An evaluation of the establishment, early growth, and nutritive value of native New Zealand shrubs' : a thesis presented in partial fulfilment of the requirements for the degree of Masters in Environmental Management at Massey University, Palmerston North, New Zealand
Agriculture in New Zealand faces many challenges including a need to develop more environmentally focused production systems to help address issues including the need to revegetate step erosion prone hill country, improve indigenous biodiversity and improve water quality. In the past New Zealand has experienced increasingly unpredictable and severe weather which has resulted in severe damage, for example, the 2004 flooding event in the lower north island (Fuller, 2005). New Zealand has a large portion of land that is classed as hill country or steep land, much of which is also classed as highly erodible. These highly erodible areas are vulnerable to high intensity rainfall events; revegetation could help mitigate or reduce the effects of erosion. The species that are currently used in erosion control on farms are often poplars and willows due to their ability to stabilise hill slopes and ease of planting. Native species are not often used in erosion control projects, potentially due to planting difficulties but more likely due to a lack of consistent and long-term information (Phillips, 2005). Species chosen for the present study have been shown to have benefits for erosion previously, as well as being preferred in some ungulate diets. These species were Hoheria populnea, Griselinia littoralis, Pittosporum crassifolium, Coprosma robusta, Pseudopanax arboreus, Coprosma repens, Melicytus ramiflorus, and Salix kinuyanagi. S. kinuyanagi is used as the control species in the present study due to its existing uses in slope stabilisation and forage supplementation on farms in New Zealand. The research objective of this study was to fill the gaps in the knowledge on certain native species and corroborate what is already known from the literature with results from this study, and assess their potential uses as forage. To achieve this objective several species were assessed at two sites: Massey University Dairy No. 4, and Pongaroa Station, Mahia. Measurements included height and stem basal diameter at the start of the trial in July/August 2019 and following summer in March 2020, sampling leaf and edible stem (<5mm) for nutritional content and assessing vigour and survival at the end of the first summer following planting. Survival and early growth at Massey No.4 were higher than at Mahia. Potential reasons for the differences in survival, and growth at Massey No.4 and Mahia, include unplanned browsing damage that occurred early on in the trial at Mahia, as well as the potential effects of the different aspects of the sites. Mahia had a north-facing aspects which has been shown to have effects on soil moisture, soil temperature etc. whereas the Massey No.4 site has a south-facing aspect. The nutritional traits of the native species tested compared favourably to S. kinuyanagi, which is utilised on as a browse shrub in New Zealand. Crude protein was highest in H. populnea for both stem and leaf material while metabolisable energy was highest in P. arboreus for stem and leaf samples. C. robusta foliage had similar metabolisable energy and crude protein to S. kinuyanagi. Several species including H. populnea, and C. robusta showed good early growth suggesting they have potential to be effective species for mitigating erosion on hill slopes. However, further testing over time and at further sites is required to make firm conclusions about the potential for these shrubs as browse species.