Survival and growth of the tree species and provenances in response to salinity on a discharge site

Abstract

The survival and growth of 24 native tree species planted in 2 trials on a saline discharge site, which had a soil salinity gradient as well as watertable depth and salinity, near Wellington in central-west New South Wales were investigated. Several provenances of some species (including Acacia stenophylla, Eucalyptus camaldulensis and E. spathulata) and clones of E. camaldulensis and E. spathulata, were also evaluated. Each accession was represented by a 5-tree row plot with 8 replications.

Root-zone salinity (EC_{e 0–60 cm}) at the tree and plot level was calculated from in situ measurements of bulk soil salinity using an EM-38 device (Geonics, Canada). Growth measurements are reported at 72 (trial 1) and 61 months (trial 2) after planting. For each trial, 4 replicates were classified as either non-saline (mean EC_e <2 dS/m) or saline (EC_e range from about 6 to 10 dS/m). Watertable depths varied from 0 to 1.5 m (depending on season) in the saline areas to >4 m in the non-saline, upslope areas.

Survival and growth differed significantly between species, provenances and clones in both trials and under both saline and non-saline conditions. For most accessions, trees survived and grew better under non-saline conditions. Under non-saline conditions A. mearnsii, E. camaldulensis and E. occidentalis performed best; for example, A. mearnsii (16268) attained a mean height of 7 m and mean DBH of 11 cm at 61 months in trial 2. Under saline conditions, A. stenophylla, E. camaldulensis, E. occidentalis and E. spathulata performed best; for example, E. occidentalis attained a height of 6.9 m height and 12.3 cm DBH after 61 months in trial 2. Responses of selected species to root-zone salinity are provided; significant differences were found between species with E. occidentalis and A. stenophylla showing no growth decline up to EC_e of 10 dS/m, while most other species showed varying rates of decline with increasing salinity. Three years after thinning each trial, good coppice regrowth was observed from cut stumps of all species except A. mearnsii and Melaleuca halmaturorum.