Removal of understory dwarf bamboo (Sasa kurilensis) induces changes in water-relations characteristics of overstory Betula ermanii trees

Abstract

We investigated how removal of understory dwarf bamboo (Sasa kurilensis Makino et Shibata) affected growth and water use of young Betula ermanii Cham. trees in a secondary forest in northern Japan. We compared current-year shoot morphology, leaf water-relations characteristics, and whole-tree water use of B. ermanii trees growing with dwarf bamboo in the understory (intact plot) to those of trees growing where dwarf bamboo was experimentally removed (removal plot). Current-year shoot length and internode frequency increased, while internode length and individual leaf area decreased in response to dwarf bamboo removal. Carbon isotope composition (δ¹³C) of leaves did not change indicating that leaf water-use efficiency was unaffected by the presence/absence of dwarf bamboo. Pressure–volume analysis indicated that leaves in the removal plot had lower water uptake ability. During mid-summer, trees in the removal plot sustained high sap flow velocity after peaking at midday, while that of trees in the intact plot declined. In addition, whole-tree sap flux and soil-to-leaf hydraulic conductance were both higher for trees in the removal plot. We inferred that the observed changes reflect hydraulic homeostasis of B. ermanii trees to maintain constant water-use efficiency in response to belowground competition with dwarf bamboo. Removal of dwarf bamboo is, therefore, an effective silvicultural prescription to enhance growth of overstory trees by relieving belowground competition for soil water.

Keywords:

• Hydraulic homeostasis
• Sap flow
• Shoot morphology
• Understory management
• Water-use efficiency

Acknowledgments

The authors thank A. Tabata, E. Nabeshima, T. Endo and J. Dolezal for field assistance, and Y. Tanaka, Moshiri Field Station technical staff for facilitating our study. Many members and students of the Uryu Experimental Forest and Field Science Center for Northern Biosphere, Hokkaido University, also supported our study. We thank the Center for Ecological Research, Kyoto University, for use of facilities for isotope analysis. Dr. K. Sakuta and Dr. T. Saito provided constructive comments and discussion during this study. This research was funded by the COE project fund of the Ministry of Education, Culture, Sports, Science and Technology, Japan, and by the Grant for Joint Research Program of ILTS, Hokkaido University.