Anthropogenic emissions of the greenhouse gases carbon dioxide and methane have stimulated a rise in global surface temperature of 0.76 ºC since the turn of the 20th Century. Such climate warming has already had significant impacts on the terrestrial biosphere, raising concerns that ecosystems will feed back to future climate by altering the balance of carbon flow between the land and atmosphere. It is well established that warming can directly affect rates of photosynthesis and ecosystem respiration, which together dictate the carbon balance of most ecosystems. However, warming is also causing shifts in the productivity and composition of vegetation, and there is growing recognition that this can have indirect effects on carbon cycling via its influence over soil properties and the activity of the soil microbial community. Despite this, much uncertainty currently surrounds the effects of warming on vegetation, both between individuals of the same species and at the plant community scale. Furthermore, the consequences of vegetation change at either scale for carbon dynamics are not well understood when considered in tandem with warming.Northern peatlands are of particular relevance to ecosystem climate feedbacks, holding one third of global soil carbon in regions vulnerable to rapid temperature change. The aim of this thesis was to explore how different scales of vegetation change regulate peatland carbon cycle responses to warming. This was achieved using field experiments across Europe, including manipulations, reciprocal transplants and gradient studies, which integrated a range of approaches for detecting responses from the genetic to ecosystem scale. By measuring the growth responses of dominant plant species to warming and the presence or absence of different plant functional types (Chapter 2), I reveal interdependencies between peatland plants that will cause community change over decades to centuries. I suggest that such responses occur due to both plant-plant interactions and the influence of vegetation over microclimate, the latter of which I also show to be regulated by vegetation composition (Chapter 3). Additionally, I demonstrate that warming at different temporal scales has contrasting effects on the metabolism, photosynthesis and growth of Eriophorum vaginatum (Chapter 5), causing decreases in growth over seasons to years through phenotypic plasticity and increases in growth over centuries to millennia through natural selection. I show that such adaptation of individual plants to rising temperature has potential consequences for peatland carbon dynamics. Moreover, I reveal that changes in vegetation composition at the community level could destabilise the peatland carbon stock under warming by accelerating decomposition of ancient carbon (Chapter 4). Through these findings, I provide novel insight into the scales and mechanisms by which vegetation responses to warming impact carbon dynamics. Given the key role of northern peatlands in the global carbon cycle, I suggest that warming effects on peatland vegetation may have considerable consequences for future climate by controlling liberation of peatland carbon into the atmosphere.