Photo: August, 2011 in Namtso, Tibet.
To be honest, it was a little intimidating to take this picture. Although I recognized this yak by his asymmetrically curved horns and knew he was relatively docile in spite of his large size, I also knew that if he wanted to he could easily yank the metal stake holding his tether out of the ground. In four years of bringing yaks to graze plots in my experiment in Tibet, however, none of them have ever done more than occasionally stamp their feet and shake their horns in my direction.
Domesticated yaks have been used by pastoralists on the Tibetan Plateau for thousands of years. In this harsh environment, yaks are crucial for supplying people with resources to meet their basic needs, including milk, meat, wool, dung for fuel, and transportation across Tibet’s alpine ecosystems. Over millennia Tibet’s vegetation has evolved in the presence of grazing by livestock and wild herbivores. However, the plateau is now facing declining vegetation quality, rapidly warming temperatures driven by global climate change, and new government policies aimed at improving ecosystem health by restricting, reducing, or eliminating grazing by livestock altogether in some areas.
The argument for widespread overgrazing as the primary cause of rangeland degradation on the plateau is embedded in a complicated political context, and it has not been well substantiated by rigorous scientific investigation. Therefore, the aim of our research is to explicitly test how changing climate – including warming temperatures and more severe snowstorms – as well as changing grazing management policies – which are aimed at reducing herbivory both by livestock and Plateau pikas – are affecting the plants, soil resources, and ultimately the herders who depend on these ecosystems for their livelihoods.
To understand the effects of climate change and removal of herbivores on Tibet’s alpine meadow ecosystems, we have set up an experiment at Namtso, in the Tibet Autonomous Region. We use open top chambers made of fiberglass to produce a greenhouse effect that induces warming over half of our treatment plots. These warming chambers are visible behind the yak. For about four weeks spread out across the summer, we rent yaks from local herders in order to maintain grazing pressure inside the experiment similar to what the surrounding ecosystem experiences as pastoralists take their herds of yaks, sheep, and goats on daily forays into the surrounding hills. By using yaks in our experiment, in contrast to clipping plants with scissors to mimic grazing, we also get the added, realistic effects of yaks’ particular eating habits, as well as the trampling of soil and vegetation by their hooves and their deposition of dung and urine, which act as fertilizer for the vegetation. We also shovel snow onto our plots to simulate snowstorms, and we relocate pikas from half of the study site to create pika-free areas similar to those left in the wake of China’s massive pika poisoning program. In the end, we will use what we’ve learned about the effects of climate change and grazing to tease apart the factors that may be causing declining ecosystem health in Tibet. So far, it doesn’t appear that this big guy and his fellow herbivores are the most likely culprits.
Kelly Hopping is a PhD candidate in Dr. Julia Klein’s lab at NREL. In addition to her research on the impacts of climate change and grazing in Tibet, she is also working hard to become a yak yogurt connoisseur.