Composition, structure, light attenuation and nutrient content of the understorey vegetation in a Eucalyptus sieberi regrowth stand 6 years after thinning and fertilisation

In this study, we investigated the effects of commercial thinning and fertiliser application 6 years after treatment on the structure, composition, and nutrient concentrations of understorey vegetation in a Eucalyptus sieberi regrowth forest in East Gippsland. The stand was thinned at age 26 years, reducing the basal area by ca. 50% and lowering the stocking from ca. 1350 to ca. 250 stems ha^-1. Whereas the species diversity and richness of the understorey were not significantly affected by the treatments, thinning promoted the abundance of herbaceous species, and fertilisation increased the proportion of ground ferns such as Pteridium esculentum. Fertilisation with 100 kg N ha^-1 and 100 kg P ha^-1 decreased the foliage N concentration in Tetrarrhena juncea and Gonocarpus teucrioides, and increased the foliage P concentrations in four of the five most frequent species. This suggested that the understorey was more limited by P than by N. The photosynthetically active radiation above the understorey was 41% of that in the open in thinned stands and 32-34% in unthinned stands, showing that 6 years after thinning the canopy density had not yet returned to pre-treatment levels. However, light attenuation within the understorey did not differ among treatments, confirming that the understorey cover had not increased in response to increased light and nutrient availability. The small changes in the understorey may be attributed to the fact that light and nutrients are not the major factors limiting its development, and that most species are well adapted to disturbance.