Abstract
Grasslands cover an estimated 31–43% of terrestrial land and contribute many important ecosystem services. However, grasslands are under threat from development, fragmentation and, of course, climate change with incrementally rising temperatures, changes in precipitation patterns and extreme climate events. Although grasslands lag behind in terms of the international policy airtime afforded to forests, they are no less important, especially given their global extent. Grasslands are also a geologically relatively new ecosystem and many, including the chalk grasslands that I look out onto every day from my home, are semi-natural plagioclimax communities that require a certain amount of human ‘management’ in order to maintain the high plant and invertebrate diversity that makes them so special.
The first thing to say is that this book is eminently readable. Gibson and Newman have done a great job in setting the scene in the introductory chapter, so that even those who are not ecologists or plant specialists can quickly and succinctly grasp the extent of grasslands, their importance especially to human health and wellbeing, and the likely threats from climate change before delving deeper in the following chapters. The book pulls together work from across a broad spectrum of science with chapters varying between literature reviews, case studies, meta-analysis and modelling predictions. The book is split into four sections. The Introduction covers the changes in extant grassland, modelling to predict impacts and remote sensing to detect change. Part I examines in more detail how grasslands may be affected by climate change, while Part II takes a deep dive into various aspects of grassland functional plant traits. Finally, Part III considers grassland management, past, present and future.
Chapters 4–8 in Part I follow on smoothly from the introductory chapters. While the main tenet of this book is the effect of climate change on grasslands, I do not think I read one chapter that did not touch on the human impacts on grasslands. We rely heavily on grasslands for agriculture; indeed, 80% is the quoted figure here for grasslands in agricultural production. Yet poor management can exacerbate climate change impacts. It can weaken grassland plant community resilience and could tip some grassland ecosystems over their critical threshold. Such changes can be irreversible, leading to permanent loss. Critically, grasslands can be carbon sinks and help to mitigate the increases in CO2. But the issue is far from straightforward as soil moisture plays an important role in whether grasslands act as sinks or sources, and if precipitation patterns change, this may lead to a change within grassland nutrient cycling. In this context, Lavorel (Chapter 8) offers a cautionary tale, suggesting that loss of functional grasslands through the loss of plant functional traits and associated biota will lead to the loss of vital ecosystem services. In addition, the way the land is used will either hinder or help grassland systems functioning, especially when coupled with climate change. Lavorel also suggests that the changing climate may increase certain services while simultaneously degrading others.
The meta-analysis on the current body of research on climate impacts on grassland (Chapter 4) was enlightening, while it also confirmed some of my suspicions that, while there is a strong body of research out there, at the same time it can be quite limited in some respects. Generally, temperature and precipitation are the main climate factors manipulated, most often in isolation, while the ubiquitous biomass as aboveground primary productivity is the most observed variable. Because of the great variety of ways in which we conduct experiments, the parameters used, the variables selected for measurement and language used, this can make the task of meta-analysis and predicting likely climate impacts from empirical research less than straightforward. Jones argues, and rightly so I believe, for a more joined-up and coordinated research approach so that we can start to fill some of the gaps, and improve climate change predictions for grasslands. Of course, grassland systems are very diverse, often with very site-specific abiotic and biotic factors, and abundance and diversity of plant species and plant traits. Fraser (Chapter 5) points out that this can make site-specific predictions quite complex.
Part II kicks off with an investigation into why invasive species may do well in grasslands under different climate change scenarios. Tying in beautifully with the end of Part I, Catford and Jones explain that human use and pressures on grasslands may intensify if adaptation measures are not taken to ameliorate climate change impacts. This could lead to an increase in invasive species while simultaneously losing dominant species and their functional traits, thereby reducing system functioning overall and impacting ecosystem services. Yurkonis and Harris (Chapter 13) remind us though, that many grassland plant species are phenotypically plastic and are already well adapted to a variety of geographic and environmental conditions which may confer resilience to direct climate change. Can plants use this plasticity plus epigenetics and genetics, and varied dispersal mechanisms to keep up with incremental climate change? I believe there is a note of hope there. Chapter 11 (Hartley and Beale) was one of my favourites, probably because this was something I had never really considered before. How will climate change affect forage quality? Increasing levels of CO2, changes in precipitation and increased temperatures may change the chemical content of grasses, which in turn affects not only the palatability of the sward but also the nutritional content that herbivores rely on.
Part III looks at how we can manage our grasslands better in order to mitigate climate change impacts. It addresses learning from the past, reassessing how we currently evaluate grasslands and how to use current scientific knowledge to mitigate climate effects through restoration. Knowledge of potential shifts in plant ranges can help determine which species to use at restoration sites, from sourcing plants/seeds to determining which sites to restore. Food security is also discussed, particularly for those with a subsistence way of life, such as the traditional pastoralists and farmers in developing countries who are often the most vulnerable and least resilient to climate change. This discussion goes hand-in-hand with Dove’s case study (Chapter 16) of Imperata cylindrica, a dominant grass of Southeast Asia. Imperata is generally categorised as an invasive or nuisance species. However, Dove tells a cautionary tale of differences in perception at local/regional and governmental levels about the value of this species, which has led to a historic failure to successfully control it where it does need management. This is an illustration of top-down management missing the opportunity to use invaluable local knowledge in maintaining and protecting these ecosystems.
The final Chapter 19 synthesises the areas for further research as highlighted in the previous 18 chapters. It ends with the cautionary note that the current rate of change coupled with no pre-existing knowledge of how grassland ecosystems will fare under current climate change scenarios, will make some aspects of predicting responses, for example, about which novel systems may evolve, and how they will function, a complex task. Complex maybe, but not impossible I hope, for well-managed grasslands can be more resilient than we might expect.