Diurnal, seasonal, and altitudinal trends in microclimate across a tropical montane cloud forest

Altitudinal gradients are often used as natural laboratories to study ecosystem dynamics, biodiversity, and species' distribution response to climate gradients. However, the underlying climate gradients are rarely described in detail, especially in the tropics. In this study, we describe the diurnal and seasonal patterns in microclimate across a 3900 m altitudinal gradient in and adjacent to the Kosnipata Valley in Manu National Park, Peru, on the eastern slope of the tropical Andes. We focus on the understudied altitudinal range between 1500 and 3500 m using micrometeorological data associated with a permanent tree plot network designed to study cloud forest biodiversity and ecosystem dynamics. Data from this plot network were supplemented with data in the public domain across a 20 000 km(2) area with time series at individual sites lasting from 2 to 17 yr. Observed diurnal and seasonal trends in microclimate variables were explained by diurnal and seasonal variation in solar radiation and atmospheric moisture flux. Altitudinal trends in microclimate varied seasonally, with solar radiation, vapor pressure deficit, and temperature reaching their annual maximum earlier at higher altitudes, likely because of seasonally shifting cloud dynamics. Cloud dynamics were important in determining diurnal, seasonal, and altitudinal trends in several microclimate variables, suggesting that changes to cloud frequency and altitudinal occurrence associated with global climate change could have important impacts on cloud forest ecosystem dynamics, in addition to those of rising temperatures.