This page outlines the proposed new threshold indicators for assessing forest health in the Lake Tahoe Basin. These indicators are intended to measure how current forest conditions compare to desired ecological standards. Grounded in the best available science and regional data, each indicator represents a key component of forest structure or ecological process that contributes to forest resilience and function. Together, they provide a framework for evaluating progress toward forest health goals.
The table below presents the proposed threshold for Stand Density, reported in Trees Per Acre (TPA) and Basal Area (BA in ft²/acre). These values help evaluate forest structure and crowding, which are critical for understanding forest health. Overstocked forests tend to have greater competition for water and nutrients, and higher risk of severe wildfire.
The chart shows the distribution of tree density and basal area across the Basin. Values exceeding the proposed thresholds suggest areas where mechanical thinning, prescribed fire, or other treatments may be necessary to reduce fire risk and promote resilience.
The chart shows the distribution of the assessed stand density targets. Values exceeding the proposed thresholds suggest areas where mechanical thinning, prescribed fire, or other treatments may be necessary to reduce fire risk and promote resilience.
Methods to Make a Threshold Attainment Call
The seral stage metric describes the distribution of forest age classes. A resilient landscape contains a mix of early-, mid-, and late-seral forests, supporting biodiversity, regeneration, and adaptation to disturbance. Uniformly aging forests or dominance by a single stage can reduce ecological resilience and increase vulnerability to pests and catastrophic fire.
This chart compares the current forest composition (by age class) with desired reference conditions. It helps identify where recruitment of younger forests or retention of older stands may be lacking.
This map displays the current forest composition.
Methods to Make a Threshold Attainment Call
Map the attainment ratio to a qualitative category:
| Attainment Class | Category |
|---|---|
| Considerably Better | |
| Somewhat Better | |
| On Target | |
| Somewhat Worse | |
| Considerably Worse |
Analysis of forest structure across three major forest types shows a consistent underrepresentation of early and late open seral stages. Overrepresented mid-closed canopy stages dominate, especially in Jeffrey Pine and Mixed Conifer types. Weighted across the basin, only ~55% of area is within desired conditions, resulting in a “Somewhat Worse than Target” call.
| Forest Type | % Area within Range | Acres Evaluated | Notes |
|---|---|---|---|
| Jeffrey Pine | ~40,000 | Late open under; mid closed over | |
| Mixed Conifer / White Fir | ~64,000 | Early and late both under | |
| Red Fir | ~22,000 | Best performance, still mid over | |
| Total | ~126,000 | Red fir closer to target than others |
The Wildland Urban Interface (WUI) is where homes and communities meet wild, undeveloped lands. In the Lake Tahoe region, nearly half the area falls within the WUI, divided into the Defense Zone — the immediate buffer around structures and evacuation routes — and the Threat Zone, which surrounds the Defense Zone and focuses on reducing fire starts.
Effective wildfire protection aims to reduce flame lengths during extreme fire weather to 4 feet or less within the Defense Zone, allowing firefighters to suppress fires before they threaten structures.
Wildfire risk was modeled using the FSim Wildfire Risk Simulation Software, which integrates current fuels, topography, historic weather, and fire occurrence to predict fire likelihood and intensity. These data help assess wildfire vulnerability and guide targeted fuel reduction in priority areas.
This indicator assesses fire severity . The goal is to evaluate whether wildfire activity has been ecologically beneficial or harmful. Functional fire maintains ecosystem processes and structure, whereas uncharacteristically high-severity fire can degrade habitat and soil productivity.
By Management Zone:
This chart shows the proportion of burned area by severity category (low, moderate, high) within each zone. These summaries support region-specific assessments of fire impacts and recovery needs.
The map visualizes fire severity spatially, allowing planners to assess patterns and identify areas where ecological fire may have been lost or maintained.
In addition to ecological thresholds, performance measures track management activities like fuel reduction. These metrics help determine whether restoration efforts are keeping pace with ecological needs and regional goals.
The chart summarizes annual forest fuels treatment activity over time, including thinning, mastication, and prescribed burning. Understanding these trends informs whether management is occurring at sufficient pace and scale.
The map shows the spatial extent of past fuel treatments, which can be compared with fire severity and stand density data to assess treatment effectiveness.
The forest health metrics presented here rely heavily on spatial datasets compiled and maintained by the California Wildfire Taskforce’s Regional Resource Kit project. These datasets include high-resolution vegetation composition, forest type, stand structure, and fire severity layers developed through advanced remote sensing and ecological modeling. The Regional Resource Kits provide a comprehensive foundation for assessing forest conditions across the Lake Tahoe Basin and support local restoration and fire resilience planning.
Learn more and access the original data sources here:
Regional Resource Kits - Wildfire Task Force
All metrics were derived from high-resolution remote sensing datasets. The methodology emphasizes transparency, repeatability, and alignment with regional forest goals. Thresholds were developed based on literature review and expert input.
📘 Analysis Notebook:
ForestHealth_ThresholdUpdate_Analysis.ipynb
Contains the logic, thresholds, and data processing steps used to generate stand density, seral stage, and fire severity metrics.
📗 Results Notebook:
ForestHealth_ThresholdUpdate_Results.ipynb
Creates the summary charts, maps, and tables featured in this results page.