Due to poor access to higher elevations, the previous understanding of local meteorological conditions was incomplete. Traditional understanding of species distributions at different altitudes has focused on the temperature regimes, and seasonal drought stress has been largely disregarded in this context due to high annual precipitation in this region.
With aims to obtain further knowledge on the transition of the forest types found at different elevations in subtropical mountain forests of Southwest China, Prof. Zhang Yiping and his research team of Xishuangbanna Tropical Botanical Garden (XTBG) investigated temperature and aridity at two elevations with different forest types in the northern part of Ailaoshan National Natural Reserve (24°32′N, 101°01′E; 2,480 m a.s.l.). They measured short-term micrometeorological variables at 2,480 m and 2,680 m, where different forest types occur.
The objectives of the study were to answer the following questions: (1) related to temperature-controlled transition of forest types, what is temperature difference between these two elevations? (2) Does aridity, the combined effect of water evaporation demand and soil water content, increase with altitude?
As temperature decreases only slightly from 2,480 m to 2,680 m, it was concluded that transition of forest types at these two elevations is likely neither driven by the decease in temperature, nor by winter freezing. Therefore, predictions of forest distribution following climate change should not depend exclusively on temperature.
They also found that from 2,480 m to 2,680 m, water evaporation demand increased and volumetric water content decreased, especially in the dry season. Consequently, plants growing at the higher elevation experience higher water evaporation demand, lower volumetric water content and poorer soil condition especially in the dry season.
In seeking to understand the mountain forest distribution, the researchers propose that further studies should consider the effects of drought stress alongside those of altitude.
The study entitled “Investigation of temperature and aridity at different elevations of Mt. Ailao, SW China” has been published online in International Journal of Biometeorology, DOI:10.1007/s00484-012-0570-6