Assessing the Impact of Catchment-Oriented Harvest Scheduling on Financial Returns and Rainfall-Induced Landslide Susceptibility of Radiata Pine (Pinus radiata D.Don) Plantations in the Uawa Catchment, Gisborne, New Zealand

Severe storm damage has prompted calls to restrict large-scale clearfelling on Aotearoa, New Zealand’s erosion-prone land. We evaluated the impact of traditional versus catchment-oriented forest harvest scheduling of radiata pine (Pinus radiata D.Don) plantations on profitability and rainfall-induced landslide susceptibility in the Uawa catchment, Aotearoa, New Zealand. Fifty-nine per cent of the Uawa catchment area is covered with radiata pine plantations (31,899 hectares). These plantations are located within 89 catchment management units (CMUs) and 1123 hill slope units (HSUs). The HSUs are assumed to be the forest stands with stand ages as measured in 2024. We maximised the net present value of the forests subject to non-declining yield constraints, considering different maximum harvesting levels (MHLs) (10% to 50% of CMU area) that could be allowed for any single CMU during any single 5-year period. We found that profitability increased rapidly when the MHL increased from 10% to 20%, with only marginal increases after 25%. We chose an MHL 25% as optimal as it marginally reduced the internal rate of return (IRR) from the business-as-usual scenario (8.92%) to 8.52%. We calculated a proxy for rainfall-induced landslide (RIL) susceptibility as the aggregated sum of the area harvested from each HSU, multiplied by its RIL susceptibility. We then imposed on the MHL 25% scenario constraints for the RIL proxy to become constant over successive periods. This new scenario further reduced the IRR to 6.97% mainly explained by excluding the highest RIL prone stands from harvesting. Forest owners’ concerns about the economic and operational effects of catchment-oriented harvest scheduling appear to be surmountable.