Climatic warming, driven by greenhouse gas emissions, is predicted to increase average global surface temperatures 2-4 °C by 2090. The effects of warming are especially pronounced in mountain systems, where much of our drinking water comes from, where more than one billion people live, and where most terrestrial biodiversity occurs. Thus, a fundamental challenge facing community and ecosystem ecologists is to be able to predict ecosystem functions and services in mountains in response to climatic warming. But, the responses of communities and ecosystems might vary from place to place on the planet: the effects we see in the Swiss Alps might be different from the effects of climate change in the Patagonian Andes. Therefore, there is an urgent need to understand better the consequences of these suites of interactions in an ever-warming world, and whether the community- and ecosystem-level responses to warming are globally consistent or vary from place to place. This project will tackle this challenge by building an international network of globally replicated experiments distributed in mountain regions throughout the world to understand the links among biodiversity, climate change, and the services that biodiversity provides for people. “I’ve spent my entire life hiking up and down mountains, trying to understand the biodiversity that’s found there. With this incredible Semper Ardens Research Grant from the Carlsberg Foundation, we’re now trying to predict how climate change will affect that biodiversity,” says Nate Sanders. Background The scientific evidence for global warming is clear. Similarly, we are beginning to understand the consequences of the loss of important species from ecosystems. The next major challenge is in trying to understand and predict the effects of warming and species loss, especially in vulnerable ecosystems such as mountain regions. WARM is lead by Professor Nathan Sanders and involves leaders in ecosystem ecology (Aimee Classen) and montane plant ecology (Maja Sundqvist) at the University of Copenhagen. But the entire team consists of ecologists from nearly 20 institutions around the world. A growing number of experiments have shown how increases in temperature at a particular place might lead to shifts in plant communities or alter biodiversity belowground. Likewise, there is a cottage industry of studies that have looked at the consequences of losing an important or dominant species from a community. And now, there are enough studies that some investigators are compiling all of the data from many experiments to do what is known as a meta-analysis - simply combining the results from different studies conducted in different places, often with very different methodologies - to look for general trends in the effects of warming or species loss on biodiversity and ecosystem function. Meta-analyses have obvious shortcomings though. Perhaps most importantly, the data are often not collected in the same way, or the experiments are conducted in similar fashion, oftentimes making the results incomparable. Another shortcoming of most studies is that they treat warming and species loss as independent factors, when clearly species are being lost and the planet is warming simultaneously. Figure 1: The WARM network. The University of Copenhagen will be the hub of the network. Stars indicate sites where the experiment is up and running, and circles indicate where we plan to establish sites in the very near future. If we really want to understand whether the effects of warming and species are general among many different places on the planet, and we want to investigate the combined and interactive effects of species loss and warming, what we really need is an experimental design that is replicated in exactly the same way, in multiple places. In fact, that is exactly what our WARM project does. WARM (Warming And Removal in Mountains) is an unparalleled globally distributed experiment that crosses experimental warming and dominant plant species removal among 10 globally-distributed elevational gradients (Figure 1) to enable the simultaneous study of community- and ecosystem-level responses to the direct and indirect effects of warming and species loss. This coordinated cross-site research effort will provide a strong test of the generality of these experimental results. Key Objectives To determine the relative influences of climate and interactions among species on biodiversity and ecosystem carbon dynamics in a global change context. To examine the patterns and processes that shape ecosystem function among disparate ecosystems. To build an international team, led by Danish researchers, to continue to investigate the controls on biodiversity and ecosystem function, and how climate change affects those relationships. “We are only beginning to scratch the surface of our understanding of biodiversity belowground, and what that biodiversity does for the functioning of ecosystems in a changing world. This project will go a long way toward increasing that understanding,” says Aimée Classen. Why Study Mountains from Denmark? Despite being in a relatively flat country, the University of Copenhagen has a long and storied history of research in mountain regions around the world, especially in the Andes in South America and the Eastern Arc Mountains in Tanzania. There are at least three reasons why mountains are the ideal testbeds for this project. First, the impacts of global warming will be especially pronounced in montane ecosystems. Because these ecosystems typically harbour high levels of biodiversity and large amounts of carbon in soils, they are important focal systems for making predictions about how ecosystems will respond to warming and how these responses will ultimately shape the amount of carbon in the atmosphere. A second reason why mountains are ideal for this project is that temperature often varies systematically with elevation in mountains. And, as a result, ecologists and bio-geographers have long been aware of the value of elevational gradients for understanding how plant and animal communities respond to climate. Third, the Natural History Museum of Denmark (SNM) at the University of Copenhagen has a long history of research in mountains all over the world, but no studies to date, at SNM or elsewhere, have explored how changing climate mediates the relationship between biodiversity and ecosystem function in mountains. Figure 2: We warm plant communities, remove dominant species, and both warm and remove dominant species to understand how these factors interact to shape biodiversity and ecosystem function in mountain ecosystems. But there are also socio-ecological reasons to focus on the effects of species loss and global warming in mountains. 1.2 billion people on the planet live in or near mountains but, amazingly, more than 3 billion people rely on mountains for drinking water. Thus, intensity and frequency of crises over water availability are likely to increase in coming decades, understanding the interplay between society and ecology in mountains is essential. What Will We Actually Do? In at least 10 mountain regions around the world (see Figure 1) we will artificially increase air and soil temperatures using open-top chambers (see Figure 2) and manually remove the most dominant plant species in what is called a full-factorial design. That means there will be some plots in which we do not do anything (controls), some plots where only dominant species are removed, some plots that are only warmed, and some plots that are both warmed and have their dominant species removed. We will repeat this at high-elevation, cold sites and low-elevation warm sites in each mountain region. “I am really excited to be a part of this incredible team of collaborators as we take on some of the big challenges in ecology. Tackling these questions wouldn’t be possible without support from the Carlsberg Foundation,” says Nate Sanders. Then, we will measure the responses of biodiversity, both aboveground (the plants) and below ground (soil microbes and micro arthropods), and ecosystem function (how carbon fluxes through the ecosystem). Because we are replicating this experiment at high and low-elevation sites at so many mountain regions around the world, we will be able to, for the first time, assess the generality of the effects of species loss and warming on biodiversity and ecosystem function.