Abstract: Experiments were carried out to test the impacts of improved climate on biomass in three upland grassland systems . This was achieved by transplanting lysimeters of different soil/vegetation types between two sites down an altitudinal gradient at Great Dun Fell (GDF) in the northern Pennines, U. K. Three soil types were moved (acid brown earth, peaty gley and micropodzol) with associated vegetation,and the temperature difference between the sites was an annual average of 4.2℃. Parallel fertilizer experiments were performed using the three soil/vegetation types at the same two sites, to examine the vegetation responses to additions of N (20kg · hm-2 · a-1) and P (10kg · hm-2 · a-1) in order to assess whether climatically-linked improvements in growth were related to soil nutritional changes. The experiment showed that the change in altitude resulted in a marked and significant (p<0.01) increase in total above-ground productivity, with productivity at the warmer site being increased by 51%, 66 % and 78 % for the peaty gley, micropodzol and acid brown earth, respectively. Change in species composition were observed with, in particular , the grass Agrostis capillaris showing the greatest positive response to climatic improvement. The fertilizer additions did not show any significant effect on above ground productivity on any soil type, at either of the two transplant sites, Therefore, we conclude that temperature acting on the plants directly, and not through soil nutrient supply, is the major limiting factor to primary productivity at this upland site.