Survival and growth responses of a number of Australian tree species planted on a saline site in tropical north Australia

Published source details Sun D. & Dickinson G.R. (1995) Survival and growth responses of a number of Australian tree species planted on a saline site in tropical north Australia. Journal of Applied Ecology, 32, 817-826.
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Summary

Rising groundwater tables due to clearance of native trees and shrubs for agricultural and grazing land, coupled with irrigation, is a major cause of increasing soil salinity in some semi-arid sub-tropical and tropical regions. In order to investigate the potential to restore open woodland cover in areas formerly cleared of eucalypt woodland in northern Australia, the salt tolerance and responses of 15 native tree species to soil salinity was examined.

Study site: The study was undertaken at Kalamia Sugar Mill 2km north of the town of Ayr (19º31'S, 147º24'E) in Queensland, northeast Australia. Average annula rainfall is 893 mm, 75% falling between December and March. The 3.22 ha tree planting site had been used for growing irrigated sugar cane but was abandoned due to increasing soil salinity. Salinity surveys were undertaken and the site divided according to high (>110 mS/m), moderate (60-110 mS/m) and low (<60mS/m) salinity areas.

Tree species: Tree species (12 plus three provenances of Acacia auriculiformis) were chosen which were considered suitable for this dry tropical region and are relatively salt tolerant:

Acacia aulacocarpa, A.auriculiformis, Casurina cristata, C.cunninghamiana, C.equisetifolia, C.glauca, Eucalyptus alba, E.camaldulensis, E.tereticornis, E.tessellaris, Melaleuca bracteata, M.leucadendra and M.quinquenervia.

Tree planting: Planting ridges (60 cm high) were made 5 months prior to planting. Tree seedlings were planted by hand in May 1991, placing organic mulch (rice husks) around each to a depth of 7 cm. A week later, fertilizer (11.9%N, 4.3% P, 18.9% K) was applied at a rate of 100 g per tree. The planting area of each tree was kept weed-free for 18 months by spraying with glyphosate herbicide.

Plantings were in a randomized block design with six replicates (blocks) in high, 14 in moderate and eight in low salinity areas. In total there were 420 plots each comprising a line of five seedlings.

Measurements: Soil salinity was recorded 3, 12 and 24 months after planting at various depths in the soil profile. Soli samples were collected for chemical analysis. Tree survival and height were recorded at 3 and 24 months, and at 24 months the third tree in a row of five was selected for measurements of crown size, growth form, branch number, number of forks, leaf length leaf width and leaf thickness.

Data were statistically analysed to examine the effect of salinity on tree survival and growth and the differences in response between taxa.

The survival and growth varied with salinity and species. Trees grown on the high salinity subsite had the lowest survival and poorest growth rate. Casuarina cunninghamiana (90% survival), C.glauca (97% survival) and Eucalyptus camaldulensis (97% survival) achieved the highest survival after 24 months, fastest growth rate and best growth form. Acacia aulacocarpa showed the poorest general performance with only 30% survival after 24 months.

Conclusions: The authors suggest that tree species selection for planting of saline sites should be made according to soil salinity, species salt tolerance and management objectives. Plant height and diameter, crown size and branch number are important characteristics which indicate salt tolerance. Those species with an ability to maintain a relatively large crown and a high number of branches when subjected to salinity are most likely to be highly salt tolerant.

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