Forest Influences on Climate and Water Resources at the Landscape to Regional Scale - Landscape Ecology for Sustainable Environment and Culture - page 307

Q ¼ P ET S
In general, when compared to un-vegetated or less vegetated land surfaces, ET
rates of trees or forests are higher, and thus streamflow is lower in forest domi-
nated watersheds Whitehead and Robinson ( 1993 ). Worldwide 'paired watershed'
experiments have confirmed this general conclusion: that is deforestation will
decrease ET and increase streamflow, but afforestation or reforestation will
increase ET and decrease streamflow (Zhang et al. 2001 ; Andreassian 2004 ;
Brown et al. 2005 ; Jackson et al. 2005 ). However, these experiments do not track
the lateral water vapor exchange in the atmosphere above the topographical
watershed boundaries. It is also worthy of noting that there is a large variability for
the general forest-water relationships. For example, clearing a fully forested
upland watershed may increase flow by as high as 700 mm/year in the rainforest
region, but the same forest management activity may not have much effect on a
wetland-dominated forested watershed (Sun et al. 2001 ). This large variability is
presumably due to the variability of the type, extent and magnitude of forest
disturbances (Sun et al. 2001 ; Sun et al. 2008 ), climatic regime including pre-
cipitation form (snow vs. rain) and distribution (Jones et al. 2012 ), watershed
aspects and altitude (Ford et al. 2011 ), geology, soil depth (Scott et al. 2005 ), and
forest types (conifer vs. deciduous) treated (Swank and Douglass 1974 ).
15.3 Case Study 1: Effects of Forest Management
on Water Yield at a Small Watershed Scale—
The Coweeta Experiments
The Coweeta Hydrological Laboratory is located near the town of Otto in western
North Carolina in the southeastern U.S. (Fig. 15.4 ). Coweeta presents one of the
oldest forest hydrology research sites in the world. This outdoor Lab is managed
by the US Department of Agriculture Forest Service Southern Research Station
and serves as one of the core Long Term Ecological Research (LTER) sites.
Numerous 'paired watershed' studies have been conducted over the past 78 years
at Coweeta for examining the hydrologic and ecological impacts of natural and
human disturbances and design best watershed management practices. In the fall
of 2009, Coweeta celebrated its 75th anniversary of establishment in 1934. The-
oretical and applied research continues at Coweeta to this day. The typical
experimental design followed at Coweeta is based upon the paired watershed
concept in which a control watershed and a treatment watershed represent the
experimental domain. The watershed pair is selected because the watersheds are
known to have similar hydrological characteristics. The undisrupted continuous
watershed research contributes much of our understanding of forest-climate-water
relationship in the humid southern Appalachian Mountains and is an important
source of our global knowledge in forest hydrology. The results from these