6Bruce L. Veteran Pollard Survey: Ashtead and Epsom Commons, Surrey[EB/OL]. Tree work Environmental Practice www.treeworks. co.uk. 2009.
7Fay N. Environmental Arboriculture, Tree Ecology and Veteran Tree Management [J]. Arboricultural Journal, 2002,26(3):213-238.
8De Boer A H. Potassium translocation into the root xylem[J]. Plant Biology, 1999(1 ):36-45.
9Peterson D L. Anderson D R. Content of chemical elements in tree rings of lodgepole pine and whitebark pine from a subalpine Sierra Nevada forest[R].Research Paper PWW-200.Berkeley, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture, 1990:9.