Lecture 37 Fire and Forests

Presenter: Kristen Shive, Assistant Cooperative Extension Specialist, Berkeley
Institution: University of California, Department of Environmental Science, Policy, and Management, Forestry and Fuels, UC Agriculture and Natural Resources, UC Cooperative Extension

Source: CalFire Resource Assessment Program; referenced work: Stephens et al. 2007
Graph Information: Visual representation of acres burned from 1923 to 2023.
- **Key Data Points:
- 0 to 4 million acres burned
- Significant peaks observed in recent years (e.g., 2020 data)
- Historical context provided by the pre-exclusion era average.**

Factors Contributing to Increased Wildfire Severity:
- Increased human population and infrastructure in wildland areas.
- Higher fire severity due to shifting climate patterns.
- Historical fire exclusion practices.
- Other legacies from past land usage.
Reference: Photo from an L.A. Times web story illustrating changes.

Topics Covered:
- Fire Ecology Basics
- Modern Wildfires in Sierra Nevada Forests
- Stewardship of Forests into the Future

California Ecosystems:
- Each vegetation type has a distinctive historical relationship with fire, described through their respective fire regimes.

Definitions:
- Fire Regime: A pattern of fire occurrence characterized by frequency, severity, seasonality, and size.
- Fire Frequency: Refers to how often an area experiences fire, on average.
- Fire Severity: Refers to the amount of live vegetation killed during a fire, categorized into classes:
- Low Severity: <25% mortality.
- Moderate Severity: 25-75% mortality.
- High Severity: >75% mortality, increasingly more than 90% in extreme cases.
- **Controls on Fire Severity: ** Influenced by fuels available, weather conditions, and topographical features.

Two Examples of Historic Fire Regimes:
- High Severity Regime:
- Infrequent fires, occurring every 30-100 years.
- Often characterized by high-severity crown fires due to a buildup of dense vegetation.
- Example: Chaparral ecosystem.
- Low-Moderate Severity Regime:
- High frequency with fire return intervals of approximately 10 years.
- Example: Mixed conifer forests, which exhibit small patches of high severity.

Techniques:
- Fire-Scarred Tree Rings: Used to determine past fire events and their frequency.
- Indigenous Oral Histories: Important for understanding historical fire-adapted ecosystems.
- Historic Accounts from Euro-Americans: Illustrative quotes reflecting the ecological role of fire in forest management provided by:
- Lieberg (1900): Discussing frequency and effects of forest fires in yellow-pine types.
- Sterling (1904): Noting low damage from fires in virgin timber, highlighting ground fire behaviors.

Consequences for Mixed Conifer Forests:
- Reduced fuel loads, more regenerating trees and shrubs.
- Favoring of fire/drought-adapted tree species.
- Recycled nutrients enhancing plant diversity.
- The shaping of forest structures conducive to resilience and health of ecosystems.

Definitions:
- The concept regarding how ecological goals guide forest management practices to increase resilience and manage fire severity.

Key Changes Observed:
- Changes in fuels, weather patterns, and topographical factors affecting modern wildfire behavior.
- The impact of Euro-American interventions that led to the suppression of indigenous burning practices over the decades (1890, 1961, 1994).

Consequences of Lack of Fire:
- Increased accumulation of woody fuels and tree density, leading to less fire-tolerant species.
- Loss of biodiversity, particularly in the understory.
- Decreased resilience of forests against drought, pests, and diseases.
- Overall loss of habitat diversity across landscapes.

Climate Change Effects:
- An increase in forest wildfires in response to rising temperatures, with direct correlations drawn from data spanning decades (1970-2010).
- Reference Data: Shown in graph forms from Westerling et al. 2016.

Example References: Post-fire assessments regarding ecological impacts following major fires, such as the Rim Fire (2013), with reference observations before and after significant wildfire events.

Increasing Resilience: Actions suggested for reducing fire severity include:
- Actively restoring conditions that support fire resilience through reductions in tree density and woody fuels based on historical cues and scientific data.

Techniques Discussed:
- Prescribed Fire : A controlled fire aimed at reducing tree density and surface fuels while restoring ecological processes, albeit challenging to execute.
- Mechanical Thinning: Reduces smaller tree densities but poses its limitations, such as higher costs and inability to enact on steep slopes.

Data on Treatment Effectiveness: Outcomes from thinning treatments alone or combined with prescribed fire, showcasing their comparative benefits against untreated landscapes.

Lightning Ignition Practices: Allowing natural ignitions to burn under controlled conditions for landscape management, catering to ecological objectives while being cost-effective.

Identified Barriers: Issues inhibiting effective forest management practices:
- Funding limitations.
- Staffing shortages within governmental agencies.
- Lack of public acceptance regarding fire usage as a tool.
- Narrow window opportunities for burning.

Narrative Change: Revisiting discussions about wildfire management and the necessity of co-existing with fire as a natural phenomenon.

Institutional Credits: Reiteration of institutional support from UC Cooperative Extension and the University of California, Berkeley.