© 2004 Heron Publishing—Victoria, Canada
Water use by fast-growing Eucalyptus urophylla plantations in southern China
Jim Morris (1, 2), Zhang Ningnan (3), Yang Zengjiang (3), John Collopy (1) and Xu Daping (3)
1. Forest Science Centre, Heidelberg, Victoria 3084, Australia / 2. Corresponding author (jim.morris@dse.vic.gov.au) / 3. Research Institute for Tropical Forestry, Chinese Academy of Forestry, Guangzhou 510520, China / Received October 6, 2003; accepted January 24, 2004; published online July 1, 2004
Summary
Tree growth, water use, climate and soil water conditions were monitored over 12 months in two 3–4-year-old Eucalyptus urophylla S.T. Blake plantations on the Leizhou Peninsula of southern China. The Hetou plantation was established on a sandy soil of
sedimentary origin with low water storage capacity, and the Jijia plantation was established on a clay soil formed on basalt.
Sapwood area was ~50% higher at Jijia than at Hetou because of differences in plant spacing (1994 versus 1356 stems ha–1). Annual water use, assessed by heat pulse measurements, was 542 mm at Hetou and 559 mm at Jijia, with mean sap flux densities
of 2772 and 1839 l m–2 day–1, respectively. Limitations to water use, imposed by climatic and soil factors, were quantified by analysis of daily canopy
conductance in relation to daytime vapor pressure deficit (VPD) and soil water content. Similar annual water use at the two
sites was a result of higher VPD and soil water availability at Hetou compensating for the greater sapwood area at Jijia.
Potential annual water use in the absence of soil water limitation was estimated at 916 mm at Jijia and 815 mm at Hetou. Higher
water availability during the dry season and early wet season at Hetou than at Jijia was the result of deep root systems.
The results imply that water use by plantations on soils with high water availability and in areas of high VPD may be reduced
by establishment at wider spacing. The environmental cost of water use by plantations must be weighed against their economic
and environmental values to determine an appropriate mix of forestry, agriculture and other land uses in regions where water
resources are limited.
Keywords:
canopy conductance, Guangdong, heat pulse, sap flow, soil moisture, transpiration, vapor pressure deficit.
