Screening of trees suited for growth on landfill sites

Abstract

A field survey was conducted on the completed Gin Drinkers’ Bay (GDB) landfill. Hong Kong, to investigate the causes of adverse tree growth. Ten tree species, belonging to eight families, were transplanted to two sites there. One site had a high concentration of landfill gas in the cover soil (high-gas- site, HQS), while the other had a relatively low concentration of gas (low-gas-site, LGS). Besides gaseous composition, general soil properties in these sites were similar. A strong negative correlation between tree growth and landfill gas concentration was observed. A controlled laboratory simulation study was performed to study the influence of landfill gas on plants. The responses to gas varied greatly among species: some were very sensitive but others were tolerant. Generally, the growth of tap roots was reduced while the horizontal growth of adventitious roots was stimulated. The results indicate that landfill gas does not have acute toxic effects on trees. The excessive quantity of CO(_2) in cover soil limits the depth of the root system. Trees with a shallow root system become very susceptible to water stress. The effects of low O(_2) concentration in soil are less important. Trees suited for growth on sub-tropical completed landfill sites are listed, and their common characteristics are discussed.