Soil ecology and conservation

Soil reports from Manaaki Whenua - Landcare Research show the area around the regional park is predominantly made up of Humose Orthic Brown soils and Weathered Orthic Recent soils, deposited over time from glacial melt and river flows. These are generally well-draining soils due to the sandy/silty composition and have a variable water-holding capacity. Most of these soils have low vulnerability to water logging. The soils in the regional park are weakly structured and are very vulnerable to wind erosion if left bare – they have undergone significant erosion in the past and this was problematic for the soils themselves and for the adjacent highway, which often had poor visibility due to soil blown from the area that is now the regional park. The presence of vegetation was established to mitigate this wind erosion.

This information was carefully considered when designing our replanting plan along with the topography/geography and ecological features of the area. The replanting of the established trees will be done in stages and will be managed to minimise soil disturbance as much as possible. The forest floor will be left intact as much as possible to ensure soil is not left vulnerable to erosion while new species are establishing, and replacement species will be planted within 18 months once the existing trees have been felled. This is to facilitate control of emerging seedlings and weeds present in the soil seed bank. This timeline will be reviewed after stage one planting along with the monitoring of soil erosion during this time.

Data from Environment Canterbury’s soil monitoring programmes has shown that soil properties don’t differ markedly under exotic and indigenous forest, so we don’t expect that the replacement of pest conifers with indigenous and exotic species will have a substantial effect on soil quality. However, preliminary data suggests that soils under indigenous vegetation may have higher microbiological activity, so it is possible that the establishment of indigenous species may improve soil microbiological conditions. This in turn can lead to improvements in soil structure.

The exotic replacement is a non-pest conifer that exhibits the same resilience and growth rate in Takapō as the pest species targeted for removal. We expect their success and growth rate to be at least as good as the established species, or potentially better as we will be applying two years of post-harvest maintenance that focusses on improving survivability and reducing pest regeneration. We currently have native plant reserves located in specific areas within the park best suited for those species. Native species composition will complement local genetic diversity, historical composition relevant to current and future climate and consequent survivability if planted in suitable areas. Native establishment will be supported with the use of mulch to both protect soil and provide organic matter to the soil. We expect a similar success rate to that achieved in our ongoing native planting activity (approximately 70%).

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