Dynamic cloud regimes, incident sunlight, and leaf temperatures in the endemic Espeletia grandiflora and the indigenous Chusquea tessellata, northern Andean páramo, Colombia

The alpine Paramo of Chingaza National Park, Colombia, has a highly variable cloud regime typical of many tropical alpine areas. Yet, little information is available regarding the effects of such dynamic sunlight regimes on alpine temperatures. A close association between changes in incident sunlight and corresponding air (T-a) and leaf (T-1) temperatures occurred in two dominant species with strongly contrasting leaf form and whole-plant architecture. Spikes in sunlight incidence of >3000 mu mol m(-2) s(-1) occurred during cloud cover and corresponded to increases in T-1 of 4-5 degrees C in a 1-min-interval in both species. Although T-1 was predominately above Ta, during the day, depressions below Ta of over 6 degrees C occurred during cloudy conditions when photosynthetic photon flux density (PFDs) was <400 mu mol m(-2) s(-1). The greatest frequency (69%) of changes in incident sunlight (PFDs; over 2-min intervals) was less than 100 mu mol m(-2) s(-1), although changes >1000 gmol m(-2) s(-1) occurred for 2.4% of the day, including a maximum change of 1512 mu mol m(-2) s(-1). These data may be valuable for predicting the ecophysiological impact of climate warming and associated changes in future cloud regimes experienced by tropical alpine species.