*Article* **Importance of the Local Environment on Nutrient Cycling and Litter Decomposition in a Tall Eucalypt Forest**

### **Jessie C. Buettel \*, Elise M. Ringwaldt, Mark J. Hovenden and Barry W. Brook**

Discipline of Biological Sciences, School of Natural Sciences, University of Tasmania, Hobart 7000, Australia; Elise.Ringwaldt@utas.edu.au (E.M.R.); Mark.Hovenden@utas.edu.au (M.J.H.); Barry.Brook@utas.edu.au (B.W.B.) **\*** Correspondence: jessie.buettel@utas.edu.au; Tel.: +614-57-666-016

Received: 28 February 2019; Accepted: 3 April 2019; Published: 16 April 2019

**Abstract:** The relative abundance of nitrogen-fixing species has been hypothesised to influence tree biomass, decomposition, and nitrogen availability in eucalypt forests. This prediction has been demonstrated in experimental settings (two-species mixtures) but is ye<sup>t</sup> to be observed in the field with more realistically complex communities. We used a combination of (a) field measurements of tree-community composition, (b) sampling of soil from a subset of these sites (i.e., the local environment), and (c) a decomposition experiment of forest litter to examine whether there is a local-scale e ffect of the nitrogen-fixing *Acacia dealbata* Link (presence and abundance) on nitrogen availability, and whether increases in this essential nutrient led to greater biomass of the canopy tree species, *Eucalyptus obliqua* L'Hér. Average *A. dealbata* tree size was a significant predictor of forest basal area in 24 plots (12% deviance explained) and, when combined with average distance between trees, explained 29.1% variance in *E. obliqua* biomass. However, static patterns of local nitrogen concentration were unrelated to the presence or size of *A. dealbata*, despite our experiments showing that *A. dealbata* leaf litter controls decomposition rates in the soil (due to three times higher N). Such results are important for forest managemen<sup>t</sup> in the context of understanding the timing and turnover of shorter-lived species like acacias, where higher N (through either litter or soil) might be better detected early in community establishment (when growth is faster and intraspecific competition more intense) but with that early signal subsequently dissipated.

**Keywords:** forests; nutrients; disturbance; management; diversity; biomass
