There is growing global interest in large-scale tree-planting initiatives as a powerful means of mitigating the effects of climate change while achieving multiple social and environmental goals, including biodiversity conservation, socio-economic benefits, and sustainability. Nevertheless, a number of these initiatives have increased the risk to native forests and biodiversity while expanding the cover of exotic trees. In addition, although the addition of woody vegetation to agricultural landscapes has been recognized globally as a ‘nature based solution’ for mitigating and adapting to climate change and reversing biodiversity loss, there is still a lack of research on the potential contributions of woody vegetation in agricultural landscapes for enhancing carbon stocks, tree and shrub diversity, and ecosystem multifunctionality. Recent tree planting and carbon credit policies in Aotearoa New Zealand make woody vegetation patches, such as remnant native forests frequently found on sheep and cattle farms, susceptible to conversion into new exotic forests. Few quantitative estimates of the potential carbon stock densities in agricultural landscapes have been made, and as such, estimates have not been incorporated into the quantification and future predictions of the multifunctionality of woody vegetation on farms. This research aimed to (1) evaluate how existing tree planting initiatives can contribute to biodiversity and carbon objectives, (2) examine how existing woody vegetation in sheep and beef cattle farms could contribute to climate change mitigation, and (3) quantify multifunctional landscape contributions under possible future land-use change scenarios where existing native woody vegetation is protected and new trees are added. Using Aotearoa New Zealand’s One Billion Trees program as a case study, I offered ten recommendations for how large-scale tree planting should be modified to prevent unintended consequences for native species while simultaneously meeting our carbon and biodiversity objectives. I then characterized and quantified carbon stocks and multifunctionality from woody vegetation on three case-study farms in northern, central and southern Aotearoa New Zealand, and showed that native-dominated woodland and shrubland communities had higher multifunctionality scores than exotic-dominated woodland communities. Finally, I developed a spatially-explicit simulation model to compare and contrast the multifunctionality outcomes of a range of native woody vegetation restoration and revegetation scenarios in the three Aotearoa New Zealand case study landscapes. The modelling results demonstrated the significance of understanding the distinctive characteristics of each landscape, as different scenarios of woody vegetation restoration and gully revegetation will create outcomes that are highly dependent on the initial quantities, types, and configurations of woody vegetation and gully distributions in each landscape. The study illustrated how land management decision-making can better consider a combination of co-benefits and trade-offs to identify the most appropriate actions for achieving multifunctionality in agricultural landscapes. This thesis significantly improves our understanding of the potential contribution of woody vegetation on sheep and beef cattle farms in Aotearoa New Zealand to climate change mitigation and biodiversity conservation.