Recently, much attention has been given to soil animal because they play an important role in nutrient cycling as well as a potential bioindicator of soil fertility in the forest ecosystem. However, there is lack of the information on soil animal under the eucalypt (Eucalyptus grandis) plantation in Hongya County, Sichuan, which is difficult to meet needs of man-made forest management. The groups and the densities of soil animal communities in the eucalypt plantation and oak (Quercus acutissima) secondary forest were investigated here to understand the nutrient cycling, provide the information on changes in soil fertility, and evaluate the ecological effects of conversion of secondary forest to eucalypt plantation. Soil macrofauna were picked up by hand in the fields. Nematodes and mesofauna were separated and collected from the soil samples by Baermann and Tullgren methods, respectively.
By preliminary identification, there were 1311 specimens of soil animals, which belonged to 6 phyla, 10 classes and 20 orders in the eucalypt plantation. Acarina, Collembola, Nematoda and Hymenoptera were the dominant groups in the eucalypt plantation. Although Acarina, Nematoda and Hymenoptera were the dominant groups in the oak forest, there was lack of Collembola. The results here indicated that soil animal community structure has changed with plant species composition when oak secondary forest was converted to eucalypt plantation.
The groups and individual number were lower in eucalypt plantation than in oak secondary forest. Moreover, the Shannon-Wiener index and DG (Density-groups) index of soil animals in the eucalypt plantation were 1.818 and 4.002, which were also lower than those of oak secondary forest. It implies that soil biodiversity might decline when oak secondary forest was converted to eucalypt plantation.
The percentage of saprozoic animal, which was used as a potential bioindicator of soil fertility, was 81.78% in the eucalypt plantation, and was higher than that in oak secondary forest (65.00%), resulting from higher organic material returns via litterfall in the former in comparison with the latter.
The groups and individual numbers decreased with the increase of soil depth in two forest ecosystems. However, there was no significant difference in soil animal density between eucalypt plantation and oak secondary forest.
There were higher Jaccard and Gower coefficients between the two studied forests, implying that the group composition of soil animal community was similar to a certain extent in the two forest ecosystems. The results indicated that soil animal community structure had not changed significantly although the soil biodiversity declined slightly when oak secondary forest was converted to eucalypt plantation. To deeply understand the ecological processes in the eucalypt plantation, soil ecological processes related to soil animal need to be performed in the future.