Land use change, such as occurs when grasslands are converted to croplands, can have strong effects on regional climate through the alteration of soil moisture and the timing and rate of transpiration. Thirty one percent and eight percent of original vegetation in the South Platte River Basin has been converted to dry or irrigated croplands, respectively. We found that greater differences in ecosystem processes were caused by land cover changes than by temperature changes, and annual water budgets for the entire basin and for individual hillslopes, except on irrigated lands, did not differ greatly between vegetation types, because water limits plant growth in the Basin. The greatest changes were seasonal shifts in transpiration resulting from shifts of C4 grassland communities to C3 cropland communities. Snow remains on the ground throughout the year at a -2 C cooling.
Soil water is drier through the winter and stayed wetter through the summer.
Evaporation, transpiration, net photosynthesis, and respiration were all lower at cooler temperatures. Cooler temperatures mean shorter growing seasons, and favorable conditions for alpine tundra, with little overall effect on stream processes. The soil water deficit increased to the point that tundra was unable to photosynthesize during July and August due to drought conditions. Long term warming will be detrimental to tundra. R.B. Lammers, J.S. Baron, D.W. Cline, L.E. Band, and C. Tague.