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Site Preparation Experiment

Xstrata Coal Mount Owen Complex

Reconstructing a vertically structured native forest or woodland ecosystem on abandoned pastureland offers a number of challenges, such as soil compaction and weed and grass competition. It requires the planting of seedlings, rather than direct seeding. Planting seedlings can involve the use of tree guards, fertilizer, ripping the ground prior to planting and watering.

To determine the most cost-effective way of planting native seedlings into pastureland.

Summary of Results:
A total of 16 treatment combinations were tested using 4 factors: ripping vs auguring a planting hole, ± fertilizer, ± tree guard and ± watering fortnightly over the summer months. Times were recorded for setting up each aspect of each treatment, for cost-benefit analysis. One set of planting was done in spring and another in autumn using a tree, understorey and shrub species each time. In the autumn planting, watering was omitted as one of the factors.

Treatment effects were essentially the same in both planting seasons, but more pronounced in the spring planting. Seedlings in ripped plots of the spring planting had more than twice the survival (see figure below) and almost twice the growth during the first six months, compared to plants growing in un-ripped plots. This is most likely due to the de-compaction of the ground increasing water infiltration and root penetration.

Fertilizer tablets decreased overall survival, as natives can be sensitive to excess nutrients, but they increased plant growth. Tree guards increased both survival and growth due to protection from herbivory and by creating a favourable micro-climate. Watering increased plant survival in the un-ripped plots and plant growth in the ripped plots. Generally, survival was greater in the autumn than the spring planting, particularly in un-ripped areas.

Cost-benefit analysis revealed that just ripping the plots was the most cost-effective way of achieving 80% overall survival in the spring planting after 6 months (see figure below). Adding tree guards increased survival to 95% but at almost twice the cost. This could differ with higher herbivory pressure, where the omission of a tree guard may be more detrimental than in this experiment, therefore increasing the cost-effectiveness of implementing them. Tree guards were also essential for the shrub species, which survived poorly without their protection. Watering increased costs by 3.5 times, without enough benefit to justify it.

In terms of plant height, the addition of fertilizer to the ripped plots produced a 38% increase in height over the first six months for only a 10% increase in price. However, this has to be balanced against reducing survival by one third. There were some species-specific effects which, differed from the overall results.

If possible, plant seedlings in autumn, in ripped, un-fertilizer ground, adding tree-guards for shrub species or if there is much herbivory occurring. If a spring planting is necessary, the same method is the most cost-effective but overall less effective.