Seed availability, landscape suitability and the regeneration of perennial grasses in moderately degraded rangelands in semiarid Australia
Judith M. Bean A B E , Gavin J. Melville A , Ronald B. Hacker A C and Stephen P. Clipperton A DA NSW Department of Primary Industries, Trangie Agricultural Research Centre, PMB 19, Trangie, NSW 2823, Australia.
B Present address: PO Box 578, Gunnedah, NSW 2380, Australia.
C Present address: Tenambit, NSW 2323, Australia.
D Present address: Mineral Resources, NSW Trade and Investment, Locked Bag 21, Orange, NSW 2800, Australia.
E Corresponding author. Email: lund@hwy.com.au
The Rangeland Journal 37(3) 249-259 https://doi.org/10.1071/RJ14105
Submitted: 4 August 2014 Accepted: 18 February 2015 Published: 20 April 2015
Abstract
Two experimental sites were selected in the semiarid rangelands of north-west New South Wales, Australia. The sites had contrasting soil types and vegetation communities, but were similar in the existence of topographically high areas occupied by populations of perennial grasses. Adjacent slopes had very low numbers of perennial grass plants, indicating a moderate level of degradation. Shrubs, including Eremophila sturtii R.Br. (turpentine), were present but had not thickened to cause severe degradation. The topographically high areas were fenced as seed production areas. Replicates of a control and two cultural treatments: (1) piles of fine branches of turpentine placed along the topographic contour and (2) pits dug by a revolving metal drum, were established on the adjacent slopes. Maximum regeneration of perennial grasses took place, during favourable seasonal weather conditions, under the piles of branches on the site characterised by long gentle slopes of relatively impervious hard-setting red earths. Seed availability was not a limiting factor and a significant amount of seed was apparently sourced from the seed production areas. The piles of branches were very effective in promoting germination and survival of the perennial grasses, Monachather paradoxus Steud. and Aristida jerichoensis (Domin) Henrad, and species with large seed-retaining inflorescences, but not Thyridolepis mitchelliana (Nees) S.T. Blake. The piles of branches increased capture of seed, developed an improved seedbed and established a more mesic micro-environment and were, therefore, effective in enhancing natural landscape processes. At the site characterised by a medium-textured lithosol, even during favourable seasonal weather conditions, numbers of new plants were much lower. Pits were obliterated during the first heavy rains and the piles of branches had a negative impact on the survival of the second cohort of T. mitchelliana. At both sites, levels of germination and survival needed for regeneration of perennial grasses only occurred where a treatment effective in enhancing natural landscape processes had been established prior to favourable seasonal conditions. Pits were not effective in doing this at either site, nor for any of the perennial grass species.
Additional keywords: brush piles, germination, pits, seed production, seedling survival.
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