Book review "Wattles: Australian Acacia species around the world" by David M. Richardson, Johannes J. Le Roux and Elizabete Marchante

In a world of Google and AI, developing an encyclopedic coverage of a theme that is of great interest to biologists, social scientists, politicians and environmental managers, is a daunting challenge. Wattles is a book that presents new knowledge, makes interesting reading, and has the potential to stimulate research in a variety of disciplines. We learn that Acacia, commonly known as the wattles or acacias, is a genus of shrubs and trees comprising 1,083 species of which 417 are known to have been introduced to areas outside their native range. We are surprised to read that Australian acacias are found almost everywhere, in virtually all terrestrial habitats, including woodlands, grasslands, alpine settings, rainforests, coastal dunes and deserts, causing major environmental and socio-economic changes in the invaded regions. Until recently, Acacia comprised a group of plant species native to Africa, South America and Australasia, but the name is now reserved for species predominantly from Australia, including some from Southeast Asia. The genus name Acacia is Neo-Latin, and refers to a preparation extracted from the leaves and fruit pods of Vachellia nilotica, the original type of the genus.

The lead Editor, Dr. David Richardson, Professor of Invasion Biology at the University of Stellenbosch, is a highly cited author who has made his mark in many countries through his publications, scientific leadership, and active involvement in international research networks. The book summarizes, on 584 pages, and in 31 chapters with a team of around 120 authors, current information on the ecology and biogeography of one of the world's most important woody plant genera. Some species are commercially used forestry trees, others are useful as a source of energy, for ornamentation or for stabilizing sand dunes. Some species are highly invasive causing major impacts in a variety of ecosystems.

An excellent introductory overview, entitled Australian Acacia species around the world, is presented by the three editors David Richardson (South Africa), Elisabete Marchante (Portugal) and Johannes Le Roux (Australia). The main part of the book is divided into six sections which are entitled The Species Pool - History and the Global Conquest - Biotic Interactions (biological control, taxonomy and phylogeny); Ecological and Social Impacts - Managing Invasive Wattles - The Wattles Invasion Syndrome. Details are available at: https://www.cabidigitallibrary.org/doi/10.1079/9781800622197.0000. Some chapters contain supplementary material that is available in open access, e.g. evidence about the global distribution, and details of Australian Acacia species in Europe and Africa, as well as in Brazil, Chile, and New Zealand, and in the U.S. state of California.

Among the numerous highlights of the book is the chapter Linking the Functional Traits of Australian Acacia Species to their Geographic Distribution and Invasion Status by Irene Martín-Forés and co-authors of the School of Biological Sciences at the University of Adelaide, Australia. The authors found the performance of wattle species to be profoundly influenced by their historical range size and niche breadth, based on evidence provided by AusTraits, an open-source database of Australian plant trait data that synthesizes data on nearly 500 traits across more than 30,000 taxa.

The study of plant traits has emerged as one of the most important developments in biology. Traits are measurable features of an organism that provide a new perspective on diversity, one that does not ask: who are you? But rather: how do you respond to a specific environment? "Functional traits" are ecologically relevant, though often characterized primarily by availability and implied importance not by their ecological information content. Research is needed to identify functions of interest and then to identify specific traits that can serve as quantifiable proxies. Streit and Bellwood (2023) thus proposed "A taxonomy of traits", a framework to characterize traits and to identify the requirements for what a trait needs to capture.

I also found chapter 25 especially interesting and relevant. In just a few decades, wattles have deeply influenced rural livelihoods in many regions of the world. Wattle plantations now dominate as a primary land use in certain areas in Vietnam with a potential to alleviate logging pressures in natural forests. The objective of the "Five Million Hectare Reforestation Program" (also known as the Acacia Boom) was to increase forest cover in Vietnam by establishing plantations of exotic tree species, mainly acacias. Between 6 and 9 percent of the national land area of Vietnam is currently planted with tropical wattles (Acacia auriculiformis; A. mangium and hybrids), mainly in degraded bushland. However, like any boom crop, wattle plantions are exposed to the risk of pathogens (chapter 20 of this book), soil degradation and market swings.

A major impact of the Anthropocene is that of burgeoning neobiota (chapter 8 of this book). The ideas of Frederic Clements led many to believe that ecosystems would develop climax communities that would, without outside disturbance, be self-regulating and eventually converge to some stable equilibrium. A "hands-off" philosophy of environmental management emerged in the 1960s alongside the rise of environmentalism and the desire to preserve current natural communities, ecosystems that happen to exist at a particular time. Extensive areas of wattle, often mixed with pines and eucalypts, are found in South Africa. A question that often comes to mind is how resilient and sustainable are these new woodlands, what ecosystem goods and services do they provide? Sporadic eradication (locally known as "hacking") is a popular social fun activity that does, however, not solve the challenge of controlling the extensive new wattle woods. Wattles are long living organisms, and there is a need for appropriate long-term observational infrastructures to understand the population dynamics, not only of pure wattle woodlands, but also of acacias in mixtures with other woody species. Details of the layout, method of assessment, re-measurement intervals and data analysis are presented by Condit et al. (2013); Gadow et al. (2021, chapter 2.3) and Lin et al. (2024). Long-term observational infrastructures that provide essential empirical evidence about the effects of structure, density and diversity on the resilience of invasive communities under changing environmental conditions are indispensable for unbiased scientific recommendations to policy makers.

The book is aimed at academics and students of ecology, especially those interested in the study of the internal dynamics of wooded landscapes, and the response of such landscapes to changing environmental conditions and human demands. Policy-makers and managers of domesticated ecosystems, especially those involved in combating invasive plant species, will find many helpful references to particular case studies, like the "wattle boom" in Vietnam. The book collates information on numerous aspects of this fascinating genus, and is likely to be of much interest to the readers of Forest Ecosystems.

Final comment

"Wattles" is an adventurous journey into the world of invasion ecology, plant biology and functional traits, and the challenges of the Anthropocene. A treasure chest of facts about one of the world's most important woody plant genera, designed and developed by a team of very experienced scientists. I am impressed.

CRediT authorship contribution statement

Klaus von Gadow: Writing – original draft, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.