Introduction

We developed a set of forest growth, management, and disturbance scenarios for Washington state to analyze carbon storage in the standing forest and quantify harvest volume by species and log size class. Harvest volumes were used to conduct a life-cycle analysis of the wood products. Scenarios were defined by three major factors: management strategy (no action, business as usual, extended rotations, intensive shortened rotations, and extended rotations with increased thinning), wildfire (with and without wildfire), and climate change (with and without growth model adjustments for climate change). In total, 20 scenarios were developed for Washington state. Forest Inventory and Analysis (FIA) plots were used to represent initial forest conditions. The Forest Vegetation Simulator (FVS) was used simulate growth, treatments, and fire.

Methods

We defined representative forest treatments (pre-commercial thin, two commercial thins, and final harvest) by owner and forest type across Washington state. This included specifying residual stand condition, planted and (expected) natural regeneration, and minimum harvest age. We specified moderate and severe wildfire conditions to simulate in the Fire and Fuels Extension for FVS. Finally, we identified a set of site index, maximum stand density index, and growth modifiers for FVS to represent declining forest productivity due to climate change. Using techniques we developed for the Forest and Ecosystem Management System (Forest and Ecosystem Management System (nrsig.org)), we simulated a comprehensive set of realistic growth, management, and disturbance pathways for each FIA Plot and stored the results in a database. In total, across 6003 FIA Plots, we simulated nearly 10.6 million pathways.

We queried the database of pathways to develop 20 statewide scenarios. These scenarios were the combination of five management strategies (no action, business as usual, extended rotations, shortened rotations, and extended rotations with increased thinning), two fire scenarios (with and without fire), and two climate change scenarios (with and without growth adjustments for climate change). We used historical mill-delivered log volumes to set harvest rates for business as usual. We analyzed FIA remeasured Plots to estimate the 10 year average annual burn rate. Scenarios were designed to harvest a similar amount of volume but target different Plots by adjusting the target age for final harvest. Business as usual set the target age for final harvest at 45, 65, and 75 years, respectively, for Private and Tribal, State, and National Forest owner classes. Extended rotations set the target harvest age for all owner classes at 75 years. Shortened rotations reduced the target harvest age to 30 years for Private and Tribal and State owner classes.

Results

For each scenario we evaulated the number of treated and burned acres and the average final harvest age to ensure scenarios behaved as expected. We then summarized the scenarios by calculating 1) forest carbon and 2) log volumes by owner class, species, and small end diameter size class. In 2020 we estimated nearly 1.5 billion tons of carbon in the forest (standing live trees, roots, snags, and downed woody debris but not soil carbon). At the end of the simulation period forest carbon estimates ranged from approximatly 3 billion tons (no action, no fire, and no climate change) to 1.75 billion tons (active management scenarios, with fire, and with climate change). The percentage of harvested log volume by size class responded to management scenarios as expected. Under business as usual, approximately 50% of log volume was in the 4 to 8 inch diameter class, with 30% in the 8 to 12 inch class. Extended rotations increased volume in the larger size classes. Shortened rotations increased the percentage of log volume in the smallest size class. The outputs from this study will be used to conduct a life cycle analysis of the mix of wood products generated by each scenario.

Deliverables

Scenario Output Files

ScenarioDescriptions.txt

LogCF_ByScenario.zip

CutResidualHarvestBiomass_ByScenario.zip

ForestCarbonTons_ByScenario.zip

LogCF_ByPlot_ByScenario.zip

ForestCarbonTons_ByPlot_ByScenario.zip

Project Report

TNC-Wood-Innovation-Project-Report.pdf