Abstract
The seasonal variations of litter-fall and grazing loss by herbivorous insects were studied in a mature stand and a young stand of Quercus serrata in Kyoto City.
In the mature stand located in the suburbs of Kyoto, from July, 1971 to March, 1975 and in the young stand cultivated on the nursery of Kyoto University campus, from August, 1971 to March, 1975, respectively, in the former, fifteen traps of square of 50 cm×50 cm and in the latter, similar five traps were set up fifty centimeter above the ground in the investigated stands. The litter was collected ten-days interval and monthly. These traps made of Tetoron-cloth of fine mesh were made in the shape of funnel.
The litter was divided into following six fractions by hand sorting:
Leaves (including cut leaves by insects), branches and sexual organs of Quercus serrata
Dead bodies of insects
Feces of herbivorous insects
Others
Each flaction was oven-dried and weighed in the laboratory. The grazing loss by herbivorous insects in Quercus canopies was estimated from insects feces captured by traps.
The mean amount of annual leaf-fall for four years was estimated at 2.87 ton/ha･y in mature stand and 3.12 ton/ha･y in young stand. In each year, seasonal variations of leaf-fall were shown to be similar in mature and young stands. Natural defoliation of Quercus leaves was observed from November to December (Fig. 1).
Two peak fall of branches during spring months from April to May and autumn-winter months from September to January appeared in both stands. Annual branch-fall were estimated at 1.52 ton (0.47～2.71 ton)/ha･y in mature stand and 0.74 ton (0.56～0.88 ton)/ha･y in young stand, and annual variation in the former was larger than in the letter (Fig. 2, Table 2).
The fall of sexual organs had two peaks of male flower from April to May and seed from September to October. Annual fall of sexual organs were estimated at 0.66 ton (0.12～0.98 ton)/ha･y in mature and 0.17 ton (0.07～0.26 ton)/ha･y in young stand (Fig. 3, Table 2).
The greater part of annual insect bodies and feces was caught during months from late spring to summar, these annual fall were 4.4～6.6 kg/ha･y and 54.9～94.9 kg/ha･y in mature stand and 6.9～11.8 kg/ha･y and 49.9～197.4 kg/ha･y, respectively (Fig. 4 and 5, Table 2).
Total litter-fall were estimated at 5.8 ton (4.4～7.0 ton)/ha･y in mature stand and 4.4 ton (4.2～4.9 ton)/ha･y in young stand (Table 2).
The amount of annual feeding leaves by herbivorous insects was estimated at 100～196 kg/ha･y in mature stand and 90～355 kg/ha･y in young stand from insect feces. The annual loss of Quercus canopies by insect grazing was estimated at 124～217 kg/ha･y in the former and 107～372 kg/ha･y in the latter. These losses were suited to 4.3～8.0% and 3.5～12.9% of leaf-fall, respectively (Table 4).
