throughfall values reported by Navar et al. 1999 for six study plots within the Northern Gulf of Mexico Coastal Plain 73.4-83.7. Cumulative stemflow
generated, although not significantly different, is similarr to the average values observed by Navar et al.1999 0.4-6.5. Other observations have been
made for other montane rainforests. At the Australian tropical rainforest, McJannet et al. 2007 reported 65 3739 mm and 7 418 mm of gross
precipitation for throughfall and stemflow respectively. The significant discrepancy between these findings warrants further attention. Throughfall and
stemflow importance varie from the total incident precipitation, depending on branch and stand morphology and on bark roughness.
In this study, comparison of the two species of tree indicated the importance of crown form. Michelia Montana was found in site with more direct
overhead rainfall interception on average than Castanopsis argentea, generallysmall leaves in the canopy. Michelia Montana was more highly branched
with a shell of drooping leaves on the outside of the crown. Castanopsis argentea had whorle branches in tiers with planar foliage arrays. Michelia montana
appeared moreefficient at intercepting the larger amounts of rainfall available in rain forest understorey sites.
4.2.3. Erosion and runoff for the different plots
Measured runoff and soil loss data from the vegetation patches showed that Castanopsis argentea and Michelia Montana produced significantly less runoff
and erosion than the Control. The maximum values of runoff were approximately 2.45, 1.54 and 1.28 mm for the Control, Castanopsis argentea and Michelia
montana, respectively. Total runoff measured was 49.32, 15.74 and 10.87 mm, for plots. Runoff values were similar among Castanopsis argentea and Michelia
montana, and they differ from the Control. The plots of Castanopsis argentea and Michelia montana reduced runoff by 31.33 and 45.37 , respectively, as
compared to the control surface. Runoff coefficients estimated from the observed data were 0.06, 0.019, and 0.013 for the Control, Castanopsis argentea, and
Michelia montana, respectively. The values for Castanopsis argentea, and Michelia montana are similar to those reported by Vásquez-Méndez et al. 2010
for Acacia farnesiana and Opuntia sp 0.01 in a semiarid area in Central
Mexico. Nevertheless, the value for the Control plot was lower than those reported by the same authors 0.33.
It was observed that an increase in rainfall did not produce an increment in runoff for the patches of Castanopsis argentea and Michelia montana likely the
Control Fig 10. Given the leaf area index and woody surface area index that characterize Castanopsis argentea and Michelia montana, the probability of a
raindrop passing through the canopy without contacting a vegetative surface is relatively low even under strong wind conditions. The aerial structures of the two
species intercept a significant amount of rainfall, which is subsequently translocated as stemflow to the soil,increasing infiltration and diminishing the
potential for runoff. Cumulative soil loss values were quantified in 1.98, 0.82 and 0.76 ton ha
-1
year
-1
for the Control, Castanopsis argentea and Michelia montana, respectively. Increases in the amount of surface runoff lead to an increase in soil
erosion. However, these relationships are inconsistent in Castanopsis argentea and Michelia montana plot. This result suggests that vegetation patches of
Castanopsis argentea and Michelia montana create soil fertility where soil organic matter contents are greater, bulk densities are lower, and consequently,
the stability of aggregates and water intake increases, reducing the amount of runoff and soil erosion.
4.3. Correlation BetweenSoil Conservation Parameters
Linear multiple regressions onto rainfall, throughfall, stemflow, runoff and erosion are computed:
Fig 10 Runoff relationship A and rainfall-erosion relationship B for different plots.
0,0 0,5
1,0 1,5
2,0 2,5
3,0
5 10
15 20
25 30
35 40
45 50
55 60
65 70
S oil
e rosion
ra te
g m
2
Rainfall mm Castanopsis
Michelia Control
A
1 2
3 4
5 10
15 20
25 30
35 40
45 50
55 60
65 70
R unof
f mm
Rainfall mm Castanopsis
Michelia Control
B
