15 Throughfall and Stemflow
Juan Bellot, Anna .Avila and Anselm Rodrigo
15.1 Introduction
Forest canopies affect the amounts of water and nutrients reaching forest
soils. Water and nutrient inputs under forest canopies are thus different from
those in nearby open areas. Canopies intercept and retain part of the incident precipitation (intercepted water), which is eventually evaporated from
the canopy and lost to the atmosphere. Water passing through the canopy
can reach the forest floor after dripping from leaves and branches (throughfall) or flowing down the stems of trees (stemflow). The sum of throughfall
and stemflow is called net or effective precipitation (Parker 1983). The part
of incident precipitation that does not appear on the forest floor by either of
these routes is called interception loss. Interception has received special attention in a number of forest hydrology studies using experimental or modelling approaches (e.g. Rutter and Morton 1977; Gash 1979; Massman 1983;
Bouten et al. 1996).
The distribution of incident rainwater can be summarized, after Helvey
and Patric (1965), by the expression: rainfall = interception loss + throughfall
+ stemflow (units in mm). The relative importance of each component depends on climatological characteristics (amount of rain, rain intensity, wind
velocity during rain events, rain duration, temperature) and stand structure
characteristics (canopy closure, crown homogeneity and density, age, tree
species). In the Mediterranean climate, high temperatures and high potential
evapotranspiration favour high interception losses. On the other hand, the
heavy storms that characterize the Mediterranean rainfall regime produce
less interception.
The alteration of the chemistry of rainfall after contact with the canopy
has long been recognized (Eaton et al. 1973; Parker 1983; Lindberg et al. 1986;
Lovett 1994). The chemistry of throughfall and stemflow is influenced by the
incident rain chemistry, canopy evaporation, washing of dry deposition from
the surfaces of leaves and barks, and canopy leaching (Lovett and Lindberg
1984). Usually, ion concentrations in throughfall and stemflow are higher
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Juan Bellot, Anna .Avila and Anselm Rodrigo
15.1 Introduction
Forest canopies affect the amounts of water and nutrients reaching forest
soils. Water and nutrient inputs under forest canopies are thus different from
those in nearby open areas. Canopies intercept and retain part of the incident precipitation (intercepted water), which is eventually evaporated from
the canopy and lost to the atmosphere. Water passing through the canopy
can reach the forest floor after dripping from leaves and branches (throughfall) or flowing down the stems of trees (stemflow). The sum of throughfall
and stemflow is called net or effective precipitation (Parker 1983). The part
of incident precipitation that does not appear on the forest floor by either of
these routes is called interception loss. Interception has received special attention in a number of forest hydrology studies using experimental or modelling approaches (e.g. Rutter and Morton 1977; Gash 1979; Massman 1983;
Bouten et al. 1996).
The distribution of incident rainwater can be summarized, after Helvey
and Patric (1965), by the expression: rainfall = interception loss + throughfall
+ stemflow (units in mm). The relative importance of each component depends on climatological characteristics (amount of rain, rain intensity, wind
velocity during rain events, rain duration, temperature) and stand structure
characteristics (canopy closure, crown homogeneity and density, age, tree
species). In the Mediterranean climate, high temperatures and high potential
evapotranspiration favour high interception losses. On the other hand, the
heavy storms that characterize the Mediterranean rainfall regime produce
less interception.
The alteration of the chemistry of rainfall after contact with the canopy
has long been recognized (Eaton et al. 1973; Parker 1983; Lindberg et al. 1986;
Lovett 1994). The chemistry of throughfall and stemflow is influenced by the
incident rain chemistry, canopy evaporation, washing of dry deposition from
the surfaces of leaves and barks, and canopy leaching (Lovett and Lindberg
1984). Usually, ion concentrations in throughfall and stemflow are higher
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999