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Rainforest deforestation and subsequent reforestation not only alter above-ground vegetation, but also lead to significant changes in the physical and chemical characteristics of soil and in biochemical cycles, which in turn are likely to influence the growth of rainforest plants. However, little research has directly linked soil condition to seedling growth under different forms of rainforest restoration. This study compared the early growth of three rainforest pioneer species (Alphitonia excelsa, Guioa semiglauca, Omalanthus nutans) among soils collected from three different reforestation pathways, and from reference sites in remnant rainforest and pasture in subtropical eastern Australia. The types of reforestation were tree-planting for ecological restoration purposes, autogenic regrowth dominated by the non-native tree species camphor laurel (Cinnamomum camphora), and management of this regrowth to encourage native regeneration. Growth was measured in a shade-house, using soil from five sites in each site-type and three replicate plants of each species. Fifteen physical and biochemical properties were also measured in soil from each site; five of which were related to carbon and eight to nitrogen-dynamics. Two-factor ANOVA of the exponential growth coefficients of seedling height and diameter showed that there was no interaction between tree species and site-type, but there were significant main effects of both these factors. Seedling growth rates did not differ between pasture and rainforest soils, but were around 25% lower in soils from camphor-dominated regrowth sites than in soils from treated camphor and replanted sites. Seedling growth rates were correlated with two independently-varying soil properties: soil pH and plant-available nitrate-nitrogen, whose inclusion as covariates in the ANOVA largely removed the significant site-type effect. These results indicate that reforestation pathways can affect seedling growth by altering the physical and biochemical properties of soil. However, the absolute magnitude of this effect was not large.
