Assessing the Impact of Catchment-Oriented Harvest Scheduling on Financial Returns and Rainfall-Induced Landslide Susceptibility of Radiata Pine Plantations in the Uawa Catchment, Gisborne, New Zealand

We evaluated the impact of traditional versus catchment-oriented forest harvest scheduling of radiata pine plantations on profitability and rainfall-induced landslide susceptibility in the Uawa catchment, Aotearoa|New Zealand. Our hypothetical case study assumed that 59% 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 hillslope 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 (NPV) subject to non-declining yield (NDY) constraints, considering different maximum harvesting levels (MHL) (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 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 constraints for our RIL proxy to become constant over successive periods. Our final catchment-oriented harvest schedule marginally reduced the Internal Rate of Return from the business-as-usual scenario, from 8.92% to 8.52%. Forest owners’ concerns about the economic and operational effects of catchment-oriented harvest scheduling appear to be surmountable.