Applications of spatially explicit timber harvest scheduling : sustained yield unit size and corridor analysis
Creators: name: Rouck, Kerry Brian
Publisher: name: University of British Columbia
Year: 2009

description: This thesis addresses two major topics. First, impacts on timber supply and economics associated with sustained yield unit size are investigated. Partitioning the forest into sustained yield units is a complex task that involves assessing timber supply, allocation of cutting rights, and social, economic, and environmental impacts. There are numerous ways to vary the timing and intensity of harvests within individual drainages while still meeting the objectives of sustained yield. In this paper a spatial forest planning model is used to examine economic and environmental implications of varying the sustained yield unit size. Harvests for a Timber Supply Area in British Columbia are calculated using four sizes of sustained yield units: 1) 12 small units, 2) 4 moderately sized units 3) 2 large units, and 4) 1 unit representing the entire forest. Relative to the 12 small units, short-term (20 year) harvest levels for the Timber Supply Area increased by 7.6%, 10%, and 10.8% for the 4,2, and 1 unit aggregations, respectively. Medium-(21-60 years) and long-term (61-120 years) increases in harvest levels averaged approximately 75% and 40%, respectively, of those realized in the short-term. Reductions in the length of active road and delivered wood costs were also observed as sustained yield units increased in size. Small units often restrict short-term timber supply and provide continuous road access to important wildlife habitat. While larger units afford greater flexibility in meeting short-term harvests, the intensity of the harvest within individual drainages increases. However, with large units the inactive drainages can be closed for extended periods, thus limiting human access to the active drainages. Second, landscape level management strategies aimed at maintaining and enhancing biological diversity have given rise to the need to incorporate spatially explicit modeling techniques in timber supply planning. Of particular interest to forest managers is the requirement to maintain connectivity of critical habitats when developing harvest patterns. While identification of the habitat islands is a complicated issue, maintaining connectivity of the islands can be achieved through manual identification of stands, or by using algorithms which exploit the underlying network structure of spatially explicit forest inventory data. In this study, three methods of identifying corridors - permanent reserves, replacement corridors, and floating corridors - are compared with respect to the effects on harvested areas, timber supply, and road activity and corridor structure. Permanent and replacement corridors are identified manually, whereas floating corridors are located using a heuristic network algorithm. While permanent reserves are adequate for modeling short-term timber supply 20 years), the longevity of stands is questionable. Replacement corridors are intuitively attractive, but lead to substantial reductions in timber supply due to the additional reserved areas and long rotations. Timber supply impacts due to floating corridors vary according to the harvest constraints in place; heavily constrained areas respond similarly to permanent corridors, whereas loosely constrained areas benefit as stands become eligible for harvest late in the planning horizon.