Wildfire effects and postfire trajectories from an augmented, spatially balanced forest monitoring system

Project Description

To measure the effects of wildfire on a forest, knowledge about the forest before the fire is needed. The pre-existence of permanent forest inventory plots, set up and monitored by the Forest Service’s Forest Inventory and Analysis program, provides an exceptional opportunity to assess the effects of fire on specific forest attributes. Data from more than 500 previously established plots in western Oregon and southwest Washington will be assessed for prefire structure, composition, management history, topography, and fire weather. All plots lie within the perimeters of wildfires that burned in the last 30 years, including the 2020 Labor Day fires.

We are linking the data collected before and after fire events and building a longitudinal dataset of inventory re-measurements, which allows them to look at changes over time. Founded on a statistically representative sample, this longitudinal data is unusually well-suited for inference across all west-side forests, which enhances its relevance to land managers.

The results also will provide insights on postfire trajectories that proceeded largely free of management intervention, creating a powerful baseline against which to assess the impacts of potential management. This will facilitate evaluation of fire’s impact on woody carbon, with and without postfire management.

Purpose and Scope

By linking forest data from before and after wildfire, this study will yield insights on the potential ecological impacts that might be expected when managed and unmanaged west-side forests burn under a broad range of current forest conditions and weather severities. This will generate critical information about forest ecosystem responses to wildfire across a severity spectrum, and across time.

Key questions to be addressed center on implications for habitat elements over time, dependence of regeneration on persistence of residual live trees, vegetation cover development by life form, fuel and carbon dynamics in the postfire environment, the emergence and waning of early seral habitat, and the influence of prefire forest stand structure and composition on postfire trajectories.

Methods from this study include:

• Inventory analysis among all temporal pairings, at tree and plot level, including growth, removals and mortality analysis; estimation of fire impact (for example on tree mortality, growth, live and dead carbon pool fluxes) via traditional FIA post-stratification-based estimation techniques.
• Paired plot and propensity score matching to account for the counterfactual outcomes of fire not occurring to assess impacts of stand density, tree size, ownership, forest type, and other potential explanatory variables on the postfire environment and subsequent ecosystem trajectories.

Project Deliverables

Results from this study will provide clues as to the kinds of management that may mitigate fire severity and reduce the probability that fire will be stand-replacing.