Forest Influences on Climate and Water Resources at the Landscape to Regional Scale - Landscape Ecology for Sustainable Environment and Culture - page 304

Fig. 15.2 A comparison of monthly mean net radiation (Rn) and albedo for a mid-rotation
loblolly pine plantation (LP) and a clear-cut (young plantation) (CC) sites on the lower coastal
plain in North Carolina, USA (see more data in Sun et al. 2010 )
forest shows that albedo and net ration fluctuate seasonal and change over time due
to the climate variation and plant development resulting a decrease in albedo and
an increase in net radiation (Fig. 15.2 ) (Sun et al. 2010 ).
15.2.3 Surface Roughness
Due to uneven canopies, lands covered by tress or other vegetation have larger
surface roughness than bare ground, leading to stronger turbulence and therefore
smaller aerodynamic resistance for air and water vapor mixing. The measured
roughness by Liu et al. ( 2007 ), for example, was 0.0058 and 0.0259 m for bare and
maize soil, respectively, with the corresponding aerodynamic resistance ranges of
30-130 and 10-90 s m -1 during the day time. Lower aerodynamic resistance for
vegetated soil suggests that water loss from lands would be higher if other
meteorological conditions are the same. Higher surface roughness also means
lower wind speed. Recent observed global trend of decreasing wind speed is
believed to do with increase in surface roughness due to increase in plant biomass
and reforestation in some cases (Liu et al. 2008 ; Vautard et al. 2010 ; McVicar
et al. 2012 ).