CONTENTS and LINKS
National Science Foundation--Environmental
Start Date: January 1, 1997
A. Terry Rambo and Jefferson M. Fox
Dr. Le Trong Cuc
We have conducted intensive field studies of the influences of landscape fragmentation on hydrologic processes. In particular, we studied effects of vegetation patchiness on regional evaporation and storm runoff. To study forest edge effect on evaporation, we measured meteorological, soil, and ecophysiological variables in and near a 12-ha forest patch in Ban Tat Hamlet, Hoa Binh Province, northern Vietnam. Preliminary results indicate transpiration is significantly higher for trees near the edge of the patch than those in the interior. This effect is more pronounced during the wet season. This result implies that reduction of regional evaporation due to deforestation is mitigated to some extent by enhanced evaporation near forest edges. For a given fractional forest cover, regional evaporation in highly fragmented landscapes is not reduced as much as in areas where cleared and forested patches are relatively large. Regarding storm runoff, we are investigating whether patches of vegetation on hillslopes can significantly reduce the delivery of storm runoff to streams. In general, clearing of forest reduces soil infiltration rates which can lead to overland flow during intense rainfall. This type of runoff is considered to have negative impacts due to associated flooding, soil erosion, and sedimentation of water resources. We believe landscape fragmentation may partially offset the generally negative effects of deforestation on overland flow by providing buffers zones were water flowing down slope can infiltrate the soil.
It is well known that partitioning of incident solar radiation depends on the type of land cover. For example, net radiation, soil heat flux, sensible heat flux to the atmosphere, and latent heat flux are significantly affected by clearing forest. Estimates of energy and water fluxes for regions with heterogeneous land cover can take account of the relative proportions of the dominant land cover types relatively easily by computing area-weighted averages of the fluxes over each land cover type. However, patch-scale fluxes are not independent of the surroundings. Horizontal transfer of energy and water vapor in the atmosphere may significantly alter the fluxes within a patch and hence invalidate a strictly one-dimensional approach to estimating regional average fluxes. Such effects are greatest at the boundaries of dissimilar land covers. Near the upwind margin of a forest patch, processes are influenced by the advection of sensible energy generated in the clearing. Air entering the forest edge is relatively warm and dry, thus increasing evaporation potential. This edge effect diminishes with distance toward the patch interior, but remains significant for several tens of meters. In a highly fragmented landscape, edge effects, if not recognized, could contribute considerable uncertainty to regional energy and water flux estimates.
1. Evaluate the spatial patterns of transpiration within a forest patch.
2. Evaluate changes in spatial patterns of transpiration with a forest patch as influenced by changes in:
3. Evaluate the use of the Klaassen (1992) model to simulate the spatial pattern of transpiration within a forest patch under different conditions
Ban Tat Forest Patch Experiment
Ban Tat Hamlet, Tan Minh Village, Hoa Binh, Vietnam
Measurements taken June-July 1997 and March-June 1998
Contact: T. Giambelluca: email@example.com
Four-station transect of meteorological stations
301 Located in actively used swidden field located near western edge of forest patch
302 Located in forest near western edge of forest patch
304 Located in secondary vegetation near northeast edge of forest patch
Note: Rnet = net radiation, Kd = downward shortwave radiation, Ku= upward shortwave radiation, Tir = surface (canopy) temperature using infrared thermometer, G = soil heat conduction, Tsoil = soil temperature, Tair = air temperature, RH = relative humidity, U = wind speed, WD, SM0-30 = soil moisture (TDR) at 0 to 30 cm depth, SM50-80 = soil moisture (TDR) at 50-80 cm depth, SM120-150 = soil moisture (TDR) at 120 to 1500 cm depth, RF = rainfall
305 Located near western edge of forest patch; coincides with meteorological station 302
306 Located in the interior of the forest patch; coincides with meteorological station 303
Publications and Presentations
Giambelluca, T.W., Ziegler, A.D., Nullet, M.A., Dao, T.M., and Tran, L.T. In review. Transpiration in a small tropical forest patch.
Ziegler, A.D., T.W. Giambelluca, D. Plondke. T.T. Vana, J. Fox, T.D. Vien. M.A. Nullet., S. Evett. In review. Near-surface hydrologic response in a fragmented landscape in northern Vietnam. [draft]
Giambelluca, T.W., Ziegler, A.D., Nullet, M.A., and Dao, T. 2001. Spatial Variation in Transpiration within a Small Forest Patch in Hoa Binh, Northern Vietnam. American Geophysical Union Fall Meeting, San Francisco, December, 2001.
Ziegler, A.D. and Giambelluca, T.W. 2001. Alteration of hydrological flow paths by fragmentation: Tat Hamlet, Da River Watershed, northern Vietnam. Symposium IV, Rio de Janiero, September 2001.
Giambelluca, T.W., Ziegler, A.D., Tran, L.T., Sutherland, R.A., and Nullet, M.A. 1999. How changing land-use is modifying hydrologic processes in mountainous areas of Southeast Asia, Environmental services and land use change: Bridging the gap between policy and research in Southeast Asia, Chiang Mai, Thailand, June 1999. (Invited).
Giambelluca, T.W. 1999. Influences of landscape fragmentation on hydrological processes, Hoa Binh, Vietnam, 95th Annual Meeting of the Association of American Geographers, Honolulu, March 1999. [Abstract]
Giambelluca, T.W., Modeling land-atmosphere interaction over tropical forests: lessons from the field, PILPS Strategy Forum, Honolulu, February 1999 (Invited).
Giambelluca, T.W. Reality check: Observing processes at small scales, First SEA/BASINS Partner Workshop, Chiang Rai, Thailand, November 1998 (Invited).
Giambelluca, T.W. Influence of forest fragmentation on watershed functions in northern Vietnam--Hydrological objective: Quantifying the influences of patch size on watershed hydrology, 1998 Water and Watersheds Program Review, EPA/NSF Partnership for Environmental Research, Corvallis, Oregon, January 1998 (Invited).