Rainfall interception and spatial distribution of throughfall in a pine forest planted in an arid zone

Afforestation in arid zones is of increasing importance as it is one of the favored approaches to combat desertification. Rainfall interception by the canopy plays an important role in determining the amount of rainfall reaching the forest floor. The throughfall patterns of coniferous forests planted in arid zones have hitherto not been well documented. The research site in which the measurements were carried out was located within a mature pine forest (Pinus halepensis, Mill) planted in an arid zone (average annual precipitation: 280 mm and annual class-A evaporation pan: 2500 mm). Measurements of precipitation, throughfall, stemflow, soil water content and transpiration were recorded during three years. Canopy cover was estimated from the analysis of hemispherical photographs obtained during the winter. The spatially averaged throughfall, obtained for each event from 20 rainfall gauges installed below the canopy was linearly correlated with gross rainfall and independent of rainfall intensity. We found that the spatial distribution of the throughfall on the forest floor was highly heterogeneous. A fairly consistent distribution of throughfall was evident with some gauges steadily showing a higher percentage of throughfall than others. However, we could not find any relation between the degree of canopy openness (or any other quantifiable canopy characteristic) and the relative throughfall. The spatial pattern of throughfall was however found to be significant when assessed by means of the “K-means Clustering” analysis.