**5. Pros and cons of different space-planted approaches**

There are important reasons why poplar and willow have been adopted as spaceplanted trees for erosion control in New Zealand. They are highly effective at reducing landslides, generally grow 2–3 m per year, and they can be planted as 3 m unrooted poles in the presence of livestock. The plastic protection sleeves are easy to apply, are durable, and split apart as the tree grows. However, few of the discarded sleeves are recycled, so they are being reviewed as a pollutant and not sustainable. The trees provide a highly palatable drought fodder source, and shed leaves are consumed by stock. Tree shading reduces pasture production considerably as the trees age [45], but this effect was less significant on poorly grassed slopes, and pasture production per hectare reduced by only 7–12%. (https://www.poplarandwillow.org.nz/documents/ influence-of-shading-by-poplar-trees-on-pasture-production-rb02.pdf). Removing lower branches to create a timber tree or pollarding for fodder production are management techniques employed to reduce shading and promote pasture production under the trees.

The preliminary results of the kānuka trial show that it is possible to establish native seedlings in hill country; however, survival rates were mixed, and the best current protection method is time-consuming to use. Forming a better understanding as to why survival rates were low on some of the aspects and improving on the current protection method will be essential for the uptake of native silvopastoral systems with kānuka in New Zealand. Also, it is important to extend research to other native species in space-planted systems to assess the viability of native space-planted systems more generally. These considerations are very relevant to the indigenous Maori wanting to develop their pastoral land use to include spaced plantings of native woody species used for traditional medicines. Research initiatives that strengthen Maori culture and livelihoods are encouraged by the New Zealand government.

In terms of other co-benefits of trees, a recent study has reported pasture production to be over 100% greater under isolated and mature kanuka trees compared to open pasture at two hill country sites [44]. Although these results are preliminary and require further validation on other sites, they indicate there could be advantages when using kānuka in space-planted systems in New Zealand when compared to poplar and willow, with research finding that poplars greater than 15 years old negatively impact pasture production between 12 and 65% [45]. It is likely there will always be a place for faster growing space-planted trees such as poplar and willow, especially in areas that are highly susceptible to erosion. However, when they can be established more easily, other native species could provide other benefits to areas that are less susceptible to erosion and that do not require immediate erosion protection. Mature kānuka can be found growing higher up drier north-facing slopes, locations generally too dry for poplars and willows to establish with the current methods. It may be that kānuka seedlings will establish in these locations. Further research will test this hypothesis.

Spatial decision support tools for targeted erosion mitigation are of particular benefit to regional land managers advising landowners on species choice and location of plantings and providing landowners with a reasoned cost/benefit assessment when planting tree in high risk, low survival positions on the slope.
