Forest Influences on Climate and Water Resources at the Landscape to Regional Scale - Landscape Ecology for Sustainable Environment and Culture - page 309

for evapotranspiration, partially explaining the 20 % lower water yield observed
for one watershed that was converted from native southern hardwoods to pine
forests. Actual forest ET at Coweeta is generally higher than potential ET (PET) as
estimated with references to water or grass surfaces (Rao et al. 2011 ).
15.3.2 Seasonal and Annual Water Yield
At Coweeta, various watershed manipulations experiments have been conducted to
demonstrate and quantify the effects of forest management practices on water
quantity and water quality. Although these studies were conducted in watershed
less than 200 ha, they provide the basis for understanding the forest-water relations
at a landscape scale and beyond, such as a regional scale (i.e., southern Appala-
chian Mountains).
15.3.2.1 Mountain Farming
Mountain farming experiments (Watershed 3) were conducted in 1940s to dem-
onstrate the impacts of common farming practices in the steep southern Appala-
chian Mountain regions on water resources. Watershed monitoring data show that
mountain farming that involved tree felling, brush burning, cattle grazing, plowing
and cultivation for corns, severely reduced surface soil infiltration capacity, thus
increased overland flow, peak flow rate (over 8 times higher compared to before
treatment), and sediment loading rate (increase 2-80 times). Crop yield without
fertilizer use was low due to intense storm and wildlife damages in the studied
watershed (USFS 1948 ).
15.3.2.2 Mountain Grazing
About 20 % of the land area in the Coweeta area was intensively grazed with
fenced cattle for local economic support. Woodlands grazing experiments
(Watershed 7) show that soil compactions are significant. Within the first year, soil
macro-porosity of top 10 cm soil decreased 10 % (USFS 1948 ). The loss of
understory (palatable seedlings) lowed wind to blow litter out of the forests and
reduced organic matter, thus eliminating the hydrological functions of forests
(Munns 1947 ).
15.3.2.3 Clear Cutting Forests
To demonstrate that the significant effects of forest clear-cutting only (i.e., no trees
removed from the sites) on evapotranspiration and water yield, Coweeta conducted