From July 2002 to July 2004, we investigated the soil fauna in the Dongjiao coco forest of Hainan Island. The objective of the project is to examine the soil usage and potential problems in the coco nut production, and provide scientific foundations for planning of coco nut production in Hainan from a ecological perspective.
The Dongjiao coco forest is located at the Dongjian Peninsula, eastern Wenchang. The peninsula has a flat topology with elevation below 10 meters. The area has a typical monsoon climate of tropical ocean in north edge, with major climatic parameters as the following: mean annual average temperature through 24.4℃；mean annual precipitation 1529.8mm; mean annual sunshine 2026 hours; Active accumulated temperature 8928℃/a, total annual solar radiation 482 kJ/(cm2•a); mean annual average relative humidity 85%～88%. The Soil is typical seashore sandy soil with high level of moisture (0～20cm relative soil moisture >21.9), and a pH of 6～7. The environmental conditions are considered as well suitable for coco tree and Syzygium jambos community. Since the coco trees were first introduced to the area approximately 2000 years ago, the total grow area has increased to 2×104hm2, and the area has became the primary coco nut production area in China.
The sample sites were determined by the characteristic of the coco forest community. For large size soil animal species, samples were collected from each 50×50cm2 sample sites; difference layers of soil were sorted and collected by hands. For medium and small size soil animal species, the Tullgren methods and the Baermann method were used. A total of 5378 specimens were obtained. To closely represent the community structure, a total of 4033 specimens, which collected in the dry season (Januray) and wet season (July), were identified and studies. Among them, there were 1253 Nematode and other moisture dependant species, and 2780 drought tolerant species. These species represented 4 phyla, 12 classes and 27 genera.
(1) All major animal groups presented in a tropical rain forest are present in the Dongjiao Coco woods soil community. The dominant groups included Acarina, Nematoda, Collembola, together they account for 88.10% of total amount. Other groups, Hymenoptera (Antes), Isoptera (Termites), Enchytraeidae, and Symphyla, account for 8.67% of total amount. There were 20 rare groups, which only account for 3.23% of total catch, but they represent a large number of species diversity. Therefore, these rare species may play an important role in the material and energy conversion process and is an important part of the community.
(2) The Dongjiao Coco woods demonstrated typical characteristics of tropical soil animal community. The number of species and the diversity index (H) increase from the high latitude areas toward the equator; The dominance index (C) decrease from the high latitude areas toward the equator; the ratio of Acarina /Collembola, the percentage value of Hymenoptera (Antes) along latitudinal declination increment; a typical member-termite of tropical community, varies from absentence to a dramatic increasement with the declination of latitude.
(3) Comparing to primary tropical rain forest, the Dongjian coco forest community is relatively low in species diversity, and has a high dominance index and low diversity index. This may partially due to some characters of the forest: singular tree species, monsoon climate, seashore location, high pH and salinity of the soil, high soil moisture and other environmental factors. Seasonal change of community structure occurs but is not obvious.
(4) The Dongjiao coco forest communitys display heterogeneity among various microhabitats. Soil around human residence has a higher organic material content, and has higher counts of number of specimens and number of species, comparing to other three sampling sites.
(5) The coco nuts production at the location around human residence is higher than other microhabitat. The high production is positively correlated with the richness of animal community in the soil.