In anticipation of the new academic year, we have bring you the first of many exciting Environment Cluster events.
4 August 2015 (Tuesday), 11am – 12:30pm
Research Division Seminar Room (Block AS7 #06-42), NUS Kent Ridge Campus
Post-event edit: Thank you to all who were there! Here are some snapshots from the afternoon.
ABOUT THE SPEAKER
Sampurno Bruijnzeel was professor of Land Use and Hydrology at the VU University Amsterdam until March 2015 and currently Visiting Senior Research Fellow at King’s College London. He has nearly 40 years of experience with hydrological process research across the humid tropics with a primary focus on rainfall and cloud water interception, transpiration, runoff generation, nutrient cycling and sediment delivery as well as impacts of deforestation and reforestation on water yield, soil erosion and sedimentation. He (co-)authored over 220 scientific publications [Google Scholar H-index = 45], including several state-of-knowledge reviews (Hydrology of Moist Tropical Forests and Effects of Conversion (UNESCO, 1990), Forests, Water and People in the Humid Tropics (Cambridge University Press, 2005), Tropical Montane Cloud Forests (Cambridge University Press, 2010), a monograph on Highland-lowland interactions in the Ganges-Brahmaputra River Basin (ICIMOD, 1989), and a documentary DVD on the biodiversity and hydrological values of cloud forests (Forests in the Mist, Halsundbeinbruch-CH, 2004). He serves on the editorial boards of the Journal of Tropical Ecology, Hydrological Processes (until 2012), Ecohydrology, and Geo_Oekologie. In 2005 he received the Busk Medal of the Royal Geographical Society (UK) for his contributions to Biosphere research in the humid tropics.
Extended talk: http://www.youtube.com/user/usaskgiws
ABOUT THE SEMINAR
In response to widespread soil degradation, large tracts of land have been reforested across the (sub)tropics in the expectation that floods and droughts would diminish, and erosion and landsliding be eliminated. This ‘traditional’ view came under severe scrutiny in the 1980s when ‘scientific’ evidence to the contrary emerged and was used by some to influence tropical land-use policies and causing major debate as well as confusion. Ever since, much has been made of the high water use of fast-growing tree plantations causing streams to dry up after foresting grass- or croplands. However, upon closer inspection this generally accepted contention is based exclusively on controlled experimental studies in which soil degradation was not prevalent. As such, the observed declines in streamflow at all times of the year after forestation largely reflect the (undisputed) higher water use of the trees compared to that of the shorter vegetation they replaced, while the positive effects of tree planting or vegetation recovery such as improved rainfall infiltration were not manifested. Evidence is on the increase that the enhanced infiltration afforded by a well-developed and well-managed vegetation cover established on highly degraded soils can indeed exceed the new vegetation’s higher water use, implying the distinct possibility of boosting dry season streamflow by tree planting and re-greening. An as yet unpublished global modelling exercise of the ‘trade-off’ between the changes in rainfall infiltration and vegetation water use after reforesting all degraded tropical land indicates the greatest positive impact on dry season flows is likely to occur in highly degraded areas with high rainfall. These global predictions are confirmed by recently published improvements in streamflow after reforestation in South Korea, southern China and Southwest India, inter alia, although vegetation recovery under semi-arid conditions appears to lead to a gradual decline in both total flows and baseflows despite positive effects on infiltration. In line with the reduction in overland flow occurrence and amounts after successful forestation, surface erosion is typically halted within a decade whereas occurrence of shallow landslides is positively affected as well leading to generally strongly reduced sediment yields at the local scale. At larger scales, impacts are less pronounced or even negligible due to changes in the volume of previously stored sediment.
The rainfall-enhancing effect of forest has received renewed attention of late with the advent of moisture-tracking models predicting where moisture evaporated by regional-scale forests may be returned again as precipitation. The topic remains contentious, however, with model-predicted effects seemingly at odds with stable isotope based evidence as to the source of the rainfall (oceanic vs. terrestrial evaporation). Other gaps in knowledge with respect to the general theme of forestation and water include the quantification of the water use of regenerating forests (possibly enhanced relative to old-growth forest) and agro-forestry systems (likely less water-demanding); the possibility of using trees in degraded but foggy areas (especially under semi-arid conditions) to capture passing fog to increase soil- and groundwater recharge; and the relative capacity of agro-forestry systems versus planted forests and natural regrowth to restore soil hydrological functioning.
As always, if you’d like to keep informed about what the Environment Cluster is up to, shoot us an email at firstname.lastname@example.org and we’ll be in touch.