An Extended Unit Restriction Model with Environmental Considerations for Forest Harvesting

Abstract

This paper addresses a forest harvesting problem with adjacency constraints, including additional environmental constraints to protect wildlife habitats and minimize infrastructure deployment costs. To this end, we propose an integer programming model to include those considerations during the optimization of the harvest regime of a Mexican forest. The model considered was based on the Unit Restriction Model, a benchmark approach that merges the management units before the optimization process. The resulting model, namely the Green Unit Restriction Model (GURM) and the benchmark model (URM) from the literature were tested with the forest Las Bayas, using information obtained from the SiPlaFor project from Universidad Juárez. The proposed model was solvable in all tested instances. Furthermore, a sensitivity analysis study over a core data set of test instances was carried out on the different parameters of the GURM model to determine optimal configurations for the specific case study. Several environmental measures were assessed in our experimental work. The parameters evaluated were the distance value between pairs of units harvested in the same period, the distance value between those considered natural reserve units, the timber volume to be harvested, the green-up period, and the minimum forest reserve area. An interesting observation from the experiments was that the maximum area inversely affected the URM and GURM models; larger regions resulted in a reduced number of management units in the URM model, thus reducing the computational time to solve the instance of the problem, but in this case, at the expense of a reduced profit. One of the interesting findings was that, in all experiments under all different factors, harvesting every 5 or 6 years yields better profits than harvesting every 10 or 12 years. The current standard in the Mexican system is to harvest every 10 years.

An Updated Review of Spatial Forest Planning: Approaches, Techniques, Challenges, and Future Directions

“…Minimum area requirements for such clusters are often imposed in harvest scheduling with adjacency constraints [82]. Unlike the URM, Ríos-Mercado et al [83] introduced the green unit restriction model (GURM), where nearby native or old forest stands are selected as wildlife reserves or protection areas to remain standing throughout the planning horizon. The GURM adjacency constraint aims to establish a maximum distance between native forest stands.…”

“…They established thresholds for allowable differences between neighboring stands and found that it was feasible to reduce vulnerable edge length while experiencing moderate reductions in NPV, leading to clustering of dominant stand heights among neighboring stands. In a recent study, Ríos-Mercado et al [83] formulated a forest harvesting problem with adjacency and environmental constraints based on the extended URM model (GURM) using IP. They tested the effects of parameters such as distance between harvested units, timber volume, green-up period, and minimum forest reserve.…”