Growth of Trees Planted for Rehabilitation of a Saline Area of the Wheatbelt in Western Australia

概要

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We clarified the relationship between environmental factors and the growth of seven Eucalyptus species and Casuarina obesa planted at an afforestation site in southern Western Australia's wheatbelt. The site consisted of abandoned fields damaged by secondary salinity associated with waterlogging. Afforestation is expected to progressively rehabilitate the land, which has a slight slope generating a large environmental gradient. During the rainy season, waterlogging (soil becoming saturated with water) occurred at the lower part of the site, but not at the higher part. The level of salt in the soil (EC1:5) increased gradually from higher to lower ground (0.34—2.7 dS m-1). Tree size and growth rate were negatively related to waterlogging intensity and showed small values at the lower part of the site, with only a slight effect on tree size and growth rate. Moreover, interspecific differences in size and growth rate were observed. Eucalyptus sargentii and E. occidentalis had larger sizes and faster growth rates than E. camaldulensis. Trees planted under waterlogging conditions at the lower part of the site are likely to fail due to poor growth; therefore, afforestation should begin on higher ground where trees would experience normal growth, and in doing so, reduce the soil water content to rehabilitate the land. Improvement of water balance through afforestation would confirm the benefits of appropriate agroforestry management.