Surface runoff and planting density relationship
The surface runoff, runoff production in slope, is related to the soil
infiltration. On raining, the soil evaporation is too small to neglect
due to the relatively low temperatures, greater air humidity and lower
air vapor pressure deficit near the ground. Thus, the rainwater that
reaches the soil surface through forest canopies infiltrate into the
soil or run off as overland flow. In the period from April, 2002 to
October, 2003, there were many greater rain events, but there were only
five rain events generated runoff in our plots because of the gentle
terrain, small rainfall intensity, higher planting density and higher
cover degree of Caragana shrublands and the runoff amount ranged from to
. The equation describing the relationship between surface runoff SR and
precipitation outside caragana forest P2 was found to be
(Guo & Shao
2004,2013), see table 3
SR = 0.01P2+ 0.1765
The runoff in Loess Plateau, China normally is infiltration-excess
runoff production and it occurred when the rainfall intensity exceeds
the infiltration rate (Guo and Shao 2013). Because vegetation cover can
increase surface roughness and vegetation canopy interception reduce the
kinetic energy of raindrops impacting the soil surface and the degree of
aggregate breakdown and compaction causing surface sealing. The barrier
effect of standing forest on runoff can increases the surface runoff
resistance, thus vegetation reduces velocity of the surface runoff and
increases the rainfall infiltration.
The surface runoff declined with increasing planting density, which is
consistent with the reported by Zhang et. al. (2002). The relationship
between surface runoff R and planting density PD can be can be written
as follows (Guo & Shao 2013), see table 4
R = 78.454 – 16.899Ln (PD)
Where, R is surface runoff and PD is planting density