Use of New Zealand native browse shrubs on sheep and beef hill country farms : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at the School of Agriculture and Environment, Massey University, Palmerston North, Manawatū, New Zealand

Abstract

Sheep and beef cattle farming on hill country through the historic clearing of native vegetation for pasture has caused biodiversity loss and increased the risk of soil erosion. Exotic tree species such as poplar and radiata pine can be used to control erosion, but there is current interest in using native plants on the hill country for indigenous biodiversity restoration in addition to erosion control. However, there is limited information on the forage value, biomass, carbon stock, and potential economic impacts of native plants compared to exotics species. This thesis was aimed to address the lack of information available on native shrubs and their comparison to exotics trees and shrubs. The forage feeding value results revealed that native shrubs had consistent nutritional composition across seasons, higher metabolizable energy, and lower crude protein than the exotic shrub Salix schwerinii (Kinuyanagi). Findings on in vitro fermentation characteristics showed that native shrubs were highly digestible, yielded higher volatile fatty acids, microbial proteins, and greenhouse gases than S. schwerinii. Estimation of biomass revealed that the native shrubs were similar in aboveground biomass accumulation, but differed in allocation to foliage, branch, and stem. Melicytus ramiflorus (Mahoe) had lower foliage biomass while Coprosma robusta (Karamū) had lower branch biomass, among the evaluated shrubs. Estimated carbon stock accumulation was higher for Pittosporum crassifolium (Karo) due to a greater woodier portion (branch and stem) than M. ramiflorus and C. robusta but lower than exotic trees. The data from the native shrub studies was used in the bioeconomic model and showed that planting native shrubs or radiata pine on steep slopes equal to 10% of the farm area would reduce farm feed supply. This reduction would result in a decrease in sheep flock size and sheep flock net cashflow, particularly with higher planting rates and with of radiata pine. While radiata pine had a surplus overall farm net cashflow, native shrubs had negative cashflow due to high seedling costs and low carbon income, making their use on the farm currently unprofitable at the modelled prices. The study's findings suggest that replacing exotic trees with native shrubs can provide high-quality summer browse for livestock. The decision to plant native shrubs on steep hill country slopes would depend on the farmer’s financial situation and interest in biodiversity conservation and profits. However, reducing planting costs and increasing the carbon price would be necessary to make investing in native shrubs profitable and more attractive to farmers.