Location

 Danzhou Key Field Station of Observation and Research for Tropical Agricultural Resources and Environments, Ministry of Agriculture affiliated to the Rubber Research Institute, Chinese Academy of Tropical Agricultural Sciences.

The Danzhou Station is located at No. 3 zone of experimental farm of CATAS, and it is 15 km away from Danzhou city, western region of Hainan Island, southern of P. R. China. There are two flux measurement towers, the tower A (109°28′30″E、19°32′47″N，114m a.s.l.) is used to observe adult rubber trees, which was planted in 2001; the tower B (109°28′30″E、19°32′47″N，116m a.s.l.) is used to observe young rubber trees, which was planted in 2008. The Underlying surface plant of the towers are rubber plantation, and the study areas stand for the rubber plantation in western region of Hainan Island.

Climatic

 The experimental fields are in typical tropical oceanic monsoon climate zone and one year can be divided into dry season and wet season, among which May to October is wet season, November to next April is dry season. The annual mean temperature is between 21.5~28.5℃, accumulative temperature of whole year daily mean temperature (≥10℃) is between 8500~9100℃. Solar radiation is 116 Kcal./cm2 and sunlight hour is 2100 hrs each year. Average annual precipitation is 1607mm, mainly distributing in July, August and September (accounted for more than 70% of total annual precipitation), and average relative humidity reaches 83%. Wind speed is 2~2.5 m•s^-1.

There are many abnormal climates, dry weather frequently occurs in spring, typhoon and rainstorm occurs in summer and autumn.

Vegetation and soil

 The tower A is used to observe adult rubber trees, which was planted in 2001.The clone of rubber is Reyan 7-33-97, and the Planting density is 476 plants per hectare. The average height of the rubber community (canopy) is 14 m in 2014, and the single structure has clear stratification. Upper layer is rubber canopy with 12-16m height and lower layer is understory herb layer with about 0.4m.

The tower B is used to observe young rubber trees, which was planted in 2008. It was planted many clone of rubber, and the planting density is 476 plants per hectare. The average height of the rubber community (canopy) is 9.0m in 2014, and the single structure has clear stratification. Upper layer is rubber canopy with 8-11m height and lower layer is understory herb layer with about 0.3m.

The herbaceous vegetation include Cyrtococcum Patens, Eupatorium odoratum, Urena lobata, Ottochloa nodosa, Elephantopus scaber, Borrenia articulalis, Phyllanthus simplex, Momosa pudica, Melastoma candidum, L. japonicum and so on .

The altitude is 114m to 120m, flat terrain, and the relative height difference is not more than 20m. The soil is granite laterite, silty clay loam, the thickness of the soil is about 100cm, pH 4.5~5.5, medium organic matter, more kalium and lack phosphorus.

Observation system

 Instruments relevant include 3 parts: forest gradient observation system, open eddy covariance system and closed vapor-CO₂ profile system. And installations and settings of the instruments in details are as follows:

Forest gradient observation system is a 50m tower, which is composed of: Vertical gradient observation system of temperature, humidity and wind: 7 layers wind speed sensor (Model 010C, Met One Inc., USA) and temperature, relative humidity probe (HMP45C, Vaisala, Finland) at the height of 1.5m, 6m, 10m, 15m, 33m, 41m, 50m, and wind direction sensor (Met 020C-1, Met One Inc., USA) and tipping bucket rain gage (TE525MM, Texas, USA) at 50m of the tower top; Observation system of radiation and energy: quantum sensor (LI-190SB, Li-cor, USA) at 30m and 5 layers quantum sensors (LQS70-10, Apogee, USA), net radiometer (CNR1, Kipp & Zonen, Netherlands) at 25 m and infrared radiometer (IRR-P, Apogee, USA) at height of 1.5m and 30 m; Soil observation system of temperature, moisture and energy: averaging soil thermocouple probe (TCAV-L, Campbell, USA) at 4 cm under the earth (-4 cm), 5 layers soil temperature probe (109, Campbell, USA) at -2, -5, -20, -50, -100 cm, 3 layers soil heat flux plate (HFP01SC, Hukseflux, Netherlands) and water content reflectometer (CS616, Campbell, USA) at -5, -20, -50 cm. And all the data will be collected and stored with 2 CR3000 (Campbell, USA) datalogger at 2 m and 30 m at each 10 minutes, 30 minutes and 1 hour step length.

Soil observation system of temperature, moisture and energy: averaging soil thermocouple probe (TCAV-L, Campbell, USA) at 4 cm under the earth (-4 cm), 5 layers soil temperature probe (109, Campbell, USA) at -2, -5, -20, -50, -100 cm, 3 layers soil heat flux plate (HFP01SC, Hukseflux, Netherlands) and water content reflectometer (CS616, Campbell, USA) at -5, -20, -50 cm. And all the data will be collected and stored with 2 CR3000 (Campbell, USA) datalogger at 2 m and 30 m at each 10 minutes, 30 minutes and 1 hour step length.

 Figure 1 Installing sketch of instruments on the microclimatic iron tower in Danzhou station

Principal Investigator

Zhixiang Wu

E-mail: wzxrri@163.com