Background Lower pruning is one mainly method of forest tending. Canopy interception is an important process of forest hydrological cycle. Lower pruning can effectively change the characteristics of canopy interception. Few researches focus on this aspect. In this study, 6 kinds of typical Beijing mountain afforestation tree species Platycladus orientalis, Pinus tabuliformis Carr., Quercus variabilis Blume, Acer elegantulum Bunge, Pinus bungeana Zucc. and Cotinus coggygria Scop. are used to be the research objects, exploring the way of lower pruning treatments for characteristics changes in the canopy interception.

Method The method of indoor simulated rainfall was adopted in the experiment. An equipment of canopy interception measurement was made to measure the amount of water interception. There are three parts of the equipment, a bench scale to measure the weight, a metal rain cover to block rain drops and barbed wire to put litters. We put the pot with experimental trees on the bench scale and then start raining. We read the weight on bench scale every 30 seconds. After one hour's raining, continue reading the weight until the weight reading was unchanged. In this research we used weight to express the canopy interception. The final weight reading is the minimum interception(C_min) of the tree. The maximum of bench scale during the raining is called the maximum interception(C_max). We can get the data of canopy interception with higher precision in this way. After lower pruning, put trees on the equipment under the rainfall device to repeat experiment. After that, tree litters were put on the barbed wire. The thickness was 2 cm. We repeated the rainfall experiment.

Results 1) Lower pruning treatment influenced the conifer's canopy interception more than that of broad-leaved tree. The maximum interception of coniferous species decreased by more than 50%. However broad-leaved tree species decreased by less than 20%. 2) The interception ability of the lower layer leaves of broad-leaved trees was much stronger than that of the lower branches. While the interception ability of the lower and lower leaves of the coniferous trees was equal. The interception percentage of lower leaves of coniferous species was significantly less than that of broad-leaved species (P < 0.05). Therefore, the interception percentage of lower branches was opposite. 3) After laying tree litters of 2cm, the difference of the maximum interception and the minimum interception between before and after lower pruning was below 10%.

Conclusions The results show that the interception characteristics of coniferous and broad-leaved canopy vary with the intensity of the lower pruning, which is mainly reflected in that the coniferous tree species has stronger response strength than the broad-leaved tree species. Laying litters under the forest may effectively reduce the influence of lower pruning on the flow of trees.