ecosystem functioning, and human livelihoods in many parts of the world. Despite the increasing attention to trees as invasive species
worldwide, problems associated with these invasions are becoming increasingly widespread and complex. Syntheses on patterns and processes of tree invasions are currently
based on only a small number of invasive species and invaded regions. Consequently, the roles of some fundamental driving forces are still poorly understood and difficult
to generalize. Many introduced tree species are crops of commercial importance in some parts of the landscape, but serious pests in others. This creates complex conflicts
of interest which hinder management efforts. With these factors in mind, it was timely to hold a workshop to produce a synthesis, in the form of a journal special issue,
which will move discussions on tree invasions beyond the elucidation of case studies. According to Dave Richardson, who chaired the workshop: “We need to strive for a general
understanding of the wide range of factors involved in mediating the outcome of tree introductions and that shape the options for management”.
The workshop was held on the spectacular Isla Victoria, an island in Nahuel Huapi Lake, a ferry ride from Bariloche. The island, now part of a National Park, was privately
owned in the early 20th century during which time deer and wild boar were introduced to the area. In the 1920s the island came under government jurisdiction, and
large areas of the island were planted with alien trees to “improve the area for tourism” and to sustain the local forestry industry. Several of the alien tree
species have become naturalised and spread into the native vegetation. Important studies have been conducted on the island to determine, for example:
interactions between native and alien mammals and introduced trees;
the role of below-ground mutualisms in driving conifer invasions;
the role of propagule pressure in driving tree invasions;
and seed predation as a barrier to alien conifer invasions.
This “natural tree introduction/invasion laboratory” and the stunning scenery made the island the ideal location for serious deliberations on many aspects of
Befitting its status as a global hot-spot of tree invasions, South Africa was well represented at the meeting, with eight participants from the C·I·B—Dave
Richardson (who chaired the workshop), Brian van Wilgen, Mark Robertson, Cang Hui, John Wilson, post-doc Vernon Visser, and students Luke Potgieter and Jason Donaldson. Other
researchers came from across the globe: Estela Rafaele, Maria Andrea Relva and Martín Nuñez (Universidad Nacional del Comahue, Argentina), Brett Bennett (University of
Western Sydney, Australia), Bruce Webber (CSIRO, W. Australia), Aníbal Pauchard (Universidad de Concepción, Chile), Annabel Porté (Université Bordeaux,
France), Ian Dickie (Landcare Research, New Zealand), Michael Gundale (Swedish University of Agricultural Sciences), Paul Caplat (Lund University, Sweden), Bruce Maxwell (Montana
State University, USA), Marcel Rejmanek (UC Davis, USA) and Phil Rundel (UCLA, USA).
The workshop involved presentations and discussions on many topics related to tree invasions, including topics as diverse as the role of fungi in tree invasions, the history
of social perceptions of tree introductions, and the development of an inventory of invasive trees worldwide. The main product of the workshop will be a special issue of the
journal Biological Invasions which will aim to synthesize the current understanding of many facets of invasive trees. It is hoped that this workshop will also lead to
many new collaborations on a range of topics.
A pre-workshop field trip was arranged to allow the delegates to see other woody plant invasions in Patagonia and the regionís spectacular scenery which includes massive
glacial lakes, snow-capped mountains and semi-desert landscapes that could easily be mistaken for parts of the Karoo in South Africa. Delegates explored the native
Araucaria aurucana forests which occur high in the snowy mountains among clear lakes and streams and got to see many examples of the very widespread invasions of
lodgepole pine (Pinus contorta), rose (Rosa rubiginosa) and willows (Salix spp.).
According to Dave Richardson, “the workshop is an example of how the Centre for Invasion Biology aims to forge strong international collaborations to address pressing
questions in invasion ecology. Another important aim of the workshop was to expose C·I·B core team members, post-docs and students to international meetings and
Financial support for the attendance of the workshop by the C·I·B team came from the Oppenheimer Memorial Trust, the Hans Sigrist Foundation, Elsevier and
the DST-NRF Centre of Excellence for Invasion Biology.