The 2010 ASHS Annual Conference

Southeast Asia includes both the wet characterized by brief dry periods, and monsoonal tropics divided between distinct wet and dry seasons.  Both an uncertain future and the reconstructed paleo climate  point to likelihood of higher temperatures, more intra-monsoonal drought, and potentially complete monsoonal failure.   Tree species in monsoonal climates typically have deeper rooting to avoid dry season drought as long as possible, but tend to be divided between evergreen species tolerating the 4-6 month drought, and drought deciduous of many flavors that vary in terms of timing and duration of defoliation.  Drought deciduous species typically have much higher transpiration and photosynthetic rates than evergreen species that is approximately similar on a yearly basis.  Downscaled IPCC air temperatures using the A4 scenario suggest that deciduous species will expand area at the expense of evergreen species, possibly due to greater capacity for transpirational cooling through more open stomata that would allow more yearly photosynthesis.  Dry evergreen species are more likely to be subjected to higher vapor pressure deficits and more prolonged stomatal closure, suggesting they may be less adaptable to climate change.