212
Juan Bellot, Anna Avila and Anselm Rodrigo
pollution. From this study, and for consistency with the other three studies,
we will only use here data from the less polluted site (La Castanya). Table 15.1 summarizes the site characteristics and sampling layouts. Analytical
methods are described in Bellot (1989) and Roda et al. (1990). Stemflow was
measured in the first Prades study and in the second Montseny study. Sample
trees were chosen to cover the range of tree diameters at each site. At Montseny, throughfall and stemflow were studied only under holm oak, since it
was practically the only tree species. In the more diverse forest of the Avic
catchment, the two major companion tree species (Arbutus unedo and Phillyrea latifolia) were also included in the first Prades study.
15.3 Throughfall and Stemflow Hydrology
Mean water fluxes in throughfall, stemflow, net precipitation and interception
loss for the two sites and periods are shown in Table 15.2. It must be noted
that at both sites precipitation was much higher in the second period than in
the first one. Throughfall estimates range between 66 and 75% of annual
rainfall at each site, while stemflow percentages were 2.6% of annual precipitation for Montseny and 12% for Prades.
A similarity in throughfall percentages in Prades and Montseny is expected in view of the fact that holm oak canopies have a similar LAI in both
sites (Chap. 9). However, structural differences in tree size and density between sites are reflected in the much higher amount of water channelled by
stemflow in Prades. Interception loss is lower at Prades than at Montseny (13
and 22% of annual precipitation, respectively). Since annual throughfall percentages were similar in both studies, differences in interception should be
linked to differences in stem density, producing a greater channelling effect
Table 15.2. Average water fluxes (mm year-I) for the Prades and Montseny holm oak forests. The
four data sets are defined in Table 15.1. The last three rows give water fluxes as percentage of the
mean annual precipitation of each data set
Water flux
Prades-l
Precipitation
518
Throughfall
389
Stemflow
62
Interception loss
67
Net precipitation
451
Precipitation (%)
Throughfall
75.0
Stemflow
12.1
Interception loss
12.9
Prades-2
939
609
64.9
Data set
Montseny-l
857
565
65.9
Montseny-2
1275
963
34
279
997
75.5
2.6
21.9
Juan Bellot, Anna Avila and Anselm Rodrigo
pollution. From this study, and for consistency with the other three studies,
we will only use here data from the less polluted site (La Castanya). Table 15.1 summarizes the site characteristics and sampling layouts. Analytical
methods are described in Bellot (1989) and Roda et al. (1990). Stemflow was
measured in the first Prades study and in the second Montseny study. Sample
trees were chosen to cover the range of tree diameters at each site. At Montseny, throughfall and stemflow were studied only under holm oak, since it
was practically the only tree species. In the more diverse forest of the Avic
catchment, the two major companion tree species (Arbutus unedo and Phillyrea latifolia) were also included in the first Prades study.
15.3 Throughfall and Stemflow Hydrology
Mean water fluxes in throughfall, stemflow, net precipitation and interception
loss for the two sites and periods are shown in Table 15.2. It must be noted
that at both sites precipitation was much higher in the second period than in
the first one. Throughfall estimates range between 66 and 75% of annual
rainfall at each site, while stemflow percentages were 2.6% of annual precipitation for Montseny and 12% for Prades.
A similarity in throughfall percentages in Prades and Montseny is expected in view of the fact that holm oak canopies have a similar LAI in both
sites (Chap. 9). However, structural differences in tree size and density between sites are reflected in the much higher amount of water channelled by
stemflow in Prades. Interception loss is lower at Prades than at Montseny (13
and 22% of annual precipitation, respectively). Since annual throughfall percentages were similar in both studies, differences in interception should be
linked to differences in stem density, producing a greater channelling effect
Table 15.2. Average water fluxes (mm year-I) for the Prades and Montseny holm oak forests. The
four data sets are defined in Table 15.1. The last three rows give water fluxes as percentage of the
mean annual precipitation of each data set
Water flux
Prades-l
Precipitation
518
Throughfall
389
Stemflow
62
Interception loss
67
Net precipitation
451
Precipitation (%)
Throughfall
75.0
Stemflow
12.1
Interception loss
12.9
Prades-2
939
609
64.9
Data set
Montseny-l
857
565
65.9
Montseny-2
1275
963
34
279
997
75.5
2.6
21.9